| File: | lib/Transforms/Scalar/JumpThreading.cpp |
| Warning: | line 2440, column 3 Called C++ object pointer is null |
Press '?' to see keyboard shortcuts
Keyboard shortcuts:
| 1 | //===- JumpThreading.cpp - Thread control through conditional blocks ------===// | |||
| 2 | // | |||
| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. | |||
| 4 | // See https://llvm.org/LICENSE.txt for license information. | |||
| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception | |||
| 6 | // | |||
| 7 | //===----------------------------------------------------------------------===// | |||
| 8 | // | |||
| 9 | // This file implements the Jump Threading pass. | |||
| 10 | // | |||
| 11 | //===----------------------------------------------------------------------===// | |||
| 12 | ||||
| 13 | #include "llvm/Transforms/Scalar/JumpThreading.h" | |||
| 14 | #include "llvm/ADT/DenseMap.h" | |||
| 15 | #include "llvm/ADT/DenseSet.h" | |||
| 16 | #include "llvm/ADT/Optional.h" | |||
| 17 | #include "llvm/ADT/STLExtras.h" | |||
| 18 | #include "llvm/ADT/SmallPtrSet.h" | |||
| 19 | #include "llvm/ADT/SmallVector.h" | |||
| 20 | #include "llvm/ADT/Statistic.h" | |||
| 21 | #include "llvm/Analysis/AliasAnalysis.h" | |||
| 22 | #include "llvm/Analysis/BlockFrequencyInfo.h" | |||
| 23 | #include "llvm/Analysis/BranchProbabilityInfo.h" | |||
| 24 | #include "llvm/Analysis/CFG.h" | |||
| 25 | #include "llvm/Analysis/ConstantFolding.h" | |||
| 26 | #include "llvm/Analysis/DomTreeUpdater.h" | |||
| 27 | #include "llvm/Analysis/GlobalsModRef.h" | |||
| 28 | #include "llvm/Analysis/GuardUtils.h" | |||
| 29 | #include "llvm/Analysis/InstructionSimplify.h" | |||
| 30 | #include "llvm/Analysis/LazyValueInfo.h" | |||
| 31 | #include "llvm/Analysis/Loads.h" | |||
| 32 | #include "llvm/Analysis/LoopInfo.h" | |||
| 33 | #include "llvm/Analysis/TargetLibraryInfo.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/Local.h" | |||
| 69 | #include "llvm/Transforms/Utils/SSAUpdater.h" | |||
| 70 | #include "llvm/Transforms/Utils/ValueMapper.h" | |||
| 71 | #include <algorithm> | |||
| 72 | #include <cassert> | |||
| 73 | #include <cstddef> | |||
| 74 | #include <cstdint> | |||
| 75 | #include <iterator> | |||
| 76 | #include <memory> | |||
| 77 | #include <utility> | |||
| 78 | ||||
| 79 | using namespace llvm; | |||
| 80 | using namespace jumpthreading; | |||
| 81 | ||||
| 82 | #define DEBUG_TYPE"jump-threading" "jump-threading" | |||
| 83 | ||||
| 84 | STATISTIC(NumThreads, "Number of jumps threaded")static llvm::Statistic NumThreads = {"jump-threading", "NumThreads" , "Number of jumps threaded"}; | |||
| 85 | STATISTIC(NumFolds, "Number of terminators folded")static llvm::Statistic NumFolds = {"jump-threading", "NumFolds" , "Number of terminators folded"}; | |||
| 86 | STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi")static llvm::Statistic NumDupes = {"jump-threading", "NumDupes" , "Number of branch blocks duplicated to eliminate phi"}; | |||
| 87 | ||||
| 88 | static cl::opt<unsigned> | |||
| 89 | BBDuplicateThreshold("jump-threading-threshold", | |||
| 90 | cl::desc("Max block size to duplicate for jump threading"), | |||
| 91 | cl::init(6), cl::Hidden); | |||
| 92 | ||||
| 93 | static cl::opt<unsigned> | |||
| 94 | ImplicationSearchThreshold( | |||
| 95 | "jump-threading-implication-search-threshold", | |||
| 96 | cl::desc("The number of predecessors to search for a stronger " | |||
| 97 | "condition to use to thread over a weaker condition"), | |||
| 98 | cl::init(3), cl::Hidden); | |||
| 99 | ||||
| 100 | static cl::opt<bool> PrintLVIAfterJumpThreading( | |||
| 101 | "print-lvi-after-jump-threading", | |||
| 102 | cl::desc("Print the LazyValueInfo cache after JumpThreading"), cl::init(false), | |||
| 103 | cl::Hidden); | |||
| 104 | ||||
| 105 | static cl::opt<bool> ThreadAcrossLoopHeaders( | |||
| 106 | "jump-threading-across-loop-headers", | |||
| 107 | cl::desc("Allow JumpThreading to thread across loop headers, for testing"), | |||
| 108 | cl::init(false), cl::Hidden); | |||
| 109 | ||||
| 110 | ||||
| 111 | namespace { | |||
| 112 | ||||
| 113 | /// This pass performs 'jump threading', which looks at blocks that have | |||
| 114 | /// multiple predecessors and multiple successors. If one or more of the | |||
| 115 | /// predecessors of the block can be proven to always jump to one of the | |||
| 116 | /// successors, we forward the edge from the predecessor to the successor by | |||
| 117 | /// duplicating the contents of this block. | |||
| 118 | /// | |||
| 119 | /// An example of when this can occur is code like this: | |||
| 120 | /// | |||
| 121 | /// if () { ... | |||
| 122 | /// X = 4; | |||
| 123 | /// } | |||
| 124 | /// if (X < 3) { | |||
| 125 | /// | |||
| 126 | /// In this case, the unconditional branch at the end of the first if can be | |||
| 127 | /// revectored to the false side of the second if. | |||
| 128 | class JumpThreading : public FunctionPass { | |||
| 129 | JumpThreadingPass Impl; | |||
| 130 | ||||
| 131 | public: | |||
| 132 | static char ID; // Pass identification | |||
| 133 | ||||
| 134 | JumpThreading(int T = -1) : FunctionPass(ID), Impl(T) { | |||
| 135 | initializeJumpThreadingPass(*PassRegistry::getPassRegistry()); | |||
| 136 | } | |||
| 137 | ||||
| 138 | bool runOnFunction(Function &F) override; | |||
| 139 | ||||
| 140 | void getAnalysisUsage(AnalysisUsage &AU) const override { | |||
| 141 | AU.addRequired<DominatorTreeWrapperPass>(); | |||
| 142 | AU.addPreserved<DominatorTreeWrapperPass>(); | |||
| 143 | AU.addRequired<AAResultsWrapperPass>(); | |||
| 144 | AU.addRequired<LazyValueInfoWrapperPass>(); | |||
| 145 | AU.addPreserved<LazyValueInfoWrapperPass>(); | |||
| 146 | AU.addPreserved<GlobalsAAWrapperPass>(); | |||
| 147 | AU.addRequired<TargetLibraryInfoWrapperPass>(); | |||
| 148 | } | |||
| 149 | ||||
| 150 | void releaseMemory() override { Impl.releaseMemory(); } | |||
| 151 | }; | |||
| 152 | ||||
| 153 | } // end anonymous namespace | |||
| 154 | ||||
| 155 | char JumpThreading::ID = 0; | |||
| 156 | ||||
| 157 | INITIALIZE_PASS_BEGIN(JumpThreading, "jump-threading",static void *initializeJumpThreadingPassOnce(PassRegistry & Registry) { | |||
| 158 | "Jump Threading", false, false)static void *initializeJumpThreadingPassOnce(PassRegistry & Registry) { | |||
| 159 | INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry); | |||
| 160 | INITIALIZE_PASS_DEPENDENCY(LazyValueInfoWrapperPass)initializeLazyValueInfoWrapperPassPass(Registry); | |||
| 161 | INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)initializeTargetLibraryInfoWrapperPassPass(Registry); | |||
| 162 | INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)initializeAAResultsWrapperPassPass(Registry); | |||
| 163 | INITIALIZE_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)); } | |||
| 164 | "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)); } | |||
| 165 | ||||
| 166 | // Public interface to the Jump Threading pass | |||
| 167 | FunctionPass *llvm::createJumpThreadingPass(int Threshold) { | |||
| 168 | return new JumpThreading(Threshold); | |||
| 169 | } | |||
| 170 | ||||
| 171 | JumpThreadingPass::JumpThreadingPass(int T) { | |||
| 172 | BBDupThreshold = (T == -1) ? BBDuplicateThreshold : unsigned(T); | |||
