Bug Summary

File:lib/Transforms/Scalar/JumpThreading.cpp
Warning:line 1411, column 7
Called C++ object pointer is null

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clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name JumpThreading.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-eagerly-assume -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 -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -momit-leaf-frame-pointer -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-7/lib/clang/7.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/include -I /build/llvm-toolchain-snapshot-7~svn338205/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/backward -internal-isystem /usr/include/clang/7.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-7/lib/clang/7.0.0/include -internal-externc-isystem /usr/lib/gcc/x86_64-linux-gnu/8/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-comment -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/lib/Transforms/Scalar -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2018-07-29-043837-17923-1 -x c++ /build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp -faddrsig
1//===- JumpThreading.cpp - Thread control through conditional blocks ------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the Jump Threading pass.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Transforms/Scalar/JumpThreading.h"
15#include "llvm/ADT/DenseMap.h"
16#include "llvm/ADT/DenseSet.h"
17#include "llvm/ADT/Optional.h"
18#include "llvm/ADT/STLExtras.h"
19#include "llvm/ADT/SmallPtrSet.h"
20#include "llvm/ADT/SmallVector.h"
21#include "llvm/ADT/Statistic.h"
22#include "llvm/Analysis/AliasAnalysis.h"
23#include "llvm/Analysis/BlockFrequencyInfo.h"
24#include "llvm/Analysis/BranchProbabilityInfo.h"
25#include "llvm/Analysis/CFG.h"
26#include "llvm/Analysis/ConstantFolding.h"
27#include "llvm/Analysis/GlobalsModRef.h"
28#include "llvm/Analysis/InstructionSimplify.h"
29#include "llvm/Analysis/LazyValueInfo.h"
30#include "llvm/Analysis/Loads.h"
31#include "llvm/Analysis/LoopInfo.h"
32#include "llvm/Analysis/TargetLibraryInfo.h"
33#include "llvm/Transforms/Utils/Local.h"
34#include "llvm/Analysis/ValueTracking.h"
35#include "llvm/IR/BasicBlock.h"
36#include "llvm/IR/CFG.h"
37#include "llvm/IR/Constant.h"
38#include "llvm/IR/ConstantRange.h"
39#include "llvm/IR/Constants.h"
40#include "llvm/IR/DataLayout.h"
41#include "llvm/IR/Dominators.h"
42#include "llvm/IR/Function.h"
43#include "llvm/IR/InstrTypes.h"
44#include "llvm/IR/Instruction.h"
45#include "llvm/IR/Instructions.h"
46#include "llvm/IR/IntrinsicInst.h"
47#include "llvm/IR/Intrinsics.h"
48#include "llvm/IR/LLVMContext.h"
49#include "llvm/IR/MDBuilder.h"
50#include "llvm/IR/Metadata.h"
51#include "llvm/IR/Module.h"
52#include "llvm/IR/PassManager.h"
53#include "llvm/IR/PatternMatch.h"
54#include "llvm/IR/Type.h"
55#include "llvm/IR/Use.h"
56#include "llvm/IR/User.h"
57#include "llvm/IR/Value.h"
58#include "llvm/Pass.h"
59#include "llvm/Support/BlockFrequency.h"
60#include "llvm/Support/BranchProbability.h"
61#include "llvm/Support/Casting.h"
62#include "llvm/Support/CommandLine.h"
63#include "llvm/Support/Debug.h"
64#include "llvm/Support/raw_ostream.h"
65#include "llvm/Transforms/Scalar.h"
66#include "llvm/Transforms/Utils/BasicBlockUtils.h"
67#include "llvm/Transforms/Utils/Cloning.h"
68#include "llvm/Transforms/Utils/SSAUpdater.h"
69#include "llvm/Transforms/Utils/ValueMapper.h"
70#include <algorithm>
71#include <cassert>
72#include <cstddef>
73#include <cstdint>
74#include <iterator>
75#include <memory>
76#include <utility>
77
78using namespace llvm;
79using namespace jumpthreading;
80
81#define DEBUG_TYPE"jump-threading" "jump-threading"
82
83STATISTIC(NumThreads, "Number of jumps threaded")static llvm::Statistic NumThreads = {"jump-threading", "NumThreads"
, "Number of jumps threaded", {0}, {false}}
;
84STATISTIC(NumFolds, "Number of terminators folded")static llvm::Statistic NumFolds = {"jump-threading", "NumFolds"
, "Number of terminators folded", {0}, {false}}
;
85STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi")static llvm::Statistic NumDupes = {"jump-threading", "NumDupes"
, "Number of branch blocks duplicated to eliminate phi", {0},
{false}}
;
86
87static cl::opt<unsigned>
88BBDuplicateThreshold("jump-threading-threshold",
89 cl::desc("Max block size to duplicate for jump threading"),
90 cl::init(6), cl::Hidden);
91
92static cl::opt<unsigned>
93ImplicationSearchThreshold(
94 "jump-threading-implication-search-threshold",
95 cl::desc("The number of predecessors to search for a stronger "
96 "condition to use to thread over a weaker condition"),
97 cl::init(3), cl::Hidden);
98
99static cl::opt<bool> PrintLVIAfterJumpThreading(
100 "print-lvi-after-jump-threading",
101 cl::desc("Print the LazyValueInfo cache after JumpThreading"), cl::init(false),
102 cl::Hidden);
103
104namespace {
105
106 /// This pass performs 'jump threading', which looks at blocks that have
107 /// multiple predecessors and multiple successors. If one or more of the
108 /// predecessors of the block can be proven to always jump to one of the
109 /// successors, we forward the edge from the predecessor to the successor by
110 /// duplicating the contents of this block.
111 ///
112 /// An example of when this can occur is code like this:
113 ///
114 /// if () { ...
115 /// X = 4;
116 /// }
117 /// if (X < 3) {
118 ///
119 /// In this case, the unconditional branch at the end of the first if can be
120 /// revectored to the false side of the second if.
121 class JumpThreading : public FunctionPass {
122 JumpThreadingPass Impl;
123
124 public:
125 static char ID; // Pass identification
126
127 JumpThreading(int T = -1) : FunctionPass(ID), Impl(T) {
128 initializeJumpThreadingPass(*PassRegistry::getPassRegistry());
129 }
130
131 bool runOnFunction(Function &F) override;
132
133 void getAnalysisUsage(AnalysisUsage &AU) const override {
134 AU.addRequired<DominatorTreeWrapperPass>();
135 AU.addPreserved<DominatorTreeWrapperPass>();
136 AU.addRequired<AAResultsWrapperPass>();
137 AU.addRequired<LazyValueInfoWrapperPass>();
138 AU.addPreserved<LazyValueInfoWrapperPass>();
139 AU.addPreserved<GlobalsAAWrapperPass>();
140 AU.addRequired<TargetLibraryInfoWrapperPass>();
141 }
142
143 void releaseMemory() override { Impl.releaseMemory(); }
144 };
145
146} // end anonymous namespace
147
148char JumpThreading::ID = 0;
149
150INITIALIZE_PASS_BEGIN(JumpThreading, "jump-threading",static void *initializeJumpThreadingPassOnce(PassRegistry &
Registry) {
151 "Jump Threading", false, false)static void *initializeJumpThreadingPassOnce(PassRegistry &
Registry) {
152INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
153INITIALIZE_PASS_DEPENDENCY(LazyValueInfoWrapperPass)initializeLazyValueInfoWrapperPassPass(Registry);
154INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)initializeTargetLibraryInfoWrapperPassPass(Registry);
155INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)initializeAAResultsWrapperPassPass(Registry);
156INITIALIZE_PASS_END(JumpThreading, "jump-threading",PassInfo *PI = new PassInfo( "Jump Threading", "jump-threading"
, &JumpThreading::ID, PassInfo::NormalCtor_t(callDefaultCtor
<JumpThreading>), false, false); Registry.registerPass(
*PI, true); return PI; } static llvm::once_flag InitializeJumpThreadingPassFlag
; void llvm::initializeJumpThreadingPass(PassRegistry &Registry
) { llvm::call_once(InitializeJumpThreadingPassFlag, initializeJumpThreadingPassOnce
, std::ref(Registry)); }
157 "Jump Threading", false, false)PassInfo *PI = new PassInfo( "Jump Threading", "jump-threading"
, &JumpThreading::ID, PassInfo::NormalCtor_t(callDefaultCtor
<JumpThreading>), false, false); Registry.registerPass(
*PI, true); return PI; } static llvm::once_flag InitializeJumpThreadingPassFlag
; void llvm::initializeJumpThreadingPass(PassRegistry &Registry
) { llvm::call_once(InitializeJumpThreadingPassFlag, initializeJumpThreadingPassOnce
, std::ref(Registry)); }
158
159// Public interface to the Jump Threading pass
160FunctionPass *llvm::createJumpThreadingPass(int Threshold) {
161 return new JumpThreading(Threshold);
162}
163
164JumpThreadingPass::JumpThreadingPass(int T) {
165 BBDupThreshold = (T == -1) ? BBDuplicateThreshold : unsigned(T);
166}
167
168// Update branch probability information according to conditional
169// branch probability. This is usually made possible for cloned branches
170// in inline instances by the context specific profile in the caller.
171// For instance,
172//
173// [Block PredBB]
174// [Branch PredBr]
175// if (t) {
176// Block A;
177// } else {
178// Block B;
179// }
180//
181// [Block BB]
182// cond = PN([true, %A], [..., %B]); // PHI node
183// [Branch CondBr]
184// if (cond) {
185// ... // P(cond == true) = 1%
186// }
187//
188// Here we know that when block A is taken, cond must be true, which means
189// P(cond == true | A) = 1
190//
191// Given that P(cond == true) = P(cond == true | A) * P(A) +
192// P(cond == true | B) * P(B)
193// we get:
194// P(cond == true ) = P(A) + P(cond == true | B) * P(B)
195//
196// which gives us:
197// P(A) is less than P(cond == true), i.e.
198// P(t == true) <= P(cond == true)
199//
200// In other words, if we know P(cond == true) is unlikely, we know
201// that P(t == true) is also unlikely.
202//
203static void updatePredecessorProfileMetadata(PHINode *PN, BasicBlock *BB) {
204 BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
205 if (!CondBr)
206 return;
207
208 BranchProbability BP;
209 uint64_t TrueWeight, FalseWeight;
210 if (!CondBr->extractProfMetadata(TrueWeight, FalseWeight))
211 return;
212
213 // Returns the outgoing edge of the dominating predecessor block
214 // that leads to the PhiNode's incoming block:
215 auto GetPredOutEdge =
216 [](BasicBlock *IncomingBB,
217 BasicBlock *PhiBB) -> std::pair<BasicBlock *, BasicBlock *> {
218 auto *PredBB = IncomingBB;
219 auto *SuccBB = PhiBB;
220 while (true) {
221 BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator());
222 if (PredBr && PredBr->isConditional())
223 return {PredBB, SuccBB};
224 auto *SinglePredBB = PredBB->getSinglePredecessor();
225 if (!SinglePredBB)
226 return {nullptr, nullptr};
227 SuccBB = PredBB;
228 PredBB = SinglePredBB;
229 }
230 };
231
232 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
233 Value *PhiOpnd = PN->getIncomingValue(i);
234 ConstantInt *CI = dyn_cast<ConstantInt>(PhiOpnd);
235
236 if (!CI || !CI->getType()->isIntegerTy(1))
237 continue;
238
239 BP = (CI->isOne() ? BranchProbability::getBranchProbability(
240 TrueWeight, TrueWeight + FalseWeight)
241 : BranchProbability::getBranchProbability(
242 FalseWeight, TrueWeight + FalseWeight));
243
244 auto PredOutEdge = GetPredOutEdge(PN->getIncomingBlock(i), BB);
245 if (!PredOutEdge.first)
246 return;
247
248 BasicBlock *PredBB = PredOutEdge.first;
249 BranchInst *PredBr = cast<BranchInst>(PredBB->getTerminator());
250
251 uint64_t PredTrueWeight, PredFalseWeight;
252 // FIXME: We currently only set the profile data when it is missing.
253 // With PGO, this can be used to refine even existing profile data with
254 // context information. This needs to be done after more performance
255 // testing.
256 if (PredBr->extractProfMetadata(PredTrueWeight, PredFalseWeight))
257 continue;
258
259 // We can not infer anything useful when BP >= 50%, because BP is the
260 // upper bound probability value.
261 if (BP >= BranchProbability(50, 100))
262 continue;
263
264 SmallVector<uint32_t, 2> Weights;
265 if (PredBr->getSuccessor(0) == PredOutEdge.second) {
266 Weights.push_back(BP.getNumerator());
267 Weights.push_back(BP.getCompl().getNumerator());
268 } else {
269 Weights.push_back(BP.getCompl().getNumerator());
270 Weights.push_back(BP.getNumerator());
271 }
272 PredBr->setMetadata(LLVMContext::MD_prof,
273 MDBuilder(PredBr->getParent()->getContext())
274 .createBranchWeights(Weights));
275 }
276}
277
278/// runOnFunction - Toplevel algorithm.
279bool JumpThreading::runOnFunction(Function &F) {
280 if (skipFunction(F))
281 return false;
282 auto TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
283 // Get DT analysis before LVI. When LVI is initialized it conditionally adds
284 // DT if it's available.
285 auto DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
286 auto LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
287 auto AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
288 DeferredDominance DDT(*DT);
289 std::unique_ptr<BlockFrequencyInfo> BFI;
290 std::unique_ptr<BranchProbabilityInfo> BPI;
291 bool HasProfileData = F.hasProfileData();
292 if (HasProfileData) {
293 LoopInfo LI{DominatorTree(F)};
294 BPI.reset(new BranchProbabilityInfo(F, LI, TLI));
295 BFI.reset(new BlockFrequencyInfo(F, *BPI, LI));
296 }
297
298 bool Changed = Impl.runImpl(F, TLI, LVI, AA, &DDT, HasProfileData,
299 std::move(BFI), std::move(BPI));
300 if (PrintLVIAfterJumpThreading) {
301 dbgs() << "LVI for function '" << F.getName() << "':\n";
302 LVI->printLVI(F, *DT, dbgs());
303 }
304 return Changed;
305}
306
307PreservedAnalyses JumpThreadingPass::run(Function &F,
308 FunctionAnalysisManager &AM) {
309 auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
310 // Get DT analysis before LVI. When LVI is initialized it conditionally adds
311 // DT if it's available.
312 auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
313 auto &LVI = AM.getResult<LazyValueAnalysis>(F);
314 auto &AA = AM.getResult<AAManager>(F);
315 DeferredDominance DDT(DT);
316
317 std::unique_ptr<BlockFrequencyInfo> BFI;
318 std::unique_ptr<BranchProbabilityInfo> BPI;
319 if (F.hasProfileData()) {
320 LoopInfo LI{DominatorTree(F)};
321 BPI.reset(new BranchProbabilityInfo(F, LI, &TLI));
322 BFI.reset(new BlockFrequencyInfo(F, *BPI, LI));
323 }
324
325 bool Changed = runImpl(F, &TLI, &LVI, &AA, &DDT, HasProfileData,
326 std::move(BFI), std::move(BPI));
327
328 if (!Changed)
329 return PreservedAnalyses::all();
330 PreservedAnalyses PA;
331 PA.preserve<GlobalsAA>();
332 PA.preserve<DominatorTreeAnalysis>();
333 PA.preserve<LazyValueAnalysis>();
334 return PA;
335}
336
337bool JumpThreadingPass::runImpl(Function &F, TargetLibraryInfo *TLI_,
338 LazyValueInfo *LVI_, AliasAnalysis *AA_,
339 DeferredDominance *DDT_, bool HasProfileData_,
340 std::unique_ptr<BlockFrequencyInfo> BFI_,
341 std::unique_ptr<BranchProbabilityInfo> BPI_) {
342 LLVM_DEBUG(dbgs() << "Jump threading on function '" << F.getName() << "'\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "Jump threading on function '"
<< F.getName() << "'\n"; } } while (false)
;
343 TLI = TLI_;
344 LVI = LVI_;
345 AA = AA_;
346 DDT = DDT_;
347 BFI.reset();
348 BPI.reset();
349 // When profile data is available, we need to update edge weights after
350 // successful jump threading, which requires both BPI and BFI being available.
351 HasProfileData = HasProfileData_;
352 auto *GuardDecl = F.getParent()->getFunction(
353 Intrinsic::getName(Intrinsic::experimental_guard));
354 HasGuards = GuardDecl && !GuardDecl->use_empty();
355 if (HasProfileData) {
356 BPI = std::move(BPI_);
357 BFI = std::move(BFI_);
358 }
359
360 // JumpThreading must not processes blocks unreachable from entry. It's a
361 // waste of compute time and can potentially lead to hangs.
362 SmallPtrSet<BasicBlock *, 16> Unreachable;
363 DominatorTree &DT = DDT->flush();
364 for (auto &BB : F)
365 if (!DT.isReachableFromEntry(&BB))
366 Unreachable.insert(&BB);
367
368 FindLoopHeaders(F);
369
370 bool EverChanged = false;
371 bool Changed;
372 do {
373 Changed = false;
374 for (auto &BB : F) {
375 if (Unreachable.count(&BB))
376 continue;
377 while (ProcessBlock(&BB)) // Thread all of the branches we can over BB.
