/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp

Bug Summary

File:	lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
Warning:	line 2763, column 24 The left operand of '>=' is a garbage value

Annotated Source Code

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clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name SimpleLoopUnswitch.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -mthread-model posix -mframe-pointer=none -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-10/lib/clang/10.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-10~svn374877/build-llvm/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-10~svn374877/build-llvm/include -I /build/llvm-toolchain-snapshot-10~svn374877/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/backward -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-10/lib/clang/10.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-10~svn374877/build-llvm/lib/Transforms/Scalar -fdebug-prefix-map=/build/llvm-toolchain-snapshot-10~svn374877=. -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -o /tmp/scan-build-2019-10-15-233810-7101-1 -x c++ /build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp

/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp

→

1///===- SimpleLoopUnswitch.cpp - Hoist loop-invariant control flow ---------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//

9#include "llvm/Transforms/Scalar/SimpleLoopUnswitch.h"
10#include "llvm/ADT/DenseMap.h"
11#include "llvm/ADT/STLExtras.h"
12#include "llvm/ADT/Sequence.h"
13#include "llvm/ADT/SetVector.h"
14#include "llvm/ADT/SmallPtrSet.h"
15#include "llvm/ADT/SmallVector.h"
16#include "llvm/ADT/Statistic.h"
17#include "llvm/ADT/Twine.h"
18#include "llvm/Analysis/AssumptionCache.h"
19#include "llvm/Analysis/CFG.h"
20#include "llvm/Analysis/CodeMetrics.h"
21#include "llvm/Analysis/GuardUtils.h"
22#include "llvm/Analysis/InstructionSimplify.h"
23#include "llvm/Analysis/LoopAnalysisManager.h"
24#include "llvm/Analysis/LoopInfo.h"
25#include "llvm/Analysis/LoopIterator.h"
26#include "llvm/Analysis/LoopPass.h"
27#include "llvm/Analysis/MemorySSA.h"
28#include "llvm/Analysis/MemorySSAUpdater.h"
29#include "llvm/Analysis/Utils/Local.h"
30#include "llvm/IR/BasicBlock.h"
31#include "llvm/IR/Constant.h"
32#include "llvm/IR/Constants.h"
33#include "llvm/IR/Dominators.h"
34#include "llvm/IR/Function.h"
35#include "llvm/IR/InstrTypes.h"
36#include "llvm/IR/Instruction.h"
37#include "llvm/IR/Instructions.h"
38#include "llvm/IR/IntrinsicInst.h"
39#include "llvm/IR/Use.h"
40#include "llvm/IR/Value.h"
41#include "llvm/Pass.h"
42#include "llvm/Support/Casting.h"
43#include "llvm/Support/Debug.h"
44#include "llvm/Support/ErrorHandling.h"
45#include "llvm/Support/GenericDomTree.h"
46#include "llvm/Support/raw_ostream.h"
47#include "llvm/Transforms/Scalar/SimpleLoopUnswitch.h"
48#include "llvm/Transforms/Utils/BasicBlockUtils.h"
49#include "llvm/Transforms/Utils/Cloning.h"
50#include "llvm/Transforms/Utils/LoopUtils.h"
51#include "llvm/Transforms/Utils/ValueMapper.h"
52#include <algorithm>
53#include <cassert>
54#include <iterator>
55#include <numeric>
56#include <utility>

58#define DEBUG_TYPE"simple-loop-unswitch" "simple-loop-unswitch"

60using namespace llvm;

62STATISTIC(NumBranches, "Number of branches unswitched")static llvm::Statistic NumBranches = {"simple-loop-unswitch",
 "NumBranches", "Number of branches unswitched"};
63STATISTIC(NumSwitches, "Number of switches unswitched")static llvm::Statistic NumSwitches = {"simple-loop-unswitch",
 "NumSwitches", "Number of switches unswitched"};
64STATISTIC(NumGuards, "Number of guards turned into branches for unswitching")static llvm::Statistic NumGuards = {"simple-loop-unswitch", "NumGuards"
, "Number of guards turned into branches for unswitching"};
65STATISTIC(NumTrivial, "Number of unswitches that are trivial")static llvm::Statistic NumTrivial = {"simple-loop-unswitch", "NumTrivial"
, "Number of unswitches that are trivial"};
66STATISTIC(static llvm::Statistic NumCostMultiplierSkipped = {"simple-loop-unswitch"
, "NumCostMultiplierSkipped", "Number of unswitch candidates that had their cost multiplier skipped"
}
  NumCostMultiplierSkipped,static llvm::Statistic NumCostMultiplierSkipped = {"simple-loop-unswitch"
, "NumCostMultiplierSkipped", "Number of unswitch candidates that had their cost multiplier skipped"
}
  "Number of unswitch candidates that had their cost multiplier skipped")static llvm::Statistic NumCostMultiplierSkipped = {"simple-loop-unswitch"
, "NumCostMultiplierSkipped", "Number of unswitch candidates that had their cost multiplier skipped"
};

70static cl::opt<bool> EnableNonTrivialUnswitch(
  "enable-nontrivial-unswitch", cl::init(false), cl::Hidden,
  cl::desc("Forcibly enables non-trivial loop unswitching rather than "
           "following the configuration passed into the pass."));

75static cl::opt<int>
  UnswitchThreshold("unswitch-threshold", cl::init(50), cl::Hidden,
                    cl::desc("The cost threshold for unswitching a loop."));

79static cl::opt<bool> EnableUnswitchCostMultiplier(
  "enable-unswitch-cost-multiplier", cl::init(true), cl::Hidden,
  cl::desc("Enable unswitch cost multiplier that prohibits exponential "
           "explosion in nontrivial unswitch."));
83static cl::opt<int> UnswitchSiblingsToplevelDiv(
  "unswitch-siblings-toplevel-div", cl::init(2), cl::Hidden,
  cl::desc("Toplevel siblings divisor for cost multiplier."));
86static cl::opt<int> UnswitchNumInitialUnscaledCandidates(
  "unswitch-num-initial-unscaled-candidates", cl::init(8), cl::Hidden,
  cl::desc("Number of unswitch candidates that are ignored when calculating "
           "cost multiplier."));
90static cl::opt<bool> UnswitchGuards(
  "simple-loop-unswitch-guards", cl::init(true), cl::Hidden,
  cl::desc("If enabled, simple loop unswitching will also consider "
           "llvm.experimental.guard intrinsics as unswitch candidates."));

95/// Collect all of the loop invariant input values transitively used by the
96/// homogeneous instruction graph from a given root.
97///
98/// This essentially walks from a root recursively through loop variant operands
99/// which have the exact same opcode and finds all inputs which are loop
100/// invariant. For some operations these can be re-associated and unswitched out
101/// of the loop entirely.
102static TinyPtrVector<Value *>
103collectHomogenousInstGraphLoopInvariants(Loop &L, Instruction &Root,
                                       LoopInfo &LI) {
assert(!L.isLoopInvariant(&Root) &&((!L.isLoopInvariant(&Root) && "Only need to walk the graph if root itself is not invariant."
) ? static_cast<void> (0) : __assert_fail ("!L.isLoopInvariant(&Root) && \"Only need to walk the graph if root itself is not invariant.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 106, __PRETTY_FUNCTION__))
       "Only need to walk the graph if root itself is not invariant.")((!L.isLoopInvariant(&Root) && "Only need to walk the graph if root itself is not invariant."
) ? static_cast<void> (0) : __assert_fail ("!L.isLoopInvariant(&Root) && \"Only need to walk the graph if root itself is not invariant.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 106, __PRETTY_FUNCTION__));
TinyPtrVector<Value *> Invariants;

// Build a worklist and recurse through operators collecting invariants.
SmallVector<Instruction *, 4> Worklist;
SmallPtrSet<Instruction *, 8> Visited;
Worklist.push_back(&Root);
Visited.insert(&Root);
do {
  Instruction &I = *Worklist.pop_back_val();
  for (Value *OpV : I.operand_values()) {
    // Skip constants as unswitching isn't interesting for them.
    if (isa<Constant>(OpV))
      continue;

    // Add it to our result if loop invariant.
    if (L.isLoopInvariant(OpV)) {
      Invariants.push_back(OpV);
      continue;
    }

    // If not an instruction with the same opcode, nothing we can do.
    Instruction *OpI = dyn_cast<Instruction>(OpV);
    if (!OpI || OpI->getOpcode() != Root.getOpcode())
      continue;

    // Visit this operand.
    if (Visited.insert(OpI).second)
      Worklist.push_back(OpI);
  }
} while (!Worklist.empty());

return Invariants;
139}

141static void replaceLoopInvariantUses(Loop &L, Value *Invariant,
                                   Constant &Replacement) {
assert(!isa<Constant>(Invariant) && "Why are we unswitching on a constant?")((!isa<Constant>(Invariant) && "Why are we unswitching on a constant?"
) ? static_cast<void> (0) : __assert_fail ("!isa<Constant>(Invariant) && \"Why are we unswitching on a constant?\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 143, __PRETTY_FUNCTION__));

// Replace uses of LIC in the loop with the given constant.
for (auto UI = Invariant->use_begin(), UE = Invariant->use_end(); UI != UE;) {
  // Grab the use and walk past it so we can clobber it in the use list.
  Use *U = &*UI++;
  Instruction *UserI = dyn_cast<Instruction>(U->getUser());

  // Replace this use within the loop body.
  if (UserI && L.contains(UserI))
    U->set(&Replacement);
}
155}

157/// Check that all the LCSSA PHI nodes in the loop exit block have trivial
158/// incoming values along this edge.
159static bool areLoopExitPHIsLoopInvariant(Loop &L, BasicBlock &ExitingBB,
                                       BasicBlock &ExitBB) {
for (Instruction &I : ExitBB) {
  auto *PN = dyn_cast<PHINode>(&I);
  if (!PN)
    // No more PHIs to check.
    return true;

  // If the incoming value for this edge isn't loop invariant the unswitch
  // won't be trivial.
  if (!L.isLoopInvariant(PN->getIncomingValueForBlock(&ExitingBB)))
    return false;
}
llvm_unreachable("Basic blocks should never be empty!")::llvm::llvm_unreachable_internal("Basic blocks should never be empty!"
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 172);
173}

175/// Insert code to test a set of loop invariant values, and conditionally branch
176/// on them.
177static void buildPartialUnswitchConditionalBranch(BasicBlock &BB,
                                                ArrayRef<Value *> Invariants,
                                                bool Direction,
                                                BasicBlock &UnswitchedSucc,
                                                BasicBlock &NormalSucc) {
IRBuilder<> IRB(&BB);

Value *Cond = Direction ? IRB.CreateOr(Invariants) :
  IRB.CreateAnd(Invariants);
IRB.CreateCondBr(Cond, Direction ? &UnswitchedSucc : &NormalSucc,
                 Direction ? &NormalSucc : &UnswitchedSucc);
188}

190/// Rewrite the PHI nodes in an unswitched loop exit basic block.
191///
192/// Requires that the loop exit and unswitched basic block are the same, and
193/// that the exiting block was a unique predecessor of that block. Rewrites the
194/// PHI nodes in that block such that what were LCSSA PHI nodes become trivial
195/// PHI nodes from the old preheader that now contains the unswitched
196/// terminator.
197static void rewritePHINodesForUnswitchedExitBlock(BasicBlock &UnswitchedBB,
                                                BasicBlock &OldExitingBB,
                                                BasicBlock &OldPH) {
for (PHINode &PN : UnswitchedBB.phis()) {
  // When the loop exit is directly unswitched we just need to update the
  // incoming basic block. We loop to handle weird cases with repeated
  // incoming blocks, but expect to typically only have one operand here.
  for (auto i : seq<int>(0, PN.getNumOperands())) {
    assert(PN.getIncomingBlock(i) == &OldExitingBB &&((PN.getIncomingBlock(i) == &OldExitingBB && "Found incoming block different from unique predecessor!"
) ? static_cast<void> (0) : __assert_fail ("PN.getIncomingBlock(i) == &OldExitingBB && \"Found incoming block different from unique predecessor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 206, __PRETTY_FUNCTION__))
           "Found incoming block different from unique predecessor!")((PN.getIncomingBlock(i) == &OldExitingBB && "Found incoming block different from unique predecessor!"
) ? static_cast<void> (0) : __assert_fail ("PN.getIncomingBlock(i) == &OldExitingBB && \"Found incoming block different from unique predecessor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 206, __PRETTY_FUNCTION__));
    PN.setIncomingBlock(i, &OldPH);
  }
}
210}

212/// Rewrite the PHI nodes in the loop exit basic block and the split off
213/// unswitched block.
214///
215/// Because the exit block remains an exit from the loop, this rewrites the
216/// LCSSA PHI nodes in it to remove the unswitched edge and introduces PHI
217/// nodes into the unswitched basic block to select between the value in the
218/// old preheader and the loop exit.
219static void rewritePHINodesForExitAndUnswitchedBlocks(BasicBlock &ExitBB,
                                                    BasicBlock &UnswitchedBB,
                                                    BasicBlock &OldExitingBB,
                                                    BasicBlock &OldPH,
                                                    bool FullUnswitch) {
assert(&ExitBB != &UnswitchedBB &&((&ExitBB != &UnswitchedBB && "Must have different loop exit and unswitched blocks!"
) ? static_cast<void> (0) : __assert_fail ("&ExitBB != &UnswitchedBB && \"Must have different loop exit and unswitched blocks!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 225, __PRETTY_FUNCTION__))
       "Must have different loop exit and unswitched blocks!")((&ExitBB != &UnswitchedBB && "Must have different loop exit and unswitched blocks!"
) ? static_cast<void> (0) : __assert_fail ("&ExitBB != &UnswitchedBB && \"Must have different loop exit and unswitched blocks!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 225, __PRETTY_FUNCTION__));
Instruction *InsertPt = &*UnswitchedBB.begin();
for (PHINode &PN : ExitBB.phis()) {
  auto *NewPN = PHINode::Create(PN.getType(), /*NumReservedValues*/ 2,
                                PN.getName() + ".split", InsertPt);

  // Walk backwards over the old PHI node's inputs to minimize the cost of
  // removing each one. We have to do this weird loop manually so that we
  // create the same number of new incoming edges in the new PHI as we expect
  // each case-based edge to be included in the unswitched switch in some
  // cases.
  // FIXME: This is really, really gross. It would be much cleaner if LLVM
  // allowed us to create a single entry for a predecessor block without
  // having separate entries for each "edge" even though these edges are
  // required to produce identical results.
  for (int i = PN.getNumIncomingValues() - 1; i >= 0; --i) {
    if (PN.getIncomingBlock(i) != &OldExitingBB)
      continue;

    Value *Incoming = PN.getIncomingValue(i);
    if (FullUnswitch)
      // No more edge from the old exiting block to the exit block.
      PN.removeIncomingValue(i);

    NewPN->addIncoming(Incoming, &OldPH);
  }

  // Now replace the old PHI with the new one and wire the old one in as an
  // input to the new one.
  PN.replaceAllUsesWith(NewPN);
  NewPN->addIncoming(&PN, &ExitBB);
}
257}

259/// Hoist the current loop up to the innermost loop containing a remaining exit.
260///
261/// Because we've removed an exit from the loop, we may have changed the set of
262/// loops reachable and need to move the current loop up the loop nest or even
263/// to an entirely separate nest.
264static void hoistLoopToNewParent(Loop &L, BasicBlock &Preheader,
                               DominatorTree &DT, LoopInfo &LI,
                               MemorySSAUpdater *MSSAU) {
// If the loop is already at the top level, we can't hoist it anywhere.
Loop *OldParentL = L.getParentLoop();
if (!OldParentL)
  return;

SmallVector<BasicBlock *, 4> Exits;
L.getExitBlocks(Exits);
Loop *NewParentL = nullptr;
for (auto *ExitBB : Exits)
  if (Loop *ExitL = LI.getLoopFor(ExitBB))
    if (!NewParentL || NewParentL->contains(ExitL))
      NewParentL = ExitL;

if (NewParentL == OldParentL)
  return;

// The new parent loop (if different) should always contain the old one.
if (NewParentL)
  assert(NewParentL->contains(OldParentL) &&((NewParentL->contains(OldParentL) && "Can only hoist this loop up the nest!"
) ? static_cast<void> (0) : __assert_fail ("NewParentL->contains(OldParentL) && \"Can only hoist this loop up the nest!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 286, __PRETTY_FUNCTION__))
         "Can only hoist this loop up the nest!")((NewParentL->contains(OldParentL) && "Can only hoist this loop up the nest!"
) ? static_cast<void> (0) : __assert_fail ("NewParentL->contains(OldParentL) && \"Can only hoist this loop up the nest!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 286, __PRETTY_FUNCTION__));

// The preheader will need to move with the body of this loop. However,
// because it isn't in this loop we also need to update the primary loop map.
assert(OldParentL == LI.getLoopFor(&Preheader) &&((OldParentL == LI.getLoopFor(&Preheader) && "Parent loop of this loop should contain this loop's preheader!"
) ? static_cast<void> (0) : __assert_fail ("OldParentL == LI.getLoopFor(&Preheader) && \"Parent loop of this loop should contain this loop's preheader!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 291, __PRETTY_FUNCTION__))
       "Parent loop of this loop should contain this loop's preheader!")((OldParentL == LI.getLoopFor(&Preheader) && "Parent loop of this loop should contain this loop's preheader!"
) ? static_cast<void> (0) : __assert_fail ("OldParentL == LI.getLoopFor(&Preheader) && \"Parent loop of this loop should contain this loop's preheader!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 291, __PRETTY_FUNCTION__));
LI.changeLoopFor(&Preheader, NewParentL);

// Remove this loop from its old parent.
OldParentL->removeChildLoop(&L);

// Add the loop either to the new parent or as a top-level loop.
if (NewParentL)
  NewParentL->addChildLoop(&L);
else
  LI.addTopLevelLoop(&L);

// Remove this loops blocks from the old parent and every other loop up the
// nest until reaching the new parent. Also update all of these
// no-longer-containing loops to reflect the nesting change.
for (Loop *OldContainingL = OldParentL; OldContainingL != NewParentL;
     OldContainingL = OldContainingL->getParentLoop()) {
  llvm::erase_if(OldContainingL->getBlocksVector(),
                 [&](const BasicBlock *BB) {
                   return BB == &Preheader || L.contains(BB);
                 });

  OldContainingL->getBlocksSet().erase(&Preheader);
  for (BasicBlock *BB : L.blocks())
    OldContainingL->getBlocksSet().erase(BB);

  // Because we just hoisted a loop out of this one, we have essentially
  // created new exit paths from it. That means we need to form LCSSA PHI
  // nodes for values used in the no-longer-nested loop.
  formLCSSA(*OldContainingL, DT, &LI, nullptr);

  // We shouldn't need to form dedicated exits because the exit introduced
  // here is the (just split by unswitching) preheader. However, after trivial
  // unswitching it is possible to get new non-dedicated exits out of parent
  // loop so let's conservatively form dedicated exit blocks and figure out
  // if we can optimize later.
  formDedicatedExitBlocks(OldContainingL, &DT, &LI, MSSAU,
                          /*PreserveLCSSA*/ true);
}
330}

332/// Unswitch a trivial branch if the condition is loop invariant.
333///
334/// This routine should only be called when loop code leading to the branch has
335/// been validated as trivial (no side effects). This routine checks if the
336/// condition is invariant and one of the successors is a loop exit. This
337/// allows us to unswitch without duplicating the loop, making it trivial.
338///
339/// If this routine fails to unswitch the branch it returns false.
340///
341/// If the branch can be unswitched, this routine splits the preheader and
342/// hoists the branch above that split. Preserves loop simplified form
343/// (splitting the exit block as necessary). It simplifies the branch within
344/// the loop to an unconditional branch but doesn't remove it entirely. Further
345/// cleanup can be done with some simplify-cfg like pass.
346///
347/// If `SE` is not null, it will be updated based on the potential loop SCEVs
348/// invalidated by this.
349static bool unswitchTrivialBranch(Loop &L, BranchInst &BI, DominatorTree &DT,
                                LoopInfo &LI, ScalarEvolution *SE,
                                MemorySSAUpdater *MSSAU) {
assert(BI.isConditional() && "Can only unswitch a conditional branch!")((BI.isConditional() && "Can only unswitch a conditional branch!"
) ? static_cast<void> (0) : __assert_fail ("BI.isConditional() && \"Can only unswitch a conditional branch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 352, __PRETTY_FUNCTION__));
LLVM_DEBUG(dbgs() << "  Trying to unswitch branch: " << BI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Trying to unswitch branch: "
 << BI << "\n"; } } while (false);

// The loop invariant values that we want to unswitch.
TinyPtrVector<Value *> Invariants;

// When true, we're fully unswitching the branch rather than just unswitching
// some input conditions to the branch.
bool FullUnswitch = false;

if (L.isLoopInvariant(BI.getCondition())) {
  Invariants.push_back(BI.getCondition());
  FullUnswitch = true;
} else {
  if (auto *CondInst = dyn_cast<Instruction>(BI.getCondition()))
    Invariants = collectHomogenousInstGraphLoopInvariants(L, *CondInst, LI);
  if (Invariants.empty())
    // Couldn't find invariant inputs!
    return false;
}

// Check that one of the branch's successors exits, and which one.
bool ExitDirection = true;
int LoopExitSuccIdx = 0;
auto *LoopExitBB = BI.getSuccessor(0);
if (L.contains(LoopExitBB)) {
  ExitDirection = false;
  LoopExitSuccIdx = 1;
  LoopExitBB = BI.getSuccessor(1);
  if (L.contains(LoopExitBB))
    return false;
}
auto *ContinueBB = BI.getSuccessor(1 - LoopExitSuccIdx);
auto *ParentBB = BI.getParent();
if (!areLoopExitPHIsLoopInvariant(L, *ParentBB, *LoopExitBB))
  return false;

// When unswitching only part of the branch's condition, we need the exit
// block to be reached directly from the partially unswitched input. This can
// be done when the exit block is along the true edge and the branch condition
// is a graph of `or` operations, or the exit block is along the false edge
// and the condition is a graph of `and` operations.
if (!FullUnswitch) {
  if (ExitDirection) {
    if (cast<Instruction>(BI.getCondition())->getOpcode() != Instruction::Or)
      return false;
  } else {
    if (cast<Instruction>(BI.getCondition())->getOpcode() != Instruction::And)
      return false;
  }
}

LLVM_DEBUG({do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << "    unswitching trivial invariant conditions for: "
 << BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << "      " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
  dbgs() << "    unswitching trivial invariant conditions for: " << BIdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << "    unswitching trivial invariant conditions for: "
 << BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << "      " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
         << "\n";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << "    unswitching trivial invariant conditions for: "
 << BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << "      " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
  for (Value *Invariant : Invariants) {do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << "    unswitching trivial invariant conditions for: "
 << BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << "      " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
    dbgs() << "      " << *Invariant << " == true";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << "    unswitching trivial invariant conditions for: "
 << BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << "      " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
    if (Invariant != Invariants.back())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << "    unswitching trivial invariant conditions for: "
 << BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << "      " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
      dbgs() << " ||";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << "    unswitching trivial invariant conditions for: "
 << BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << "      " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
    dbgs() << "\n";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << "    unswitching trivial invariant conditions for: "
 << BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << "      " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
  }do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << "    unswitching trivial invariant conditions for: "
 << BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << "      " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
})do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << "    unswitching trivial invariant conditions for: "
 << BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << "      " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false);

// If we have scalar evolutions, we need to invalidate them including this
// loop and the loop containing the exit block.
if (SE) {
  if (Loop *ExitL = LI.getLoopFor(LoopExitBB))
    SE->forgetLoop(ExitL);
  else
    // Forget the entire nest as this exits the entire nest.
    SE->forgetTopmostLoop(&L);
}

if (MSSAU && VerifyMemorySSA)
  MSSAU->getMemorySSA()->verifyMemorySSA();

// Split the preheader, so that we know that there is a safe place to insert
// the conditional branch. We will change the preheader to have a conditional
// branch on LoopCond.
BasicBlock *OldPH = L.getLoopPreheader();
BasicBlock *NewPH = SplitEdge(OldPH, L.getHeader(), &DT, &LI, MSSAU);

// Now that we have a place to insert the conditional branch, create a place
// to branch to: this is the exit block out of the loop that we are
// unswitching. We need to split this if there are other loop predecessors.
// Because the loop is in simplified form, *any* other predecessor is enough.
BasicBlock *UnswitchedBB;
if (FullUnswitch && LoopExitBB->getUniquePredecessor()) {
  assert(LoopExitBB->getUniquePredecessor() == BI.getParent() &&((LoopExitBB->getUniquePredecessor() == BI.getParent() &&
 "A branch's parent isn't a predecessor!") ? static_cast<void
> (0) : __assert_fail ("LoopExitBB->getUniquePredecessor() == BI.getParent() && \"A branch's parent isn't a predecessor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 441, __PRETTY_FUNCTION__))
         "A branch's parent isn't a predecessor!")((LoopExitBB->getUniquePredecessor() == BI.getParent() &&
 "A branch's parent isn't a predecessor!") ? static_cast<void
> (0) : __assert_fail ("LoopExitBB->getUniquePredecessor() == BI.getParent() && \"A branch's parent isn't a predecessor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 441, __PRETTY_FUNCTION__));
  UnswitchedBB = LoopExitBB;
} else {
  UnswitchedBB =
      SplitBlock(LoopExitBB, &LoopExitBB->front(), &DT, &LI, MSSAU);
}

if (MSSAU && VerifyMemorySSA)
  MSSAU->getMemorySSA()->verifyMemorySSA();