| 173 | } | |||
| 174 | ||||
| 175 | // Update branch probability information according to conditional | |||
| 176 | // branch probability. This is usually made possible for cloned branches | |||
| 177 | // in inline instances by the context specific profile in the caller. | |||
| 178 | // For instance, | |||
| 179 | // | |||
| 180 | // [Block PredBB] | |||
| 181 | // [Branch PredBr] | |||
| 182 | // if (t) { | |||
| 183 | // Block A; | |||
| 184 | // } else { | |||
| 185 | // Block B; | |||
| 186 | // } | |||
| 187 | // | |||
| 188 | // [Block BB] | |||
| 189 | // cond = PN([true, %A], [..., %B]); // PHI node | |||
| 190 | // [Branch CondBr] | |||
| 191 | // if (cond) { | |||
| 192 | // ... // P(cond == true) = 1% | |||
| 193 | // } | |||
| 194 | // | |||
| 195 | // Here we know that when block A is taken, cond must be true, which means | |||
| 196 | // P(cond == true | A) = 1 | |||
| 197 | // | |||
| 198 | // Given that P(cond == true) = P(cond == true | A) * P(A) + | |||
| 199 | // P(cond == true | B) * P(B) | |||
| 200 | // we get: | |||
| 201 | // P(cond == true ) = P(A) + P(cond == true | B) * P(B) | |||
| 202 | // | |||
| 203 | // which gives us: | |||
| 204 | // P(A) is less than P(cond == true), i.e. | |||
| 205 | // P(t == true) <= P(cond == true) | |||
| 206 | // | |||
| 207 | // In other words, if we know P(cond == true) is unlikely, we know | |||
| 208 | // that P(t == true) is also unlikely. | |||
| 209 | // | |||
| 210 | static void updatePredecessorProfileMetadata(PHINode *PN, BasicBlock *BB) { | |||
| 211 | BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator()); | |||
| 212 | if (!CondBr) | |||
| 213 | return; | |||
| 214 | ||||
| 215 | BranchProbability BP; | |||
| 216 | uint64_t TrueWeight, FalseWeight; | |||
| 217 | if (!CondBr->extractProfMetadata(TrueWeight, FalseWeight)) | |||
| 218 | return; | |||
| 219 | ||||
| 220 | // Returns the outgoing edge of the dominating predecessor block | |||
| 221 | // that leads to the PhiNode's incoming block: | |||
| 222 | auto GetPredOutEdge = | |||
| 223 | [](BasicBlock *IncomingBB, | |||
| 224 | BasicBlock *PhiBB) -> std::pair<BasicBlock *, BasicBlock *> { | |||
| 225 | auto *PredBB = IncomingBB; | |||
| 226 | auto *SuccBB = PhiBB; | |||
| 227 | SmallPtrSet<BasicBlock *, 16> Visited; | |||
| 228 | while (true) { | |||
| 229 | BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator()); | |||
| 230 | if (PredBr && PredBr->isConditional()) | |||
| 231 | return {PredBB, SuccBB}; | |||
| 232 | Visited.insert(PredBB); | |||
| 233 | auto *SinglePredBB = PredBB->getSinglePredecessor(); | |||
| 234 | if (!SinglePredBB) | |||
| 235 | return {nullptr, nullptr}; | |||
| 236 | ||||
| 237 | // Stop searching when SinglePredBB has been visited. It means we see | |||
| 238 | // an unreachable loop. | |||
| 239 | if (Visited.count(SinglePredBB)) | |||
| 240 | return {nullptr, nullptr}; | |||
| 241 | ||||
| 242 | SuccBB = PredBB; | |||
| 243 | PredBB = SinglePredBB; | |||
| 244 | } | |||
| 245 | }; | |||
| 246 | ||||
| 247 | for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { | |||
| 248 | Value *PhiOpnd = PN->getIncomingValue(i); | |||
| 249 | ConstantInt *CI = dyn_cast<ConstantInt>(PhiOpnd); | |||
| 250 | ||||
| 251 | if (!CI || !CI->getType()->isIntegerTy(1)) | |||
| 252 | continue; | |||
| 253 | ||||
| 254 | BP = (CI->isOne() ? BranchProbability::getBranchProbability( | |||
| 255 | TrueWeight, TrueWeight + FalseWeight) | |||
| 256 | : BranchProbability::getBranchProbability( | |||
| 257 | FalseWeight, TrueWeight + FalseWeight)); | |||
| 258 | ||||
| 259 | auto PredOutEdge = GetPredOutEdge(PN->getIncomingBlock(i), BB); | |||
| 260 | if (!PredOutEdge.first) | |||
| 261 | return; | |||
| 262 | ||||
| 263 | BasicBlock *PredBB = PredOutEdge.first; | |||
| 264 | BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator()); | |||
| 265 | if (!PredBr) | |||
| 266 | return; | |||
| 267 | ||||
| 268 | uint64_t PredTrueWeight, PredFalseWeight; | |||
| 269 | // FIXME: We currently only set the profile data when it is missing. | |||
| 270 | // With PGO, this can be used to refine even existing profile data with | |||
| 271 | // context information. This needs to be done after more performance | |||
| 272 | // testing. | |||
| 273 | if (PredBr->extractProfMetadata(PredTrueWeight, PredFalseWeight)) | |||
| 274 | continue; | |||
| 275 | ||||
| 276 | // We can not infer anything useful when BP >= 50%, because BP is the | |||
| 277 | // upper bound probability value. | |||
| 278 | if (BP >= BranchProbability(50, 100)) | |||
| 279 | continue; | |||
| 280 | ||||
| 281 | SmallVector<uint32_t, 2> Weights; | |||
| 282 | if (PredBr->getSuccessor(0) == PredOutEdge.second) { | |||
| 283 | Weights.push_back(BP.getNumerator()); | |||
| 284 | Weights.push_back(BP.getCompl().getNumerator()); | |||
| 285 | } else { | |||
| 286 | Weights.push_back(BP.getCompl().getNumerator()); | |||
| 287 | Weights.push_back(BP.getNumerator()); | |||
| 288 | } | |||
| 289 | PredBr->setMetadata(LLVMContext::MD_prof, | |||
| 290 | MDBuilder(PredBr->getParent()->getContext()) | |||
| 291 | .createBranchWeights(Weights)); | |||
| 292 | } | |||
| 293 | } | |||
| 294 | ||||
| 295 | /// runOnFunction - Toplevel algorithm. | |||
| 296 | bool JumpThreading::runOnFunction(Function &F) { | |||
| 297 | if (skipFunction(F)) | |||
| 298 | return false; | |||
| 299 | auto TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); | |||
| 300 | // Get DT analysis before LVI. When LVI is initialized it conditionally adds | |||
| 301 | // DT if it's available. | |||
| 302 | auto DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); | |||
| 303 | auto LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI(); | |||
| 304 | auto AA = &getAnalysis<AAResultsWrapperPass>().getAAResults(); | |||
| 305 | DomTreeUpdater DTU(*DT, DomTreeUpdater::UpdateStrategy::Lazy); | |||
| 306 | std::unique_ptr<BlockFrequencyInfo> BFI; | |||
| 307 | std::unique_ptr<BranchProbabilityInfo> BPI; | |||
| 308 | bool HasProfileData = F.hasProfileData(); | |||
| 309 | if (HasProfileData) { | |||
| 310 | LoopInfo LI{DominatorTree(F)}; | |||
| 311 | BPI.reset(new BranchProbabilityInfo(F, LI, TLI)); | |||
| 312 | BFI.reset(new BlockFrequencyInfo(F, *BPI, LI)); | |||
| 313 | } | |||
| 314 | ||||
| 315 | bool Changed = Impl.runImpl(F, TLI, LVI, AA, &DTU, HasProfileData, | |||
| 316 | std::move(BFI), std::move(BPI)); | |||
| 317 | if (PrintLVIAfterJumpThreading) { | |||
| 318 | dbgs() << "LVI for function '" << F.getName() << "':\n"; | |||
| 319 | LVI->printLVI(F, *DT, dbgs()); | |||
| 320 | } | |||
| 321 | return Changed; | |||
| 322 | } | |||
| 323 | ||||
| 324 | PreservedAnalyses JumpThreadingPass::run(Function &F, | |||
| 325 | FunctionAnalysisManager &AM) { | |||
| 326 | auto &TLI = AM.getResult<TargetLibraryAnalysis>(F); | |||
| 327 | // Get DT analysis before LVI. When LVI is initialized it conditionally adds | |||
| 328 | // DT if it's available. | |||
| 329 | auto &DT = AM.getResult<DominatorTreeAnalysis>(F); | |||
| 330 | auto &LVI = AM.getResult<LazyValueAnalysis>(F); | |||
| 331 | auto &AA = AM.getResult<AAManager>(F); | |||
| 332 | DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy); | |||
| 333 | ||||