378 Changed = true;
379 // Stop processing BB if it's the entry or is now deleted. The following
380 // routines attempt to eliminate BB and locating a suitable replacement
381 // for the entry is non-trivial.
382 if (&BB == &F.getEntryBlock() || DDT->pendingDeletedBB(&BB))
383 continue;
384
385 if (pred_empty(&BB)) {
386 // When ProcessBlock makes BB unreachable it doesn't bother to fix up
387 // the instructions in it. We must remove BB to prevent invalid IR.
388 LLVM_DEBUG(dbgs() << " JT: Deleting dead block '" << BB.getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " JT: Deleting dead block '"
<< BB.getName() << "' with terminator: " <<
*BB.getTerminator() << '\n'; } } while (false)
389 << "' with terminator: " << *BB.getTerminator()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " JT: Deleting dead block '"
<< BB.getName() << "' with terminator: " <<
*BB.getTerminator() << '\n'; } } while (false)
390 << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " JT: Deleting dead block '"
<< BB.getName() << "' with terminator: " <<
*BB.getTerminator() << '\n'; } } while (false)
;
391 LoopHeaders.erase(&BB);
392 LVI->eraseBlock(&BB);
393 DeleteDeadBlock(&BB, DDT);
394 Changed = true;
395 continue;
396 }
397
398 // ProcessBlock doesn't thread BBs with unconditional TIs. However, if BB
399 // is "almost empty", we attempt to merge BB with its sole successor.
400 auto *BI = dyn_cast<BranchInst>(BB.getTerminator());
401 if (BI && BI->isUnconditional() &&
402 // The terminator must be the only non-phi instruction in BB.
403 BB.getFirstNonPHIOrDbg()->isTerminator() &&
404 // Don't alter Loop headers and latches to ensure another pass can
405 // detect and transform nested loops later.
406 !LoopHeaders.count(&BB) && !LoopHeaders.count(BI->getSuccessor(0)) &&
407 TryToSimplifyUncondBranchFromEmptyBlock(&BB, DDT)) {
408 // BB is valid for cleanup here because we passed in DDT. F remains
409 // BB's parent until a DDT->flush() event.
410 LVI->eraseBlock(&BB);
411 Changed = true;
412 }
413 }
414 EverChanged |= Changed;
415 } while (Changed);
416
417 LoopHeaders.clear();
418 DDT->flush();
419 LVI->enableDT();
420 return EverChanged;
421}
422
423// Replace uses of Cond with ToVal when safe to do so. If all uses are
424// replaced, we can remove Cond. We cannot blindly replace all uses of Cond
425// because we may incorrectly replace uses when guards/assumes are uses of
426// of `Cond` and we used the guards/assume to reason about the `Cond` value
427// at the end of block. RAUW unconditionally replaces all uses
428// including the guards/assumes themselves and the uses before the
429// guard/assume.
430static void ReplaceFoldableUses(Instruction *Cond, Value *ToVal) {
431 assert(Cond->getType() == ToVal->getType())(static_cast <bool> (Cond->getType() == ToVal->getType
()) ? void (0) : __assert_fail ("Cond->getType() == ToVal->getType()"
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 431, __extension__ __PRETTY_FUNCTION__))
;
432 auto *BB = Cond->getParent();
433 // We can unconditionally replace all uses in non-local blocks (i.e. uses
434 // strictly dominated by BB), since LVI information is true from the
435 // terminator of BB.
436 replaceNonLocalUsesWith(Cond, ToVal);
437 for (Instruction &I : reverse(*BB)) {
438 // Reached the Cond whose uses we are trying to replace, so there are no
439 // more uses.
440 if (&I == Cond)
441 break;
442 // We only replace uses in instructions that are guaranteed to reach the end
443 // of BB, where we know Cond is ToVal.
444 if (!isGuaranteedToTransferExecutionToSuccessor(&I))
445 break;
446 I.replaceUsesOfWith(Cond, ToVal);
447 }
448 if (Cond->use_empty() && !Cond->mayHaveSideEffects())
449 Cond->eraseFromParent();
450}
451
452/// Return the cost of duplicating a piece of this block from first non-phi
453/// and before StopAt instruction to thread across it. Stop scanning the block
454/// when exceeding the threshold. If duplication is impossible, returns ~0U.
455static unsigned getJumpThreadDuplicationCost(BasicBlock *BB,
456 Instruction *StopAt,
457 unsigned Threshold) {
458 assert(StopAt->getParent() == BB && "Not an instruction from proper BB?")(static_cast <bool> (StopAt->getParent() == BB &&
"Not an instruction from proper BB?") ? void (0) : __assert_fail
("StopAt->getParent() == BB && \"Not an instruction from proper BB?\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 458, __extension__ __PRETTY_FUNCTION__))
;
459 /// Ignore PHI nodes, these will be flattened when duplication happens.
460 BasicBlock::const_iterator I(BB->getFirstNonPHI());
461
462 // FIXME: THREADING will delete values that are just used to compute the
463 // branch, so they shouldn't count against the duplication cost.
464
465 unsigned Bonus = 0;
466 if (BB->getTerminator() == StopAt) {
467 // Threading through a switch statement is particularly profitable. If this
468 // block ends in a switch, decrease its cost to make it more likely to
469 // happen.
470 if (isa<SwitchInst>(StopAt))
471 Bonus = 6;
472
473 // The same holds for indirect branches, but slightly more so.
474 if (isa<IndirectBrInst>(StopAt))
475 Bonus = 8;
476 }
477
478 // Bump the threshold up so the early exit from the loop doesn't skip the
479 // terminator-based Size adjustment at the end.
480 Threshold += Bonus;
481
482 // Sum up the cost of each instruction until we get to the terminator. Don't
483 // include the terminator because the copy won't include it.
484 unsigned Size = 0;
485 for (; &*I != StopAt; ++I) {
486
487 // Stop scanning the block if we've reached the threshold.
488 if (Size > Threshold)
489 return Size;
490
491 // Debugger intrinsics don't incur code size.
492 if (isa<DbgInfoIntrinsic>(I)) continue;
493
494 // If this is a pointer->pointer bitcast, it is free.
495 if (isa<BitCastInst>(I) && I->getType()->isPointerTy())
496 continue;
497
498 // Bail out if this instruction gives back a token type, it is not possible
499 // to duplicate it if it is used outside this BB.
500 if (I->getType()->isTokenTy() && I->isUsedOutsideOfBlock(BB))
501 return ~0U;
502
503 // All other instructions count for at least one unit.
504 ++Size;
505
506 // Calls are more expensive. If they are non-intrinsic calls, we model them
507 // as having cost of 4. If they are a non-vector intrinsic, we model them
508 // as having cost of 2 total, and if they are a vector intrinsic, we model
509 // them as having cost 1.
510 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
511 if (CI->cannotDuplicate() || CI->isConvergent())
512 // Blocks with NoDuplicate are modelled as having infinite cost, so they
513 // are never duplicated.
514 return ~0U;
515 else if (!isa<IntrinsicInst>(CI))
516 Size += 3;
517 else if (!CI->getType()->isVectorTy())
518 Size += 1;
519 }
520 }
521
522 return Size > Bonus ? Size - Bonus : 0;
523}
524
525/// FindLoopHeaders - We do not want jump threading to turn proper loop
526/// structures into irreducible loops. Doing this breaks up the loop nesting
527/// hierarchy and pessimizes later transformations. To prevent this from
528/// happening, we first have to find the loop headers. Here we approximate this
529/// by finding targets of backedges in the CFG.
530///
531/// Note that there definitely are cases when we want to allow threading of
532/// edges across a loop header. For example, threading a jump from outside the
533/// loop (the preheader) to an exit block of the loop is definitely profitable.
534/// It is also almost always profitable to thread backedges from within the loop
535/// to exit blocks, and is often profitable to thread backedges to other blocks
536/// within the loop (forming a nested loop). This simple analysis is not rich
537/// enough to track all of these properties and keep it up-to-date as the CFG
538/// mutates, so we don't allow any of these transformations.
539void JumpThreadingPass::FindLoopHeaders(Function &F) {
540 SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges;
541 FindFunctionBackedges(F, Edges);
542
543 for (const auto &Edge : Edges)
544 LoopHeaders.insert(Edge.second);
545}
546
547/// getKnownConstant - Helper method to determine if we can thread over a
548/// terminator with the given value as its condition, and if so what value to
549/// use for that. What kind of value this is depends on whether we want an
550/// integer or a block address, but an undef is always accepted.
551/// Returns null if Val is null or not an appropriate constant.
552static Constant *getKnownConstant(Value *Val, ConstantPreference Preference) {
553 if (!Val)
554 return nullptr;
555
556 // Undef is "known" enough.
557 if (UndefValue *U = dyn_cast<UndefValue>(Val))
558 return U;
559
560 if (Preference == WantBlockAddress)
561 return dyn_cast<BlockAddress>(Val->stripPointerCasts());
562
563 return dyn_cast<ConstantInt>(Val);
564}
565
566/// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see
567/// if we can infer that the value is a known ConstantInt/BlockAddress or undef
568/// in any of our predecessors. If so, return the known list of value and pred
569/// BB in the result vector.
570///
571/// This returns true if there were any known values.
572bool JumpThreadingPass::ComputeValueKnownInPredecessors(
573 Value *V, BasicBlock *BB, PredValueInfo &Result,
574 ConstantPreference Preference, Instruction *CxtI) {
575 // This method walks up use-def chains recursively. Because of this, we could
576 // get into an infinite loop going around loops in the use-def chain. To
577 // prevent this, keep track of what (value, block) pairs we've already visited
578 // and terminate the search if we loop back to them
579 if (!RecursionSet.insert(std::make_pair(V, BB)).second)
580 return false;
581
582 // An RAII help to remove this pair from the recursion set once the recursion
583 // stack pops back out again.
584 RecursionSetRemover remover(RecursionSet, std::make_pair(V, BB));
585
586 // If V is a constant, then it is known in all predecessors.
587 if (Constant *KC = getKnownConstant(V, Preference)) {
588 for (BasicBlock *Pred : predecessors(BB))
589 Result.push_back(std::make_pair(KC, Pred));
590
591 return !Result.empty();
592 }
593
594 // If V is a non-instruction value, or an instruction in a different block,
595 // then it can't be derived from a PHI.
596 Instruction *I = dyn_cast<Instruction>(V);
597 if (!I || I->getParent() != BB) {
598
599 // Okay, if this is a live-in value, see if it has a known value at the end
600 // of any of our predecessors.
601 //
602 // FIXME: This should be an edge property, not a block end property.
603 /// TODO: Per PR2563, we could infer value range information about a
604 /// predecessor based on its terminator.
605 //
606 // FIXME: change this to use the more-rich 'getPredicateOnEdge' method if
607 // "I" is a non-local compare-with-a-constant instruction. This would be
608 // able to handle value inequalities better, for example if the compare is
609 // "X < 4" and "X < 3" is known true but "X < 4" itself is not available.
610 // Perhaps getConstantOnEdge should be smart enough to do this?
611
612 if (DDT->pending())
613 LVI->disableDT();
614 else
615 LVI->enableDT();
616 for (BasicBlock *P : predecessors(BB)) {
617 // If the value is known by LazyValueInfo to be a constant in a
618 // predecessor, use that information to try to thread this block.
619 Constant *PredCst = LVI->getConstantOnEdge(V, P, BB, CxtI);
620 if (Constant *KC = getKnownConstant(PredCst, Preference))
621 Result.push_back(std::make_pair(KC, P));
622 }
623
624 return !Result.empty();
625 }
626
627 /// If I is a PHI node, then we know the incoming values for any constants.
628 if (PHINode *PN = dyn_cast<PHINode>(I)) {
629 if (DDT->pending())
630 LVI->disableDT();
631 else
632 LVI->enableDT();
633 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
634 Value *InVal = PN->getIncomingValue(i);
635 if (Constant *KC = getKnownConstant(InVal, Preference)) {
636 Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i)));
637 } else {
638 Constant *CI = LVI->getConstantOnEdge(InVal,
639 PN->getIncomingBlock(i),
640 BB, CxtI);
641 if (Constant *KC = getKnownConstant(CI, Preference))
642 Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i)));
643 }
644 }
645
646 return !Result.empty();
647 }
648
649 // Handle Cast instructions. Only see through Cast when the source operand is
650 // PHI or Cmp to save the compilation time.
651 if (CastInst *CI = dyn_cast<CastInst>(I)) {
652 Value *Source = CI->getOperand(0);
653 if (!isa<PHINode>(Source) && !isa<CmpInst>(Source))
654 return false;
655 ComputeValueKnownInPredecessors(Source, BB, Result, Preference, CxtI);
656 if (Result.empty())
657 return false;
658
659 // Convert the known values.
660 for (auto &R : Result)
661 R.first = ConstantExpr::getCast(CI->getOpcode(), R.first, CI->getType());
662
663 return true;
664 }
665
666 // Handle some boolean conditions.
667 if (I->getType()->getPrimitiveSizeInBits() == 1) {
668 assert(Preference == WantInteger && "One-bit non-integer type?")(static_cast <bool> (Preference == WantInteger &&
"One-bit non-integer type?") ? void (0) : __assert_fail ("Preference == WantInteger && \"One-bit non-integer type?\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 668, __extension__ __PRETTY_FUNCTION__))
;
669 // X | true -> true
670 // X & false -> false
671 if (I->getOpcode() == Instruction::Or ||
672 I->getOpcode() == Instruction::And) {
673 PredValueInfoTy LHSVals, RHSVals;
674
675 ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals,
676 WantInteger, CxtI);
677 ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals,
678 WantInteger, CxtI);
679
680 if (LHSVals.empty() && RHSVals.empty())
681 return false;
682
683 ConstantInt *InterestingVal;
684 if (I->getOpcode() == Instruction::Or)
685 InterestingVal = ConstantInt::getTrue(I->getContext());
686 else
687 InterestingVal = ConstantInt::getFalse(I->getContext());
688
689 SmallPtrSet<BasicBlock*, 4> LHSKnownBBs;
690
691 // Scan for the sentinel. If we find an undef, force it to the
692 // interesting value: x|undef -> true and x&undef -> false.
693 for (const auto &LHSVal : LHSVals)
694 if (LHSVal.first == InterestingVal || isa<UndefValue>(LHSVal.first)) {
695 Result.emplace_back(InterestingVal, LHSVal.second);
696 LHSKnownBBs.insert(LHSVal.second);
697 }
698 for (const auto &RHSVal : RHSVals)
699 if (RHSVal.first == InterestingVal || isa<UndefValue>(RHSVal.first)) {
700 // If we already inferred a value for this block on the LHS, don't
701 // re-add it.
702 if (!LHSKnownBBs.count(RHSVal.second))
703 Result.emplace_back(InterestingVal, RHSVal.second);
704 }
705
706 return !Result.empty();
707 }
708
709 // Handle the NOT form of XOR.
710 if (I->getOpcode() == Instruction::Xor &&
711 isa<ConstantInt>(I->getOperand(1)) &&
712 cast<ConstantInt>(I->getOperand(1))->isOne()) {
713 ComputeValueKnownInPredecessors(I->getOperand(0), BB, Result,
714 WantInteger, CxtI);
715 if (Result.empty())
716 return false;
717
718 // Invert the known values.
719 for (auto &R : Result)
720 R.first = ConstantExpr::getNot(R.first);
721
722 return true;
723 }
724
725 // Try to simplify some other binary operator values.
726 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) {
727 assert(Preference != WantBlockAddress(static_cast <bool> (Preference != WantBlockAddress &&
"A binary operator creating a block address?") ? void (0) : __assert_fail
("Preference != WantBlockAddress && \"A binary operator creating a block address?\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 728, __extension__ __PRETTY_FUNCTION__))
728 && "A binary operator creating a block address?")(static_cast <bool> (Preference != WantBlockAddress &&
"A binary operator creating a block address?") ? void (0) : __assert_fail
("Preference != WantBlockAddress && \"A binary operator creating a block address?\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 728, __extension__ __PRETTY_FUNCTION__))
;
729 if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) {
730 PredValueInfoTy LHSVals;
731 ComputeValueKnownInPredecessors(BO->getOperand(0), BB, LHSVals,
732 WantInteger, CxtI);
733
734 // Try to use constant folding to simplify the binary operator.
735 for (const auto &LHSVal : LHSVals) {
736 Constant *V = LHSVal.first;
737 Constant *Folded = ConstantExpr::get(BO->getOpcode(), V, CI);
738
739 if (Constant *KC = getKnownConstant(Folded, WantInteger))
740 Result.push_back(std::make_pair(KC, LHSVal.second));
741 }
742 }
743
744 return !Result.empty();
745 }
746
747 // Handle compare with phi operand, where the PHI is defined in this block.
