Bug Summary

File:build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
Warning:line 2913, column 21
Called C++ object pointer is null

Annotated Source Code

Press '?' to see keyboard shortcuts

clang -cc1 -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -clear-ast-before-backend -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 -setup-static-analyzer -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -mframe-pointer=none -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -ffunction-sections -fdata-sections -fcoverage-compilation-dir=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/build-llvm -resource-dir /usr/lib/llvm-15/lib/clang/15.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/llvm/lib/Transforms/Scalar -I include -I /build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/llvm/include -D _FORTIFY_SOURCE=2 -D NDEBUG -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/x86_64-linux-gnu/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/backward -internal-isystem /usr/lib/llvm-15/lib/clang/15.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fmacro-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/build-llvm=build-llvm -fmacro-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/= -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/build-llvm=build-llvm -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/= -O3 -Wno-unused-command-line-argument -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/build-llvm=build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/= -ferror-limit 19 -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -fcolor-diagnostics -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/scan-build-2022-04-20-140412-16051-1 -x c++ /build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp

/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/llvm/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//===----------------------------------------------------------------------===//
8
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/LoopAnalysisManager.h"
23#include "llvm/Analysis/LoopInfo.h"
24#include "llvm/Analysis/LoopIterator.h"
25#include "llvm/Analysis/LoopPass.h"
26#include "llvm/Analysis/MemorySSA.h"
27#include "llvm/Analysis/MemorySSAUpdater.h"
28#include "llvm/Analysis/MustExecute.h"
29#include "llvm/Analysis/ScalarEvolution.h"
30#include "llvm/Analysis/TargetTransformInfo.h"
31#include "llvm/Analysis/ValueTracking.h"
32#include "llvm/IR/BasicBlock.h"
33#include "llvm/IR/Constant.h"
34#include "llvm/IR/Constants.h"
35#include "llvm/IR/Dominators.h"
36#include "llvm/IR/Function.h"
37#include "llvm/IR/IRBuilder.h"
38#include "llvm/IR/InstrTypes.h"
39#include "llvm/IR/Instruction.h"
40#include "llvm/IR/Instructions.h"
41#include "llvm/IR/IntrinsicInst.h"
42#include "llvm/IR/PatternMatch.h"
43#include "llvm/IR/Use.h"
44#include "llvm/IR/Value.h"
45#include "llvm/InitializePasses.h"
46#include "llvm/Pass.h"
47#include "llvm/Support/Casting.h"
48#include "llvm/Support/CommandLine.h"
49#include "llvm/Support/Debug.h"
50#include "llvm/Support/ErrorHandling.h"
51#include "llvm/Support/GenericDomTree.h"
52#include "llvm/Support/InstructionCost.h"
53#include "llvm/Support/raw_ostream.h"
54#include "llvm/Transforms/Scalar/LoopPassManager.h"
55#include "llvm/Transforms/Utils/BasicBlockUtils.h"
56#include "llvm/Transforms/Utils/Cloning.h"
57#include "llvm/Transforms/Utils/Local.h"
58#include "llvm/Transforms/Utils/LoopUtils.h"
59#include "llvm/Transforms/Utils/ValueMapper.h"
60#include <algorithm>
61#include <cassert>
62#include <iterator>
63#include <numeric>
64#include <utility>
65
66#define DEBUG_TYPE"simple-loop-unswitch" "simple-loop-unswitch"
67
68using namespace llvm;
69using namespace llvm::PatternMatch;
70
71STATISTIC(NumBranches, "Number of branches unswitched")static llvm::Statistic NumBranches = {"simple-loop-unswitch",
"NumBranches", "Number of branches unswitched"}
;
72STATISTIC(NumSwitches, "Number of switches unswitched")static llvm::Statistic NumSwitches = {"simple-loop-unswitch",
"NumSwitches", "Number of switches unswitched"}
;
73STATISTIC(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"}
;
74STATISTIC(NumTrivial, "Number of unswitches that are trivial")static llvm::Statistic NumTrivial = {"simple-loop-unswitch", "NumTrivial"
, "Number of unswitches that are trivial"}
;
75STATISTIC(static llvm::Statistic NumCostMultiplierSkipped = {"simple-loop-unswitch"
, "NumCostMultiplierSkipped", "Number of unswitch candidates that had their cost multiplier skipped"
}
76 NumCostMultiplierSkipped,static llvm::Statistic NumCostMultiplierSkipped = {"simple-loop-unswitch"
, "NumCostMultiplierSkipped", "Number of unswitch candidates that had their cost multiplier skipped"
}
77 "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"
}
;
78
79static cl::opt<bool> EnableNonTrivialUnswitch(
80 "enable-nontrivial-unswitch", cl::init(false), cl::Hidden,
81 cl::desc("Forcibly enables non-trivial loop unswitching rather than "
82 "following the configuration passed into the pass."));
83
84static cl::opt<int>
85 UnswitchThreshold("unswitch-threshold", cl::init(50), cl::Hidden,
86 cl::ZeroOrMore,
87 cl::desc("The cost threshold for unswitching a loop."));
88
89static cl::opt<bool> EnableUnswitchCostMultiplier(
90 "enable-unswitch-cost-multiplier", cl::init(true), cl::Hidden,
91 cl::desc("Enable unswitch cost multiplier that prohibits exponential "
92 "explosion in nontrivial unswitch."));
93static cl::opt<int> UnswitchSiblingsToplevelDiv(
94 "unswitch-siblings-toplevel-div", cl::init(2), cl::Hidden,
95 cl::desc("Toplevel siblings divisor for cost multiplier."));
96static cl::opt<int> UnswitchNumInitialUnscaledCandidates(
97 "unswitch-num-initial-unscaled-candidates", cl::init(8), cl::Hidden,
98 cl::desc("Number of unswitch candidates that are ignored when calculating "
99 "cost multiplier."));
100static cl::opt<bool> UnswitchGuards(
101 "simple-loop-unswitch-guards", cl::init(true), cl::Hidden,
102 cl::desc("If enabled, simple loop unswitching will also consider "
103 "llvm.experimental.guard intrinsics as unswitch candidates."));
104static cl::opt<bool> DropNonTrivialImplicitNullChecks(
105 "simple-loop-unswitch-drop-non-trivial-implicit-null-checks",
106 cl::init(false), cl::Hidden,
107 cl::desc("If enabled, drop make.implicit metadata in unswitched implicit "
108 "null checks to save time analyzing if we can keep it."));
109static cl::opt<unsigned>
110 MSSAThreshold("simple-loop-unswitch-memoryssa-threshold",
111 cl::desc("Max number of memory uses to explore during "
112 "partial unswitching analysis"),
113 cl::init(100), cl::Hidden);
114static cl::opt<bool> FreezeLoopUnswitchCond(
115 "freeze-loop-unswitch-cond", cl::init(false), cl::Hidden,
116 cl::desc("If enabled, the freeze instruction will be added to condition "
117 "of loop unswitch to prevent miscompilation."));
118
119/// Collect all of the loop invariant input values transitively used by the
120/// homogeneous instruction graph from a given root.
121///
122/// This essentially walks from a root recursively through loop variant operands
123/// which have the exact same opcode and finds all inputs which are loop
124/// invariant. For some operations these can be re-associated and unswitched out
125/// of the loop entirely.
126static TinyPtrVector<Value *>
127collectHomogenousInstGraphLoopInvariants(Loop &L, Instruction &Root,
128 LoopInfo &LI) {
129 assert(!L.isLoopInvariant(&Root) &&(static_cast <bool> (!L.isLoopInvariant(&Root) &&
"Only need to walk the graph if root itself is not invariant."
) ? void (0) : __assert_fail ("!L.isLoopInvariant(&Root) && \"Only need to walk the graph if root itself is not invariant.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 130, __extension__
__PRETTY_FUNCTION__))
130 "Only need to walk the graph if root itself is not invariant.")(static_cast <bool> (!L.isLoopInvariant(&Root) &&
"Only need to walk the graph if root itself is not invariant."
) ? void (0) : __assert_fail ("!L.isLoopInvariant(&Root) && \"Only need to walk the graph if root itself is not invariant.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 130, __extension__
__PRETTY_FUNCTION__))
;
131 TinyPtrVector<Value *> Invariants;
132
133 bool IsRootAnd = match(&Root, m_LogicalAnd());
134 bool IsRootOr = match(&Root, m_LogicalOr());
135
136 // Build a worklist and recurse through operators collecting invariants.
137 SmallVector<Instruction *, 4> Worklist;
138 SmallPtrSet<Instruction *, 8> Visited;
139 Worklist.push_back(&Root);
140 Visited.insert(&Root);
141 do {
142 Instruction &I = *Worklist.pop_back_val();
143 for (Value *OpV : I.operand_values()) {
144 // Skip constants as unswitching isn't interesting for them.
145 if (isa<Constant>(OpV))
146 continue;
147
148 // Add it to our result if loop invariant.
149 if (L.isLoopInvariant(OpV)) {
150 Invariants.push_back(OpV);
151 continue;
152 }
153
154 // If not an instruction with the same opcode, nothing we can do.
155 Instruction *OpI = dyn_cast<Instruction>(OpV);
156
157 if (OpI && ((IsRootAnd && match(OpI, m_LogicalAnd())) ||
158 (IsRootOr && match(OpI, m_LogicalOr())))) {
159 // Visit this operand.
160 if (Visited.insert(OpI).second)
161 Worklist.push_back(OpI);
162 }
163 }
164 } while (!Worklist.empty());
165
166 return Invariants;
167}
168
169static void replaceLoopInvariantUses(Loop &L, Value *Invariant,
170 Constant &Replacement) {
171 assert(!isa<Constant>(Invariant) && "Why are we unswitching on a constant?")(static_cast <bool> (!isa<Constant>(Invariant) &&
"Why are we unswitching on a constant?") ? void (0) : __assert_fail
("!isa<Constant>(Invariant) && \"Why are we unswitching on a constant?\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 171, __extension__
__PRETTY_FUNCTION__))
;
172
173 // Replace uses of LIC in the loop with the given constant.
174 // We use make_early_inc_range as set invalidates the iterator.
175 for (Use &U : llvm::make_early_inc_range(Invariant->uses())) {
176 Instruction *UserI = dyn_cast<Instruction>(U.getUser());
177
178 // Replace this use within the loop body.
179 if (UserI && L.contains(UserI))
180 U.set(&Replacement);
181 }
182}
183
184/// Check that all the LCSSA PHI nodes in the loop exit block have trivial
185/// incoming values along this edge.
186static bool areLoopExitPHIsLoopInvariant(Loop &L, BasicBlock &ExitingBB,
187 BasicBlock &ExitBB) {
188 for (Instruction &I : ExitBB) {
189 auto *PN = dyn_cast<PHINode>(&I);
190 if (!PN)
191 // No more PHIs to check.
192 return true;
193
194 // If the incoming value for this edge isn't loop invariant the unswitch
195 // won't be trivial.
196 if (!L.isLoopInvariant(PN->getIncomingValueForBlock(&ExitingBB)))
197 return false;
198 }
199 llvm_unreachable("Basic blocks should never be empty!")::llvm::llvm_unreachable_internal("Basic blocks should never be empty!"
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 199)
;
200}
201
202/// Copy a set of loop invariant values \p ToDuplicate and insert them at the
203/// end of \p BB and conditionally branch on the copied condition. We only
204/// branch on a single value.
205static void buildPartialUnswitchConditionalBranch(
206 BasicBlock &BB, ArrayRef<Value *> Invariants, bool Direction,
207 BasicBlock &UnswitchedSucc, BasicBlock &NormalSucc, bool InsertFreeze) {
208 IRBuilder<> IRB(&BB);
209
210 Value *Cond = Direction ? IRB.CreateOr(Invariants) :
211 IRB.CreateAnd(Invariants);
212 if (InsertFreeze)
213 Cond = IRB.CreateFreeze(Cond, Cond->getName() + ".fr");
214 IRB.CreateCondBr(Cond, Direction ? &UnswitchedSucc : &NormalSucc,
215 Direction ? &NormalSucc : &UnswitchedSucc);
216}
217
218/// Copy a set of loop invariant values, and conditionally branch on them.
219static void buildPartialInvariantUnswitchConditionalBranch(
220 BasicBlock &BB, ArrayRef<Value *> ToDuplicate, bool Direction,
221 BasicBlock &UnswitchedSucc, BasicBlock &NormalSucc, Loop &L,
222 MemorySSAUpdater *MSSAU) {
223 ValueToValueMapTy VMap;
224 for (auto *Val : reverse(ToDuplicate)) {
225 Instruction *Inst = cast<Instruction>(Val);
226 Instruction *NewInst = Inst->clone();
227 BB.getInstList().insert(BB.end(), NewInst);
228 RemapInstruction(NewInst, VMap,
229 RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
230 VMap[Val] = NewInst;
231
232 if (!MSSAU)
233 continue;
234
235 MemorySSA *MSSA = MSSAU->getMemorySSA();
236 if (auto *MemUse =
237 dyn_cast_or_null<MemoryUse>(MSSA->getMemoryAccess(Inst))) {
238 auto *DefiningAccess = MemUse->getDefiningAccess();
239 // Get the first defining access before the loop.
240 while (L.contains(DefiningAccess->getBlock())) {
241 // If the defining access is a MemoryPhi, get the incoming
242 // value for the pre-header as defining access.
243 if (auto *MemPhi = dyn_cast<MemoryPhi>(DefiningAccess))
244 DefiningAccess =
245 MemPhi->getIncomingValueForBlock(L.getLoopPreheader());
246 else
247 DefiningAccess = cast<MemoryDef>(DefiningAccess)->getDefiningAccess();
248 }
249 MSSAU->createMemoryAccessInBB(NewInst, DefiningAccess,
250 NewInst->getParent(),
251 MemorySSA::BeforeTerminator);
252 }
253 }
254
255 IRBuilder<> IRB(&BB);
256 Value *Cond = VMap[ToDuplicate[0]];
257 IRB.CreateCondBr(Cond, Direction ? &UnswitchedSucc : &NormalSucc,
258 Direction ? &NormalSucc : &UnswitchedSucc);
259}
260
261/// Rewrite the PHI nodes in an unswitched loop exit basic block.
262///
263/// Requires that the loop exit and unswitched basic block are the same, and
264/// that the exiting block was a unique predecessor of that block. Rewrites the
265/// PHI nodes in that block such that what were LCSSA PHI nodes become trivial
266/// PHI nodes from the old preheader that now contains the unswitched
267/// terminator.
268static void rewritePHINodesForUnswitchedExitBlock(BasicBlock &UnswitchedBB,
269 BasicBlock &OldExitingBB,
270 BasicBlock &OldPH) {
271 for (PHINode &PN : UnswitchedBB.phis()) {
272 // When the loop exit is directly unswitched we just need to update the
273 // incoming basic block. We loop to handle weird cases with repeated
274 // incoming blocks, but expect to typically only have one operand here.
275 for (auto i : seq<int>(0, PN.getNumOperands())) {
276 assert(PN.getIncomingBlock(i) == &OldExitingBB &&(static_cast <bool> (PN.getIncomingBlock(i) == &OldExitingBB
&& "Found incoming block different from unique predecessor!"
) ? void (0) : __assert_fail ("PN.getIncomingBlock(i) == &OldExitingBB && \"Found incoming block different from unique predecessor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 277, __extension__
__PRETTY_FUNCTION__))
277 "Found incoming block different from unique predecessor!")(static_cast <bool> (PN.getIncomingBlock(i) == &OldExitingBB
&& "Found incoming block different from unique predecessor!"
) ? void (0) : __assert_fail ("PN.getIncomingBlock(i) == &OldExitingBB && \"Found incoming block different from unique predecessor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 277, __extension__
__PRETTY_FUNCTION__))
;
278 PN.setIncomingBlock(i, &OldPH);
279 }
280 }
281}
282
283/// Rewrite the PHI nodes in the loop exit basic block and the split off
284/// unswitched block.
285///
286/// Because the exit block remains an exit from the loop, this rewrites the
287/// LCSSA PHI nodes in it to remove the unswitched edge and introduces PHI
288/// nodes into the unswitched basic block to select between the value in the
289/// old preheader and the loop exit.
290static void rewritePHINodesForExitAndUnswitchedBlocks(BasicBlock &ExitBB,
291 BasicBlock &UnswitchedBB,
292 BasicBlock &OldExitingBB,
293 BasicBlock &OldPH,
294 bool FullUnswitch) {
295 assert(&ExitBB != &UnswitchedBB &&(static_cast <bool> (&ExitBB != &UnswitchedBB &&
"Must have different loop exit and unswitched blocks!") ? void
(0) : __assert_fail ("&ExitBB != &UnswitchedBB && \"Must have different loop exit and unswitched blocks!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 296, __extension__
__PRETTY_FUNCTION__))
296 "Must have different loop exit and unswitched blocks!")(static_cast <bool> (&ExitBB != &UnswitchedBB &&
"Must have different loop exit and unswitched blocks!") ? void
(0) : __assert_fail ("&ExitBB != &UnswitchedBB && \"Must have different loop exit and unswitched blocks!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 296, __extension__
__PRETTY_FUNCTION__))
;
297 Instruction *InsertPt = &*UnswitchedBB.begin();
298 for (PHINode &PN : ExitBB.phis()) {
299 auto *NewPN = PHINode::Create(PN.getType(), /*NumReservedValues*/ 2,
300 PN.getName() + ".split", InsertPt);
301
302 // Walk backwards over the old PHI node's inputs to minimize the cost of
303 // removing each one. We have to do this weird loop manually so that we
304 // create the same number of new incoming edges in the new PHI as we expect
305 // each case-based edge to be included in the unswitched switch in some
306 // cases.
307 // FIXME: This is really, really gross. It would be much cleaner if LLVM
308 // allowed us to create a single entry for a predecessor block without
309 // having separate entries for each "edge" even though these edges are
310 // required to produce identical results.
311 for (int i = PN.getNumIncomingValues() - 1; i >= 0; --i) {
312 if (PN.getIncomingBlock(i) != &OldExitingBB)
313 continue;
314
315 Value *Incoming = PN.getIncomingValue(i);
316 if (FullUnswitch)
317 // No more edge from the old exiting block to the exit block.
318 PN.removeIncomingValue(i);
319
320 NewPN->addIncoming(Incoming, &OldPH);
321 }
322
323 // Now replace the old PHI with the new one and wire the old one in as an
324 // input to the new one.
325 PN.replaceAllUsesWith(NewPN);
326 NewPN->addIncoming(&PN, &ExitBB);
327 }
328}
329
330/// Hoist the current loop up to the innermost loop containing a remaining exit.
331///
332/// Because we've removed an exit from the loop, we may have changed the set of
333/// loops reachable and need to move the current loop up the loop nest or even
334/// to an entirely separate nest.
335static void hoistLoopToNewParent(Loop &L, BasicBlock &Preheader,
336 DominatorTree &DT, LoopInfo &LI,
337 MemorySSAUpdater *MSSAU, ScalarEvolution *SE) {
338 // If the loop is already at the top level, we can't hoist it anywhere.
339 Loop *OldParentL = L.getParentLoop();
340 if (!OldParentL)
341 return;
342
343 SmallVector<BasicBlock *, 4> Exits;
344 L.getExitBlocks(Exits);
345 Loop *NewParentL = nullptr;
346 for (auto *ExitBB : Exits)
347 if (Loop *ExitL = LI.getLoopFor(ExitBB))
348 if (!NewParentL || NewParentL->contains(ExitL))
349 NewParentL = ExitL;
350
351 if (NewParentL == OldParentL)
352 return;
353
354 // The new parent loop (if different) should always contain the old one.
355 if (NewParentL)
356 assert(NewParentL->contains(OldParentL) &&(static_cast <bool> (NewParentL->contains(OldParentL
) && "Can only hoist this loop up the nest!") ? void (
0) : __assert_fail ("NewParentL->contains(OldParentL) && \"Can only hoist this loop up the nest!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 357, __extension__
__PRETTY_FUNCTION__))
357 "Can only hoist this loop up the nest!")(static_cast <bool> (NewParentL->contains(OldParentL
) && "Can only hoist this loop up the nest!") ? void (
0) : __assert_fail ("NewParentL->contains(OldParentL) && \"Can only hoist this loop up the nest!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 357, __extension__
__PRETTY_FUNCTION__))
;
358
359 // The preheader will need to move with the body of this loop. However,
360 // because it isn't in this loop we also need to update the primary loop map.
361 assert(OldParentL == LI.getLoopFor(&Preheader) &&(static_cast <bool> (OldParentL == LI.getLoopFor(&Preheader
) && "Parent loop of this loop should contain this loop's preheader!"
) ? void (0) : __assert_fail ("OldParentL == LI.getLoopFor(&Preheader) && \"Parent loop of this loop should contain this loop's preheader!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 362, __extension__
__PRETTY_FUNCTION__))
362 "Parent loop of this loop should contain this loop's preheader!")(static_cast <bool> (OldParentL == LI.getLoopFor(&Preheader
) && "Parent loop of this loop should contain this loop's preheader!"
) ? void (0) : __assert_fail ("OldParentL == LI.getLoopFor(&Preheader) && \"Parent loop of this loop should contain this loop's preheader!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 362, __extension__
__PRETTY_FUNCTION__))
;
363 LI.changeLoopFor(&Preheader, NewParentL);
364
365 // Remove this loop from its old parent.
366 OldParentL->removeChildLoop(&L);
367
368 // Add the loop either to the new parent or as a top-level loop.
369 if (NewParentL)
370 NewParentL->addChildLoop(&L);
371 else
372 LI.addTopLevelLoop(&L);
373
374 // Remove this loops blocks from the old parent and every other loop up the
375 // nest until reaching the new parent. Also update all of these
376 // no-longer-containing loops to reflect the nesting change.
377 for (Loop *OldContainingL = OldParentL; OldContainingL != NewParentL;
378 OldContainingL = OldContainingL->getParentLoop()) {
379 llvm::erase_if(OldContainingL->getBlocksVector(),
380 [&](const BasicBlock *BB) {
381 return BB == &Preheader || L.contains(BB);
382 });
383
384 OldContainingL->getBlocksSet().erase(&Preheader);
385 for (BasicBlock *BB : L.blocks())
386 OldContainingL->getBlocksSet().erase(BB);
387
388 // Because we just hoisted a loop out of this one, we have essentially
389 // created new exit paths from it. That means we need to form LCSSA PHI
390 // nodes for values used in the no-longer-nested loop.
391 formLCSSA(*OldContainingL, DT, &LI, SE);
392
393 // We shouldn't need to form dedicated exits because the exit introduced
394 // here is the (just split by unswitching) preheader. However, after trivial
395 // unswitching it is possible to get new non-dedicated exits out of parent
396 // loop so let's conservatively form dedicated exit blocks and figure out
397 // if we can optimize later.
398 formDedicatedExitBlocks(OldContainingL, &DT, &LI, MSSAU,
399 /*PreserveLCSSA*/ true);
400 }
401}
402
403// Return the top-most loop containing ExitBB and having ExitBB as exiting block
404// or the loop containing ExitBB, if there is no parent loop containing ExitBB
405// as exiting block.
406static Loop *getTopMostExitingLoop(BasicBlock *ExitBB, LoopInfo &LI) {
407 Loop *TopMost = LI.getLoopFor(ExitBB);
408 Loop *Current = TopMost;
409 while (Current) {
410 if (Current->isLoopExiting(ExitBB))
411 TopMost = Current;
412 Current = Current->getParentLoop();
413 }
414 return TopMost;
415}
416
417/// Unswitch a trivial branch if the condition is loop invariant.
418///
419/// This routine should only be called when loop code leading to the branch has
420/// been validated as trivial (no side effects). This routine checks if the
421/// condition is invariant and one of the successors is a loop exit. This
422/// allows us to unswitch without duplicating the loop, making it trivial.
423///
424/// If this routine fails to unswitch the branch it returns false.
425///
426/// If the branch can be unswitched, this routine splits the preheader and
427/// hoists the branch above that split. Preserves loop simplified form
428/// (splitting the exit block as necessary). It simplifies the branch within
429/// the loop to an unconditional branch but doesn't remove it entirely. Further
430/// cleanup can be done with some simplifycfg like pass.
431///
432/// If `SE` is not null, it will be updated based on the potential loop SCEVs
433/// invalidated by this.
434static bool unswitchTrivialBranch(Loop &L, BranchInst &BI, DominatorTree &DT,
435 LoopInfo &LI, ScalarEvolution *SE,
436 MemorySSAUpdater *MSSAU) {
437 assert(BI.isConditional() && "Can only unswitch a conditional branch!")(static_cast <bool> (BI.isConditional() && "Can only unswitch a conditional branch!"
) ? void (0) : __assert_fail ("BI.isConditional() && \"Can only unswitch a conditional branch!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 437, __extension__
__PRETTY_FUNCTION__))
;
438 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)
;
439
440 // The loop invariant values that we want to unswitch.
441 TinyPtrVector<Value *> Invariants;
442
443 // When true, we're fully unswitching the branch rather than just unswitching
444 // some input conditions to the branch.
445 bool FullUnswitch = false;
446
447 if (L.isLoopInvariant(BI.getCondition())) {
448 Invariants.push_back(BI.getCondition());
449 FullUnswitch = true;
450 } else {
451 if (auto *CondInst = dyn_cast<Instruction>(BI.getCondition()))
452 Invariants = collectHomogenousInstGraphLoopInvariants(L, *CondInst, LI);
453 if (Invariants.empty()) {
454 LLVM_DEBUG(dbgs() << " Couldn't find invariant inputs!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Couldn't find invariant inputs!\n"
; } } while (false)
;
455 return false;
456 }
457 }
458
459 // Check that one of the branch's successors exits, and which one.
460 bool ExitDirection = true;
461 int LoopExitSuccIdx = 0;
462 auto *LoopExitBB = BI.getSuccessor(0);
463 if (L.contains(LoopExitBB)) {
464 ExitDirection = false;
465 LoopExitSuccIdx = 1;
466 LoopExitBB = BI.getSuccessor(1);
467 if (L.contains(LoopExitBB)) {
468 LLVM_DEBUG(dbgs() << " Branch doesn't exit the loop!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Branch doesn't exit the loop!\n"
; } } while (false)
;
469 return false;
470 }
471 }
472 auto *ContinueBB = BI.getSuccessor(1 - LoopExitSuccIdx);
473 auto *ParentBB = BI.getParent();
474 if (!areLoopExitPHIsLoopInvariant(L, *ParentBB, *LoopExitBB)) {
475 LLVM_DEBUG(dbgs() << " Loop exit PHI's aren't loop-invariant!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Loop exit PHI's aren't loop-invariant!\n"
; } } while (false)
;
476 return false;
477 }
478
479 // When unswitching only part of the branch's condition, we need the exit
480 // block to be reached directly from the partially unswitched input. This can
481 // be done when the exit block is along the true edge and the branch condition
482 // is a graph of `or` operations, or the exit block is along the false edge
483 // and the condition is a graph of `and` operations.
484 if (!FullUnswitch) {
485 if (ExitDirection ? !match(BI.getCondition(), m_LogicalOr())
486 : !match(BI.getCondition(), m_LogicalAnd())) {
487 LLVM_DEBUG(dbgs() << " Branch condition is in improper form for "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Branch condition is in improper form for "
"non-full unswitch!\n"; } } while (false)
488 "non-full unswitch!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Branch condition is in improper form for "
"non-full unswitch!\n"; } } while (false)
;
489 return false;
490 }
491 }
492
493 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)
494 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)
495 << "\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)
496 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)
497 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)
498 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)
499 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)
500 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)
501 }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)
502 })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)
;
503
504 // If we have scalar evolutions, we need to invalidate them including this
505 // loop, the loop containing the exit block and the topmost parent loop
506 // exiting via LoopExitBB.