| 334 | std::unique_ptr<BlockFrequencyInfo> BFI; | |||
| 335 | std::unique_ptr<BranchProbabilityInfo> BPI; | |||
| 336 | if (F.hasProfileData()) { | |||
| 337 | LoopInfo LI{DominatorTree(F)}; | |||
| 338 | BPI.reset(new BranchProbabilityInfo(F, LI, &TLI)); | |||
| 339 | BFI.reset(new BlockFrequencyInfo(F, *BPI, LI)); | |||
| 340 | } | |||
| 341 | ||||
| 342 | bool Changed = runImpl(F, &TLI, &LVI, &AA, &DTU, HasProfileData, | |||
| 343 | std::move(BFI), std::move(BPI)); | |||
| 344 | ||||
| 345 | if (!Changed) | |||
| 346 | return PreservedAnalyses::all(); | |||
| 347 | PreservedAnalyses PA; | |||
| 348 | PA.preserve<GlobalsAA>(); | |||
| 349 | PA.preserve<DominatorTreeAnalysis>(); | |||
| 350 | PA.preserve<LazyValueAnalysis>(); | |||
| 351 | return PA; | |||
| 352 | } | |||
| 353 | ||||
| 354 | bool JumpThreadingPass::runImpl(Function &F, TargetLibraryInfo *TLI_, | |||
| 355 | LazyValueInfo *LVI_, AliasAnalysis *AA_, | |||
| 356 | DomTreeUpdater *DTU_, bool HasProfileData_, | |||
| 357 | std::unique_ptr<BlockFrequencyInfo> BFI_, | |||
| 358 | std::unique_ptr<BranchProbabilityInfo> BPI_) { | |||
| 359 | 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); | |||
| 360 | TLI = TLI_; | |||
| 361 | LVI = LVI_; | |||
| 362 | AA = AA_; | |||
| 363 | DTU = DTU_; | |||
| 364 | BFI.reset(); | |||
| 365 | BPI.reset(); | |||
| 366 | // When profile data is available, we need to update edge weights after | |||
| 367 | // successful jump threading, which requires both BPI and BFI being available. | |||
| 368 | HasProfileData = HasProfileData_; | |||
| 369 | auto *GuardDecl = F.getParent()->getFunction( | |||
| 370 | Intrinsic::getName(Intrinsic::experimental_guard)); | |||
| 371 | HasGuards = GuardDecl && !GuardDecl->use_empty(); | |||
| 372 | if (HasProfileData) { | |||
| 373 | BPI = std::move(BPI_); | |||
| 374 | BFI = std::move(BFI_); | |||
| 375 | } | |||
| 376 | ||||
| 377 | // JumpThreading must not processes blocks unreachable from entry. It's a | |||
| 378 | // waste of compute time and can potentially lead to hangs. | |||
| 379 | SmallPtrSet<BasicBlock *, 16> Unreachable; | |||
| 380 | assert(DTU && "DTU isn't passed into JumpThreading before using it.")((DTU && "DTU isn't passed into JumpThreading before using it." ) ? static_cast<void> (0) : __assert_fail ("DTU && \"DTU isn't passed into JumpThreading before using it.\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 380, __PRETTY_FUNCTION__)); | |||
| 381 | assert(DTU->hasDomTree() && "JumpThreading relies on DomTree to proceed.")((DTU->hasDomTree() && "JumpThreading relies on DomTree to proceed." ) ? static_cast<void> (0) : __assert_fail ("DTU->hasDomTree() && \"JumpThreading relies on DomTree to proceed.\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 381, __PRETTY_FUNCTION__)); | |||
| 382 | DominatorTree &DT = DTU->getDomTree(); | |||
| 383 | for (auto &BB : F) | |||
| 384 | if (!DT.isReachableFromEntry(&BB)) | |||
| 385 | Unreachable.insert(&BB); | |||
| 386 | ||||
| 387 | if (!ThreadAcrossLoopHeaders) | |||
| 388 | FindLoopHeaders(F); | |||
| 389 | ||||
| 390 | bool EverChanged = false; | |||
| 391 | bool Changed; | |||
| 392 | do { | |||
| 393 | Changed = false; | |||
| 394 | for (auto &BB : F) { | |||
| 395 | if (Unreachable.count(&BB)) | |||
| 396 | continue; | |||
| 397 | while (ProcessBlock(&BB)) // Thread all of the branches we can over BB. | |||
| 398 | Changed = true; | |||
| 399 | // Stop processing BB if it's the entry or is now deleted. The following | |||
| 400 | // routines attempt to eliminate BB and locating a suitable replacement | |||
| 401 | // for the entry is non-trivial. | |||
| 402 | if (&BB == &F.getEntryBlock() || DTU->isBBPendingDeletion(&BB)) | |||
| 403 | continue; | |||
| 404 | ||||
| 405 | if (pred_empty(&BB)) { | |||
| 406 | // When ProcessBlock makes BB unreachable it doesn't bother to fix up | |||
| 407 | // the instructions in it. We must remove BB to prevent invalid IR. | |||
| 408 | 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) | |||
| 409 | << "' 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) | |||
| 410 | << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("jump-threading")) { dbgs() << " JT: Deleting dead block '" << BB.getName() << "' with terminator: " << *BB.getTerminator() << '\n'; } } while (false); | |||
| 411 | LoopHeaders.erase(&BB); | |||
| 412 | LVI->eraseBlock(&BB); | |||
| 413 | DeleteDeadBlock(&BB, DTU); | |||
| 414 | Changed = true; | |||
| 415 | continue; | |||
| 416 | } | |||
| 417 | ||||
| 418 | // ProcessBlock doesn't thread BBs with unconditional TIs. However, if BB | |||
| 419 | // is "almost empty", we attempt to merge BB with its sole successor. | |||
| 420 | auto *BI = dyn_cast<BranchInst>(BB.getTerminator()); | |||
| 421 | if (BI && BI->isUnconditional() && | |||
| 422 | // The terminator must be the only non-phi instruction in BB. | |||
| 423 | BB.getFirstNonPHIOrDbg()->isTerminator() && | |||
| 424 | // Don't alter Loop headers and latches to ensure another pass can | |||
| 425 | // detect and transform nested loops later. | |||
| 426 | !LoopHeaders.count(&BB) && !LoopHeaders.count(BI->getSuccessor(0)) && | |||
| 427 | TryToSimplifyUncondBranchFromEmptyBlock(&BB, DTU)) { | |||
| 428 | // BB is valid for cleanup here because we passed in DTU. F remains | |||
| 429 | // BB's parent until a DTU->getDomTree() event. | |||
| 430 | LVI->eraseBlock(&BB); | |||
| 431 | Changed = true; | |||
| 432 | } | |||
| 433 | } | |||
| 434 | EverChanged |= Changed; | |||
| 435 | } while (Changed); | |||
| 436 | ||||
| 437 | LoopHeaders.clear(); | |||
| 438 | // Flush only the Dominator Tree. | |||
| 439 | DTU->getDomTree(); | |||
| 440 | LVI->enableDT(); | |||
| 441 | return EverChanged; | |||
| 442 | } | |||
| 443 | ||||
| 444 | // Replace uses of Cond with ToVal when safe to do so. If all uses are | |||
| 445 | // replaced, we can remove Cond. We cannot blindly replace all uses of Cond | |||
| 446 | // because we may incorrectly replace uses when guards/assumes are uses of | |||
| 447 | // of `Cond` and we used the guards/assume to reason about the `Cond` value | |||
| 448 | // at the end of block. RAUW unconditionally replaces all uses | |||
| 449 | // including the guards/assumes themselves and the uses before the | |||
| 450 | // guard/assume. | |||
| 451 | static void ReplaceFoldableUses(Instruction *Cond, Value *ToVal) { | |||
| 452 | assert(Cond->getType() == ToVal->getType())((Cond->getType() == ToVal->getType()) ? static_cast< void> (0) : __assert_fail ("Cond->getType() == ToVal->getType()" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 452, __PRETTY_FUNCTION__)); | |||
| 453 | auto *BB = Cond->getParent(); | |||
| 454 | // We can unconditionally replace all uses in non-local blocks (i.e. uses | |||
| 455 | // strictly dominated by BB), since LVI information is true from the | |||
| 456 | // terminator of BB. | |||
| 457 | replaceNonLocalUsesWith(Cond, ToVal); | |||
| 458 | for (Instruction &I : reverse(*BB)) { | |||
| 459 | // Reached the Cond whose uses we are trying to replace, so there are no | |||
| 460 | // more uses. | |||
| 461 | if (&I == Cond) | |||
| 462 | break; | |||
| 463 | // We only replace uses in instructions that are guaranteed to reach the end | |||