// Actually move the invariant uses into the unswitched position. If possible,
// we do this by moving the instructions, but when doing partial unswitching
// we do it by building a new merge of the values in the unswitched position.
OldPH->getTerminator()->eraseFromParent();
if (FullUnswitch) {
  // If fully unswitching, we can use the existing branch instruction.
  // Splice it into the old PH to gate reaching the new preheader and re-point
  // its successors.
  OldPH->getInstList().splice(OldPH->end(), BI.getParent()->getInstList(),
                              BI);
  if (MSSAU) {
    // Temporarily clone the terminator, to make MSSA update cheaper by
    // separating "insert edge" updates from "remove edge" ones.
    ParentBB->getInstList().push_back(BI.clone());
  } else {
    // Create a new unconditional branch that will continue the loop as a new
    // terminator.
    BranchInst::Create(ContinueBB, ParentBB);
  }
  BI.setSuccessor(LoopExitSuccIdx, UnswitchedBB);
  BI.setSuccessor(1 - LoopExitSuccIdx, NewPH);
} else {
  // Only unswitching a subset of inputs to the condition, so we will need to
  // build a new branch that merges the invariant inputs.
  if (ExitDirection)
    assert(cast<Instruction>(BI.getCondition())->getOpcode() ==((cast<Instruction>(BI.getCondition())->getOpcode() ==
 Instruction::Or && "Must have an `or` of `i1`s for the condition!"
) ? static_cast<void> (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Must have an `or` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 478, __PRETTY_FUNCTION__))
               Instruction::Or &&((cast<Instruction>(BI.getCondition())->getOpcode() ==
 Instruction::Or && "Must have an `or` of `i1`s for the condition!"
) ? static_cast<void> (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Must have an `or` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 478, __PRETTY_FUNCTION__))
           "Must have an `or` of `i1`s for the condition!")((cast<Instruction>(BI.getCondition())->getOpcode() ==
 Instruction::Or && "Must have an `or` of `i1`s for the condition!"
) ? static_cast<void> (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Must have an `or` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 478, __PRETTY_FUNCTION__));
  else
    assert(cast<Instruction>(BI.getCondition())->getOpcode() ==((cast<Instruction>(BI.getCondition())->getOpcode() ==
 Instruction::And && "Must have an `and` of `i1`s for the condition!"
) ? static_cast<void> (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::And && \"Must have an `and` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 482, __PRETTY_FUNCTION__))
               Instruction::And &&((cast<Instruction>(BI.getCondition())->getOpcode() ==
 Instruction::And && "Must have an `and` of `i1`s for the condition!"
) ? static_cast<void> (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::And && \"Must have an `and` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 482, __PRETTY_FUNCTION__))
           "Must have an `and` of `i1`s for the condition!")((cast<Instruction>(BI.getCondition())->getOpcode() ==
 Instruction::And && "Must have an `and` of `i1`s for the condition!"
) ? static_cast<void> (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::And && \"Must have an `and` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 482, __PRETTY_FUNCTION__));
  buildPartialUnswitchConditionalBranch(*OldPH, Invariants, ExitDirection,
                                        *UnswitchedBB, *NewPH);
}

// Update the dominator tree with the added edge.
DT.insertEdge(OldPH, UnswitchedBB);

// After the dominator tree was updated with the added edge, update MemorySSA
// if available.
if (MSSAU) {
  SmallVector<CFGUpdate, 1> Updates;
  Updates.push_back({cfg::UpdateKind::Insert, OldPH, UnswitchedBB});
  MSSAU->applyInsertUpdates(Updates, DT);
}

// Finish updating dominator tree and memory ssa for full unswitch.
if (FullUnswitch) {
  if (MSSAU) {
    // Remove the cloned branch instruction.
    ParentBB->getTerminator()->eraseFromParent();
    // Create unconditional branch now.
    BranchInst::Create(ContinueBB, ParentBB);
    MSSAU->removeEdge(ParentBB, LoopExitBB);
  }
  DT.deleteEdge(ParentBB, LoopExitBB);
}

if (MSSAU && VerifyMemorySSA)
  MSSAU->getMemorySSA()->verifyMemorySSA();

// Rewrite the relevant PHI nodes.
if (UnswitchedBB == LoopExitBB)
  rewritePHINodesForUnswitchedExitBlock(*UnswitchedBB, *ParentBB, *OldPH);
else
  rewritePHINodesForExitAndUnswitchedBlocks(*LoopExitBB, *UnswitchedBB,
                                            *ParentBB, *OldPH, FullUnswitch);

// The constant we can replace all of our invariants with inside the loop
// body. If any of the invariants have a value other than this the loop won't
// be entered.
ConstantInt *Replacement = ExitDirection
                               ? ConstantInt::getFalse(BI.getContext())
                               : ConstantInt::getTrue(BI.getContext());

// Since this is an i1 condition we can also trivially replace uses of it
// within the loop with a constant.
for (Value *Invariant : Invariants)
  replaceLoopInvariantUses(L, Invariant, *Replacement);

// If this was full unswitching, we may have changed the nesting relationship
// for this loop so hoist it to its correct parent if needed.
if (FullUnswitch)
  hoistLoopToNewParent(L, *NewPH, DT, LI, MSSAU);

if (MSSAU && VerifyMemorySSA)
  MSSAU->getMemorySSA()->verifyMemorySSA();

LLVM_DEBUG(dbgs() << "    done: unswitching trivial branch...\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "    done: unswitching trivial branch...\n"
; } } while (false);
++NumTrivial;
++NumBranches;
return true;
544}

546/// Unswitch a trivial switch if the condition is loop invariant.
547///
548/// This routine should only be called when loop code leading to the switch has
549/// been validated as trivial (no side effects). This routine checks if the
550/// condition is invariant and that at least one of the successors is a loop
551/// exit. This allows us to unswitch without duplicating the loop, making it
552/// trivial.
553///
554/// If this routine fails to unswitch the switch it returns false.
555///
556/// If the switch can be unswitched, this routine splits the preheader and
557/// copies the switch above that split. If the default case is one of the
558/// exiting cases, it copies the non-exiting cases and points them at the new
559/// preheader. If the default case is not exiting, it copies the exiting cases
560/// and points the default at the preheader. It preserves loop simplified form
561/// (splitting the exit blocks as necessary). It simplifies the switch within
562/// the loop by removing now-dead cases. If the default case is one of those
563/// unswitched, it replaces its destination with a new basic block containing
564/// only unreachable. Such basic blocks, while technically loop exits, are not
565/// considered for unswitching so this is a stable transform and the same
566/// switch will not be revisited. If after unswitching there is only a single
567/// in-loop successor, the switch is further simplified to an unconditional
568/// branch. Still more cleanup can be done with some simplify-cfg like pass.
569///
570/// If `SE` is not null, it will be updated based on the potential loop SCEVs
571/// invalidated by this.
572static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
                                LoopInfo &LI, ScalarEvolution *SE,
                                MemorySSAUpdater *MSSAU) {
LLVM_DEBUG(dbgs() << "  Trying to unswitch switch: " << SI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Trying to unswitch switch: "
 << SI << "\n"; } } while (false);
Value *LoopCond = SI.getCondition();

// If this isn't switching on an invariant condition, we can't unswitch it.
if (!L.isLoopInvariant(LoopCond))
  return false;

auto *ParentBB = SI.getParent();

SmallVector<int, 4> ExitCaseIndices;
for (auto Case : SI.cases()) {
  auto *SuccBB = Case.getCaseSuccessor();
  if (!L.contains(SuccBB) &&
      areLoopExitPHIsLoopInvariant(L, *ParentBB, *SuccBB))
    ExitCaseIndices.push_back(Case.getCaseIndex());
}
BasicBlock *DefaultExitBB = nullptr;
SwitchInstProfUpdateWrapper::CaseWeightOpt DefaultCaseWeight =
    SwitchInstProfUpdateWrapper::getSuccessorWeight(SI, 0);
if (!L.contains(SI.getDefaultDest()) &&
    areLoopExitPHIsLoopInvariant(L, *ParentBB, *SI.getDefaultDest()) &&
    !isa<UnreachableInst>(SI.getDefaultDest()->getTerminator())) {
  DefaultExitBB = SI.getDefaultDest();
} else if (ExitCaseIndices.empty())
  return false;

LLVM_DEBUG(dbgs() << "    unswitching trivial switch...\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "    unswitching trivial switch...\n"
; } } while (false);

if (MSSAU && VerifyMemorySSA)
  MSSAU->getMemorySSA()->verifyMemorySSA();

// We may need to invalidate SCEVs for the outermost loop reached by any of
// the exits.
Loop *OuterL = &L;

if (DefaultExitBB) {
  // Clear out the default destination temporarily to allow accurate
  // predecessor lists to be examined below.
  SI.setDefaultDest(nullptr);
  // Check the loop containing this exit.
  Loop *ExitL = LI.getLoopFor(DefaultExitBB);
  if (!ExitL || ExitL->contains(OuterL))
    OuterL = ExitL;
}

// Store the exit cases into a separate data structure and remove them from
// the switch.
SmallVector<std::tuple<ConstantInt *, BasicBlock *,
                       SwitchInstProfUpdateWrapper::CaseWeightOpt>,
            4> ExitCases;
ExitCases.reserve(ExitCaseIndices.size());
SwitchInstProfUpdateWrapper SIW(SI);
// We walk the case indices backwards so that we remove the last case first
// and don't disrupt the earlier indices.
for (unsigned Index : reverse(ExitCaseIndices)) {
  auto CaseI = SI.case_begin() + Index;
  // Compute the outer loop from this exit.
  Loop *ExitL = LI.getLoopFor(CaseI->getCaseSuccessor());
  if (!ExitL || ExitL->contains(OuterL))
    OuterL = ExitL;
  // Save the value of this case.
  auto W = SIW.getSuccessorWeight(CaseI->getSuccessorIndex());
  ExitCases.emplace_back(CaseI->getCaseValue(), CaseI->getCaseSuccessor(), W);
  // Delete the unswitched cases.
  SIW.removeCase(CaseI);
}

if (SE) {
  if (OuterL)
    SE->forgetLoop(OuterL);
  else
    SE->forgetTopmostLoop(&L);
}

// Check if after this all of the remaining cases point at the same
// successor.
BasicBlock *CommonSuccBB = nullptr;
if (SI.getNumCases() > 0 &&
    std::all_of(std::next(SI.case_begin()), SI.case_end(),
                [&SI](const SwitchInst::CaseHandle &Case) {
                  return Case.getCaseSuccessor() ==
                         SI.case_begin()->getCaseSuccessor();
                }))
  CommonSuccBB = SI.case_begin()->getCaseSuccessor();
if (!DefaultExitBB) {
  // If we're not unswitching the default, we need it to match any cases to
  // have a common successor or if we have no cases it is the common
  // successor.
  if (SI.getNumCases() == 0)
    CommonSuccBB = SI.getDefaultDest();
  else if (SI.getDefaultDest() != CommonSuccBB)
    CommonSuccBB = nullptr;
}

// Split the preheader, so that we know that there is a safe place to insert
// the switch.
BasicBlock *OldPH = L.getLoopPreheader();
BasicBlock *NewPH = SplitEdge(OldPH, L.getHeader(), &DT, &LI, MSSAU);
OldPH->getTerminator()->eraseFromParent();

// Now add the unswitched switch.
auto *NewSI = SwitchInst::Create(LoopCond, NewPH, ExitCases.size(), OldPH);
SwitchInstProfUpdateWrapper NewSIW(*NewSI);

// Rewrite the IR for the unswitched basic blocks. This requires two steps.
// First, we split any exit blocks with remaining in-loop predecessors. Then
// we update the PHIs in one of two ways depending on if there was a split.
// We walk in reverse so that we split in the same order as the cases
// appeared. This is purely for convenience of reading the resulting IR, but
// it doesn't cost anything really.
SmallPtrSet<BasicBlock *, 2> UnswitchedExitBBs;
SmallDenseMap<BasicBlock *, BasicBlock *, 2> SplitExitBBMap;
// Handle the default exit if necessary.
// FIXME: It'd be great if we could merge this with the loop below but LLVM's
// ranges aren't quite powerful enough yet.
if (DefaultExitBB) {
  if (pred_empty(DefaultExitBB)) {
    UnswitchedExitBBs.insert(DefaultExitBB);
    rewritePHINodesForUnswitchedExitBlock(*DefaultExitBB, *ParentBB, *OldPH);
  } else {
    auto *SplitBB =
        SplitBlock(DefaultExitBB, &DefaultExitBB->front(), &DT, &LI, MSSAU);
    rewritePHINodesForExitAndUnswitchedBlocks(*DefaultExitBB, *SplitBB,
                                              *ParentBB, *OldPH,
                                              /*FullUnswitch*/ true);
    DefaultExitBB = SplitExitBBMap[DefaultExitBB] = SplitBB;
  }
}
// Note that we must use a reference in the for loop so that we update the
// container.
for (auto &ExitCase : reverse(ExitCases)) {
  // Grab a reference to the exit block in the pair so that we can update it.
  BasicBlock *ExitBB = std::get<1>(ExitCase);

  // If this case is the last edge into the exit block, we can simply reuse it
  // as it will no longer be a loop exit. No mapping necessary.
  if (pred_empty(ExitBB)) {
    // Only rewrite once.
    if (UnswitchedExitBBs.insert(ExitBB).second)
      rewritePHINodesForUnswitchedExitBlock(*ExitBB, *ParentBB, *OldPH);
    continue;
  }

  // Otherwise we need to split the exit block so that we retain an exit
  // block from the loop and a target for the unswitched condition.
  BasicBlock *&SplitExitBB = SplitExitBBMap[ExitBB];
  if (!SplitExitBB) {
    // If this is the first time we see this, do the split and remember it.
    SplitExitBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI, MSSAU);
    rewritePHINodesForExitAndUnswitchedBlocks(*ExitBB, *SplitExitBB,
                                              *ParentBB, *OldPH,
                                              /*FullUnswitch*/ true);
  }
  // Update the case pair to point to the split block.
  std::get<1>(ExitCase) = SplitExitBB;
}

// Now add the unswitched cases. We do this in reverse order as we built them
// in reverse order.
for (auto &ExitCase : reverse(ExitCases)) {
  ConstantInt *CaseVal = std::get<0>(ExitCase);
  BasicBlock *UnswitchedBB = std::get<1>(ExitCase);

  NewSIW.addCase(CaseVal, UnswitchedBB, std::get<2>(ExitCase));
}

// If the default was unswitched, re-point it and add explicit cases for
// entering the loop.
if (DefaultExitBB) {
  NewSIW->setDefaultDest(DefaultExitBB);
  NewSIW.setSuccessorWeight(0, DefaultCaseWeight);

  // We removed all the exit cases, so we just copy the cases to the
  // unswitched switch.
  for (const auto &Case : SI.cases())
    NewSIW.addCase(Case.getCaseValue(), NewPH,
                   SIW.getSuccessorWeight(Case.getSuccessorIndex()));
} else if (DefaultCaseWeight) {
  // We have to set branch weight of the default case.
  uint64_t SW = *DefaultCaseWeight;
  for (const auto &Case : SI.cases()) {
    auto W = SIW.getSuccessorWeight(Case.getSuccessorIndex());
    assert(W &&((W && "case weight must be defined as default case weight is defined"
) ? static_cast<void> (0) : __assert_fail ("W && \"case weight must be defined as default case weight is defined\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 758, __PRETTY_FUNCTION__))
           "case weight must be defined as default case weight is defined")((W && "case weight must be defined as default case weight is defined"
) ? static_cast<void> (0) : __assert_fail ("W && \"case weight must be defined as default case weight is defined\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 758, __PRETTY_FUNCTION__));
    SW += *W;
  }
  NewSIW.setSuccessorWeight(0, SW);
}

// If we ended up with a common successor for every path through the switch
// after unswitching, rewrite it to an unconditional branch to make it easy
// to recognize. Otherwise we potentially have to recognize the default case
// pointing at unreachable and other complexity.
if (CommonSuccBB) {
  BasicBlock *BB = SI.getParent();
  // We may have had multiple edges to this common successor block, so remove
  // them as predecessors. We skip the first one, either the default or the
  // actual first case.
  bool SkippedFirst = DefaultExitBB == nullptr;
  for (auto Case : SI.cases()) {
    assert(Case.getCaseSuccessor() == CommonSuccBB &&((Case.getCaseSuccessor() == CommonSuccBB && "Non-common successor!"
) ? static_cast<void> (0) : __assert_fail ("Case.getCaseSuccessor() == CommonSuccBB && \"Non-common successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 776, __PRETTY_FUNCTION__))
           "Non-common successor!")((Case.getCaseSuccessor() == CommonSuccBB && "Non-common successor!"
) ? static_cast<void> (0) : __assert_fail ("Case.getCaseSuccessor() == CommonSuccBB && \"Non-common successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 776, __PRETTY_FUNCTION__));
    (void)Case;
    if (!SkippedFirst) {
      SkippedFirst = true;
      continue;
    }
    CommonSuccBB->removePredecessor(BB,
                                    /*KeepOneInputPHIs*/ true);
  }
  // Now nuke the switch and replace it with a direct branch.
  SIW.eraseFromParent();
  BranchInst::Create(CommonSuccBB, BB);
} else if (DefaultExitBB) {
  assert(SI.getNumCases() > 0 &&((SI.getNumCases() > 0 && "If we had no cases we'd have a common successor!"
) ? static_cast<void> (0) : __assert_fail ("SI.getNumCases() > 0 && \"If we had no cases we'd have a common successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 790, __PRETTY_FUNCTION__))
         "If we had no cases we'd have a common successor!")((SI.getNumCases() > 0 && "If we had no cases we'd have a common successor!"
) ? static_cast<void> (0) : __assert_fail ("SI.getNumCases() > 0 && \"If we had no cases we'd have a common successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 790, __PRETTY_FUNCTION__));
  // Move the last case to the default successor. This is valid as if the
  // default got unswitched it cannot be reached. This has the advantage of
  // being simple and keeping the number of edges from this switch to
  // successors the same, and avoiding any PHI update complexity.
  auto LastCaseI = std::prev(SI.case_end());

  SI.setDefaultDest(LastCaseI->getCaseSuccessor());
  SIW.setSuccessorWeight(
      0, SIW.getSuccessorWeight(LastCaseI->getSuccessorIndex()));
  SIW.removeCase(LastCaseI);
}

// Walk the unswitched exit blocks and the unswitched split blocks and update
// the dominator tree based on the CFG edits. While we are walking unordered
// containers here, the API for applyUpdates takes an unordered list of
// updates and requires them to not contain duplicates.
SmallVector<DominatorTree::UpdateType, 4> DTUpdates;
for (auto *UnswitchedExitBB : UnswitchedExitBBs) {
  DTUpdates.push_back({DT.Delete, ParentBB, UnswitchedExitBB});
  DTUpdates.push_back({DT.Insert, OldPH, UnswitchedExitBB});
}
for (auto SplitUnswitchedPair : SplitExitBBMap) {
  DTUpdates.push_back({DT.Delete, ParentBB, SplitUnswitchedPair.first});
  DTUpdates.push_back({DT.Insert, OldPH, SplitUnswitchedPair.second});
}
DT.applyUpdates(DTUpdates);

if (MSSAU) {
  MSSAU->applyUpdates(DTUpdates, DT);
  if (VerifyMemorySSA)
    MSSAU->getMemorySSA()->verifyMemorySSA();
}

assert(DT.verify(DominatorTree::VerificationLevel::Fast))((DT.verify(DominatorTree::VerificationLevel::Fast)) ? static_cast
<void> (0) : __assert_fail ("DT.verify(DominatorTree::VerificationLevel::Fast)"
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 824, __PRETTY_FUNCTION__));

// We may have changed the nesting relationship for this loop so hoist it to
// its correct parent if needed.
hoistLoopToNewParent(L, *NewPH, DT, LI, MSSAU);

if (MSSAU && VerifyMemorySSA)
  MSSAU->getMemorySSA()->verifyMemorySSA();

++NumTrivial;
++NumSwitches;
LLVM_DEBUG(dbgs() << "    done: unswitching trivial switch...\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "    done: unswitching trivial switch...\n"
; } } while (false);
return true;
837}

839/// This routine scans the loop to find a branch or switch which occurs before
840/// any side effects occur. These can potentially be unswitched without
841/// duplicating the loop. If a branch or switch is successfully unswitched the
842/// scanning continues to see if subsequent branches or switches have become
843/// trivial. Once all trivial candidates have been unswitched, this routine
844/// returns.
845///
846/// The return value indicates whether anything was unswitched (and therefore
847/// changed).
848///
849/// If `SE` is not null, it will be updated based on the potential loop SCEVs
850/// invalidated by this.
851static bool unswitchAllTrivialConditions(Loop &L, DominatorTree &DT,
                                       LoopInfo &LI, ScalarEvolution *SE,
                                       MemorySSAUpdater *MSSAU) {
bool Changed = false;

// If loop header has only one reachable successor we should keep looking for
// trivial condition candidates in the successor as well. An alternative is
// to constant fold conditions and merge successors into loop header (then we
// only need to check header's terminator). The reason for not doing this in
// LoopUnswitch pass is that it could potentially break LoopPassManager's
// invariants. Folding dead branches could either eliminate the current loop
// or make other loops unreachable. LCSSA form might also not be preserved
// after deleting branches. The following code keeps traversing loop header's
// successors until it finds the trivial condition candidate (condition that
// is not a constant). Since unswitching generates branches with constant
// conditions, this scenario could be very common in practice.
BasicBlock *CurrentBB = L.getHeader();
SmallPtrSet<BasicBlock *, 8> Visited;
Visited.insert(CurrentBB);
do {
  // Check if there are any side-effecting instructions (e.g. stores, calls,
  // volatile loads) in the part of the loop that the code *would* execute
  // without unswitching.
  if (MSSAU) // Possible early exit with MSSA
    if (auto *Defs = MSSAU->getMemorySSA()->getBlockDefs(CurrentBB))
      if (!isa<MemoryPhi>(*Defs->begin()) || (++Defs->begin() != Defs->end()))
        return Changed;
  if (llvm::any_of(*CurrentBB,
                   [](Instruction &I) { return I.mayHaveSideEffects(); }))
    return Changed;

  Instruction *CurrentTerm = CurrentBB->getTerminator();

  if (auto *SI = dyn_cast<SwitchInst>(CurrentTerm)) {
    // Don't bother trying to unswitch past a switch with a constant
    // condition. This should be removed prior to running this pass by
    // simplify-cfg.
    if (isa<Constant>(SI->getCondition()))
      return Changed;

    if (!unswitchTrivialSwitch(L, *SI, DT, LI, SE, MSSAU))
      // Couldn't unswitch this one so we're done.
      return Changed;

    // Mark that we managed to unswitch something.
    Changed = true;

    // If unswitching turned the terminator into an unconditional branch then
    // we can continue. The unswitching logic specifically works to fold any
    // cases it can into an unconditional branch to make it easier to
    // recognize here.
    auto *BI = dyn_cast<BranchInst>(CurrentBB->getTerminator());
    if (!BI || BI->isConditional())
      return Changed;

    CurrentBB = BI->getSuccessor(0);
    continue;
  }

  auto *BI = dyn_cast<BranchInst>(CurrentTerm);
  if (!BI)
    // We do not understand other terminator instructions.
    return Changed;

  // Don't bother trying to unswitch past an unconditional branch or a branch
  // with a constant value. These should be removed by simplify-cfg prior to
  // running this pass.
  if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
    return Changed;

  // Found a trivial condition candidate: non-foldable conditional branch. If
  // we fail to unswitch this, we can't do anything else that is trivial.
  if (!unswitchTrivialBranch(L, *BI, DT, LI, SE, MSSAU))
    return Changed;

  // Mark that we managed to unswitch something.
  Changed = true;

  // If we only unswitched some of the conditions feeding the branch, we won't
  // have collapsed it to a single successor.
  BI = cast<BranchInst>(CurrentBB->getTerminator());
  if (BI->isConditional())
    return Changed;

  // Follow the newly unconditional branch into its successor.
  CurrentBB = BI->getSuccessor(0);

  // When continuing, if we exit the loop or reach a previous visited block,
  // then we can not reach any trivial condition candidates (unfoldable
  // branch instructions or switch instructions) and no unswitch can happen.
} while (L.contains(CurrentBB) && Visited.insert(CurrentBB).second);

return Changed;
944}

946/// Build the cloned blocks for an unswitched copy of the given loop.
947///
948/// The cloned blocks are inserted before the loop preheader (`LoopPH`) and
949/// after the split block (`SplitBB`) that will be used to select between the
950/// cloned and original loop.
951///
952/// This routine handles cloning all of the necessary loop blocks and exit
953/// blocks including rewriting their instructions and the relevant PHI nodes.
954/// Any loop blocks or exit blocks which are dominated by a different successor
955/// than the one for this clone of the loop blocks can be trivially skipped. We
956/// use the `DominatingSucc` map to determine whether a block satisfies that
957/// property with a simple map lookup.
958///
959/// It also correctly creates the unconditional branch in the cloned
960/// unswitched parent block to only point at the unswitched successor.
961///
962/// This does not handle most of the necessary updates to `LoopInfo`. Only exit
963/// block splitting is correctly reflected in `LoopInfo`, essentially all of
964/// the cloned blocks (and their loops) are left without full `LoopInfo`
965/// updates. This also doesn't fully update `DominatorTree`. It adds the cloned
966/// blocks to them but doesn't create the cloned `DominatorTree` structure and
967/// instead the caller must recompute an accurate DT. It *does* correctly
968/// update the `AssumptionCache` provided in `AC`.
969static BasicBlock *buildClonedLoopBlocks(
  Loop &L, BasicBlock *LoopPH, BasicBlock *SplitBB,
  ArrayRef<BasicBlock *> ExitBlocks, BasicBlock *ParentBB,
  BasicBlock *UnswitchedSuccBB, BasicBlock *ContinueSuccBB,
  const SmallDenseMap<BasicBlock *, BasicBlock *, 16> &DominatingSucc,
  ValueToValueMapTy &VMap,
  SmallVectorImpl<DominatorTree::UpdateType> &DTUpdates, AssumptionCache &AC,
  DominatorTree &DT, LoopInfo &LI, MemorySSAUpdater *MSSAU) {
SmallVector<BasicBlock *, 4> NewBlocks;
NewBlocks.reserve(L.getNumBlocks() + ExitBlocks.size());

// We will need to clone a bunch of blocks, wrap up the clone operation in
// a helper.
auto CloneBlock = [&](BasicBlock *OldBB) {
  // Clone the basic block and insert it before the new preheader.
  BasicBlock *NewBB = CloneBasicBlock(OldBB, VMap, ".us", OldBB->getParent());
  NewBB->moveBefore(LoopPH);

  // Record this block and the mapping.
  NewBlocks.push_back(NewBB);
  VMap[OldBB] = NewBB;

  return NewBB;
};

// We skip cloning blocks when they have a dominating succ that is not the
// succ we are cloning for.
auto SkipBlock = [&](BasicBlock *BB) {
  auto It = DominatingSucc.find(BB);
  return It != DominatingSucc.end() && It->second != UnswitchedSuccBB;
};

// First, clone the preheader.
auto *ClonedPH = CloneBlock(LoopPH);

// Then clone all the loop blocks, skipping the ones that aren't necessary.
for (auto *LoopBB : L.blocks())
  if (!SkipBlock(LoopBB))
    CloneBlock(LoopBB);

// Split all the loop exit edges so that when we clone the exit blocks, if
// any of the exit blocks are *also* a preheader for some other loop, we
// don't create multiple predecessors entering the loop header.
for (auto *ExitBB : ExitBlocks) {
  if (SkipBlock(ExitBB))
    continue;

  // When we are going to clone an exit, we don't need to clone all the
  // instructions in the exit block and we want to ensure we have an easy
  // place to merge the CFG, so split the exit first. This is always safe to
  // do because there cannot be any non-loop predecessors of a loop exit in
  // loop simplified form.
  auto *MergeBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI, MSSAU);