748 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
749 assert(Preference == WantInteger && "Compares only produce integers")(static_cast <bool> (Preference == WantInteger &&
"Compares only produce integers") ? void (0) : __assert_fail
("Preference == WantInteger && \"Compares only produce integers\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 749, __extension__ __PRETTY_FUNCTION__))
;
750 Type *CmpType = Cmp->getType();
751 Value *CmpLHS = Cmp->getOperand(0);
752 Value *CmpRHS = Cmp->getOperand(1);
753 CmpInst::Predicate Pred = Cmp->getPredicate();
754
755 PHINode *PN = dyn_cast<PHINode>(CmpLHS);
756 if (!PN)
757 PN = dyn_cast<PHINode>(CmpRHS);
758 if (PN && PN->getParent() == BB) {
759 const DataLayout &DL = PN->getModule()->getDataLayout();
760 // We can do this simplification if any comparisons fold to true or false.
761 // See if any do.
762 if (DDT->pending())
763 LVI->disableDT();
764 else
765 LVI->enableDT();
766 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
767 BasicBlock *PredBB = PN->getIncomingBlock(i);
768 Value *LHS, *RHS;
769 if (PN == CmpLHS) {
770 LHS = PN->getIncomingValue(i);
771 RHS = CmpRHS->DoPHITranslation(BB, PredBB);
772 } else {
773 LHS = CmpLHS->DoPHITranslation(BB, PredBB);
774 RHS = PN->getIncomingValue(i);
775 }
776 Value *Res = SimplifyCmpInst(Pred, LHS, RHS, {DL});
777 if (!Res) {
778 if (!isa<Constant>(RHS))
779 continue;
780
781 // getPredicateOnEdge call will make no sense if LHS is defined in BB.
782 auto LHSInst = dyn_cast<Instruction>(LHS);
783 if (LHSInst && LHSInst->getParent() == BB)
784 continue;
785
786 LazyValueInfo::Tristate
787 ResT = LVI->getPredicateOnEdge(Pred, LHS,
788 cast<Constant>(RHS), PredBB, BB,
789 CxtI ? CxtI : Cmp);
790 if (ResT == LazyValueInfo::Unknown)
791 continue;
792 Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT);
793 }
794
795 if (Constant *KC = getKnownConstant(Res, WantInteger))
796 Result.push_back(std::make_pair(KC, PredBB));
797 }
798
799 return !Result.empty();
800 }
801
802 // If comparing a live-in value against a constant, see if we know the
803 // live-in value on any predecessors.
804 if (isa<Constant>(CmpRHS) && !CmpType->isVectorTy()) {
805 Constant *CmpConst = cast<Constant>(CmpRHS);
806
807 if (!isa<Instruction>(CmpLHS) ||
808 cast<Instruction>(CmpLHS)->getParent() != BB) {
809 if (DDT->pending())
810 LVI->disableDT();
811 else
812 LVI->enableDT();
813 for (BasicBlock *P : predecessors(BB)) {
814 // If the value is known by LazyValueInfo to be a constant in a
815 // predecessor, use that information to try to thread this block.
816 LazyValueInfo::Tristate Res =
817 LVI->getPredicateOnEdge(Pred, CmpLHS,
818 CmpConst, P, BB, CxtI ? CxtI : Cmp);
819 if (Res == LazyValueInfo::Unknown)
820 continue;
821
822 Constant *ResC = ConstantInt::get(CmpType, Res);
823 Result.push_back(std::make_pair(ResC, P));
824 }
825
826 return !Result.empty();
827 }
828
829 // InstCombine can fold some forms of constant range checks into
830 // (icmp (add (x, C1)), C2). See if we have we have such a thing with
831 // x as a live-in.
832 {
833 using namespace PatternMatch;
834
835 Value *AddLHS;
836 ConstantInt *AddConst;
837 if (isa<ConstantInt>(CmpConst) &&
838 match(CmpLHS, m_Add(m_Value(AddLHS), m_ConstantInt(AddConst)))) {
839 if (!isa<Instruction>(AddLHS) ||
840 cast<Instruction>(AddLHS)->getParent() != BB) {
841 if (DDT->pending())
842 LVI->disableDT();
843 else
844 LVI->enableDT();
845 for (BasicBlock *P : predecessors(BB)) {
846 // If the value is known by LazyValueInfo to be a ConstantRange in
847 // a predecessor, use that information to try to thread this
848 // block.
849 ConstantRange CR = LVI->getConstantRangeOnEdge(
850 AddLHS, P, BB, CxtI ? CxtI : cast<Instruction>(CmpLHS));
851 // Propagate the range through the addition.
852 CR = CR.add(AddConst->getValue());
853
854 // Get the range where the compare returns true.
855 ConstantRange CmpRange = ConstantRange::makeExactICmpRegion(
856 Pred, cast<ConstantInt>(CmpConst)->getValue());
857
858 Constant *ResC;
859 if (CmpRange.contains(CR))
860 ResC = ConstantInt::getTrue(CmpType);
861 else if (CmpRange.inverse().contains(CR))
862 ResC = ConstantInt::getFalse(CmpType);
863 else
864 continue;
865
866 Result.push_back(std::make_pair(ResC, P));
867 }
868
869 return !Result.empty();
870 }
871 }
872 }
873
874 // Try to find a constant value for the LHS of a comparison,
875 // and evaluate it statically if we can.
876 PredValueInfoTy LHSVals;
877 ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals,
878 WantInteger, CxtI);
879
880 for (const auto &LHSVal : LHSVals) {
881 Constant *V = LHSVal.first;
882 Constant *Folded = ConstantExpr::getCompare(Pred, V, CmpConst);
883 if (Constant *KC = getKnownConstant(Folded, WantInteger))
884 Result.push_back(std::make_pair(KC, LHSVal.second));
885 }
886
887 return !Result.empty();
888 }
889 }
890
891 if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
892 // Handle select instructions where at least one operand is a known constant
893 // and we can figure out the condition value for any predecessor block.
894 Constant *TrueVal = getKnownConstant(SI->getTrueValue(), Preference);
895 Constant *FalseVal = getKnownConstant(SI->getFalseValue(), Preference);
896 PredValueInfoTy Conds;
897 if ((TrueVal || FalseVal) &&
898 ComputeValueKnownInPredecessors(SI->getCondition(), BB, Conds,
899 WantInteger, CxtI)) {
900 for (auto &C : Conds) {
901 Constant *Cond = C.first;
902
903 // Figure out what value to use for the condition.
904 bool KnownCond;
905 if (ConstantInt *CI = dyn_cast<ConstantInt>(Cond)) {
906 // A known boolean.
907 KnownCond = CI->isOne();
908 } else {
909 assert(isa<UndefValue>(Cond) && "Unexpected condition value")(static_cast <bool> (isa<UndefValue>(Cond) &&
"Unexpected condition value") ? void (0) : __assert_fail ("isa<UndefValue>(Cond) && \"Unexpected condition value\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 909, __extension__ __PRETTY_FUNCTION__))
;
910 // Either operand will do, so be sure to pick the one that's a known
911 // constant.
912 // FIXME: Do this more cleverly if both values are known constants?
913 KnownCond = (TrueVal != nullptr);
914 }
915
916 // See if the select has a known constant value for this predecessor.
917 if (Constant *Val = KnownCond ? TrueVal : FalseVal)
918 Result.push_back(std::make_pair(Val, C.second));
919 }
920
921 return !Result.empty();
922 }
923 }
924
925 // If all else fails, see if LVI can figure out a constant value for us.
926 if (DDT->pending())
927 LVI->disableDT();
928 else
929 LVI->enableDT();
930 Constant *CI = LVI->getConstant(V, BB, CxtI);
931 if (Constant *KC = getKnownConstant(CI, Preference)) {
932 for (BasicBlock *Pred : predecessors(BB))
933 Result.push_back(std::make_pair(KC, Pred));
934 }
935
936 return !Result.empty();
937}
938
939/// GetBestDestForBranchOnUndef - If we determine that the specified block ends
940/// in an undefined jump, decide which block is best to revector to.
941///
942/// Since we can pick an arbitrary destination, we pick the successor with the
943/// fewest predecessors. This should reduce the in-degree of the others.
944static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) {
945 TerminatorInst *BBTerm = BB->getTerminator();
946 unsigned MinSucc = 0;
947 BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc);
948 // Compute the successor with the minimum number of predecessors.
949 unsigned MinNumPreds = pred_size(TestBB);
950 for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) {
951 TestBB = BBTerm->getSuccessor(i);
952 unsigned NumPreds = pred_size(TestBB);
953 if (NumPreds < MinNumPreds) {
954 MinSucc = i;
955 MinNumPreds = NumPreds;
956 }
957 }
958
959 return MinSucc;
960}
961
962static bool hasAddressTakenAndUsed(BasicBlock *BB) {
963 if (!BB->hasAddressTaken()) return false;
964
965 // If the block has its address taken, it may be a tree of dead constants
966 // hanging off of it. These shouldn't keep the block alive.
967 BlockAddress *BA = BlockAddress::get(BB);
968 BA->removeDeadConstantUsers();
969 return !BA->use_empty();
970}
971
972/// ProcessBlock - If there are any predecessors whose control can be threaded
973/// through to a successor, transform them now.
974bool JumpThreadingPass::ProcessBlock(BasicBlock *BB) {
975 // If the block is trivially dead, just return and let the caller nuke it.
976 // This simplifies other transformations.
977 if (DDT->pendingDeletedBB(BB) ||
1
Assuming the condition is false
978 (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()))
2
Assuming the condition is false
979 return false;
980
981 // If this block has a single predecessor, and if that pred has a single
982 // successor, merge the blocks. This encourages recursive jump threading
983 // because now the condition in this block can be threaded through
984 // predecessors of our predecessor block.
985 if (BasicBlock *SinglePred = BB->getSinglePredecessor()) {
3
Assuming 'SinglePred' is null
4
Taking false branch
986 const TerminatorInst *TI = SinglePred->getTerminator();
987 if (!TI->isExceptional() && TI->getNumSuccessors() == 1 &&
988 SinglePred != BB && !hasAddressTakenAndUsed(BB)) {
989 // If SinglePred was a loop header, BB becomes one.
990 if (LoopHeaders.erase(SinglePred))
991 LoopHeaders.insert(BB);
992
993 LVI->eraseBlock(SinglePred);
994 MergeBasicBlockIntoOnlyPred(BB, nullptr, DDT);
995
996 // Now that BB is merged into SinglePred (i.e. SinglePred Code followed by
997 // BB code within one basic block `BB`), we need to invalidate the LVI
998 // information associated with BB, because the LVI information need not be
999 // true for all of BB after the merge. For example,
1000 // Before the merge, LVI info and code is as follows:
1001 // SinglePred: <LVI info1 for %p val>
1002 // %y = use of %p
1003 // call @exit() // need not transfer execution to successor.
1004 // assume(%p) // from this point on %p is true
1005 // br label %BB
1006 // BB: <LVI info2 for %p val, i.e. %p is true>
1007 // %x = use of %p
1008 // br label exit
1009 //
1010 // Note that this LVI info for blocks BB and SinglPred is correct for %p
1011 // (info2 and info1 respectively). After the merge and the deletion of the
1012 // LVI info1 for SinglePred. We have the following code:
1013 // BB: <LVI info2 for %p val>
1014 // %y = use of %p
1015 // call @exit()
1016 // assume(%p)
1017 // %x = use of %p <-- LVI info2 is correct from here onwards.
1018 // br label exit
1019 // LVI info2 for BB is incorrect at the beginning of BB.
1020
1021 // Invalidate LVI information for BB if the LVI is not provably true for
1022 // all of BB.
1023 if (!isGuaranteedToTransferExecutionToSuccessor(BB))
1024 LVI->eraseBlock(BB);
1025 return true;
1026 }
1027 }
1028
1029 if (TryToUnfoldSelectInCurrBB(BB))
5
Taking false branch
1030 return true;
1031
1032 // Look if we can propagate guards to predecessors.
1033 if (HasGuards && ProcessGuards(BB))
6
Assuming the condition is false
1034 return true;
1035
1036 // What kind of constant we're looking for.
1037 ConstantPreference Preference = WantInteger;
1038
1039 // Look to see if the terminator is a conditional branch, switch or indirect
1040 // branch, if not we can't thread it.
1041 Value *Condition;
1042 Instruction *Terminator = BB->getTerminator();
1043 if (BranchInst *BI = dyn_cast<BranchInst>(Terminator)) {
7
Assuming 'BI' is non-null
8
Taking true branch
1044 // Can't thread an unconditional jump.
1045 if (BI->isUnconditional()) return false;
9
Taking false branch
1046 Condition = BI->getCondition();
1047 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(Terminator)) {
1048 Condition = SI->getCondition();
1049 } else if (IndirectBrInst *IB = dyn_cast<IndirectBrInst>(Terminator)) {
1050 // Can't thread indirect branch with no successors.
1051 if (IB->getNumSuccessors() == 0) return false;
1052 Condition = IB->getAddress()->stripPointerCasts();
1053 Preference = WantBlockAddress;
1054 } else {
1055 return false; // Must be an invoke.
1056 }
1057
1058 // Run constant folding to see if we can reduce the condition to a simple
1059 // constant.
1060 if (Instruction *I = dyn_cast<Instruction>(Condition)) {
10
Assuming 'I' is null
11
Taking false branch
1061 Value *SimpleVal =
1062 ConstantFoldInstruction(I, BB->getModule()->getDataLayout(), TLI);
1063 if (SimpleVal) {
1064 I->replaceAllUsesWith(SimpleVal);
1065 if (isInstructionTriviallyDead(I, TLI))
1066 I->eraseFromParent();
1067 Condition = SimpleVal;
1068 }
1069 }
1070
1071 // If the terminator is branching on an undef, we can pick any of the
1072 // successors to branch to. Let GetBestDestForJumpOnUndef decide.
1073 if (isa<UndefValue>(Condition)) {
12
Taking false branch
1074 unsigned BestSucc = GetBestDestForJumpOnUndef(BB);
1075 std::vector<DominatorTree::UpdateType> Updates;
1076
1077 // Fold the branch/switch.
1078 TerminatorInst *BBTerm = BB->getTerminator();
1079 Updates.reserve(BBTerm->getNumSuccessors());
1080 for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) {
1081 if (i == BestSucc) continue;
1082 BasicBlock *Succ = BBTerm->getSuccessor(i);
1083 Succ->removePredecessor(BB, true);
1084 Updates.push_back({DominatorTree::Delete, BB, Succ});
1085 }
1086
1087 LLVM_DEBUG(dbgs() << " In block '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " In block '" <<
BB->getName() << "' folding undef terminator: " <<
*BBTerm << '\n'; } } while (false)
1088 << "' folding undef terminator: " << *BBTerm << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " In block '" <<
BB->getName() << "' folding undef terminator: " <<
*BBTerm << '\n'; } } while (false)
;
1089 BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm);
1090 BBTerm->eraseFromParent();
1091 DDT->applyUpdates(Updates);
1092 return true;
1093 }
1094
1095 // If the terminator of this block is branching on a constant, simplify the
1096 // terminator to an unconditional branch. This can occur due to threading in
1097 // other blocks.
1098 if (getKnownConstant(Condition, Preference)) {
13
Taking false branch
1099 LLVM_DEBUG(dbgs() << " In block '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " In block '" <<
BB->getName() << "' folding terminator: " << *
BB->getTerminator() << '\n'; } } while (false)
1100 << "' folding terminator: " << *BB->getTerminator()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " In block '" <<
BB->getName() << "' folding terminator: " << *
BB->getTerminator() << '\n'; } } while (false)
1101 << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " In block '" <<
BB->getName() << "' folding terminator: " << *
BB->getTerminator() << '\n'; } } while (false)
;
1102 ++NumFolds;
1103 ConstantFoldTerminator(BB, true, nullptr, DDT);
1104 return true;
1105 }
1106
1107 Instruction *CondInst = dyn_cast<Instruction>(Condition);
1108
1109 // All the rest of our checks depend on the condition being an instruction.
1110 if (!CondInst) {
14
Assuming 'CondInst' is non-null
15
Taking false branch
1111 // FIXME: Unify this with code below.
1112 if (ProcessThreadableEdges(Condition, BB, Preference, Terminator))
1113 return true;
1114 return false;
1115 }
1116
1117 if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
16
Taking false branch
1118 // If we're branching on a conditional, LVI might be able to determine
1119 // it's value at the branch instruction. We only handle comparisons
1120 // against a constant at this time.
1121 // TODO: This should be extended to handle switches as well.
1122 BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
1123 Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
1124 if (CondBr && CondConst) {
1125 // We should have returned as soon as we turn a conditional branch to
1126 // unconditional. Because its no longer interesting as far as jump
1127 // threading is concerned.