| 464 | // of BB, where we know Cond is ToVal. | |||
| 465 | if (!isGuaranteedToTransferExecutionToSuccessor(&I)) | |||
| 466 | break; | |||
| 467 | I.replaceUsesOfWith(Cond, ToVal); | |||
| 468 | } | |||
| 469 | if (Cond->use_empty() && !Cond->mayHaveSideEffects()) | |||
| 470 | Cond->eraseFromParent(); | |||
| 471 | } | |||
| 472 | ||||
| 473 | /// Return the cost of duplicating a piece of this block from first non-phi | |||
| 474 | /// and before StopAt instruction to thread across it. Stop scanning the block | |||
| 475 | /// when exceeding the threshold. If duplication is impossible, returns ~0U. | |||
| 476 | static unsigned getJumpThreadDuplicationCost(BasicBlock *BB, | |||
| 477 | Instruction *StopAt, | |||
| 478 | unsigned Threshold) { | |||
| 479 | assert(StopAt->getParent() == BB && "Not an instruction from proper BB?")((StopAt->getParent() == BB && "Not an instruction from proper BB?" ) ? static_cast<void> (0) : __assert_fail ("StopAt->getParent() == BB && \"Not an instruction from proper BB?\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 479, __PRETTY_FUNCTION__)); | |||
| 480 | /// Ignore PHI nodes, these will be flattened when duplication happens. | |||
| 481 | BasicBlock::const_iterator I(BB->getFirstNonPHI()); | |||
| 482 | ||||
| 483 | // FIXME: THREADING will delete values that are just used to compute the | |||
| 484 | // branch, so they shouldn't count against the duplication cost. | |||
| 485 | ||||
| 486 | unsigned Bonus = 0; | |||
| 487 | if (BB->getTerminator() == StopAt) { | |||
| 488 | // Threading through a switch statement is particularly profitable. If this | |||
| 489 | // block ends in a switch, decrease its cost to make it more likely to | |||
| 490 | // happen. | |||
| 491 | if (isa<SwitchInst>(StopAt)) | |||
| 492 | Bonus = 6; | |||
| 493 | ||||
| 494 | // The same holds for indirect branches, but slightly more so. | |||
| 495 | if (isa<IndirectBrInst>(StopAt)) | |||
| 496 | Bonus = 8; | |||
| 497 | } | |||
| 498 | ||||
| 499 | // Bump the threshold up so the early exit from the loop doesn't skip the | |||
| 500 | // terminator-based Size adjustment at the end. | |||
| 501 | Threshold += Bonus; | |||
| 502 | ||||
| 503 | // Sum up the cost of each instruction until we get to the terminator. Don't | |||
| 504 | // include the terminator because the copy won't include it. | |||
| 505 | unsigned Size = 0; | |||
| 506 | for (; &*I != StopAt; ++I) { | |||
| 507 | ||||
| 508 | // Stop scanning the block if we've reached the threshold. | |||
| 509 | if (Size > Threshold) | |||
| 510 | return Size; | |||
| 511 | ||||
| 512 | // Debugger intrinsics don't incur code size. | |||
| 513 | if (isa<DbgInfoIntrinsic>(I)) continue; | |||
| 514 | ||||
| 515 | // If this is a pointer->pointer bitcast, it is free. | |||
| 516 | if (isa<BitCastInst>(I) && I->getType()->isPointerTy()) | |||
| 517 | continue; | |||
| 518 | ||||
| 519 | // Bail out if this instruction gives back a token type, it is not possible | |||
| 520 | // to duplicate it if it is used outside this BB. | |||
| 521 | if (I->getType()->isTokenTy() && I->isUsedOutsideOfBlock(BB)) | |||
| 522 | return ~0U; | |||
| 523 | ||||
| 524 | // All other instructions count for at least one unit. | |||
| 525 | ++Size; | |||
| 526 | ||||
| 527 | // Calls are more expensive. If they are non-intrinsic calls, we model them | |||
| 528 | // as having cost of 4. If they are a non-vector intrinsic, we model them | |||
| 529 | // as having cost of 2 total, and if they are a vector intrinsic, we model | |||
| 530 | // them as having cost 1. | |||
| 531 | if (const CallInst *CI = dyn_cast<CallInst>(I)) { | |||
| 532 | if (CI->cannotDuplicate() || CI->isConvergent()) | |||
| 533 | // Blocks with NoDuplicate are modelled as having infinite cost, so they | |||
| 534 | // are never duplicated. | |||
| 535 | return ~0U; | |||
| 536 | else if (!isa<IntrinsicInst>(CI)) | |||
| 537 | Size += 3; | |||
| 538 | else if (!CI->getType()->isVectorTy()) | |||
| 539 | Size += 1; | |||
| 540 | } | |||
| 541 | } | |||
| 542 | ||||
| 543 | return Size > Bonus ? Size - Bonus : 0; | |||
| 544 | } | |||
| 545 | ||||
| 546 | /// FindLoopHeaders - We do not want jump threading to turn proper loop | |||
| 547 | /// structures into irreducible loops. Doing this breaks up the loop nesting | |||
| 548 | /// hierarchy and pessimizes later transformations. To prevent this from | |||
| 549 | /// happening, we first have to find the loop headers. Here we approximate this | |||
| 550 | /// by finding targets of backedges in the CFG. | |||
| 551 | /// | |||
| 552 | /// Note that there definitely are cases when we want to allow threading of | |||
| 553 | /// edges across a loop header. For example, threading a jump from outside the | |||
| 554 | /// loop (the preheader) to an exit block of the loop is definitely profitable. | |||
| 555 | /// It is also almost always profitable to thread backedges from within the loop | |||
| 556 | /// to exit blocks, and is often profitable to thread backedges to other blocks | |||
| 557 | /// within the loop (forming a nested loop). This simple analysis is not rich | |||
| 558 | /// enough to track all of these properties and keep it up-to-date as the CFG | |||
| 559 | /// mutates, so we don't allow any of these transformations. | |||
| 560 | void JumpThreadingPass::FindLoopHeaders(Function &F) { | |||
| 561 | SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges; | |||
| 562 | FindFunctionBackedges(F, Edges); | |||
| 563 | ||||
| 564 | for (const auto &Edge : Edges) | |||
| 565 | LoopHeaders.insert(Edge.second); | |||
| 566 | } | |||
| 567 | ||||
| 568 | /// getKnownConstant - Helper method to determine if we can thread over a | |||
| 569 | /// terminator with the given value as its condition, and if so what value to | |||
| 570 | /// use for that. What kind of value this is depends on whether we want an | |||
| 571 | /// integer or a block address, but an undef is always accepted. | |||
| 572 | /// Returns null if Val is null or not an appropriate constant. | |||
| 573 | static Constant *getKnownConstant(Value *Val, ConstantPreference Preference) { | |||
| 574 | if (!Val) | |||
| 575 | return nullptr; | |||
| 576 | ||||
| 577 | // Undef is "known" enough. | |||
| 578 | if (UndefValue *U = dyn_cast<UndefValue>(Val)) | |||
| 579 | return U; | |||
| 580 | ||||
| 581 | if (Preference == WantBlockAddress) | |||
| 582 | return dyn_cast<BlockAddress>(Val->stripPointerCasts()); | |||
| 583 | ||||
| 584 | return dyn_cast<ConstantInt>(Val); | |||
| 585 | } | |||
| 586 | ||||
| 587 | /// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see | |||
| 588 | /// if we can infer that the value is a known ConstantInt/BlockAddress or undef | |||
| 589 | /// in any of our predecessors. If so, return the known list of value and pred | |||
| 590 | /// BB in the result vector. | |||
| 591 | /// | |||
| 592 | /// This returns true if there were any known values. | |||
| 593 | bool JumpThreadingPass::ComputeValueKnownInPredecessorsImpl( | |||
| 594 | Value *V, BasicBlock *BB, PredValueInfo &Result, | |||
| 595 | ConstantPreference Preference, | |||
| 596 | DenseSet<std::pair<Value *, BasicBlock *>> &RecursionSet, | |||
| 597 | Instruction *CxtI) { | |||