  // Rearrange the names to make it easier to write test cases by having the
  // exit block carry the suffix rather than the merge block carrying the
  // suffix.
  MergeBB->takeName(ExitBB);
  ExitBB->setName(Twine(MergeBB->getName()) + ".split");

  // Now clone the original exit block.
  auto *ClonedExitBB = CloneBlock(ExitBB);
  assert(ClonedExitBB->getTerminator()->getNumSuccessors() == 1 &&((ClonedExitBB->getTerminator()->getNumSuccessors() == 1
 && "Exit block should have been split to have one successor!"
) ? static_cast<void> (0) : __assert_fail ("ClonedExitBB->getTerminator()->getNumSuccessors() == 1 && \"Exit block should have been split to have one successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1032, __PRETTY_FUNCTION__))
         "Exit block should have been split to have one successor!")((ClonedExitBB->getTerminator()->getNumSuccessors() == 1
 && "Exit block should have been split to have one successor!"
) ? static_cast<void> (0) : __assert_fail ("ClonedExitBB->getTerminator()->getNumSuccessors() == 1 && \"Exit block should have been split to have one successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1032, __PRETTY_FUNCTION__));
  assert(ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB &&((ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB
 && "Cloned exit block has the wrong successor!") ? static_cast
<void> (0) : __assert_fail ("ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB && \"Cloned exit block has the wrong successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1034, __PRETTY_FUNCTION__))
         "Cloned exit block has the wrong successor!")((ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB
 && "Cloned exit block has the wrong successor!") ? static_cast
<void> (0) : __assert_fail ("ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB && \"Cloned exit block has the wrong successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1034, __PRETTY_FUNCTION__));

  // Remap any cloned instructions and create a merge phi node for them.
  for (auto ZippedInsts : llvm::zip_first(
           llvm::make_range(ExitBB->begin(), std::prev(ExitBB->end())),
           llvm::make_range(ClonedExitBB->begin(),
                            std::prev(ClonedExitBB->end())))) {
    Instruction &I = std::get<0>(ZippedInsts);
    Instruction &ClonedI = std::get<1>(ZippedInsts);

    // The only instructions in the exit block should be PHI nodes and
    // potentially a landing pad.
    assert((((isa<PHINode>(I) || isa<LandingPadInst>(I) || isa
<CatchPadInst>(I)) && "Bad instruction in exit block!"
) ? static_cast<void> (0) : __assert_fail ("(isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) && \"Bad instruction in exit block!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1048, __PRETTY_FUNCTION__))
        (isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) &&(((isa<PHINode>(I) || isa<LandingPadInst>(I) || isa
<CatchPadInst>(I)) && "Bad instruction in exit block!"
) ? static_cast<void> (0) : __assert_fail ("(isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) && \"Bad instruction in exit block!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1048, __PRETTY_FUNCTION__))
        "Bad instruction in exit block!")(((isa<PHINode>(I) || isa<LandingPadInst>(I) || isa
<CatchPadInst>(I)) && "Bad instruction in exit block!"
) ? static_cast<void> (0) : __assert_fail ("(isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) && \"Bad instruction in exit block!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1048, __PRETTY_FUNCTION__));
    // We should have a value map between the instruction and its clone.
    assert(VMap.lookup(&I) == &ClonedI && "Mismatch in the value map!")((VMap.lookup(&I) == &ClonedI && "Mismatch in the value map!"
) ? static_cast<void> (0) : __assert_fail ("VMap.lookup(&I) == &ClonedI && \"Mismatch in the value map!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1050, __PRETTY_FUNCTION__));

    auto *MergePN =
        PHINode::Create(I.getType(), /*NumReservedValues*/ 2, ".us-phi",
                        &*MergeBB->getFirstInsertionPt());
    I.replaceAllUsesWith(MergePN);
    MergePN->addIncoming(&I, ExitBB);
    MergePN->addIncoming(&ClonedI, ClonedExitBB);
  }
}

// Rewrite the instructions in the cloned blocks to refer to the instructions
// in the cloned blocks. We have to do this as a second pass so that we have
// everything available. Also, we have inserted new instructions which may
// include assume intrinsics, so we update the assumption cache while
// processing this.
for (auto *ClonedBB : NewBlocks)
  for (Instruction &I : *ClonedBB) {
    RemapInstruction(&I, VMap,
                     RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
    if (auto *II = dyn_cast<IntrinsicInst>(&I))
      if (II->getIntrinsicID() == Intrinsic::assume)
        AC.registerAssumption(II);
  }

// Update any PHI nodes in the cloned successors of the skipped blocks to not
// have spurious incoming values.
for (auto *LoopBB : L.blocks())
  if (SkipBlock(LoopBB))
    for (auto *SuccBB : successors(LoopBB))
      if (auto *ClonedSuccBB = cast_or_null<BasicBlock>(VMap.lookup(SuccBB)))
        for (PHINode &PN : ClonedSuccBB->phis())
          PN.removeIncomingValue(LoopBB, /*DeletePHIIfEmpty*/ false);

// Remove the cloned parent as a predecessor of any successor we ended up
// cloning other than the unswitched one.
auto *ClonedParentBB = cast<BasicBlock>(VMap.lookup(ParentBB));
for (auto *SuccBB : successors(ParentBB)) {
  if (SuccBB == UnswitchedSuccBB)
    continue;

  auto *ClonedSuccBB = cast_or_null<BasicBlock>(VMap.lookup(SuccBB));
  if (!ClonedSuccBB)
    continue;

  ClonedSuccBB->removePredecessor(ClonedParentBB,
                                  /*KeepOneInputPHIs*/ true);
}

// Replace the cloned branch with an unconditional branch to the cloned
// unswitched successor.
auto *ClonedSuccBB = cast<BasicBlock>(VMap.lookup(UnswitchedSuccBB));
ClonedParentBB->getTerminator()->eraseFromParent();
BranchInst::Create(ClonedSuccBB, ClonedParentBB);

// If there are duplicate entries in the PHI nodes because of multiple edges
// to the unswitched successor, we need to nuke all but one as we replaced it
// with a direct branch.
for (PHINode &PN : ClonedSuccBB->phis()) {
  bool Found = false;
  // Loop over the incoming operands backwards so we can easily delete as we
  // go without invalidating the index.
  for (int i = PN.getNumOperands() - 1; i >= 0; --i) {
    if (PN.getIncomingBlock(i) != ClonedParentBB)
      continue;
    if (!Found) {
      Found = true;
      continue;
    }
    PN.removeIncomingValue(i, /*DeletePHIIfEmpty*/ false);
  }
}

// Record the domtree updates for the new blocks.
SmallPtrSet<BasicBlock *, 4> SuccSet;
for (auto *ClonedBB : NewBlocks) {
  for (auto *SuccBB : successors(ClonedBB))
    if (SuccSet.insert(SuccBB).second)
      DTUpdates.push_back({DominatorTree::Insert, ClonedBB, SuccBB});
  SuccSet.clear();
}

return ClonedPH;
1133}

1135/// Recursively clone the specified loop and all of its children.
1136///
1137/// The target parent loop for the clone should be provided, or can be null if
1138/// the clone is a top-level loop. While cloning, all the blocks are mapped
1139/// with the provided value map. The entire original loop must be present in
1140/// the value map. The cloned loop is returned.
1141static Loop *cloneLoopNest(Loop &OrigRootL, Loop *RootParentL,
                         const ValueToValueMapTy &VMap, LoopInfo &LI) {
auto AddClonedBlocksToLoop = [&](Loop &OrigL, Loop &ClonedL) {
  assert(ClonedL.getBlocks().empty() && "Must start with an empty loop!")((ClonedL.getBlocks().empty() && "Must start with an empty loop!"
) ? static_cast<void> (0) : __assert_fail ("ClonedL.getBlocks().empty() && \"Must start with an empty loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1144, __PRETTY_FUNCTION__));
  ClonedL.reserveBlocks(OrigL.getNumBlocks());
  for (auto *BB : OrigL.blocks()) {
    auto *ClonedBB = cast<BasicBlock>(VMap.lookup(BB));
    ClonedL.addBlockEntry(ClonedBB);
    if (LI.getLoopFor(BB) == &OrigL)
      LI.changeLoopFor(ClonedBB, &ClonedL);
  }
};

// We specially handle the first loop because it may get cloned into
// a different parent and because we most commonly are cloning leaf loops.
Loop *ClonedRootL = LI.AllocateLoop();
if (RootParentL)
  RootParentL->addChildLoop(ClonedRootL);
else
  LI.addTopLevelLoop(ClonedRootL);
AddClonedBlocksToLoop(OrigRootL, *ClonedRootL);

if (OrigRootL.empty())
  return ClonedRootL;

// If we have a nest, we can quickly clone the entire loop nest using an
// iterative approach because it is a tree. We keep the cloned parent in the
// data structure to avoid repeatedly querying through a map to find it.
SmallVector<std::pair<Loop *, Loop *>, 16> LoopsToClone;
// Build up the loops to clone in reverse order as we'll clone them from the
// back.
for (Loop *ChildL : llvm::reverse(OrigRootL))
  LoopsToClone.push_back({ClonedRootL, ChildL});
do {
  Loop *ClonedParentL, *L;
  std::tie(ClonedParentL, L) = LoopsToClone.pop_back_val();
  Loop *ClonedL = LI.AllocateLoop();
  ClonedParentL->addChildLoop(ClonedL);
  AddClonedBlocksToLoop(*L, *ClonedL);
  for (Loop *ChildL : llvm::reverse(*L))
    LoopsToClone.push_back({ClonedL, ChildL});
} while (!LoopsToClone.empty());

return ClonedRootL;
1185}

1187/// Build the cloned loops of an original loop from unswitching.
1188///
1189/// Because unswitching simplifies the CFG of the loop, this isn't a trivial
1190/// operation. We need to re-verify that there even is a loop (as the backedge
1191/// may not have been cloned), and even if there are remaining backedges the
1192/// backedge set may be different. However, we know that each child loop is
1193/// undisturbed, we only need to find where to place each child loop within
1194/// either any parent loop or within a cloned version of the original loop.
1195///
1196/// Because child loops may end up cloned outside of any cloned version of the
1197/// original loop, multiple cloned sibling loops may be created. All of them
1198/// are returned so that the newly introduced loop nest roots can be
1199/// identified.
1200static void buildClonedLoops(Loop &OrigL, ArrayRef<BasicBlock *> ExitBlocks,
                           const ValueToValueMapTy &VMap, LoopInfo &LI,
                           SmallVectorImpl<Loop *> &NonChildClonedLoops) {
Loop *ClonedL = nullptr;

auto *OrigPH = OrigL.getLoopPreheader();
auto *OrigHeader = OrigL.getHeader();

auto *ClonedPH = cast<BasicBlock>(VMap.lookup(OrigPH));
auto *ClonedHeader = cast<BasicBlock>(VMap.lookup(OrigHeader));

// We need to know the loops of the cloned exit blocks to even compute the
// accurate parent loop. If we only clone exits to some parent of the
// original parent, we want to clone into that outer loop. We also keep track
// of the loops that our cloned exit blocks participate in.
Loop *ParentL = nullptr;
SmallVector<BasicBlock *, 4> ClonedExitsInLoops;
SmallDenseMap<BasicBlock *, Loop *, 16> ExitLoopMap;
ClonedExitsInLoops.reserve(ExitBlocks.size());
for (auto *ExitBB : ExitBlocks)
  if (auto *ClonedExitBB = cast_or_null<BasicBlock>(VMap.lookup(ExitBB)))
    if (Loop *ExitL = LI.getLoopFor(ExitBB)) {
      ExitLoopMap[ClonedExitBB] = ExitL;
      ClonedExitsInLoops.push_back(ClonedExitBB);
      if (!ParentL || (ParentL != ExitL && ParentL->contains(ExitL)))
        ParentL = ExitL;
    }
assert((!ParentL || ParentL == OrigL.getParentLoop() ||(((!ParentL || ParentL == OrigL.getParentLoop() || ParentL->
contains(OrigL.getParentLoop())) && "The computed parent loop should always contain (or be) the parent of "
 "the original loop.") ? static_cast<void> (0) : __assert_fail
 ("(!ParentL || ParentL == OrigL.getParentLoop() || ParentL->contains(OrigL.getParentLoop())) && \"The computed parent loop should always contain (or be) the parent of \" \"the original loop.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1230, __PRETTY_FUNCTION__))
        ParentL->contains(OrigL.getParentLoop())) &&(((!ParentL || ParentL == OrigL.getParentLoop() || ParentL->
contains(OrigL.getParentLoop())) && "The computed parent loop should always contain (or be) the parent of "
 "the original loop.") ? static_cast<void> (0) : __assert_fail
 ("(!ParentL || ParentL == OrigL.getParentLoop() || ParentL->contains(OrigL.getParentLoop())) && \"The computed parent loop should always contain (or be) the parent of \" \"the original loop.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1230, __PRETTY_FUNCTION__))
       "The computed parent loop should always contain (or be) the parent of "(((!ParentL || ParentL == OrigL.getParentLoop() || ParentL->
contains(OrigL.getParentLoop())) && "The computed parent loop should always contain (or be) the parent of "
 "the original loop.") ? static_cast<void> (0) : __assert_fail
 ("(!ParentL || ParentL == OrigL.getParentLoop() || ParentL->contains(OrigL.getParentLoop())) && \"The computed parent loop should always contain (or be) the parent of \" \"the original loop.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1230, __PRETTY_FUNCTION__))
       "the original loop.")(((!ParentL || ParentL == OrigL.getParentLoop() || ParentL->
contains(OrigL.getParentLoop())) && "The computed parent loop should always contain (or be) the parent of "
 "the original loop.") ? static_cast<void> (0) : __assert_fail
 ("(!ParentL || ParentL == OrigL.getParentLoop() || ParentL->contains(OrigL.getParentLoop())) && \"The computed parent loop should always contain (or be) the parent of \" \"the original loop.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1230, __PRETTY_FUNCTION__));

// We build the set of blocks dominated by the cloned header from the set of
// cloned blocks out of the original loop. While not all of these will
// necessarily be in the cloned loop, it is enough to establish that they
// aren't in unreachable cycles, etc.
SmallSetVector<BasicBlock *, 16> ClonedLoopBlocks;
for (auto *BB : OrigL.blocks())
  if (auto *ClonedBB = cast_or_null<BasicBlock>(VMap.lookup(BB)))
    ClonedLoopBlocks.insert(ClonedBB);

// Rebuild the set of blocks that will end up in the cloned loop. We may have
// skipped cloning some region of this loop which can in turn skip some of
// the backedges so we have to rebuild the blocks in the loop based on the
// backedges that remain after cloning.
SmallVector<BasicBlock *, 16> Worklist;
SmallPtrSet<BasicBlock *, 16> BlocksInClonedLoop;
for (auto *Pred : predecessors(ClonedHeader)) {
  // The only possible non-loop header predecessor is the preheader because
  // we know we cloned the loop in simplified form.
  if (Pred == ClonedPH)
    continue;

  // Because the loop was in simplified form, the only non-loop predecessor
  // should be the preheader.
  assert(ClonedLoopBlocks.count(Pred) && "Found a predecessor of the loop "((ClonedLoopBlocks.count(Pred) && "Found a predecessor of the loop "
 "header other than the preheader " "that is not part of the loop!"
) ? static_cast<void> (0) : __assert_fail ("ClonedLoopBlocks.count(Pred) && \"Found a predecessor of the loop \" \"header other than the preheader \" \"that is not part of the loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1257, __PRETTY_FUNCTION__))
                                         "header other than the preheader "((ClonedLoopBlocks.count(Pred) && "Found a predecessor of the loop "
 "header other than the preheader " "that is not part of the loop!"
) ? static_cast<void> (0) : __assert_fail ("ClonedLoopBlocks.count(Pred) && \"Found a predecessor of the loop \" \"header other than the preheader \" \"that is not part of the loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1257, __PRETTY_FUNCTION__))
                                         "that is not part of the loop!")((ClonedLoopBlocks.count(Pred) && "Found a predecessor of the loop "
 "header other than the preheader " "that is not part of the loop!"
) ? static_cast<void> (0) : __assert_fail ("ClonedLoopBlocks.count(Pred) && \"Found a predecessor of the loop \" \"header other than the preheader \" \"that is not part of the loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1257, __PRETTY_FUNCTION__));

  // Insert this block into the loop set and on the first visit (and if it
  // isn't the header we're currently walking) put it into the worklist to
  // recurse through.
  if (BlocksInClonedLoop.insert(Pred).second && Pred != ClonedHeader)
    Worklist.push_back(Pred);
}

// If we had any backedges then there *is* a cloned loop. Put the header into
// the loop set and then walk the worklist backwards to find all the blocks
// that remain within the loop after cloning.
if (!BlocksInClonedLoop.empty()) {
  BlocksInClonedLoop.insert(ClonedHeader);

  while (!Worklist.empty()) {
    BasicBlock *BB = Worklist.pop_back_val();
    assert(BlocksInClonedLoop.count(BB) &&((BlocksInClonedLoop.count(BB) && "Didn't put block into the loop set!"
) ? static_cast<void> (0) : __assert_fail ("BlocksInClonedLoop.count(BB) && \"Didn't put block into the loop set!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1275, __PRETTY_FUNCTION__))
           "Didn't put block into the loop set!")((BlocksInClonedLoop.count(BB) && "Didn't put block into the loop set!"
) ? static_cast<void> (0) : __assert_fail ("BlocksInClonedLoop.count(BB) && \"Didn't put block into the loop set!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1275, __PRETTY_FUNCTION__));

    // Insert any predecessors that are in the possible set into the cloned
    // set, and if the insert is successful, add them to the worklist. Note
    // that we filter on the blocks that are definitely reachable via the
    // backedge to the loop header so we may prune out dead code within the
    // cloned loop.
    for (auto *Pred : predecessors(BB))
      if (ClonedLoopBlocks.count(Pred) &&
          BlocksInClonedLoop.insert(Pred).second)
        Worklist.push_back(Pred);
  }

  ClonedL = LI.AllocateLoop();
  if (ParentL) {
    ParentL->addBasicBlockToLoop(ClonedPH, LI);
    ParentL->addChildLoop(ClonedL);
  } else {
    LI.addTopLevelLoop(ClonedL);
  }
  NonChildClonedLoops.push_back(ClonedL);

  ClonedL->reserveBlocks(BlocksInClonedLoop.size());
  // We don't want to just add the cloned loop blocks based on how we
  // discovered them. The original order of blocks was carefully built in
  // a way that doesn't rely on predecessor ordering. Rather than re-invent
  // that logic, we just re-walk the original blocks (and those of the child
  // loops) and filter them as we add them into the cloned loop.
  for (auto *BB : OrigL.blocks()) {
    auto *ClonedBB = cast_or_null<BasicBlock>(VMap.lookup(BB));
    if (!ClonedBB || !BlocksInClonedLoop.count(ClonedBB))
      continue;

    // Directly add the blocks that are only in this loop.
    if (LI.getLoopFor(BB) == &OrigL) {
      ClonedL->addBasicBlockToLoop(ClonedBB, LI);
      continue;
    }

    // We want to manually add it to this loop and parents.
    // Registering it with LoopInfo will happen when we clone the top
    // loop for this block.
    for (Loop *PL = ClonedL; PL; PL = PL->getParentLoop())
      PL->addBlockEntry(ClonedBB);
  }

  // Now add each child loop whose header remains within the cloned loop. All
  // of the blocks within the loop must satisfy the same constraints as the
  // header so once we pass the header checks we can just clone the entire
  // child loop nest.
  for (Loop *ChildL : OrigL) {
    auto *ClonedChildHeader =
        cast_or_null<BasicBlock>(VMap.lookup(ChildL->getHeader()));
    if (!ClonedChildHeader || !BlocksInClonedLoop.count(ClonedChildHeader))
      continue;

1331#ifndef NDEBUG
    // We should never have a cloned child loop header but fail to have
    // all of the blocks for that child loop.
    for (auto *ChildLoopBB : ChildL->blocks())
      assert(BlocksInClonedLoop.count(((BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup
(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
 "loop but not all of its blocks!") ? static_cast<void>
 (0) : __assert_fail ("BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup(ChildLoopBB))) && \"Child cloned loop has a header within the cloned outer \" \"loop but not all of its blocks!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1338, __PRETTY_FUNCTION__))
                 cast<BasicBlock>(VMap.lookup(ChildLoopBB))) &&((BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup
(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
 "loop but not all of its blocks!") ? static_cast<void>
 (0) : __assert_fail ("BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup(ChildLoopBB))) && \"Child cloned loop has a header within the cloned outer \" \"loop but not all of its blocks!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1338, __PRETTY_FUNCTION__))
             "Child cloned loop has a header within the cloned outer "((BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup
(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
 "loop but not all of its blocks!") ? static_cast<void>
 (0) : __assert_fail ("BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup(ChildLoopBB))) && \"Child cloned loop has a header within the cloned outer \" \"loop but not all of its blocks!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1338, __PRETTY_FUNCTION__))
             "loop but not all of its blocks!")((BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup
(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
 "loop but not all of its blocks!") ? static_cast<void>
 (0) : __assert_fail ("BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup(ChildLoopBB))) && \"Child cloned loop has a header within the cloned outer \" \"loop but not all of its blocks!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1338, __PRETTY_FUNCTION__));
1339#endif

    cloneLoopNest(*ChildL, ClonedL, VMap, LI);
  }
}

// Now that we've handled all the components of the original loop that were
// cloned into a new loop, we still need to handle anything from the original
// loop that wasn't in a cloned loop.

// Figure out what blocks are left to place within any loop nest containing
// the unswitched loop. If we never formed a loop, the cloned PH is one of
// them.
SmallPtrSet<BasicBlock *, 16> UnloopedBlockSet;
if (BlocksInClonedLoop.empty())
  UnloopedBlockSet.insert(ClonedPH);
for (auto *ClonedBB : ClonedLoopBlocks)
  if (!BlocksInClonedLoop.count(ClonedBB))
    UnloopedBlockSet.insert(ClonedBB);

// Copy the cloned exits and sort them in ascending loop depth, we'll work
// backwards across these to process them inside out. The order shouldn't
// matter as we're just trying to build up the map from inside-out; we use
// the map in a more stably ordered way below.
auto OrderedClonedExitsInLoops = ClonedExitsInLoops;
llvm::sort(OrderedClonedExitsInLoops, [&](BasicBlock *LHS, BasicBlock *RHS) {
  return ExitLoopMap.lookup(LHS)->getLoopDepth() <
         ExitLoopMap.lookup(RHS)->getLoopDepth();
});

// Populate the existing ExitLoopMap with everything reachable from each
// exit, starting from the inner most exit.
while (!UnloopedBlockSet.empty() && !OrderedClonedExitsInLoops.empty()) {
  assert(Worklist.empty() && "Didn't clear worklist!")((Worklist.empty() && "Didn't clear worklist!") ? static_cast
<void> (0) : __assert_fail ("Worklist.empty() && \"Didn't clear worklist!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1372, __PRETTY_FUNCTION__));

  BasicBlock *ExitBB = OrderedClonedExitsInLoops.pop_back_val();
  Loop *ExitL = ExitLoopMap.lookup(ExitBB);

  // Walk the CFG back until we hit the cloned PH adding everything reachable
  // and in the unlooped set to this exit block's loop.
  Worklist.push_back(ExitBB);
  do {
    BasicBlock *BB = Worklist.pop_back_val();
    // We can stop recursing at the cloned preheader (if we get there).
    if (BB == ClonedPH)
      continue;

    for (BasicBlock *PredBB : predecessors(BB)) {
      // If this pred has already been moved to our set or is part of some
      // (inner) loop, no update needed.
      if (!UnloopedBlockSet.erase(PredBB)) {
        assert((((BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB
)) && "Predecessor not mapped to a loop!") ? static_cast
<void> (0) : __assert_fail ("(BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) && \"Predecessor not mapped to a loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1392, __PRETTY_FUNCTION__))
            (BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) &&(((BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB
)) && "Predecessor not mapped to a loop!") ? static_cast
<void> (0) : __assert_fail ("(BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) && \"Predecessor not mapped to a loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1392, __PRETTY_FUNCTION__))
            "Predecessor not mapped to a loop!")(((BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB
)) && "Predecessor not mapped to a loop!") ? static_cast
<void> (0) : __assert_fail ("(BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) && \"Predecessor not mapped to a loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1392, __PRETTY_FUNCTION__));
        continue;
      }

      // We just insert into the loop set here. We'll add these blocks to the
      // exit loop after we build up the set in an order that doesn't rely on
      // predecessor order (which in turn relies on use list order).
      bool Inserted = ExitLoopMap.insert({PredBB, ExitL}).second;
      (void)Inserted;
      assert(Inserted && "Should only visit an unlooped block once!")((Inserted && "Should only visit an unlooped block once!"
) ? static_cast<void> (0) : __assert_fail ("Inserted && \"Should only visit an unlooped block once!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1401, __PRETTY_FUNCTION__));

      // And recurse through to its predecessors.
      Worklist.push_back(PredBB);
    }
  } while (!Worklist.empty());
}

// Now that the ExitLoopMap gives as  mapping for all the non-looping cloned
// blocks to their outer loops, walk the cloned blocks and the cloned exits
// in their original order adding them to the correct loop.