1128 assert(CondBr->isConditional() && "Threading on unconditional terminator")(static_cast <bool> (CondBr->isConditional() &&
"Threading on unconditional terminator") ? void (0) : __assert_fail
("CondBr->isConditional() && \"Threading on unconditional terminator\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1128, __extension__ __PRETTY_FUNCTION__))
;
1129
1130 if (DDT->pending())
1131 LVI->disableDT();
1132 else
1133 LVI->enableDT();
1134 LazyValueInfo::Tristate Ret =
1135 LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0),
1136 CondConst, CondBr);
1137 if (Ret != LazyValueInfo::Unknown) {
1138 unsigned ToRemove = Ret == LazyValueInfo::True ? 1 : 0;
1139 unsigned ToKeep = Ret == LazyValueInfo::True ? 0 : 1;
1140 BasicBlock *ToRemoveSucc = CondBr->getSuccessor(ToRemove);
1141 ToRemoveSucc->removePredecessor(BB, true);
1142 BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
1143 CondBr->eraseFromParent();
1144 if (CondCmp->use_empty())
1145 CondCmp->eraseFromParent();
1146 // We can safely replace *some* uses of the CondInst if it has
1147 // exactly one value as returned by LVI. RAUW is incorrect in the
1148 // presence of guards and assumes, that have the `Cond` as the use. This
1149 // is because we use the guards/assume to reason about the `Cond` value
1150 // at the end of block, but RAUW unconditionally replaces all uses
1151 // including the guards/assumes themselves and the uses before the
1152 // guard/assume.
1153 else if (CondCmp->getParent() == BB) {
1154 auto *CI = Ret == LazyValueInfo::True ?
1155 ConstantInt::getTrue(CondCmp->getType()) :
1156 ConstantInt::getFalse(CondCmp->getType());
1157 ReplaceFoldableUses(CondCmp, CI);
1158 }
1159 DDT->deleteEdge(BB, ToRemoveSucc);
1160 return true;
1161 }
1162
1163 // We did not manage to simplify this branch, try to see whether
1164 // CondCmp depends on a known phi-select pattern.
1165 if (TryToUnfoldSelect(CondCmp, BB))
1166 return true;
1167 }
1168 }
1169
1170 // Check for some cases that are worth simplifying. Right now we want to look
1171 // for loads that are used by a switch or by the condition for the branch. If
1172 // we see one, check to see if it's partially redundant. If so, insert a PHI
1173 // which can then be used to thread the values.
1174 Value *SimplifyValue = CondInst;
1175 if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue))
17
Taking false branch
1176 if (isa<Constant>(CondCmp->getOperand(1)))
1177 SimplifyValue = CondCmp->getOperand(0);
1178
1179 // TODO: There are other places where load PRE would be profitable, such as
1180 // more complex comparisons.
1181 if (LoadInst *LoadI = dyn_cast<LoadInst>(SimplifyValue))
18
Assuming 'LoadI' is non-null
19
Taking true branch
1182 if (SimplifyPartiallyRedundantLoad(LoadI))
20
Calling 'JumpThreadingPass::SimplifyPartiallyRedundantLoad'
1183 return true;
1184
1185 // Before threading, try to propagate profile data backwards:
1186 if (PHINode *PN = dyn_cast<PHINode>(CondInst))
1187 if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
1188 updatePredecessorProfileMetadata(PN, BB);
1189
1190 // Handle a variety of cases where we are branching on something derived from
1191 // a PHI node in the current block. If we can prove that any predecessors
1192 // compute a predictable value based on a PHI node, thread those predecessors.
1193 if (ProcessThreadableEdges(CondInst, BB, Preference, Terminator))
1194 return true;
1195
1196 // If this is an otherwise-unfoldable branch on a phi node in the current
1197 // block, see if we can simplify.
1198 if (PHINode *PN = dyn_cast<PHINode>(CondInst))
1199 if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
1200 return ProcessBranchOnPHI(PN);
1201
1202 // If this is an otherwise-unfoldable branch on a XOR, see if we can simplify.
1203 if (CondInst->getOpcode() == Instruction::Xor &&
1204 CondInst->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
1205 return ProcessBranchOnXOR(cast<BinaryOperator>(CondInst));
1206
1207 // Search for a stronger dominating condition that can be used to simplify a
1208 // conditional branch leaving BB.
1209 if (ProcessImpliedCondition(BB))
1210 return true;
1211
1212 return false;
1213}
1214
1215bool JumpThreadingPass::ProcessImpliedCondition(BasicBlock *BB) {
1216 auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
1217 if (!BI || !BI->isConditional())
1218 return false;
1219
1220 Value *Cond = BI->getCondition();
1221 BasicBlock *CurrentBB = BB;
1222 BasicBlock *CurrentPred = BB->getSinglePredecessor();
1223 unsigned Iter = 0;
1224
1225 auto &DL = BB->getModule()->getDataLayout();
1226
1227 while (CurrentPred && Iter++ < ImplicationSearchThreshold) {
1228 auto *PBI = dyn_cast<BranchInst>(CurrentPred->getTerminator());
1229 if (!PBI || !PBI->isConditional())
1230 return false;
1231 if (PBI->getSuccessor(0) != CurrentBB && PBI->getSuccessor(1) != CurrentBB)
1232 return false;
1233
1234 bool CondIsTrue = PBI->getSuccessor(0) == CurrentBB;
1235 Optional<bool> Implication =
1236 isImpliedCondition(PBI->getCondition(), Cond, DL, CondIsTrue);
1237 if (Implication) {
1238 BasicBlock *KeepSucc = BI->getSuccessor(*Implication ? 0 : 1);
1239 BasicBlock *RemoveSucc = BI->getSuccessor(*Implication ? 1 : 0);
1240 RemoveSucc->removePredecessor(BB);
1241 BranchInst::Create(KeepSucc, BI);
1242 BI->eraseFromParent();
1243 DDT->deleteEdge(BB, RemoveSucc);
1244 return true;
1245 }
1246 CurrentBB = CurrentPred;
1247 CurrentPred = CurrentBB->getSinglePredecessor();
1248 }
1249
1250 return false;
1251}
1252
1253/// Return true if Op is an instruction defined in the given block.
1254static bool isOpDefinedInBlock(Value *Op, BasicBlock *BB) {
1255 if (Instruction *OpInst = dyn_cast<Instruction>(Op))
1256 if (OpInst->getParent() == BB)
1257 return true;
1258 return false;
1259}
1260
1261/// SimplifyPartiallyRedundantLoad - If LoadI is an obviously partially
1262/// redundant load instruction, eliminate it by replacing it with a PHI node.
1263/// This is an important optimization that encourages jump threading, and needs
1264/// to be run interlaced with other jump threading tasks.
1265bool JumpThreadingPass::SimplifyPartiallyRedundantLoad(LoadInst *LoadI) {
1266 // Don't hack volatile and ordered loads.
1267 if (!LoadI->isUnordered()) return false;
21
Taking false branch
1268
1269 // If the load is defined in a block with exactly one predecessor, it can't be
1270 // partially redundant.
1271 BasicBlock *LoadBB = LoadI->getParent();
1272 if (LoadBB->getSinglePredecessor())
22
Assuming the condition is false
23
Taking false branch
1273 return false;
1274
1275 // If the load is defined in an EH pad, it can't be partially redundant,
1276 // because the edges between the invoke and the EH pad cannot have other
1277 // instructions between them.
1278 if (LoadBB->isEHPad())
24
Assuming the condition is false
25
Taking false branch
1279 return false;
1280
1281 Value *LoadedPtr = LoadI->getOperand(0);
1282
1283 // If the loaded operand is defined in the LoadBB and its not a phi,
1284 // it can't be available in predecessors.
1285 if (isOpDefinedInBlock(LoadedPtr, LoadBB) && !isa<PHINode>(LoadedPtr))
1286 return false;
1287
1288 // Scan a few instructions up from the load, to see if it is obviously live at
1289 // the entry to its block.
1290 BasicBlock::iterator BBIt(LoadI);
1291 bool IsLoadCSE;
1292 if (Value *AvailableVal = FindAvailableLoadedValue(
26
Assuming 'AvailableVal' is null
27
Taking false branch
1293 LoadI, LoadBB, BBIt, DefMaxInstsToScan, AA, &IsLoadCSE)) {
1294 // If the value of the load is locally available within the block, just use
1295 // it. This frequently occurs for reg2mem'd allocas.
1296
1297 if (IsLoadCSE) {
1298 LoadInst *NLoadI = cast<LoadInst>(AvailableVal);
1299 combineMetadataForCSE(NLoadI, LoadI);
1300 };
1301
1302 // If the returned value is the load itself, replace with an undef. This can
1303 // only happen in dead loops.
1304 if (AvailableVal == LoadI)
1305 AvailableVal = UndefValue::get(LoadI->getType());
1306 if (AvailableVal->getType() != LoadI->getType())
1307 AvailableVal = CastInst::CreateBitOrPointerCast(
1308 AvailableVal, LoadI->getType(), "", LoadI);
1309 LoadI->replaceAllUsesWith(AvailableVal);
1310 LoadI->eraseFromParent();
1311 return true;
1312 }
1313
1314 // Otherwise, if we scanned the whole block and got to the top of the block,
1315 // we know the block is locally transparent to the load. If not, something
1316 // might clobber its value.
1317 if (BBIt != LoadBB->begin())
28
Taking false branch
1318 return false;
1319
1320 // If all of the loads and stores that feed the value have the same AA tags,
1321 // then we can propagate them onto any newly inserted loads.
1322 AAMDNodes AATags;
1323 LoadI->getAAMetadata(AATags);
1324
1325 SmallPtrSet<BasicBlock*, 8> PredsScanned;
1326
1327 using AvailablePredsTy = SmallVector<std::pair<BasicBlock *, Value *>, 8>;
1328
1329 AvailablePredsTy AvailablePreds;
1330 BasicBlock *OneUnavailablePred = nullptr;
29
'OneUnavailablePred' initialized to a null pointer value
1331 SmallVector<LoadInst*, 8> CSELoads;
1332
1333 // If we got here, the loaded value is transparent through to the start of the
1334 // block. Check to see if it is available in any of the predecessor blocks.
1335 for (BasicBlock *PredBB : predecessors(LoadBB)) {
1336 // If we already scanned this predecessor, skip it.
1337 if (!PredsScanned.insert(PredBB).second)
1338 continue;
1339
1340 BBIt = PredBB->end();
1341 unsigned NumScanedInst = 0;
1342 Value *PredAvailable = nullptr;
1343 // NOTE: We don't CSE load that is volatile or anything stronger than
1344 // unordered, that should have been checked when we entered the function.
1345 assert(LoadI->isUnordered() &&(static_cast <bool> (LoadI->isUnordered() &&
"Attempting to CSE volatile or atomic loads") ? void (0) : __assert_fail
("LoadI->isUnordered() && \"Attempting to CSE volatile or atomic loads\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1346, __extension__ __PRETTY_FUNCTION__))
1346 "Attempting to CSE volatile or atomic loads")(static_cast <bool> (LoadI->isUnordered() &&
"Attempting to CSE volatile or atomic loads") ? void (0) : __assert_fail
("LoadI->isUnordered() && \"Attempting to CSE volatile or atomic loads\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1346, __extension__ __PRETTY_FUNCTION__))
;
1347 // If this is a load on a phi pointer, phi-translate it and search
1348 // for available load/store to the pointer in predecessors.
1349 Value *Ptr = LoadedPtr->DoPHITranslation(LoadBB, PredBB);
1350 PredAvailable = FindAvailablePtrLoadStore(
1351 Ptr, LoadI->getType(), LoadI->isAtomic(), PredBB, BBIt,
1352 DefMaxInstsToScan, AA, &IsLoadCSE, &NumScanedInst);
1353
1354 // If PredBB has a single predecessor, continue scanning through the
1355 // single predecessor.
1356 BasicBlock *SinglePredBB = PredBB;
1357 while (!PredAvailable && SinglePredBB && BBIt == SinglePredBB->begin() &&
1358 NumScanedInst < DefMaxInstsToScan) {
1359 SinglePredBB = SinglePredBB->getSinglePredecessor();
1360 if (SinglePredBB) {
1361 BBIt = SinglePredBB->end();
1362 PredAvailable = FindAvailablePtrLoadStore(
1363 Ptr, LoadI->getType(), LoadI->isAtomic(), SinglePredBB, BBIt,
1364 (DefMaxInstsToScan - NumScanedInst), AA, &IsLoadCSE,
1365 &NumScanedInst);
1366 }
1367 }
1368
1369 if (!PredAvailable) {
1370 OneUnavailablePred = PredBB;
1371 continue;
1372 }
1373
1374 if (IsLoadCSE)
1375 CSELoads.push_back(cast<LoadInst>(PredAvailable));
1376
1377 // If so, this load is partially redundant. Remember this info so that we
1378 // can create a PHI node.
1379 AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable));
1380 }
1381
1382 // If the loaded value isn't available in any predecessor, it isn't partially
1383 // redundant.
1384 if (AvailablePreds.empty()) return false;
30
Taking false branch
1385
1386 // Okay, the loaded value is available in at least one (and maybe all!)
1387 // predecessors. If the value is unavailable in more than one unique
1388 // predecessor, we want to insert a merge block for those common predecessors.
1389 // This ensures that we only have to insert one reload, thus not increasing
1390 // code size.
1391 BasicBlock *UnavailablePred = nullptr;
1392
1393 // If the value is unavailable in one of predecessors, we will end up
1394 // inserting a new instruction into them. It is only valid if all the
1395 // instructions before LoadI are guaranteed to pass execution to its
1396 // successor, or if LoadI is safe to speculate.
1397 // TODO: If this logic becomes more complex, and we will perform PRE insertion
1398 // farther than to a predecessor, we need to reuse the code from GVN's PRE.
1399 // It requires domination tree analysis, so for this simple case it is an
1400 // overkill.
1401 if (PredsScanned.size() != AvailablePreds.size() &&
31
Assuming the condition is false
1402 !isSafeToSpeculativelyExecute(LoadI))
1403 for (auto I = LoadBB->begin(); &*I != LoadI; ++I)
1404 if (!isGuaranteedToTransferExecutionToSuccessor(&*I))
1405 return false;
1406
1407 // If there is exactly one predecessor where the value is unavailable, the
1408 // already computed 'OneUnavailablePred' block is it. If it ends in an
1409 // unconditional branch, we know that it isn't a critical edge.
1410 if (PredsScanned.size() == AvailablePreds.size()+1 &&
32
Assuming the condition is true
1411 OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) {
33
Called C++ object pointer is null
1412 UnavailablePred = OneUnavailablePred;
1413 } else if (PredsScanned.size() != AvailablePreds.size()) {
1414 // Otherwise, we had multiple unavailable predecessors or we had a critical
1415 // edge from the one.
1416 SmallVector<BasicBlock*, 8> PredsToSplit;
1417 SmallPtrSet<BasicBlock*, 8> AvailablePredSet;
1418
1419 for (const auto &AvailablePred : AvailablePreds)
1420 AvailablePredSet.insert(AvailablePred.first);
1421
1422 // Add all the unavailable predecessors to the PredsToSplit list.
1423 for (BasicBlock *P : predecessors(LoadBB)) {
1424 // If the predecessor is an indirect goto, we can't split the edge.
1425 if (isa<IndirectBrInst>(P->getTerminator()))
1426 return false;
1427
1428 if (!AvailablePredSet.count(P))
1429 PredsToSplit.push_back(P);
1430 }
1431
1432 // Split them out to their own block.
1433 UnavailablePred = SplitBlockPreds(LoadBB, PredsToSplit, "thread-pre-split");
1434 }
1435
1436 // If the value isn't available in all predecessors, then there will be
1437 // exactly one where it isn't available. Insert a load on that edge and add
1438 // it to the AvailablePreds list.
1439 if (UnavailablePred) {
1440 assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&(static_cast <bool> (UnavailablePred->getTerminator(
)->getNumSuccessors() == 1 && "Can't handle critical edge here!"
) ? void (0) : __assert_fail ("UnavailablePred->getTerminator()->getNumSuccessors() == 1 && \"Can't handle critical edge here!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1441, __extension__ __PRETTY_FUNCTION__))
1441 "Can't handle critical edge here!")(static_cast <bool> (UnavailablePred->getTerminator(
)->getNumSuccessors() == 1 && "Can't handle critical edge here!"
) ? void (0) : __assert_fail ("UnavailablePred->getTerminator()->getNumSuccessors() == 1 && \"Can't handle critical edge here!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1441, __extension__ __PRETTY_FUNCTION__))
;
1442 LoadInst *NewVal =
1443 new LoadInst(LoadedPtr->DoPHITranslation(LoadBB, UnavailablePred),
1444 LoadI->getName() + ".pr", false, LoadI->getAlignment(),
1445 LoadI->getOrdering(), LoadI->getSyncScopeID(),
1446 UnavailablePred->getTerminator());
1447 NewVal->setDebugLoc(LoadI->getDebugLoc());
1448 if (AATags)
1449 NewVal->setAAMetadata(AATags);
1450
1451 AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
1452 }
1453
1454 // Now we know that each predecessor of this block has a value in
1455 // AvailablePreds, sort them for efficient access as we're walking the preds.
1456 array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
1457
1458 // Create a PHI node at the start of the block for the PRE'd load value.
1459 pred_iterator PB = pred_begin(LoadBB), PE = pred_end(LoadBB);
1460 PHINode *PN = PHINode::Create(LoadI->getType(), std::distance(PB, PE), "",
1461 &LoadBB->front());
1462 PN->takeName(LoadI);
1463 PN->setDebugLoc(LoadI->getDebugLoc());
1464
1465 // Insert new entries into the PHI for each predecessor. A single block may
1466 // have multiple entries here.