| 598 | // This method walks up use-def chains recursively. Because of this, we could | |||
| 599 | // get into an infinite loop going around loops in the use-def chain. To | |||
| 600 | // prevent this, keep track of what (value, block) pairs we've already visited | |||
| 601 | // and terminate the search if we loop back to them | |||
| 602 | if (!RecursionSet.insert(std::make_pair(V, BB)).second) | |||
| 603 | return false; | |||
| 604 | ||||
| 605 | // If V is a constant, then it is known in all predecessors. | |||
| 606 | if (Constant *KC = getKnownConstant(V, Preference)) { | |||
| 607 | for (BasicBlock *Pred : predecessors(BB)) | |||
| 608 | Result.push_back(std::make_pair(KC, Pred)); | |||
| 609 | ||||
| 610 | return !Result.empty(); | |||
| 611 | } | |||
| 612 | ||||
| 613 | // If V is a non-instruction value, or an instruction in a different block, | |||
| 614 | // then it can't be derived from a PHI. | |||
| 615 | Instruction *I = dyn_cast<Instruction>(V); | |||
| 616 | if (!I || I->getParent() != BB) { | |||
| 617 | ||||
| 618 | // Okay, if this is a live-in value, see if it has a known value at the end | |||
| 619 | // of any of our predecessors. | |||
| 620 | // | |||
| 621 | // FIXME: This should be an edge property, not a block end property. | |||
| 622 | /// TODO: Per PR2563, we could infer value range information about a | |||
| 623 | /// predecessor based on its terminator. | |||
| 624 | // | |||
| 625 | // FIXME: change this to use the more-rich 'getPredicateOnEdge' method if | |||
| 626 | // "I" is a non-local compare-with-a-constant instruction. This would be | |||
| 627 | // able to handle value inequalities better, for example if the compare is | |||
| 628 | // "X < 4" and "X < 3" is known true but "X < 4" itself is not available. | |||
| 629 | // Perhaps getConstantOnEdge should be smart enough to do this? | |||
| 630 | ||||
| 631 | if (DTU->hasPendingDomTreeUpdates()) | |||
| 632 | LVI->disableDT(); | |||
| 633 | else | |||
| 634 | LVI->enableDT(); | |||
| 635 | for (BasicBlock *P : predecessors(BB)) { | |||
| 636 | // If the value is known by LazyValueInfo to be a constant in a | |||
| 637 | // predecessor, use that information to try to thread this block. | |||
| 638 | Constant *PredCst = LVI->getConstantOnEdge(V, P, BB, CxtI); | |||
| 639 | if (Constant *KC = getKnownConstant(PredCst, Preference)) | |||
| 640 | Result.push_back(std::make_pair(KC, P)); | |||
| 641 | } | |||
| 642 | ||||
| 643 | return !Result.empty(); | |||
| 644 | } | |||
| 645 | ||||
| 646 | /// If I is a PHI node, then we know the incoming values for any constants. | |||
| 647 | if (PHINode *PN = dyn_cast<PHINode>(I)) { | |||
| 648 | if (DTU->hasPendingDomTreeUpdates()) | |||
| 649 | LVI->disableDT(); | |||
| 650 | else | |||
| 651 | LVI->enableDT(); | |||
| 652 | for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { | |||
| 653 | Value *InVal = PN->getIncomingValue(i); | |||
| 654 | if (Constant *KC = getKnownConstant(InVal, Preference)) { | |||
| 655 | Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i))); | |||
| 656 | } else { | |||
| 657 | Constant *CI = LVI->getConstantOnEdge(InVal, | |||
| 658 | PN->getIncomingBlock(i), | |||
| 659 | BB, CxtI); | |||
| 660 | if (Constant *KC = getKnownConstant(CI, Preference)) | |||
| 661 | Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i))); | |||
| 662 | } | |||
| 663 | } | |||
| 664 | ||||
| 665 | return !Result.empty(); | |||
| 666 | } | |||
| 667 | ||||
| 668 | // Handle Cast instructions. Only see through Cast when the source operand is | |||
| 669 | // PHI or Cmp to save the compilation time. | |||
| 670 | if (CastInst *CI = dyn_cast<CastInst>(I)) { | |||
| 671 | Value *Source = CI->getOperand(0); | |||
| 672 | if (!isa<PHINode>(Source) && !isa<CmpInst>(Source)) | |||
| 673 | return false; | |||
| 674 | ComputeValueKnownInPredecessorsImpl(Source, BB, Result, Preference, | |||
| 675 | RecursionSet, CxtI); | |||
| 676 | if (Result.empty()) | |||
| 677 | return false; | |||
| 678 | ||||
| 679 | // Convert the known values. | |||
| 680 | for (auto &R : Result) | |||
| 681 | R.first = ConstantExpr::getCast(CI->getOpcode(), R.first, CI->getType()); | |||
| 682 | ||||
| 683 | return true; | |||
| 684 | } | |||
| 685 | ||||
| 686 | // Handle some boolean conditions. | |||
| 687 | if (I->getType()->getPrimitiveSizeInBits() == 1) { | |||
| 688 | assert(Preference == WantInteger && "One-bit non-integer type?")((Preference == WantInteger && "One-bit non-integer type?" ) ? static_cast<void> (0) : __assert_fail ("Preference == WantInteger && \"One-bit non-integer type?\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 688, __PRETTY_FUNCTION__)); | |||
| 689 | // X | true -> true | |||
| 690 | // X & false -> false | |||
| 691 | if (I->getOpcode() == Instruction::Or || | |||
| 692 | I->getOpcode() == Instruction::And) { | |||
| 693 | PredValueInfoTy LHSVals, RHSVals; | |||
| 694 | ||||
| 695 | ComputeValueKnownInPredecessorsImpl(I->getOperand(0), BB, LHSVals, | |||
| 696 | WantInteger, RecursionSet, CxtI); | |||
| 697 | ComputeValueKnownInPredecessorsImpl(I->getOperand(1), BB, RHSVals, | |||
| 698 | WantInteger, RecursionSet, CxtI); | |||
| 699 | ||||
| 700 | if (LHSVals.empty() && RHSVals.empty()) | |||
| 701 | return false; | |||
| 702 | ||||
| 703 | ConstantInt *InterestingVal; | |||
| 704 | if (I->getOpcode() == Instruction::Or) | |||
| 705 | InterestingVal = ConstantInt::getTrue(I->getContext()); | |||
| 706 | else | |||
| 707 | InterestingVal = ConstantInt::getFalse(I->getContext()); | |||
| 708 | ||||
| 709 | SmallPtrSet<BasicBlock*, 4> LHSKnownBBs; | |||
| 710 | ||||
| 711 | // Scan for the sentinel. If we find an undef, force it to the | |||
| 712 | // interesting value: x|undef -> true and x&undef -> false. | |||
| 713 | for (const auto &LHSVal : LHSVals) | |||
| 714 | if (LHSVal.first == InterestingVal || isa<UndefValue>(LHSVal.first)) { | |||
| 715 | Result.emplace_back(InterestingVal, LHSVal.second); | |||
| 716 | LHSKnownBBs.insert(LHSVal.second); | |||
| 717 | } | |||
| 718 | for (const auto &RHSVal : RHSVals) | |||
| 719 | if (RHSVal.first == InterestingVal || isa<UndefValue>(RHSVal.first)) { | |||
| 720 | // If we already inferred a value for this block on the LHS, don't | |||
| 721 | // re-add it. | |||
| 722 | if (!LHSKnownBBs.count(RHSVal.second)) | |||
| 723 | Result.emplace_back(InterestingVal, RHSVal.second); | |||
| 724 | } | |||
| 725 | ||||
| 726 | return !Result.empty(); | |||
| 727 | } | |||
| 728 | ||||
| 729 | // Handle the NOT form of XOR. | |||
| 730 | if (I->getOpcode() == Instruction::Xor && | |||
| 731 | isa<ConstantInt>(I->getOperand(1)) && | |||
| 732 | cast<ConstantInt>(I->getOperand(1))->isOne()) { | |||
| 733 | ComputeValueKnownInPredecessorsImpl(I->getOperand(0), BB, Result, | |||
| 734 | WantInteger, RecursionSet, CxtI); | |||
| 735 | if (Result.empty()) | |||
| 736 | return false; | |||
| 737 | ||||
| 738 | // Invert the known values. | |||
| 739 | for (auto &R : Result) | |||
| 740 | R.first = ConstantExpr::getNot(R.first); | |||
| 741 | ||||
| 742 | return true; | |||
| 743 | } | |||
| 744 | ||||
| 745 | // Try to simplify some other binary operator values. | |||
| 746 | } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) { | |||