// We need a stable insertion order. We use the order of the original loop
// order and map into the correct parent loop.
for (auto *BB : llvm::concat<BasicBlock *const>(
         makeArrayRef(ClonedPH), ClonedLoopBlocks, ClonedExitsInLoops))
  if (Loop *OuterL = ExitLoopMap.lookup(BB))
    OuterL->addBasicBlockToLoop(BB, LI);

1420#ifndef NDEBUG
for (auto &BBAndL : ExitLoopMap) {
  auto *BB = BBAndL.first;
  auto *OuterL = BBAndL.second;
  assert(LI.getLoopFor(BB) == OuterL &&((LI.getLoopFor(BB) == OuterL && "Failed to put all blocks into outer loops!"
) ? static_cast<void> (0) : __assert_fail ("LI.getLoopFor(BB) == OuterL && \"Failed to put all blocks into outer loops!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1425, __PRETTY_FUNCTION__))
         "Failed to put all blocks into outer loops!")((LI.getLoopFor(BB) == OuterL && "Failed to put all blocks into outer loops!"
) ? static_cast<void> (0) : __assert_fail ("LI.getLoopFor(BB) == OuterL && \"Failed to put all blocks into outer loops!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1425, __PRETTY_FUNCTION__));
}
1427#endif

// Now that all the blocks are placed into the correct containing loop in the
// absence of child loops, find all the potentially cloned child loops and
// clone them into whatever outer loop we placed their header into.
for (Loop *ChildL : OrigL) {
  auto *ClonedChildHeader =
      cast_or_null<BasicBlock>(VMap.lookup(ChildL->getHeader()));
  if (!ClonedChildHeader || BlocksInClonedLoop.count(ClonedChildHeader))
    continue;

1438#ifndef NDEBUG
  for (auto *ChildLoopBB : ChildL->blocks())
    assert(VMap.count(ChildLoopBB) &&((VMap.count(ChildLoopBB) && "Cloned a child loop header but not all of that loops blocks!"
) ? static_cast<void> (0) : __assert_fail ("VMap.count(ChildLoopBB) && \"Cloned a child loop header but not all of that loops blocks!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1441, __PRETTY_FUNCTION__))
           "Cloned a child loop header but not all of that loops blocks!")((VMap.count(ChildLoopBB) && "Cloned a child loop header but not all of that loops blocks!"
) ? static_cast<void> (0) : __assert_fail ("VMap.count(ChildLoopBB) && \"Cloned a child loop header but not all of that loops blocks!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1441, __PRETTY_FUNCTION__));
1442#endif

  NonChildClonedLoops.push_back(cloneLoopNest(
      *ChildL, ExitLoopMap.lookup(ClonedChildHeader), VMap, LI));
}
1447}

1449static void
1450deleteDeadClonedBlocks(Loop &L, ArrayRef<BasicBlock *> ExitBlocks,
                     ArrayRef<std::unique_ptr<ValueToValueMapTy>> VMaps,
                     DominatorTree &DT, MemorySSAUpdater *MSSAU) {
// Find all the dead clones, and remove them from their successors.
SmallVector<BasicBlock *, 16> DeadBlocks;
for (BasicBlock *BB : llvm::concat<BasicBlock *const>(L.blocks(), ExitBlocks))
  for (auto &VMap : VMaps)
    if (BasicBlock *ClonedBB = cast_or_null<BasicBlock>(VMap->lookup(BB)))
      if (!DT.isReachableFromEntry(ClonedBB)) {
        for (BasicBlock *SuccBB : successors(ClonedBB))
          SuccBB->removePredecessor(ClonedBB);
        DeadBlocks.push_back(ClonedBB);
      }

// Remove all MemorySSA in the dead blocks
if (MSSAU) {
  SmallSetVector<BasicBlock *, 8> DeadBlockSet(DeadBlocks.begin(),
                                               DeadBlocks.end());
  MSSAU->removeBlocks(DeadBlockSet);
}

// Drop any remaining references to break cycles.
for (BasicBlock *BB : DeadBlocks)
  BB->dropAllReferences();
// Erase them from the IR.
for (BasicBlock *BB : DeadBlocks)
  BB->eraseFromParent();
1477}

1479static void deleteDeadBlocksFromLoop(Loop &L,
                                   SmallVectorImpl<BasicBlock *> &ExitBlocks,
                                   DominatorTree &DT, LoopInfo &LI,
                                   MemorySSAUpdater *MSSAU) {
// Find all the dead blocks tied to this loop, and remove them from their
// successors.
SmallSetVector<BasicBlock *, 8> DeadBlockSet;

// Start with loop/exit blocks and get a transitive closure of reachable dead
// blocks.
SmallVector<BasicBlock *, 16> DeathCandidates(ExitBlocks.begin(),
                                              ExitBlocks.end());
DeathCandidates.append(L.blocks().begin(), L.blocks().end());
while (!DeathCandidates.empty()) {
  auto *BB = DeathCandidates.pop_back_val();
  if (!DeadBlockSet.count(BB) && !DT.isReachableFromEntry(BB)) {
    for (BasicBlock *SuccBB : successors(BB)) {
      SuccBB->removePredecessor(BB);
      DeathCandidates.push_back(SuccBB);
    }
    DeadBlockSet.insert(BB);
  }
}

// Remove all MemorySSA in the dead blocks
if (MSSAU)
  MSSAU->removeBlocks(DeadBlockSet);

// Filter out the dead blocks from the exit blocks list so that it can be
// used in the caller.
llvm::erase_if(ExitBlocks,
               [&](BasicBlock *BB) { return DeadBlockSet.count(BB); });

// Walk from this loop up through its parents removing all of the dead blocks.
for (Loop *ParentL = &L; ParentL; ParentL = ParentL->getParentLoop()) {
  for (auto *BB : DeadBlockSet)
    ParentL->getBlocksSet().erase(BB);
  llvm::erase_if(ParentL->getBlocksVector(),
                 [&](BasicBlock *BB) { return DeadBlockSet.count(BB); });
}

// Now delete the dead child loops. This raw delete will clear them
// recursively.
llvm::erase_if(L.getSubLoopsVector(), [&](Loop *ChildL) {
  if (!DeadBlockSet.count(ChildL->getHeader()))
    return false;

  assert(llvm::all_of(ChildL->blocks(),((llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB
) { return DeadBlockSet.count(ChildBB); }) && "If the child loop header is dead all blocks in the child loop must "
 "be dead as well!") ? static_cast<void> (0) : __assert_fail
 ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1531, __PRETTY_FUNCTION__))
                      [&](BasicBlock *ChildBB) {((llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB
) { return DeadBlockSet.count(ChildBB); }) && "If the child loop header is dead all blocks in the child loop must "
 "be dead as well!") ? static_cast<void> (0) : __assert_fail
 ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1531, __PRETTY_FUNCTION__))
                        return DeadBlockSet.count(ChildBB);((llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB
) { return DeadBlockSet.count(ChildBB); }) && "If the child loop header is dead all blocks in the child loop must "
 "be dead as well!") ? static_cast<void> (0) : __assert_fail
 ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1531, __PRETTY_FUNCTION__))
                      }) &&((llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB
) { return DeadBlockSet.count(ChildBB); }) && "If the child loop header is dead all blocks in the child loop must "
 "be dead as well!") ? static_cast<void> (0) : __assert_fail
 ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1531, __PRETTY_FUNCTION__))
         "If the child loop header is dead all blocks in the child loop must "((llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB
) { return DeadBlockSet.count(ChildBB); }) && "If the child loop header is dead all blocks in the child loop must "
 "be dead as well!") ? static_cast<void> (0) : __assert_fail
 ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1531, __PRETTY_FUNCTION__))
         "be dead as well!")((llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB
) { return DeadBlockSet.count(ChildBB); }) && "If the child loop header is dead all blocks in the child loop must "
 "be dead as well!") ? static_cast<void> (0) : __assert_fail
 ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1531, __PRETTY_FUNCTION__));
  LI.destroy(ChildL);
  return true;
});

// Remove the loop mappings for the dead blocks and drop all the references
// from these blocks to others to handle cyclic references as we start
// deleting the blocks themselves.
for (auto *BB : DeadBlockSet) {
  // Check that the dominator tree has already been updated.
  assert(!DT.getNode(BB) && "Should already have cleared domtree!")((!DT.getNode(BB) && "Should already have cleared domtree!"
) ? static_cast<void> (0) : __assert_fail ("!DT.getNode(BB) && \"Should already have cleared domtree!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1541, __PRETTY_FUNCTION__));
  LI.changeLoopFor(BB, nullptr);
  BB->dropAllReferences();
}

// Actually delete the blocks now that they've been fully unhooked from the
// IR.
for (auto *BB : DeadBlockSet)
  BB->eraseFromParent();
1550}

1552/// Recompute the set of blocks in a loop after unswitching.
1553///
1554/// This walks from the original headers predecessors to rebuild the loop. We
1555/// take advantage of the fact that new blocks can't have been added, and so we
1556/// filter by the original loop's blocks. This also handles potentially
1557/// unreachable code that we don't want to explore but might be found examining
1558/// the predecessors of the header.
1559///
1560/// If the original loop is no longer a loop, this will return an empty set. If
1561/// it remains a loop, all the blocks within it will be added to the set
1562/// (including those blocks in inner loops).
1563static SmallPtrSet<const BasicBlock *, 16> recomputeLoopBlockSet(Loop &L,
                                                               LoopInfo &LI) {
SmallPtrSet<const BasicBlock *, 16> LoopBlockSet;

auto *PH = L.getLoopPreheader();
auto *Header = L.getHeader();

// A worklist to use while walking backwards from the header.
SmallVector<BasicBlock *, 16> Worklist;

// First walk the predecessors of the header to find the backedges. This will
// form the basis of our walk.
for (auto *Pred : predecessors(Header)) {
  // Skip the preheader.
  if (Pred == PH)
    continue;

  // Because the loop was in simplified form, the only non-loop predecessor
  // is the preheader.
  assert(L.contains(Pred) && "Found a predecessor of the loop header other "((L.contains(Pred) && "Found a predecessor of the loop header other "
 "than the preheader that is not part of the " "loop!") ? static_cast
<void> (0) : __assert_fail ("L.contains(Pred) && \"Found a predecessor of the loop header other \" \"than the preheader that is not part of the \" \"loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1584, __PRETTY_FUNCTION__))
                             "than the preheader that is not part of the "((L.contains(Pred) && "Found a predecessor of the loop header other "
 "than the preheader that is not part of the " "loop!") ? static_cast
<void> (0) : __assert_fail ("L.contains(Pred) && \"Found a predecessor of the loop header other \" \"than the preheader that is not part of the \" \"loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1584, __PRETTY_FUNCTION__))
                             "loop!")((L.contains(Pred) && "Found a predecessor of the loop header other "
 "than the preheader that is not part of the " "loop!") ? static_cast
<void> (0) : __assert_fail ("L.contains(Pred) && \"Found a predecessor of the loop header other \" \"than the preheader that is not part of the \" \"loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1584, __PRETTY_FUNCTION__));

  // Insert this block into the loop set and on the first visit and, if it
  // isn't the header we're currently walking, put it into the worklist to
  // recurse through.
  if (LoopBlockSet.insert(Pred).second && Pred != Header)
    Worklist.push_back(Pred);
}

// If no backedges were found, we're done.
if (LoopBlockSet.empty())
  return LoopBlockSet;

// We found backedges, recurse through them to identify the loop blocks.
while (!Worklist.empty()) {
  BasicBlock *BB = Worklist.pop_back_val();
  assert(LoopBlockSet.count(BB) && "Didn't put block into the loop set!")((LoopBlockSet.count(BB) && "Didn't put block into the loop set!"
) ? static_cast<void> (0) : __assert_fail ("LoopBlockSet.count(BB) && \"Didn't put block into the loop set!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1600, __PRETTY_FUNCTION__));

  // No need to walk past the header.
  if (BB == Header)
    continue;

  // Because we know the inner loop structure remains valid we can use the
  // loop structure to jump immediately across the entire nested loop.
  // Further, because it is in loop simplified form, we can directly jump
  // to its preheader afterward.
  if (Loop *InnerL = LI.getLoopFor(BB))
    if (InnerL != &L) {
      assert(L.contains(InnerL) &&((L.contains(InnerL) && "Should not reach a loop *outside* this loop!"
) ? static_cast<void> (0) : __assert_fail ("L.contains(InnerL) && \"Should not reach a loop *outside* this loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1613, __PRETTY_FUNCTION__))
             "Should not reach a loop *outside* this loop!")((L.contains(InnerL) && "Should not reach a loop *outside* this loop!"
) ? static_cast<void> (0) : __assert_fail ("L.contains(InnerL) && \"Should not reach a loop *outside* this loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1613, __PRETTY_FUNCTION__));
      // The preheader is the only possible predecessor of the loop so
      // insert it into the set and check whether it was already handled.
      auto *InnerPH = InnerL->getLoopPreheader();
      assert(L.contains(InnerPH) && "Cannot contain an inner loop block "((L.contains(InnerPH) && "Cannot contain an inner loop block "
 "but not contain the inner loop " "preheader!") ? static_cast
<void> (0) : __assert_fail ("L.contains(InnerPH) && \"Cannot contain an inner loop block \" \"but not contain the inner loop \" \"preheader!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1619, __PRETTY_FUNCTION__))
                                    "but not contain the inner loop "((L.contains(InnerPH) && "Cannot contain an inner loop block "
 "but not contain the inner loop " "preheader!") ? static_cast
<void> (0) : __assert_fail ("L.contains(InnerPH) && \"Cannot contain an inner loop block \" \"but not contain the inner loop \" \"preheader!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1619, __PRETTY_FUNCTION__))
                                    "preheader!")((L.contains(InnerPH) && "Cannot contain an inner loop block "
 "but not contain the inner loop " "preheader!") ? static_cast
<void> (0) : __assert_fail ("L.contains(InnerPH) && \"Cannot contain an inner loop block \" \"but not contain the inner loop \" \"preheader!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1619, __PRETTY_FUNCTION__));
      if (!LoopBlockSet.insert(InnerPH).second)
        // The only way to reach the preheader is through the loop body
        // itself so if it has been visited the loop is already handled.
        continue;

      // Insert all of the blocks (other than those already present) into
      // the loop set. We expect at least the block that led us to find the
      // inner loop to be in the block set, but we may also have other loop
      // blocks if they were already enqueued as predecessors of some other
      // outer loop block.
      for (auto *InnerBB : InnerL->blocks()) {
        if (InnerBB == BB) {
          assert(LoopBlockSet.count(InnerBB) &&((LoopBlockSet.count(InnerBB) && "Block should already be in the set!"
) ? static_cast<void> (0) : __assert_fail ("LoopBlockSet.count(InnerBB) && \"Block should already be in the set!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1633, __PRETTY_FUNCTION__))
                 "Block should already be in the set!")((LoopBlockSet.count(InnerBB) && "Block should already be in the set!"
) ? static_cast<void> (0) : __assert_fail ("LoopBlockSet.count(InnerBB) && \"Block should already be in the set!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1633, __PRETTY_FUNCTION__));
          continue;
        }

        LoopBlockSet.insert(InnerBB);
      }

      // Add the preheader to the worklist so we will continue past the
      // loop body.
      Worklist.push_back(InnerPH);
      continue;
    }

  // Insert any predecessors that were in the original loop into the new
  // set, and if the insert is successful, add them to the worklist.
  for (auto *Pred : predecessors(BB))
    if (L.contains(Pred) && LoopBlockSet.insert(Pred).second)
      Worklist.push_back(Pred);
}

assert(LoopBlockSet.count(Header) && "Cannot fail to add the header!")((LoopBlockSet.count(Header) && "Cannot fail to add the header!"
) ? static_cast<void> (0) : __assert_fail ("LoopBlockSet.count(Header) && \"Cannot fail to add the header!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1653, __PRETTY_FUNCTION__));

// We've found all the blocks participating in the loop, return our completed
// set.
return LoopBlockSet;
1658}

1660/// Rebuild a loop after unswitching removes some subset of blocks and edges.
1661///
1662/// The removal may have removed some child loops entirely but cannot have
1663/// disturbed any remaining child loops. However, they may need to be hoisted
1664/// to the parent loop (or to be top-level loops). The original loop may be
1665/// completely removed.
1666///
1667/// The sibling loops resulting from this update are returned. If the original
1668/// loop remains a valid loop, it will be the first entry in this list with all
1669/// of the newly sibling loops following it.
1670///
1671/// Returns true if the loop remains a loop after unswitching, and false if it
1672/// is no longer a loop after unswitching (and should not continue to be
1673/// referenced).
1674static bool rebuildLoopAfterUnswitch(Loop &L, ArrayRef<BasicBlock *> ExitBlocks,
                                   LoopInfo &LI,
                                   SmallVectorImpl<Loop *> &HoistedLoops) {
auto *PH = L.getLoopPreheader();

// Compute the actual parent loop from the exit blocks. Because we may have
// pruned some exits the loop may be different from the original parent.
Loop *ParentL = nullptr;
SmallVector<Loop *, 4> ExitLoops;
SmallVector<BasicBlock *, 4> ExitsInLoops;
ExitsInLoops.reserve(ExitBlocks.size());
for (auto *ExitBB : ExitBlocks)
  if (Loop *ExitL = LI.getLoopFor(ExitBB)) {
    ExitLoops.push_back(ExitL);
    ExitsInLoops.push_back(ExitBB);
    if (!ParentL || (ParentL != ExitL && ParentL->contains(ExitL)))
      ParentL = ExitL;
  }

// Recompute the blocks participating in this loop. This may be empty if it
// is no longer a loop.
auto LoopBlockSet = recomputeLoopBlockSet(L, LI);

// If we still have a loop, we need to re-set the loop's parent as the exit
// block set changing may have moved it within the loop nest. Note that this
// can only happen when this loop has a parent as it can only hoist the loop
// *up* the nest.
if (!LoopBlockSet.empty() && L.getParentLoop() != ParentL) {
  // Remove this loop's (original) blocks from all of the intervening loops.
  for (Loop *IL = L.getParentLoop(); IL != ParentL;
       IL = IL->getParentLoop()) {
    IL->getBlocksSet().erase(PH);
    for (auto *BB : L.blocks())
      IL->getBlocksSet().erase(BB);
    llvm::erase_if(IL->getBlocksVector(), [&](BasicBlock *BB) {
      return BB == PH || L.contains(BB);
    });
  }

  LI.changeLoopFor(PH, ParentL);
  L.getParentLoop()->removeChildLoop(&L);
  if (ParentL)
    ParentL->addChildLoop(&L);
  else
    LI.addTopLevelLoop(&L);
}

// Now we update all the blocks which are no longer within the loop.
auto &Blocks = L.getBlocksVector();
auto BlocksSplitI =
    LoopBlockSet.empty()
        ? Blocks.begin()
        : std::stable_partition(
              Blocks.begin(), Blocks.end(),
              [&](BasicBlock *BB) { return LoopBlockSet.count(BB); });

// Before we erase the list of unlooped blocks, build a set of them.
SmallPtrSet<BasicBlock *, 16> UnloopedBlocks(BlocksSplitI, Blocks.end());
if (LoopBlockSet.empty())
  UnloopedBlocks.insert(PH);

// Now erase these blocks from the loop.
for (auto *BB : make_range(BlocksSplitI, Blocks.end()))
  L.getBlocksSet().erase(BB);
Blocks.erase(BlocksSplitI, Blocks.end());

// Sort the exits in ascending loop depth, we'll work backwards across these
// to process them inside out.
llvm::stable_sort(ExitsInLoops, [&](BasicBlock *LHS, BasicBlock *RHS) {
  return LI.getLoopDepth(LHS) < LI.getLoopDepth(RHS);
});

// We'll build up a set for each exit loop.
SmallPtrSet<BasicBlock *, 16> NewExitLoopBlocks;
Loop *PrevExitL = L.getParentLoop(); // The deepest possible exit loop.

auto RemoveUnloopedBlocksFromLoop =
    [](Loop &L, SmallPtrSetImpl<BasicBlock *> &UnloopedBlocks) {
      for (auto *BB : UnloopedBlocks)
        L.getBlocksSet().erase(BB);
      llvm::erase_if(L.getBlocksVector(), [&](BasicBlock *BB) {
        return UnloopedBlocks.count(BB);
      });
    };

SmallVector<BasicBlock *, 16> Worklist;
while (!UnloopedBlocks.empty() && !ExitsInLoops.empty()) {
  assert(Worklist.empty() && "Didn't clear worklist!")((Worklist.empty() && "Didn't clear worklist!") ? static_cast
<void> (0) : __assert_fail ("Worklist.empty() && \"Didn't clear worklist!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1761, __PRETTY_FUNCTION__));
  assert(NewExitLoopBlocks.empty() && "Didn't clear loop set!")((NewExitLoopBlocks.empty() && "Didn't clear loop set!"
) ? static_cast<void> (0) : __assert_fail ("NewExitLoopBlocks.empty() && \"Didn't clear loop set!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1762, __PRETTY_FUNCTION__));

  // Grab the next exit block, in decreasing loop depth order.
  BasicBlock *ExitBB = ExitsInLoops.pop_back_val();
  Loop &ExitL = *LI.getLoopFor(ExitBB);
  assert(ExitL.contains(&L) && "Exit loop must contain the inner loop!")((ExitL.contains(&L) && "Exit loop must contain the inner loop!"
) ? static_cast<void> (0) : __assert_fail ("ExitL.contains(&L) && \"Exit loop must contain the inner loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1767, __PRETTY_FUNCTION__));

  // Erase all of the unlooped blocks from the loops between the previous
  // exit loop and this exit loop. This works because the ExitInLoops list is
  // sorted in increasing order of loop depth and thus we visit loops in
  // decreasing order of loop depth.
  for (; PrevExitL != &ExitL; PrevExitL = PrevExitL->getParentLoop())
    RemoveUnloopedBlocksFromLoop(*PrevExitL, UnloopedBlocks);

  // Walk the CFG back until we hit the cloned PH adding everything reachable
  // and in the unlooped set to this exit block's loop.
  Worklist.push_back(ExitBB);
  do {
    BasicBlock *BB = Worklist.pop_back_val();
    // We can stop recursing at the cloned preheader (if we get there).
    if (BB == PH)
      continue;

    for (BasicBlock *PredBB : predecessors(BB)) {
      // If this pred has already been moved to our set or is part of some
      // (inner) loop, no update needed.
      if (!UnloopedBlocks.erase(PredBB)) {
        assert((NewExitLoopBlocks.count(PredBB) ||(((NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor
(PredBB))) && "Predecessor not in a nested loop (or already visited)!"
) ? static_cast<void> (0) : __assert_fail ("(NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor(PredBB))) && \"Predecessor not in a nested loop (or already visited)!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1791, __PRETTY_FUNCTION__))
                ExitL.contains(LI.getLoopFor(PredBB))) &&(((NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor
(PredBB))) && "Predecessor not in a nested loop (or already visited)!"
) ? static_cast<void> (0) : __assert_fail ("(NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor(PredBB))) && \"Predecessor not in a nested loop (or already visited)!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1791, __PRETTY_FUNCTION__))
               "Predecessor not in a nested loop (or already visited)!")(((NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor
(PredBB))) && "Predecessor not in a nested loop (or already visited)!"
) ? static_cast<void> (0) : __assert_fail ("(NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor(PredBB))) && \"Predecessor not in a nested loop (or already visited)!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1791, __PRETTY_FUNCTION__));
        continue;
      }

      // We just insert into the loop set here. We'll add these blocks to the
      // exit loop after we build up the set in a deterministic order rather
      // than the predecessor-influenced visit order.
      bool Inserted = NewExitLoopBlocks.insert(PredBB).second;
      (void)Inserted;
      assert(Inserted && "Should only visit an unlooped block once!")((Inserted && "Should only visit an unlooped block once!"
) ? static_cast<void> (0) : __assert_fail ("Inserted && \"Should only visit an unlooped block once!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1800, __PRETTY_FUNCTION__));

      // And recurse through to its predecessors.
      Worklist.push_back(PredBB);
    }
  } while (!Worklist.empty());

  // If blocks in this exit loop were directly part of the original loop (as
  // opposed to a child loop) update the map to point to this exit loop. This
  // just updates a map and so the fact that the order is unstable is fine.
  for (auto *BB : NewExitLoopBlocks)
    if (Loop *BBL = LI.getLoopFor(BB))
      if (BBL == &L || !L.contains(BBL))
        LI.changeLoopFor(BB, &ExitL);

  // We will remove the remaining unlooped blocks from this loop in the next
  // iteration or below.
  NewExitLoopBlocks.clear();
}

// Any remaining unlooped blocks are no longer part of any loop unless they
// are part of some child loop.
for (; PrevExitL; PrevExitL = PrevExitL->getParentLoop())
  RemoveUnloopedBlocksFromLoop(*PrevExitL, UnloopedBlocks);
for (auto *BB : UnloopedBlocks)
  if (Loop *BBL = LI.getLoopFor(BB))
    if (BBL == &L || !L.contains(BBL))
      LI.changeLoopFor(BB, nullptr);

// Sink all the child loops whose headers are no longer in the loop set to
// the parent (or to be top level loops). We reach into the loop and directly
// update its subloop vector to make this batch update efficient.
auto &SubLoops = L.getSubLoopsVector();
auto SubLoopsSplitI =
    LoopBlockSet.empty()
        ? SubLoops.begin()
        : std::stable_partition(
              SubLoops.begin(), SubLoops.end(), [&](Loop *SubL) {
                return LoopBlockSet.count(SubL->getHeader());
              });
for (auto *HoistedL : make_range(SubLoopsSplitI, SubLoops.end())) {
  HoistedLoops.push_back(HoistedL);
  HoistedL->setParentLoop(nullptr);

  // To compute the new parent of this hoisted loop we look at where we
  // placed the preheader above. We can't lookup the header itself because we
  // retained the mapping from the header to the hoisted loop. But the
  // preheader and header should have the exact same new parent computed
  // based on the set of exit blocks from the original loop as the preheader
  // is a predecessor of the header and so reached in the reverse walk. And
  // because the loops were all in simplified form the preheader of the
  // hoisted loop can't be part of some *other* loop.
  if (auto *NewParentL = LI.getLoopFor(HoistedL->getLoopPreheader()))
    NewParentL->addChildLoop(HoistedL);
  else
    LI.addTopLevelLoop(HoistedL);
}
SubLoops.erase(SubLoopsSplitI, SubLoops.end());

// Actually delete the loop if nothing remained within it.
if (Blocks.empty()) {
  assert(SubLoops.empty() &&((SubLoops.empty() && "Failed to remove all subloops from the original loop!"
) ? static_cast<void> (0) : __assert_fail ("SubLoops.empty() && \"Failed to remove all subloops from the original loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1862, __PRETTY_FUNCTION__))
         "Failed to remove all subloops from the original loop!")((SubLoops.empty() && "Failed to remove all subloops from the original loop!"
) ? static_cast<void> (0) : __assert_fail ("SubLoops.empty() && \"Failed to remove all subloops from the original loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1862, __PRETTY_FUNCTION__));
  if (Loop *ParentL = L.getParentLoop())
    ParentL->removeChildLoop(llvm::find(*ParentL, &L));
  else
    LI.removeLoop(llvm::find(LI, &L));
  LI.destroy(&L);
  return false;
}

return true;
1872}

1874/// Helper to visit a dominator subtree, invoking a callable on each node.
1875///
1876/// Returning false at any point will stop walking past that node of the tree.
1877template <typename CallableT>
1878void visitDomSubTree(DominatorTree &DT, BasicBlock *BB, CallableT Callable) {
SmallVector<DomTreeNode *, 4> DomWorklist;
DomWorklist.push_back(DT[BB]);
1881#ifndef NDEBUG
SmallPtrSet<DomTreeNode *, 4> Visited;
Visited.insert(DT[BB]);
1884#endif
do {
  DomTreeNode *N = DomWorklist.pop_back_val();

  // Visit this node.
  if (!Callable(N->getBlock()))
    continue;

  // Accumulate the child nodes.
  for (DomTreeNode *ChildN : *N) {
    assert(Visited.insert(ChildN).second &&((Visited.insert(ChildN).second && "Cannot visit a node twice when walking a tree!"
) ? static_cast<void> (0) : __assert_fail ("Visited.insert(ChildN).second && \"Cannot visit a node twice when walking a tree!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1895, __PRETTY_FUNCTION__))
           "Cannot visit a node twice when walking a tree!")((Visited.insert(ChildN).second && "Cannot visit a node twice when walking a tree!"
) ? static_cast<void> (0) : __assert_fail ("Visited.insert(ChildN).second && \"Cannot visit a node twice when walking a tree!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1895, __PRETTY_FUNCTION__));
    DomWorklist.push_back(ChildN);
  }
} while (!DomWorklist.empty());
1899}