507 if (SE) {
508 if (Loop *ExitL = getTopMostExitingLoop(LoopExitBB, LI))
509 SE->forgetLoop(ExitL);
510 else
511 // Forget the entire nest as this exits the entire nest.
512 SE->forgetTopmostLoop(&L);
513 }
514
515 if (MSSAU && VerifyMemorySSA)
516 MSSAU->getMemorySSA()->verifyMemorySSA();
517
518 // Split the preheader, so that we know that there is a safe place to insert
519 // the conditional branch. We will change the preheader to have a conditional
520 // branch on LoopCond.
521 BasicBlock *OldPH = L.getLoopPreheader();
522 BasicBlock *NewPH = SplitEdge(OldPH, L.getHeader(), &DT, &LI, MSSAU);
523
524 // Now that we have a place to insert the conditional branch, create a place
525 // to branch to: this is the exit block out of the loop that we are
526 // unswitching. We need to split this if there are other loop predecessors.
527 // Because the loop is in simplified form, *any* other predecessor is enough.
528 BasicBlock *UnswitchedBB;
529 if (FullUnswitch && LoopExitBB->getUniquePredecessor()) {
530 assert(LoopExitBB->getUniquePredecessor() == BI.getParent() &&(static_cast <bool> (LoopExitBB->getUniquePredecessor
() == BI.getParent() && "A branch's parent isn't a predecessor!"
) ? void (0) : __assert_fail ("LoopExitBB->getUniquePredecessor() == BI.getParent() && \"A branch's parent isn't a predecessor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 531, __extension__
__PRETTY_FUNCTION__))
531 "A branch's parent isn't a predecessor!")(static_cast <bool> (LoopExitBB->getUniquePredecessor
() == BI.getParent() && "A branch's parent isn't a predecessor!"
) ? void (0) : __assert_fail ("LoopExitBB->getUniquePredecessor() == BI.getParent() && \"A branch's parent isn't a predecessor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 531, __extension__
__PRETTY_FUNCTION__))
;
532 UnswitchedBB = LoopExitBB;
533 } else {
534 UnswitchedBB =
535 SplitBlock(LoopExitBB, &LoopExitBB->front(), &DT, &LI, MSSAU);
536 }
537
538 if (MSSAU && VerifyMemorySSA)
539 MSSAU->getMemorySSA()->verifyMemorySSA();
540
541 // Actually move the invariant uses into the unswitched position. If possible,
542 // we do this by moving the instructions, but when doing partial unswitching
543 // we do it by building a new merge of the values in the unswitched position.
544 OldPH->getTerminator()->eraseFromParent();
545 if (FullUnswitch) {
546 // If fully unswitching, we can use the existing branch instruction.
547 // Splice it into the old PH to gate reaching the new preheader and re-point
548 // its successors.
549 OldPH->getInstList().splice(OldPH->end(), BI.getParent()->getInstList(),
550 BI);
551 if (MSSAU) {
552 // Temporarily clone the terminator, to make MSSA update cheaper by
553 // separating "insert edge" updates from "remove edge" ones.
554 ParentBB->getInstList().push_back(BI.clone());
555 } else {
556 // Create a new unconditional branch that will continue the loop as a new
557 // terminator.
558 BranchInst::Create(ContinueBB, ParentBB);
559 }
560 BI.setSuccessor(LoopExitSuccIdx, UnswitchedBB);
561 BI.setSuccessor(1 - LoopExitSuccIdx, NewPH);
562 } else {
563 // Only unswitching a subset of inputs to the condition, so we will need to
564 // build a new branch that merges the invariant inputs.
565 if (ExitDirection)
566 assert(match(BI.getCondition(), m_LogicalOr()) &&(static_cast <bool> (match(BI.getCondition(), m_LogicalOr
()) && "Must have an `or` of `i1`s or `select i1 X, true, Y`s for the "
"condition!") ? void (0) : __assert_fail ("match(BI.getCondition(), m_LogicalOr()) && \"Must have an `or` of `i1`s or `select i1 X, true, Y`s for the \" \"condition!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 568, __extension__
__PRETTY_FUNCTION__))
567 "Must have an `or` of `i1`s or `select i1 X, true, Y`s for the "(static_cast <bool> (match(BI.getCondition(), m_LogicalOr
()) && "Must have an `or` of `i1`s or `select i1 X, true, Y`s for the "
"condition!") ? void (0) : __assert_fail ("match(BI.getCondition(), m_LogicalOr()) && \"Must have an `or` of `i1`s or `select i1 X, true, Y`s for the \" \"condition!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 568, __extension__
__PRETTY_FUNCTION__))
568 "condition!")(static_cast <bool> (match(BI.getCondition(), m_LogicalOr
()) && "Must have an `or` of `i1`s or `select i1 X, true, Y`s for the "
"condition!") ? void (0) : __assert_fail ("match(BI.getCondition(), m_LogicalOr()) && \"Must have an `or` of `i1`s or `select i1 X, true, Y`s for the \" \"condition!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 568, __extension__
__PRETTY_FUNCTION__))
;
569 else
570 assert(match(BI.getCondition(), m_LogicalAnd()) &&(static_cast <bool> (match(BI.getCondition(), m_LogicalAnd
()) && "Must have an `and` of `i1`s or `select i1 X, Y, false`s for the"
" condition!") ? void (0) : __assert_fail ("match(BI.getCondition(), m_LogicalAnd()) && \"Must have an `and` of `i1`s or `select i1 X, Y, false`s for the\" \" condition!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 572, __extension__
__PRETTY_FUNCTION__))
571 "Must have an `and` of `i1`s or `select i1 X, Y, false`s for the"(static_cast <bool> (match(BI.getCondition(), m_LogicalAnd
()) && "Must have an `and` of `i1`s or `select i1 X, Y, false`s for the"
" condition!") ? void (0) : __assert_fail ("match(BI.getCondition(), m_LogicalAnd()) && \"Must have an `and` of `i1`s or `select i1 X, Y, false`s for the\" \" condition!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 572, __extension__
__PRETTY_FUNCTION__))
572 " condition!")(static_cast <bool> (match(BI.getCondition(), m_LogicalAnd
()) && "Must have an `and` of `i1`s or `select i1 X, Y, false`s for the"
" condition!") ? void (0) : __assert_fail ("match(BI.getCondition(), m_LogicalAnd()) && \"Must have an `and` of `i1`s or `select i1 X, Y, false`s for the\" \" condition!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 572, __extension__
__PRETTY_FUNCTION__))
;
573 buildPartialUnswitchConditionalBranch(*OldPH, Invariants, ExitDirection,
574 *UnswitchedBB, *NewPH, false);
575 }
576
577 // Update the dominator tree with the added edge.
578 DT.insertEdge(OldPH, UnswitchedBB);
579
580 // After the dominator tree was updated with the added edge, update MemorySSA
581 // if available.
582 if (MSSAU) {
583 SmallVector<CFGUpdate, 1> Updates;
584 Updates.push_back({cfg::UpdateKind::Insert, OldPH, UnswitchedBB});
585 MSSAU->applyInsertUpdates(Updates, DT);
586 }
587
588 // Finish updating dominator tree and memory ssa for full unswitch.
589 if (FullUnswitch) {
590 if (MSSAU) {
591 // Remove the cloned branch instruction.
592 ParentBB->getTerminator()->eraseFromParent();
593 // Create unconditional branch now.
594 BranchInst::Create(ContinueBB, ParentBB);
595 MSSAU->removeEdge(ParentBB, LoopExitBB);
596 }
597 DT.deleteEdge(ParentBB, LoopExitBB);
598 }
599
600 if (MSSAU && VerifyMemorySSA)
601 MSSAU->getMemorySSA()->verifyMemorySSA();
602
603 // Rewrite the relevant PHI nodes.
604 if (UnswitchedBB == LoopExitBB)
605 rewritePHINodesForUnswitchedExitBlock(*UnswitchedBB, *ParentBB, *OldPH);
606 else
607 rewritePHINodesForExitAndUnswitchedBlocks(*LoopExitBB, *UnswitchedBB,
608 *ParentBB, *OldPH, FullUnswitch);
609
610 // The constant we can replace all of our invariants with inside the loop
611 // body. If any of the invariants have a value other than this the loop won't
612 // be entered.
613 ConstantInt *Replacement = ExitDirection
614 ? ConstantInt::getFalse(BI.getContext())
615 : ConstantInt::getTrue(BI.getContext());
616
617 // Since this is an i1 condition we can also trivially replace uses of it
618 // within the loop with a constant.
619 for (Value *Invariant : Invariants)
620 replaceLoopInvariantUses(L, Invariant, *Replacement);
621
622 // If this was full unswitching, we may have changed the nesting relationship
623 // for this loop so hoist it to its correct parent if needed.
624 if (FullUnswitch)
625 hoistLoopToNewParent(L, *NewPH, DT, LI, MSSAU, SE);
626
627 if (MSSAU && VerifyMemorySSA)
628 MSSAU->getMemorySSA()->verifyMemorySSA();
629
630 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)
;
631 ++NumTrivial;
632 ++NumBranches;
633 return true;
634}
635
636/// Unswitch a trivial switch if the condition is loop invariant.
637///
638/// This routine should only be called when loop code leading to the switch has
639/// been validated as trivial (no side effects). This routine checks if the
640/// condition is invariant and that at least one of the successors is a loop
641/// exit. This allows us to unswitch without duplicating the loop, making it
642/// trivial.
643///
644/// If this routine fails to unswitch the switch it returns false.
645///
646/// If the switch can be unswitched, this routine splits the preheader and
647/// copies the switch above that split. If the default case is one of the
648/// exiting cases, it copies the non-exiting cases and points them at the new
649/// preheader. If the default case is not exiting, it copies the exiting cases
650/// and points the default at the preheader. It preserves loop simplified form
651/// (splitting the exit blocks as necessary). It simplifies the switch within
652/// the loop by removing now-dead cases. If the default case is one of those
653/// unswitched, it replaces its destination with a new basic block containing
654/// only unreachable. Such basic blocks, while technically loop exits, are not
655/// considered for unswitching so this is a stable transform and the same
656/// switch will not be revisited. If after unswitching there is only a single
657/// in-loop successor, the switch is further simplified to an unconditional
658/// branch. Still more cleanup can be done with some simplifycfg like pass.
659///
660/// If `SE` is not null, it will be updated based on the potential loop SCEVs
661/// invalidated by this.
662static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
663 LoopInfo &LI, ScalarEvolution *SE,
664 MemorySSAUpdater *MSSAU) {
665 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)
;
666 Value *LoopCond = SI.getCondition();
667
668 // If this isn't switching on an invariant condition, we can't unswitch it.
669 if (!L.isLoopInvariant(LoopCond))
670 return false;
671
672 auto *ParentBB = SI.getParent();
673
674 // The same check must be used both for the default and the exit cases. We
675 // should never leave edges from the switch instruction to a basic block that
676 // we are unswitching, hence the condition used to determine the default case
677 // needs to also be used to populate ExitCaseIndices, which is then used to
678 // remove cases from the switch.
679 auto IsTriviallyUnswitchableExitBlock = [&](BasicBlock &BBToCheck) {
680 // BBToCheck is not an exit block if it is inside loop L.
681 if (L.contains(&BBToCheck))
682 return false;
683 // BBToCheck is not trivial to unswitch if its phis aren't loop invariant.
684 if (!areLoopExitPHIsLoopInvariant(L, *ParentBB, BBToCheck))
685 return false;
686 // We do not unswitch a block that only has an unreachable statement, as
687 // it's possible this is a previously unswitched block. Only unswitch if
688 // either the terminator is not unreachable, or, if it is, it's not the only
689 // instruction in the block.
690 auto *TI = BBToCheck.getTerminator();
691 bool isUnreachable = isa<UnreachableInst>(TI);
692 return !isUnreachable ||
693 (isUnreachable && (BBToCheck.getFirstNonPHIOrDbg() != TI));
694 };
695
696 SmallVector<int, 4> ExitCaseIndices;
697 for (auto Case : SI.cases())
698 if (IsTriviallyUnswitchableExitBlock(*Case.getCaseSuccessor()))
699 ExitCaseIndices.push_back(Case.getCaseIndex());
700 BasicBlock *DefaultExitBB = nullptr;
701 SwitchInstProfUpdateWrapper::CaseWeightOpt DefaultCaseWeight =
702 SwitchInstProfUpdateWrapper::getSuccessorWeight(SI, 0);
703 if (IsTriviallyUnswitchableExitBlock(*SI.getDefaultDest())) {
704 DefaultExitBB = SI.getDefaultDest();
705 } else if (ExitCaseIndices.empty())
706 return false;
707
708 LLVM_DEBUG(dbgs() << " unswitching trivial switch...\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " unswitching trivial switch...\n"
; } } while (false)
;
709
710 if (MSSAU && VerifyMemorySSA)
711 MSSAU->getMemorySSA()->verifyMemorySSA();
712
713 // We may need to invalidate SCEVs for the outermost loop reached by any of
714 // the exits.
715 Loop *OuterL = &L;
716
717 if (DefaultExitBB) {
718 // Clear out the default destination temporarily to allow accurate
719 // predecessor lists to be examined below.
720 SI.setDefaultDest(nullptr);
721 // Check the loop containing this exit.
722 Loop *ExitL = LI.getLoopFor(DefaultExitBB);
723 if (!ExitL || ExitL->contains(OuterL))
724 OuterL = ExitL;
725 }
726
727 // Store the exit cases into a separate data structure and remove them from
728 // the switch.
729 SmallVector<std::tuple<ConstantInt *, BasicBlock *,
730 SwitchInstProfUpdateWrapper::CaseWeightOpt>,
731 4> ExitCases;
732 ExitCases.reserve(ExitCaseIndices.size());
733 SwitchInstProfUpdateWrapper SIW(SI);
734 // We walk the case indices backwards so that we remove the last case first
735 // and don't disrupt the earlier indices.
736 for (unsigned Index : reverse(ExitCaseIndices)) {
737 auto CaseI = SI.case_begin() + Index;
738 // Compute the outer loop from this exit.
739 Loop *ExitL = LI.getLoopFor(CaseI->getCaseSuccessor());
740 if (!ExitL || ExitL->contains(OuterL))
741 OuterL = ExitL;
742 // Save the value of this case.
743 auto W = SIW.getSuccessorWeight(CaseI->getSuccessorIndex());
744 ExitCases.emplace_back(CaseI->getCaseValue(), CaseI->getCaseSuccessor(), W);
745 // Delete the unswitched cases.
746 SIW.removeCase(CaseI);
747 }
748
749 if (SE) {
750 if (OuterL)
751 SE->forgetLoop(OuterL);
752 else
753 SE->forgetTopmostLoop(&L);
754 }
755
756 // Check if after this all of the remaining cases point at the same
757 // successor.
758 BasicBlock *CommonSuccBB = nullptr;
759 if (SI.getNumCases() > 0 &&
760 all_of(drop_begin(SI.cases()), [&SI](const SwitchInst::CaseHandle &Case) {
761 return Case.getCaseSuccessor() == SI.case_begin()->getCaseSuccessor();
762 }))
763 CommonSuccBB = SI.case_begin()->getCaseSuccessor();
764 if (!DefaultExitBB) {
765 // If we're not unswitching the default, we need it to match any cases to
766 // have a common successor or if we have no cases it is the common
767 // successor.
768 if (SI.getNumCases() == 0)
769 CommonSuccBB = SI.getDefaultDest();
770 else if (SI.getDefaultDest() != CommonSuccBB)
771 CommonSuccBB = nullptr;
772 }
773
774 // Split the preheader, so that we know that there is a safe place to insert
775 // the switch.
776 BasicBlock *OldPH = L.getLoopPreheader();
777 BasicBlock *NewPH = SplitEdge(OldPH, L.getHeader(), &DT, &LI, MSSAU);
778 OldPH->getTerminator()->eraseFromParent();
779
780 // Now add the unswitched switch.
781 auto *NewSI = SwitchInst::Create(LoopCond, NewPH, ExitCases.size(), OldPH);
782 SwitchInstProfUpdateWrapper NewSIW(*NewSI);
783
784 // Rewrite the IR for the unswitched basic blocks. This requires two steps.
785 // First, we split any exit blocks with remaining in-loop predecessors. Then
786 // we update the PHIs in one of two ways depending on if there was a split.
787 // We walk in reverse so that we split in the same order as the cases
788 // appeared. This is purely for convenience of reading the resulting IR, but
789 // it doesn't cost anything really.
790 SmallPtrSet<BasicBlock *, 2> UnswitchedExitBBs;
791 SmallDenseMap<BasicBlock *, BasicBlock *, 2> SplitExitBBMap;
792 // Handle the default exit if necessary.
793 // FIXME: It'd be great if we could merge this with the loop below but LLVM's
794 // ranges aren't quite powerful enough yet.
795 if (DefaultExitBB) {
796 if (pred_empty(DefaultExitBB)) {
797 UnswitchedExitBBs.insert(DefaultExitBB);
798 rewritePHINodesForUnswitchedExitBlock(*DefaultExitBB, *ParentBB, *OldPH);
799 } else {
800 auto *SplitBB =
801 SplitBlock(DefaultExitBB, &DefaultExitBB->front(), &DT, &LI, MSSAU);
802 rewritePHINodesForExitAndUnswitchedBlocks(*DefaultExitBB, *SplitBB,
803 *ParentBB, *OldPH,
804 /*FullUnswitch*/ true);
805 DefaultExitBB = SplitExitBBMap[DefaultExitBB] = SplitBB;
806 }
807 }
808 // Note that we must use a reference in the for loop so that we update the
809 // container.
810 for (auto &ExitCase : reverse(ExitCases)) {
811 // Grab a reference to the exit block in the pair so that we can update it.
812 BasicBlock *ExitBB = std::get<1>(ExitCase);
813
814 // If this case is the last edge into the exit block, we can simply reuse it
815 // as it will no longer be a loop exit. No mapping necessary.
816 if (pred_empty(ExitBB)) {
817 // Only rewrite once.
818 if (UnswitchedExitBBs.insert(ExitBB).second)
819 rewritePHINodesForUnswitchedExitBlock(*ExitBB, *ParentBB, *OldPH);
820 continue;
821 }
822
823 // Otherwise we need to split the exit block so that we retain an exit
824 // block from the loop and a target for the unswitched condition.
825 BasicBlock *&SplitExitBB = SplitExitBBMap[ExitBB];
826 if (!SplitExitBB) {
827 // If this is the first time we see this, do the split and remember it.
828 SplitExitBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI, MSSAU);
829 rewritePHINodesForExitAndUnswitchedBlocks(*ExitBB, *SplitExitBB,
830 *ParentBB, *OldPH,
831 /*FullUnswitch*/ true);
832 }
833 // Update the case pair to point to the split block.
834 std::get<1>(ExitCase) = SplitExitBB;
835 }
836
837 // Now add the unswitched cases. We do this in reverse order as we built them
838 // in reverse order.
839 for (auto &ExitCase : reverse(ExitCases)) {
840 ConstantInt *CaseVal = std::get<0>(ExitCase);
841 BasicBlock *UnswitchedBB = std::get<1>(ExitCase);
842
843 NewSIW.addCase(CaseVal, UnswitchedBB, std::get<2>(ExitCase));
844 }
845
846 // If the default was unswitched, re-point it and add explicit cases for
847 // entering the loop.
848 if (DefaultExitBB) {
849 NewSIW->setDefaultDest(DefaultExitBB);
850 NewSIW.setSuccessorWeight(0, DefaultCaseWeight);
851
852 // We removed all the exit cases, so we just copy the cases to the
853 // unswitched switch.
854 for (const auto &Case : SI.cases())
855 NewSIW.addCase(Case.getCaseValue(), NewPH,
856 SIW.getSuccessorWeight(Case.getSuccessorIndex()));
857 } else if (DefaultCaseWeight) {
858 // We have to set branch weight of the default case.
859 uint64_t SW = *DefaultCaseWeight;
860 for (const auto &Case : SI.cases()) {
861 auto W = SIW.getSuccessorWeight(Case.getSuccessorIndex());
862 assert(W &&(static_cast <bool> (W && "case weight must be defined as default case weight is defined"
) ? void (0) : __assert_fail ("W && \"case weight must be defined as default case weight is defined\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 863, __extension__
__PRETTY_FUNCTION__))
863 "case weight must be defined as default case weight is defined")(static_cast <bool> (W && "case weight must be defined as default case weight is defined"
) ? void (0) : __assert_fail ("W && \"case weight must be defined as default case weight is defined\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 863, __extension__
__PRETTY_FUNCTION__))
;
864 SW += *W;
865 }
866 NewSIW.setSuccessorWeight(0, SW);
867 }
868
869 // If we ended up with a common successor for every path through the switch
870 // after unswitching, rewrite it to an unconditional branch to make it easy
871 // to recognize. Otherwise we potentially have to recognize the default case
872 // pointing at unreachable and other complexity.
873 if (CommonSuccBB) {
874 BasicBlock *BB = SI.getParent();
875 // We may have had multiple edges to this common successor block, so remove
876 // them as predecessors. We skip the first one, either the default or the
877 // actual first case.
878 bool SkippedFirst = DefaultExitBB == nullptr;
879 for (auto Case : SI.cases()) {
880 assert(Case.getCaseSuccessor() == CommonSuccBB &&(static_cast <bool> (Case.getCaseSuccessor() == CommonSuccBB
&& "Non-common successor!") ? void (0) : __assert_fail
("Case.getCaseSuccessor() == CommonSuccBB && \"Non-common successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 881, __extension__
__PRETTY_FUNCTION__))
881 "Non-common successor!")(static_cast <bool> (Case.getCaseSuccessor() == CommonSuccBB
&& "Non-common successor!") ? void (0) : __assert_fail
("Case.getCaseSuccessor() == CommonSuccBB && \"Non-common successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 881, __extension__
__PRETTY_FUNCTION__))
;
882 (void)Case;
883 if (!SkippedFirst) {
884 SkippedFirst = true;
885 continue;
886 }
887 CommonSuccBB->removePredecessor(BB,
888 /*KeepOneInputPHIs*/ true);
889 }
890 // Now nuke the switch and replace it with a direct branch.
891 SIW.eraseFromParent();
892 BranchInst::Create(CommonSuccBB, BB);
893 } else if (DefaultExitBB) {
894 assert(SI.getNumCases() > 0 &&(static_cast <bool> (SI.getNumCases() > 0 &&
"If we had no cases we'd have a common successor!") ? void (
0) : __assert_fail ("SI.getNumCases() > 0 && \"If we had no cases we'd have a common successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 895, __extension__
__PRETTY_FUNCTION__))
895 "If we had no cases we'd have a common successor!")(static_cast <bool> (SI.getNumCases() > 0 &&
"If we had no cases we'd have a common successor!") ? void (
0) : __assert_fail ("SI.getNumCases() > 0 && \"If we had no cases we'd have a common successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 895, __extension__
__PRETTY_FUNCTION__))
;
896 // Move the last case to the default successor. This is valid as if the
897 // default got unswitched it cannot be reached. This has the advantage of
898 // being simple and keeping the number of edges from this switch to
899 // successors the same, and avoiding any PHI update complexity.
900 auto LastCaseI = std::prev(SI.case_end());
901
902 SI.setDefaultDest(LastCaseI->getCaseSuccessor());
903 SIW.setSuccessorWeight(
904 0, SIW.getSuccessorWeight(LastCaseI->getSuccessorIndex()));
905 SIW.removeCase(LastCaseI);
906 }
907
908 // Walk the unswitched exit blocks and the unswitched split blocks and update
909 // the dominator tree based on the CFG edits. While we are walking unordered
910 // containers here, the API for applyUpdates takes an unordered list of
911 // updates and requires them to not contain duplicates.
912 SmallVector<DominatorTree::UpdateType, 4> DTUpdates;
913 for (auto *UnswitchedExitBB : UnswitchedExitBBs) {
914 DTUpdates.push_back({DT.Delete, ParentBB, UnswitchedExitBB});
915 DTUpdates.push_back({DT.Insert, OldPH, UnswitchedExitBB});
916 }
917 for (auto SplitUnswitchedPair : SplitExitBBMap) {
918 DTUpdates.push_back({DT.Delete, ParentBB, SplitUnswitchedPair.first});
919 DTUpdates.push_back({DT.Insert, OldPH, SplitUnswitchedPair.second});
920 }
921
922 if (MSSAU) {
923 MSSAU->applyUpdates(DTUpdates, DT, /*UpdateDT=*/true);
924 if (VerifyMemorySSA)
925 MSSAU->getMemorySSA()->verifyMemorySSA();
926 } else {
927 DT.applyUpdates(DTUpdates);
928 }
929
930 assert(DT.verify(DominatorTree::VerificationLevel::Fast))(static_cast <bool> (DT.verify(DominatorTree::VerificationLevel
::Fast)) ? void (0) : __assert_fail ("DT.verify(DominatorTree::VerificationLevel::Fast)"
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 930, __extension__
__PRETTY_FUNCTION__))
;
931
932 // We may have changed the nesting relationship for this loop so hoist it to
933 // its correct parent if needed.
934 hoistLoopToNewParent(L, *NewPH, DT, LI, MSSAU, SE);
935
936 if (MSSAU && VerifyMemorySSA)
937 MSSAU->getMemorySSA()->verifyMemorySSA();
938
939 ++NumTrivial;
940 ++NumSwitches;
941 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)
;
942 return true;
943}
944
945/// This routine scans the loop to find a branch or switch which occurs before
946/// any side effects occur. These can potentially be unswitched without
947/// duplicating the loop. If a branch or switch is successfully unswitched the
948/// scanning continues to see if subsequent branches or switches have become
949/// trivial. Once all trivial candidates have been unswitched, this routine
950/// returns.
951///
952/// The return value indicates whether anything was unswitched (and therefore
953/// changed).
954///
955/// If `SE` is not null, it will be updated based on the potential loop SCEVs
956/// invalidated by this.
957static bool unswitchAllTrivialConditions(Loop &L, DominatorTree &DT,
958 LoopInfo &LI, ScalarEvolution *SE,
959 MemorySSAUpdater *MSSAU) {
960 bool Changed = false;
961
962 // If loop header has only one reachable successor we should keep looking for
963 // trivial condition candidates in the successor as well. An alternative is
964 // to constant fold conditions and merge successors into loop header (then we
965 // only need to check header's terminator). The reason for not doing this in
966 // LoopUnswitch pass is that it could potentially break LoopPassManager's
967 // invariants. Folding dead branches could either eliminate the current loop
968 // or make other loops unreachable. LCSSA form might also not be preserved
969 // after deleting branches. The following code keeps traversing loop header's
970 // successors until it finds the trivial condition candidate (condition that
971 // is not a constant). Since unswitching generates branches with constant
972 // conditions, this scenario could be very common in practice.
973 BasicBlock *CurrentBB = L.getHeader();
974 SmallPtrSet<BasicBlock *, 8> Visited;
975 Visited.insert(CurrentBB);
976 do {
977 // Check if there are any side-effecting instructions (e.g. stores, calls,
978 // volatile loads) in the part of the loop that the code *would* execute
979 // without unswitching.
980 if (MSSAU) // Possible early exit with MSSA
981 if (auto *Defs = MSSAU->getMemorySSA()->getBlockDefs(CurrentBB))
982 if (!isa<MemoryPhi>(*Defs->begin()) || (++Defs->begin() != Defs->end()))
983 return Changed;
984 if (llvm::any_of(*CurrentBB,
985 [](Instruction &I) { return I.mayHaveSideEffects(); }))
986 return Changed;
987
988 Instruction *CurrentTerm = CurrentBB->getTerminator();
989
990 if (auto *SI = dyn_cast<SwitchInst>(CurrentTerm)) {
991 // Don't bother trying to unswitch past a switch with a constant
992 // condition. This should be removed prior to running this pass by
993 // simplifycfg.