| 747 | assert(Preference != WantBlockAddress((Preference != WantBlockAddress && "A binary operator creating a block address?" ) ? static_cast<void> (0) : __assert_fail ("Preference != WantBlockAddress && \"A binary operator creating a block address?\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 748, __PRETTY_FUNCTION__)) | |||
| 748 | && "A binary operator creating a block address?")((Preference != WantBlockAddress && "A binary operator creating a block address?" ) ? static_cast<void> (0) : __assert_fail ("Preference != WantBlockAddress && \"A binary operator creating a block address?\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 748, __PRETTY_FUNCTION__)); | |||
| 749 | if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) { | |||
| 750 | PredValueInfoTy LHSVals; | |||
| 751 | ComputeValueKnownInPredecessorsImpl(BO->getOperand(0), BB, LHSVals, | |||
| 752 | WantInteger, RecursionSet, CxtI); | |||
| 753 | ||||
| 754 | // Try to use constant folding to simplify the binary operator. | |||
| 755 | for (const auto &LHSVal : LHSVals) { | |||
| 756 | Constant *V = LHSVal.first; | |||
| 757 | Constant *Folded = ConstantExpr::get(BO->getOpcode(), V, CI); | |||
| 758 | ||||
| 759 | if (Constant *KC = getKnownConstant(Folded, WantInteger)) | |||
| 760 | Result.push_back(std::make_pair(KC, LHSVal.second)); | |||
| 761 | } | |||
| 762 | } | |||
| 763 | ||||
| 764 | return !Result.empty(); | |||
| 765 | } | |||
| 766 | ||||
| 767 | // Handle compare with phi operand, where the PHI is defined in this block. | |||
| 768 | if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) { | |||
| 769 | assert(Preference == WantInteger && "Compares only produce integers")((Preference == WantInteger && "Compares only produce integers" ) ? static_cast<void> (0) : __assert_fail ("Preference == WantInteger && \"Compares only produce integers\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 769, __PRETTY_FUNCTION__)); | |||
| 770 | Type *CmpType = Cmp->getType(); | |||
| 771 | Value *CmpLHS = Cmp->getOperand(0); | |||
| 772 | Value *CmpRHS = Cmp->getOperand(1); | |||
| 773 | CmpInst::Predicate Pred = Cmp->getPredicate(); | |||
| 774 | ||||
| 775 | PHINode *PN = dyn_cast<PHINode>(CmpLHS); | |||
| 776 | if (!PN) | |||
| 777 | PN = dyn_cast<PHINode>(CmpRHS); | |||
| 778 | if (PN && PN->getParent() == BB) { | |||
| 779 | const DataLayout &DL = PN->getModule()->getDataLayout(); | |||
| 780 | // We can do this simplification if any comparisons fold to true or false. | |||
| 781 | // See if any do. | |||
| 782 | if (DTU->hasPendingDomTreeUpdates()) | |||
| 783 | LVI->disableDT(); | |||
| 784 | else | |||
| 785 | LVI->enableDT(); | |||
| 786 | for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { | |||
| 787 | BasicBlock *PredBB = PN->getIncomingBlock(i); | |||
| 788 | Value *LHS, *RHS; | |||
| 789 | if (PN == CmpLHS) { | |||
| 790 | LHS = PN->getIncomingValue(i); | |||
| 791 | RHS = CmpRHS->DoPHITranslation(BB, PredBB); | |||
| 792 | } else { | |||
| 793 | LHS = CmpLHS->DoPHITranslation(BB, PredBB); | |||
| 794 | RHS = PN->getIncomingValue(i); | |||
| 795 | } | |||
| 796 | Value *Res = SimplifyCmpInst(Pred, LHS, RHS, {DL}); | |||
| 797 | if (!Res) { | |||
| 798 | if (!isa<Constant>(RHS)) | |||
| 799 | continue; | |||
| 800 | ||||
| 801 | // getPredicateOnEdge call will make no sense if LHS is defined in BB. | |||
| 802 | auto LHSInst = dyn_cast<Instruction>(LHS); | |||
| 803 | if (LHSInst && LHSInst->getParent() == BB) | |||
| 804 | continue; | |||
| 805 | ||||
| 806 | LazyValueInfo::Tristate | |||
| 807 | ResT = LVI->getPredicateOnEdge(Pred, LHS, | |||
| 808 | cast<Constant>(RHS), PredBB, BB, | |||
| 809 | CxtI ? CxtI : Cmp); | |||
| 810 | if (ResT == LazyValueInfo::Unknown) | |||
| 811 | continue; | |||
| 812 | Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT); | |||
| 813 | } | |||
| 814 | ||||
| 815 | if (Constant *KC = getKnownConstant(Res, WantInteger)) | |||
| 816 | Result.push_back(std::make_pair(KC, PredBB)); | |||
| 817 | } | |||
| 818 | ||||
| 819 | return !Result.empty(); | |||
| 820 | } | |||
| 821 | ||||
| 822 | // If comparing a live-in value against a constant, see if we know the | |||
| 823 | // live-in value on any predecessors. | |||
| 824 | if (isa<Constant>(CmpRHS) && !CmpType->isVectorTy()) { | |||
| 825 | Constant *CmpConst = cast<Constant>(CmpRHS); | |||
| 826 | ||||
| 827 | if (!isa<Instruction>(CmpLHS) || | |||
| 828 | cast<Instruction>(CmpLHS)->getParent() != BB) { | |||
| 829 | if (DTU->hasPendingDomTreeUpdates()) | |||
| 830 | LVI->disableDT(); | |||
| 831 | else | |||
| 832 | LVI->enableDT(); | |||
| 833 | for (BasicBlock *P : predecessors(BB)) { | |||
| 834 | // If the value is known by LazyValueInfo to be a constant in a | |||
| 835 | // predecessor, use that information to try to thread this block. | |||
| 836 | LazyValueInfo::Tristate Res = | |||
| 837 | LVI->getPredicateOnEdge(Pred, CmpLHS, | |||
| 838 | CmpConst, P, BB, CxtI ? CxtI : Cmp); | |||
| 839 | if (Res == LazyValueInfo::Unknown) | |||
| 840 | continue; | |||
| 841 | ||||
| 842 | Constant *ResC = ConstantInt::get(CmpType, Res); | |||
| 843 | Result.push_back(std::make_pair(ResC, P)); | |||
| 844 | } | |||
| 845 | ||||
| 846 | return !Result.empty(); | |||
| 847 | } | |||
| 848 | ||||
| 849 | // InstCombine can fold some forms of constant range checks into | |||
| 850 | // (icmp (add (x, C1)), C2). See if we have we have such a thing with | |||
| 851 | // x as a live-in. | |||
| 852 | { | |||
| 853 | using namespace PatternMatch; | |||
| 854 | ||||
| 855 | Value *AddLHS; | |||
| 856 | ConstantInt *AddConst; | |||
| 857 | if (isa<ConstantInt>(CmpConst) && | |||
| 858 | match(CmpLHS, m_Add(m_Value(AddLHS), m_ConstantInt(AddConst)))) { | |||
| 859 | if (!isa<Instruction>(AddLHS) || | |||
| 860 | cast<Instruction>(AddLHS)->getParent() != BB) { | |||
| 861 | if (DTU->hasPendingDomTreeUpdates()) | |||
| 862 | LVI->disableDT(); | |||
| 863 | else | |||
| 864 | LVI->enableDT(); | |||
| 865 | for (BasicBlock *P : predecessors(BB)) { | |||
| 866 | // If the value is known by LazyValueInfo to be a ConstantRange in | |||
| 867 | // a predecessor, use that information to try to thread this | |||
| 868 | // block. | |||
| 869 | ConstantRange CR = LVI->getConstantRangeOnEdge( | |||
| 870 | AddLHS, P, BB, CxtI ? CxtI : cast<Instruction>(CmpLHS)); | |||
| 871 | // Propagate the range through the addition. | |||
| 872 | CR = CR.add(AddConst->getValue()); | |||
| 873 | ||||
| 874 | // Get the range where the compare returns true. | |||
| 875 | ConstantRange CmpRange = ConstantRange::makeExactICmpRegion( | |||
| 876 | Pred, cast<ConstantInt>(CmpConst)->getValue()); | |||
| 877 | ||||
| 878 | Constant *ResC; | |||
| 879 | if (CmpRange.contains(CR)) | |||
| 880 | ResC = ConstantInt::getTrue(CmpType); | |||
| 881 | else if (CmpRange.inverse().contains(CR)) | |||
| 882 | ResC = ConstantInt::getFalse(CmpType); | |||
| 883 | else | |||
| 884 | continue; | |||
| 885 | ||||
| 886 | Result.push_back(std::make_pair(ResC, P)); | |||
| 887 | } | |||
| 888 | ||||
| 889 | return !Result.empty(); | |||
| 890 | } | |||
| 891 | } | |||
| 892 | } | |||
| 893 | ||||
| 894 | // Try to find a constant value for the LHS of a comparison, | |||