1901static void unswitchNontrivialInvariants(
  Loop &L, Instruction &TI, ArrayRef<Value *> Invariants,
  SmallVectorImpl<BasicBlock *> &ExitBlocks, DominatorTree &DT, LoopInfo &LI,
  AssumptionCache &AC, function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB,
  ScalarEvolution *SE, MemorySSAUpdater *MSSAU) {
auto *ParentBB = TI.getParent();
BranchInst *BI = dyn_cast<BranchInst>(&TI);
SwitchInst *SI = BI ? nullptr : cast<SwitchInst>(&TI);

// We can only unswitch switches, conditional branches with an invariant
// condition, or combining invariant conditions with an instruction.
assert((SI || BI->isConditional()) &&(((SI || BI->isConditional()) && "Can only unswitch switches and conditional branch!"
) ? static_cast<void> (0) : __assert_fail ("(SI || BI->isConditional()) && \"Can only unswitch switches and conditional branch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1913, __PRETTY_FUNCTION__))
       "Can only unswitch switches and conditional branch!")(((SI || BI->isConditional()) && "Can only unswitch switches and conditional branch!"
) ? static_cast<void> (0) : __assert_fail ("(SI || BI->isConditional()) && \"Can only unswitch switches and conditional branch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1913, __PRETTY_FUNCTION__));
bool FullUnswitch = SI || BI->getCondition() == Invariants[0];
if (FullUnswitch)
  assert(Invariants.size() == 1 &&((Invariants.size() == 1 && "Cannot have other invariants with full unswitching!"
) ? static_cast<void> (0) : __assert_fail ("Invariants.size() == 1 && \"Cannot have other invariants with full unswitching!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1917, __PRETTY_FUNCTION__))
         "Cannot have other invariants with full unswitching!")((Invariants.size() == 1 && "Cannot have other invariants with full unswitching!"
) ? static_cast<void> (0) : __assert_fail ("Invariants.size() == 1 && \"Cannot have other invariants with full unswitching!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1917, __PRETTY_FUNCTION__));
else
  assert(isa<Instruction>(BI->getCondition()) &&((isa<Instruction>(BI->getCondition()) && "Partial unswitching requires an instruction as the condition!"
) ? static_cast<void> (0) : __assert_fail ("isa<Instruction>(BI->getCondition()) && \"Partial unswitching requires an instruction as the condition!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1920, __PRETTY_FUNCTION__))
         "Partial unswitching requires an instruction as the condition!")((isa<Instruction>(BI->getCondition()) && "Partial unswitching requires an instruction as the condition!"
) ? static_cast<void> (0) : __assert_fail ("isa<Instruction>(BI->getCondition()) && \"Partial unswitching requires an instruction as the condition!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1920, __PRETTY_FUNCTION__));

if (MSSAU && VerifyMemorySSA)
  MSSAU->getMemorySSA()->verifyMemorySSA();

// Constant and BBs tracking the cloned and continuing successor. When we are
// unswitching the entire condition, this can just be trivially chosen to
// unswitch towards `true`. However, when we are unswitching a set of
// invariants combined with `and` or `or`, the combining operation determines
// the best direction to unswitch: we want to unswitch the direction that will
// collapse the branch.
bool Direction = true;
int ClonedSucc = 0;
if (!FullUnswitch) {
  if (cast<Instruction>(BI->getCondition())->getOpcode() != Instruction::Or) {
    assert(cast<Instruction>(BI->getCondition())->getOpcode() ==((cast<Instruction>(BI->getCondition())->getOpcode
() == Instruction::And && "Only `or` and `and` instructions can combine invariants being "
 "unswitched.") ? static_cast<void> (0) : __assert_fail
 ("cast<Instruction>(BI->getCondition())->getOpcode() == Instruction::And && \"Only `or` and `and` instructions can combine invariants being \" \"unswitched.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1938, __PRETTY_FUNCTION__))
               Instruction::And &&((cast<Instruction>(BI->getCondition())->getOpcode
() == Instruction::And && "Only `or` and `and` instructions can combine invariants being "
 "unswitched.") ? static_cast<void> (0) : __assert_fail
 ("cast<Instruction>(BI->getCondition())->getOpcode() == Instruction::And && \"Only `or` and `and` instructions can combine invariants being \" \"unswitched.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1938, __PRETTY_FUNCTION__))
           "Only `or` and `and` instructions can combine invariants being "((cast<Instruction>(BI->getCondition())->getOpcode
() == Instruction::And && "Only `or` and `and` instructions can combine invariants being "
 "unswitched.") ? static_cast<void> (0) : __assert_fail
 ("cast<Instruction>(BI->getCondition())->getOpcode() == Instruction::And && \"Only `or` and `and` instructions can combine invariants being \" \"unswitched.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1938, __PRETTY_FUNCTION__))
           "unswitched.")((cast<Instruction>(BI->getCondition())->getOpcode
() == Instruction::And && "Only `or` and `and` instructions can combine invariants being "
 "unswitched.") ? static_cast<void> (0) : __assert_fail
 ("cast<Instruction>(BI->getCondition())->getOpcode() == Instruction::And && \"Only `or` and `and` instructions can combine invariants being \" \"unswitched.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1938, __PRETTY_FUNCTION__));
    Direction = false;
    ClonedSucc = 1;
  }
}

BasicBlock *RetainedSuccBB =
    BI ? BI->getSuccessor(1 - ClonedSucc) : SI->getDefaultDest();
SmallSetVector<BasicBlock *, 4> UnswitchedSuccBBs;
if (BI)
  UnswitchedSuccBBs.insert(BI->getSuccessor(ClonedSucc));
else
  for (auto Case : SI->cases())
    if (Case.getCaseSuccessor() != RetainedSuccBB)
      UnswitchedSuccBBs.insert(Case.getCaseSuccessor());

assert(!UnswitchedSuccBBs.count(RetainedSuccBB) &&((!UnswitchedSuccBBs.count(RetainedSuccBB) && "Should not unswitch the same successor we are retaining!"
) ? static_cast<void> (0) : __assert_fail ("!UnswitchedSuccBBs.count(RetainedSuccBB) && \"Should not unswitch the same successor we are retaining!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1955, __PRETTY_FUNCTION__))
       "Should not unswitch the same successor we are retaining!")((!UnswitchedSuccBBs.count(RetainedSuccBB) && "Should not unswitch the same successor we are retaining!"
) ? static_cast<void> (0) : __assert_fail ("!UnswitchedSuccBBs.count(RetainedSuccBB) && \"Should not unswitch the same successor we are retaining!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1955, __PRETTY_FUNCTION__));

// The branch should be in this exact loop. Any inner loop's invariant branch
// should be handled by unswitching that inner loop. The caller of this
// routine should filter out any candidates that remain (but were skipped for
// whatever reason).
assert(LI.getLoopFor(ParentBB) == &L && "Branch in an inner loop!")((LI.getLoopFor(ParentBB) == &L && "Branch in an inner loop!"
) ? static_cast<void> (0) : __assert_fail ("LI.getLoopFor(ParentBB) == &L && \"Branch in an inner loop!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1961, __PRETTY_FUNCTION__));

// Compute the parent loop now before we start hacking on things.
Loop *ParentL = L.getParentLoop();
// Get blocks in RPO order for MSSA update, before changing the CFG.
LoopBlocksRPO LBRPO(&L);
if (MSSAU)
  LBRPO.perform(&LI);

// Compute the outer-most loop containing one of our exit blocks. This is the
// furthest up our loopnest which can be mutated, which we will use below to
// update things.
Loop *OuterExitL = &L;
for (auto *ExitBB : ExitBlocks) {
  Loop *NewOuterExitL = LI.getLoopFor(ExitBB);
  if (!NewOuterExitL) {
    // We exited the entire nest with this block, so we're done.
    OuterExitL = nullptr;
    break;
  }
  if (NewOuterExitL != OuterExitL && NewOuterExitL->contains(OuterExitL))
    OuterExitL = NewOuterExitL;
}

// At this point, we're definitely going to unswitch something so invalidate
// any cached information in ScalarEvolution for the outer most loop
// containing an exit block and all nested loops.
if (SE) {
  if (OuterExitL)
    SE->forgetLoop(OuterExitL);
  else
    SE->forgetTopmostLoop(&L);
}

// If the edge from this terminator to a successor dominates that successor,
// store a map from each block in its dominator subtree to it. This lets us
// tell when cloning for a particular successor if a block is dominated by
// some *other* successor with a single data structure. We use this to
// significantly reduce cloning.
SmallDenseMap<BasicBlock *, BasicBlock *, 16> DominatingSucc;
for (auto *SuccBB : llvm::concat<BasicBlock *const>(
         makeArrayRef(RetainedSuccBB), UnswitchedSuccBBs))
  if (SuccBB->getUniquePredecessor() ||
      llvm::all_of(predecessors(SuccBB), [&](BasicBlock *PredBB) {
        return PredBB == ParentBB || DT.dominates(SuccBB, PredBB);
      }))
    visitDomSubTree(DT, SuccBB, [&](BasicBlock *BB) {
      DominatingSucc[BB] = SuccBB;
      return true;
    });

// Split the preheader, so that we know that there is a safe place to insert
// the conditional branch. We will change the preheader to have a conditional
// branch on LoopCond. The original preheader will become the split point
// between the unswitched versions, and we will have a new preheader for the
// original loop.
BasicBlock *SplitBB = L.getLoopPreheader();
BasicBlock *LoopPH = SplitEdge(SplitBB, L.getHeader(), &DT, &LI, MSSAU);

// Keep track of the dominator tree updates needed.
SmallVector<DominatorTree::UpdateType, 4> DTUpdates;

// Clone the loop for each unswitched successor.
SmallVector<std::unique_ptr<ValueToValueMapTy>, 4> VMaps;
VMaps.reserve(UnswitchedSuccBBs.size());
SmallDenseMap<BasicBlock *, BasicBlock *, 4> ClonedPHs;
for (auto *SuccBB : UnswitchedSuccBBs) {
  VMaps.emplace_back(new ValueToValueMapTy());
  ClonedPHs[SuccBB] = buildClonedLoopBlocks(
      L, LoopPH, SplitBB, ExitBlocks, ParentBB, SuccBB, RetainedSuccBB,
      DominatingSucc, *VMaps.back(), DTUpdates, AC, DT, LI, MSSAU);
}

// The stitching of the branched code back together depends on whether we're
// doing full unswitching or not with the exception that we always want to
// nuke the initial terminator placed in the split block.
SplitBB->getTerminator()->eraseFromParent();
if (FullUnswitch) {
  // Splice the terminator from the original loop and rewrite its
  // successors.
  SplitBB->getInstList().splice(SplitBB->end(), ParentBB->getInstList(), TI);

  // Keep a clone of the terminator for MSSA updates.
  Instruction *NewTI = TI.clone();
  ParentBB->getInstList().push_back(NewTI);

  // First wire up the moved terminator to the preheaders.
  if (BI) {
    BasicBlock *ClonedPH = ClonedPHs.begin()->second;
    BI->setSuccessor(ClonedSucc, ClonedPH);
    BI->setSuccessor(1 - ClonedSucc, LoopPH);
    DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH});
  } else {
    assert(SI && "Must either be a branch or switch!")((SI && "Must either be a branch or switch!") ? static_cast
<void> (0) : __assert_fail ("SI && \"Must either be a branch or switch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2054, __PRETTY_FUNCTION__));

    // Walk the cases and directly update their successors.
    assert(SI->getDefaultDest() == RetainedSuccBB &&((SI->getDefaultDest() == RetainedSuccBB && "Not retaining default successor!"
) ? static_cast<void> (0) : __assert_fail ("SI->getDefaultDest() == RetainedSuccBB && \"Not retaining default successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2058, __PRETTY_FUNCTION__))
           "Not retaining default successor!")((SI->getDefaultDest() == RetainedSuccBB && "Not retaining default successor!"
) ? static_cast<void> (0) : __assert_fail ("SI->getDefaultDest() == RetainedSuccBB && \"Not retaining default successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2058, __PRETTY_FUNCTION__));
    SI->setDefaultDest(LoopPH);
    for (auto &Case : SI->cases())
      if (Case.getCaseSuccessor() == RetainedSuccBB)
        Case.setSuccessor(LoopPH);
      else
        Case.setSuccessor(ClonedPHs.find(Case.getCaseSuccessor())->second);

    // We need to use the set to populate domtree updates as even when there
    // are multiple cases pointing at the same successor we only want to
    // remove and insert one edge in the domtree.
    for (BasicBlock *SuccBB : UnswitchedSuccBBs)
      DTUpdates.push_back(
          {DominatorTree::Insert, SplitBB, ClonedPHs.find(SuccBB)->second});
  }

  if (MSSAU) {
    DT.applyUpdates(DTUpdates);
    DTUpdates.clear();

    // Remove all but one edge to the retained block and all unswitched
    // blocks. This is to avoid having duplicate entries in the cloned Phis,
    // when we know we only keep a single edge for each case.
    MSSAU->removeDuplicatePhiEdgesBetween(ParentBB, RetainedSuccBB);
    for (BasicBlock *SuccBB : UnswitchedSuccBBs)
      MSSAU->removeDuplicatePhiEdgesBetween(ParentBB, SuccBB);

    for (auto &VMap : VMaps)
      MSSAU->updateForClonedLoop(LBRPO, ExitBlocks, *VMap,
                                 /*IgnoreIncomingWithNoClones=*/true);
    MSSAU->updateExitBlocksForClonedLoop(ExitBlocks, VMaps, DT);

    // Remove all edges to unswitched blocks.
    for (BasicBlock *SuccBB : UnswitchedSuccBBs)
      MSSAU->removeEdge(ParentBB, SuccBB);
  }

  // Now unhook the successor relationship as we'll be replacing
  // the terminator with a direct branch. This is much simpler for branches
  // than switches so we handle those first.
  if (BI) {
    // Remove the parent as a predecessor of the unswitched successor.
    assert(UnswitchedSuccBBs.size() == 1 &&((UnswitchedSuccBBs.size() == 1 && "Only one possible unswitched block for a branch!"
) ? static_cast<void> (0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2101, __PRETTY_FUNCTION__))
           "Only one possible unswitched block for a branch!")((UnswitchedSuccBBs.size() == 1 && "Only one possible unswitched block for a branch!"
) ? static_cast<void> (0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2101, __PRETTY_FUNCTION__));
    BasicBlock *UnswitchedSuccBB = *UnswitchedSuccBBs.begin();
    UnswitchedSuccBB->removePredecessor(ParentBB,
                                        /*KeepOneInputPHIs*/ true);
    DTUpdates.push_back({DominatorTree::Delete, ParentBB, UnswitchedSuccBB});
  } else {
    // Note that we actually want to remove the parent block as a predecessor
    // of *every* case successor. The case successor is either unswitched,
    // completely eliminating an edge from the parent to that successor, or it
    // is a duplicate edge to the retained successor as the retained successor
    // is always the default successor and as we'll replace this with a direct
    // branch we no longer need the duplicate entries in the PHI nodes.
    SwitchInst *NewSI = cast<SwitchInst>(NewTI);
    assert(NewSI->getDefaultDest() == RetainedSuccBB &&((NewSI->getDefaultDest() == RetainedSuccBB && "Not retaining default successor!"
) ? static_cast<void> (0) : __assert_fail ("NewSI->getDefaultDest() == RetainedSuccBB && \"Not retaining default successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2115, __PRETTY_FUNCTION__))
           "Not retaining default successor!")((NewSI->getDefaultDest() == RetainedSuccBB && "Not retaining default successor!"
) ? static_cast<void> (0) : __assert_fail ("NewSI->getDefaultDest() == RetainedSuccBB && \"Not retaining default successor!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2115, __PRETTY_FUNCTION__));
    for (auto &Case : NewSI->cases())
      Case.getCaseSuccessor()->removePredecessor(
          ParentBB,
          /*KeepOneInputPHIs*/ true);

    // We need to use the set to populate domtree updates as even when there
    // are multiple cases pointing at the same successor we only want to
    // remove and insert one edge in the domtree.
    for (BasicBlock *SuccBB : UnswitchedSuccBBs)
      DTUpdates.push_back({DominatorTree::Delete, ParentBB, SuccBB});
  }

  // After MSSAU update, remove the cloned terminator instruction NewTI.
  ParentBB->getTerminator()->eraseFromParent();

  // Create a new unconditional branch to the continuing block (as opposed to
  // the one cloned).
  BranchInst::Create(RetainedSuccBB, ParentBB);
} else {
  assert(BI && "Only branches have partial unswitching.")((BI && "Only branches have partial unswitching.") ? static_cast
<void> (0) : __assert_fail ("BI && \"Only branches have partial unswitching.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2135, __PRETTY_FUNCTION__));
  assert(UnswitchedSuccBBs.size() == 1 &&((UnswitchedSuccBBs.size() == 1 && "Only one possible unswitched block for a branch!"
) ? static_cast<void> (0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2137, __PRETTY_FUNCTION__))
         "Only one possible unswitched block for a branch!")((UnswitchedSuccBBs.size() == 1 && "Only one possible unswitched block for a branch!"
) ? static_cast<void> (0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2137, __PRETTY_FUNCTION__));
  BasicBlock *ClonedPH = ClonedPHs.begin()->second;
  // When doing a partial unswitch, we have to do a bit more work to build up
  // the branch in the split block.
  buildPartialUnswitchConditionalBranch(*SplitBB, Invariants, Direction,
                                        *ClonedPH, *LoopPH);
  if (MSSAU) {
    // Perform MSSA cloning updates.
    for (auto &VMap : VMaps)
      MSSAU->updateForClonedLoop(LBRPO, ExitBlocks, *VMap,
                                 /*IgnoreIncomingWithNoClones=*/true);
    MSSAU->updateExitBlocksForClonedLoop(ExitBlocks, VMaps, DT);
  }
  DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH});
}

// Apply the updates accumulated above to get an up-to-date dominator tree.
DT.applyUpdates(DTUpdates);
if (!FullUnswitch && MSSAU) {
  // Update MSSA for partial unswitch, after DT update.
  SmallVector<CFGUpdate, 1> Updates;
  Updates.push_back(
      {cfg::UpdateKind::Insert, SplitBB, ClonedPHs.begin()->second});
  MSSAU->applyInsertUpdates(Updates, DT);
}

// Now that we have an accurate dominator tree, first delete the dead cloned
// blocks so that we can accurately build any cloned loops. It is important to
// not delete the blocks from the original loop yet because we still want to
// reference the original loop to understand the cloned loop's structure.
deleteDeadClonedBlocks(L, ExitBlocks, VMaps, DT, MSSAU);

// Build the cloned loop structure itself. This may be substantially
// different from the original structure due to the simplified CFG. This also
// handles inserting all the cloned blocks into the correct loops.
SmallVector<Loop *, 4> NonChildClonedLoops;
for (std::unique_ptr<ValueToValueMapTy> &VMap : VMaps)
  buildClonedLoops(L, ExitBlocks, *VMap, LI, NonChildClonedLoops);

// Now that our cloned loops have been built, we can update the original loop.
// First we delete the dead blocks from it and then we rebuild the loop
// structure taking these deletions into account.
deleteDeadBlocksFromLoop(L, ExitBlocks, DT, LI, MSSAU);

if (MSSAU && VerifyMemorySSA)
  MSSAU->getMemorySSA()->verifyMemorySSA();

SmallVector<Loop *, 4> HoistedLoops;
bool IsStillLoop = rebuildLoopAfterUnswitch(L, ExitBlocks, LI, HoistedLoops);

if (MSSAU && VerifyMemorySSA)
  MSSAU->getMemorySSA()->verifyMemorySSA();

// This transformation has a high risk of corrupting the dominator tree, and
// the below steps to rebuild loop structures will result in hard to debug
// errors in that case so verify that the dominator tree is sane first.
// FIXME: Remove this when the bugs stop showing up and rely on existing
// verification steps.
assert(DT.verify(DominatorTree::VerificationLevel::Fast))((DT.verify(DominatorTree::VerificationLevel::Fast)) ? static_cast
<void> (0) : __assert_fail ("DT.verify(DominatorTree::VerificationLevel::Fast)"
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2195, __PRETTY_FUNCTION__));

if (BI) {
  // If we unswitched a branch which collapses the condition to a known
  // constant we want to replace all the uses of the invariants within both
  // the original and cloned blocks. We do this here so that we can use the
  // now updated dominator tree to identify which side the users are on.
  assert(UnswitchedSuccBBs.size() == 1 &&((UnswitchedSuccBBs.size() == 1 && "Only one possible unswitched block for a branch!"
) ? static_cast<void> (0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2203, __PRETTY_FUNCTION__))
         "Only one possible unswitched block for a branch!")((UnswitchedSuccBBs.size() == 1 && "Only one possible unswitched block for a branch!"
) ? static_cast<void> (0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2203, __PRETTY_FUNCTION__));
  BasicBlock *ClonedPH = ClonedPHs.begin()->second;

  // When considering multiple partially-unswitched invariants
  // we cant just go replace them with constants in both branches.
  //
  // For 'AND' we infer that true branch ("continue") means true
  // for each invariant operand.
  // For 'OR' we can infer that false branch ("continue") means false
  // for each invariant operand.
  // So it happens that for multiple-partial case we dont replace
  // in the unswitched branch.
  bool ReplaceUnswitched = FullUnswitch || (Invariants.size() == 1);

  ConstantInt *UnswitchedReplacement =
      Direction ? ConstantInt::getTrue(BI->getContext())
                : ConstantInt::getFalse(BI->getContext());
  ConstantInt *ContinueReplacement =
      Direction ? ConstantInt::getFalse(BI->getContext())
                : ConstantInt::getTrue(BI->getContext());
  for (Value *Invariant : Invariants)
    for (auto UI = Invariant->use_begin(), UE = Invariant->use_end();
         UI != UE;) {
      // Grab the use and walk past it so we can clobber it in the use list.
      Use *U = &*UI++;
      Instruction *UserI = dyn_cast<Instruction>(U->getUser());
      if (!UserI)
        continue;

      // Replace it with the 'continue' side if in the main loop body, and the
      // unswitched if in the cloned blocks.
      if (DT.dominates(LoopPH, UserI->getParent()))
        U->set(ContinueReplacement);
      else if (ReplaceUnswitched &&
               DT.dominates(ClonedPH, UserI->getParent()))
        U->set(UnswitchedReplacement);
    }
}

// We can change which blocks are exit blocks of all the cloned sibling
// loops, the current loop, and any parent loops which shared exit blocks
// with the current loop. As a consequence, we need to re-form LCSSA for
// them. But we shouldn't need to re-form LCSSA for any child loops.
// FIXME: This could be made more efficient by tracking which exit blocks are
// new, and focusing on them, but that isn't likely to be necessary.
//
// In order to reasonably rebuild LCSSA we need to walk inside-out across the
// loop nest and update every loop that could have had its exits changed. We
// also need to cover any intervening loops. We add all of these loops to
// a list and sort them by loop depth to achieve this without updating
// unnecessary loops.
auto UpdateLoop = [&](Loop &UpdateL) {
2255#ifndef NDEBUG
  UpdateL.verifyLoop();
  for (Loop *ChildL : UpdateL) {
    ChildL->verifyLoop();
    assert(ChildL->isRecursivelyLCSSAForm(DT, LI) &&((ChildL->isRecursivelyLCSSAForm(DT, LI) && "Perturbed a child loop's LCSSA form!"
) ? static_cast<void> (0) : __assert_fail ("ChildL->isRecursivelyLCSSAForm(DT, LI) && \"Perturbed a child loop's LCSSA form!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2260, __PRETTY_FUNCTION__))
           "Perturbed a child loop's LCSSA form!")((ChildL->isRecursivelyLCSSAForm(DT, LI) && "Perturbed a child loop's LCSSA form!"
) ? static_cast<void> (0) : __assert_fail ("ChildL->isRecursivelyLCSSAForm(DT, LI) && \"Perturbed a child loop's LCSSA form!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2260, __PRETTY_FUNCTION__));
  }
2262#endif
  // First build LCSSA for this loop so that we can preserve it when
  // forming dedicated exits. We don't want to perturb some other loop's
  // LCSSA while doing that CFG edit.
  formLCSSA(UpdateL, DT, &LI, nullptr);

  // For loops reached by this loop's original exit blocks we may
  // introduced new, non-dedicated exits. At least try to re-form dedicated
  // exits for these loops. This may fail if they couldn't have dedicated
  // exits to start with.
  formDedicatedExitBlocks(&UpdateL, &DT, &LI, MSSAU, /*PreserveLCSSA*/ true);
};

// For non-child cloned loops and hoisted loops, we just need to update LCSSA
// and we can do it in any order as they don't nest relative to each other.
//
// Also check if any of the loops we have updated have become top-level loops
// as that will necessitate widening the outer loop scope.
for (Loop *UpdatedL :
     llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops)) {
  UpdateLoop(*UpdatedL);
  if (!UpdatedL->getParentLoop())
    OuterExitL = nullptr;
}
if (IsStillLoop) {
  UpdateLoop(L);
  if (!L.getParentLoop())
    OuterExitL = nullptr;
}

// If the original loop had exit blocks, walk up through the outer most loop
// of those exit blocks to update LCSSA and form updated dedicated exits.
if (OuterExitL != &L)
  for (Loop *OuterL = ParentL; OuterL != OuterExitL;
       OuterL = OuterL->getParentLoop())
    UpdateLoop(*OuterL);

2299#ifndef NDEBUG
// Verify the entire loop structure to catch any incorrect updates before we
// progress in the pass pipeline.
LI.verify(DT);
2303#endif

// Now that we've unswitched something, make callbacks to report the changes.
// For that we need to merge together the updated loops and the cloned loops
// and check whether the original loop survived.
SmallVector<Loop *, 4> SibLoops;
for (Loop *UpdatedL : llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops))
  if (UpdatedL->getParentLoop() == ParentL)
    SibLoops.push_back(UpdatedL);
UnswitchCB(IsStillLoop, SibLoops);

if (MSSAU && VerifyMemorySSA)
  MSSAU->getMemorySSA()->verifyMemorySSA();

if (BI)
  ++NumBranches;
else
  ++NumSwitches;
2321}

2323/// Recursively compute the cost of a dominator subtree based on the per-block
2324/// cost map provided.
2325///
2326/// The recursive computation is memozied into the provided DT-indexed cost map
2327/// to allow querying it for most nodes in the domtree without it becoming
2328/// quadratic.
2329static int
2330computeDomSubtreeCost(DomTreeNode &N,
                    const SmallDenseMap<BasicBlock *, int, 4> &BBCostMap,
                    SmallDenseMap<DomTreeNode *, int, 4> &DTCostMap) {
// Don't accumulate cost (or recurse through) blocks not in our block cost
// map and thus not part of the duplication cost being considered.
auto BBCostIt = BBCostMap.find(N.getBlock());
if (BBCostIt == BBCostMap.end())
  return 0;