994 if (isa<Constant>(SI->getCondition()))
995 return Changed;
996
997 if (!unswitchTrivialSwitch(L, *SI, DT, LI, SE, MSSAU))
998 // Couldn't unswitch this one so we're done.
999 return Changed;
1000
1001 // Mark that we managed to unswitch something.
1002 Changed = true;
1003
1004 // If unswitching turned the terminator into an unconditional branch then
1005 // we can continue. The unswitching logic specifically works to fold any
1006 // cases it can into an unconditional branch to make it easier to
1007 // recognize here.
1008 auto *BI = dyn_cast<BranchInst>(CurrentBB->getTerminator());
1009 if (!BI || BI->isConditional())
1010 return Changed;
1011
1012 CurrentBB = BI->getSuccessor(0);
1013 continue;
1014 }
1015
1016 auto *BI = dyn_cast<BranchInst>(CurrentTerm);
1017 if (!BI)
1018 // We do not understand other terminator instructions.
1019 return Changed;
1020
1021 // Don't bother trying to unswitch past an unconditional branch or a branch
1022 // with a constant value. These should be removed by simplifycfg prior to
1023 // running this pass.
1024 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1025 return Changed;
1026
1027 // Found a trivial condition candidate: non-foldable conditional branch. If
1028 // we fail to unswitch this, we can't do anything else that is trivial.
1029 if (!unswitchTrivialBranch(L, *BI, DT, LI, SE, MSSAU))
1030 return Changed;
1031
1032 // Mark that we managed to unswitch something.
1033 Changed = true;
1034
1035 // If we only unswitched some of the conditions feeding the branch, we won't
1036 // have collapsed it to a single successor.
1037 BI = cast<BranchInst>(CurrentBB->getTerminator());
1038 if (BI->isConditional())
1039 return Changed;
1040
1041 // Follow the newly unconditional branch into its successor.
1042 CurrentBB = BI->getSuccessor(0);
1043
1044 // When continuing, if we exit the loop or reach a previous visited block,
1045 // then we can not reach any trivial condition candidates (unfoldable
1046 // branch instructions or switch instructions) and no unswitch can happen.
1047 } while (L.contains(CurrentBB) && Visited.insert(CurrentBB).second);
1048
1049 return Changed;
1050}
1051
1052/// Build the cloned blocks for an unswitched copy of the given loop.
1053///
1054/// The cloned blocks are inserted before the loop preheader (`LoopPH`) and
1055/// after the split block (`SplitBB`) that will be used to select between the
1056/// cloned and original loop.
1057///
1058/// This routine handles cloning all of the necessary loop blocks and exit
1059/// blocks including rewriting their instructions and the relevant PHI nodes.
1060/// Any loop blocks or exit blocks which are dominated by a different successor
1061/// than the one for this clone of the loop blocks can be trivially skipped. We
1062/// use the `DominatingSucc` map to determine whether a block satisfies that
1063/// property with a simple map lookup.
1064///
1065/// It also correctly creates the unconditional branch in the cloned
1066/// unswitched parent block to only point at the unswitched successor.
1067///
1068/// This does not handle most of the necessary updates to `LoopInfo`. Only exit
1069/// block splitting is correctly reflected in `LoopInfo`, essentially all of
1070/// the cloned blocks (and their loops) are left without full `LoopInfo`
1071/// updates. This also doesn't fully update `DominatorTree`. It adds the cloned
1072/// blocks to them but doesn't create the cloned `DominatorTree` structure and
1073/// instead the caller must recompute an accurate DT. It *does* correctly
1074/// update the `AssumptionCache` provided in `AC`.
1075static BasicBlock *buildClonedLoopBlocks(
1076 Loop &L, BasicBlock *LoopPH, BasicBlock *SplitBB,
1077 ArrayRef<BasicBlock *> ExitBlocks, BasicBlock *ParentBB,
1078 BasicBlock *UnswitchedSuccBB, BasicBlock *ContinueSuccBB,
1079 const SmallDenseMap<BasicBlock *, BasicBlock *, 16> &DominatingSucc,
1080 ValueToValueMapTy &VMap,
1081 SmallVectorImpl<DominatorTree::UpdateType> &DTUpdates, AssumptionCache &AC,
1082 DominatorTree &DT, LoopInfo &LI, MemorySSAUpdater *MSSAU) {
1083 SmallVector<BasicBlock *, 4> NewBlocks;
1084 NewBlocks.reserve(L.getNumBlocks() + ExitBlocks.size());
1085
1086 // We will need to clone a bunch of blocks, wrap up the clone operation in
1087 // a helper.
1088 auto CloneBlock = [&](BasicBlock *OldBB) {
1089 // Clone the basic block and insert it before the new preheader.
1090 BasicBlock *NewBB = CloneBasicBlock(OldBB, VMap, ".us", OldBB->getParent());
1091 NewBB->moveBefore(LoopPH);
1092
1093 // Record this block and the mapping.
1094 NewBlocks.push_back(NewBB);
1095 VMap[OldBB] = NewBB;
1096
1097 return NewBB;
1098 };
1099
1100 // We skip cloning blocks when they have a dominating succ that is not the
1101 // succ we are cloning for.
1102 auto SkipBlock = [&](BasicBlock *BB) {
1103 auto It = DominatingSucc.find(BB);
1104 return It != DominatingSucc.end() && It->second != UnswitchedSuccBB;
1105 };
1106
1107 // First, clone the preheader.
1108 auto *ClonedPH = CloneBlock(LoopPH);
1109
1110 // Then clone all the loop blocks, skipping the ones that aren't necessary.
1111 for (auto *LoopBB : L.blocks())
1112 if (!SkipBlock(LoopBB))
1113 CloneBlock(LoopBB);
1114
1115 // Split all the loop exit edges so that when we clone the exit blocks, if
1116 // any of the exit blocks are *also* a preheader for some other loop, we
1117 // don't create multiple predecessors entering the loop header.
1118 for (auto *ExitBB : ExitBlocks) {
1119 if (SkipBlock(ExitBB))
1120 continue;
1121
1122 // When we are going to clone an exit, we don't need to clone all the
1123 // instructions in the exit block and we want to ensure we have an easy
1124 // place to merge the CFG, so split the exit first. This is always safe to
1125 // do because there cannot be any non-loop predecessors of a loop exit in
1126 // loop simplified form.
1127 auto *MergeBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI, MSSAU);
1128
1129 // Rearrange the names to make it easier to write test cases by having the
1130 // exit block carry the suffix rather than the merge block carrying the
1131 // suffix.
1132 MergeBB->takeName(ExitBB);
1133 ExitBB->setName(Twine(MergeBB->getName()) + ".split");
1134
1135 // Now clone the original exit block.
1136 auto *ClonedExitBB = CloneBlock(ExitBB);
1137 assert(ClonedExitBB->getTerminator()->getNumSuccessors() == 1 &&(static_cast <bool> (ClonedExitBB->getTerminator()->
getNumSuccessors() == 1 && "Exit block should have been split to have one successor!"
) ? void (0) : __assert_fail ("ClonedExitBB->getTerminator()->getNumSuccessors() == 1 && \"Exit block should have been split to have one successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1138, __extension__
__PRETTY_FUNCTION__))
1138 "Exit block should have been split to have one successor!")(static_cast <bool> (ClonedExitBB->getTerminator()->
getNumSuccessors() == 1 && "Exit block should have been split to have one successor!"
) ? void (0) : __assert_fail ("ClonedExitBB->getTerminator()->getNumSuccessors() == 1 && \"Exit block should have been split to have one successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1138, __extension__
__PRETTY_FUNCTION__))
;
1139 assert(ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB &&(static_cast <bool> (ClonedExitBB->getTerminator()->
getSuccessor(0) == MergeBB && "Cloned exit block has the wrong successor!"
) ? void (0) : __assert_fail ("ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB && \"Cloned exit block has the wrong successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1140, __extension__
__PRETTY_FUNCTION__))
1140 "Cloned exit block has the wrong successor!")(static_cast <bool> (ClonedExitBB->getTerminator()->
getSuccessor(0) == MergeBB && "Cloned exit block has the wrong successor!"
) ? void (0) : __assert_fail ("ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB && \"Cloned exit block has the wrong successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1140, __extension__
__PRETTY_FUNCTION__))
;
1141
1142 // Remap any cloned instructions and create a merge phi node for them.
1143 for (auto ZippedInsts : llvm::zip_first(
1144 llvm::make_range(ExitBB->begin(), std::prev(ExitBB->end())),
1145 llvm::make_range(ClonedExitBB->begin(),
1146 std::prev(ClonedExitBB->end())))) {
1147 Instruction &I = std::get<0>(ZippedInsts);
1148 Instruction &ClonedI = std::get<1>(ZippedInsts);
1149
1150 // The only instructions in the exit block should be PHI nodes and
1151 // potentially a landing pad.
1152 assert((static_cast <bool> ((isa<PHINode>(I) || isa<LandingPadInst
>(I) || isa<CatchPadInst>(I)) && "Bad instruction in exit block!"
) ? void (0) : __assert_fail ("(isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) && \"Bad instruction in exit block!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1154, __extension__
__PRETTY_FUNCTION__))
1153 (isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) &&(static_cast <bool> ((isa<PHINode>(I) || isa<LandingPadInst
>(I) || isa<CatchPadInst>(I)) && "Bad instruction in exit block!"
) ? void (0) : __assert_fail ("(isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) && \"Bad instruction in exit block!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1154, __extension__
__PRETTY_FUNCTION__))
1154 "Bad instruction in exit block!")(static_cast <bool> ((isa<PHINode>(I) || isa<LandingPadInst
>(I) || isa<CatchPadInst>(I)) && "Bad instruction in exit block!"
) ? void (0) : __assert_fail ("(isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) && \"Bad instruction in exit block!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1154, __extension__
__PRETTY_FUNCTION__))
;
1155 // We should have a value map between the instruction and its clone.
1156 assert(VMap.lookup(&I) == &ClonedI && "Mismatch in the value map!")(static_cast <bool> (VMap.lookup(&I) == &ClonedI
&& "Mismatch in the value map!") ? void (0) : __assert_fail
("VMap.lookup(&I) == &ClonedI && \"Mismatch in the value map!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1156, __extension__
__PRETTY_FUNCTION__))
;
1157
1158 auto *MergePN =
1159 PHINode::Create(I.getType(), /*NumReservedValues*/ 2, ".us-phi",
1160 &*MergeBB->getFirstInsertionPt());
1161 I.replaceAllUsesWith(MergePN);
1162 MergePN->addIncoming(&I, ExitBB);
1163 MergePN->addIncoming(&ClonedI, ClonedExitBB);
1164 }
1165 }
1166
1167 // Rewrite the instructions in the cloned blocks to refer to the instructions
1168 // in the cloned blocks. We have to do this as a second pass so that we have
1169 // everything available. Also, we have inserted new instructions which may
1170 // include assume intrinsics, so we update the assumption cache while
1171 // processing this.
1172 for (auto *ClonedBB : NewBlocks)
1173 for (Instruction &I : *ClonedBB) {
1174 RemapInstruction(&I, VMap,
1175 RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
1176 if (auto *II = dyn_cast<AssumeInst>(&I))
1177 AC.registerAssumption(II);
1178 }
1179
1180 // Update any PHI nodes in the cloned successors of the skipped blocks to not
1181 // have spurious incoming values.
1182 for (auto *LoopBB : L.blocks())
1183 if (SkipBlock(LoopBB))
1184 for (auto *SuccBB : successors(LoopBB))
1185 if (auto *ClonedSuccBB = cast_or_null<BasicBlock>(VMap.lookup(SuccBB)))
1186 for (PHINode &PN : ClonedSuccBB->phis())
1187 PN.removeIncomingValue(LoopBB, /*DeletePHIIfEmpty*/ false);
1188
1189 // Remove the cloned parent as a predecessor of any successor we ended up
1190 // cloning other than the unswitched one.
1191 auto *ClonedParentBB = cast<BasicBlock>(VMap.lookup(ParentBB));
1192 for (auto *SuccBB : successors(ParentBB)) {
1193 if (SuccBB == UnswitchedSuccBB)
1194 continue;
1195
1196 auto *ClonedSuccBB = cast_or_null<BasicBlock>(VMap.lookup(SuccBB));
1197 if (!ClonedSuccBB)
1198 continue;
1199
1200 ClonedSuccBB->removePredecessor(ClonedParentBB,
1201 /*KeepOneInputPHIs*/ true);
1202 }
1203
1204 // Replace the cloned branch with an unconditional branch to the cloned
1205 // unswitched successor.
1206 auto *ClonedSuccBB = cast<BasicBlock>(VMap.lookup(UnswitchedSuccBB));
1207 Instruction *ClonedTerminator = ClonedParentBB->getTerminator();
1208 // Trivial Simplification. If Terminator is a conditional branch and
1209 // condition becomes dead - erase it.
1210 Value *ClonedConditionToErase = nullptr;
1211 if (auto *BI = dyn_cast<BranchInst>(ClonedTerminator))
1212 ClonedConditionToErase = BI->getCondition();
1213 else if (auto *SI = dyn_cast<SwitchInst>(ClonedTerminator))
1214 ClonedConditionToErase = SI->getCondition();
1215
1216 ClonedTerminator->eraseFromParent();
1217 BranchInst::Create(ClonedSuccBB, ClonedParentBB);
1218
1219 if (ClonedConditionToErase)
1220 RecursivelyDeleteTriviallyDeadInstructions(ClonedConditionToErase, nullptr,
1221 MSSAU);
1222
1223 // If there are duplicate entries in the PHI nodes because of multiple edges
1224 // to the unswitched successor, we need to nuke all but one as we replaced it
1225 // with a direct branch.
1226 for (PHINode &PN : ClonedSuccBB->phis()) {
1227 bool Found = false;
1228 // Loop over the incoming operands backwards so we can easily delete as we
1229 // go without invalidating the index.
1230 for (int i = PN.getNumOperands() - 1; i >= 0; --i) {
1231 if (PN.getIncomingBlock(i) != ClonedParentBB)
1232 continue;
1233 if (!Found) {
1234 Found = true;
1235 continue;
1236 }
1237 PN.removeIncomingValue(i, /*DeletePHIIfEmpty*/ false);
1238 }
1239 }
1240
1241 // Record the domtree updates for the new blocks.
1242 SmallPtrSet<BasicBlock *, 4> SuccSet;
1243 for (auto *ClonedBB : NewBlocks) {
1244 for (auto *SuccBB : successors(ClonedBB))
1245 if (SuccSet.insert(SuccBB).second)
1246 DTUpdates.push_back({DominatorTree::Insert, ClonedBB, SuccBB});
1247 SuccSet.clear();
1248 }
1249
1250 return ClonedPH;
1251}
1252
1253/// Recursively clone the specified loop and all of its children.
1254///
1255/// The target parent loop for the clone should be provided, or can be null if
1256/// the clone is a top-level loop. While cloning, all the blocks are mapped
1257/// with the provided value map. The entire original loop must be present in
1258/// the value map. The cloned loop is returned.
1259static Loop *cloneLoopNest(Loop &OrigRootL, Loop *RootParentL,
1260 const ValueToValueMapTy &VMap, LoopInfo &LI) {
1261 auto AddClonedBlocksToLoop = [&](Loop &OrigL, Loop &ClonedL) {
1262 assert(ClonedL.getBlocks().empty() && "Must start with an empty loop!")(static_cast <bool> (ClonedL.getBlocks().empty() &&
"Must start with an empty loop!") ? void (0) : __assert_fail
("ClonedL.getBlocks().empty() && \"Must start with an empty loop!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1262, __extension__
__PRETTY_FUNCTION__))
;
1263 ClonedL.reserveBlocks(OrigL.getNumBlocks());
1264 for (auto *BB : OrigL.blocks()) {
1265 auto *ClonedBB = cast<BasicBlock>(VMap.lookup(BB));
1266 ClonedL.addBlockEntry(ClonedBB);
1267 if (LI.getLoopFor(BB) == &OrigL)
1268 LI.changeLoopFor(ClonedBB, &ClonedL);
1269 }
1270 };
1271
1272 // We specially handle the first loop because it may get cloned into
1273 // a different parent and because we most commonly are cloning leaf loops.
1274 Loop *ClonedRootL = LI.AllocateLoop();
1275 if (RootParentL)
1276 RootParentL->addChildLoop(ClonedRootL);
1277 else
1278 LI.addTopLevelLoop(ClonedRootL);
1279 AddClonedBlocksToLoop(OrigRootL, *ClonedRootL);
1280
1281 if (OrigRootL.isInnermost())
1282 return ClonedRootL;
1283
1284 // If we have a nest, we can quickly clone the entire loop nest using an
1285 // iterative approach because it is a tree. We keep the cloned parent in the
1286 // data structure to avoid repeatedly querying through a map to find it.
1287 SmallVector<std::pair<Loop *, Loop *>, 16> LoopsToClone;
1288 // Build up the loops to clone in reverse order as we'll clone them from the
1289 // back.
1290 for (Loop *ChildL : llvm::reverse(OrigRootL))
1291 LoopsToClone.push_back({ClonedRootL, ChildL});
1292 do {
1293 Loop *ClonedParentL, *L;
1294 std::tie(ClonedParentL, L) = LoopsToClone.pop_back_val();
1295 Loop *ClonedL = LI.AllocateLoop();
1296 ClonedParentL->addChildLoop(ClonedL);
1297 AddClonedBlocksToLoop(*L, *ClonedL);
1298 for (Loop *ChildL : llvm::reverse(*L))
1299 LoopsToClone.push_back({ClonedL, ChildL});
1300 } while (!LoopsToClone.empty());
1301
1302 return ClonedRootL;
1303}
1304
1305/// Build the cloned loops of an original loop from unswitching.
1306///
1307/// Because unswitching simplifies the CFG of the loop, this isn't a trivial
1308/// operation. We need to re-verify that there even is a loop (as the backedge
1309/// may not have been cloned), and even if there are remaining backedges the
1310/// backedge set may be different. However, we know that each child loop is
1311/// undisturbed, we only need to find where to place each child loop within
1312/// either any parent loop or within a cloned version of the original loop.
1313///
1314/// Because child loops may end up cloned outside of any cloned version of the
1315/// original loop, multiple cloned sibling loops may be created. All of them
1316/// are returned so that the newly introduced loop nest roots can be
1317/// identified.
1318static void buildClonedLoops(Loop &OrigL, ArrayRef<BasicBlock *> ExitBlocks,
1319 const ValueToValueMapTy &VMap, LoopInfo &LI,
1320 SmallVectorImpl<Loop *> &NonChildClonedLoops) {
1321 Loop *ClonedL = nullptr;
1322
1323 auto *OrigPH = OrigL.getLoopPreheader();
1324 auto *OrigHeader = OrigL.getHeader();
1325
1326 auto *ClonedPH = cast<BasicBlock>(VMap.lookup(OrigPH));
1327 auto *ClonedHeader = cast<BasicBlock>(VMap.lookup(OrigHeader));
1328
1329 // We need to know the loops of the cloned exit blocks to even compute the
1330 // accurate parent loop. If we only clone exits to some parent of the
1331 // original parent, we want to clone into that outer loop. We also keep track
1332 // of the loops that our cloned exit blocks participate in.
1333 Loop *ParentL = nullptr;
1334 SmallVector<BasicBlock *, 4> ClonedExitsInLoops;
1335 SmallDenseMap<BasicBlock *, Loop *, 16> ExitLoopMap;
1336 ClonedExitsInLoops.reserve(ExitBlocks.size());
1337 for (auto *ExitBB : ExitBlocks)
1338 if (auto *ClonedExitBB = cast_or_null<BasicBlock>(VMap.lookup(ExitBB)))
1339 if (Loop *ExitL = LI.getLoopFor(ExitBB)) {
1340 ExitLoopMap[ClonedExitBB] = ExitL;
1341 ClonedExitsInLoops.push_back(ClonedExitBB);
1342 if (!ParentL || (ParentL != ExitL && ParentL->contains(ExitL)))
1343 ParentL = ExitL;
1344 }
1345 assert((!ParentL || ParentL == OrigL.getParentLoop() ||(static_cast <bool> ((!ParentL || ParentL == OrigL.getParentLoop
() || ParentL->contains(OrigL.getParentLoop())) &&
"The computed parent loop should always contain (or be) the parent of "
"the original loop.") ? 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.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1348, __extension__
__PRETTY_FUNCTION__))
1346 ParentL->contains(OrigL.getParentLoop())) &&(static_cast <bool> ((!ParentL || ParentL == OrigL.getParentLoop
() || ParentL->contains(OrigL.getParentLoop())) &&
"The computed parent loop should always contain (or be) the parent of "
"the original loop.") ? 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.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1348, __extension__
__PRETTY_FUNCTION__))
1347 "The computed parent loop should always contain (or be) the parent of "(static_cast <bool> ((!ParentL || ParentL == OrigL.getParentLoop
() || ParentL->contains(OrigL.getParentLoop())) &&
"The computed parent loop should always contain (or be) the parent of "
"the original loop.") ? 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.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1348, __extension__
__PRETTY_FUNCTION__))
1348 "the original loop.")(static_cast <bool> ((!ParentL || ParentL == OrigL.getParentLoop
() || ParentL->contains(OrigL.getParentLoop())) &&
"The computed parent loop should always contain (or be) the parent of "
"the original loop.") ? 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.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1348, __extension__
__PRETTY_FUNCTION__))
;
1349
1350 // We build the set of blocks dominated by the cloned header from the set of
1351 // cloned blocks out of the original loop. While not all of these will
1352 // necessarily be in the cloned loop, it is enough to establish that they
1353 // aren't in unreachable cycles, etc.
1354 SmallSetVector<BasicBlock *, 16> ClonedLoopBlocks;
1355 for (auto *BB : OrigL.blocks())
1356 if (auto *ClonedBB = cast_or_null<BasicBlock>(VMap.lookup(BB)))
1357 ClonedLoopBlocks.insert(ClonedBB);
1358
1359 // Rebuild the set of blocks that will end up in the cloned loop. We may have
1360 // skipped cloning some region of this loop which can in turn skip some of
1361 // the backedges so we have to rebuild the blocks in the loop based on the
1362 // backedges that remain after cloning.
1363 SmallVector<BasicBlock *, 16> Worklist;
1364 SmallPtrSet<BasicBlock *, 16> BlocksInClonedLoop;
1365 for (auto *Pred : predecessors(ClonedHeader)) {
1366 // The only possible non-loop header predecessor is the preheader because
1367 // we know we cloned the loop in simplified form.
1368 if (Pred == ClonedPH)
1369 continue;
1370
1371 // Because the loop was in simplified form, the only non-loop predecessor
1372 // should be the preheader.
1373 assert(ClonedLoopBlocks.count(Pred) && "Found a predecessor of the loop "(static_cast <bool> (ClonedLoopBlocks.count(Pred) &&
"Found a predecessor of the loop " "header other than the preheader "
"that is not part of the loop!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1375, __extension__
__PRETTY_FUNCTION__))
1374 "header other than the preheader "(static_cast <bool> (ClonedLoopBlocks.count(Pred) &&
"Found a predecessor of the loop " "header other than the preheader "
"that is not part of the loop!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1375, __extension__
__PRETTY_FUNCTION__))
1375 "that is not part of the loop!")(static_cast <bool> (ClonedLoopBlocks.count(Pred) &&
"Found a predecessor of the loop " "header other than the preheader "
"that is not part of the loop!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1375, __extension__
__PRETTY_FUNCTION__))
;
1376
1377 // Insert this block into the loop set and on the first visit (and if it
1378 // isn't the header we're currently walking) put it into the worklist to
1379 // recurse through.
1380 if (BlocksInClonedLoop.insert(Pred).second && Pred != ClonedHeader)
1381 Worklist.push_back(Pred);
1382 }
1383
1384 // If we had any backedges then there *is* a cloned loop. Put the header into
1385 // the loop set and then walk the worklist backwards to find all the blocks
1386 // that remain within the loop after cloning.
1387 if (!BlocksInClonedLoop.empty()) {
1388 BlocksInClonedLoop.insert(ClonedHeader);
1389
1390 while (!Worklist.empty()) {
1391 BasicBlock *BB = Worklist.pop_back_val();
1392 assert(BlocksInClonedLoop.count(BB) &&(static_cast <bool> (BlocksInClonedLoop.count(BB) &&
"Didn't put block into the loop set!") ? void (0) : __assert_fail
("BlocksInClonedLoop.count(BB) && \"Didn't put block into the loop set!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1393, __extension__
__PRETTY_FUNCTION__))
1393 "Didn't put block into the loop set!")(static_cast <bool> (BlocksInClonedLoop.count(BB) &&
"Didn't put block into the loop set!") ? void (0) : __assert_fail
("BlocksInClonedLoop.count(BB) && \"Didn't put block into the loop set!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1393, __extension__
__PRETTY_FUNCTION__))
;
1394
1395 // Insert any predecessors that are in the possible set into the cloned
1396 // set, and if the insert is successful, add them to the worklist. Note
1397 // that we filter on the blocks that are definitely reachable via the
1398 // backedge to the loop header so we may prune out dead code within the
1399 // cloned loop.
1400 for (auto *Pred : predecessors(BB))
1401 if (ClonedLoopBlocks.count(Pred) &&
1402 BlocksInClonedLoop.insert(Pred).second)
1403 Worklist.push_back(Pred);
1404 }
1405
1406 ClonedL = LI.AllocateLoop();
1407 if (ParentL) {
1408 ParentL->addBasicBlockToLoop(ClonedPH, LI);
1409 ParentL->addChildLoop(ClonedL);
1410 } else {
1411 LI.addTopLevelLoop(ClonedL);
1412 }
1413 NonChildClonedLoops.push_back(ClonedL);
1414
1415 ClonedL->reserveBlocks(BlocksInClonedLoop.size());
1416 // We don't want to just add the cloned loop blocks based on how we
1417 // discovered them. The original order of blocks was carefully built in
1418 // a way that doesn't rely on predecessor ordering. Rather than re-invent
1419 // that logic, we just re-walk the original blocks (and those of the child
1420 // loops) and filter them as we add them into the cloned loop.
1421 for (auto *BB : OrigL.blocks()) {
1422 auto *ClonedBB = cast_or_null<BasicBlock>(VMap.lookup(BB));
1423 if (!ClonedBB || !BlocksInClonedLoop.count(ClonedBB))
1424 continue;
1425
1426 // Directly add the blocks that are only in this loop.
1427 if (LI.getLoopFor(BB) == &OrigL) {
1428 ClonedL->addBasicBlockToLoop(ClonedBB, LI);
1429 continue;
1430 }
1431
1432 // We want to manually add it to this loop and parents.
1433 // Registering it with LoopInfo will happen when we clone the top
1434 // loop for this block.
1435 for (Loop *PL = ClonedL; PL; PL = PL->getParentLoop())
1436 PL->addBlockEntry(ClonedBB);
1437 }
1438
1439 // Now add each child loop whose header remains within the cloned loop. All
1440 // of the blocks within the loop must satisfy the same constraints as the
1441 // header so once we pass the header checks we can just clone the entire
1442 // child loop nest.