| 895 | // and evaluate it statically if we can. | |||
| 896 | PredValueInfoTy LHSVals; | |||
| 897 | ComputeValueKnownInPredecessorsImpl(I->getOperand(0), BB, LHSVals, | |||
| 898 | WantInteger, RecursionSet, CxtI); | |||
| 899 | ||||
| 900 | for (const auto &LHSVal : LHSVals) { | |||
| 901 | Constant *V = LHSVal.first; | |||
| 902 | Constant *Folded = ConstantExpr::getCompare(Pred, V, CmpConst); | |||
| 903 | if (Constant *KC = getKnownConstant(Folded, WantInteger)) | |||
| 904 | Result.push_back(std::make_pair(KC, LHSVal.second)); | |||
| 905 | } | |||
| 906 | ||||
| 907 | return !Result.empty(); | |||
| 908 | } | |||
| 909 | } | |||
| 910 | ||||
| 911 | if (SelectInst *SI = dyn_cast<SelectInst>(I)) { | |||
| 912 | // Handle select instructions where at least one operand is a known constant | |||
| 913 | // and we can figure out the condition value for any predecessor block. | |||
| 914 | Constant *TrueVal = getKnownConstant(SI->getTrueValue(), Preference); | |||
| 915 | Constant *FalseVal = getKnownConstant(SI->getFalseValue(), Preference); | |||
| 916 | PredValueInfoTy Conds; | |||
| 917 | if ((TrueVal || FalseVal) && | |||
| 918 | ComputeValueKnownInPredecessorsImpl(SI->getCondition(), BB, Conds, | |||
| 919 | WantInteger, RecursionSet, CxtI)) { | |||
| 920 | for (auto &C : Conds) { | |||
| 921 | Constant *Cond = C.first; | |||
| 922 | ||||
| 923 | // Figure out what value to use for the condition. | |||
| 924 | bool KnownCond; | |||
| 925 | if (ConstantInt *CI = dyn_cast<ConstantInt>(Cond)) { | |||
| 926 | // A known boolean. | |||
| 927 | KnownCond = CI->isOne(); | |||
| 928 | } else { | |||
| 929 | assert(isa<UndefValue>(Cond) && "Unexpected condition value")((isa<UndefValue>(Cond) && "Unexpected condition value" ) ? static_cast<void> (0) : __assert_fail ("isa<UndefValue>(Cond) && \"Unexpected condition value\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 929, __PRETTY_FUNCTION__)); | |||
| 930 | // Either operand will do, so be sure to pick the one that's a known | |||
| 931 | // constant. | |||
| 932 | // FIXME: Do this more cleverly if both values are known constants? | |||
| 933 | KnownCond = (TrueVal != nullptr); | |||
| 934 | } | |||
| 935 | ||||
| 936 | // See if the select has a known constant value for this predecessor. | |||
| 937 | if (Constant *Val = KnownCond ? TrueVal : FalseVal) | |||
| 938 | Result.push_back(std::make_pair(Val, C.second)); | |||
| 939 | } | |||
| 940 | ||||
| 941 | return !Result.empty(); | |||
| 942 | } | |||
| 943 | } | |||
| 944 | ||||
| 945 | // If all else fails, see if LVI can figure out a constant value for us. | |||
| 946 | if (DTU->hasPendingDomTreeUpdates()) | |||
| 947 | LVI->disableDT(); | |||
| 948 | else | |||
| 949 | LVI->enableDT(); | |||
| 950 | Constant *CI = LVI->getConstant(V, BB, CxtI); | |||
| 951 | if (Constant *KC = getKnownConstant(CI, Preference)) { | |||
| 952 | for (BasicBlock *Pred : predecessors(BB)) | |||
| 953 | Result.push_back(std::make_pair(KC, Pred)); | |||
| 954 | } | |||
| 955 | ||||
| 956 | return !Result.empty(); | |||
| 957 | } | |||
| 958 | ||||
| 959 | /// GetBestDestForBranchOnUndef - If we determine that the specified block ends | |||
| 960 | /// in an undefined jump, decide which block is best to revector to. | |||
| 961 | /// | |||
| 962 | /// Since we can pick an arbitrary destination, we pick the successor with the | |||
| 963 | /// fewest predecessors. This should reduce the in-degree of the others. | |||
| 964 | static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) { | |||
| 965 | Instruction *BBTerm = BB->getTerminator(); | |||
| 966 | unsigned MinSucc = 0; | |||
| 967 | BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc); | |||
| 968 | // Compute the successor with the minimum number of predecessors. | |||
| 969 | unsigned MinNumPreds = pred_size(TestBB); | |||
| 970 | for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) { | |||
| 971 | TestBB = BBTerm->getSuccessor(i); | |||
| 972 | unsigned NumPreds = pred_size(TestBB); | |||
| 973 | if (NumPreds < MinNumPreds) { | |||
| 974 | MinSucc = i; | |||
| 975 | MinNumPreds = NumPreds; | |||
| 976 | } | |||
| 977 | } | |||
| 978 | ||||
| 979 | return MinSucc; | |||
| 980 | } | |||
| 981 | ||||
| 982 | static bool hasAddressTakenAndUsed(BasicBlock *BB) { | |||
| 983 | if (!BB->hasAddressTaken()) return false; | |||
| 984 | ||||
| 985 | // If the block has its address taken, it may be a tree of dead constants | |||
| 986 | // hanging off of it. These shouldn't keep the block alive. | |||
| 987 | BlockAddress *BA = BlockAddress::get(BB); | |||
| 988 | BA->removeDeadConstantUsers(); | |||
| 989 | return !BA->use_empty(); | |||
| 990 | } | |||
| 991 | ||||
| 992 | /// ProcessBlock - If there are any predecessors whose control can be threaded | |||
| 993 | /// through to a successor, transform them now. | |||
| 994 | bool JumpThreadingPass::ProcessBlock(BasicBlock *BB) { | |||
| 995 | // If the block is trivially dead, just return and let the caller nuke it. | |||
| 996 | // This simplifies other transformations. | |||
| 997 | if (DTU->isBBPendingDeletion(BB) || | |||
| ||||
| 998 | (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock())) | |||
| 999 | return false; | |||
| 1000 | ||||
| 1001 | // If this block has a single predecessor, and if that pred has a single | |||
| 1002 | // successor, merge the blocks. This encourages recursive jump threading | |||
| 1003 | // because now the condition in this block can be threaded through | |||
| 1004 | // predecessors of our predecessor block. | |||
| 1005 | if (BasicBlock *SinglePred = BB->getSinglePredecessor()) { | |||
| 1006 | const Instruction *TI = SinglePred->getTerminator(); | |||
| 1007 | if (!TI->isExceptionalTerminator() && TI->getNumSuccessors() == 1 && | |||
| 1008 | SinglePred != BB && !hasAddressTakenAndUsed(BB)) { | |||
| 1009 | // If SinglePred was a loop header, BB becomes one. | |||
| 1010 | if (LoopHeaders.erase(SinglePred)) | |||
| 1011 | LoopHeaders.insert(BB); | |||
| 1012 | ||||
| 1013 | LVI->eraseBlock(SinglePred); | |||
| 1014 | MergeBasicBlockIntoOnlyPred(BB, DTU); | |||
| 1015 | ||||
| 1016 | // Now that BB is merged into SinglePred (i.e. SinglePred Code followed by | |||
| 1017 | // BB code within one basic block `BB`), we need to invalidate the LVI | |||
| 1018 | // information associated with BB, because the LVI information need not be | |||
| 1019 | // true for all of BB after the merge. For example, | |||
| 1020 | // Before the merge, LVI info and code is as follows: | |||
| 1021 | // SinglePred: <LVI info1 for %p val> | |||
| 1022 | // %y = use of %p | |||
| 1023 | // call @exit() // need not transfer execution to successor. | |||
| 1024 | // assume(%p) // from this point on %p is true | |||
| 1025 | // br label %BB | |||
| 1026 | // BB: <LVI info2 for %p val, i.e. %p is true> | |||
| 1027 | // %x = use of %p | |||
| 1028 | // br label exit | |||
| 1029 | // | |||
| 1030 | // Note that this LVI info for blocks BB and SinglPred is correct for %p | |||
| 1031 | // (info2 and info1 respectively). After the merge and the deletion of the | |||
| 1032 | // LVI info1 for SinglePred. We have the following code: | |||
| 1033 | // BB: <LVI info2 for %p val> | |||
| 1034 | // %y = use of %p | |||