// Lookup this node to see if we already computed its cost.
auto DTCostIt = DTCostMap.find(&N);
if (DTCostIt != DTCostMap.end())
  return DTCostIt->second;

// If not, we have to compute it. We can't use insert above and update
// because computing the cost may insert more things into the map.
int Cost = std::accumulate(
    N.begin(), N.end(), BBCostIt->second, [&](int Sum, DomTreeNode *ChildN) {
      return Sum + computeDomSubtreeCost(*ChildN, BBCostMap, DTCostMap);
    });
bool Inserted = DTCostMap.insert({&N, Cost}).second;
(void)Inserted;
assert(Inserted && "Should not insert a node while visiting children!")((Inserted && "Should not insert a node while visiting children!"
) ? static_cast<void> (0) : __assert_fail ("Inserted && \"Should not insert a node while visiting children!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2352, __PRETTY_FUNCTION__));
return Cost;
2354}

2356/// Turns a llvm.experimental.guard intrinsic into implicit control flow branch,
2357/// making the following replacement:
2358///
2359///   --code before guard--
2360///   call void (i1, ...) @llvm.experimental.guard(i1 %cond) [ "deopt"() ]
2361///   --code after guard--
2362///
2363/// into
2364///
2365///   --code before guard--
2366///   br i1 %cond, label %guarded, label %deopt
2367///
2368/// guarded:
2369///   --code after guard--
2370///
2371/// deopt:
2372///   call void (i1, ...) @llvm.experimental.guard(i1 false) [ "deopt"() ]
2373///   unreachable
2374///
2375/// It also makes all relevant DT and LI updates, so that all structures are in
2376/// valid state after this transform.
2377static BranchInst *
2378turnGuardIntoBranch(IntrinsicInst *GI, Loop &L,
                  SmallVectorImpl<BasicBlock *> &ExitBlocks,
                  DominatorTree &DT, LoopInfo &LI, MemorySSAUpdater *MSSAU) {
SmallVector<DominatorTree::UpdateType, 4> DTUpdates;
LLVM_DEBUG(dbgs() << "Turning " << *GI << " into a branch.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Turning " <<
 *GI << " into a branch.\n"; } } while (false);
BasicBlock *CheckBB = GI->getParent();

if (MSSAU && VerifyMemorySSA)
   MSSAU->getMemorySSA()->verifyMemorySSA();

// Remove all CheckBB's successors from DomTree. A block can be seen among
// successors more than once, but for DomTree it should be added only once.
SmallPtrSet<BasicBlock *, 4> Successors;
for (auto *Succ : successors(CheckBB))
  if (Successors.insert(Succ).second)
    DTUpdates.push_back({DominatorTree::Delete, CheckBB, Succ});

Instruction *DeoptBlockTerm =
    SplitBlockAndInsertIfThen(GI->getArgOperand(0), GI, true);
BranchInst *CheckBI = cast<BranchInst>(CheckBB->getTerminator());
// SplitBlockAndInsertIfThen inserts control flow that branches to
// DeoptBlockTerm if the condition is true.  We want the opposite.
CheckBI->swapSuccessors();

BasicBlock *GuardedBlock = CheckBI->getSuccessor(0);
GuardedBlock->setName("guarded");
CheckBI->getSuccessor(1)->setName("deopt");
BasicBlock *DeoptBlock = CheckBI->getSuccessor(1);

// We now have a new exit block.
ExitBlocks.push_back(CheckBI->getSuccessor(1));

if (MSSAU)
  MSSAU->moveAllAfterSpliceBlocks(CheckBB, GuardedBlock, GI);

GI->moveBefore(DeoptBlockTerm);
GI->setArgOperand(0, ConstantInt::getFalse(GI->getContext()));

// Add new successors of CheckBB into DomTree.
for (auto *Succ : successors(CheckBB))
  DTUpdates.push_back({DominatorTree::Insert, CheckBB, Succ});

// Now the blocks that used to be CheckBB's successors are GuardedBlock's
// successors.
for (auto *Succ : Successors)
  DTUpdates.push_back({DominatorTree::Insert, GuardedBlock, Succ});

// Make proper changes to DT.
DT.applyUpdates(DTUpdates);
// Inform LI of a new loop block.
L.addBasicBlockToLoop(GuardedBlock, LI);

if (MSSAU) {
  MemoryDef *MD = cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(GI));
  MSSAU->moveToPlace(MD, DeoptBlock, MemorySSA::End);
  if (VerifyMemorySSA)
    MSSAU->getMemorySSA()->verifyMemorySSA();
}

++NumGuards;
return CheckBI;
2439}

2441/// Cost multiplier is a way to limit potentially exponential behavior
2442/// of loop-unswitch. Cost is multipied in proportion of 2^number of unswitch
2443/// candidates available. Also accounting for the number of "sibling" loops with
2444/// the idea to account for previous unswitches that already happened on this
2445/// cluster of loops. There was an attempt to keep this formula simple,
2446/// just enough to limit the worst case behavior. Even if it is not that simple
2447/// now it is still not an attempt to provide a detailed heuristic size
2448/// prediction.
2449///
2450/// TODO: Make a proper accounting of "explosion" effect for all kinds of
2451/// unswitch candidates, making adequate predictions instead of wild guesses.
2452/// That requires knowing not just the number of "remaining" candidates but
2453/// also costs of unswitching for each of these candidates.
2454static int calculateUnswitchCostMultiplier(
  Instruction &TI, Loop &L, LoopInfo &LI, DominatorTree &DT,
  ArrayRef<std::pair<Instruction *, TinyPtrVector<Value *>>>
      UnswitchCandidates) {

// Guards and other exiting conditions do not contribute to exponential
// explosion as soon as they dominate the latch (otherwise there might be
// another path to the latch remaining that does not allow to eliminate the
// loop copy on unswitch).
BasicBlock *Latch = L.getLoopLatch();
BasicBlock *CondBlock = TI.getParent();
if (DT.dominates(CondBlock, Latch) &&
    (isGuard(&TI) ||
     llvm::count_if(successors(&TI), [&L](BasicBlock *SuccBB) {
       return L.contains(SuccBB);
     }) <= 1)) {
  NumCostMultiplierSkipped++;
  return 1;
}

auto *ParentL = L.getParentLoop();
int SiblingsCount = (ParentL ? ParentL->getSubLoopsVector().size()
                             : std::distance(LI.begin(), LI.end()));
// Count amount of clones that all the candidates might cause during
// unswitching. Branch/guard counts as 1, switch counts as log2 of its cases.
int UnswitchedClones = 0;
for (auto Candidate : UnswitchCandidates) {
  Instruction *CI = Candidate.first;
  BasicBlock *CondBlock = CI->getParent();
  bool SkipExitingSuccessors = DT.dominates(CondBlock, Latch);
  if (isGuard(CI)) {
    if (!SkipExitingSuccessors)
      UnswitchedClones++;
    continue;
  }
  int NonExitingSuccessors = llvm::count_if(
      successors(CondBlock), [SkipExitingSuccessors, &L](BasicBlock *SuccBB) {
        return !SkipExitingSuccessors || L.contains(SuccBB);
      });
  UnswitchedClones += Log2_32(NonExitingSuccessors);
}

// Ignore up to the "unscaled candidates" number of unswitch candidates
// when calculating the power-of-two scaling of the cost. The main idea
// with this control is to allow a small number of unswitches to happen
// and rely more on siblings multiplier (see below) when the number
// of candidates is small.
unsigned ClonesPower =
    std::max(UnswitchedClones - (int)UnswitchNumInitialUnscaledCandidates, 0);

// Allowing top-level loops to spread a bit more than nested ones.
int SiblingsMultiplier =
    std::max((ParentL ? SiblingsCount
                      : SiblingsCount / (int)UnswitchSiblingsToplevelDiv),
             1);
// Compute the cost multiplier in a way that won't overflow by saturating
// at an upper bound.
int CostMultiplier;
if (ClonesPower > Log2_32(UnswitchThreshold) ||
    SiblingsMultiplier > UnswitchThreshold)
  CostMultiplier = UnswitchThreshold;
else
  CostMultiplier = std::min(SiblingsMultiplier * (1 << ClonesPower),
                            (int)UnswitchThreshold);

LLVM_DEBUG(dbgs() << "  Computed multiplier  " << CostMultiplierdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Computed multiplier  "
 << CostMultiplier << " (siblings " << SiblingsMultiplier
 << " * clones " << (1 << ClonesPower) <<
 ")" << " for unswitch candidate: " << TI <<
 "\n"; } } while (false)
                  << " (siblings " << SiblingsMultiplier << " * clones "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Computed multiplier  "
 << CostMultiplier << " (siblings " << SiblingsMultiplier
 << " * clones " << (1 << ClonesPower) <<
 ")" << " for unswitch candidate: " << TI <<
 "\n"; } } while (false)
                  << (1 << ClonesPower) << ")"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Computed multiplier  "
 << CostMultiplier << " (siblings " << SiblingsMultiplier
 << " * clones " << (1 << ClonesPower) <<
 ")" << " for unswitch candidate: " << TI <<
 "\n"; } } while (false)
                  << " for unswitch candidate: " << TI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Computed multiplier  "
 << CostMultiplier << " (siblings " << SiblingsMultiplier
 << " * clones " << (1 << ClonesPower) <<
 ")" << " for unswitch candidate: " << TI <<
 "\n"; } } while (false);
return CostMultiplier;
2524}

2526static bool
2527unswitchBestCondition(Loop &L, DominatorTree &DT, LoopInfo &LI,
                    AssumptionCache &AC, TargetTransformInfo &TTI,
                    function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB,
                    ScalarEvolution *SE, MemorySSAUpdater *MSSAU) {
// Collect all invariant conditions within this loop (as opposed to an inner
// loop which would be handled when visiting that inner loop).
SmallVector<std::pair<Instruction *, TinyPtrVector<Value *>>, 4>
    UnswitchCandidates;

// Whether or not we should also collect guards in the loop.
bool CollectGuards = false;
if (UnswitchGuards) {
1
Assuming the condition is false→
2
←
Taking false branch→
  auto *GuardDecl = L.getHeader()->getParent()->getParent()->getFunction(
      Intrinsic::getName(Intrinsic::experimental_guard));
  if (GuardDecl && !GuardDecl->use_empty())
    CollectGuards = true;
}

for (auto *BB : L.blocks()) {
3
←
Assuming '__begin1' is equal to '__end1'→
  if (LI.getLoopFor(BB) != &L)
    continue;

  if (CollectGuards)
    for (auto &I : *BB)
      if (isGuard(&I)) {
        auto *Cond = cast<IntrinsicInst>(&I)->getArgOperand(0);
        // TODO: Support AND, OR conditions and partial unswitching.
        if (!isa<Constant>(Cond) && L.isLoopInvariant(Cond))
          UnswitchCandidates.push_back({&I, {Cond}});
      }

  if (auto *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
    // We can only consider fully loop-invariant switch conditions as we need
    // to completely eliminate the switch after unswitching.
    if (!isa<Constant>(SI->getCondition()) &&
        L.isLoopInvariant(SI->getCondition()) && !BB->getUniqueSuccessor())
      UnswitchCandidates.push_back({SI, {SI->getCondition()}});
    continue;
  }

  auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
  if (!BI || !BI->isConditional() || isa<Constant>(BI->getCondition()) ||
      BI->getSuccessor(0) == BI->getSuccessor(1))
    continue;

  if (L.isLoopInvariant(BI->getCondition())) {
    UnswitchCandidates.push_back({BI, {BI->getCondition()}});
    continue;
  }

  Instruction &CondI = *cast<Instruction>(BI->getCondition());
  if (CondI.getOpcode() != Instruction::And &&
    CondI.getOpcode() != Instruction::Or)
    continue;

  TinyPtrVector<Value *> Invariants =
      collectHomogenousInstGraphLoopInvariants(L, CondI, LI);
  if (Invariants.empty())
    continue;

  UnswitchCandidates.push_back({BI, std::move(Invariants)});
}

// If we didn't find any candidates, we're done.
if (UnswitchCandidates.empty())
4
←
Calling 'SmallVectorBase::empty'→
7
←
Returning from 'SmallVectorBase::empty'→
8
←
Taking false branch→
  return false;

// Check if there are irreducible CFG cycles in this loop. If so, we cannot
// easily unswitch non-trivial edges out of the loop. Doing so might turn the
// irreducible control flow into reducible control flow and introduce new
// loops "out of thin air". If we ever discover important use cases for doing
// this, we can add support to loop unswitch, but it is a lot of complexity
// for what seems little or no real world benefit.
LoopBlocksRPO RPOT(&L);
RPOT.perform(&LI);
if (containsIrreducibleCFG<const BasicBlock *>(RPOT, LI))
9
←
Calling 'containsIrreducibleCFG<const llvm::BasicBlock *, llvm::LoopBlocksRPO, llvm::LoopInfo, llvm::GraphTraits<const llvm::BasicBlock *>>'→
11
←
Returning from 'containsIrreducibleCFG<const llvm::BasicBlock *, llvm::LoopBlocksRPO, llvm::LoopInfo, llvm::GraphTraits<const llvm::BasicBlock *>>'→
12
←
Taking false branch→
  return false;

SmallVector<BasicBlock *, 4> ExitBlocks;
L.getUniqueExitBlocks(ExitBlocks);

// We cannot unswitch if exit blocks contain a cleanuppad instruction as we
// don't know how to split those exit blocks.
// FIXME: We should teach SplitBlock to handle this and remove this
// restriction.
for (auto *ExitBB : ExitBlocks)
13
←
Assuming '__begin1' is equal to '__end1'→
  if (isa<CleanupPadInst>(ExitBB->getFirstNonPHI())) {
    dbgs() << "Cannot unswitch because of cleanuppad in exit block\n";
    return false;
  }

LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Considering " <<
 UnswitchCandidates.size() << " non-trivial loop invariant conditions for unswitching.\n"
; } } while (false)
14
←
Assuming 'DebugFlag' is false→
15
←
Loop condition is false.  Exiting loop→
    dbgs() << "Considering " << UnswitchCandidates.size()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Considering " <<
 UnswitchCandidates.size() << " non-trivial loop invariant conditions for unswitching.\n"
; } } while (false)
           << " non-trivial loop invariant conditions for unswitching.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Considering " <<
 UnswitchCandidates.size() << " non-trivial loop invariant conditions for unswitching.\n"
; } } while (false);

// Given that unswitching these terminators will require duplicating parts of
// the loop, so we need to be able to model that cost. Compute the ephemeral
// values and set up a data structure to hold per-BB costs. We cache each
// block's cost so that we don't recompute this when considering different
// subsets of the loop for duplication during unswitching.
SmallPtrSet<const Value *, 4> EphValues;
CodeMetrics::collectEphemeralValues(&L, &AC, EphValues);
SmallDenseMap<BasicBlock *, int, 4> BBCostMap;

// Compute the cost of each block, as well as the total loop cost. Also, bail
// out if we see instructions which are incompatible with loop unswitching
// (convergent, noduplicate, or cross-basic-block tokens).
// FIXME: We might be able to safely handle some of these in non-duplicated
// regions.
int LoopCost = 0;
for (auto *BB : L.blocks()) {
16
←
Assuming '__begin1' is equal to '__end1'→
  int Cost = 0;
  for (auto &I : *BB) {
    if (EphValues.count(&I))
      continue;

    if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB))
      return false;
    if (auto CS = CallSite(&I))
      if (CS.isConvergent() || CS.cannotDuplicate())
        return false;

    Cost += TTI.getUserCost(&I);
  }
  assert(Cost >= 0 && "Must not have negative costs!")((Cost >= 0 && "Must not have negative costs!") ? static_cast
<void> (0) : __assert_fail ("Cost >= 0 && \"Must not have negative costs!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2651, __PRETTY_FUNCTION__));
  LoopCost += Cost;
  assert(LoopCost >= 0 && "Must not have negative loop costs!")((LoopCost >= 0 && "Must not have negative loop costs!"
) ? static_cast<void> (0) : __assert_fail ("LoopCost >= 0 && \"Must not have negative loop costs!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2653, __PRETTY_FUNCTION__));
  BBCostMap[BB] = Cost;
}
LLVM_DEBUG(dbgs() << "  Total loop cost: " << LoopCost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Total loop cost: "
 << LoopCost << "\n"; } } while (false);
17
←
Assuming 'DebugFlag' is false→
18
←
Loop condition is false.  Exiting loop→

// Now we find the best candidate by searching for the one with the following
// properties in order:
//
// 1) An unswitching cost below the threshold
// 2) The smallest number of duplicated unswitch candidates (to avoid
//    creating redundant subsequent unswitching)
// 3) The smallest cost after unswitching.
//
// We prioritize reducing fanout of unswitch candidates provided the cost
// remains below the threshold because this has a multiplicative effect.
//
// This requires memoizing each dominator subtree to avoid redundant work.
//
// FIXME: Need to actually do the number of candidates part above.
SmallDenseMap<DomTreeNode *, int, 4> DTCostMap;
// Given a terminator which might be unswitched, computes the non-duplicated
// cost for that terminator.
auto ComputeUnswitchedCost = [&](Instruction &TI, bool FullUnswitch) {
  BasicBlock &BB = *TI.getParent();
  SmallPtrSet<BasicBlock *, 4> Visited;

  int Cost = LoopCost;
  for (BasicBlock *SuccBB : successors(&BB)) {
    // Don't count successors more than once.
    if (!Visited.insert(SuccBB).second)
      continue;

    // If this is a partial unswitch candidate, then it must be a conditional
    // branch with a condition of either `or` or `and`. In that case, one of
    // the successors is necessarily duplicated, so don't even try to remove
    // its cost.
    if (!FullUnswitch) {
      auto &BI = cast<BranchInst>(TI);
      if (cast<Instruction>(BI.getCondition())->getOpcode() ==
          Instruction::And) {
        if (SuccBB == BI.getSuccessor(1))
          continue;
      } else {
        assert(cast<Instruction>(BI.getCondition())->getOpcode() ==((cast<Instruction>(BI.getCondition())->getOpcode() ==
 Instruction::Or && "Only `and` and `or` conditions can result in a partial "
 "unswitch!") ? static_cast<void> (0) : __assert_fail (
"cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Only `and` and `or` conditions can result in a partial \" \"unswitch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2699, __PRETTY_FUNCTION__))
                   Instruction::Or &&((cast<Instruction>(BI.getCondition())->getOpcode() ==
 Instruction::Or && "Only `and` and `or` conditions can result in a partial "
 "unswitch!") ? static_cast<void> (0) : __assert_fail (
"cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Only `and` and `or` conditions can result in a partial \" \"unswitch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2699, __PRETTY_FUNCTION__))
               "Only `and` and `or` conditions can result in a partial "((cast<Instruction>(BI.getCondition())->getOpcode() ==
 Instruction::Or && "Only `and` and `or` conditions can result in a partial "
 "unswitch!") ? static_cast<void> (0) : __assert_fail (
"cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Only `and` and `or` conditions can result in a partial \" \"unswitch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2699, __PRETTY_FUNCTION__))
               "unswitch!")((cast<Instruction>(BI.getCondition())->getOpcode() ==
 Instruction::Or && "Only `and` and `or` conditions can result in a partial "
 "unswitch!") ? static_cast<void> (0) : __assert_fail (
"cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Only `and` and `or` conditions can result in a partial \" \"unswitch!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2699, __PRETTY_FUNCTION__));
        if (SuccBB == BI.getSuccessor(0))
          continue;
      }
    }

    // This successor's domtree will not need to be duplicated after
    // unswitching if the edge to the successor dominates it (and thus the
    // entire tree). This essentially means there is no other path into this
    // subtree and so it will end up live in only one clone of the loop.
    if (SuccBB->getUniquePredecessor() ||
        llvm::all_of(predecessors(SuccBB), [&](BasicBlock *PredBB) {
          return PredBB == &BB || DT.dominates(SuccBB, PredBB);
        })) {
      Cost -= computeDomSubtreeCost(*DT[SuccBB], BBCostMap, DTCostMap);
      assert(Cost >= 0 &&((Cost >= 0 && "Non-duplicated cost should never exceed total loop cost!"
) ? static_cast<void> (0) : __assert_fail ("Cost >= 0 && \"Non-duplicated cost should never exceed total loop cost!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2715, __PRETTY_FUNCTION__))
             "Non-duplicated cost should never exceed total loop cost!")((Cost >= 0 && "Non-duplicated cost should never exceed total loop cost!"
) ? static_cast<void> (0) : __assert_fail ("Cost >= 0 && \"Non-duplicated cost should never exceed total loop cost!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2715, __PRETTY_FUNCTION__));
    }
  }

  // Now scale the cost by the number of unique successors minus one. We
  // subtract one because there is already at least one copy of the entire
  // loop. This is computing the new cost of unswitching a condition.
  // Note that guards always have 2 unique successors that are implicit and
  // will be materialized if we decide to unswitch it.
  int SuccessorsCount = isGuard(&TI) ? 2 : Visited.size();
  assert(SuccessorsCount > 1 &&((SuccessorsCount > 1 && "Cannot unswitch a condition without multiple distinct successors!"
) ? static_cast<void> (0) : __assert_fail ("SuccessorsCount > 1 && \"Cannot unswitch a condition without multiple distinct successors!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2726, __PRETTY_FUNCTION__))
         "Cannot unswitch a condition without multiple distinct successors!")((SuccessorsCount > 1 && "Cannot unswitch a condition without multiple distinct successors!"
) ? static_cast<void> (0) : __assert_fail ("SuccessorsCount > 1 && \"Cannot unswitch a condition without multiple distinct successors!\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2726, __PRETTY_FUNCTION__));
  return Cost * (SuccessorsCount - 1);
};
Instruction *BestUnswitchTI = nullptr;
int BestUnswitchCost;
19
←
'BestUnswitchCost' declared without an initial value→
ArrayRef<Value *> BestUnswitchInvariants;
for (auto &TerminatorAndInvariants : UnswitchCandidates) {
20
←
Assuming '__begin1' is equal to '__end1'→
  Instruction &TI = *TerminatorAndInvariants.first;
  ArrayRef<Value *> Invariants = TerminatorAndInvariants.second;
  BranchInst *BI = dyn_cast<BranchInst>(&TI);
  int CandidateCost = ComputeUnswitchedCost(
      TI, /*FullUnswitch*/ !BI || (Invariants.size() == 1 &&
                                   Invariants[0] == BI->getCondition()));
  // Calculate cost multiplier which is a tool to limit potentially
  // exponential behavior of loop-unswitch.
  if (EnableUnswitchCostMultiplier) {
    int CostMultiplier =
        calculateUnswitchCostMultiplier(TI, L, LI, DT, UnswitchCandidates);
    assert((((CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold
) && "cost multiplier needs to be in the range of 1..UnswitchThreshold"
) ? static_cast<void> (0) : __assert_fail ("(CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold) && \"cost multiplier needs to be in the range of 1..UnswitchThreshold\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2746, __PRETTY_FUNCTION__))
        (CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold) &&(((CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold
) && "cost multiplier needs to be in the range of 1..UnswitchThreshold"
) ? static_cast<void> (0) : __assert_fail ("(CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold) && \"cost multiplier needs to be in the range of 1..UnswitchThreshold\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2746, __PRETTY_FUNCTION__))
        "cost multiplier needs to be in the range of 1..UnswitchThreshold")(((CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold
) && "cost multiplier needs to be in the range of 1..UnswitchThreshold"
) ? static_cast<void> (0) : __assert_fail ("(CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold) && \"cost multiplier needs to be in the range of 1..UnswitchThreshold\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2746, __PRETTY_FUNCTION__));
    CandidateCost *= CostMultiplier;
    LLVM_DEBUG(dbgs() << "  Computed cost of " << CandidateCostdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Computed cost of "
 << CandidateCost << " (multiplier: " << CostMultiplier
 << ")" << " for unswitch candidate: " << TI
 << "\n"; } } while (false)
                      << " (multiplier: " << CostMultiplier << ")"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Computed cost of "
 << CandidateCost << " (multiplier: " << CostMultiplier
 << ")" << " for unswitch candidate: " << TI
 << "\n"; } } while (false)
                      << " for unswitch candidate: " << TI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Computed cost of "
 << CandidateCost << " (multiplier: " << CostMultiplier
 << ")" << " for unswitch candidate: " << TI
 << "\n"; } } while (false);
  } else {
    LLVM_DEBUG(dbgs() << "  Computed cost of " << CandidateCostdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Computed cost of "
 << CandidateCost << " for unswitch candidate: " <<
 TI << "\n"; } } while (false)
                      << " for unswitch candidate: " << TI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Computed cost of "
 << CandidateCost << " for unswitch candidate: " <<
 TI << "\n"; } } while (false);
  }

  if (!BestUnswitchTI || CandidateCost < BestUnswitchCost) {
    BestUnswitchTI = &TI;
    BestUnswitchCost = CandidateCost;
    BestUnswitchInvariants = Invariants;
  }
}

if (BestUnswitchCost >= UnswitchThreshold) {
21
←
The left operand of '>=' is a garbage value
  LLVM_DEBUG(dbgs() << "Cannot unswitch, lowest cost found: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Cannot unswitch, lowest cost found: "
 << BestUnswitchCost << "\n"; } } while (false)
                    << BestUnswitchCost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Cannot unswitch, lowest cost found: "
 << BestUnswitchCost << "\n"; } } while (false);
  return false;
}

// If the best candidate is a guard, turn it into a branch.
if (isGuard(BestUnswitchTI))
  BestUnswitchTI = turnGuardIntoBranch(cast<IntrinsicInst>(BestUnswitchTI), L,
                                       ExitBlocks, DT, LI, MSSAU);

LLVM_DEBUG(dbgs() << "  Unswitching non-trivial (cost = "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Unswitching non-trivial (cost = "
 << BestUnswitchCost << ") terminator: " <<
 *BestUnswitchTI << "\n"; } } while (false)
                  << BestUnswitchCost << ") terminator: " << *BestUnswitchTIdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Unswitching non-trivial (cost = "
 << BestUnswitchCost << ") terminator: " <<
 *BestUnswitchTI << "\n"; } } while (false)
                  << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "  Unswitching non-trivial (cost = "
 << BestUnswitchCost << ") terminator: " <<
 *BestUnswitchTI << "\n"; } } while (false);
unswitchNontrivialInvariants(L, *BestUnswitchTI, BestUnswitchInvariants,
                             ExitBlocks, DT, LI, AC, UnswitchCB, SE, MSSAU);
return true;
2780}

2782/// Unswitch control flow predicated on loop invariant conditions.
2783///
2784/// This first hoists all branches or switches which are trivial (IE, do not
2785/// require duplicating any part of the loop) out of the loop body. It then
2786/// looks at other loop invariant control flows and tries to unswitch those as
2787/// well by cloning the loop if the result is small enough.
2788///
2789/// The `DT`, `LI`, `AC`, `TTI` parameters are required analyses that are also
2790/// updated based on the unswitch.
2791/// The `MSSA` analysis is also updated if valid (i.e. its use is enabled).
2792///
2793/// If either `NonTrivial` is true or the flag `EnableNonTrivialUnswitch` is
2794/// true, we will attempt to do non-trivial unswitching as well as trivial
2795/// unswitching.
2796///
2797/// The `UnswitchCB` callback provided will be run after unswitching is
2798/// complete, with the first parameter set to `true` if the provided loop
2799/// remains a loop, and a list of new sibling loops created.
2800///
2801/// If `SE` is non-null, we will update that analysis based on the unswitching
2802/// done.
2803static bool unswitchLoop(Loop &L, DominatorTree &DT, LoopInfo &LI,
                       AssumptionCache &AC, TargetTransformInfo &TTI,
                       bool NonTrivial,
                       function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB,
                       ScalarEvolution *SE, MemorySSAUpdater *MSSAU) {
assert(L.isRecursivelyLCSSAForm(DT, LI) &&((L.isRecursivelyLCSSAForm(DT, LI) && "Loops must be in LCSSA form before unswitching."
) ? static_cast<void> (0) : __assert_fail ("L.isRecursivelyLCSSAForm(DT, LI) && \"Loops must be in LCSSA form before unswitching.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2809, __PRETTY_FUNCTION__))
       "Loops must be in LCSSA form before unswitching.")((L.isRecursivelyLCSSAForm(DT, LI) && "Loops must be in LCSSA form before unswitching."
) ? static_cast<void> (0) : __assert_fail ("L.isRecursivelyLCSSAForm(DT, LI) && \"Loops must be in LCSSA form before unswitching.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2809, __PRETTY_FUNCTION__));
bool Changed = false;

// Must be in loop simplified form: we need a preheader and dedicated exits.
if (!L.isLoopSimplifyForm())
  return false;

// Try trivial unswitch first before loop over other basic blocks in the loop.
if (unswitchAllTrivialConditions(L, DT, LI, SE, MSSAU)) {
  // If we unswitched successfully we will want to clean up the loop before
  // processing it further so just mark it as unswitched and return.
  UnswitchCB(/*CurrentLoopValid*/ true, {});
  return true;
}

// If we're not doing non-trivial unswitching, we're done. We both accept
// a parameter but also check a local flag that can be used for testing
// a debugging.
if (!NonTrivial && !EnableNonTrivialUnswitch)
  return false;

// For non-trivial unswitching, because it often creates new loops, we rely on
// the pass manager to iterate on the loops rather than trying to immediately
// reach a fixed point. There is no substantial advantage to iterating
// internally, and if any of the new loops are simplified enough to contain
// trivial unswitching we want to prefer those.