1443 for (Loop *ChildL : OrigL) {
1444 auto *ClonedChildHeader =
1445 cast_or_null<BasicBlock>(VMap.lookup(ChildL->getHeader()));
1446 if (!ClonedChildHeader || !BlocksInClonedLoop.count(ClonedChildHeader))
1447 continue;
1448
1449#ifndef NDEBUG
1450 // We should never have a cloned child loop header but fail to have
1451 // all of the blocks for that child loop.
1452 for (auto *ChildLoopBB : ChildL->blocks())
1453 assert(BlocksInClonedLoop.count((static_cast <bool> (BlocksInClonedLoop.count( cast<
BasicBlock>(VMap.lookup(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
"loop but not all of its blocks!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1456, __extension__
__PRETTY_FUNCTION__))
1454 cast<BasicBlock>(VMap.lookup(ChildLoopBB))) &&(static_cast <bool> (BlocksInClonedLoop.count( cast<
BasicBlock>(VMap.lookup(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
"loop but not all of its blocks!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1456, __extension__
__PRETTY_FUNCTION__))
1455 "Child cloned loop has a header within the cloned outer "(static_cast <bool> (BlocksInClonedLoop.count( cast<
BasicBlock>(VMap.lookup(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
"loop but not all of its blocks!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1456, __extension__
__PRETTY_FUNCTION__))
1456 "loop but not all of its blocks!")(static_cast <bool> (BlocksInClonedLoop.count( cast<
BasicBlock>(VMap.lookup(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
"loop but not all of its blocks!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1456, __extension__
__PRETTY_FUNCTION__))
;
1457#endif
1458
1459 cloneLoopNest(*ChildL, ClonedL, VMap, LI);
1460 }
1461 }
1462
1463 // Now that we've handled all the components of the original loop that were
1464 // cloned into a new loop, we still need to handle anything from the original
1465 // loop that wasn't in a cloned loop.
1466
1467 // Figure out what blocks are left to place within any loop nest containing
1468 // the unswitched loop. If we never formed a loop, the cloned PH is one of
1469 // them.
1470 SmallPtrSet<BasicBlock *, 16> UnloopedBlockSet;
1471 if (BlocksInClonedLoop.empty())
1472 UnloopedBlockSet.insert(ClonedPH);
1473 for (auto *ClonedBB : ClonedLoopBlocks)
1474 if (!BlocksInClonedLoop.count(ClonedBB))
1475 UnloopedBlockSet.insert(ClonedBB);
1476
1477 // Copy the cloned exits and sort them in ascending loop depth, we'll work
1478 // backwards across these to process them inside out. The order shouldn't
1479 // matter as we're just trying to build up the map from inside-out; we use
1480 // the map in a more stably ordered way below.
1481 auto OrderedClonedExitsInLoops = ClonedExitsInLoops;
1482 llvm::sort(OrderedClonedExitsInLoops, [&](BasicBlock *LHS, BasicBlock *RHS) {
1483 return ExitLoopMap.lookup(LHS)->getLoopDepth() <
1484 ExitLoopMap.lookup(RHS)->getLoopDepth();
1485 });
1486
1487 // Populate the existing ExitLoopMap with everything reachable from each
1488 // exit, starting from the inner most exit.
1489 while (!UnloopedBlockSet.empty() && !OrderedClonedExitsInLoops.empty()) {
1490 assert(Worklist.empty() && "Didn't clear worklist!")(static_cast <bool> (Worklist.empty() && "Didn't clear worklist!"
) ? void (0) : __assert_fail ("Worklist.empty() && \"Didn't clear worklist!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1490, __extension__
__PRETTY_FUNCTION__))
;
1491
1492 BasicBlock *ExitBB = OrderedClonedExitsInLoops.pop_back_val();
1493 Loop *ExitL = ExitLoopMap.lookup(ExitBB);
1494
1495 // Walk the CFG back until we hit the cloned PH adding everything reachable
1496 // and in the unlooped set to this exit block's loop.
1497 Worklist.push_back(ExitBB);
1498 do {
1499 BasicBlock *BB = Worklist.pop_back_val();
1500 // We can stop recursing at the cloned preheader (if we get there).
1501 if (BB == ClonedPH)
1502 continue;
1503
1504 for (BasicBlock *PredBB : predecessors(BB)) {
1505 // If this pred has already been moved to our set or is part of some
1506 // (inner) loop, no update needed.
1507 if (!UnloopedBlockSet.erase(PredBB)) {
1508 assert((static_cast <bool> ((BlocksInClonedLoop.count(PredBB) ||
ExitLoopMap.count(PredBB)) && "Predecessor not mapped to a loop!"
) ? void (0) : __assert_fail ("(BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) && \"Predecessor not mapped to a loop!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1510, __extension__
__PRETTY_FUNCTION__))
1509 (BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) &&(static_cast <bool> ((BlocksInClonedLoop.count(PredBB) ||
ExitLoopMap.count(PredBB)) && "Predecessor not mapped to a loop!"
) ? void (0) : __assert_fail ("(BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) && \"Predecessor not mapped to a loop!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1510, __extension__
__PRETTY_FUNCTION__))
1510 "Predecessor not mapped to a loop!")(static_cast <bool> ((BlocksInClonedLoop.count(PredBB) ||
ExitLoopMap.count(PredBB)) && "Predecessor not mapped to a loop!"
) ? void (0) : __assert_fail ("(BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) && \"Predecessor not mapped to a loop!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1510, __extension__
__PRETTY_FUNCTION__))
;
1511 continue;
1512 }
1513
1514 // We just insert into the loop set here. We'll add these blocks to the
1515 // exit loop after we build up the set in an order that doesn't rely on
1516 // predecessor order (which in turn relies on use list order).
1517 bool Inserted = ExitLoopMap.insert({PredBB, ExitL}).second;
1518 (void)Inserted;
1519 assert(Inserted && "Should only visit an unlooped block once!")(static_cast <bool> (Inserted && "Should only visit an unlooped block once!"
) ? void (0) : __assert_fail ("Inserted && \"Should only visit an unlooped block once!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1519, __extension__
__PRETTY_FUNCTION__))
;
1520
1521 // And recurse through to its predecessors.
1522 Worklist.push_back(PredBB);
1523 }
1524 } while (!Worklist.empty());
1525 }
1526
1527 // Now that the ExitLoopMap gives as mapping for all the non-looping cloned
1528 // blocks to their outer loops, walk the cloned blocks and the cloned exits
1529 // in their original order adding them to the correct loop.
1530
1531 // We need a stable insertion order. We use the order of the original loop
1532 // order and map into the correct parent loop.
1533 for (auto *BB : llvm::concat<BasicBlock *const>(
1534 makeArrayRef(ClonedPH), ClonedLoopBlocks, ClonedExitsInLoops))
1535 if (Loop *OuterL = ExitLoopMap.lookup(BB))
1536 OuterL->addBasicBlockToLoop(BB, LI);
1537
1538#ifndef NDEBUG
1539 for (auto &BBAndL : ExitLoopMap) {
1540 auto *BB = BBAndL.first;
1541 auto *OuterL = BBAndL.second;
1542 assert(LI.getLoopFor(BB) == OuterL &&(static_cast <bool> (LI.getLoopFor(BB) == OuterL &&
"Failed to put all blocks into outer loops!") ? void (0) : __assert_fail
("LI.getLoopFor(BB) == OuterL && \"Failed to put all blocks into outer loops!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1543, __extension__
__PRETTY_FUNCTION__))
1543 "Failed to put all blocks into outer loops!")(static_cast <bool> (LI.getLoopFor(BB) == OuterL &&
"Failed to put all blocks into outer loops!") ? void (0) : __assert_fail
("LI.getLoopFor(BB) == OuterL && \"Failed to put all blocks into outer loops!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1543, __extension__
__PRETTY_FUNCTION__))
;
1544 }
1545#endif
1546
1547 // Now that all the blocks are placed into the correct containing loop in the
1548 // absence of child loops, find all the potentially cloned child loops and
1549 // clone them into whatever outer loop we placed their header into.
1550 for (Loop *ChildL : OrigL) {
1551 auto *ClonedChildHeader =
1552 cast_or_null<BasicBlock>(VMap.lookup(ChildL->getHeader()));
1553 if (!ClonedChildHeader || BlocksInClonedLoop.count(ClonedChildHeader))
1554 continue;
1555
1556#ifndef NDEBUG
1557 for (auto *ChildLoopBB : ChildL->blocks())
1558 assert(VMap.count(ChildLoopBB) &&(static_cast <bool> (VMap.count(ChildLoopBB) &&
"Cloned a child loop header but not all of that loops blocks!"
) ? void (0) : __assert_fail ("VMap.count(ChildLoopBB) && \"Cloned a child loop header but not all of that loops blocks!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1559, __extension__
__PRETTY_FUNCTION__))
1559 "Cloned a child loop header but not all of that loops blocks!")(static_cast <bool> (VMap.count(ChildLoopBB) &&
"Cloned a child loop header but not all of that loops blocks!"
) ? void (0) : __assert_fail ("VMap.count(ChildLoopBB) && \"Cloned a child loop header but not all of that loops blocks!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1559, __extension__
__PRETTY_FUNCTION__))
;
1560#endif
1561
1562 NonChildClonedLoops.push_back(cloneLoopNest(
1563 *ChildL, ExitLoopMap.lookup(ClonedChildHeader), VMap, LI));
1564 }
1565}
1566
1567static void
1568deleteDeadClonedBlocks(Loop &L, ArrayRef<BasicBlock *> ExitBlocks,
1569 ArrayRef<std::unique_ptr<ValueToValueMapTy>> VMaps,
1570 DominatorTree &DT, MemorySSAUpdater *MSSAU) {
1571 // Find all the dead clones, and remove them from their successors.
1572 SmallVector<BasicBlock *, 16> DeadBlocks;
1573 for (BasicBlock *BB : llvm::concat<BasicBlock *const>(L.blocks(), ExitBlocks))
1574 for (auto &VMap : VMaps)
1575 if (BasicBlock *ClonedBB = cast_or_null<BasicBlock>(VMap->lookup(BB)))
1576 if (!DT.isReachableFromEntry(ClonedBB)) {
1577 for (BasicBlock *SuccBB : successors(ClonedBB))
1578 SuccBB->removePredecessor(ClonedBB);
1579 DeadBlocks.push_back(ClonedBB);
1580 }
1581
1582 // Remove all MemorySSA in the dead blocks
1583 if (MSSAU) {
1584 SmallSetVector<BasicBlock *, 8> DeadBlockSet(DeadBlocks.begin(),
1585 DeadBlocks.end());
1586 MSSAU->removeBlocks(DeadBlockSet);
1587 }
1588
1589 // Drop any remaining references to break cycles.
1590 for (BasicBlock *BB : DeadBlocks)
1591 BB->dropAllReferences();
1592 // Erase them from the IR.
1593 for (BasicBlock *BB : DeadBlocks)
1594 BB->eraseFromParent();
1595}
1596
1597static void
1598deleteDeadBlocksFromLoop(Loop &L,
1599 SmallVectorImpl<BasicBlock *> &ExitBlocks,
1600 DominatorTree &DT, LoopInfo &LI,
1601 MemorySSAUpdater *MSSAU,
1602 function_ref<void(Loop &, StringRef)> DestroyLoopCB) {
1603 // Find all the dead blocks tied to this loop, and remove them from their
1604 // successors.
1605 SmallSetVector<BasicBlock *, 8> DeadBlockSet;
1606
1607 // Start with loop/exit blocks and get a transitive closure of reachable dead
1608 // blocks.
1609 SmallVector<BasicBlock *, 16> DeathCandidates(ExitBlocks.begin(),
1610 ExitBlocks.end());
1611 DeathCandidates.append(L.blocks().begin(), L.blocks().end());
1612 while (!DeathCandidates.empty()) {
1613 auto *BB = DeathCandidates.pop_back_val();
1614 if (!DeadBlockSet.count(BB) && !DT.isReachableFromEntry(BB)) {
1615 for (BasicBlock *SuccBB : successors(BB)) {
1616 SuccBB->removePredecessor(BB);
1617 DeathCandidates.push_back(SuccBB);
1618 }
1619 DeadBlockSet.insert(BB);
1620 }
1621 }
1622
1623 // Remove all MemorySSA in the dead blocks
1624 if (MSSAU)
1625 MSSAU->removeBlocks(DeadBlockSet);
1626
1627 // Filter out the dead blocks from the exit blocks list so that it can be
1628 // used in the caller.
1629 llvm::erase_if(ExitBlocks,
1630 [&](BasicBlock *BB) { return DeadBlockSet.count(BB); });
1631
1632 // Walk from this loop up through its parents removing all of the dead blocks.
1633 for (Loop *ParentL = &L; ParentL; ParentL = ParentL->getParentLoop()) {
1634 for (auto *BB : DeadBlockSet)
1635 ParentL->getBlocksSet().erase(BB);
1636 llvm::erase_if(ParentL->getBlocksVector(),
1637 [&](BasicBlock *BB) { return DeadBlockSet.count(BB); });
1638 }
1639
1640 // Now delete the dead child loops. This raw delete will clear them
1641 // recursively.
1642 llvm::erase_if(L.getSubLoopsVector(), [&](Loop *ChildL) {
1643 if (!DeadBlockSet.count(ChildL->getHeader()))
1644 return false;
1645
1646 assert(llvm::all_of(ChildL->blocks(),(static_cast <bool> (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!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1651, __extension__
__PRETTY_FUNCTION__))
1647 [&](BasicBlock *ChildBB) {(static_cast <bool> (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!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1651, __extension__
__PRETTY_FUNCTION__))
1648 return DeadBlockSet.count(ChildBB);(static_cast <bool> (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!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1651, __extension__
__PRETTY_FUNCTION__))
1649 }) &&(static_cast <bool> (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!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1651, __extension__
__PRETTY_FUNCTION__))
1650 "If the child loop header is dead all blocks in the child loop must "(static_cast <bool> (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!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1651, __extension__
__PRETTY_FUNCTION__))
1651 "be dead as well!")(static_cast <bool> (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!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1651, __extension__
__PRETTY_FUNCTION__))
;
1652 DestroyLoopCB(*ChildL, ChildL->getName());
1653 LI.destroy(ChildL);
1654 return true;
1655 });
1656
1657 // Remove the loop mappings for the dead blocks and drop all the references
1658 // from these blocks to others to handle cyclic references as we start
1659 // deleting the blocks themselves.
1660 for (auto *BB : DeadBlockSet) {
1661 // Check that the dominator tree has already been updated.
1662 assert(!DT.getNode(BB) && "Should already have cleared domtree!")(static_cast <bool> (!DT.getNode(BB) && "Should already have cleared domtree!"
) ? void (0) : __assert_fail ("!DT.getNode(BB) && \"Should already have cleared domtree!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1662, __extension__
__PRETTY_FUNCTION__))
;
1663 LI.changeLoopFor(BB, nullptr);
1664 // Drop all uses of the instructions to make sure we won't have dangling
1665 // uses in other blocks.
1666 for (auto &I : *BB)
1667 if (!I.use_empty())
1668 I.replaceAllUsesWith(UndefValue::get(I.getType()));
1669 BB->dropAllReferences();
1670 }
1671
1672 // Actually delete the blocks now that they've been fully unhooked from the
1673 // IR.
1674 for (auto *BB : DeadBlockSet)
1675 BB->eraseFromParent();
1676}
1677
1678/// Recompute the set of blocks in a loop after unswitching.
1679///
1680/// This walks from the original headers predecessors to rebuild the loop. We
1681/// take advantage of the fact that new blocks can't have been added, and so we
1682/// filter by the original loop's blocks. This also handles potentially
1683/// unreachable code that we don't want to explore but might be found examining
1684/// the predecessors of the header.
1685///
1686/// If the original loop is no longer a loop, this will return an empty set. If
1687/// it remains a loop, all the blocks within it will be added to the set
1688/// (including those blocks in inner loops).
1689static SmallPtrSet<const BasicBlock *, 16> recomputeLoopBlockSet(Loop &L,
1690 LoopInfo &LI) {
1691 SmallPtrSet<const BasicBlock *, 16> LoopBlockSet;
1692
1693 auto *PH = L.getLoopPreheader();
1694 auto *Header = L.getHeader();
1695
1696 // A worklist to use while walking backwards from the header.
1697 SmallVector<BasicBlock *, 16> Worklist;
1698
1699 // First walk the predecessors of the header to find the backedges. This will
1700 // form the basis of our walk.
1701 for (auto *Pred : predecessors(Header)) {
1702 // Skip the preheader.
1703 if (Pred == PH)
1704 continue;
1705
1706 // Because the loop was in simplified form, the only non-loop predecessor
1707 // is the preheader.
1708 assert(L.contains(Pred) && "Found a predecessor of the loop header other "(static_cast <bool> (L.contains(Pred) && "Found a predecessor of the loop header other "
"than the preheader that is not part of the " "loop!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1710, __extension__
__PRETTY_FUNCTION__))
1709 "than the preheader that is not part of the "(static_cast <bool> (L.contains(Pred) && "Found a predecessor of the loop header other "
"than the preheader that is not part of the " "loop!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1710, __extension__
__PRETTY_FUNCTION__))
1710 "loop!")(static_cast <bool> (L.contains(Pred) && "Found a predecessor of the loop header other "
"than the preheader that is not part of the " "loop!") ? 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!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1710, __extension__
__PRETTY_FUNCTION__))
;
1711
1712 // Insert this block into the loop set and on the first visit and, if it
1713 // isn't the header we're currently walking, put it into the worklist to
1714 // recurse through.
1715 if (LoopBlockSet.insert(Pred).second && Pred != Header)
1716 Worklist.push_back(Pred);
1717 }
1718
1719 // If no backedges were found, we're done.
1720 if (LoopBlockSet.empty())
1721 return LoopBlockSet;
1722
1723 // We found backedges, recurse through them to identify the loop blocks.
1724 while (!Worklist.empty()) {
1725 BasicBlock *BB = Worklist.pop_back_val();
1726 assert(LoopBlockSet.count(BB) && "Didn't put block into the loop set!")(static_cast <bool> (LoopBlockSet.count(BB) && "Didn't put block into the loop set!"
) ? void (0) : __assert_fail ("LoopBlockSet.count(BB) && \"Didn't put block into the loop set!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1726, __extension__
__PRETTY_FUNCTION__))
;
1727
1728 // No need to walk past the header.
1729 if (BB == Header)
1730 continue;
1731
1732 // Because we know the inner loop structure remains valid we can use the
1733 // loop structure to jump immediately across the entire nested loop.
1734 // Further, because it is in loop simplified form, we can directly jump
1735 // to its preheader afterward.
1736 if (Loop *InnerL = LI.getLoopFor(BB))
1737 if (InnerL != &L) {
1738 assert(L.contains(InnerL) &&(static_cast <bool> (L.contains(InnerL) && "Should not reach a loop *outside* this loop!"
) ? void (0) : __assert_fail ("L.contains(InnerL) && \"Should not reach a loop *outside* this loop!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1739, __extension__
__PRETTY_FUNCTION__))
1739 "Should not reach a loop *outside* this loop!")(static_cast <bool> (L.contains(InnerL) && "Should not reach a loop *outside* this loop!"
) ? void (0) : __assert_fail ("L.contains(InnerL) && \"Should not reach a loop *outside* this loop!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1739, __extension__
__PRETTY_FUNCTION__))
;
1740 // The preheader is the only possible predecessor of the loop so
1741 // insert it into the set and check whether it was already handled.
1742 auto *InnerPH = InnerL->getLoopPreheader();
1743 assert(L.contains(InnerPH) && "Cannot contain an inner loop block "(static_cast <bool> (L.contains(InnerPH) && "Cannot contain an inner loop block "
"but not contain the inner loop " "preheader!") ? void (0) :
__assert_fail ("L.contains(InnerPH) && \"Cannot contain an inner loop block \" \"but not contain the inner loop \" \"preheader!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1745, __extension__
__PRETTY_FUNCTION__))
1744 "but not contain the inner loop "(static_cast <bool> (L.contains(InnerPH) && "Cannot contain an inner loop block "
"but not contain the inner loop " "preheader!") ? void (0) :
__assert_fail ("L.contains(InnerPH) && \"Cannot contain an inner loop block \" \"but not contain the inner loop \" \"preheader!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1745, __extension__
__PRETTY_FUNCTION__))
1745 "preheader!")(static_cast <bool> (L.contains(InnerPH) && "Cannot contain an inner loop block "
"but not contain the inner loop " "preheader!") ? void (0) :
__assert_fail ("L.contains(InnerPH) && \"Cannot contain an inner loop block \" \"but not contain the inner loop \" \"preheader!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1745, __extension__
__PRETTY_FUNCTION__))
;
1746 if (!LoopBlockSet.insert(InnerPH).second)
1747 // The only way to reach the preheader is through the loop body
1748 // itself so if it has been visited the loop is already handled.
1749 continue;
1750
1751 // Insert all of the blocks (other than those already present) into
1752 // the loop set. We expect at least the block that led us to find the
1753 // inner loop to be in the block set, but we may also have other loop
1754 // blocks if they were already enqueued as predecessors of some other
1755 // outer loop block.
1756 for (auto *InnerBB : InnerL->blocks()) {
1757 if (InnerBB == BB) {
1758 assert(LoopBlockSet.count(InnerBB) &&(static_cast <bool> (LoopBlockSet.count(InnerBB) &&
"Block should already be in the set!") ? void (0) : __assert_fail
("LoopBlockSet.count(InnerBB) && \"Block should already be in the set!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1759, __extension__
__PRETTY_FUNCTION__))
1759 "Block should already be in the set!")(static_cast <bool> (LoopBlockSet.count(InnerBB) &&
"Block should already be in the set!") ? void (0) : __assert_fail
("LoopBlockSet.count(InnerBB) && \"Block should already be in the set!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1759, __extension__
__PRETTY_FUNCTION__))
;
1760 continue;
1761 }
1762
1763 LoopBlockSet.insert(InnerBB);
1764 }
1765
1766 // Add the preheader to the worklist so we will continue past the
1767 // loop body.
1768 Worklist.push_back(InnerPH);
1769 continue;
1770 }
1771
1772 // Insert any predecessors that were in the original loop into the new
1773 // set, and if the insert is successful, add them to the worklist.
1774 for (auto *Pred : predecessors(BB))
1775 if (L.contains(Pred) && LoopBlockSet.insert(Pred).second)
1776 Worklist.push_back(Pred);
1777 }
1778
1779 assert(LoopBlockSet.count(Header) && "Cannot fail to add the header!")(static_cast <bool> (LoopBlockSet.count(Header) &&
"Cannot fail to add the header!") ? void (0) : __assert_fail
("LoopBlockSet.count(Header) && \"Cannot fail to add the header!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1779, __extension__
__PRETTY_FUNCTION__))
;
1780
1781 // We've found all the blocks participating in the loop, return our completed
1782 // set.
1783 return LoopBlockSet;
1784}
1785
1786/// Rebuild a loop after unswitching removes some subset of blocks and edges.
1787///
1788/// The removal may have removed some child loops entirely but cannot have
1789/// disturbed any remaining child loops. However, they may need to be hoisted
1790/// to the parent loop (or to be top-level loops). The original loop may be
1791/// completely removed.
1792///
1793/// The sibling loops resulting from this update are returned. If the original
1794/// loop remains a valid loop, it will be the first entry in this list with all
1795/// of the newly sibling loops following it.
1796///
1797/// Returns true if the loop remains a loop after unswitching, and false if it
1798/// is no longer a loop after unswitching (and should not continue to be
1799/// referenced).
1800static bool rebuildLoopAfterUnswitch(Loop &L, ArrayRef<BasicBlock *> ExitBlocks,
1801 LoopInfo &LI,
1802 SmallVectorImpl<Loop *> &HoistedLoops) {
1803 auto *PH = L.getLoopPreheader();
1804
1805 // Compute the actual parent loop from the exit blocks. Because we may have
1806 // pruned some exits the loop may be different from the original parent.
1807 Loop *ParentL = nullptr;
1808 SmallVector<Loop *, 4> ExitLoops;
1809 SmallVector<BasicBlock *, 4> ExitsInLoops;
1810 ExitsInLoops.reserve(ExitBlocks.size());
1811 for (auto *ExitBB : ExitBlocks)
1812 if (Loop *ExitL = LI.getLoopFor(ExitBB)) {
1813 ExitLoops.push_back(ExitL);
1814 ExitsInLoops.push_back(ExitBB);
1815 if (!ParentL || (ParentL != ExitL && ParentL->contains(ExitL)))
1816 ParentL = ExitL;
1817 }
1818
1819 // Recompute the blocks participating in this loop. This may be empty if it
1820 // is no longer a loop.
1821 auto LoopBlockSet = recomputeLoopBlockSet(L, LI);
1822
1823 // If we still have a loop, we need to re-set the loop's parent as the exit
1824 // block set changing may have moved it within the loop nest. Note that this
1825 // can only happen when this loop has a parent as it can only hoist the loop
1826 // *up* the nest.
1827 if (!LoopBlockSet.empty() && L.getParentLoop() != ParentL) {
1828 // Remove this loop's (original) blocks from all of the intervening loops.
1829 for (Loop *IL = L.getParentLoop(); IL != ParentL;
1830 IL = IL->getParentLoop()) {
1831 IL->getBlocksSet().erase(PH);
1832 for (auto *BB : L.blocks())
1833 IL->getBlocksSet().erase(BB);
1834 llvm::erase_if(IL->getBlocksVector(), [&](BasicBlock *BB) {
1835 return BB == PH || L.contains(BB);
1836 });
1837 }
1838
1839 LI.changeLoopFor(PH, ParentL);
1840 L.getParentLoop()->removeChildLoop(&L);
1841 if (ParentL)
1842 ParentL->addChildLoop(&L);
1843 else
1844 LI.addTopLevelLoop(&L);
1845 }
1846
1847 // Now we update all the blocks which are no longer within the loop.
1848 auto &Blocks = L.getBlocksVector();
1849 auto BlocksSplitI =
1850 LoopBlockSet.empty()
1851 ? Blocks.begin()
1852 : std::stable_partition(
1853 Blocks.begin(), Blocks.end(),
1854 [&](BasicBlock *BB) { return LoopBlockSet.count(BB); });
1855
1856 // Before we erase the list of unlooped blocks, build a set of them.
1857 SmallPtrSet<BasicBlock *, 16> UnloopedBlocks(BlocksSplitI, Blocks.end());
1858 if (LoopBlockSet.empty())
1859 UnloopedBlocks.insert(PH);
1860
1861 // Now erase these blocks from the loop.
1862 for (auto *BB : make_range(BlocksSplitI, Blocks.end()))
1863 L.getBlocksSet().erase(BB);
1864 Blocks.erase(BlocksSplitI, Blocks.end());
1865
1866 // Sort the exits in ascending loop depth, we'll work backwards across these
1867 // to process them inside out.
1868 llvm::stable_sort(ExitsInLoops, [&](BasicBlock *LHS, BasicBlock *RHS) {
1869 return LI.getLoopDepth(LHS) < LI.getLoopDepth(RHS);
1870 });
1871
1872 // We'll build up a set for each exit loop.
1873 SmallPtrSet<BasicBlock *, 16> NewExitLoopBlocks;
1874 Loop *PrevExitL = L.getParentLoop(); // The deepest possible exit loop.
1875
1876 auto RemoveUnloopedBlocksFromLoop =
1877 [](Loop &L, SmallPtrSetImpl<BasicBlock *> &UnloopedBlocks) {
1878 for (auto *BB : UnloopedBlocks)
1879 L.getBlocksSet().erase(BB);
1880 llvm::erase_if(L.getBlocksVector(), [&](BasicBlock *BB) {
1881 return UnloopedBlocks.count(BB);
1882 });
1883 };
1884
1885 SmallVector<BasicBlock *, 16> Worklist;
1886 while (!UnloopedBlocks.empty() && !ExitsInLoops.empty()) {
1887 assert(Worklist.empty() && "Didn't clear worklist!")(static_cast <bool> (Worklist.empty() && "Didn't clear worklist!"