1467 for (pred_iterator PI = PB; PI != PE; ++PI) {
1468 BasicBlock *P = *PI;
1469 AvailablePredsTy::iterator I =
1470 std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(),
1471 std::make_pair(P, (Value*)nullptr));
1472
1473 assert(I != AvailablePreds.end() && I->first == P &&(static_cast <bool> (I != AvailablePreds.end() &&
I->first == P && "Didn't find entry for predecessor!"
) ? void (0) : __assert_fail ("I != AvailablePreds.end() && I->first == P && \"Didn't find entry for predecessor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1474, __extension__ __PRETTY_FUNCTION__))
1474 "Didn't find entry for predecessor!")(static_cast <bool> (I != AvailablePreds.end() &&
I->first == P && "Didn't find entry for predecessor!"
) ? void (0) : __assert_fail ("I != AvailablePreds.end() && I->first == P && \"Didn't find entry for predecessor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1474, __extension__ __PRETTY_FUNCTION__))
;
1475
1476 // If we have an available predecessor but it requires casting, insert the
1477 // cast in the predecessor and use the cast. Note that we have to update the
1478 // AvailablePreds vector as we go so that all of the PHI entries for this
1479 // predecessor use the same bitcast.
1480 Value *&PredV = I->second;
1481 if (PredV->getType() != LoadI->getType())
1482 PredV = CastInst::CreateBitOrPointerCast(PredV, LoadI->getType(), "",
1483 P->getTerminator());
1484
1485 PN->addIncoming(PredV, I->first);
1486 }
1487
1488 for (LoadInst *PredLoadI : CSELoads) {
1489 combineMetadataForCSE(PredLoadI, LoadI);
1490 }
1491
1492 LoadI->replaceAllUsesWith(PN);
1493 LoadI->eraseFromParent();
1494
1495 return true;
1496}
1497
1498/// FindMostPopularDest - The specified list contains multiple possible
1499/// threadable destinations. Pick the one that occurs the most frequently in
1500/// the list.
1501static BasicBlock *
1502FindMostPopularDest(BasicBlock *BB,
1503 const SmallVectorImpl<std::pair<BasicBlock *,
1504 BasicBlock *>> &PredToDestList) {
1505 assert(!PredToDestList.empty())(static_cast <bool> (!PredToDestList.empty()) ? void (0
) : __assert_fail ("!PredToDestList.empty()", "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1505, __extension__ __PRETTY_FUNCTION__))
;
1506
1507 // Determine popularity. If there are multiple possible destinations, we
1508 // explicitly choose to ignore 'undef' destinations. We prefer to thread
1509 // blocks with known and real destinations to threading undef. We'll handle
1510 // them later if interesting.
1511 DenseMap<BasicBlock*, unsigned> DestPopularity;
1512 for (const auto &PredToDest : PredToDestList)
1513 if (PredToDest.second)
1514 DestPopularity[PredToDest.second]++;
1515
1516 if (DestPopularity.empty())
1517 return nullptr;
1518
1519 // Find the most popular dest.
1520 DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin();
1521 BasicBlock *MostPopularDest = DPI->first;
1522 unsigned Popularity = DPI->second;
1523 SmallVector<BasicBlock*, 4> SamePopularity;
1524
1525 for (++DPI; DPI != DestPopularity.end(); ++DPI) {
1526 // If the popularity of this entry isn't higher than the popularity we've
1527 // seen so far, ignore it.
1528 if (DPI->second < Popularity)
1529 ; // ignore.
1530 else if (DPI->second == Popularity) {
1531 // If it is the same as what we've seen so far, keep track of it.
1532 SamePopularity.push_back(DPI->first);
1533 } else {
1534 // If it is more popular, remember it.
1535 SamePopularity.clear();
1536 MostPopularDest = DPI->first;
1537 Popularity = DPI->second;
1538 }
1539 }
1540
1541 // Okay, now we know the most popular destination. If there is more than one
1542 // destination, we need to determine one. This is arbitrary, but we need
1543 // to make a deterministic decision. Pick the first one that appears in the
1544 // successor list.
1545 if (!SamePopularity.empty()) {
1546 SamePopularity.push_back(MostPopularDest);
1547 TerminatorInst *TI = BB->getTerminator();
1548 for (unsigned i = 0; ; ++i) {
1549 assert(i != TI->getNumSuccessors() && "Didn't find any successor!")(static_cast <bool> (i != TI->getNumSuccessors() &&
"Didn't find any successor!") ? void (0) : __assert_fail ("i != TI->getNumSuccessors() && \"Didn't find any successor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1549, __extension__ __PRETTY_FUNCTION__))
;
1550
1551 if (!is_contained(SamePopularity, TI->getSuccessor(i)))
1552 continue;
1553
1554 MostPopularDest = TI->getSuccessor(i);
1555 break;
1556 }
1557 }
1558
1559 // Okay, we have finally picked the most popular destination.
1560 return MostPopularDest;
1561}
1562
1563bool JumpThreadingPass::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
1564 ConstantPreference Preference,
1565 Instruction *CxtI) {
1566 // If threading this would thread across a loop header, don't even try to
1567 // thread the edge.
1568 if (LoopHeaders.count(BB))
1569 return false;
1570
1571 PredValueInfoTy PredValues;
1572 if (!ComputeValueKnownInPredecessors(Cond, BB, PredValues, Preference, CxtI))
1573 return false;
1574
1575 assert(!PredValues.empty() &&(static_cast <bool> (!PredValues.empty() && "ComputeValueKnownInPredecessors returned true with no values"
) ? void (0) : __assert_fail ("!PredValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1576, __extension__ __PRETTY_FUNCTION__))
1576 "ComputeValueKnownInPredecessors returned true with no values")(static_cast <bool> (!PredValues.empty() && "ComputeValueKnownInPredecessors returned true with no values"
) ? void (0) : __assert_fail ("!PredValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1576, __extension__ __PRETTY_FUNCTION__))
;
1577
1578 LLVM_DEBUG(dbgs() << "IN BB: " << *BB;do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (const auto &PredValue : PredValues) { dbgs() <<
" BB '" << BB->getName() << "': FOUND condition = "
<< *PredValue.first << " for pred '" << PredValue
.second->getName() << "'.\n"; }; } } while (false)
1579 for (const auto &PredValue : PredValues) {do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (const auto &PredValue : PredValues) { dbgs() <<
" BB '" << BB->getName() << "': FOUND condition = "
<< *PredValue.first << " for pred '" << PredValue
.second->getName() << "'.\n"; }; } } while (false)
1580 dbgs() << " BB '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (const auto &PredValue : PredValues) { dbgs() <<
" BB '" << BB->getName() << "': FOUND condition = "
<< *PredValue.first << " for pred '" << PredValue
.second->getName() << "'.\n"; }; } } while (false)
1581 << "': FOUND condition = " << *PredValue.firstdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (const auto &PredValue : PredValues) { dbgs() <<
" BB '" << BB->getName() << "': FOUND condition = "
<< *PredValue.first << " for pred '" << PredValue
.second->getName() << "'.\n"; }; } } while (false)
1582 << " for pred '" << PredValue.second->getName() << "'.\n";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (const auto &PredValue : PredValues) { dbgs() <<
" BB '" << BB->getName() << "': FOUND condition = "
<< *PredValue.first << " for pred '" << PredValue
.second->getName() << "'.\n"; }; } } while (false)
1583 })do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "IN BB: " << *BB;
for (const auto &PredValue : PredValues) { dbgs() <<
" BB '" << BB->getName() << "': FOUND condition = "
<< *PredValue.first << " for pred '" << PredValue
.second->getName() << "'.\n"; }; } } while (false)
;
1584
1585 // Decide what we want to thread through. Convert our list of known values to
1586 // a list of known destinations for each pred. This also discards duplicate
1587 // predecessors and keeps track of the undefined inputs (which are represented
1588 // as a null dest in the PredToDestList).
1589 SmallPtrSet<BasicBlock*, 16> SeenPreds;
1590 SmallVector<std::pair<BasicBlock*, BasicBlock*>, 16> PredToDestList;
1591
1592 BasicBlock *OnlyDest = nullptr;
1593 BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL;
1594 Constant *OnlyVal = nullptr;
1595 Constant *MultipleVal = (Constant *)(intptr_t)~0ULL;
1596
1597 unsigned PredWithKnownDest = 0;
1598 for (const auto &PredValue : PredValues) {
1599 BasicBlock *Pred = PredValue.second;
1600 if (!SeenPreds.insert(Pred).second)
1601 continue; // Duplicate predecessor entry.
1602
1603 Constant *Val = PredValue.first;
1604
1605 BasicBlock *DestBB;
1606 if (isa<UndefValue>(Val))
1607 DestBB = nullptr;
1608 else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1609 assert(isa<ConstantInt>(Val) && "Expecting a constant integer")(static_cast <bool> (isa<ConstantInt>(Val) &&
"Expecting a constant integer") ? void (0) : __assert_fail (
"isa<ConstantInt>(Val) && \"Expecting a constant integer\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1609, __extension__ __PRETTY_FUNCTION__))
;
1610 DestBB = BI->getSuccessor(cast<ConstantInt>(Val)->isZero());
1611 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1612 assert(isa<ConstantInt>(Val) && "Expecting a constant integer")(static_cast <bool> (isa<ConstantInt>(Val) &&
"Expecting a constant integer") ? void (0) : __assert_fail (
"isa<ConstantInt>(Val) && \"Expecting a constant integer\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1612, __extension__ __PRETTY_FUNCTION__))
;
1613 DestBB = SI->findCaseValue(cast<ConstantInt>(Val))->getCaseSuccessor();
1614 } else {
1615 assert(isa<IndirectBrInst>(BB->getTerminator())(static_cast <bool> (isa<IndirectBrInst>(BB->getTerminator
()) && "Unexpected terminator") ? void (0) : __assert_fail
("isa<IndirectBrInst>(BB->getTerminator()) && \"Unexpected terminator\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1616, __extension__ __PRETTY_FUNCTION__))
1616 && "Unexpected terminator")(static_cast <bool> (isa<IndirectBrInst>(BB->getTerminator
()) && "Unexpected terminator") ? void (0) : __assert_fail
("isa<IndirectBrInst>(BB->getTerminator()) && \"Unexpected terminator\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1616, __extension__ __PRETTY_FUNCTION__))
;
1617 assert(isa<BlockAddress>(Val) && "Expecting a constant blockaddress")(static_cast <bool> (isa<BlockAddress>(Val) &&
"Expecting a constant blockaddress") ? void (0) : __assert_fail
("isa<BlockAddress>(Val) && \"Expecting a constant blockaddress\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1617, __extension__ __PRETTY_FUNCTION__))
;
1618 DestBB = cast<BlockAddress>(Val)->getBasicBlock();
1619 }
1620
1621 // If we have exactly one destination, remember it for efficiency below.
1622 if (PredToDestList.empty()) {
1623 OnlyDest = DestBB;
1624 OnlyVal = Val;
1625 } else {
1626 if (OnlyDest != DestBB)
1627 OnlyDest = MultipleDestSentinel;
1628 // It possible we have same destination, but different value, e.g. default
1629 // case in switchinst.
1630 if (Val != OnlyVal)
1631 OnlyVal = MultipleVal;
1632 }
1633
1634 // We know where this predecessor is going.
1635 ++PredWithKnownDest;
1636
1637 // If the predecessor ends with an indirect goto, we can't change its
1638 // destination.
1639 if (isa<IndirectBrInst>(Pred->getTerminator()))
1640 continue;
1641
1642 PredToDestList.push_back(std::make_pair(Pred, DestBB));
1643 }
1644
1645 // If all edges were unthreadable, we fail.
1646 if (PredToDestList.empty())
1647 return false;
1648
1649 // If all the predecessors go to a single known successor, we want to fold,
1650 // not thread. By doing so, we do not need to duplicate the current block and
1651 // also miss potential opportunities in case we dont/cant duplicate.
1652 if (OnlyDest && OnlyDest != MultipleDestSentinel) {
1653 if (PredWithKnownDest == (size_t)pred_size(BB)) {
1654 bool SeenFirstBranchToOnlyDest = false;
1655 std::vector <DominatorTree::UpdateType> Updates;
1656 Updates.reserve(BB->getTerminator()->getNumSuccessors() - 1);
1657 for (BasicBlock *SuccBB : successors(BB)) {
1658 if (SuccBB == OnlyDest && !SeenFirstBranchToOnlyDest) {
1659 SeenFirstBranchToOnlyDest = true; // Don't modify the first branch.
1660 } else {
1661 SuccBB->removePredecessor(BB, true); // This is unreachable successor.
1662 Updates.push_back({DominatorTree::Delete, BB, SuccBB});
1663 }
1664 }
1665
1666 // Finally update the terminator.
1667 TerminatorInst *Term = BB->getTerminator();
1668 BranchInst::Create(OnlyDest, Term);
1669 Term->eraseFromParent();
1670 DDT->applyUpdates(Updates);
1671
1672 // If the condition is now dead due to the removal of the old terminator,
1673 // erase it.
1674 if (auto *CondInst = dyn_cast<Instruction>(Cond)) {
1675 if (CondInst->use_empty() && !CondInst->mayHaveSideEffects())
1676 CondInst->eraseFromParent();
1677 // We can safely replace *some* uses of the CondInst if it has
1678 // exactly one value as returned by LVI. RAUW is incorrect in the
1679 // presence of guards and assumes, that have the `Cond` as the use. This
1680 // is because we use the guards/assume to reason about the `Cond` value
1681 // at the end of block, but RAUW unconditionally replaces all uses
1682 // including the guards/assumes themselves and the uses before the
1683 // guard/assume.
1684 else if (OnlyVal && OnlyVal != MultipleVal &&
1685 CondInst->getParent() == BB)
1686 ReplaceFoldableUses(CondInst, OnlyVal);
1687 }
1688 return true;
1689 }
1690 }
1691
1692 // Determine which is the most common successor. If we have many inputs and
1693 // this block is a switch, we want to start by threading the batch that goes
1694 // to the most popular destination first. If we only know about one
1695 // threadable destination (the common case) we can avoid this.
1696 BasicBlock *MostPopularDest = OnlyDest;
1697
1698 if (MostPopularDest == MultipleDestSentinel) {
1699 // Remove any loop headers from the Dest list, ThreadEdge conservatively
1700 // won't process them, but we might have other destination that are eligible
1701 // and we still want to process.
1702 erase_if(PredToDestList,
1703 [&](const std::pair<BasicBlock *, BasicBlock *> &PredToDest) {
1704 return LoopHeaders.count(PredToDest.second) != 0;
1705 });
1706
1707 if (PredToDestList.empty())
1708 return false;
1709
1710 MostPopularDest = FindMostPopularDest(BB, PredToDestList);
1711 }
1712
1713 // Now that we know what the most popular destination is, factor all
1714 // predecessors that will jump to it into a single predecessor.
1715 SmallVector<BasicBlock*, 16> PredsToFactor;
1716 for (const auto &PredToDest : PredToDestList)
1717 if (PredToDest.second == MostPopularDest) {
1718 BasicBlock *Pred = PredToDest.first;
1719
1720 // This predecessor may be a switch or something else that has multiple
1721 // edges to the block. Factor each of these edges by listing them
1722 // according to # occurrences in PredsToFactor.
1723 for (BasicBlock *Succ : successors(Pred))
1724 if (Succ == BB)
1725 PredsToFactor.push_back(Pred);
1726 }
1727
1728 // If the threadable edges are branching on an undefined value, we get to pick
1729 // the destination that these predecessors should get to.
1730 if (!MostPopularDest)
1731 MostPopularDest = BB->getTerminator()->
1732 getSuccessor(GetBestDestForJumpOnUndef(BB));
1733
1734 // Ok, try to thread it!
1735 return ThreadEdge(BB, PredsToFactor, MostPopularDest);
1736}
1737
1738/// ProcessBranchOnPHI - We have an otherwise unthreadable conditional branch on
1739/// a PHI node in the current block. See if there are any simplifications we
1740/// can do based on inputs to the phi node.
1741bool JumpThreadingPass::ProcessBranchOnPHI(PHINode *PN) {
1742 BasicBlock *BB = PN->getParent();
1743
1744 // TODO: We could make use of this to do it once for blocks with common PHI
1745 // values.
1746 SmallVector<BasicBlock*, 1> PredBBs;
1747 PredBBs.resize(1);
1748
1749 // If any of the predecessor blocks end in an unconditional branch, we can
1750 // *duplicate* the conditional branch into that block in order to further
1751 // encourage jump threading and to eliminate cases where we have branch on a
1752 // phi of an icmp (branch on icmp is much better).
1753 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1754 BasicBlock *PredBB = PN->getIncomingBlock(i);
1755 if (BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator()))
1756 if (PredBr->isUnconditional()) {
1757 PredBBs[0] = PredBB;
1758 // Try to duplicate BB into PredBB.
1759 if (DuplicateCondBranchOnPHIIntoPred(BB, PredBBs))
1760 return true;
1761 }
1762 }
1763
1764 return false;
1765}
1766
1767/// ProcessBranchOnXOR - We have an otherwise unthreadable conditional branch on
1768/// a xor instruction in the current block. See if there are any
1769/// simplifications we can do based on inputs to the xor.