// Try to unswitch the best invariant condition. We prefer this full unswitch to
// a partial unswitch when possible below the threshold.
if (unswitchBestCondition(L, DT, LI, AC, TTI, UnswitchCB, SE, MSSAU))
  return true;

// No other opportunities to unswitch.
return Changed;
2843}

2845PreservedAnalyses SimpleLoopUnswitchPass::run(Loop &L, LoopAnalysisManager &AM,
                                            LoopStandardAnalysisResults &AR,
                                            LPMUpdater &U) {
Function &F = *L.getHeader()->getParent();
(void)F;

LLVM_DEBUG(dbgs() << "Unswitching loop in " << F.getName() << ": " << Ldo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Unswitching loop in "
 << F.getName() << ": " << L << "\n";
 } } while (false)
                  << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Unswitching loop in "
 << F.getName() << ": " << L << "\n";
 } } while (false);

// Save the current loop name in a variable so that we can report it even
// after it has been deleted.
std::string LoopName = L.getName();

auto UnswitchCB = [&L, &U, &LoopName](bool CurrentLoopValid,
                                      ArrayRef<Loop *> NewLoops) {
  // If we did a non-trivial unswitch, we have added new (cloned) loops.
  if (!NewLoops.empty())
    U.addSiblingLoops(NewLoops);

  // If the current loop remains valid, we should revisit it to catch any
  // other unswitch opportunities. Otherwise, we need to mark it as deleted.
  if (CurrentLoopValid)
    U.revisitCurrentLoop();
  else
    U.markLoopAsDeleted(L, LoopName);
};

Optional<MemorySSAUpdater> MSSAU;
if (AR.MSSA) {
  MSSAU = MemorySSAUpdater(AR.MSSA);
  if (VerifyMemorySSA)
    AR.MSSA->verifyMemorySSA();
}
if (!unswitchLoop(L, AR.DT, AR.LI, AR.AC, AR.TTI, NonTrivial, UnswitchCB,
                  &AR.SE, MSSAU.hasValue() ? MSSAU.getPointer() : nullptr))
  return PreservedAnalyses::all();

if (AR.MSSA && VerifyMemorySSA)
  AR.MSSA->verifyMemorySSA();

// Historically this pass has had issues with the dominator tree so verify it
// in asserts builds.
assert(AR.DT.verify(DominatorTree::VerificationLevel::Fast))((AR.DT.verify(DominatorTree::VerificationLevel::Fast)) ? static_cast
<void> (0) : __assert_fail ("AR.DT.verify(DominatorTree::VerificationLevel::Fast)"
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2887, __PRETTY_FUNCTION__));

auto PA = getLoopPassPreservedAnalyses();
if (AR.MSSA)
  PA.preserve<MemorySSAAnalysis>();
return PA;
2893}

2895namespace {

2897class SimpleLoopUnswitchLegacyPass : public LoopPass {
bool NonTrivial;

2900public:
static char ID; // Pass ID, replacement for typeid

explicit SimpleLoopUnswitchLegacyPass(bool NonTrivial = false)
    : LoopPass(ID), NonTrivial(NonTrivial) {
  initializeSimpleLoopUnswitchLegacyPassPass(
      *PassRegistry::getPassRegistry());
}

bool runOnLoop(Loop *L, LPPassManager &LPM) override;

void getAnalysisUsage(AnalysisUsage &AU) const override {
  AU.addRequired<AssumptionCacheTracker>();
  AU.addRequired<TargetTransformInfoWrapperPass>();
  if (EnableMSSALoopDependency) {
    AU.addRequired<MemorySSAWrapperPass>();
    AU.addPreserved<MemorySSAWrapperPass>();
  }
  getLoopAnalysisUsage(AU);
}
2920};

2922} // end anonymous namespace

2924bool SimpleLoopUnswitchLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) {
if (skipLoop(L))
  return false;

Function &F = *L->getHeader()->getParent();

LLVM_DEBUG(dbgs() << "Unswitching loop in " << F.getName() << ": " << *Ldo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Unswitching loop in "
 << F.getName() << ": " << *L << "\n"
; } } while (false)
                  << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Unswitching loop in "
 << F.getName() << ": " << *L << "\n"
; } } while (false);

auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
MemorySSA *MSSA = nullptr;
Optional<MemorySSAUpdater> MSSAU;
if (EnableMSSALoopDependency) {
  MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
  MSSAU = MemorySSAUpdater(MSSA);
}

auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
auto *SE = SEWP ? &SEWP->getSE() : nullptr;

auto UnswitchCB = [&L, &LPM](bool CurrentLoopValid,
                             ArrayRef<Loop *> NewLoops) {
  // If we did a non-trivial unswitch, we have added new (cloned) loops.
  for (auto *NewL : NewLoops)
    LPM.addLoop(*NewL);

  // If the current loop remains valid, re-add it to the queue. This is
  // a little wasteful as we'll finish processing the current loop as well,
  // but it is the best we can do in the old PM.
  if (CurrentLoopValid)
    LPM.addLoop(*L);
  else
    LPM.markLoopAsDeleted(*L);
};

if (MSSA && VerifyMemorySSA)
  MSSA->verifyMemorySSA();

bool Changed = unswitchLoop(*L, DT, LI, AC, TTI, NonTrivial, UnswitchCB, SE,
                            MSSAU.hasValue() ? MSSAU.getPointer() : nullptr);

if (MSSA && VerifyMemorySSA)
  MSSA->verifyMemorySSA();

// If anything was unswitched, also clear any cached information about this
// loop.
LPM.deleteSimpleAnalysisLoop(L);

// Historically this pass has had issues with the dominator tree so verify it
// in asserts builds.
assert(DT.verify(DominatorTree::VerificationLevel::Fast))((DT.verify(DominatorTree::VerificationLevel::Fast)) ? static_cast
<void> (0) : __assert_fail ("DT.verify(DominatorTree::VerificationLevel::Fast)"
, "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2977, __PRETTY_FUNCTION__));

return Changed;
2980}

2982char SimpleLoopUnswitchLegacyPass::ID = 0;
2983INITIALIZE_PASS_BEGIN(SimpleLoopUnswitchLegacyPass, "simple-loop-unswitch",static void *initializeSimpleLoopUnswitchLegacyPassPassOnce(PassRegistry
 &Registry) {
                    "Simple unswitch loops", false, false)static void *initializeSimpleLoopUnswitchLegacyPassPassOnce(PassRegistry
 &Registry) {
2985INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)initializeAssumptionCacheTrackerPass(Registry);
2986INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
2987INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)initializeLoopInfoWrapperPassPass(Registry);
2988INITIALIZE_PASS_DEPENDENCY(LoopPass)initializeLoopPassPass(Registry);
2989INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)initializeMemorySSAWrapperPassPass(Registry);
2990INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)initializeTargetTransformInfoWrapperPassPass(Registry);
2991INITIALIZE_PASS_END(SimpleLoopUnswitchLegacyPass, "simple-loop-unswitch",PassInfo *PI = new PassInfo( "Simple unswitch loops", "simple-loop-unswitch"
, &SimpleLoopUnswitchLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<SimpleLoopUnswitchLegacyPass>), false,
 false); Registry.registerPass(*PI, true); return PI; } static
 llvm::once_flag InitializeSimpleLoopUnswitchLegacyPassPassFlag
; void llvm::initializeSimpleLoopUnswitchLegacyPassPass(PassRegistry
 &Registry) { llvm::call_once(InitializeSimpleLoopUnswitchLegacyPassPassFlag
, initializeSimpleLoopUnswitchLegacyPassPassOnce, std::ref(Registry
)); }
                  "Simple unswitch loops", false, false)PassInfo *PI = new PassInfo( "Simple unswitch loops", "simple-loop-unswitch"
, &SimpleLoopUnswitchLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<SimpleLoopUnswitchLegacyPass>), false,
 false); Registry.registerPass(*PI, true); return PI; } static
 llvm::once_flag InitializeSimpleLoopUnswitchLegacyPassPassFlag
; void llvm::initializeSimpleLoopUnswitchLegacyPassPass(PassRegistry
 &Registry) { llvm::call_once(InitializeSimpleLoopUnswitchLegacyPassPassFlag
, initializeSimpleLoopUnswitchLegacyPassPassOnce, std::ref(Registry
)); }

2994Pass *llvm::createSimpleLoopUnswitchLegacyPass(bool NonTrivial) {
return new SimpleLoopUnswitchLegacyPass(NonTrivial);
2996}

←

/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h

→

1//===- llvm/ADT/SmallVector.h - 'Normally small' vectors --------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file defines the SmallVector class.
10//
11//===----------------------------------------------------------------------===//

13#ifndef LLVM_ADT_SMALLVECTOR_H
14#define LLVM_ADT_SMALLVECTOR_H

16#include "llvm/ADT/iterator_range.h"
17#include "llvm/Support/AlignOf.h"
18#include "llvm/Support/Compiler.h"
19#include "llvm/Support/MathExtras.h"
20#include "llvm/Support/MemAlloc.h"
21#include "llvm/Support/type_traits.h"
22#include "llvm/Support/ErrorHandling.h"
23#include <algorithm>
24#include <cassert>
25#include <cstddef>
26#include <cstdlib>
27#include <cstring>
28#include <initializer_list>
29#include <iterator>
30#include <memory>
31#include <new>
32#include <type_traits>
33#include <utility>

35namespace llvm {

37/// This is all the non-templated stuff common to all SmallVectors.
38class SmallVectorBase {
39protected:
void *BeginX;
unsigned Size = 0, Capacity;

SmallVectorBase() = delete;
SmallVectorBase(void *FirstEl, size_t TotalCapacity)
    : BeginX(FirstEl), Capacity(TotalCapacity) {}

/// This is an implementation of the grow() method which only works
/// on POD-like data types and is out of line to reduce code duplication.
void grow_pod(void *FirstEl, size_t MinCapacity, size_t TSize);

51public:
size_t size() const { return Size; }
size_t capacity() const { return Capacity; }

LLVM_NODISCARD[[clang::warn_unused_result]] bool empty() const { return !Size; }
5
←
Assuming field 'Size' is not equal to 0, which participates in a condition later→
6
←
Returning zero, which participates in a condition later→

/// Set the array size to \p N, which the current array must have enough
/// capacity for.
///
/// This does not construct or destroy any elements in the vector.
///
/// Clients can use this in conjunction with capacity() to write past the end
/// of the buffer when they know that more elements are available, and only
/// update the size later. This avoids the cost of value initializing elements
/// which will only be overwritten.
void set_size(size_t N) {
  assert(N <= capacity())((N <= capacity()) ? static_cast<void> (0) : __assert_fail
 ("N <= capacity()", "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 67, __PRETTY_FUNCTION__));
  Size = N;
}
70};

72/// Figure out the offset of the first element.
73template <class T, typename = void> struct SmallVectorAlignmentAndSize {
AlignedCharArrayUnion<SmallVectorBase> Base;
AlignedCharArrayUnion<T> FirstEl;
76};

78/// This is the part of SmallVectorTemplateBase which does not depend on whether
79/// the type T is a POD. The extra dummy template argument is used by ArrayRef
80/// to avoid unnecessarily requiring T to be complete.
81template <typename T, typename = void>
82class SmallVectorTemplateCommon : public SmallVectorBase {
/// Find the address of the first element.  For this pointer math to be valid
/// with small-size of 0 for T with lots of alignment, it's important that
/// SmallVectorStorage is properly-aligned even for small-size of 0.
void *getFirstEl() const {
  return const_cast<void *>(reinterpret_cast<const void *>(
      reinterpret_cast<const char *>(this) +
      offsetof(SmallVectorAlignmentAndSize<T>, FirstEl)__builtin_offsetof(SmallVectorAlignmentAndSize<T>, FirstEl
)));
}
// Space after 'FirstEl' is clobbered, do not add any instance vars after it.

93protected:
SmallVectorTemplateCommon(size_t Size)
    : SmallVectorBase(getFirstEl(), Size) {}

void grow_pod(size_t MinCapacity, size_t TSize) {
  SmallVectorBase::grow_pod(getFirstEl(), MinCapacity, TSize);
}

/// Return true if this is a smallvector which has not had dynamic
/// memory allocated for it.
bool isSmall() const { return BeginX == getFirstEl(); }

/// Put this vector in a state of being small.
void resetToSmall() {
  BeginX = getFirstEl();
  Size = Capacity = 0; // FIXME: Setting Capacity to 0 is suspect.
}

111public:
using size_type = size_t;
using difference_type = ptrdiff_t;
using value_type = T;
using iterator = T *;
using const_iterator = const T *;

using const_reverse_iterator = std::reverse_iterator<const_iterator>;
using reverse_iterator = std::reverse_iterator<iterator>;

using reference = T &;
using const_reference = const T &;
using pointer = T *;
using const_pointer = const T *;

// forward iterator creation methods.
iterator begin() { return (iterator)this->BeginX; }
const_iterator begin() const { return (const_iterator)this->BeginX; }
iterator end() { return begin() + size(); }
const_iterator end() const { return begin() + size(); }

// reverse iterator creation methods.
reverse_iterator rbegin()            { return reverse_iterator(end()); }
const_reverse_iterator rbegin() const{ return const_reverse_iterator(end()); }
reverse_iterator rend()              { return reverse_iterator(begin()); }
const_reverse_iterator rend() const { return const_reverse_iterator(begin());}

size_type size_in_bytes() const { return size() * sizeof(T); }
size_type max_size() const { return size_type(-1) / sizeof(T); }

size_t capacity_in_bytes() const { return capacity() * sizeof(T); }

/// Return a pointer to the vector's buffer, even if empty().
pointer data() { return pointer(begin()); }
/// Return a pointer to the vector's buffer, even if empty().
const_pointer data() const { return const_pointer(begin()); }

reference operator[](size_type idx) {
  assert(idx < size())((idx < size()) ? static_cast<void> (0) : __assert_fail
 ("idx < size()", "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 149, __PRETTY_FUNCTION__));
  return begin()[idx];
}
const_reference operator[](size_type idx) const {
  assert(idx < size())((idx < size()) ? static_cast<void> (0) : __assert_fail
 ("idx < size()", "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 153, __PRETTY_FUNCTION__));
  return begin()[idx];
}

reference front() {
  assert(!empty())((!empty()) ? static_cast<void> (0) : __assert_fail ("!empty()"
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 158, __PRETTY_FUNCTION__));
  return begin()[0];
}
const_reference front() const {
  assert(!empty())((!empty()) ? static_cast<void> (0) : __assert_fail ("!empty()"
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 162, __PRETTY_FUNCTION__));
  return begin()[0];
}

reference back() {
  assert(!empty())((!empty()) ? static_cast<void> (0) : __assert_fail ("!empty()"
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 167, __PRETTY_FUNCTION__));
  return end()[-1];
}
const_reference back() const {
  assert(!empty())((!empty()) ? static_cast<void> (0) : __assert_fail ("!empty()"
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 171, __PRETTY_FUNCTION__));
  return end()[-1];
}
174};

176/// SmallVectorTemplateBase<TriviallyCopyable = false> - This is where we put method
177/// implementations that are designed to work with non-POD-like T's.
178template <typename T, bool = is_trivially_copyable<T>::value>
179class SmallVectorTemplateBase : public SmallVectorTemplateCommon<T> {
180protected:
SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}

static void destroy_range(T *S, T *E) {
  while (S != E) {
    --E;
    E->~T();
  }
}

/// Move the range [I, E) into the uninitialized memory starting with "Dest",
/// constructing elements as needed.
template<typename It1, typename It2>
static void uninitialized_move(It1 I, It1 E, It2 Dest) {
  std::uninitialized_copy(std::make_move_iterator(I),
                          std::make_move_iterator(E), Dest);
}

/// Copy the range [I, E) onto the uninitialized memory starting with "Dest",
/// constructing elements as needed.
template<typename It1, typename It2>
static void uninitialized_copy(It1 I, It1 E, It2 Dest) {
  std::uninitialized_copy(I, E, Dest);
}

/// Grow the allocated memory (without initializing new elements), doubling
/// the size of the allocated memory. Guarantees space for at least one more
/// element, or MinSize more elements if specified.
void grow(size_t MinSize = 0);

210public:
void push_back(const T &Elt) {
  if (LLVM_UNLIKELY(this->size() >= this->capacity())__builtin_expect((bool)(this->size() >= this->capacity
()), false))
    this->grow();
  ::new ((void*) this->end()) T(Elt);
  this->set_size(this->size() + 1);
}

void push_back(T &&Elt) {
  if (LLVM_UNLIKELY(this->size() >= this->capacity())__builtin_expect((bool)(this->size() >= this->capacity
()), false))
    this->grow();
  ::new ((void*) this->end()) T(::std::move(Elt));
  this->set_size(this->size() + 1);
}

void pop_back() {
  this->set_size(this->size() - 1);
  this->end()->~T();
}
229};

231// Define this out-of-line to dissuade the C++ compiler from inlining it.
232template <typename T, bool TriviallyCopyable>
233void SmallVectorTemplateBase<T, TriviallyCopyable>::grow(size_t MinSize) {
if (MinSize > UINT32_MAX(4294967295U))
  report_bad_alloc_error("SmallVector capacity overflow during allocation");

// Always grow, even from zero.
size_t NewCapacity = size_t(NextPowerOf2(this->capacity() + 2));
NewCapacity = std::min(std::max(NewCapacity, MinSize), size_t(UINT32_MAX(4294967295U)));
T *NewElts = static_cast<T*>(llvm::safe_malloc(NewCapacity*sizeof(T)));

// Move the elements over.
this->uninitialized_move(this->begin(), this->end(), NewElts);

// Destroy the original elements.
destroy_range(this->begin(), this->end());

// If this wasn't grown from the inline copy, deallocate the old space.
if (!this->isSmall())
  free(this->begin());

this->BeginX = NewElts;
this->Capacity = NewCapacity;
254}

256/// SmallVectorTemplateBase<TriviallyCopyable = true> - This is where we put
257/// method implementations that are designed to work with POD-like T's.
258template <typename T>
259class SmallVectorTemplateBase<T, true> : public SmallVectorTemplateCommon<T> {
260protected:
SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}

// No need to do a destroy loop for POD's.
static void destroy_range(T *, T *) {}

/// Move the range [I, E) onto the uninitialized memory
/// starting with "Dest", constructing elements into it as needed.
template<typename It1, typename It2>
static void uninitialized_move(It1 I, It1 E, It2 Dest) {
  // Just do a copy.
  uninitialized_copy(I, E, Dest);
}

/// Copy the range [I, E) onto the uninitialized memory
/// starting with "Dest", constructing elements into it as needed.
template<typename It1, typename It2>
static void uninitialized_copy(It1 I, It1 E, It2 Dest) {
  // Arbitrary iterator types; just use the basic implementation.
  std::uninitialized_copy(I, E, Dest);
}

/// Copy the range [I, E) onto the uninitialized memory
/// starting with "Dest", constructing elements into it as needed.
template <typename T1, typename T2>
static void uninitialized_copy(
    T1 *I, T1 *E, T2 *Dest,
    typename std::enable_if<std::is_same<typename std::remove_const<T1>::type,
                                         T2>::value>::type * = nullptr) {
  // Use memcpy for PODs iterated by pointers (which includes SmallVector
  // iterators): std::uninitialized_copy optimizes to memmove, but we can
  // use memcpy here. Note that I and E are iterators and thus might be
  // invalid for memcpy if they are equal.
  if (I != E)
    memcpy(reinterpret_cast<void *>(Dest), I, (E - I) * sizeof(T));
}

/// Double the size of the allocated memory, guaranteeing space for at
/// least one more element or MinSize if specified.
void grow(size_t MinSize = 0) { this->grow_pod(MinSize, sizeof(T)); }

301public:
void push_back(const T &Elt) {
  if (LLVM_UNLIKELY(this->size() >= this->capacity())__builtin_expect((bool)(this->size() >= this->capacity
()), false))
    this->grow();
  memcpy(reinterpret_cast<void *>(this->end()), &Elt, sizeof(T));
  this->set_size(this->size() + 1);
}

void pop_back() { this->set_size(this->size() - 1); }
310};

312/// This class consists of common code factored out of the SmallVector class to
313/// reduce code duplication based on the SmallVector 'N' template parameter.
314template <typename T>
315class SmallVectorImpl : public SmallVectorTemplateBase<T> {
using SuperClass = SmallVectorTemplateBase<T>;

318public:
using iterator = typename SuperClass::iterator;
using const_iterator = typename SuperClass::const_iterator;
using reference = typename SuperClass::reference;
using size_type = typename SuperClass::size_type;

324protected:
// Default ctor - Initialize to empty.
explicit SmallVectorImpl(unsigned N)
    : SmallVectorTemplateBase<T>(N) {}

329public:
SmallVectorImpl(const SmallVectorImpl &) = delete;

~SmallVectorImpl() {
  // Subclass has already destructed this vector's elements.
  // If this wasn't grown from the inline copy, deallocate the old space.
  if (!this->isSmall())
    free(this->begin());
}

void clear() {
  this->destroy_range(this->begin(), this->end());
  this->Size = 0;
}

void resize(size_type N) {
  if (N < this->size()) {
    this->destroy_range(this->begin()+N, this->end());
    this->set_size(N);
  } else if (N > this->size()) {
    if (this->capacity() < N)
      this->grow(N);
    for (auto I = this->end(), E = this->begin() + N; I != E; ++I)
      new (&*I) T();
    this->set_size(N);
  }
}

void resize(size_type N, const T &NV) {
  if (N < this->size()) {
    this->destroy_range(this->begin()+N, this->end());
    this->set_size(N);
  } else if (N > this->size()) {
    if (this->capacity() < N)
      this->grow(N);
    std::uninitialized_fill(this->end(), this->begin()+N, NV);
    this->set_size(N);
  }
}

void reserve(size_type N) {
  if (this->capacity() < N)
    this->grow(N);
}

LLVM_NODISCARD[[clang::warn_unused_result]] T pop_back_val() {
  T Result = ::std::move(this->back());
  this->pop_back();
  return Result;
}

void swap(SmallVectorImpl &RHS);

/// Add the specified range to the end of the SmallVector.
template <typename in_iter,
          typename = typename std::enable_if<std::is_convertible<
              typename std::iterator_traits<in_iter>::iterator_category,
              std::input_iterator_tag>::value>::type>
void append(in_iter in_start, in_iter in_end) {
  size_type NumInputs = std::distance(in_start, in_end);
  if (NumInputs > this->capacity() - this->size())
    this->grow(this->size()+NumInputs);

  this->uninitialized_copy(in_start, in_end, this->end());
  this->set_size(this->size() + NumInputs);
}

/// Append \p NumInputs copies of \p Elt to the end.
void append(size_type NumInputs, const T &Elt) {
  if (NumInputs > this->capacity() - this->size())
    this->grow(this->size()+NumInputs);

  std::uninitialized_fill_n(this->end(), NumInputs, Elt);
  this->set_size(this->size() + NumInputs);
}

void append(std::initializer_list<T> IL) {
  append(IL.begin(), IL.end());
}

// FIXME: Consider assigning over existing elements, rather than clearing &
// re-initializing them - for all assign(...) variants.