) ? void (0) : __assert_fail ("Worklist.empty() && \"Didn't clear worklist!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1887, __extension__
__PRETTY_FUNCTION__))
;
1888 assert(NewExitLoopBlocks.empty() && "Didn't clear loop set!")(static_cast <bool> (NewExitLoopBlocks.empty() &&
"Didn't clear loop set!") ? void (0) : __assert_fail ("NewExitLoopBlocks.empty() && \"Didn't clear loop set!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1888, __extension__
__PRETTY_FUNCTION__))
;
1889
1890 // Grab the next exit block, in decreasing loop depth order.
1891 BasicBlock *ExitBB = ExitsInLoops.pop_back_val();
1892 Loop &ExitL = *LI.getLoopFor(ExitBB);
1893 assert(ExitL.contains(&L) && "Exit loop must contain the inner loop!")(static_cast <bool> (ExitL.contains(&L) && "Exit loop must contain the inner loop!"
) ? void (0) : __assert_fail ("ExitL.contains(&L) && \"Exit loop must contain the inner loop!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1893, __extension__
__PRETTY_FUNCTION__))
;
1894
1895 // Erase all of the unlooped blocks from the loops between the previous
1896 // exit loop and this exit loop. This works because the ExitInLoops list is
1897 // sorted in increasing order of loop depth and thus we visit loops in
1898 // decreasing order of loop depth.
1899 for (; PrevExitL != &ExitL; PrevExitL = PrevExitL->getParentLoop())
1900 RemoveUnloopedBlocksFromLoop(*PrevExitL, UnloopedBlocks);
1901
1902 // Walk the CFG back until we hit the cloned PH adding everything reachable
1903 // and in the unlooped set to this exit block's loop.
1904 Worklist.push_back(ExitBB);
1905 do {
1906 BasicBlock *BB = Worklist.pop_back_val();
1907 // We can stop recursing at the cloned preheader (if we get there).
1908 if (BB == PH)
1909 continue;
1910
1911 for (BasicBlock *PredBB : predecessors(BB)) {
1912 // If this pred has already been moved to our set or is part of some
1913 // (inner) loop, no update needed.
1914 if (!UnloopedBlocks.erase(PredBB)) {
1915 assert((NewExitLoopBlocks.count(PredBB) ||(static_cast <bool> ((NewExitLoopBlocks.count(PredBB) ||
ExitL.contains(LI.getLoopFor(PredBB))) && "Predecessor not in a nested loop (or already visited)!"
) ? void (0) : __assert_fail ("(NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor(PredBB))) && \"Predecessor not in a nested loop (or already visited)!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1917, __extension__
__PRETTY_FUNCTION__))
1916 ExitL.contains(LI.getLoopFor(PredBB))) &&(static_cast <bool> ((NewExitLoopBlocks.count(PredBB) ||
ExitL.contains(LI.getLoopFor(PredBB))) && "Predecessor not in a nested loop (or already visited)!"
) ? void (0) : __assert_fail ("(NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor(PredBB))) && \"Predecessor not in a nested loop (or already visited)!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1917, __extension__
__PRETTY_FUNCTION__))
1917 "Predecessor not in a nested loop (or already visited)!")(static_cast <bool> ((NewExitLoopBlocks.count(PredBB) ||
ExitL.contains(LI.getLoopFor(PredBB))) && "Predecessor not in a nested loop (or already visited)!"
) ? void (0) : __assert_fail ("(NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor(PredBB))) && \"Predecessor not in a nested loop (or already visited)!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1917, __extension__
__PRETTY_FUNCTION__))
;
1918 continue;
1919 }
1920
1921 // We just insert into the loop set here. We'll add these blocks to the
1922 // exit loop after we build up the set in a deterministic order rather
1923 // than the predecessor-influenced visit order.
1924 bool Inserted = NewExitLoopBlocks.insert(PredBB).second;
1925 (void)Inserted;
1926 assert(Inserted && "Should only visit an unlooped block once!")(static_cast <bool> (Inserted && "Should only visit an unlooped block once!"
) ? void (0) : __assert_fail ("Inserted && \"Should only visit an unlooped block once!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1926, __extension__
__PRETTY_FUNCTION__))
;
1927
1928 // And recurse through to its predecessors.
1929 Worklist.push_back(PredBB);
1930 }
1931 } while (!Worklist.empty());
1932
1933 // If blocks in this exit loop were directly part of the original loop (as
1934 // opposed to a child loop) update the map to point to this exit loop. This
1935 // just updates a map and so the fact that the order is unstable is fine.
1936 for (auto *BB : NewExitLoopBlocks)
1937 if (Loop *BBL = LI.getLoopFor(BB))
1938 if (BBL == &L || !L.contains(BBL))
1939 LI.changeLoopFor(BB, &ExitL);
1940
1941 // We will remove the remaining unlooped blocks from this loop in the next
1942 // iteration or below.
1943 NewExitLoopBlocks.clear();
1944 }
1945
1946 // Any remaining unlooped blocks are no longer part of any loop unless they
1947 // are part of some child loop.
1948 for (; PrevExitL; PrevExitL = PrevExitL->getParentLoop())
1949 RemoveUnloopedBlocksFromLoop(*PrevExitL, UnloopedBlocks);
1950 for (auto *BB : UnloopedBlocks)
1951 if (Loop *BBL = LI.getLoopFor(BB))
1952 if (BBL == &L || !L.contains(BBL))
1953 LI.changeLoopFor(BB, nullptr);
1954
1955 // Sink all the child loops whose headers are no longer in the loop set to
1956 // the parent (or to be top level loops). We reach into the loop and directly
1957 // update its subloop vector to make this batch update efficient.
1958 auto &SubLoops = L.getSubLoopsVector();
1959 auto SubLoopsSplitI =
1960 LoopBlockSet.empty()
1961 ? SubLoops.begin()
1962 : std::stable_partition(
1963 SubLoops.begin(), SubLoops.end(), [&](Loop *SubL) {
1964 return LoopBlockSet.count(SubL->getHeader());
1965 });
1966 for (auto *HoistedL : make_range(SubLoopsSplitI, SubLoops.end())) {
1967 HoistedLoops.push_back(HoistedL);
1968 HoistedL->setParentLoop(nullptr);
1969
1970 // To compute the new parent of this hoisted loop we look at where we
1971 // placed the preheader above. We can't lookup the header itself because we
1972 // retained the mapping from the header to the hoisted loop. But the
1973 // preheader and header should have the exact same new parent computed
1974 // based on the set of exit blocks from the original loop as the preheader
1975 // is a predecessor of the header and so reached in the reverse walk. And
1976 // because the loops were all in simplified form the preheader of the
1977 // hoisted loop can't be part of some *other* loop.
1978 if (auto *NewParentL = LI.getLoopFor(HoistedL->getLoopPreheader()))
1979 NewParentL->addChildLoop(HoistedL);
1980 else
1981 LI.addTopLevelLoop(HoistedL);
1982 }
1983 SubLoops.erase(SubLoopsSplitI, SubLoops.end());
1984
1985 // Actually delete the loop if nothing remained within it.
1986 if (Blocks.empty()) {
1987 assert(SubLoops.empty() &&(static_cast <bool> (SubLoops.empty() && "Failed to remove all subloops from the original loop!"
) ? void (0) : __assert_fail ("SubLoops.empty() && \"Failed to remove all subloops from the original loop!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1988, __extension__
__PRETTY_FUNCTION__))
1988 "Failed to remove all subloops from the original loop!")(static_cast <bool> (SubLoops.empty() && "Failed to remove all subloops from the original loop!"
) ? void (0) : __assert_fail ("SubLoops.empty() && \"Failed to remove all subloops from the original loop!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 1988, __extension__
__PRETTY_FUNCTION__))
;
1989 if (Loop *ParentL = L.getParentLoop())
1990 ParentL->removeChildLoop(llvm::find(*ParentL, &L));
1991 else
1992 LI.removeLoop(llvm::find(LI, &L));
1993 // markLoopAsDeleted for L should be triggered by the caller (it is typically
1994 // done by using the UnswitchCB callback).
1995 LI.destroy(&L);
1996 return false;
1997 }
1998
1999 return true;
2000}
2001
2002/// Helper to visit a dominator subtree, invoking a callable on each node.
2003///
2004/// Returning false at any point will stop walking past that node of the tree.
2005template <typename CallableT>
2006void visitDomSubTree(DominatorTree &DT, BasicBlock *BB, CallableT Callable) {
2007 SmallVector<DomTreeNode *, 4> DomWorklist;
2008 DomWorklist.push_back(DT[BB]);
2009#ifndef NDEBUG
2010 SmallPtrSet<DomTreeNode *, 4> Visited;
2011 Visited.insert(DT[BB]);
2012#endif
2013 do {
2014 DomTreeNode *N = DomWorklist.pop_back_val();
2015
2016 // Visit this node.
2017 if (!Callable(N->getBlock()))
2018 continue;
2019
2020 // Accumulate the child nodes.
2021 for (DomTreeNode *ChildN : *N) {
2022 assert(Visited.insert(ChildN).second &&(static_cast <bool> (Visited.insert(ChildN).second &&
"Cannot visit a node twice when walking a tree!") ? void (0)
: __assert_fail ("Visited.insert(ChildN).second && \"Cannot visit a node twice when walking a tree!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2023, __extension__
__PRETTY_FUNCTION__))
2023 "Cannot visit a node twice when walking a tree!")(static_cast <bool> (Visited.insert(ChildN).second &&
"Cannot visit a node twice when walking a tree!") ? void (0)
: __assert_fail ("Visited.insert(ChildN).second && \"Cannot visit a node twice when walking a tree!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2023, __extension__
__PRETTY_FUNCTION__))
;
2024 DomWorklist.push_back(ChildN);
2025 }
2026 } while (!DomWorklist.empty());
2027}
2028
2029static void unswitchNontrivialInvariants(
2030 Loop &L, Instruction &TI, ArrayRef<Value *> Invariants,
2031 SmallVectorImpl<BasicBlock *> &ExitBlocks, IVConditionInfo &PartialIVInfo,
2032 DominatorTree &DT, LoopInfo &LI, AssumptionCache &AC,
2033 function_ref<void(bool, bool, ArrayRef<Loop *>)> UnswitchCB,
2034 ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
2035 function_ref<void(Loop &, StringRef)> DestroyLoopCB) {
2036 auto *ParentBB = TI.getParent();
2037 BranchInst *BI = dyn_cast<BranchInst>(&TI);
2038 SwitchInst *SI = BI ? nullptr : cast<SwitchInst>(&TI);
2039
2040 // We can only unswitch switches, conditional branches with an invariant
2041 // condition, or combining invariant conditions with an instruction or
2042 // partially invariant instructions.
2043 assert((SI || (BI && BI->isConditional())) &&(static_cast <bool> ((SI || (BI && BI->isConditional
())) && "Can only unswitch switches and conditional branch!"
) ? void (0) : __assert_fail ("(SI || (BI && BI->isConditional())) && \"Can only unswitch switches and conditional branch!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2044, __extension__
__PRETTY_FUNCTION__))
2044 "Can only unswitch switches and conditional branch!")(static_cast <bool> ((SI || (BI && BI->isConditional
())) && "Can only unswitch switches and conditional branch!"
) ? void (0) : __assert_fail ("(SI || (BI && BI->isConditional())) && \"Can only unswitch switches and conditional branch!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2044, __extension__
__PRETTY_FUNCTION__))
;
2045 bool PartiallyInvariant = !PartialIVInfo.InstToDuplicate.empty();
2046 bool FullUnswitch =
2047 SI || (BI->getCondition() == Invariants[0] && !PartiallyInvariant);
2048 if (FullUnswitch)
2049 assert(Invariants.size() == 1 &&(static_cast <bool> (Invariants.size() == 1 && "Cannot have other invariants with full unswitching!"
) ? void (0) : __assert_fail ("Invariants.size() == 1 && \"Cannot have other invariants with full unswitching!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2050, __extension__
__PRETTY_FUNCTION__))
2050 "Cannot have other invariants with full unswitching!")(static_cast <bool> (Invariants.size() == 1 && "Cannot have other invariants with full unswitching!"
) ? void (0) : __assert_fail ("Invariants.size() == 1 && \"Cannot have other invariants with full unswitching!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2050, __extension__
__PRETTY_FUNCTION__))
;
2051 else
2052 assert(isa<Instruction>(BI->getCondition()) &&(static_cast <bool> (isa<Instruction>(BI->getCondition
()) && "Partial unswitching requires an instruction as the condition!"
) ? void (0) : __assert_fail ("isa<Instruction>(BI->getCondition()) && \"Partial unswitching requires an instruction as the condition!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2053, __extension__
__PRETTY_FUNCTION__))
2053 "Partial unswitching requires an instruction as the condition!")(static_cast <bool> (isa<Instruction>(BI->getCondition
()) && "Partial unswitching requires an instruction as the condition!"
) ? void (0) : __assert_fail ("isa<Instruction>(BI->getCondition()) && \"Partial unswitching requires an instruction as the condition!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2053, __extension__
__PRETTY_FUNCTION__))
;
2054
2055 if (MSSAU && VerifyMemorySSA)
2056 MSSAU->getMemorySSA()->verifyMemorySSA();
2057
2058 // Constant and BBs tracking the cloned and continuing successor. When we are
2059 // unswitching the entire condition, this can just be trivially chosen to
2060 // unswitch towards `true`. However, when we are unswitching a set of
2061 // invariants combined with `and` or `or` or partially invariant instructions,
2062 // the combining operation determines the best direction to unswitch: we want
2063 // to unswitch the direction that will collapse the branch.
2064 bool Direction = true;
2065 int ClonedSucc = 0;
2066 if (!FullUnswitch) {
2067 Value *Cond = BI->getCondition();
2068 (void)Cond;
2069 assert(((match(Cond, m_LogicalAnd()) ^ match(Cond, m_LogicalOr())) ||(static_cast <bool> (((match(Cond, m_LogicalAnd()) ^ match
(Cond, m_LogicalOr())) || PartiallyInvariant) && "Only `or`, `and`, an `select`, partially invariant instructions "
"can combine invariants being unswitched.") ? void (0) : __assert_fail
("((match(Cond, m_LogicalAnd()) ^ match(Cond, m_LogicalOr())) || PartiallyInvariant) && \"Only `or`, `and`, an `select`, partially invariant instructions \" \"can combine invariants being unswitched.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2072, __extension__
__PRETTY_FUNCTION__))
2070 PartiallyInvariant) &&(static_cast <bool> (((match(Cond, m_LogicalAnd()) ^ match
(Cond, m_LogicalOr())) || PartiallyInvariant) && "Only `or`, `and`, an `select`, partially invariant instructions "
"can combine invariants being unswitched.") ? void (0) : __assert_fail
("((match(Cond, m_LogicalAnd()) ^ match(Cond, m_LogicalOr())) || PartiallyInvariant) && \"Only `or`, `and`, an `select`, partially invariant instructions \" \"can combine invariants being unswitched.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2072, __extension__
__PRETTY_FUNCTION__))
2071 "Only `or`, `and`, an `select`, partially invariant instructions "(static_cast <bool> (((match(Cond, m_LogicalAnd()) ^ match
(Cond, m_LogicalOr())) || PartiallyInvariant) && "Only `or`, `and`, an `select`, partially invariant instructions "
"can combine invariants being unswitched.") ? void (0) : __assert_fail
("((match(Cond, m_LogicalAnd()) ^ match(Cond, m_LogicalOr())) || PartiallyInvariant) && \"Only `or`, `and`, an `select`, partially invariant instructions \" \"can combine invariants being unswitched.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2072, __extension__
__PRETTY_FUNCTION__))
2072 "can combine invariants being unswitched.")(static_cast <bool> (((match(Cond, m_LogicalAnd()) ^ match
(Cond, m_LogicalOr())) || PartiallyInvariant) && "Only `or`, `and`, an `select`, partially invariant instructions "
"can combine invariants being unswitched.") ? void (0) : __assert_fail
("((match(Cond, m_LogicalAnd()) ^ match(Cond, m_LogicalOr())) || PartiallyInvariant) && \"Only `or`, `and`, an `select`, partially invariant instructions \" \"can combine invariants being unswitched.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2072, __extension__
__PRETTY_FUNCTION__))
;
2073 if (!match(BI->getCondition(), m_LogicalOr())) {
2074 if (match(BI->getCondition(), m_LogicalAnd()) ||
2075 (PartiallyInvariant && !PartialIVInfo.KnownValue->isOneValue())) {
2076 Direction = false;
2077 ClonedSucc = 1;
2078 }
2079 }
2080 }
2081
2082 BasicBlock *RetainedSuccBB =
2083 BI ? BI->getSuccessor(1 - ClonedSucc) : SI->getDefaultDest();
2084 SmallSetVector<BasicBlock *, 4> UnswitchedSuccBBs;
2085 if (BI)
2086 UnswitchedSuccBBs.insert(BI->getSuccessor(ClonedSucc));
2087 else
2088 for (auto Case : SI->cases())
2089 if (Case.getCaseSuccessor() != RetainedSuccBB)
2090 UnswitchedSuccBBs.insert(Case.getCaseSuccessor());
2091
2092 assert(!UnswitchedSuccBBs.count(RetainedSuccBB) &&(static_cast <bool> (!UnswitchedSuccBBs.count(RetainedSuccBB
) && "Should not unswitch the same successor we are retaining!"
) ? void (0) : __assert_fail ("!UnswitchedSuccBBs.count(RetainedSuccBB) && \"Should not unswitch the same successor we are retaining!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2093, __extension__
__PRETTY_FUNCTION__))
2093 "Should not unswitch the same successor we are retaining!")(static_cast <bool> (!UnswitchedSuccBBs.count(RetainedSuccBB
) && "Should not unswitch the same successor we are retaining!"
) ? void (0) : __assert_fail ("!UnswitchedSuccBBs.count(RetainedSuccBB) && \"Should not unswitch the same successor we are retaining!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2093, __extension__
__PRETTY_FUNCTION__))
;
2094
2095 // The branch should be in this exact loop. Any inner loop's invariant branch
2096 // should be handled by unswitching that inner loop. The caller of this
2097 // routine should filter out any candidates that remain (but were skipped for
2098 // whatever reason).
2099 assert(LI.getLoopFor(ParentBB) == &L && "Branch in an inner loop!")(static_cast <bool> (LI.getLoopFor(ParentBB) == &L &&
"Branch in an inner loop!") ? void (0) : __assert_fail ("LI.getLoopFor(ParentBB) == &L && \"Branch in an inner loop!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2099, __extension__
__PRETTY_FUNCTION__))
;
2100
2101 // Compute the parent loop now before we start hacking on things.
2102 Loop *ParentL = L.getParentLoop();
2103 // Get blocks in RPO order for MSSA update, before changing the CFG.
2104 LoopBlocksRPO LBRPO(&L);
2105 if (MSSAU)
2106 LBRPO.perform(&LI);
2107
2108 // Compute the outer-most loop containing one of our exit blocks. This is the
2109 // furthest up our loopnest which can be mutated, which we will use below to
2110 // update things.
2111 Loop *OuterExitL = &L;
2112 for (auto *ExitBB : ExitBlocks) {
2113 Loop *NewOuterExitL = LI.getLoopFor(ExitBB);
2114 if (!NewOuterExitL) {
2115 // We exited the entire nest with this block, so we're done.
2116 OuterExitL = nullptr;
2117 break;
2118 }
2119 if (NewOuterExitL != OuterExitL && NewOuterExitL->contains(OuterExitL))
2120 OuterExitL = NewOuterExitL;
2121 }
2122
2123 // At this point, we're definitely going to unswitch something so invalidate
2124 // any cached information in ScalarEvolution for the outer most loop
2125 // containing an exit block and all nested loops.
2126 if (SE) {
2127 if (OuterExitL)
2128 SE->forgetLoop(OuterExitL);
2129 else
2130 SE->forgetTopmostLoop(&L);
2131 }
2132
2133 bool InsertFreeze = false;
2134 if (FreezeLoopUnswitchCond) {
2135 ICFLoopSafetyInfo SafetyInfo;
2136 SafetyInfo.computeLoopSafetyInfo(&L);
2137 InsertFreeze = !SafetyInfo.isGuaranteedToExecute(TI, &DT, &L);
2138 }
2139
2140 // If the edge from this terminator to a successor dominates that successor,
2141 // store a map from each block in its dominator subtree to it. This lets us
2142 // tell when cloning for a particular successor if a block is dominated by
2143 // some *other* successor with a single data structure. We use this to
2144 // significantly reduce cloning.
2145 SmallDenseMap<BasicBlock *, BasicBlock *, 16> DominatingSucc;
2146 for (auto *SuccBB : llvm::concat<BasicBlock *const>(
2147 makeArrayRef(RetainedSuccBB), UnswitchedSuccBBs))
2148 if (SuccBB->getUniquePredecessor() ||
2149 llvm::all_of(predecessors(SuccBB), [&](BasicBlock *PredBB) {
2150 return PredBB == ParentBB || DT.dominates(SuccBB, PredBB);
2151 }))
2152 visitDomSubTree(DT, SuccBB, [&](BasicBlock *BB) {
2153 DominatingSucc[BB] = SuccBB;
2154 return true;
2155 });
2156
2157 // Split the preheader, so that we know that there is a safe place to insert
2158 // the conditional branch. We will change the preheader to have a conditional
2159 // branch on LoopCond. The original preheader will become the split point
2160 // between the unswitched versions, and we will have a new preheader for the
2161 // original loop.
2162 BasicBlock *SplitBB = L.getLoopPreheader();
2163 BasicBlock *LoopPH = SplitEdge(SplitBB, L.getHeader(), &DT, &LI, MSSAU);
2164
2165 // Keep track of the dominator tree updates needed.
2166 SmallVector<DominatorTree::UpdateType, 4> DTUpdates;
2167
2168 // Clone the loop for each unswitched successor.
2169 SmallVector<std::unique_ptr<ValueToValueMapTy>, 4> VMaps;
2170 VMaps.reserve(UnswitchedSuccBBs.size());
2171 SmallDenseMap<BasicBlock *, BasicBlock *, 4> ClonedPHs;
2172 for (auto *SuccBB : UnswitchedSuccBBs) {
2173 VMaps.emplace_back(new ValueToValueMapTy());
2174 ClonedPHs[SuccBB] = buildClonedLoopBlocks(
2175 L, LoopPH, SplitBB, ExitBlocks, ParentBB, SuccBB, RetainedSuccBB,
2176 DominatingSucc, *VMaps.back(), DTUpdates, AC, DT, LI, MSSAU);
2177 }
2178
2179 // Drop metadata if we may break its semantics by moving this instr into the
2180 // split block.
2181 if (TI.getMetadata(LLVMContext::MD_make_implicit)) {
2182 if (DropNonTrivialImplicitNullChecks)
2183 // Do not spend time trying to understand if we can keep it, just drop it
2184 // to save compile time.
2185 TI.setMetadata(LLVMContext::MD_make_implicit, nullptr);
2186 else {
2187 // It is only legal to preserve make.implicit metadata if we are
2188 // guaranteed no reach implicit null check after following this branch.
2189 ICFLoopSafetyInfo SafetyInfo;
2190 SafetyInfo.computeLoopSafetyInfo(&L);
2191 if (!SafetyInfo.isGuaranteedToExecute(TI, &DT, &L))
2192 TI.setMetadata(LLVMContext::MD_make_implicit, nullptr);
2193 }
2194 }
2195
2196 // The stitching of the branched code back together depends on whether we're
2197 // doing full unswitching or not with the exception that we always want to
2198 // nuke the initial terminator placed in the split block.
2199 SplitBB->getTerminator()->eraseFromParent();
2200 if (FullUnswitch) {
2201 // Splice the terminator from the original loop and rewrite its
2202 // successors.
2203 SplitBB->getInstList().splice(SplitBB->end(), ParentBB->getInstList(), TI);
2204
2205 // Keep a clone of the terminator for MSSA updates.
2206 Instruction *NewTI = TI.clone();
2207 ParentBB->getInstList().push_back(NewTI);
2208
2209 // First wire up the moved terminator to the preheaders.
2210 if (BI) {
2211 BasicBlock *ClonedPH = ClonedPHs.begin()->second;
2212 BI->setSuccessor(ClonedSucc, ClonedPH);
2213 BI->setSuccessor(1 - ClonedSucc, LoopPH);
2214 if (InsertFreeze) {
2215 auto Cond = BI->getCondition();
2216 if (!isGuaranteedNotToBeUndefOrPoison(Cond, &AC, BI, &DT))
2217 BI->setCondition(new FreezeInst(Cond, Cond->getName() + ".fr", BI));
2218 }
2219 DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH});
2220 } else {
2221 assert(SI && "Must either be a branch or switch!")(static_cast <bool> (SI && "Must either be a branch or switch!"
) ? void (0) : __assert_fail ("SI && \"Must either be a branch or switch!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2221, __extension__
__PRETTY_FUNCTION__))
;
2222
2223 // Walk the cases and directly update their successors.
2224 assert(SI->getDefaultDest() == RetainedSuccBB &&(static_cast <bool> (SI->getDefaultDest() == RetainedSuccBB
&& "Not retaining default successor!") ? void (0) : __assert_fail
("SI->getDefaultDest() == RetainedSuccBB && \"Not retaining default successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2225, __extension__
__PRETTY_FUNCTION__))
2225 "Not retaining default successor!")(static_cast <bool> (SI->getDefaultDest() == RetainedSuccBB
&& "Not retaining default successor!") ? void (0) : __assert_fail
("SI->getDefaultDest() == RetainedSuccBB && \"Not retaining default successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2225, __extension__
__PRETTY_FUNCTION__))
;
2226 SI->setDefaultDest(LoopPH);
2227 for (auto &Case : SI->cases())
2228 if (Case.getCaseSuccessor() == RetainedSuccBB)
2229 Case.setSuccessor(LoopPH);
2230 else
2231 Case.setSuccessor(ClonedPHs.find(Case.getCaseSuccessor())->second);
2232
2233 if (InsertFreeze) {
2234 auto Cond = SI->getCondition();
2235 if (!isGuaranteedNotToBeUndefOrPoison(Cond, &AC, SI, &DT))
2236 SI->setCondition(new FreezeInst(Cond, Cond->getName() + ".fr", SI));
2237 }
2238 // We need to use the set to populate domtree updates as even when there
2239 // are multiple cases pointing at the same successor we only want to
2240 // remove and insert one edge in the domtree.
2241 for (BasicBlock *SuccBB : UnswitchedSuccBBs)
2242 DTUpdates.push_back(
2243 {DominatorTree::Insert, SplitBB, ClonedPHs.find(SuccBB)->second});
2244 }
2245
2246 if (MSSAU) {
2247 DT.applyUpdates(DTUpdates);
2248 DTUpdates.clear();
2249
2250 // Remove all but one edge to the retained block and all unswitched
2251 // blocks. This is to avoid having duplicate entries in the cloned Phis,
2252 // when we know we only keep a single edge for each case.
2253 MSSAU->removeDuplicatePhiEdgesBetween(ParentBB, RetainedSuccBB);
2254 for (BasicBlock *SuccBB : UnswitchedSuccBBs)
2255 MSSAU->removeDuplicatePhiEdgesBetween(ParentBB, SuccBB);
2256
2257 for (auto &VMap : VMaps)
2258 MSSAU->updateForClonedLoop(LBRPO, ExitBlocks, *VMap,
2259 /*IgnoreIncomingWithNoClones=*/true);
2260 MSSAU->updateExitBlocksForClonedLoop(ExitBlocks, VMaps, DT);
2261
2262 // Remove all edges to unswitched blocks.