1770bool JumpThreadingPass::ProcessBranchOnXOR(BinaryOperator *BO) {
1771 BasicBlock *BB = BO->getParent();
1772
1773 // If either the LHS or RHS of the xor is a constant, don't do this
1774 // optimization.
1775 if (isa<ConstantInt>(BO->getOperand(0)) ||
1776 isa<ConstantInt>(BO->getOperand(1)))
1777 return false;
1778
1779 // If the first instruction in BB isn't a phi, we won't be able to infer
1780 // anything special about any particular predecessor.
1781 if (!isa<PHINode>(BB->front()))
1782 return false;
1783
1784 // If this BB is a landing pad, we won't be able to split the edge into it.
1785 if (BB->isEHPad())
1786 return false;
1787
1788 // If we have a xor as the branch input to this block, and we know that the
1789 // LHS or RHS of the xor in any predecessor is true/false, then we can clone
1790 // the condition into the predecessor and fix that value to true, saving some
1791 // logical ops on that path and encouraging other paths to simplify.
1792 //
1793 // This copies something like this:
1794 //
1795 // BB:
1796 // %X = phi i1 [1], [%X']
1797 // %Y = icmp eq i32 %A, %B
1798 // %Z = xor i1 %X, %Y
1799 // br i1 %Z, ...
1800 //
1801 // Into:
1802 // BB':
1803 // %Y = icmp ne i32 %A, %B
1804 // br i1 %Y, ...
1805
1806 PredValueInfoTy XorOpValues;
1807 bool isLHS = true;
1808 if (!ComputeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues,
1809 WantInteger, BO)) {
1810 assert(XorOpValues.empty())(static_cast <bool> (XorOpValues.empty()) ? void (0) : __assert_fail
("XorOpValues.empty()", "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1810, __extension__ __PRETTY_FUNCTION__))
;
1811 if (!ComputeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues,
1812 WantInteger, BO))
1813 return false;
1814 isLHS = false;
1815 }
1816
1817 assert(!XorOpValues.empty() &&(static_cast <bool> (!XorOpValues.empty() && "ComputeValueKnownInPredecessors returned true with no values"
) ? void (0) : __assert_fail ("!XorOpValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1818, __extension__ __PRETTY_FUNCTION__))
1818 "ComputeValueKnownInPredecessors returned true with no values")(static_cast <bool> (!XorOpValues.empty() && "ComputeValueKnownInPredecessors returned true with no values"
) ? void (0) : __assert_fail ("!XorOpValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 1818, __extension__ __PRETTY_FUNCTION__))
;
1819
1820 // Scan the information to see which is most popular: true or false. The
1821 // predecessors can be of the set true, false, or undef.
1822 unsigned NumTrue = 0, NumFalse = 0;
1823 for (const auto &XorOpValue : XorOpValues) {
1824 if (isa<UndefValue>(XorOpValue.first))
1825 // Ignore undefs for the count.
1826 continue;
1827 if (cast<ConstantInt>(XorOpValue.first)->isZero())
1828 ++NumFalse;
1829 else
1830 ++NumTrue;
1831 }
1832
1833 // Determine which value to split on, true, false, or undef if neither.
1834 ConstantInt *SplitVal = nullptr;
1835 if (NumTrue > NumFalse)
1836 SplitVal = ConstantInt::getTrue(BB->getContext());
1837 else if (NumTrue != 0 || NumFalse != 0)
1838 SplitVal = ConstantInt::getFalse(BB->getContext());
1839
1840 // Collect all of the blocks that this can be folded into so that we can
1841 // factor this once and clone it once.
1842 SmallVector<BasicBlock*, 8> BlocksToFoldInto;
1843 for (const auto &XorOpValue : XorOpValues) {
1844 if (XorOpValue.first != SplitVal && !isa<UndefValue>(XorOpValue.first))
1845 continue;
1846
1847 BlocksToFoldInto.push_back(XorOpValue.second);
1848 }
1849
1850 // If we inferred a value for all of the predecessors, then duplication won't
1851 // help us. However, we can just replace the LHS or RHS with the constant.
1852 if (BlocksToFoldInto.size() ==
1853 cast<PHINode>(BB->front()).getNumIncomingValues()) {
1854 if (!SplitVal) {
1855 // If all preds provide undef, just nuke the xor, because it is undef too.
1856 BO->replaceAllUsesWith(UndefValue::get(BO->getType()));
1857 BO->eraseFromParent();
1858 } else if (SplitVal->isZero()) {
1859 // If all preds provide 0, replace the xor with the other input.
1860 BO->replaceAllUsesWith(BO->getOperand(isLHS));
1861 BO->eraseFromParent();
1862 } else {
1863 // If all preds provide 1, set the computed value to 1.
1864 BO->setOperand(!isLHS, SplitVal);
1865 }
1866
1867 return true;
1868 }
1869
1870 // Try to duplicate BB into PredBB.
1871 return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto);
1872}
1873
1874/// AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new
1875/// predecessor to the PHIBB block. If it has PHI nodes, add entries for
1876/// NewPred using the entries from OldPred (suitably mapped).
1877static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB,
1878 BasicBlock *OldPred,
1879 BasicBlock *NewPred,
1880 DenseMap<Instruction*, Value*> &ValueMap) {
1881 for (PHINode &PN : PHIBB->phis()) {
1882 // Ok, we have a PHI node. Figure out what the incoming value was for the
1883 // DestBlock.
1884 Value *IV = PN.getIncomingValueForBlock(OldPred);
1885
1886 // Remap the value if necessary.
1887 if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
1888 DenseMap<Instruction*, Value*>::iterator I = ValueMap.find(Inst);
1889 if (I != ValueMap.end())
1890 IV = I->second;
1891 }
1892
1893 PN.addIncoming(IV, NewPred);
1894 }
1895}
1896
1897/// ThreadEdge - We have decided that it is safe and profitable to factor the
1898/// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB
1899/// across BB. Transform the IR to reflect this change.
1900bool JumpThreadingPass::ThreadEdge(BasicBlock *BB,
1901 const SmallVectorImpl<BasicBlock *> &PredBBs,
1902 BasicBlock *SuccBB) {
1903 // If threading to the same block as we come from, we would infinite loop.
1904 if (SuccBB == BB) {
1905 LLVM_DEBUG(dbgs() << " Not threading across BB '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not threading across BB '"
<< BB->getName() << "' - would thread to self!\n"
; } } while (false)
1906 << "' - would thread to self!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not threading across BB '"
<< BB->getName() << "' - would thread to self!\n"
; } } while (false)
;
1907 return false;
1908 }
1909
1910 // If threading this would thread across a loop header, don't thread the edge.
1911 // See the comments above FindLoopHeaders for justifications and caveats.
1912 if (LoopHeaders.count(BB) || LoopHeaders.count(SuccBB)) {
1913 LLVM_DEBUG({do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { { bool BBIsHeader = LoopHeaders.count(BB
); bool SuccIsHeader = LoopHeaders.count(SuccBB); dbgs() <<
" Not threading across " << (BBIsHeader ? "loop header BB '"
: "block BB '") << BB->getName() << "' to dest "
<< (SuccIsHeader ? "loop header BB '" : "block BB '") <<
SuccBB->getName() << "' - it might create an irreducible loop!\n"
; }; } } while (false)
1914 bool BBIsHeader = LoopHeaders.count(BB);do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { { bool BBIsHeader = LoopHeaders.count(BB
); bool SuccIsHeader = LoopHeaders.count(SuccBB); dbgs() <<
" Not threading across " << (BBIsHeader ? "loop header BB '"
: "block BB '") << BB->getName() << "' to dest "
<< (SuccIsHeader ? "loop header BB '" : "block BB '") <<
SuccBB->getName() << "' - it might create an irreducible loop!\n"
; }; } } while (false)
1915 bool SuccIsHeader = LoopHeaders.count(SuccBB);do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { { bool BBIsHeader = LoopHeaders.count(BB
); bool SuccIsHeader = LoopHeaders.count(SuccBB); dbgs() <<
" Not threading across " << (BBIsHeader ? "loop header BB '"
: "block BB '") << BB->getName() << "' to dest "
<< (SuccIsHeader ? "loop header BB '" : "block BB '") <<
SuccBB->getName() << "' - it might create an irreducible loop!\n"
; }; } } while (false)
1916 dbgs() << " Not threading across "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { { bool BBIsHeader = LoopHeaders.count(BB
); bool SuccIsHeader = LoopHeaders.count(SuccBB); dbgs() <<
" Not threading across " << (BBIsHeader ? "loop header BB '"
: "block BB '") << BB->getName() << "' to dest "
<< (SuccIsHeader ? "loop header BB '" : "block BB '") <<
SuccBB->getName() << "' - it might create an irreducible loop!\n"
; }; } } while (false)
1917 << (BBIsHeader ? "loop header BB '" : "block BB '") << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { { bool BBIsHeader = LoopHeaders.count(BB
); bool SuccIsHeader = LoopHeaders.count(SuccBB); dbgs() <<
" Not threading across " << (BBIsHeader ? "loop header BB '"
: "block BB '") << BB->getName() << "' to dest "
<< (SuccIsHeader ? "loop header BB '" : "block BB '") <<
SuccBB->getName() << "' - it might create an irreducible loop!\n"
; }; } } while (false)
1918 << "' to dest " << (SuccIsHeader ? "loop header BB '" : "block BB '")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { { bool BBIsHeader = LoopHeaders.count(BB
); bool SuccIsHeader = LoopHeaders.count(SuccBB); dbgs() <<
" Not threading across " << (BBIsHeader ? "loop header BB '"
: "block BB '") << BB->getName() << "' to dest "
<< (SuccIsHeader ? "loop header BB '" : "block BB '") <<
SuccBB->getName() << "' - it might create an irreducible loop!\n"
; }; } } while (false)
1919 << SuccBB->getName() << "' - it might create an irreducible loop!\n";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { { bool BBIsHeader = LoopHeaders.count(BB
); bool SuccIsHeader = LoopHeaders.count(SuccBB); dbgs() <<
" Not threading across " << (BBIsHeader ? "loop header BB '"
: "block BB '") << BB->getName() << "' to dest "
<< (SuccIsHeader ? "loop header BB '" : "block BB '") <<
SuccBB->getName() << "' - it might create an irreducible loop!\n"
; }; } } while (false)
1920 })do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { { bool BBIsHeader = LoopHeaders.count(BB
); bool SuccIsHeader = LoopHeaders.count(SuccBB); dbgs() <<
" Not threading across " << (BBIsHeader ? "loop header BB '"
: "block BB '") << BB->getName() << "' to dest "
<< (SuccIsHeader ? "loop header BB '" : "block BB '") <<
SuccBB->getName() << "' - it might create an irreducible loop!\n"
; }; } } while (false)
;
1921 return false;
1922 }
1923
1924 unsigned JumpThreadCost =
1925 getJumpThreadDuplicationCost(BB, BB->getTerminator(), BBDupThreshold);
1926 if (JumpThreadCost > BBDupThreshold) {
1927 LLVM_DEBUG(dbgs() << " Not threading BB '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not threading BB '" <<
BB->getName() << "' - Cost is too high: " << JumpThreadCost
<< "\n"; } } while (false)
1928 << "' - Cost is too high: " << JumpThreadCost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not threading BB '" <<
BB->getName() << "' - Cost is too high: " << JumpThreadCost
<< "\n"; } } while (false)
;
1929 return false;
1930 }
1931
1932 // And finally, do it! Start by factoring the predecessors if needed.
1933 BasicBlock *PredBB;
1934 if (PredBBs.size() == 1)
1935 PredBB = PredBBs[0];
1936 else {
1937 LLVM_DEBUG(dbgs() << " Factoring out " << PredBBs.size()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Factoring out " <<
PredBBs.size() << " common predecessors.\n"; } } while
(false)
1938 << " common predecessors.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Factoring out " <<
PredBBs.size() << " common predecessors.\n"; } } while
(false)
;
1939 PredBB = SplitBlockPreds(BB, PredBBs, ".thr_comm");
1940 }
1941
1942 // And finally, do it!
1943 LLVM_DEBUG(dbgs() << " Threading edge from '" << PredBB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Threading edge from '"
<< PredBB->getName() << "' to '" << SuccBB
->getName() << "' with cost: " << JumpThreadCost
<< ", across block:\n " << *BB << "\n";
} } while (false)
1944 << "' to '" << SuccBB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Threading edge from '"
<< PredBB->getName() << "' to '" << SuccBB
->getName() << "' with cost: " << JumpThreadCost
<< ", across block:\n " << *BB << "\n";
} } while (false)
1945 << "' with cost: " << JumpThreadCostdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Threading edge from '"
<< PredBB->getName() << "' to '" << SuccBB
->getName() << "' with cost: " << JumpThreadCost
<< ", across block:\n " << *BB << "\n";
} } while (false)
1946 << ", across block:\n " << *BB << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Threading edge from '"
<< PredBB->getName() << "' to '" << SuccBB
->getName() << "' with cost: " << JumpThreadCost
<< ", across block:\n " << *BB << "\n";
} } while (false)
;
1947
1948 if (DDT->pending())
1949 LVI->disableDT();
1950 else
1951 LVI->enableDT();
1952 LVI->threadEdge(PredBB, BB, SuccBB);
1953
1954 // We are going to have to map operands from the original BB block to the new
1955 // copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to
1956 // account for entry from PredBB.
1957 DenseMap<Instruction*, Value*> ValueMapping;
1958
1959 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(),
1960 BB->getName()+".thread",
1961 BB->getParent(), BB);
1962 NewBB->moveAfter(PredBB);
1963
1964 // Set the block frequency of NewBB.
1965 if (HasProfileData) {
1966 auto NewBBFreq =
1967 BFI->getBlockFreq(PredBB) * BPI->getEdgeProbability(PredBB, BB);
1968 BFI->setBlockFreq(NewBB, NewBBFreq.getFrequency());
1969 }
1970
1971 BasicBlock::iterator BI = BB->begin();
1972 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
1973 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
1974
1975 // Clone the non-phi instructions of BB into NewBB, keeping track of the
1976 // mapping and using it to remap operands in the cloned instructions.
1977 for (; !isa<TerminatorInst>(BI); ++BI) {
1978 Instruction *New = BI->clone();
1979 New->setName(BI->getName());
1980 NewBB->getInstList().push_back(New);
1981 ValueMapping[&*BI] = New;
1982
1983 // Remap operands to patch up intra-block references.
1984 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
1985 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
1986 DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
1987 if (I != ValueMapping.end())
1988 New->setOperand(i, I->second);
1989 }
1990 }
1991
1992 // We didn't copy the terminator from BB over to NewBB, because there is now
1993 // an unconditional jump to SuccBB. Insert the unconditional jump.
1994 BranchInst *NewBI = BranchInst::Create(SuccBB, NewBB);
1995 NewBI->setDebugLoc(BB->getTerminator()->getDebugLoc());
1996
1997 // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the
1998 // PHI nodes for NewBB now.
1999 AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping);
2000
2001 // Update the terminator of PredBB to jump to NewBB instead of BB. This
2002 // eliminates predecessors from BB, which requires us to simplify any PHI
2003 // nodes in BB.
2004 TerminatorInst *PredTerm = PredBB->getTerminator();
2005 for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i)
2006 if (PredTerm->getSuccessor(i) == BB) {
2007 BB->removePredecessor(PredBB, true);
2008 PredTerm->setSuccessor(i, NewBB);
2009 }
2010
2011 // Enqueue required DT updates.
2012 DDT->applyUpdates({{DominatorTree::Insert, NewBB, SuccBB},
2013 {DominatorTree::Insert, PredBB, NewBB},
2014 {DominatorTree::Delete, PredBB, BB}});
2015
2016 // If there were values defined in BB that are used outside the block, then we
2017 // now have to update all uses of the value to use either the original value,
2018 // the cloned value, or some PHI derived value. This can require arbitrary
2019 // PHI insertion, of which we are prepared to do, clean these up now.
2020 SSAUpdater SSAUpdate;
2021 SmallVector<Use*, 16> UsesToRename;
2022
2023 for (Instruction &I : *BB) {
2024 // Scan all uses of this instruction to see if their uses are no longer
2025 // dominated by the previous def and if so, record them in UsesToRename.
2026 // Also, skip phi operands from PredBB - we'll remove them anyway.
2027 for (Use &U : I.uses()) {
2028 Instruction *User = cast<Instruction>(U.getUser());
2029 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
2030 if (UserPN->getIncomingBlock(U) == BB)
2031 continue;
2032 } else if (User->getParent() == BB)
2033 continue;
2034
2035 UsesToRename.push_back(&U);
2036 }
2037
2038 // If there are no uses outside the block, we're done with this instruction.
2039 if (UsesToRename.empty())
2040 continue;
2041 LLVM_DEBUG(dbgs() << "JT: Renaming non-local uses of: " << I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "JT: Renaming non-local uses of: "
<< I << "\n"; } } while (false)
;
2042
2043 // We found a use of I outside of BB. Rename all uses of I that are outside
2044 // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
2045 // with the two values we know.