void assign(size_type NumElts, const T &Elt) {
  clear();
  if (this->capacity() < NumElts)
    this->grow(NumElts);
  this->set_size(NumElts);
  std::uninitialized_fill(this->begin(), this->end(), Elt);
}

template <typename in_iter,
          typename = typename std::enable_if<std::is_convertible<
              typename std::iterator_traits<in_iter>::iterator_category,
              std::input_iterator_tag>::value>::type>
void assign(in_iter in_start, in_iter in_end) {
  clear();
  append(in_start, in_end);
}

void assign(std::initializer_list<T> IL) {
  clear();
  append(IL);
}

iterator erase(const_iterator CI) {
  // Just cast away constness because this is a non-const member function.
  iterator I = const_cast<iterator>(CI);

  assert(I >= this->begin() && "Iterator to erase is out of bounds.")((I >= this->begin() && "Iterator to erase is out of bounds."
) ? static_cast<void> (0) : __assert_fail ("I >= this->begin() && \"Iterator to erase is out of bounds.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 438, __PRETTY_FUNCTION__));
  assert(I < this->end() && "Erasing at past-the-end iterator.")((I < this->end() && "Erasing at past-the-end iterator."
) ? static_cast<void> (0) : __assert_fail ("I < this->end() && \"Erasing at past-the-end iterator.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 439, __PRETTY_FUNCTION__));

  iterator N = I;
  // Shift all elts down one.
  std::move(I+1, this->end(), I);
  // Drop the last elt.
  this->pop_back();
  return(N);
}

iterator erase(const_iterator CS, const_iterator CE) {
  // Just cast away constness because this is a non-const member function.
  iterator S = const_cast<iterator>(CS);
  iterator E = const_cast<iterator>(CE);

  assert(S >= this->begin() && "Range to erase is out of bounds.")((S >= this->begin() && "Range to erase is out of bounds."
) ? static_cast<void> (0) : __assert_fail ("S >= this->begin() && \"Range to erase is out of bounds.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 454, __PRETTY_FUNCTION__));
  assert(S <= E && "Trying to erase invalid range.")((S <= E && "Trying to erase invalid range.") ? static_cast
<void> (0) : __assert_fail ("S <= E && \"Trying to erase invalid range.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 455, __PRETTY_FUNCTION__));
  assert(E <= this->end() && "Trying to erase past the end.")((E <= this->end() && "Trying to erase past the end."
) ? static_cast<void> (0) : __assert_fail ("E <= this->end() && \"Trying to erase past the end.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 456, __PRETTY_FUNCTION__));

  iterator N = S;
  // Shift all elts down.
  iterator I = std::move(E, this->end(), S);
  // Drop the last elts.
  this->destroy_range(I, this->end());
  this->set_size(I - this->begin());
  return(N);
}

iterator insert(iterator I, T &&Elt) {
  if (I == this->end()) {  // Important special case for empty vector.
    this->push_back(::std::move(Elt));
    return this->end()-1;
  }

  assert(I >= this->begin() && "Insertion iterator is out of bounds.")((I >= this->begin() && "Insertion iterator is out of bounds."
) ? static_cast<void> (0) : __assert_fail ("I >= this->begin() && \"Insertion iterator is out of bounds.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 473, __PRETTY_FUNCTION__));
  assert(I <= this->end() && "Inserting past the end of the vector.")((I <= this->end() && "Inserting past the end of the vector."
) ? static_cast<void> (0) : __assert_fail ("I <= this->end() && \"Inserting past the end of the vector.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 474, __PRETTY_FUNCTION__));

  if (this->size() >= this->capacity()) {
    size_t EltNo = I-this->begin();
    this->grow();
    I = this->begin()+EltNo;
  }

  ::new ((void*) this->end()) T(::std::move(this->back()));
  // Push everything else over.
  std::move_backward(I, this->end()-1, this->end());
  this->set_size(this->size() + 1);

  // If we just moved the element we're inserting, be sure to update
  // the reference.
  T *EltPtr = &Elt;
  if (I <= EltPtr && EltPtr < this->end())
    ++EltPtr;

  *I = ::std::move(*EltPtr);
  return I;
}

iterator insert(iterator I, const T &Elt) {
  if (I == this->end()) {  // Important special case for empty vector.
    this->push_back(Elt);
    return this->end()-1;
  }

  assert(I >= this->begin() && "Insertion iterator is out of bounds.")((I >= this->begin() && "Insertion iterator is out of bounds."
) ? static_cast<void> (0) : __assert_fail ("I >= this->begin() && \"Insertion iterator is out of bounds.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 503, __PRETTY_FUNCTION__));
  assert(I <= this->end() && "Inserting past the end of the vector.")((I <= this->end() && "Inserting past the end of the vector."
) ? static_cast<void> (0) : __assert_fail ("I <= this->end() && \"Inserting past the end of the vector.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 504, __PRETTY_FUNCTION__));

  if (this->size() >= this->capacity()) {
    size_t EltNo = I-this->begin();
    this->grow();
    I = this->begin()+EltNo;
  }
  ::new ((void*) this->end()) T(std::move(this->back()));
  // Push everything else over.
  std::move_backward(I, this->end()-1, this->end());
  this->set_size(this->size() + 1);

  // If we just moved the element we're inserting, be sure to update
  // the reference.
  const T *EltPtr = &Elt;
  if (I <= EltPtr && EltPtr < this->end())
    ++EltPtr;

  *I = *EltPtr;
  return I;
}

iterator insert(iterator I, size_type NumToInsert, const T &Elt) {
  // Convert iterator to elt# to avoid invalidating iterator when we reserve()
  size_t InsertElt = I - this->begin();

  if (I == this->end()) {  // Important special case for empty vector.
    append(NumToInsert, Elt);
    return this->begin()+InsertElt;
  }

  assert(I >= this->begin() && "Insertion iterator is out of bounds.")((I >= this->begin() && "Insertion iterator is out of bounds."
) ? static_cast<void> (0) : __assert_fail ("I >= this->begin() && \"Insertion iterator is out of bounds.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 535, __PRETTY_FUNCTION__));
  assert(I <= this->end() && "Inserting past the end of the vector.")((I <= this->end() && "Inserting past the end of the vector."
) ? static_cast<void> (0) : __assert_fail ("I <= this->end() && \"Inserting past the end of the vector.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 536, __PRETTY_FUNCTION__));

  // Ensure there is enough space.
  reserve(this->size() + NumToInsert);

  // Uninvalidate the iterator.
  I = this->begin()+InsertElt;

  // If there are more elements between the insertion point and the end of the
  // range than there are being inserted, we can use a simple approach to
  // insertion.  Since we already reserved space, we know that this won't
  // reallocate the vector.
  if (size_t(this->end()-I) >= NumToInsert) {
    T *OldEnd = this->end();
    append(std::move_iterator<iterator>(this->end() - NumToInsert),
           std::move_iterator<iterator>(this->end()));

    // Copy the existing elements that get replaced.
    std::move_backward(I, OldEnd-NumToInsert, OldEnd);

    std::fill_n(I, NumToInsert, Elt);
    return I;
  }

  // Otherwise, we're inserting more elements than exist already, and we're
  // not inserting at the end.

  // Move over the elements that we're about to overwrite.
  T *OldEnd = this->end();
  this->set_size(this->size() + NumToInsert);
  size_t NumOverwritten = OldEnd-I;
  this->uninitialized_move(I, OldEnd, this->end()-NumOverwritten);

  // Replace the overwritten part.
  std::fill_n(I, NumOverwritten, Elt);

  // Insert the non-overwritten middle part.
  std::uninitialized_fill_n(OldEnd, NumToInsert-NumOverwritten, Elt);
  return I;
}

template <typename ItTy,
          typename = typename std::enable_if<std::is_convertible<
              typename std::iterator_traits<ItTy>::iterator_category,
              std::input_iterator_tag>::value>::type>
iterator insert(iterator I, ItTy From, ItTy To) {
  // Convert iterator to elt# to avoid invalidating iterator when we reserve()
  size_t InsertElt = I - this->begin();

  if (I == this->end()) {  // Important special case for empty vector.
    append(From, To);
    return this->begin()+InsertElt;
  }

  assert(I >= this->begin() && "Insertion iterator is out of bounds.")((I >= this->begin() && "Insertion iterator is out of bounds."
) ? static_cast<void> (0) : __assert_fail ("I >= this->begin() && \"Insertion iterator is out of bounds.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 590, __PRETTY_FUNCTION__));
  assert(I <= this->end() && "Inserting past the end of the vector.")((I <= this->end() && "Inserting past the end of the vector."
) ? static_cast<void> (0) : __assert_fail ("I <= this->end() && \"Inserting past the end of the vector.\""
, "/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/ADT/SmallVector.h"
, 591, __PRETTY_FUNCTION__));

  size_t NumToInsert = std::distance(From, To);

  // Ensure there is enough space.
  reserve(this->size() + NumToInsert);

  // Uninvalidate the iterator.
  I = this->begin()+InsertElt;

  // If there are more elements between the insertion point and the end of the
  // range than there are being inserted, we can use a simple approach to
  // insertion.  Since we already reserved space, we know that this won't
  // reallocate the vector.
  if (size_t(this->end()-I) >= NumToInsert) {
    T *OldEnd = this->end();
    append(std::move_iterator<iterator>(this->end() - NumToInsert),
           std::move_iterator<iterator>(this->end()));

    // Copy the existing elements that get replaced.
    std::move_backward(I, OldEnd-NumToInsert, OldEnd);

    std::copy(From, To, I);
    return I;
  }

  // Otherwise, we're inserting more elements than exist already, and we're
  // not inserting at the end.

  // Move over the elements that we're about to overwrite.
  T *OldEnd = this->end();
  this->set_size(this->size() + NumToInsert);
  size_t NumOverwritten = OldEnd-I;
  this->uninitialized_move(I, OldEnd, this->end()-NumOverwritten);

  // Replace the overwritten part.
  for (T *J = I; NumOverwritten > 0; --NumOverwritten) {
    *J = *From;
    ++J; ++From;
  }

  // Insert the non-overwritten middle part.
  this->uninitialized_copy(From, To, OldEnd);
  return I;
}

void insert(iterator I, std::initializer_list<T> IL) {
  insert(I, IL.begin(), IL.end());
}

template <typename... ArgTypes> reference emplace_back(ArgTypes &&... Args) {
  if (LLVM_UNLIKELY(this->size() >= this->capacity())__builtin_expect((bool)(this->size() >= this->capacity
()), false))
    this->grow();
  ::new ((void *)this->end()) T(std::forward<ArgTypes>(Args)...);
  this->set_size(this->size() + 1);
  return this->back();
}

SmallVectorImpl &operator=(const SmallVectorImpl &RHS);

SmallVectorImpl &operator=(SmallVectorImpl &&RHS);

bool operator==(const SmallVectorImpl &RHS) const {
  if (this->size() != RHS.size()) return false;
  return std::equal(this->begin(), this->end(), RHS.begin());
}
bool operator!=(const SmallVectorImpl &RHS) const {
  return !(*this == RHS);
}

bool operator<(const SmallVectorImpl &RHS) const {
  return std::lexicographical_compare(this->begin(), this->end(),
                                      RHS.begin(), RHS.end());
}
665};

667template <typename T>
668void SmallVectorImpl<T>::swap(SmallVectorImpl<T> &RHS) {
if (this == &RHS) return;

// We can only avoid copying elements if neither vector is small.
if (!this->isSmall() && !RHS.isSmall()) {
  std::swap(this->BeginX, RHS.BeginX);
  std::swap(this->Size, RHS.Size);
  std::swap(this->Capacity, RHS.Capacity);
  return;
}
if (RHS.size() > this->capacity())
  this->grow(RHS.size());
if (this->size() > RHS.capacity())
  RHS.grow(this->size());

// Swap the shared elements.
size_t NumShared = this->size();
if (NumShared > RHS.size()) NumShared = RHS.size();
for (size_type i = 0; i != NumShared; ++i)
  std::swap((*this)[i], RHS[i]);

// Copy over the extra elts.
if (this->size() > RHS.size()) {
  size_t EltDiff = this->size() - RHS.size();
  this->uninitialized_copy(this->begin()+NumShared, this->end(), RHS.end());
  RHS.set_size(RHS.size() + EltDiff);
  this->destroy_range(this->begin()+NumShared, this->end());
  this->set_size(NumShared);
} else if (RHS.size() > this->size()) {
  size_t EltDiff = RHS.size() - this->size();
  this->uninitialized_copy(RHS.begin()+NumShared, RHS.end(), this->end());
  this->set_size(this->size() + EltDiff);
  this->destroy_range(RHS.begin()+NumShared, RHS.end());
  RHS.set_size(NumShared);
}
703}

705template <typename T>
706SmallVectorImpl<T> &SmallVectorImpl<T>::
operator=(const SmallVectorImpl<T> &RHS) {
// Avoid self-assignment.
if (this == &RHS) return *this;

// If we already have sufficient space, assign the common elements, then
// destroy any excess.
size_t RHSSize = RHS.size();
size_t CurSize = this->size();
if (CurSize >= RHSSize) {
  // Assign common elements.
  iterator NewEnd;
  if (RHSSize)
    NewEnd = std::copy(RHS.begin(), RHS.begin()+RHSSize, this->begin());
  else
    NewEnd = this->begin();

  // Destroy excess elements.
  this->destroy_range(NewEnd, this->end());

  // Trim.
  this->set_size(RHSSize);
  return *this;
}

// If we have to grow to have enough elements, destroy the current elements.
// This allows us to avoid copying them during the grow.
// FIXME: don't do this if they're efficiently moveable.
if (this->capacity() < RHSSize) {
  // Destroy current elements.
  this->destroy_range(this->begin(), this->end());
  this->set_size(0);
  CurSize = 0;
  this->grow(RHSSize);
} else if (CurSize) {
  // Otherwise, use assignment for the already-constructed elements.
  std::copy(RHS.begin(), RHS.begin()+CurSize, this->begin());
}

// Copy construct the new elements in place.
this->uninitialized_copy(RHS.begin()+CurSize, RHS.end(),
                         this->begin()+CurSize);

// Set end.
this->set_size(RHSSize);
return *this;
752}

754template <typename T>
755SmallVectorImpl<T> &SmallVectorImpl<T>::operator=(SmallVectorImpl<T> &&RHS) {
// Avoid self-assignment.
if (this == &RHS) return *this;

// If the RHS isn't small, clear this vector and then steal its buffer.
if (!RHS.isSmall()) {
  this->destroy_range(this->begin(), this->end());
  if (!this->isSmall()) free(this->begin());
  this->BeginX = RHS.BeginX;
  this->Size = RHS.Size;
  this->Capacity = RHS.Capacity;
  RHS.resetToSmall();
  return *this;
}

// If we already have sufficient space, assign the common elements, then
// destroy any excess.
size_t RHSSize = RHS.size();
size_t CurSize = this->size();
if (CurSize >= RHSSize) {
  // Assign common elements.
  iterator NewEnd = this->begin();
  if (RHSSize)
    NewEnd = std::move(RHS.begin(), RHS.end(), NewEnd);

  // Destroy excess elements and trim the bounds.
  this->destroy_range(NewEnd, this->end());
  this->set_size(RHSSize);

  // Clear the RHS.
  RHS.clear();

  return *this;
}

// If we have to grow to have enough elements, destroy the current elements.
// This allows us to avoid copying them during the grow.
// FIXME: this may not actually make any sense if we can efficiently move
// elements.
if (this->capacity() < RHSSize) {
  // Destroy current elements.
  this->destroy_range(this->begin(), this->end());
  this->set_size(0);
  CurSize = 0;
  this->grow(RHSSize);
} else if (CurSize) {
  // Otherwise, use assignment for the already-constructed elements.
  std::move(RHS.begin(), RHS.begin()+CurSize, this->begin());
}

// Move-construct the new elements in place.
this->uninitialized_move(RHS.begin()+CurSize, RHS.end(),
                         this->begin()+CurSize);

// Set end.
this->set_size(RHSSize);

RHS.clear();
return *this;
814}

816/// Storage for the SmallVector elements.  This is specialized for the N=0 case
817/// to avoid allocating unnecessary storage.
818template <typename T, unsigned N>
819struct SmallVectorStorage {
AlignedCharArrayUnion<T> InlineElts[N];
821};

823/// We need the storage to be properly aligned even for small-size of 0 so that
824/// the pointer math in \a SmallVectorTemplateCommon::getFirstEl() is
825/// well-defined.
826template <typename T> struct alignas(alignof(T)) SmallVectorStorage<T, 0> {};

828/// This is a 'vector' (really, a variable-sized array), optimized
829/// for the case when the array is small.  It contains some number of elements
830/// in-place, which allows it to avoid heap allocation when the actual number of
831/// elements is below that threshold.  This allows normal "small" cases to be
832/// fast without losing generality for large inputs.
833///
834/// Note that this does not attempt to be exception safe.
835///
836template <typename T, unsigned N>
837class SmallVector : public SmallVectorImpl<T>, SmallVectorStorage<T, N> {
838public:
SmallVector() : SmallVectorImpl<T>(N) {}

~SmallVector() {
  // Destroy the constructed elements in the vector.
  this->destroy_range(this->begin(), this->end());
}

explicit SmallVector(size_t Size, const T &Value = T())
  : SmallVectorImpl<T>(N) {
  this->assign(Size, Value);
}

template <typename ItTy,
          typename = typename std::enable_if<std::is_convertible<
              typename std::iterator_traits<ItTy>::iterator_category,
              std::input_iterator_tag>::value>::type>
SmallVector(ItTy S, ItTy E) : SmallVectorImpl<T>(N) {
  this->append(S, E);
}

template <typename RangeTy>
explicit SmallVector(const iterator_range<RangeTy> &R)
    : SmallVectorImpl<T>(N) {
  this->append(R.begin(), R.end());
}

SmallVector(std::initializer_list<T> IL) : SmallVectorImpl<T>(N) {
  this->assign(IL);
}

SmallVector(const SmallVector &RHS) : SmallVectorImpl<T>(N) {
  if (!RHS.empty())
    SmallVectorImpl<T>::operator=(RHS);
}

const SmallVector &operator=(const SmallVector &RHS) {
  SmallVectorImpl<T>::operator=(RHS);
  return *this;
}

SmallVector(SmallVector &&RHS) : SmallVectorImpl<T>(N) {
  if (!RHS.empty())
    SmallVectorImpl<T>::operator=(::std::move(RHS));
}

SmallVector(SmallVectorImpl<T> &&RHS) : SmallVectorImpl<T>(N) {
  if (!RHS.empty())
    SmallVectorImpl<T>::operator=(::std::move(RHS));
}

const SmallVector &operator=(SmallVector &&RHS) {
  SmallVectorImpl<T>::operator=(::std::move(RHS));
  return *this;
}

const SmallVector &operator=(SmallVectorImpl<T> &&RHS) {
  SmallVectorImpl<T>::operator=(::std::move(RHS));
  return *this;
}

const SmallVector &operator=(std::initializer_list<T> IL) {
  this->assign(IL);
  return *this;
}
903};

905template <typename T, unsigned N>
906inline size_t capacity_in_bytes(const SmallVector<T, N> &X) {
return X.capacity_in_bytes();
908}

910} // end namespace llvm

912namespace std {

/// Implement std::swap in terms of SmallVector swap.
template<typename T>
inline void
swap(llvm::SmallVectorImpl<T> &LHS, llvm::SmallVectorImpl<T> &RHS) {
  LHS.swap(RHS);
}

/// Implement std::swap in terms of SmallVector swap.
template<typename T, unsigned N>
inline void
swap(llvm::SmallVector<T, N> &LHS, llvm::SmallVector<T, N> &RHS) {
  LHS.swap(RHS);
}

928} // end namespace std

930#endif // LLVM_ADT_SMALLVECTOR_H

←

/build/llvm-toolchain-snapshot-10~svn374877/include/llvm/Analysis/CFG.h

1//===-- Analysis/CFG.h - BasicBlock Analyses --------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This family of functions performs analyses on basic blocks, and instructions
10// contained within basic blocks.
11//
12//===----------------------------------------------------------------------===//
13 
14#ifndef LLVM_ANALYSIS_CFG_H
15#define LLVM_ANALYSIS_CFG_H
16 
17#include "llvm/IR/BasicBlock.h"
18#include "llvm/IR/CFG.h"
19 
20namespace llvm {
21 
22class BasicBlock;
23class DominatorTree;
24class Function;
25class Instruction;
26class LoopInfo;
27 
28/// Analyze the specified function to find all of the loop backedges in the
29/// function and return them.  This is a relatively cheap (compared to
30/// computing dominators and loop info) analysis.
31///
32/// The output is added to Result, as pairs of <from,to> edge info.
33void FindFunctionBackedges(
34    const Function &F,
35    SmallVectorImpl<std::pair<const BasicBlock *, const BasicBlock *> > &
36        Result);
37 
38/// Search for the specified successor of basic block BB and return its position
39/// in the terminator instruction's list of successors.  It is an error to call
40/// this with a block that is not a successor.
41unsigned GetSuccessorNumber(const BasicBlock *BB, const BasicBlock *Succ);
42 
43/// Return true if the specified edge is a critical edge. Critical edges are
44/// edges from a block with multiple successors to a block with multiple
45/// predecessors.
46///
47bool isCriticalEdge(const Instruction *TI, unsigned SuccNum,
48                    bool AllowIdenticalEdges = false);
49bool isCriticalEdge(const Instruction *TI, const BasicBlock *Succ,
50                    bool AllowIdenticalEdges = false);
51 
52/// Determine whether instruction 'To' is reachable from 'From', without passing
53/// through any blocks in ExclusionSet, returning true if uncertain.
54///
55/// Determine whether there is a path from From to To within a single function.
56/// Returns false only if we can prove that once 'From' has been executed then
57/// 'To' can not be executed. Conservatively returns true.
58///
59/// This function is linear with respect to the number of blocks in the CFG,
60/// walking down successors from From to reach To, with a fixed threshold.
61/// Using DT or LI allows us to answer more quickly. LI reduces the cost of
62/// an entire loop of any number of blocks to be the same as the cost of a
63/// single block. DT reduces the cost by allowing the search to terminate when
64/// we find a block that dominates the block containing 'To'. DT is most useful
65/// on branchy code but not loops, and LI is most useful on code with loops but
66/// does not help on branchy code outside loops.
67bool isPotentiallyReachable(
68    const Instruction *From, const Instruction *To,
69    const SmallPtrSetImpl<BasicBlock *> *ExclusionSet = nullptr,
70    const DominatorTree *DT = nullptr, const LoopInfo *LI = nullptr);
71 
72/// Determine whether block 'To' is reachable from 'From', returning
73/// true if uncertain.
74///
75/// Determine whether there is a path from From to To within a single function.
76/// Returns false only if we can prove that once 'From' has been reached then
77/// 'To' can not be executed. Conservatively returns true.
78bool isPotentiallyReachable(const BasicBlock *From, const BasicBlock *To,
79                            const DominatorTree *DT = nullptr,
80                            const LoopInfo *LI = nullptr);
81 
82/// Determine whether there is at least one path from a block in
83/// 'Worklist' to 'StopBB', returning true if uncertain.
84///
85/// Determine whether there is a path from at least one block in Worklist to
86/// StopBB within a single function. Returns false only if we can prove that
87/// once any block in 'Worklist' has been reached then 'StopBB' can not be
88/// executed. Conservatively returns true.
89bool isPotentiallyReachableFromMany(SmallVectorImpl<BasicBlock *> &Worklist,
90                                    BasicBlock *StopBB,
91                                    const DominatorTree *DT = nullptr,
92                                    const LoopInfo *LI = nullptr);
93 
94/// Determine whether there is at least one path from a block in
95/// 'Worklist' to 'StopBB' without passing through any blocks in
96/// 'ExclusionSet', returning true if uncertain.
97///
98/// Determine whether there is a path from at least one block in Worklist to
99/// StopBB within a single function without passing through any of the blocks
100/// in 'ExclusionSet'. Returns false only if we can prove that once any block
101/// in 'Worklist' has been reached then 'StopBB' can not be executed.
102/// Conservatively returns true.
103bool isPotentiallyReachableFromMany(
104    SmallVectorImpl<BasicBlock *> &Worklist, BasicBlock *StopBB,
105    const SmallPtrSetImpl<BasicBlock *> *ExclusionSet,
106    const DominatorTree *DT = nullptr, const LoopInfo *LI = nullptr);
107 
108/// Return true if the control flow in \p RPOTraversal is irreducible.
109///
110/// This is a generic implementation to detect CFG irreducibility based on loop
111/// info analysis. It can be used for any kind of CFG (Loop, MachineLoop,
112/// Function, MachineFunction, etc.) by providing an RPO traversal (\p
113/// RPOTraversal) and the loop info analysis (\p LI) of the CFG. This utility
114/// function is only recommended when loop info analysis is available. If loop
115/// info analysis isn't available, please, don't compute it explicitly for this
116/// purpose. There are more efficient ways to detect CFG irreducibility that
117/// don't require recomputing loop info analysis (e.g., T1/T2 or Tarjan's
118/// algorithm).
119///
120/// Requirements:
121///   1) GraphTraits must be implemented for NodeT type. It is used to access
122///      NodeT successors.
123//    2) \p RPOTraversal must be a valid reverse post-order traversal of the
124///      target CFG with begin()/end() iterator interfaces.
125///   3) \p LI must be a valid LoopInfoBase that contains up-to-date loop
126///      analysis information of the CFG.
127///
128/// This algorithm uses the information about reducible loop back-edges already
129/// computed in \p LI. When a back-edge is found during the RPO traversal, the
130/// algorithm checks whether the back-edge is one of the reducible back-edges in
131/// loop info. If it isn't, the CFG is irreducible. For example, for the CFG
132/// below (canonical irreducible graph) loop info won't contain any loop, so the
133/// algorithm will return that the CFG is irreducible when checking the B <-
134/// -> C back-edge.
135///
136/// (A->B, A->C, B->C, C->B, C->D)
137///    A
138///  /   \
139/// B<- ->C
140///       |
141///       D
142///
143template <class NodeT, class RPOTraversalT, class LoopInfoT,
144          class GT = GraphTraits<NodeT>>
145bool containsIrreducibleCFG(RPOTraversalT &RPOTraversal, const LoopInfoT &LI) {
146  /// Check whether the edge (\p Src, \p Dst) is a reducible loop backedge
147  /// according to LI. I.e., check if there exists a loop that contains Src and
148  /// where Dst is the loop header.
149  auto isProperBackedge = [&](NodeT Src, NodeT Dst) {
150    for (const auto *Lp = LI.getLoopFor(Src); Lp; Lp = Lp->getParentLoop()) {
151      if (Lp->getHeader() == Dst)
152        return true;
153    }
154    return false;
155  };
156 
157  SmallPtrSet<NodeT, 32> Visited;
158  for (NodeT Node : RPOTraversal) {
159    Visited.insert(Node);
160    for (NodeT Succ : make_range(GT::child_begin(Node), GT::child_end(Node))) {
161      // Succ hasn't been visited yet
162      if (!Visited.count(Succ))
163        continue;
164      // We already visited Succ, thus Node->Succ must be a backedge. Check that
165      // the head matches what we have in the loop information. Otherwise, we
166      // have an irreducible graph.
167      if (!isProperBackedge(Node, Succ))
168        return true;
169    }
170  }
171 
172  return false;
10
←
Returning zero, which participates in a condition later→
173}
174} // End llvm namespace
175 
176#endif