2263 for (BasicBlock *SuccBB : UnswitchedSuccBBs)
2264 MSSAU->removeEdge(ParentBB, SuccBB);
2265 }
2266
2267 // Now unhook the successor relationship as we'll be replacing
2268 // the terminator with a direct branch. This is much simpler for branches
2269 // than switches so we handle those first.
2270 if (BI) {
2271 // Remove the parent as a predecessor of the unswitched successor.
2272 assert(UnswitchedSuccBBs.size() == 1 &&(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2273, __extension__
__PRETTY_FUNCTION__))
2273 "Only one possible unswitched block for a branch!")(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2273, __extension__
__PRETTY_FUNCTION__))
;
2274 BasicBlock *UnswitchedSuccBB = *UnswitchedSuccBBs.begin();
2275 UnswitchedSuccBB->removePredecessor(ParentBB,
2276 /*KeepOneInputPHIs*/ true);
2277 DTUpdates.push_back({DominatorTree::Delete, ParentBB, UnswitchedSuccBB});
2278 } else {
2279 // Note that we actually want to remove the parent block as a predecessor
2280 // of *every* case successor. The case successor is either unswitched,
2281 // completely eliminating an edge from the parent to that successor, or it
2282 // is a duplicate edge to the retained successor as the retained successor
2283 // is always the default successor and as we'll replace this with a direct
2284 // branch we no longer need the duplicate entries in the PHI nodes.
2285 SwitchInst *NewSI = cast<SwitchInst>(NewTI);
2286 assert(NewSI->getDefaultDest() == RetainedSuccBB &&(static_cast <bool> (NewSI->getDefaultDest() == RetainedSuccBB
&& "Not retaining default successor!") ? void (0) : __assert_fail
("NewSI->getDefaultDest() == RetainedSuccBB && \"Not retaining default successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2287, __extension__
__PRETTY_FUNCTION__))
2287 "Not retaining default successor!")(static_cast <bool> (NewSI->getDefaultDest() == RetainedSuccBB
&& "Not retaining default successor!") ? void (0) : __assert_fail
("NewSI->getDefaultDest() == RetainedSuccBB && \"Not retaining default successor!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2287, __extension__
__PRETTY_FUNCTION__))
;
2288 for (auto &Case : NewSI->cases())
2289 Case.getCaseSuccessor()->removePredecessor(
2290 ParentBB,
2291 /*KeepOneInputPHIs*/ true);
2292
2293 // We need to use the set to populate domtree updates as even when there
2294 // are multiple cases pointing at the same successor we only want to
2295 // remove and insert one edge in the domtree.
2296 for (BasicBlock *SuccBB : UnswitchedSuccBBs)
2297 DTUpdates.push_back({DominatorTree::Delete, ParentBB, SuccBB});
2298 }
2299
2300 // After MSSAU update, remove the cloned terminator instruction NewTI.
2301 ParentBB->getTerminator()->eraseFromParent();
2302
2303 // Create a new unconditional branch to the continuing block (as opposed to
2304 // the one cloned).
2305 BranchInst::Create(RetainedSuccBB, ParentBB);
2306 } else {
2307 assert(BI && "Only branches have partial unswitching.")(static_cast <bool> (BI && "Only branches have partial unswitching."
) ? void (0) : __assert_fail ("BI && \"Only branches have partial unswitching.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2307, __extension__
__PRETTY_FUNCTION__))
;
2308 assert(UnswitchedSuccBBs.size() == 1 &&(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2309, __extension__
__PRETTY_FUNCTION__))
2309 "Only one possible unswitched block for a branch!")(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2309, __extension__
__PRETTY_FUNCTION__))
;
2310 BasicBlock *ClonedPH = ClonedPHs.begin()->second;
2311 // When doing a partial unswitch, we have to do a bit more work to build up
2312 // the branch in the split block.
2313 if (PartiallyInvariant)
2314 buildPartialInvariantUnswitchConditionalBranch(
2315 *SplitBB, Invariants, Direction, *ClonedPH, *LoopPH, L, MSSAU);
2316 else
2317 buildPartialUnswitchConditionalBranch(*SplitBB, Invariants, Direction,
2318 *ClonedPH, *LoopPH, InsertFreeze);
2319 DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH});
2320
2321 if (MSSAU) {
2322 DT.applyUpdates(DTUpdates);
2323 DTUpdates.clear();
2324
2325 // Perform MSSA cloning updates.
2326 for (auto &VMap : VMaps)
2327 MSSAU->updateForClonedLoop(LBRPO, ExitBlocks, *VMap,
2328 /*IgnoreIncomingWithNoClones=*/true);
2329 MSSAU->updateExitBlocksForClonedLoop(ExitBlocks, VMaps, DT);
2330 }
2331 }
2332
2333 // Apply the updates accumulated above to get an up-to-date dominator tree.
2334 DT.applyUpdates(DTUpdates);
2335
2336 // Now that we have an accurate dominator tree, first delete the dead cloned
2337 // blocks so that we can accurately build any cloned loops. It is important to
2338 // not delete the blocks from the original loop yet because we still want to
2339 // reference the original loop to understand the cloned loop's structure.
2340 deleteDeadClonedBlocks(L, ExitBlocks, VMaps, DT, MSSAU);
2341
2342 // Build the cloned loop structure itself. This may be substantially
2343 // different from the original structure due to the simplified CFG. This also
2344 // handles inserting all the cloned blocks into the correct loops.
2345 SmallVector<Loop *, 4> NonChildClonedLoops;
2346 for (std::unique_ptr<ValueToValueMapTy> &VMap : VMaps)
2347 buildClonedLoops(L, ExitBlocks, *VMap, LI, NonChildClonedLoops);
2348
2349 // Now that our cloned loops have been built, we can update the original loop.
2350 // First we delete the dead blocks from it and then we rebuild the loop
2351 // structure taking these deletions into account.
2352 deleteDeadBlocksFromLoop(L, ExitBlocks, DT, LI, MSSAU, DestroyLoopCB);
2353
2354 if (MSSAU && VerifyMemorySSA)
2355 MSSAU->getMemorySSA()->verifyMemorySSA();
2356
2357 SmallVector<Loop *, 4> HoistedLoops;
2358 bool IsStillLoop = rebuildLoopAfterUnswitch(L, ExitBlocks, LI, HoistedLoops);
2359
2360 if (MSSAU && VerifyMemorySSA)
2361 MSSAU->getMemorySSA()->verifyMemorySSA();
2362
2363 // This transformation has a high risk of corrupting the dominator tree, and
2364 // the below steps to rebuild loop structures will result in hard to debug
2365 // errors in that case so verify that the dominator tree is sane first.
2366 // FIXME: Remove this when the bugs stop showing up and rely on existing
2367 // verification steps.
2368 assert(DT.verify(DominatorTree::VerificationLevel::Fast))(static_cast <bool> (DT.verify(DominatorTree::VerificationLevel
::Fast)) ? void (0) : __assert_fail ("DT.verify(DominatorTree::VerificationLevel::Fast)"
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2368, __extension__
__PRETTY_FUNCTION__))
;
2369
2370 if (BI && !PartiallyInvariant) {
2371 // If we unswitched a branch which collapses the condition to a known
2372 // constant we want to replace all the uses of the invariants within both
2373 // the original and cloned blocks. We do this here so that we can use the
2374 // now updated dominator tree to identify which side the users are on.
2375 assert(UnswitchedSuccBBs.size() == 1 &&(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2376, __extension__
__PRETTY_FUNCTION__))
2376 "Only one possible unswitched block for a branch!")(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2376, __extension__
__PRETTY_FUNCTION__))
;
2377 BasicBlock *ClonedPH = ClonedPHs.begin()->second;
2378
2379 // When considering multiple partially-unswitched invariants
2380 // we cant just go replace them with constants in both branches.
2381 //
2382 // For 'AND' we infer that true branch ("continue") means true
2383 // for each invariant operand.
2384 // For 'OR' we can infer that false branch ("continue") means false
2385 // for each invariant operand.
2386 // So it happens that for multiple-partial case we dont replace
2387 // in the unswitched branch.
2388 bool ReplaceUnswitched =
2389 FullUnswitch || (Invariants.size() == 1) || PartiallyInvariant;
2390
2391 ConstantInt *UnswitchedReplacement =
2392 Direction ? ConstantInt::getTrue(BI->getContext())
2393 : ConstantInt::getFalse(BI->getContext());
2394 ConstantInt *ContinueReplacement =
2395 Direction ? ConstantInt::getFalse(BI->getContext())
2396 : ConstantInt::getTrue(BI->getContext());
2397 for (Value *Invariant : Invariants) {
2398 assert(!isa<Constant>(Invariant) &&(static_cast <bool> (!isa<Constant>(Invariant) &&
"Should not be replacing constant values!") ? void (0) : __assert_fail
("!isa<Constant>(Invariant) && \"Should not be replacing constant values!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2399, __extension__
__PRETTY_FUNCTION__))
2399 "Should not be replacing constant values!")(static_cast <bool> (!isa<Constant>(Invariant) &&
"Should not be replacing constant values!") ? void (0) : __assert_fail
("!isa<Constant>(Invariant) && \"Should not be replacing constant values!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2399, __extension__
__PRETTY_FUNCTION__))
;
2400 // Use make_early_inc_range here as set invalidates the iterator.
2401 for (Use &U : llvm::make_early_inc_range(Invariant->uses())) {
2402 Instruction *UserI = dyn_cast<Instruction>(U.getUser());
2403 if (!UserI)
2404 continue;
2405
2406 // Replace it with the 'continue' side if in the main loop body, and the
2407 // unswitched if in the cloned blocks.
2408 if (DT.dominates(LoopPH, UserI->getParent()))
2409 U.set(ContinueReplacement);
2410 else if (ReplaceUnswitched &&
2411 DT.dominates(ClonedPH, UserI->getParent()))
2412 U.set(UnswitchedReplacement);
2413 }
2414 }
2415 }
2416
2417 // We can change which blocks are exit blocks of all the cloned sibling
2418 // loops, the current loop, and any parent loops which shared exit blocks
2419 // with the current loop. As a consequence, we need to re-form LCSSA for
2420 // them. But we shouldn't need to re-form LCSSA for any child loops.
2421 // FIXME: This could be made more efficient by tracking which exit blocks are
2422 // new, and focusing on them, but that isn't likely to be necessary.
2423 //
2424 // In order to reasonably rebuild LCSSA we need to walk inside-out across the
2425 // loop nest and update every loop that could have had its exits changed. We
2426 // also need to cover any intervening loops. We add all of these loops to
2427 // a list and sort them by loop depth to achieve this without updating
2428 // unnecessary loops.
2429 auto UpdateLoop = [&](Loop &UpdateL) {
2430#ifndef NDEBUG
2431 UpdateL.verifyLoop();
2432 for (Loop *ChildL : UpdateL) {
2433 ChildL->verifyLoop();
2434 assert(ChildL->isRecursivelyLCSSAForm(DT, LI) &&(static_cast <bool> (ChildL->isRecursivelyLCSSAForm(
DT, LI) && "Perturbed a child loop's LCSSA form!") ? void
(0) : __assert_fail ("ChildL->isRecursivelyLCSSAForm(DT, LI) && \"Perturbed a child loop's LCSSA form!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2435, __extension__
__PRETTY_FUNCTION__))
2435 "Perturbed a child loop's LCSSA form!")(static_cast <bool> (ChildL->isRecursivelyLCSSAForm(
DT, LI) && "Perturbed a child loop's LCSSA form!") ? void
(0) : __assert_fail ("ChildL->isRecursivelyLCSSAForm(DT, LI) && \"Perturbed a child loop's LCSSA form!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2435, __extension__
__PRETTY_FUNCTION__))
;
2436 }
2437#endif
2438 // First build LCSSA for this loop so that we can preserve it when
2439 // forming dedicated exits. We don't want to perturb some other loop's
2440 // LCSSA while doing that CFG edit.
2441 formLCSSA(UpdateL, DT, &LI, SE);
2442
2443 // For loops reached by this loop's original exit blocks we may
2444 // introduced new, non-dedicated exits. At least try to re-form dedicated
2445 // exits for these loops. This may fail if they couldn't have dedicated
2446 // exits to start with.
2447 formDedicatedExitBlocks(&UpdateL, &DT, &LI, MSSAU, /*PreserveLCSSA*/ true);
2448 };
2449
2450 // For non-child cloned loops and hoisted loops, we just need to update LCSSA
2451 // and we can do it in any order as they don't nest relative to each other.
2452 //
2453 // Also check if any of the loops we have updated have become top-level loops
2454 // as that will necessitate widening the outer loop scope.
2455 for (Loop *UpdatedL :
2456 llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops)) {
2457 UpdateLoop(*UpdatedL);
2458 if (UpdatedL->isOutermost())
2459 OuterExitL = nullptr;
2460 }
2461 if (IsStillLoop) {
2462 UpdateLoop(L);
2463 if (L.isOutermost())
2464 OuterExitL = nullptr;
2465 }
2466
2467 // If the original loop had exit blocks, walk up through the outer most loop
2468 // of those exit blocks to update LCSSA and form updated dedicated exits.
2469 if (OuterExitL != &L)
2470 for (Loop *OuterL = ParentL; OuterL != OuterExitL;
2471 OuterL = OuterL->getParentLoop())
2472 UpdateLoop(*OuterL);
2473
2474#ifndef NDEBUG
2475 // Verify the entire loop structure to catch any incorrect updates before we
2476 // progress in the pass pipeline.
2477 LI.verify(DT);
2478#endif
2479
2480 // Now that we've unswitched something, make callbacks to report the changes.
2481 // For that we need to merge together the updated loops and the cloned loops
2482 // and check whether the original loop survived.
2483 SmallVector<Loop *, 4> SibLoops;
2484 for (Loop *UpdatedL : llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops))
2485 if (UpdatedL->getParentLoop() == ParentL)
2486 SibLoops.push_back(UpdatedL);
2487 UnswitchCB(IsStillLoop, PartiallyInvariant, SibLoops);
2488
2489 if (MSSAU && VerifyMemorySSA)
2490 MSSAU->getMemorySSA()->verifyMemorySSA();
2491
2492 if (BI)
2493 ++NumBranches;
2494 else
2495 ++NumSwitches;
2496}
2497
2498/// Recursively compute the cost of a dominator subtree based on the per-block
2499/// cost map provided.
2500///
2501/// The recursive computation is memozied into the provided DT-indexed cost map
2502/// to allow querying it for most nodes in the domtree without it becoming
2503/// quadratic.
2504static InstructionCost computeDomSubtreeCost(
2505 DomTreeNode &N,
2506 const SmallDenseMap<BasicBlock *, InstructionCost, 4> &BBCostMap,
2507 SmallDenseMap<DomTreeNode *, InstructionCost, 4> &DTCostMap) {
2508 // Don't accumulate cost (or recurse through) blocks not in our block cost
2509 // map and thus not part of the duplication cost being considered.
2510 auto BBCostIt = BBCostMap.find(N.getBlock());
2511 if (BBCostIt == BBCostMap.end())
2512 return 0;
2513
2514 // Lookup this node to see if we already computed its cost.
2515 auto DTCostIt = DTCostMap.find(&N);
2516 if (DTCostIt != DTCostMap.end())
2517 return DTCostIt->second;
2518
2519 // If not, we have to compute it. We can't use insert above and update
2520 // because computing the cost may insert more things into the map.
2521 InstructionCost Cost = std::accumulate(
2522 N.begin(), N.end(), BBCostIt->second,
2523 [&](InstructionCost Sum, DomTreeNode *ChildN) -> InstructionCost {
2524 return Sum + computeDomSubtreeCost(*ChildN, BBCostMap, DTCostMap);
2525 });
2526 bool Inserted = DTCostMap.insert({&N, Cost}).second;
2527 (void)Inserted;
2528 assert(Inserted && "Should not insert a node while visiting children!")(static_cast <bool> (Inserted && "Should not insert a node while visiting children!"
) ? void (0) : __assert_fail ("Inserted && \"Should not insert a node while visiting children!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2528, __extension__
__PRETTY_FUNCTION__))
;
2529 return Cost;
2530}
2531
2532/// Turns a llvm.experimental.guard intrinsic into implicit control flow branch,
2533/// making the following replacement:
2534///
2535/// --code before guard--
2536/// call void (i1, ...) @llvm.experimental.guard(i1 %cond) [ "deopt"() ]
2537/// --code after guard--
2538///
2539/// into
2540///
2541/// --code before guard--
2542/// br i1 %cond, label %guarded, label %deopt
2543///
2544/// guarded:
2545/// --code after guard--
2546///
2547/// deopt:
2548/// call void (i1, ...) @llvm.experimental.guard(i1 false) [ "deopt"() ]
2549/// unreachable
2550///
2551/// It also makes all relevant DT and LI updates, so that all structures are in
2552/// valid state after this transform.
2553static BranchInst *
2554turnGuardIntoBranch(IntrinsicInst *GI, Loop &L,
2555 SmallVectorImpl<BasicBlock *> &ExitBlocks,
2556 DominatorTree &DT, LoopInfo &LI, MemorySSAUpdater *MSSAU) {
2557 SmallVector<DominatorTree::UpdateType, 4> DTUpdates;
2558 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)
;
2559 BasicBlock *CheckBB = GI->getParent();
2560
2561 if (MSSAU && VerifyMemorySSA)
2562 MSSAU->getMemorySSA()->verifyMemorySSA();
2563
2564 // Remove all CheckBB's successors from DomTree. A block can be seen among
2565 // successors more than once, but for DomTree it should be added only once.
2566 SmallPtrSet<BasicBlock *, 4> Successors;
2567 for (auto *Succ : successors(CheckBB))
2568 if (Successors.insert(Succ).second)
2569 DTUpdates.push_back({DominatorTree::Delete, CheckBB, Succ});
2570
2571 Instruction *DeoptBlockTerm =
2572 SplitBlockAndInsertIfThen(GI->getArgOperand(0), GI, true);
2573 BranchInst *CheckBI = cast<BranchInst>(CheckBB->getTerminator());
2574 // SplitBlockAndInsertIfThen inserts control flow that branches to
2575 // DeoptBlockTerm if the condition is true. We want the opposite.
2576 CheckBI->swapSuccessors();
2577
2578 BasicBlock *GuardedBlock = CheckBI->getSuccessor(0);
2579 GuardedBlock->setName("guarded");
2580 CheckBI->getSuccessor(1)->setName("deopt");
2581 BasicBlock *DeoptBlock = CheckBI->getSuccessor(1);
2582
2583 // We now have a new exit block.
2584 ExitBlocks.push_back(CheckBI->getSuccessor(1));
2585
2586 if (MSSAU)
2587 MSSAU->moveAllAfterSpliceBlocks(CheckBB, GuardedBlock, GI);
2588
2589 GI->moveBefore(DeoptBlockTerm);
2590 GI->setArgOperand(0, ConstantInt::getFalse(GI->getContext()));
2591
2592 // Add new successors of CheckBB into DomTree.
2593 for (auto *Succ : successors(CheckBB))
2594 DTUpdates.push_back({DominatorTree::Insert, CheckBB, Succ});
2595
2596 // Now the blocks that used to be CheckBB's successors are GuardedBlock's
2597 // successors.
2598 for (auto *Succ : Successors)
2599 DTUpdates.push_back({DominatorTree::Insert, GuardedBlock, Succ});
2600
2601 // Make proper changes to DT.
2602 DT.applyUpdates(DTUpdates);
2603 // Inform LI of a new loop block.
2604 L.addBasicBlockToLoop(GuardedBlock, LI);
2605
2606 if (MSSAU) {
2607 MemoryDef *MD = cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(GI));
2608 MSSAU->moveToPlace(MD, DeoptBlock, MemorySSA::BeforeTerminator);
2609 if (VerifyMemorySSA)
2610 MSSAU->getMemorySSA()->verifyMemorySSA();
2611 }
2612
2613 ++NumGuards;
2614 return CheckBI;
2615}
2616
2617/// Cost multiplier is a way to limit potentially exponential behavior
2618/// of loop-unswitch. Cost is multipied in proportion of 2^number of unswitch
2619/// candidates available. Also accounting for the number of "sibling" loops with
2620/// the idea to account for previous unswitches that already happened on this
2621/// cluster of loops. There was an attempt to keep this formula simple,
2622/// just enough to limit the worst case behavior. Even if it is not that simple
2623/// now it is still not an attempt to provide a detailed heuristic size
2624/// prediction.
2625///
2626/// TODO: Make a proper accounting of "explosion" effect for all kinds of
2627/// unswitch candidates, making adequate predictions instead of wild guesses.
2628/// That requires knowing not just the number of "remaining" candidates but
2629/// also costs of unswitching for each of these candidates.
2630static int CalculateUnswitchCostMultiplier(
2631 Instruction &TI, Loop &L, LoopInfo &LI, DominatorTree &DT,
2632 ArrayRef<std::pair<Instruction *, TinyPtrVector<Value *>>>
2633 UnswitchCandidates) {
2634
2635 // Guards and other exiting conditions do not contribute to exponential
2636 // explosion as soon as they dominate the latch (otherwise there might be
2637 // another path to the latch remaining that does not allow to eliminate the
2638 // loop copy on unswitch).
2639 BasicBlock *Latch = L.getLoopLatch();
2640 BasicBlock *CondBlock = TI.getParent();
2641 if (DT.dominates(CondBlock, Latch) &&
2642 (isGuard(&TI) ||
2643 llvm::count_if(successors(&TI), [&L](BasicBlock *SuccBB) {
2644 return L.contains(SuccBB);
2645 }) <= 1)) {
2646 NumCostMultiplierSkipped++;
2647 return 1;
2648 }
2649
2650 auto *ParentL = L.getParentLoop();
2651 int SiblingsCount = (ParentL ? ParentL->getSubLoopsVector().size()
2652 : std::distance(LI.begin(), LI.end()));
2653 // Count amount of clones that all the candidates might cause during
2654 // unswitching. Branch/guard counts as 1, switch counts as log2 of its cases.
2655 int UnswitchedClones = 0;
2656 for (auto Candidate : UnswitchCandidates) {
2657 Instruction *CI = Candidate.first;
2658 BasicBlock *CondBlock = CI->getParent();
2659 bool SkipExitingSuccessors = DT.dominates(CondBlock, Latch);
2660 if (isGuard(CI)) {
2661 if (!SkipExitingSuccessors)
2662 UnswitchedClones++;
2663 continue;
2664 }
2665 int NonExitingSuccessors = llvm::count_if(
2666 successors(CondBlock), [SkipExitingSuccessors, &L](BasicBlock *SuccBB) {
2667 return !SkipExitingSuccessors || L.contains(SuccBB);
2668 });
2669 UnswitchedClones += Log2_32(NonExitingSuccessors);
2670 }
2671
2672 // Ignore up to the "unscaled candidates" number of unswitch candidates
2673 // when calculating the power-of-two scaling of the cost. The main idea
2674 // with this control is to allow a small number of unswitches to happen
2675 // and rely more on siblings multiplier (see below) when the number
2676 // of candidates is small.
2677 unsigned ClonesPower =
2678 std::max(UnswitchedClones - (int)UnswitchNumInitialUnscaledCandidates, 0);
2679
2680 // Allowing top-level loops to spread a bit more than nested ones.
2681 int SiblingsMultiplier =
2682 std::max((ParentL ? SiblingsCount
2683 : SiblingsCount / (int)UnswitchSiblingsToplevelDiv),
2684 1);
2685 // Compute the cost multiplier in a way that won't overflow by saturating
2686 // at an upper bound.
2687 int CostMultiplier;
2688 if (ClonesPower > Log2_32(UnswitchThreshold) ||
2689 SiblingsMultiplier > UnswitchThreshold)
2690 CostMultiplier = UnswitchThreshold;
2691 else
2692 CostMultiplier = std::min(SiblingsMultiplier * (1 << ClonesPower),
2693 (int)UnswitchThreshold);
2694
2695 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)
2696 << " (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)
2697 << (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)
2698 << " 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)
;
2699 return CostMultiplier;
2700}
2701
2702static bool unswitchBestCondition(
2703 Loop &L, DominatorTree &DT, LoopInfo &LI, AssumptionCache &AC,
2704 AAResults &AA, TargetTransformInfo &TTI,
2705 function_ref<void(bool, bool, ArrayRef<Loop *>)> UnswitchCB,
2706 ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
2707 function_ref<void(Loop &, StringRef)> DestroyLoopCB) {
2708 // Collect all invariant conditions within this loop (as opposed to an inner
2709 // loop which would be handled when visiting that inner loop).
2710 SmallVector<std::pair<Instruction *, TinyPtrVector<Value *>>, 4>
2711 UnswitchCandidates;
2712
2713 // Whether or not we should also collect guards in the loop.
2714 bool CollectGuards = false;
2715 if (UnswitchGuards) {
1
Assuming the condition is false
2
Taking false branch
2716 auto *GuardDecl = L.getHeader()->getParent()->getParent()->getFunction(
2717 Intrinsic::getName(Intrinsic::experimental_guard));
2718 if (GuardDecl && !GuardDecl->use_empty())
2719 CollectGuards = true;
2720 }
2721
2722 IVConditionInfo PartialIVInfo;
3
Calling implicit default constructor for 'IVConditionInfo'
5
Returning from default constructor for 'IVConditionInfo'
2723 for (auto *BB : L.blocks()) {
6
Assuming '__begin1' is equal to '__end1'
2724 if (LI.getLoopFor(BB) != &L)
2725 continue;
2726
2727 if (CollectGuards)
2728 for (auto &I : *BB)
2729 if (isGuard(&I)) {
2730 auto *Cond = cast<IntrinsicInst>(&I)->getArgOperand(0);
2731 // TODO: Support AND, OR conditions and partial unswitching.
2732 if (!isa<Constant>(Cond) && L.isLoopInvariant(Cond))
2733 UnswitchCandidates.push_back({&I, {Cond}});
2734 }
2735
2736 if (auto *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2737 // We can only consider fully loop-invariant switch conditions as we need
2738 // to completely eliminate the switch after unswitching.