2046 SSAUpdate.Initialize(I.getType(), I.getName());
2047 SSAUpdate.AddAvailableValue(BB, &I);
2048 SSAUpdate.AddAvailableValue(NewBB, ValueMapping[&I]);
2049
2050 while (!UsesToRename.empty())
2051 SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
2052 LLVM_DEBUG(dbgs() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "\n"; } } while (false)
;
2053 }
2054
2055 // At this point, the IR is fully up to date and consistent. Do a quick scan
2056 // over the new instructions and zap any that are constants or dead. This
2057 // frequently happens because of phi translation.
2058 SimplifyInstructionsInBlock(NewBB, TLI);
2059
2060 // Update the edge weight from BB to SuccBB, which should be less than before.
2061 UpdateBlockFreqAndEdgeWeight(PredBB, BB, NewBB, SuccBB);
2062
2063 // Threaded an edge!
2064 ++NumThreads;
2065 return true;
2066}
2067
2068/// Create a new basic block that will be the predecessor of BB and successor of
2069/// all blocks in Preds. When profile data is available, update the frequency of
2070/// this new block.
2071BasicBlock *JumpThreadingPass::SplitBlockPreds(BasicBlock *BB,
2072 ArrayRef<BasicBlock *> Preds,
2073 const char *Suffix) {
2074 SmallVector<BasicBlock *, 2> NewBBs;
2075
2076 // Collect the frequencies of all predecessors of BB, which will be used to
2077 // update the edge weight of the result of splitting predecessors.
2078 DenseMap<BasicBlock *, BlockFrequency> FreqMap;
2079 if (HasProfileData)
2080 for (auto Pred : Preds)
2081 FreqMap.insert(std::make_pair(
2082 Pred, BFI->getBlockFreq(Pred) * BPI->getEdgeProbability(Pred, BB)));
2083
2084 // In the case when BB is a LandingPad block we create 2 new predecessors
2085 // instead of just one.
2086 if (BB->isLandingPad()) {
2087 std::string NewName = std::string(Suffix) + ".split-lp";
2088 SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(), NewBBs);
2089 } else {
2090 NewBBs.push_back(SplitBlockPredecessors(BB, Preds, Suffix));
2091 }
2092
2093 std::vector<DominatorTree::UpdateType> Updates;
2094 Updates.reserve((2 * Preds.size()) + NewBBs.size());
2095 for (auto NewBB : NewBBs) {
2096 BlockFrequency NewBBFreq(0);
2097 Updates.push_back({DominatorTree::Insert, NewBB, BB});
2098 for (auto Pred : predecessors(NewBB)) {
2099 Updates.push_back({DominatorTree::Delete, Pred, BB});
2100 Updates.push_back({DominatorTree::Insert, Pred, NewBB});
2101 if (HasProfileData) // Update frequencies between Pred -> NewBB.
2102 NewBBFreq += FreqMap.lookup(Pred);
2103 }
2104 if (HasProfileData) // Apply the summed frequency to NewBB.
2105 BFI->setBlockFreq(NewBB, NewBBFreq.getFrequency());
2106 }
2107
2108 DDT->applyUpdates(Updates);
2109 return NewBBs[0];
2110}
2111
2112bool JumpThreadingPass::doesBlockHaveProfileData(BasicBlock *BB) {
2113 const TerminatorInst *TI = BB->getTerminator();
2114 assert(TI->getNumSuccessors() > 1 && "not a split")(static_cast <bool> (TI->getNumSuccessors() > 1 &&
"not a split") ? void (0) : __assert_fail ("TI->getNumSuccessors() > 1 && \"not a split\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 2114, __extension__ __PRETTY_FUNCTION__))
;
2115
2116 MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof);
2117 if (!WeightsNode)
2118 return false;
2119
2120 MDString *MDName = cast<MDString>(WeightsNode->getOperand(0));
2121 if (MDName->getString() != "branch_weights")
2122 return false;
2123
2124 // Ensure there are weights for all of the successors. Note that the first
2125 // operand to the metadata node is a name, not a weight.
2126 return WeightsNode->getNumOperands() == TI->getNumSuccessors() + 1;
2127}
2128
2129/// Update the block frequency of BB and branch weight and the metadata on the
2130/// edge BB->SuccBB. This is done by scaling the weight of BB->SuccBB by 1 -
2131/// Freq(PredBB->BB) / Freq(BB->SuccBB).
2132void JumpThreadingPass::UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB,
2133 BasicBlock *BB,
2134 BasicBlock *NewBB,
2135 BasicBlock *SuccBB) {
2136 if (!HasProfileData)
2137 return;
2138
2139 assert(BFI && BPI && "BFI & BPI should have been created here")(static_cast <bool> (BFI && BPI && "BFI & BPI should have been created here"
) ? void (0) : __assert_fail ("BFI && BPI && \"BFI & BPI should have been created here\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 2139, __extension__ __PRETTY_FUNCTION__))
;
2140
2141 // As the edge from PredBB to BB is deleted, we have to update the block
2142 // frequency of BB.
2143 auto BBOrigFreq = BFI->getBlockFreq(BB);
2144 auto NewBBFreq = BFI->getBlockFreq(NewBB);
2145 auto BB2SuccBBFreq = BBOrigFreq * BPI->getEdgeProbability(BB, SuccBB);
2146 auto BBNewFreq = BBOrigFreq - NewBBFreq;
2147 BFI->setBlockFreq(BB, BBNewFreq.getFrequency());
2148
2149 // Collect updated outgoing edges' frequencies from BB and use them to update
2150 // edge probabilities.
2151 SmallVector<uint64_t, 4> BBSuccFreq;
2152 for (BasicBlock *Succ : successors(BB)) {
2153 auto SuccFreq = (Succ == SuccBB)
2154 ? BB2SuccBBFreq - NewBBFreq
2155 : BBOrigFreq * BPI->getEdgeProbability(BB, Succ);
2156 BBSuccFreq.push_back(SuccFreq.getFrequency());
2157 }
2158
2159 uint64_t MaxBBSuccFreq =
2160 *std::max_element(BBSuccFreq.begin(), BBSuccFreq.end());
2161
2162 SmallVector<BranchProbability, 4> BBSuccProbs;
2163 if (MaxBBSuccFreq == 0)
2164 BBSuccProbs.assign(BBSuccFreq.size(),
2165 {1, static_cast<unsigned>(BBSuccFreq.size())});
2166 else {
2167 for (uint64_t Freq : BBSuccFreq)
2168 BBSuccProbs.push_back(
2169 BranchProbability::getBranchProbability(Freq, MaxBBSuccFreq));
2170 // Normalize edge probabilities so that they sum up to one.
2171 BranchProbability::normalizeProbabilities(BBSuccProbs.begin(),
2172 BBSuccProbs.end());
2173 }
2174
2175 // Update edge probabilities in BPI.
2176 for (int I = 0, E = BBSuccProbs.size(); I < E; I++)
2177 BPI->setEdgeProbability(BB, I, BBSuccProbs[I]);
2178
2179 // Update the profile metadata as well.
2180 //
2181 // Don't do this if the profile of the transformed blocks was statically
2182 // estimated. (This could occur despite the function having an entry
2183 // frequency in completely cold parts of the CFG.)
2184 //
2185 // In this case we don't want to suggest to subsequent passes that the
2186 // calculated weights are fully consistent. Consider this graph:
2187 //
2188 // check_1
2189 // 50% / |
2190 // eq_1 | 50%
2191 // \ |
2192 // check_2
2193 // 50% / |
2194 // eq_2 | 50%
2195 // \ |
2196 // check_3
2197 // 50% / |
2198 // eq_3 | 50%
2199 // \ |
2200 //
2201 // Assuming the blocks check_* all compare the same value against 1, 2 and 3,
2202 // the overall probabilities are inconsistent; the total probability that the
2203 // value is either 1, 2 or 3 is 150%.
2204 //
2205 // As a consequence if we thread eq_1 -> check_2 to check_3, check_2->check_3
2206 // becomes 0%. This is even worse if the edge whose probability becomes 0% is
2207 // the loop exit edge. Then based solely on static estimation we would assume
2208 // the loop was extremely hot.
2209 //
2210 // FIXME this locally as well so that BPI and BFI are consistent as well. We
2211 // shouldn't make edges extremely likely or unlikely based solely on static
2212 // estimation.
2213 if (BBSuccProbs.size() >= 2 && doesBlockHaveProfileData(BB)) {
2214 SmallVector<uint32_t, 4> Weights;
2215 for (auto Prob : BBSuccProbs)
2216 Weights.push_back(Prob.getNumerator());
2217
2218 auto TI = BB->getTerminator();
2219 TI->setMetadata(
2220 LLVMContext::MD_prof,
2221 MDBuilder(TI->getParent()->getContext()).createBranchWeights(Weights));
2222 }
2223}
2224
2225/// DuplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch
2226/// to BB which contains an i1 PHI node and a conditional branch on that PHI.
2227/// If we can duplicate the contents of BB up into PredBB do so now, this
2228/// improves the odds that the branch will be on an analyzable instruction like
2229/// a compare.
2230bool JumpThreadingPass::DuplicateCondBranchOnPHIIntoPred(
2231 BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs) {
2232 assert(!PredBBs.empty() && "Can't handle an empty set")(static_cast <bool> (!PredBBs.empty() && "Can't handle an empty set"
) ? void (0) : __assert_fail ("!PredBBs.empty() && \"Can't handle an empty set\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 2232, __extension__ __PRETTY_FUNCTION__))
;
2233
2234 // If BB is a loop header, then duplicating this block outside the loop would
2235 // cause us to transform this into an irreducible loop, don't do this.
2236 // See the comments above FindLoopHeaders for justifications and caveats.
2237 if (LoopHeaders.count(BB)) {
2238 LLVM_DEBUG(dbgs() << " Not duplicating loop header '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not duplicating loop header '"
<< BB->getName() << "' into predecessor block '"
<< PredBBs[0]->getName() << "' - it might create an irreducible loop!\n"
; } } while (false)
2239 << "' into predecessor block '" << PredBBs[0]->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not duplicating loop header '"
<< BB->getName() << "' into predecessor block '"
<< PredBBs[0]->getName() << "' - it might create an irreducible loop!\n"
; } } while (false)
2240 << "' - it might create an irreducible loop!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not duplicating loop header '"
<< BB->getName() << "' into predecessor block '"
<< PredBBs[0]->getName() << "' - it might create an irreducible loop!\n"
; } } while (false)
;
2241 return false;
2242 }
2243
2244 unsigned DuplicationCost =
2245 getJumpThreadDuplicationCost(BB, BB->getTerminator(), BBDupThreshold);
2246 if (DuplicationCost > BBDupThreshold) {
2247 LLVM_DEBUG(dbgs() << " Not duplicating BB '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not duplicating BB '"
<< BB->getName() << "' - Cost is too high: " <<
DuplicationCost << "\n"; } } while (false)
2248 << "' - Cost is too high: " << DuplicationCost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Not duplicating BB '"
<< BB->getName() << "' - Cost is too high: " <<
DuplicationCost << "\n"; } } while (false)
;
2249 return false;
2250 }
2251
2252 // And finally, do it! Start by factoring the predecessors if needed.
2253 std::vector<DominatorTree::UpdateType> Updates;
2254 BasicBlock *PredBB;
2255 if (PredBBs.size() == 1)
2256 PredBB = PredBBs[0];
2257 else {
2258 LLVM_DEBUG(dbgs() << " Factoring out " << PredBBs.size()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Factoring out " <<
PredBBs.size() << " common predecessors.\n"; } } while
(false)
2259 << " common predecessors.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Factoring out " <<
PredBBs.size() << " common predecessors.\n"; } } while
(false)
;
2260 PredBB = SplitBlockPreds(BB, PredBBs, ".thr_comm");
2261 }
2262 Updates.push_back({DominatorTree::Delete, PredBB, BB});
2263
2264 // Okay, we decided to do this! Clone all the instructions in BB onto the end
2265 // of PredBB.
2266 LLVM_DEBUG(dbgs() << " Duplicating block '" << BB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Duplicating block '"
<< BB->getName() << "' into end of '" <<
PredBB->getName() << "' to eliminate branch on phi. Cost: "
<< DuplicationCost << " block is:" << *BB <<
"\n"; } } while (false)
2267 << "' into end of '" << PredBB->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Duplicating block '"
<< BB->getName() << "' into end of '" <<
PredBB->getName() << "' to eliminate branch on phi. Cost: "
<< DuplicationCost << " block is:" << *BB <<
"\n"; } } while (false)
2268 << "' to eliminate branch on phi. Cost: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Duplicating block '"
<< BB->getName() << "' into end of '" <<
PredBB->getName() << "' to eliminate branch on phi. Cost: "
<< DuplicationCost << " block is:" << *BB <<
"\n"; } } while (false)
2269 << DuplicationCost << " block is:" << *BB << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << " Duplicating block '"
<< BB->getName() << "' into end of '" <<
PredBB->getName() << "' to eliminate branch on phi. Cost: "
<< DuplicationCost << " block is:" << *BB <<
"\n"; } } while (false)
;
2270
2271 // Unless PredBB ends with an unconditional branch, split the edge so that we
2272 // can just clone the bits from BB into the end of the new PredBB.
2273 BranchInst *OldPredBranch = dyn_cast<BranchInst>(PredBB->getTerminator());
2274
2275 if (!OldPredBranch || !OldPredBranch->isUnconditional()) {
2276 BasicBlock *OldPredBB = PredBB;
2277 PredBB = SplitEdge(OldPredBB, BB);
2278 Updates.push_back({DominatorTree::Insert, OldPredBB, PredBB});
2279 Updates.push_back({DominatorTree::Insert, PredBB, BB});
2280 Updates.push_back({DominatorTree::Delete, OldPredBB, BB});
2281 OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
2282 }
2283
2284 // We are going to have to map operands from the original BB block into the
2285 // PredBB block. Evaluate PHI nodes in BB.
2286 DenseMap<Instruction*, Value*> ValueMapping;
2287
2288 BasicBlock::iterator BI = BB->begin();
2289 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
2290 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
2291 // Clone the non-phi instructions of BB into PredBB, keeping track of the
2292 // mapping and using it to remap operands in the cloned instructions.
2293 for (; BI != BB->end(); ++BI) {
2294 Instruction *New = BI->clone();
2295
2296 // Remap operands to patch up intra-block references.
2297 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
2298 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
2299 DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
2300 if (I != ValueMapping.end())
2301 New->setOperand(i, I->second);
2302 }
2303
2304 // If this instruction can be simplified after the operands are updated,
2305 // just use the simplified value instead. This frequently happens due to
2306 // phi translation.
2307 if (Value *IV = SimplifyInstruction(
2308 New,
2309 {BB->getModule()->getDataLayout(), TLI, nullptr, nullptr, New})) {
2310 ValueMapping[&*BI] = IV;
2311 if (!New->mayHaveSideEffects()) {
2312 New->deleteValue();
2313 New = nullptr;
2314 }
2315 } else {
2316 ValueMapping[&*BI] = New;
2317 }
2318 if (New) {
2319 // Otherwise, insert the new instruction into the block.
2320 New->setName(BI->getName());
2321 PredBB->getInstList().insert(OldPredBranch->getIterator(), New);
2322 // Update Dominance from simplified New instruction operands.
2323 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
2324 if (BasicBlock *SuccBB = dyn_cast<BasicBlock>(New->getOperand(i)))
2325 Updates.push_back({DominatorTree::Insert, PredBB, SuccBB});
2326 }
2327 }
2328
2329 // Check to see if the targets of the branch had PHI nodes. If so, we need to
2330 // add entries to the PHI nodes for branch from PredBB now.
2331 BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator());
2332 AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB,
2333 ValueMapping);
2334 AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
2335 ValueMapping);
2336
2337 // If there were values defined in BB that are used outside the block, then we
2338 // now have to update all uses of the value to use either the original value,
2339 // the cloned value, or some PHI derived value. This can require arbitrary
2340 // PHI insertion, of which we are prepared to do, clean these up now.
2341 SSAUpdater SSAUpdate;
2342 SmallVector<Use*, 16> UsesToRename;
2343 for (Instruction &I : *BB) {
2344 // Scan all uses of this instruction to see if it is used outside of its
2345 // block, and if so, record them in UsesToRename.
2346 for (Use &U : I.uses()) {
2347 Instruction *User = cast<Instruction>(U.getUser());
2348 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
2349 if (UserPN->getIncomingBlock(U) == BB)
2350 continue;
2351 } else if (User->getParent() == BB)
2352 continue;
2353
2354 UsesToRename.push_back(&U);
2355 }
2356
2357 // If there are no uses outside the block, we're done with this instruction.
2358 if (UsesToRename.empty())
2359 continue;
2360
2361 LLVM_DEBUG(dbgs() << "JT: Renaming non-local uses of: " << I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "JT: Renaming non-local uses of: "
<< I << "\n"; } } while (false)
;
2362
2363 // We found a use of I outside of BB. Rename all uses of I that are outside
2364 // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
2365 // with the two values we know.