2739 if (!isa<Constant>(SI->getCondition()) &&
2740 L.isLoopInvariant(SI->getCondition()) && !BB->getUniqueSuccessor())
2741 UnswitchCandidates.push_back({SI, {SI->getCondition()}});
2742 continue;
2743 }
2744
2745 auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
2746 if (!BI || !BI->isConditional() || isa<Constant>(BI->getCondition()) ||
2747 BI->getSuccessor(0) == BI->getSuccessor(1))
2748 continue;
2749
2750 // If BI's condition is 'select _, true, false', simplify it to confuse
2751 // matchers
2752 Value *Cond = BI->getCondition(), *CondNext;
2753 while (match(Cond, m_Select(m_Value(CondNext), m_One(), m_Zero())))
2754 Cond = CondNext;
2755 BI->setCondition(Cond);
2756
2757 if (isa<Constant>(Cond))
2758 continue;
2759
2760 if (L.isLoopInvariant(BI->getCondition())) {
2761 UnswitchCandidates.push_back({BI, {BI->getCondition()}});
2762 continue;
2763 }
2764
2765 Instruction &CondI = *cast<Instruction>(BI->getCondition());
2766 if (match(&CondI, m_CombineOr(m_LogicalAnd(), m_LogicalOr()))) {
2767 TinyPtrVector<Value *> Invariants =
2768 collectHomogenousInstGraphLoopInvariants(L, CondI, LI);
2769 if (Invariants.empty())
2770 continue;
2771
2772 UnswitchCandidates.push_back({BI, std::move(Invariants)});
2773 continue;
2774 }
2775 }
2776
2777 Instruction *PartialIVCondBranch = nullptr;
2778 if (MSSAU && !findOptionMDForLoop(&L, "llvm.loop.unswitch.partial.disable") &&
7
Assuming 'MSSAU' is null
8
Taking false branch
2779 !any_of(UnswitchCandidates, [&L](auto &TerminatorAndInvariants) {
2780 return TerminatorAndInvariants.first == L.getHeader()->getTerminator();
2781 })) {
2782 MemorySSA *MSSA = MSSAU->getMemorySSA();
2783 if (auto Info = hasPartialIVCondition(L, MSSAThreshold, *MSSA, AA)) {
2784 LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "simple-loop-unswitch: Found partially invariant condition "
<< *Info->InstToDuplicate[0] << "\n"; } } while
(false)
2785 dbgs() << "simple-loop-unswitch: Found partially invariant condition "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "simple-loop-unswitch: Found partially invariant condition "
<< *Info->InstToDuplicate[0] << "\n"; } } while
(false)
2786 << *Info->InstToDuplicate[0] << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "simple-loop-unswitch: Found partially invariant condition "
<< *Info->InstToDuplicate[0] << "\n"; } } while
(false)
;
2787 PartialIVInfo = *Info;
2788 PartialIVCondBranch = L.getHeader()->getTerminator();
2789 TinyPtrVector<Value *> ValsToDuplicate;
2790 for (auto *Inst : Info->InstToDuplicate)
2791 ValsToDuplicate.push_back(Inst);
2792 UnswitchCandidates.push_back(
2793 {L.getHeader()->getTerminator(), std::move(ValsToDuplicate)});
2794 }
2795 }
2796
2797 // If we didn't find any candidates, we're done.
2798 if (UnswitchCandidates.empty())
9
Taking false branch
2799 return false;
2800
2801 // Check if there are irreducible CFG cycles in this loop. If so, we cannot
2802 // easily unswitch non-trivial edges out of the loop. Doing so might turn the
2803 // irreducible control flow into reducible control flow and introduce new
2804 // loops "out of thin air". If we ever discover important use cases for doing
2805 // this, we can add support to loop unswitch, but it is a lot of complexity
2806 // for what seems little or no real world benefit.
2807 LoopBlocksRPO RPOT(&L);
2808 RPOT.perform(&LI);
2809 if (containsIrreducibleCFG<const BasicBlock *>(RPOT, LI))
10
Taking false branch
2810 return false;
2811
2812 SmallVector<BasicBlock *, 4> ExitBlocks;
2813 L.getUniqueExitBlocks(ExitBlocks);
2814
2815 // We cannot unswitch if exit blocks contain a cleanuppad/catchswitch
2816 // instruction as we don't know how to split those exit blocks.
2817 // FIXME: We should teach SplitBlock to handle this and remove this
2818 // restriction.
2819 for (auto *ExitBB : ExitBlocks) {
11
Assuming '__begin1' is equal to '__end1'
2820 auto *I = ExitBB->getFirstNonPHI();
2821 if (isa<CleanupPadInst>(I) || isa<CatchSwitchInst>(I)) {
2822 LLVM_DEBUG(dbgs() << "Cannot unswitch because of cleanuppad/catchswitch "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Cannot unswitch because of cleanuppad/catchswitch "
"in exit block\n"; } } while (false)
2823 "in exit block\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Cannot unswitch because of cleanuppad/catchswitch "
"in exit block\n"; } } while (false)
;
2824 return false;
2825 }
2826 }
2827
2828 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)
12
Assuming 'DebugFlag' is false
13
Loop condition is false. Exiting loop
2829 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)
2830 << " 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)
;
2831
2832 // Given that unswitching these terminators will require duplicating parts of
2833 // the loop, so we need to be able to model that cost. Compute the ephemeral
2834 // values and set up a data structure to hold per-BB costs. We cache each
2835 // block's cost so that we don't recompute this when considering different
2836 // subsets of the loop for duplication during unswitching.
2837 SmallPtrSet<const Value *, 4> EphValues;
2838 CodeMetrics::collectEphemeralValues(&L, &AC, EphValues);
2839 SmallDenseMap<BasicBlock *, InstructionCost, 4> BBCostMap;
2840
2841 // Compute the cost of each block, as well as the total loop cost. Also, bail
2842 // out if we see instructions which are incompatible with loop unswitching
2843 // (convergent, noduplicate, or cross-basic-block tokens).
2844 // FIXME: We might be able to safely handle some of these in non-duplicated
2845 // regions.
2846 TargetTransformInfo::TargetCostKind CostKind =
2847 L.getHeader()->getParent()->hasMinSize()
14
Assuming the condition is false
15
'?' condition is false
2848 ? TargetTransformInfo::TCK_CodeSize
2849 : TargetTransformInfo::TCK_SizeAndLatency;
2850 InstructionCost LoopCost = 0;
2851 for (auto *BB : L.blocks()) {
16
Assuming '__begin1' is equal to '__end1'
2852 InstructionCost Cost = 0;
2853 for (auto &I : *BB) {
2854 if (EphValues.count(&I))
2855 continue;
2856
2857 if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB))
2858 return false;
2859 if (auto *CB = dyn_cast<CallBase>(&I))
2860 if (CB->isConvergent() || CB->cannotDuplicate())
2861 return false;
2862
2863 Cost += TTI.getUserCost(&I, CostKind);
2864 }
2865 assert(Cost >= 0 && "Must not have negative costs!")(static_cast <bool> (Cost >= 0 && "Must not have negative costs!"
) ? void (0) : __assert_fail ("Cost >= 0 && \"Must not have negative costs!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2865, __extension__
__PRETTY_FUNCTION__))
;
2866 LoopCost += Cost;
2867 assert(LoopCost >= 0 && "Must not have negative loop costs!")(static_cast <bool> (LoopCost >= 0 && "Must not have negative loop costs!"
) ? void (0) : __assert_fail ("LoopCost >= 0 && \"Must not have negative loop costs!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2867, __extension__
__PRETTY_FUNCTION__))
;
2868 BBCostMap[BB] = Cost;
2869 }
2870 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
2871
2872 // Now we find the best candidate by searching for the one with the following
2873 // properties in order:
2874 //
2875 // 1) An unswitching cost below the threshold
2876 // 2) The smallest number of duplicated unswitch candidates (to avoid
2877 // creating redundant subsequent unswitching)
2878 // 3) The smallest cost after unswitching.
2879 //
2880 // We prioritize reducing fanout of unswitch candidates provided the cost
2881 // remains below the threshold because this has a multiplicative effect.
2882 //
2883 // This requires memoizing each dominator subtree to avoid redundant work.
2884 //
2885 // FIXME: Need to actually do the number of candidates part above.
2886 SmallDenseMap<DomTreeNode *, InstructionCost, 4> DTCostMap;
2887 // Given a terminator which might be unswitched, computes the non-duplicated
2888 // cost for that terminator.
2889 auto ComputeUnswitchedCost = [&](Instruction &TI,
2890 bool FullUnswitch) -> InstructionCost {
2891 BasicBlock &BB = *TI.getParent();
2892 SmallPtrSet<BasicBlock *, 4> Visited;
2893
2894 InstructionCost Cost = 0;
2895 for (BasicBlock *SuccBB : successors(&BB)) {
2896 // Don't count successors more than once.
2897 if (!Visited.insert(SuccBB).second)
23
Assuming field 'second' is true
24
Taking false branch
2898 continue;
2899
2900 // If this is a partial unswitch candidate, then it must be a conditional
2901 // branch with a condition of either `or`, `and`, their corresponding
2902 // select forms or partially invariant instructions. In that case, one of
2903 // the successors is necessarily duplicated, so don't even try to remove
2904 // its cost.
2905 if (!FullUnswitch
24.1
'FullUnswitch' is false
24.1
'FullUnswitch' is false
) {
25
Taking true branch
2906 auto &BI = cast<BranchInst>(TI);
26
'TI' is a 'BranchInst'
2907 if (match(BI.getCondition(), m_LogicalAnd())) {
27
Taking false branch
2908 if (SuccBB == BI.getSuccessor(1))
2909 continue;
2910 } else if (match(BI.getCondition(), m_LogicalOr())) {
2911 if (SuccBB == BI.getSuccessor(0))
2912 continue;
2913 } else if ((PartialIVInfo.KnownValue->isOneValue() &&
28
Called C++ object pointer is null
2914 SuccBB == BI.getSuccessor(0)) ||
2915 (!PartialIVInfo.KnownValue->isOneValue() &&
2916 SuccBB == BI.getSuccessor(1)))
2917 continue;
2918 }
2919
2920 // This successor's domtree will not need to be duplicated after
2921 // unswitching if the edge to the successor dominates it (and thus the
2922 // entire tree). This essentially means there is no other path into this
2923 // subtree and so it will end up live in only one clone of the loop.
2924 if (SuccBB->getUniquePredecessor() ||
2925 llvm::all_of(predecessors(SuccBB), [&](BasicBlock *PredBB) {
2926 return PredBB == &BB || DT.dominates(SuccBB, PredBB);
2927 })) {
2928 Cost += computeDomSubtreeCost(*DT[SuccBB], BBCostMap, DTCostMap);
2929 assert(Cost <= LoopCost &&(static_cast <bool> (Cost <= LoopCost && "Non-duplicated cost should never exceed total loop cost!"
) ? void (0) : __assert_fail ("Cost <= LoopCost && \"Non-duplicated cost should never exceed total loop cost!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2930, __extension__
__PRETTY_FUNCTION__))
2930 "Non-duplicated cost should never exceed total loop cost!")(static_cast <bool> (Cost <= LoopCost && "Non-duplicated cost should never exceed total loop cost!"
) ? void (0) : __assert_fail ("Cost <= LoopCost && \"Non-duplicated cost should never exceed total loop cost!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2930, __extension__
__PRETTY_FUNCTION__))
;
2931 }
2932 }
2933
2934 // Now scale the cost by the number of unique successors minus one. We
2935 // subtract one because there is already at least one copy of the entire
2936 // loop. This is computing the new cost of unswitching a condition.
2937 // Note that guards always have 2 unique successors that are implicit and
2938 // will be materialized if we decide to unswitch it.
2939 int SuccessorsCount = isGuard(&TI) ? 2 : Visited.size();
2940 assert(SuccessorsCount > 1 &&(static_cast <bool> (SuccessorsCount > 1 && "Cannot unswitch a condition without multiple distinct successors!"
) ? void (0) : __assert_fail ("SuccessorsCount > 1 && \"Cannot unswitch a condition without multiple distinct successors!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2941, __extension__
__PRETTY_FUNCTION__))
2941 "Cannot unswitch a condition without multiple distinct successors!")(static_cast <bool> (SuccessorsCount > 1 && "Cannot unswitch a condition without multiple distinct successors!"
) ? void (0) : __assert_fail ("SuccessorsCount > 1 && \"Cannot unswitch a condition without multiple distinct successors!\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2941, __extension__
__PRETTY_FUNCTION__))
;
2942 return (LoopCost - Cost) * (SuccessorsCount - 1);
2943 };
2944 Instruction *BestUnswitchTI = nullptr;
2945 InstructionCost BestUnswitchCost = 0;
2946 ArrayRef<Value *> BestUnswitchInvariants;
2947 for (auto &TerminatorAndInvariants : UnswitchCandidates) {
19
Assuming '__begin1' is not equal to '__end1'
2948 Instruction &TI = *TerminatorAndInvariants.first;
2949 ArrayRef<Value *> Invariants = TerminatorAndInvariants.second;
2950 BranchInst *BI = dyn_cast<BranchInst>(&TI);
20
Assuming the object is a 'BranchInst'
2951 InstructionCost CandidateCost = ComputeUnswitchedCost(
22
Calling 'operator()'
2952 TI, /*FullUnswitch*/ !BI
20.1
'BI' is non-null
20.1
'BI' is non-null
|| (Invariants.size() == 1 &&
21
Assuming the condition is false
2953 Invariants[0] == BI->getCondition()));
2954 // Calculate cost multiplier which is a tool to limit potentially
2955 // exponential behavior of loop-unswitch.
2956 if (EnableUnswitchCostMultiplier) {
2957 int CostMultiplier =
2958 CalculateUnswitchCostMultiplier(TI, L, LI, DT, UnswitchCandidates);
2959 assert((static_cast <bool> ((CostMultiplier > 0 && CostMultiplier
<= UnswitchThreshold) && "cost multiplier needs to be in the range of 1..UnswitchThreshold"
) ? void (0) : __assert_fail ("(CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold) && \"cost multiplier needs to be in the range of 1..UnswitchThreshold\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2961, __extension__
__PRETTY_FUNCTION__))
2960 (CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold) &&(static_cast <bool> ((CostMultiplier > 0 && CostMultiplier
<= UnswitchThreshold) && "cost multiplier needs to be in the range of 1..UnswitchThreshold"
) ? void (0) : __assert_fail ("(CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold) && \"cost multiplier needs to be in the range of 1..UnswitchThreshold\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2961, __extension__
__PRETTY_FUNCTION__))
2961 "cost multiplier needs to be in the range of 1..UnswitchThreshold")(static_cast <bool> ((CostMultiplier > 0 && CostMultiplier
<= UnswitchThreshold) && "cost multiplier needs to be in the range of 1..UnswitchThreshold"
) ? void (0) : __assert_fail ("(CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold) && \"cost multiplier needs to be in the range of 1..UnswitchThreshold\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2961, __extension__
__PRETTY_FUNCTION__))
;
2962 CandidateCost *= CostMultiplier;
2963 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)
2964 << " (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)
2965 << " 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)
;
2966 } else {
2967 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)
2968 << " 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)
;
2969 }
2970
2971 if (!BestUnswitchTI || CandidateCost < BestUnswitchCost) {
2972 BestUnswitchTI = &TI;
2973 BestUnswitchCost = CandidateCost;
2974 BestUnswitchInvariants = Invariants;
2975 }
2976 }
2977 assert(BestUnswitchTI && "Failed to find loop unswitch candidate")(static_cast <bool> (BestUnswitchTI && "Failed to find loop unswitch candidate"
) ? void (0) : __assert_fail ("BestUnswitchTI && \"Failed to find loop unswitch candidate\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 2977, __extension__
__PRETTY_FUNCTION__))
;
2978
2979 if (BestUnswitchCost >= UnswitchThreshold) {
2980 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)
2981 << BestUnswitchCost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Cannot unswitch, lowest cost found: "
<< BestUnswitchCost << "\n"; } } while (false)
;
2982 return false;
2983 }
2984
2985 if (BestUnswitchTI != PartialIVCondBranch)
2986 PartialIVInfo.InstToDuplicate.clear();
2987
2988 // If the best candidate is a guard, turn it into a branch.
2989 if (isGuard(BestUnswitchTI))
2990 BestUnswitchTI = turnGuardIntoBranch(cast<IntrinsicInst>(BestUnswitchTI), L,
2991 ExitBlocks, DT, LI, MSSAU);
2992
2993 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)
2994 << BestUnswitchCost << ") terminator: " << *BestUnswitchTIdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Unswitching non-trivial (cost = "
<< BestUnswitchCost << ") terminator: " <<
*BestUnswitchTI << "\n"; } } while (false)
2995 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Unswitching non-trivial (cost = "
<< BestUnswitchCost << ") terminator: " <<
*BestUnswitchTI << "\n"; } } while (false)
;
2996 unswitchNontrivialInvariants(L, *BestUnswitchTI, BestUnswitchInvariants,
2997 ExitBlocks, PartialIVInfo, DT, LI, AC,
2998 UnswitchCB, SE, MSSAU, DestroyLoopCB);
2999 return true;
3000}
3001
3002/// Unswitch control flow predicated on loop invariant conditions.
3003///
3004/// This first hoists all branches or switches which are trivial (IE, do not
3005/// require duplicating any part of the loop) out of the loop body. It then
3006/// looks at other loop invariant control flows and tries to unswitch those as
3007/// well by cloning the loop if the result is small enough.
3008///
3009/// The `DT`, `LI`, `AC`, `AA`, `TTI` parameters are required analyses that are
3010/// also updated based on the unswitch. The `MSSA` analysis is also updated if
3011/// valid (i.e. its use is enabled).
3012///
3013/// If either `NonTrivial` is true or the flag `EnableNonTrivialUnswitch` is
3014/// true, we will attempt to do non-trivial unswitching as well as trivial
3015/// unswitching.
3016///
3017/// The `UnswitchCB` callback provided will be run after unswitching is
3018/// complete, with the first parameter set to `true` if the provided loop
3019/// remains a loop, and a list of new sibling loops created.
3020///
3021/// If `SE` is non-null, we will update that analysis based on the unswitching
3022/// done.
3023static bool
3024unswitchLoop(Loop &L, DominatorTree &DT, LoopInfo &LI, AssumptionCache &AC,
3025 AAResults &AA, TargetTransformInfo &TTI, bool Trivial,
3026 bool NonTrivial,
3027 function_ref<void(bool, bool, ArrayRef<Loop *>)> UnswitchCB,
3028 ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
3029 function_ref<void(Loop &, StringRef)> DestroyLoopCB) {
3030 assert(L.isRecursivelyLCSSAForm(DT, LI) &&(static_cast <bool> (L.isRecursivelyLCSSAForm(DT, LI) &&
"Loops must be in LCSSA form before unswitching.") ? void (0
) : __assert_fail ("L.isRecursivelyLCSSAForm(DT, LI) && \"Loops must be in LCSSA form before unswitching.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 3031, __extension__
__PRETTY_FUNCTION__))
3031 "Loops must be in LCSSA form before unswitching.")(static_cast <bool> (L.isRecursivelyLCSSAForm(DT, LI) &&
"Loops must be in LCSSA form before unswitching.") ? void (0
) : __assert_fail ("L.isRecursivelyLCSSAForm(DT, LI) && \"Loops must be in LCSSA form before unswitching.\""
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 3031, __extension__
__PRETTY_FUNCTION__))
;
3032
3033 // Must be in loop simplified form: we need a preheader and dedicated exits.
3034 if (!L.isLoopSimplifyForm())
3035 return false;
3036
3037 // Try trivial unswitch first before loop over other basic blocks in the loop.
3038 if (Trivial && unswitchAllTrivialConditions(L, DT, LI, SE, MSSAU)) {
3039 // If we unswitched successfully we will want to clean up the loop before
3040 // processing it further so just mark it as unswitched and return.
3041 UnswitchCB(/*CurrentLoopValid*/ true, false, {});
3042 return true;
3043 }
3044
3045 // Check whether we should continue with non-trivial conditions.
3046 // EnableNonTrivialUnswitch: Global variable that forces non-trivial
3047 // unswitching for testing and debugging.
3048 // NonTrivial: Parameter that enables non-trivial unswitching for this
3049 // invocation of the transform. But this should be allowed only
3050 // for targets without branch divergence.
3051 //
3052 // FIXME: If divergence analysis becomes available to a loop
3053 // transform, we should allow unswitching for non-trivial uniform
3054 // branches even on targets that have divergence.
3055 // https://bugs.llvm.org/show_bug.cgi?id=48819
3056 bool ContinueWithNonTrivial =
3057 EnableNonTrivialUnswitch || (NonTrivial && !TTI.hasBranchDivergence());
3058 if (!ContinueWithNonTrivial)
3059 return false;
3060
3061 // Skip non-trivial unswitching for optsize functions.
3062 if (L.getHeader()->getParent()->hasOptSize())
3063 return false;
3064
3065 // Skip non-trivial unswitching for loops that cannot be cloned.
3066 if (!L.isSafeToClone())
3067 return false;
3068
3069 // For non-trivial unswitching, because it often creates new loops, we rely on
3070 // the pass manager to iterate on the loops rather than trying to immediately
3071 // reach a fixed point. There is no substantial advantage to iterating
3072 // internally, and if any of the new loops are simplified enough to contain
3073 // trivial unswitching we want to prefer those.
3074
3075 // Try to unswitch the best invariant condition. We prefer this full unswitch to
3076 // a partial unswitch when possible below the threshold.
3077 if (unswitchBestCondition(L, DT, LI, AC, AA, TTI, UnswitchCB, SE, MSSAU,
3078 DestroyLoopCB))
3079 return true;
3080
3081 // No other opportunities to unswitch.
3082 return false;
3083}
3084
3085PreservedAnalyses SimpleLoopUnswitchPass::run(Loop &L, LoopAnalysisManager &AM,
3086 LoopStandardAnalysisResults &AR,
3087 LPMUpdater &U) {
3088 Function &F = *L.getHeader()->getParent();
3089 (void)F;
3090
3091 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)
3092 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Unswitching loop in "
<< F.getName() << ": " << L << "\n";
} } while (false)
;
3093
3094 // Save the current loop name in a variable so that we can report it even
3095 // after it has been deleted.
3096 std::string LoopName = std::string(L.getName());
3097
3098 auto UnswitchCB = [&L, &U, &LoopName](bool CurrentLoopValid,
3099 bool PartiallyInvariant,
3100 ArrayRef<Loop *> NewLoops) {
3101 // If we did a non-trivial unswitch, we have added new (cloned) loops.
3102 if (!NewLoops.empty())
3103 U.addSiblingLoops(NewLoops);
3104
3105 // If the current loop remains valid, we should revisit it to catch any
3106 // other unswitch opportunities. Otherwise, we need to mark it as deleted.
3107 if (CurrentLoopValid) {
3108 if (PartiallyInvariant) {
3109 // Mark the new loop as partially unswitched, to avoid unswitching on
3110 // the same condition again.
3111 auto &Context = L.getHeader()->getContext();
3112 MDNode *DisableUnswitchMD = MDNode::get(
3113 Context,
3114 MDString::get(Context, "llvm.loop.unswitch.partial.disable"));
3115 MDNode *NewLoopID = makePostTransformationMetadata(
3116 Context, L.getLoopID(), {"llvm.loop.unswitch.partial"},
3117 {DisableUnswitchMD});
3118 L.setLoopID(NewLoopID);
3119 } else
3120 U.revisitCurrentLoop();
3121 } else
3122 U.markLoopAsDeleted(L, LoopName);
3123 };
3124
3125 auto DestroyLoopCB = [&U](Loop &L, StringRef Name) {
3126 U.markLoopAsDeleted(L, Name);
3127 };
3128
3129 Optional<MemorySSAUpdater> MSSAU;
3130 if (AR.MSSA) {
3131 MSSAU = MemorySSAUpdater(AR.MSSA);
3132 if (VerifyMemorySSA)
3133 AR.MSSA->verifyMemorySSA();
3134 }
3135 if (!unswitchLoop(L, AR.DT, AR.LI, AR.AC, AR.AA, AR.TTI, Trivial, NonTrivial,
3136 UnswitchCB, &AR.SE,
3137 MSSAU.hasValue() ? MSSAU.getPointer() : nullptr,
3138 DestroyLoopCB))
3139 return PreservedAnalyses::all();
3140
3141 if (AR.MSSA && VerifyMemorySSA)
3142 AR.MSSA->verifyMemorySSA();
3143
3144 // Historically this pass has had issues with the dominator tree so verify it
3145 // in asserts builds.
3146 assert(AR.DT.verify(DominatorTree::VerificationLevel::Fast))(static_cast <bool> (AR.DT.verify(DominatorTree::VerificationLevel
::Fast)) ? void (0) : __assert_fail ("AR.DT.verify(DominatorTree::VerificationLevel::Fast)"
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 3146, __extension__
__PRETTY_FUNCTION__))
;
3147
3148 auto PA = getLoopPassPreservedAnalyses();
3149 if (AR.MSSA)
3150 PA.preserve<MemorySSAAnalysis>();
3151 return PA;
3152}
3153
3154void SimpleLoopUnswitchPass::printPipeline(
3155 raw_ostream &OS, function_ref<StringRef(StringRef)> MapClassName2PassName) {
3156 static_cast<PassInfoMixin<SimpleLoopUnswitchPass> *>(this)->printPipeline(
3157 OS, MapClassName2PassName);
3158
3159 OS << "<";
3160 OS << (NonTrivial ? "" : "no-") << "nontrivial;";
3161 OS << (Trivial ? "" : "no-") << "trivial";
3162 OS << ">";
3163}
3164
3165namespace {
3166
3167class SimpleLoopUnswitchLegacyPass : public LoopPass {
3168 bool NonTrivial;
3169
3170public:
3171 static char ID; // Pass ID, replacement for typeid
3172
3173 explicit SimpleLoopUnswitchLegacyPass(bool NonTrivial = false)
3174 : LoopPass(ID), NonTrivial(NonTrivial) {
3175 initializeSimpleLoopUnswitchLegacyPassPass(
3176 *PassRegistry::getPassRegistry());
3177 }
3178
3179 bool runOnLoop(Loop *L, LPPassManager &LPM) override;
3180
3181 void getAnalysisUsage(AnalysisUsage &AU) const override {
3182 AU.addRequired<AssumptionCacheTracker>();
3183 AU.addRequired<TargetTransformInfoWrapperPass>();
3184 AU.addRequired<MemorySSAWrapperPass>();
3185 AU.addPreserved<MemorySSAWrapperPass>();
3186 getLoopAnalysisUsage(AU);
3187 }
3188};
3189
3190} // end anonymous namespace
3191
3192bool SimpleLoopUnswitchLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) {
3193 if (skipLoop(L))
3194 return false;
3195
3196 Function &F = *L->getHeader()->getParent();
3197
3198 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)
3199 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Unswitching loop in "
<< F.getName() << ": " << *L << "\n"
; } } while (false)
;
3200
3201 auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
3202 auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
3203 auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
3204 auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
3205 auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
3206 MemorySSA *MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
3207 MemorySSAUpdater MSSAU(MSSA);
3208
3209 auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
3210 auto *SE = SEWP ? &SEWP->getSE() : nullptr;
3211
3212 auto UnswitchCB = [&L, &LPM](bool CurrentLoopValid, bool PartiallyInvariant,
3213 ArrayRef<Loop *> NewLoops) {
3214 // If we did a non-trivial unswitch, we have added new (cloned) loops.
3215 for (auto *NewL : NewLoops)
3216 LPM.addLoop(*NewL);
3217
3218 // If the current loop remains valid, re-add it to the queue. This is
3219 // a little wasteful as we'll finish processing the current loop as well,
3220 // but it is the best we can do in the old PM.
3221 if (CurrentLoopValid) {
3222 // If the current loop has been unswitched using a partially invariant
3223 // condition, we should not re-add the current loop to avoid unswitching
3224 // on the same condition again.
3225 if (!PartiallyInvariant)
3226 LPM.addLoop(*L);
3227 } else
3228 LPM.markLoopAsDeleted(*L);
3229 };
3230
3231 auto DestroyLoopCB = [&LPM](Loop &L, StringRef /* Name */) {
3232 LPM.markLoopAsDeleted(L);
3233 };
3234
3235 if (VerifyMemorySSA)
3236 MSSA->verifyMemorySSA();
3237
3238 bool Changed = unswitchLoop(*L, DT, LI, AC, AA, TTI, true, NonTrivial,
3239 UnswitchCB, SE, &MSSAU, DestroyLoopCB);
3240
3241 if (VerifyMemorySSA)
3242 MSSA->verifyMemorySSA();
3243
3244 // Historically this pass has had issues with the dominator tree so verify it
3245 // in asserts builds.