2366 SSAUpdate.Initialize(I.getType(), I.getName());
2367 SSAUpdate.AddAvailableValue(BB, &I);
2368 SSAUpdate.AddAvailableValue(PredBB, ValueMapping[&I]);
2369
2370 while (!UsesToRename.empty())
2371 SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
2372 LLVM_DEBUG(dbgs() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "\n"; } } while (false)
;
2373 }
2374
2375 // PredBB no longer jumps to BB, remove entries in the PHI node for the edge
2376 // that we nuked.
2377 BB->removePredecessor(PredBB, true);
2378
2379 // Remove the unconditional branch at the end of the PredBB block.
2380 OldPredBranch->eraseFromParent();
2381 DDT->applyUpdates(Updates);
2382
2383 ++NumDupes;
2384 return true;
2385}
2386
2387/// TryToUnfoldSelect - Look for blocks of the form
2388/// bb1:
2389/// %a = select
2390/// br bb2
2391///
2392/// bb2:
2393/// %p = phi [%a, %bb1] ...
2394/// %c = icmp %p
2395/// br i1 %c
2396///
2397/// And expand the select into a branch structure if one of its arms allows %c
2398/// to be folded. This later enables threading from bb1 over bb2.
2399bool JumpThreadingPass::TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB) {
2400 BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
2401 PHINode *CondLHS = dyn_cast<PHINode>(CondCmp->getOperand(0));
2402 Constant *CondRHS = cast<Constant>(CondCmp->getOperand(1));
2403
2404 if (!CondBr || !CondBr->isConditional() || !CondLHS ||
2405 CondLHS->getParent() != BB)
2406 return false;
2407
2408 for (unsigned I = 0, E = CondLHS->getNumIncomingValues(); I != E; ++I) {
2409 BasicBlock *Pred = CondLHS->getIncomingBlock(I);
2410 SelectInst *SI = dyn_cast<SelectInst>(CondLHS->getIncomingValue(I));
2411
2412 // Look if one of the incoming values is a select in the corresponding
2413 // predecessor.
2414 if (!SI || SI->getParent() != Pred || !SI->hasOneUse())
2415 continue;
2416
2417 BranchInst *PredTerm = dyn_cast<BranchInst>(Pred->getTerminator());
2418 if (!PredTerm || !PredTerm->isUnconditional())
2419 continue;
2420
2421 // Now check if one of the select values would allow us to constant fold the
2422 // terminator in BB. We don't do the transform if both sides fold, those
2423 // cases will be threaded in any case.
2424 if (DDT->pending())
2425 LVI->disableDT();
2426 else
2427 LVI->enableDT();
2428 LazyValueInfo::Tristate LHSFolds =
2429 LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(1),
2430 CondRHS, Pred, BB, CondCmp);
2431 LazyValueInfo::Tristate RHSFolds =
2432 LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(2),
2433 CondRHS, Pred, BB, CondCmp);
2434 if ((LHSFolds != LazyValueInfo::Unknown ||
2435 RHSFolds != LazyValueInfo::Unknown) &&
2436 LHSFolds != RHSFolds) {
2437 // Expand the select.
2438 //
2439 // Pred --
2440 // | v
2441 // | NewBB
2442 // | |
2443 // |-----
2444 // v
2445 // BB
2446 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "select.unfold",
2447 BB->getParent(), BB);
2448 // Move the unconditional branch to NewBB.
2449 PredTerm->removeFromParent();
2450 NewBB->getInstList().insert(NewBB->end(), PredTerm);
2451 // Create a conditional branch and update PHI nodes.
2452 BranchInst::Create(NewBB, BB, SI->getCondition(), Pred);
2453 CondLHS->setIncomingValue(I, SI->getFalseValue());
2454 CondLHS->addIncoming(SI->getTrueValue(), NewBB);
2455 // The select is now dead.
2456 SI->eraseFromParent();
2457
2458 DDT->applyUpdates({{DominatorTree::Insert, NewBB, BB},
2459 {DominatorTree::Insert, Pred, NewBB}});
2460 // Update any other PHI nodes in BB.
2461 for (BasicBlock::iterator BI = BB->begin();
2462 PHINode *Phi = dyn_cast<PHINode>(BI); ++BI)
2463 if (Phi != CondLHS)
2464 Phi->addIncoming(Phi->getIncomingValueForBlock(Pred), NewBB);
2465 return true;
2466 }
2467 }
2468 return false;
2469}
2470
2471/// TryToUnfoldSelectInCurrBB - Look for PHI/Select or PHI/CMP/Select in the
2472/// same BB in the form
2473/// bb:
2474/// %p = phi [false, %bb1], [true, %bb2], [false, %bb3], [true, %bb4], ...
2475/// %s = select %p, trueval, falseval
2476///
2477/// or
2478///
2479/// bb:
2480/// %p = phi [0, %bb1], [1, %bb2], [0, %bb3], [1, %bb4], ...
2481/// %c = cmp %p, 0
2482/// %s = select %c, trueval, falseval
2483///
2484/// And expand the select into a branch structure. This later enables
2485/// jump-threading over bb in this pass.
2486///
2487/// Using the similar approach of SimplifyCFG::FoldCondBranchOnPHI(), unfold
2488/// select if the associated PHI has at least one constant. If the unfolded
2489/// select is not jump-threaded, it will be folded again in the later
2490/// optimizations.
2491bool JumpThreadingPass::TryToUnfoldSelectInCurrBB(BasicBlock *BB) {
2492 // If threading this would thread across a loop header, don't thread the edge.
2493 // See the comments above FindLoopHeaders for justifications and caveats.
2494 if (LoopHeaders.count(BB))
2495 return false;
2496
2497 for (BasicBlock::iterator BI = BB->begin();
2498 PHINode *PN = dyn_cast<PHINode>(BI); ++BI) {
2499 // Look for a Phi having at least one constant incoming value.
2500 if (llvm::all_of(PN->incoming_values(),
2501 [](Value *V) { return !isa<ConstantInt>(V); }))
2502 continue;
2503
2504 auto isUnfoldCandidate = [BB](SelectInst *SI, Value *V) {
2505 // Check if SI is in BB and use V as condition.
2506 if (SI->getParent() != BB)
2507 return false;
2508 Value *Cond = SI->getCondition();
2509 return (Cond && Cond == V && Cond->getType()->isIntegerTy(1));
2510 };
2511
2512 SelectInst *SI = nullptr;
2513 for (Use &U : PN->uses()) {
2514 if (ICmpInst *Cmp = dyn_cast<ICmpInst>(U.getUser())) {
2515 // Look for a ICmp in BB that compares PN with a constant and is the
2516 // condition of a Select.
2517 if (Cmp->getParent() == BB && Cmp->hasOneUse() &&
2518 isa<ConstantInt>(Cmp->getOperand(1 - U.getOperandNo())))
2519 if (SelectInst *SelectI = dyn_cast<SelectInst>(Cmp->user_back()))
2520 if (isUnfoldCandidate(SelectI, Cmp->use_begin()->get())) {
2521 SI = SelectI;
2522 break;
2523 }
2524 } else if (SelectInst *SelectI = dyn_cast<SelectInst>(U.getUser())) {
2525 // Look for a Select in BB that uses PN as condition.
2526 if (isUnfoldCandidate(SelectI, U.get())) {
2527 SI = SelectI;
2528 break;
2529 }
2530 }
2531 }
2532
2533 if (!SI)
2534 continue;
2535 // Expand the select.
2536 TerminatorInst *Term =
2537 SplitBlockAndInsertIfThen(SI->getCondition(), SI, false);
2538 BasicBlock *SplitBB = SI->getParent();
2539 BasicBlock *NewBB = Term->getParent();
2540 PHINode *NewPN = PHINode::Create(SI->getType(), 2, "", SI);
2541 NewPN->addIncoming(SI->getTrueValue(), Term->getParent());
2542 NewPN->addIncoming(SI->getFalseValue(), BB);
2543 SI->replaceAllUsesWith(NewPN);
2544 SI->eraseFromParent();
2545 // NewBB and SplitBB are newly created blocks which require insertion.
2546 std::vector<DominatorTree::UpdateType> Updates;
2547 Updates.reserve((2 * SplitBB->getTerminator()->getNumSuccessors()) + 3);
2548 Updates.push_back({DominatorTree::Insert, BB, SplitBB});
2549 Updates.push_back({DominatorTree::Insert, BB, NewBB});
2550 Updates.push_back({DominatorTree::Insert, NewBB, SplitBB});
2551 // BB's successors were moved to SplitBB, update DDT accordingly.
2552 for (auto *Succ : successors(SplitBB)) {
2553 Updates.push_back({DominatorTree::Delete, BB, Succ});
2554 Updates.push_back({DominatorTree::Insert, SplitBB, Succ});
2555 }
2556 DDT->applyUpdates(Updates);
2557 return true;
2558 }
2559 return false;
2560}
2561
2562/// Try to propagate a guard from the current BB into one of its predecessors
2563/// in case if another branch of execution implies that the condition of this
2564/// guard is always true. Currently we only process the simplest case that
2565/// looks like:
2566///
2567/// Start:
2568/// %cond = ...
2569/// br i1 %cond, label %T1, label %F1
2570/// T1:
2571/// br label %Merge
2572/// F1:
2573/// br label %Merge
2574/// Merge:
2575/// %condGuard = ...
2576/// call void(i1, ...) @llvm.experimental.guard( i1 %condGuard )[ "deopt"() ]
2577///
2578/// And cond either implies condGuard or !condGuard. In this case all the
2579/// instructions before the guard can be duplicated in both branches, and the
2580/// guard is then threaded to one of them.
2581bool JumpThreadingPass::ProcessGuards(BasicBlock *BB) {
2582 using namespace PatternMatch;
2583
2584 // We only want to deal with two predecessors.
2585 BasicBlock *Pred1, *Pred2;
2586 auto PI = pred_begin(BB), PE = pred_end(BB);
2587 if (PI == PE)
2588 return false;
2589 Pred1 = *PI++;
2590 if (PI == PE)
2591 return false;
2592 Pred2 = *PI++;
2593 if (PI != PE)
2594 return false;
2595 if (Pred1 == Pred2)
2596 return false;
2597
2598 // Try to thread one of the guards of the block.
2599 // TODO: Look up deeper than to immediate predecessor?
2600 auto *Parent = Pred1->getSinglePredecessor();
2601 if (!Parent || Parent != Pred2->getSinglePredecessor())
2602 return false;
2603
2604 if (auto *BI = dyn_cast<BranchInst>(Parent->getTerminator()))
2605 for (auto &I : *BB)
2606 if (match(&I, m_Intrinsic<Intrinsic::experimental_guard>()))
2607 if (ThreadGuard(BB, cast<IntrinsicInst>(&I), BI))
2608 return true;
2609
2610 return false;
2611}
2612
2613/// Try to propagate the guard from BB which is the lower block of a diamond
2614/// to one of its branches, in case if diamond's condition implies guard's
2615/// condition.
2616bool JumpThreadingPass::ThreadGuard(BasicBlock *BB, IntrinsicInst *Guard,
2617 BranchInst *BI) {
2618 assert(BI->getNumSuccessors() == 2 && "Wrong number of successors?")(static_cast <bool> (BI->getNumSuccessors() == 2 &&
"Wrong number of successors?") ? void (0) : __assert_fail ("BI->getNumSuccessors() == 2 && \"Wrong number of successors?\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 2618, __extension__ __PRETTY_FUNCTION__))
;
2619 assert(BI->isConditional() && "Unconditional branch has 2 successors?")(static_cast <bool> (BI->isConditional() && "Unconditional branch has 2 successors?"
) ? void (0) : __assert_fail ("BI->isConditional() && \"Unconditional branch has 2 successors?\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 2619, __extension__ __PRETTY_FUNCTION__))
;
2620 Value *GuardCond = Guard->getArgOperand(0);
2621 Value *BranchCond = BI->getCondition();
2622 BasicBlock *TrueDest = BI->getSuccessor(0);
2623 BasicBlock *FalseDest = BI->getSuccessor(1);
2624
2625 auto &DL = BB->getModule()->getDataLayout();
2626 bool TrueDestIsSafe = false;
2627 bool FalseDestIsSafe = false;
2628
2629 // True dest is safe if BranchCond => GuardCond.
2630 auto Impl = isImpliedCondition(BranchCond, GuardCond, DL);
2631 if (Impl && *Impl)
2632 TrueDestIsSafe = true;
2633 else {
2634 // False dest is safe if !BranchCond => GuardCond.
2635 Impl = isImpliedCondition(BranchCond, GuardCond, DL, /* LHSIsTrue */ false);
2636 if (Impl && *Impl)
2637 FalseDestIsSafe = true;
2638 }
2639
2640 if (!TrueDestIsSafe && !FalseDestIsSafe)
2641 return false;
2642
2643 BasicBlock *PredUnguardedBlock = TrueDestIsSafe ? TrueDest : FalseDest;
2644 BasicBlock *PredGuardedBlock = FalseDestIsSafe ? TrueDest : FalseDest;
2645
2646 ValueToValueMapTy UnguardedMapping, GuardedMapping;
2647 Instruction *AfterGuard = Guard->getNextNode();
2648 unsigned Cost = getJumpThreadDuplicationCost(BB, AfterGuard, BBDupThreshold);
2649 if (Cost > BBDupThreshold)
2650 return false;
2651 // Duplicate all instructions before the guard and the guard itself to the
2652 // branch where implication is not proved.
2653 BasicBlock *GuardedBlock = DuplicateInstructionsInSplitBetween(
2654 BB, PredGuardedBlock, AfterGuard, GuardedMapping);
2655 assert(GuardedBlock && "Could not create the guarded block?")(static_cast <bool> (GuardedBlock && "Could not create the guarded block?"
) ? void (0) : __assert_fail ("GuardedBlock && \"Could not create the guarded block?\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 2655, __extension__ __PRETTY_FUNCTION__))
;
2656 // Duplicate all instructions before the guard in the unguarded branch.
2657 // Since we have successfully duplicated the guarded block and this block
2658 // has fewer instructions, we expect it to succeed.
2659 BasicBlock *UnguardedBlock = DuplicateInstructionsInSplitBetween(
2660 BB, PredUnguardedBlock, Guard, UnguardedMapping);
2661 assert(UnguardedBlock && "Could not create the unguarded block?")(static_cast <bool> (UnguardedBlock && "Could not create the unguarded block?"
) ? void (0) : __assert_fail ("UnguardedBlock && \"Could not create the unguarded block?\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 2661, __extension__ __PRETTY_FUNCTION__))
;
2662 LLVM_DEBUG(dbgs() << "Moved guard " << *Guard << " to block "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "Moved guard " <<
*Guard << " to block " << GuardedBlock->getName
() << "\n"; } } while (false)
2663 << GuardedBlock->getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("jump-threading")) { dbgs() << "Moved guard " <<
*Guard << " to block " << GuardedBlock->getName
() << "\n"; } } while (false)
;
2664 // DuplicateInstructionsInSplitBetween inserts a new block "BB.split" between
2665 // PredBB and BB. We need to perform two inserts and one delete for each of
2666 // the above calls to update Dominators.
2667 DDT->applyUpdates(
2668 {// Guarded block split.
2669 {DominatorTree::Delete, PredGuardedBlock, BB},
2670 {DominatorTree::Insert, PredGuardedBlock, GuardedBlock},
2671 {DominatorTree::Insert, GuardedBlock, BB},
2672 // Unguarded block split.
2673 {DominatorTree::Delete, PredUnguardedBlock, BB},
2674 {DominatorTree::Insert, PredUnguardedBlock, UnguardedBlock},
2675 {DominatorTree::Insert, UnguardedBlock, BB}});
2676 // Some instructions before the guard may still have uses. For them, we need
2677 // to create Phi nodes merging their copies in both guarded and unguarded
2678 // branches. Those instructions that have no uses can be just removed.
2679 SmallVector<Instruction *, 4> ToRemove;
2680 for (auto BI = BB->begin(); &*BI != AfterGuard; ++BI)
2681 if (!isa<PHINode>(&*BI))
2682 ToRemove.push_back(&*BI);
2683
2684 Instruction *InsertionPoint = &*BB->getFirstInsertionPt();
2685 assert(InsertionPoint && "Empty block?")(static_cast <bool> (InsertionPoint && "Empty block?"
) ? void (0) : __assert_fail ("InsertionPoint && \"Empty block?\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/JumpThreading.cpp"
, 2685, __extension__ __PRETTY_FUNCTION__))
;
2686 // Substitute with Phis & remove.
2687 for (auto *Inst : reverse(ToRemove)) {
2688 if (!Inst->use_empty()) {
2689 PHINode *NewPN = PHINode::Create(Inst->getType(), 2);
2690 NewPN->addIncoming(UnguardedMapping[Inst], UnguardedBlock);
2691 NewPN->addIncoming(GuardedMapping[Inst], GuardedBlock);
2692 NewPN->insertBefore(InsertionPoint);
2693 Inst->replaceAllUsesWith(NewPN);
2694 }
2695 Inst->eraseFromParent();
2696 }
2697 return true;
2698}