3246 assert(DT.verify(DominatorTree::VerificationLevel::Fast))(static_cast <bool> (DT.verify(DominatorTree::VerificationLevel
::Fast)) ? void (0) : __assert_fail ("DT.verify(DominatorTree::VerificationLevel::Fast)"
, "llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp", 3246, __extension__
__PRETTY_FUNCTION__))
;
3247
3248 return Changed;
3249}
3250
3251char SimpleLoopUnswitchLegacyPass::ID = 0;
3252INITIALIZE_PASS_BEGIN(SimpleLoopUnswitchLegacyPass, "simple-loop-unswitch",static void *initializeSimpleLoopUnswitchLegacyPassPassOnce(PassRegistry
&Registry) {
3253 "Simple unswitch loops", false, false)static void *initializeSimpleLoopUnswitchLegacyPassPassOnce(PassRegistry
&Registry) {
3254INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)initializeAssumptionCacheTrackerPass(Registry);
3255INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
3256INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)initializeLoopInfoWrapperPassPass(Registry);
3257INITIALIZE_PASS_DEPENDENCY(LoopPass)initializeLoopPassPass(Registry);
3258INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)initializeMemorySSAWrapperPassPass(Registry);
3259INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)initializeTargetTransformInfoWrapperPassPass(Registry);
3260INITIALIZE_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
)); }
3261 "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
)); }
3262
3263Pass *llvm::createSimpleLoopUnswitchLegacyPass(bool NonTrivial) {
3264 return new SimpleLoopUnswitchLegacyPass(NonTrivial);
3265}

/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/llvm/include/llvm/Transforms/Utils/LoopUtils.h

1//===- llvm/Transforms/Utils/LoopUtils.h - Loop utilities -------*- 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 some loop transformation utilities.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_TRANSFORMS_UTILS_LOOPUTILS_H
14#define LLVM_TRANSFORMS_UTILS_LOOPUTILS_H
15
16#include "llvm/Analysis/IVDescriptors.h"
17#include "llvm/Transforms/Utils/ValueMapper.h"
18
19namespace llvm {
20
21template <typename T> class DomTreeNodeBase;
22using DomTreeNode = DomTreeNodeBase<BasicBlock>;
23class StringRef;
24class AnalysisUsage;
25class TargetTransformInfo;
26class AAResults;
27class BasicBlock;
28class BlockFrequencyInfo;
29class ICFLoopSafetyInfo;
30class IRBuilderBase;
31class Loop;
32class LoopInfo;
33class MemoryAccess;
34class MemorySSA;
35class MemorySSAUpdater;
36class OptimizationRemarkEmitter;
37class PredIteratorCache;
38class ScalarEvolution;
39class SCEV;
40class SCEVExpander;
41class TargetLibraryInfo;
42class LPPassManager;
43class Instruction;
44struct RuntimeCheckingPtrGroup;
45typedef std::pair<const RuntimeCheckingPtrGroup *,
46 const RuntimeCheckingPtrGroup *>
47 RuntimePointerCheck;
48
49template <typename T> class Optional;
50template <typename T, unsigned N> class SmallSetVector;
51template <typename T, unsigned N> class SmallPriorityWorklist;
52
53BasicBlock *InsertPreheaderForLoop(Loop *L, DominatorTree *DT, LoopInfo *LI,
54 MemorySSAUpdater *MSSAU, bool PreserveLCSSA);
55
56/// Ensure that all exit blocks of the loop are dedicated exits.
57///
58/// For any loop exit block with non-loop predecessors, we split the loop
59/// predecessors to use a dedicated loop exit block. We update the dominator
60/// tree and loop info if provided, and will preserve LCSSA if requested.
61bool formDedicatedExitBlocks(Loop *L, DominatorTree *DT, LoopInfo *LI,
62 MemorySSAUpdater *MSSAU, bool PreserveLCSSA);
63
64/// Ensures LCSSA form for every instruction from the Worklist in the scope of
65/// innermost containing loop.
66///
67/// For the given instruction which have uses outside of the loop, an LCSSA PHI
68/// node is inserted and the uses outside the loop are rewritten to use this
69/// node.
70///
71/// LoopInfo and DominatorTree are required and, since the routine makes no
72/// changes to CFG, preserved.
73///
74/// Returns true if any modifications are made.
75///
76/// This function may introduce unused PHI nodes. If \p PHIsToRemove is not
77/// nullptr, those are added to it (before removing, the caller has to check if
78/// they still do not have any uses). Otherwise the PHIs are directly removed.
79bool formLCSSAForInstructions(
80 SmallVectorImpl<Instruction *> &Worklist, const DominatorTree &DT,
81 const LoopInfo &LI, ScalarEvolution *SE, IRBuilderBase &Builder,
82 SmallVectorImpl<PHINode *> *PHIsToRemove = nullptr);
83
84/// Put loop into LCSSA form.
85///
86/// Looks at all instructions in the loop which have uses outside of the
87/// current loop. For each, an LCSSA PHI node is inserted and the uses outside
88/// the loop are rewritten to use this node. Sub-loops must be in LCSSA form
89/// already.
90///
91/// LoopInfo and DominatorTree are required and preserved.
92///
93/// If ScalarEvolution is passed in, it will be preserved.
94///
95/// Returns true if any modifications are made to the loop.
96bool formLCSSA(Loop &L, const DominatorTree &DT, const LoopInfo *LI,
97 ScalarEvolution *SE);
98
99/// Put a loop nest into LCSSA form.
100///
101/// This recursively forms LCSSA for a loop nest.
102///
103/// LoopInfo and DominatorTree are required and preserved.
104///
105/// If ScalarEvolution is passed in, it will be preserved.
106///
107/// Returns true if any modifications are made to the loop.
108bool formLCSSARecursively(Loop &L, const DominatorTree &DT, const LoopInfo *LI,
109 ScalarEvolution *SE);
110
111/// Flags controlling how much is checked when sinking or hoisting
112/// instructions. The number of memory access in the loop (and whether there
113/// are too many) is determined in the constructors when using MemorySSA.
114class SinkAndHoistLICMFlags {
115public:
116 // Explicitly set limits.
117 SinkAndHoistLICMFlags(unsigned LicmMssaOptCap,
118 unsigned LicmMssaNoAccForPromotionCap, bool IsSink,
119 Loop *L = nullptr, MemorySSA *MSSA = nullptr);
120 // Use default limits.
121 SinkAndHoistLICMFlags(bool IsSink, Loop *L = nullptr,
122 MemorySSA *MSSA = nullptr);
123
124 void setIsSink(bool B) { IsSink = B; }
125 bool getIsSink() { return IsSink; }
126 bool tooManyMemoryAccesses() { return NoOfMemAccTooLarge; }
127 bool tooManyClobberingCalls() { return LicmMssaOptCounter >= LicmMssaOptCap; }
128 void incrementClobberingCalls() { ++LicmMssaOptCounter; }
129
130protected:
131 bool NoOfMemAccTooLarge = false;
132 unsigned LicmMssaOptCounter = 0;
133 unsigned LicmMssaOptCap;
134 unsigned LicmMssaNoAccForPromotionCap;
135 bool IsSink;
136};
137
138/// Walk the specified region of the CFG (defined by all blocks
139/// dominated by the specified block, and that are in the current loop) in
140/// reverse depth first order w.r.t the DominatorTree. This allows us to visit
141/// uses before definitions, allowing us to sink a loop body in one pass without
142/// iteration. Takes DomTreeNode, AAResults, LoopInfo, DominatorTree,
143/// BlockFrequencyInfo, TargetLibraryInfo, Loop, AliasSet information for all
144/// instructions of the loop and loop safety information as
145/// arguments. Diagnostics is emitted via \p ORE. It returns changed status.
146/// \p CurLoop is a loop to do sinking on. \p OutermostLoop is used only when
147/// this function is called by \p sinkRegionForLoopNest.
148bool sinkRegion(DomTreeNode *, AAResults *, LoopInfo *, DominatorTree *,
149 BlockFrequencyInfo *, TargetLibraryInfo *,
150 TargetTransformInfo *, Loop *CurLoop, MemorySSAUpdater &,
151 ICFLoopSafetyInfo *, SinkAndHoistLICMFlags &,
152 OptimizationRemarkEmitter *, Loop *OutermostLoop = nullptr);
153
154/// Call sinkRegion on loops contained within the specified loop
155/// in order from innermost to outermost.
156bool sinkRegionForLoopNest(DomTreeNode *, AAResults *, LoopInfo *,
157 DominatorTree *, BlockFrequencyInfo *,
158 TargetLibraryInfo *, TargetTransformInfo *, Loop *,
159 MemorySSAUpdater &, ICFLoopSafetyInfo *,
160 SinkAndHoistLICMFlags &,
161 OptimizationRemarkEmitter *);
162
163/// Walk the specified region of the CFG (defined by all blocks
164/// dominated by the specified block, and that are in the current loop) in depth
165/// first order w.r.t the DominatorTree. This allows us to visit definitions
166/// before uses, allowing us to hoist a loop body in one pass without iteration.
167/// Takes DomTreeNode, AAResults, LoopInfo, DominatorTree,
168/// BlockFrequencyInfo, TargetLibraryInfo, Loop, AliasSet information for all
169/// instructions of the loop and loop safety information as arguments.
170/// Diagnostics is emitted via \p ORE. It returns changed status.
171/// \p AllowSpeculation is whether values should be hoisted even if they are not
172/// guaranteed to execute in the loop, but are safe to speculatively execute.
173bool hoistRegion(DomTreeNode *, AAResults *, LoopInfo *, DominatorTree *,
174 BlockFrequencyInfo *, TargetLibraryInfo *, Loop *,
175 MemorySSAUpdater &, ScalarEvolution *, ICFLoopSafetyInfo *,
176 SinkAndHoistLICMFlags &, OptimizationRemarkEmitter *, bool,
177 bool AllowSpeculation);
178
179/// This function deletes dead loops. The caller of this function needs to
180/// guarantee that the loop is infact dead.
181/// The function requires a bunch or prerequisites to be present:
182/// - The loop needs to be in LCSSA form
183/// - The loop needs to have a Preheader
184/// - A unique dedicated exit block must exist
185///
186/// This also updates the relevant analysis information in \p DT, \p SE, \p LI
187/// and \p MSSA if pointers to those are provided.
188/// It also updates the loop PM if an updater struct is provided.
189
190void deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
191 LoopInfo *LI, MemorySSA *MSSA = nullptr);
192
193/// Remove the backedge of the specified loop. Handles loop nests and general
194/// loop structures subject to the precondition that the loop has no parent
195/// loop and has a single latch block. Preserves all listed analyses.
196void breakLoopBackedge(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
197 LoopInfo &LI, MemorySSA *MSSA);
198
199/// Try to promote memory values to scalars by sinking stores out of
200/// the loop and moving loads to before the loop. We do this by looping over
201/// the stores in the loop, looking for stores to Must pointers which are
202/// loop invariant. It takes a set of must-alias values, Loop exit blocks
203/// vector, loop exit blocks insertion point vector, PredIteratorCache,
204/// LoopInfo, DominatorTree, Loop, AliasSet information for all instructions
205/// of the loop and loop safety information as arguments.
206/// Diagnostics is emitted via \p ORE. It returns changed status.
207/// \p AllowSpeculation is whether values should be hoisted even if they are not
208/// guaranteed to execute in the loop, but are safe to speculatively execute.
209bool promoteLoopAccessesToScalars(
210 const SmallSetVector<Value *, 8> &, SmallVectorImpl<BasicBlock *> &,
211 SmallVectorImpl<Instruction *> &, SmallVectorImpl<MemoryAccess *> &,
212 PredIteratorCache &, LoopInfo *, DominatorTree *, const TargetLibraryInfo *,
213 Loop *, MemorySSAUpdater &, ICFLoopSafetyInfo *,
214 OptimizationRemarkEmitter *, bool AllowSpeculation);
215
216/// Does a BFS from a given node to all of its children inside a given loop.
217/// The returned vector of nodes includes the starting point.
218SmallVector<DomTreeNode *, 16> collectChildrenInLoop(DomTreeNode *N,
219 const Loop *CurLoop);
220
221/// Returns the instructions that use values defined in the loop.
222SmallVector<Instruction *, 8> findDefsUsedOutsideOfLoop(Loop *L);
223
224/// Find a combination of metadata ("llvm.loop.vectorize.width" and
225/// "llvm.loop.vectorize.scalable.enable") for a loop and use it to construct a
226/// ElementCount. If the metadata "llvm.loop.vectorize.width" cannot be found
227/// then None is returned.
228Optional<ElementCount>
229getOptionalElementCountLoopAttribute(const Loop *TheLoop);
230
231/// Create a new loop identifier for a loop created from a loop transformation.
232///
233/// @param OrigLoopID The loop ID of the loop before the transformation.
234/// @param FollowupAttrs List of attribute names that contain attributes to be
235/// added to the new loop ID.
236/// @param InheritOptionsAttrsPrefix Selects which attributes should be inherited
237/// from the original loop. The following values
238/// are considered:
239/// nullptr : Inherit all attributes from @p OrigLoopID.
240/// "" : Do not inherit any attribute from @p OrigLoopID; only use
241/// those specified by a followup attribute.
242/// "<prefix>": Inherit all attributes except those which start with
243/// <prefix>; commonly used to remove metadata for the
244/// applied transformation.
245/// @param AlwaysNew If true, do not try to reuse OrigLoopID and never return
246/// None.
247///
248/// @return The loop ID for the after-transformation loop. The following values
249/// can be returned:
250/// None : No followup attribute was found; it is up to the
251/// transformation to choose attributes that make sense.
252/// @p OrigLoopID: The original identifier can be reused.
253/// nullptr : The new loop has no attributes.
254/// MDNode* : A new unique loop identifier.
255Optional<MDNode *>
256makeFollowupLoopID(MDNode *OrigLoopID, ArrayRef<StringRef> FollowupAttrs,
257 const char *InheritOptionsAttrsPrefix = "",
258 bool AlwaysNew = false);
259
260/// Look for the loop attribute that disables all transformation heuristic.
261bool hasDisableAllTransformsHint(const Loop *L);
262
263/// Look for the loop attribute that disables the LICM transformation heuristics.
264bool hasDisableLICMTransformsHint(const Loop *L);
265
266/// The mode sets how eager a transformation should be applied.
267enum TransformationMode {
268 /// The pass can use heuristics to determine whether a transformation should
269 /// be applied.
270 TM_Unspecified,
271
272 /// The transformation should be applied without considering a cost model.
273 TM_Enable,
274
275 /// The transformation should not be applied.
276 TM_Disable,
277
278 /// Force is a flag and should not be used alone.
279 TM_Force = 0x04,
280
281 /// The transformation was directed by the user, e.g. by a #pragma in
282 /// the source code. If the transformation could not be applied, a
283 /// warning should be emitted.
284 TM_ForcedByUser = TM_Enable | TM_Force,
285
286 /// The transformation must not be applied. For instance, `#pragma clang loop
287 /// unroll(disable)` explicitly forbids any unrolling to take place. Unlike
288 /// general loop metadata, it must not be dropped. Most passes should not
289 /// behave differently under TM_Disable and TM_SuppressedByUser.
290 TM_SuppressedByUser = TM_Disable | TM_Force
291};
292
293/// @{
294/// Get the mode for LLVM's supported loop transformations.
295TransformationMode hasUnrollTransformation(const Loop *L);
296TransformationMode hasUnrollAndJamTransformation(const Loop *L);
297TransformationMode hasVectorizeTransformation(const Loop *L);
298TransformationMode hasDistributeTransformation(const Loop *L);
299TransformationMode hasLICMVersioningTransformation(const Loop *L);
300/// @}
301
302/// Set input string into loop metadata by keeping other values intact.
303/// If the string is already in loop metadata update value if it is
304/// different.
305void addStringMetadataToLoop(Loop *TheLoop, const char *MDString,
306 unsigned V = 0);
307
308/// Returns a loop's estimated trip count based on branch weight metadata.
309/// In addition if \p EstimatedLoopInvocationWeight is not null it is
310/// initialized with weight of loop's latch leading to the exit.
311/// Returns 0 when the count is estimated to be 0, or None when a meaningful
312/// estimate can not be made.
313Optional<unsigned>
314getLoopEstimatedTripCount(Loop *L,
315 unsigned *EstimatedLoopInvocationWeight = nullptr);
316
317/// Set a loop's branch weight metadata to reflect that loop has \p
318/// EstimatedTripCount iterations and \p EstimatedLoopInvocationWeight exits
319/// through latch. Returns true if metadata is successfully updated, false
320/// otherwise. Note that loop must have a latch block which controls loop exit
321/// in order to succeed.
322bool setLoopEstimatedTripCount(Loop *L, unsigned EstimatedTripCount,
323 unsigned EstimatedLoopInvocationWeight);
324
325/// Check inner loop (L) backedge count is known to be invariant on all
326/// iterations of its outer loop. If the loop has no parent, this is trivially
327/// true.
328bool hasIterationCountInvariantInParent(Loop *L, ScalarEvolution &SE);
329
330/// Helper to consistently add the set of standard passes to a loop pass's \c
331/// AnalysisUsage.
332///
333/// All loop passes should call this as part of implementing their \c
334/// getAnalysisUsage.
335void getLoopAnalysisUsage(AnalysisUsage &AU);
336
337/// Returns true if is legal to hoist or sink this instruction disregarding the
338/// possible introduction of faults. Reasoning about potential faulting
339/// instructions is the responsibility of the caller since it is challenging to
340/// do efficiently from within this routine.
341/// \p TargetExecutesOncePerLoop is true only when it is guaranteed that the
342/// target executes at most once per execution of the loop body. This is used
343/// to assess the legality of duplicating atomic loads. Generally, this is
344/// true when moving out of loop and not true when moving into loops.
345/// If \p ORE is set use it to emit optimization remarks.
346bool canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT,
347 Loop *CurLoop, MemorySSAUpdater &MSSAU,
348 bool TargetExecutesOncePerLoop,
349 SinkAndHoistLICMFlags &LICMFlags,
350 OptimizationRemarkEmitter *ORE = nullptr);
351
352/// Returns the comparison predicate used when expanding a min/max reduction.
353CmpInst::Predicate getMinMaxReductionPredicate(RecurKind RK);
354
355/// See RecurrenceDescriptor::isSelectCmpPattern for a description of the
356/// pattern we are trying to match. In this pattern we are only ever selecting
357/// between two values: 1) an initial PHI start value, and 2) a loop invariant
358/// value. This function uses \p LoopExitInst to determine 2), which we then use
359/// to select between \p Left and \p Right. Any lane value in \p Left that
360/// matches 2) will be merged into \p Right.
361Value *createSelectCmpOp(IRBuilderBase &Builder, Value *StartVal, RecurKind RK,
362 Value *Left, Value *Right);
363
364/// Returns a Min/Max operation corresponding to MinMaxRecurrenceKind.
365/// The Builder's fast-math-flags must be set to propagate the expected values.
366Value *createMinMaxOp(IRBuilderBase &Builder, RecurKind RK, Value *Left,
367 Value *Right);
368
369/// Generates an ordered vector reduction using extracts to reduce the value.
370Value *getOrderedReduction(IRBuilderBase &Builder, Value *Acc, Value *Src,
371 unsigned Op, RecurKind MinMaxKind = RecurKind::None);
372
373/// Generates a vector reduction using shufflevectors to reduce the value.
374/// Fast-math-flags are propagated using the IRBuilder's setting.
375Value *getShuffleReduction(IRBuilderBase &Builder, Value *Src, unsigned Op,
376 RecurKind MinMaxKind = RecurKind::None);
377
378/// Create a target reduction of the given vector. The reduction operation
379/// is described by the \p Opcode parameter. min/max reductions require
380/// additional information supplied in \p RdxKind.
381/// The target is queried to determine if intrinsics or shuffle sequences are
382/// required to implement the reduction.
383/// Fast-math-flags are propagated using the IRBuilder's setting.
384Value *createSimpleTargetReduction(IRBuilderBase &B,
385 const TargetTransformInfo *TTI, Value *Src,
386 RecurKind RdxKind);
387
388/// Create a target reduction of the given vector \p Src for a reduction of the
389/// kind RecurKind::SelectICmp or RecurKind::SelectFCmp. The reduction operation
390/// is described by \p Desc.
391Value *createSelectCmpTargetReduction(IRBuilderBase &B,
392 const TargetTransformInfo *TTI,
393 Value *Src,
394 const RecurrenceDescriptor &Desc,
395 PHINode *OrigPhi);
396
397/// Create a generic target reduction using a recurrence descriptor \p Desc
398/// The target is queried to determine if intrinsics or shuffle sequences are
399/// required to implement the reduction.
400/// Fast-math-flags are propagated using the RecurrenceDescriptor.
401Value *createTargetReduction(IRBuilderBase &B, const TargetTransformInfo *TTI,
402 const RecurrenceDescriptor &Desc, Value *Src,
403 PHINode *OrigPhi = nullptr);
404
405/// Create an ordered reduction intrinsic using the given recurrence
406/// descriptor \p Desc.
407Value *createOrderedReduction(IRBuilderBase &B,
408 const RecurrenceDescriptor &Desc, Value *Src,
409 Value *Start);
410
411/// Get the intersection (logical and) of all of the potential IR flags
412/// of each scalar operation (VL) that will be converted into a vector (I).
413/// If OpValue is non-null, we only consider operations similar to OpValue
414/// when intersecting.
415/// Flag set: NSW, NUW, exact, and all of fast-math.
416void propagateIRFlags(Value *I, ArrayRef<Value *> VL, Value *OpValue = nullptr);
417
418/// Returns true if we can prove that \p S is defined and always negative in
419/// loop \p L.
420bool isKnownNegativeInLoop(const SCEV *S, const Loop *L, ScalarEvolution &SE);
421
422/// Returns true if we can prove that \p S is defined and always non-negative in
423/// loop \p L.
424bool isKnownNonNegativeInLoop(const SCEV *S, const Loop *L,
425 ScalarEvolution &SE);
426
427/// Returns true if \p S is defined and never is equal to signed/unsigned max.
428bool cannotBeMaxInLoop(const SCEV *S, const Loop *L, ScalarEvolution &SE,
429 bool Signed);
430
431/// Returns true if \p S is defined and never is equal to signed/unsigned min.
432bool cannotBeMinInLoop(const SCEV *S, const Loop *L, ScalarEvolution &SE,
433 bool Signed);
434
435enum ReplaceExitVal { NeverRepl, OnlyCheapRepl, NoHardUse, AlwaysRepl };
436
437/// If the final value of any expressions that are recurrent in the loop can
438/// be computed, substitute the exit values from the loop into any instructions
439/// outside of the loop that use the final values of the current expressions.
440/// Return the number of loop exit values that have been replaced, and the
441/// corresponding phi node will be added to DeadInsts.
442int rewriteLoopExitValues(Loop *L, LoopInfo *LI, TargetLibraryInfo *TLI,
443 ScalarEvolution *SE, const TargetTransformInfo *TTI,
444 SCEVExpander &Rewriter, DominatorTree *DT,
445 ReplaceExitVal ReplaceExitValue,
446 SmallVector<WeakTrackingVH, 16> &DeadInsts);
447
448/// Set weights for \p UnrolledLoop and \p RemainderLoop based on weights for
449/// \p OrigLoop and the following distribution of \p OrigLoop iteration among \p
450/// UnrolledLoop and \p RemainderLoop. \p UnrolledLoop receives weights that
451/// reflect TC/UF iterations, and \p RemainderLoop receives weights that reflect
452/// the remaining TC%UF iterations.
453///
454/// Note that \p OrigLoop may be equal to either \p UnrolledLoop or \p
455/// RemainderLoop in which case weights for \p OrigLoop are updated accordingly.
456/// Note also behavior is undefined if \p UnrolledLoop and \p RemainderLoop are
457/// equal. \p UF must be greater than zero.
458/// If \p OrigLoop has no profile info associated nothing happens.
459///
460/// This utility may be useful for such optimizations as unroller and
461/// vectorizer as it's typical transformation for them.
462void setProfileInfoAfterUnrolling(Loop *OrigLoop, Loop *UnrolledLoop,
463 Loop *RemainderLoop, uint64_t UF);
464
465/// Utility that implements appending of loops onto a worklist given a range.
466/// We want to process loops in postorder, but the worklist is a LIFO data
467/// structure, so we append to it in *reverse* postorder.
468/// For trees, a preorder traversal is a viable reverse postorder, so we
469/// actually append using a preorder walk algorithm.
470template <typename RangeT>
471void appendLoopsToWorklist(RangeT &&, SmallPriorityWorklist<Loop *, 4> &);
472/// Utility that implements appending of loops onto a worklist given a range.
473/// It has the same behavior as appendLoopsToWorklist, but assumes the range of
474/// loops has already been reversed, so it processes loops in the given order.
475template <typename RangeT>
476void appendReversedLoopsToWorklist(RangeT &&,
477 SmallPriorityWorklist<Loop *, 4> &);
478
479/// Utility that implements appending of loops onto a worklist given LoopInfo.
480/// Calls the templated utility taking a Range of loops, handing it the Loops
481/// in LoopInfo, iterated in reverse. This is because the loops are stored in
482/// RPO w.r.t. the control flow graph in LoopInfo. For the purpose of unrolling,
483/// loop deletion, and LICM, we largely want to work forward across the CFG so
484/// that we visit defs before uses and can propagate simplifications from one
485/// loop nest into the next. Calls appendReversedLoopsToWorklist with the
486/// already reversed loops in LI.
487/// FIXME: Consider changing the order in LoopInfo.
488void appendLoopsToWorklist(LoopInfo &, SmallPriorityWorklist<Loop *, 4> &);
489
490/// Recursively clone the specified loop and all of its children,
491/// mapping the blocks with the specified map.
492Loop *cloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
493 LoopInfo *LI, LPPassManager *LPM);
494
495/// Add code that checks at runtime if the accessed arrays in \p PointerChecks
496/// overlap. Returns the final comparator value or NULL if no check is needed.
497Value *
498addRuntimeChecks(Instruction *Loc, Loop *TheLoop,
499 const SmallVectorImpl<RuntimePointerCheck> &PointerChecks,
500 SCEVExpander &Expander);
501
502/// Struct to hold information about a partially invariant condition.
503struct IVConditionInfo {
504 /// Instructions that need to be duplicated and checked for the unswitching
505 /// condition.
506 SmallVector<Instruction *> InstToDuplicate;
507
508 /// Constant to indicate for which value the condition is invariant.
509 Constant *KnownValue = nullptr;
4
Null pointer value stored to 'PartialIVInfo.KnownValue'
510
511 /// True if the partially invariant path is no-op (=does not have any
512 /// side-effects and no loop value is used outside the loop).
513 bool PathIsNoop = true;
514
515 /// If the partially invariant path reaches a single exit block, ExitForPath
516 /// is set to that block. Otherwise it is nullptr.
517 BasicBlock *ExitForPath = nullptr;
518};
519
520/// Check if the loop header has a conditional branch that is not
521/// loop-invariant, because it involves load instructions. If all paths from
522/// either the true or false successor to the header or loop exists do not
523/// modify the memory feeding the condition, perform 'partial unswitching'. That
524/// is, duplicate the instructions feeding the condition in the pre-header. Then
525/// unswitch on the duplicated condition. The condition is now known in the
526/// unswitched version for the 'invariant' path through the original loop.
527///
528/// If the branch condition of the header is partially invariant, return a pair
529/// containing the instructions to duplicate and a boolean Constant to update
530/// the condition in the loops created for the true or false successors.
531Optional<IVConditionInfo> hasPartialIVCondition(Loop &L, unsigned MSSAThreshold,
532 MemorySSA &MSSA, AAResults &AA);
533
534} // end namespace llvm
535
536#endif // LLVM_TRANSFORMS_UTILS_LOOPUTILS_H