| 1035 | // call @exit() | |||
| 1036 | // assume(%p) | |||
| 1037 | // %x = use of %p <-- LVI info2 is correct from here onwards. | |||
| 1038 | // br label exit | |||
| 1039 | // LVI info2 for BB is incorrect at the beginning of BB. | |||
| 1040 | ||||
| 1041 | // Invalidate LVI information for BB if the LVI is not provably true for | |||
| 1042 | // all of BB. | |||
| 1043 | if (!isGuaranteedToTransferExecutionToSuccessor(BB)) | |||
| 1044 | LVI->eraseBlock(BB); | |||
| 1045 | return true; | |||
| 1046 | } | |||
| 1047 | } | |||
| 1048 | ||||
| 1049 | if (TryToUnfoldSelectInCurrBB(BB)) | |||
| 1050 | return true; | |||
| 1051 | ||||
| 1052 | // Look if we can propagate guards to predecessors. | |||
| 1053 | if (HasGuards && ProcessGuards(BB)) | |||
| 1054 | return true; | |||
| 1055 | ||||
| 1056 | // What kind of constant we're looking for. | |||
| 1057 | ConstantPreference Preference = WantInteger; | |||
| 1058 | ||||
| 1059 | // Look to see if the terminator is a conditional branch, switch or indirect | |||
| 1060 | // branch, if not we can't thread it. | |||
| 1061 | Value *Condition; | |||
| 1062 | Instruction *Terminator = BB->getTerminator(); | |||
| 1063 | if (BranchInst *BI
| |||
| 1064 | // Can't thread an unconditional jump. | |||
| 1065 | if (BI->isUnconditional()) return false; | |||
| 1066 | Condition = BI->getCondition(); | |||
| 1067 | } else if (SwitchInst *SI
| |||
| 1068 | Condition = SI->getCondition(); | |||
| 1069 | } else if (IndirectBrInst *IB
| |||
| 1070 | // Can't thread indirect branch with no successors. | |||
| 1071 | if (IB->getNumSuccessors() == 0) return false; | |||
| 1072 | Condition = IB->getAddress()->stripPointerCasts(); | |||
| 1073 | Preference = WantBlockAddress; | |||
| 1074 | } else { | |||
| 1075 | return false; // Must be an invoke or callbr. | |||
| 1076 | } | |||
| 1077 | ||||
| 1078 | // Run constant folding to see if we can reduce the condition to a simple | |||
| 1079 | // constant. | |||
| 1080 | if (Instruction *I
| |||
| 1081 | Value *SimpleVal = | |||
| 1082 | ConstantFoldInstruction(I, BB->getModule()->getDataLayout(), TLI); | |||
| 1083 | if (SimpleVal) { | |||
| 1084 | I->replaceAllUsesWith(SimpleVal); | |||
| 1085 | if (isInstructionTriviallyDead(I, TLI)) | |||
| 1086 | I->eraseFromParent(); | |||
| 1087 | Condition = SimpleVal; | |||
| 1088 | } | |||
| 1089 | } | |||
| 1090 | ||||
| 1091 | // If the terminator is branching on an undef, we can pick any of the | |||
| 1092 | // successors to branch to. Let GetBestDestForJumpOnUndef decide. | |||
| 1093 | if (isa<UndefValue>(Condition)) { | |||
| 1094 | unsigned BestSucc = GetBestDestForJumpOnUndef(BB); | |||
| 1095 | std::vector<DominatorTree::UpdateType> Updates; | |||
| 1096 | ||||
| 1097 | // Fold the branch/switch. | |||
| 1098 | Instruction *BBTerm = BB->getTerminator(); | |||
| 1099 | Updates.reserve(BBTerm->getNumSuccessors()); | |||
| 1100 | for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) { | |||
| 1101 | if (i == BestSucc) continue; | |||
| 1102 | BasicBlock *Succ = BBTerm->getSuccessor(i); | |||
| 1103 | Succ->removePredecessor(BB, true); | |||
| 1104 | Updates.push_back({DominatorTree::Delete, BB, Succ}); | |||
| 1105 | } | |||
| 1106 | ||||
| 1107 | 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) | |||
| 1108 | << "' 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); | |||
| 1109 | BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm); | |||
| 1110 | BBTerm->eraseFromParent(); | |||
| 1111 | DTU->applyUpdatesPermissive(Updates); | |||
| 1112 | return true; | |||
| 1113 | } | |||
| 1114 | ||||
| 1115 | // If the terminator of this block is branching on a constant, simplify the | |||
| 1116 | // terminator to an unconditional branch. This can occur due to threading in | |||
| 1117 | // other blocks. | |||
| 1118 | if (getKnownConstant(Condition, Preference)) { | |||
| 1119 | 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) | |||
| 1120 | << "' folding terminator: " << *BB->getTerminator()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("jump-threading")) { dbgs() << " In block '" << BB->getName() << "' folding terminator: " << * BB->getTerminator() << '\n'; } } while (false) | |||
| 1121 | << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("jump-threading")) { dbgs() << " In block '" << BB->getName() << "' folding terminator: " << * BB->getTerminator() << '\n'; } } while (false); | |||
| 1122 | ++NumFolds; | |||
| 1123 | ConstantFoldTerminator(BB, true, nullptr, DTU); | |||
| 1124 | return true; | |||
| 1125 | } | |||
| 1126 | ||||
| 1127 | Instruction *CondInst = dyn_cast<Instruction>(Condition); | |||
| 1128 | ||||
| 1129 | // All the rest of our checks depend on the condition being an instruction. | |||
| 1130 | if (!CondInst
| |||
| 1131 | // FIXME: Unify this with code below. | |||
| 1132 | if (ProcessThreadableEdges(Condition, BB, Preference, Terminator)) | |||
| 1133 | return true; | |||
| 1134 | return false; | |||
| 1135 | } | |||
| 1136 | ||||
| 1137 | if (CmpInst *CondCmp
| |||
| 1138 | // If we're branching on a conditional, LVI might be able to determine | |||
| 1139 | // it's value at the branch instruction. We only handle comparisons | |||
| 1140 | // against a constant at this time. | |||
| 1141 | // TODO: This should be extended to handle switches as well. | |||
| 1142 | BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator()); | |||
| 1143 | Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1)); | |||
| 1144 | if (CondBr && CondConst) { | |||
| 1145 | // We should have returned as soon as we turn a conditional branch to | |||
| 1146 | // unconditional. Because its no longer interesting as far as jump | |||
| 1147 | // threading is concerned. | |||
| 1148 | assert(CondBr->isConditional() && "Threading on unconditional terminator")((CondBr->isConditional() && "Threading on unconditional terminator" ) ? static_cast<void> (0) : __assert_fail ("CondBr->isConditional() && \"Threading on unconditional terminator\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1148, __PRETTY_FUNCTION__)); | |||
| 1149 | ||||
| 1150 | if (DTU->hasPendingDomTreeUpdates()) | |||
| 1151 | LVI->disableDT(); | |||
| 1152 | else | |||
| 1153 | LVI->enableDT(); | |||
| 1154 | LazyValueInfo::Tristate Ret = | |||
| 1155 | LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0), | |||
| 1156 | CondConst, CondBr); | |||
| 1157 | if (Ret != LazyValueInfo::Unknown) { | |||
| 1158 | unsigned ToRemove = Ret == LazyValueInfo::True ? 1 : 0; | |||
| 1159 | unsigned ToKeep = Ret == LazyValueInfo::True ? 0 : 1; | |||
| 1160 | BasicBlock *ToRemoveSucc = CondBr->getSuccessor(ToRemove); | |||
| 1161 | ToRemoveSucc->removePredecessor(BB, true); | |||
| 1162 | BranchInst *UncondBr = | |||
| 1163 | BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr); | |||
| 1164 | UncondBr->setDebugLoc(CondBr->getDebugLoc()); | |||
| 1165 | CondBr->eraseFromParent(); | |||
| 1166 | if (CondCmp->use_empty()) | |||
| 1167 | CondCmp->eraseFromParent(); | |||
| 1168 | // We can safely replace *some* uses of the CondInst if it has | |||
| 1169 | // exactly one value as returned by LVI. RAUW is incorrect in the | |||
| 1170 | // presence of guards and assumes, that have the `Cond` as the use. This | |||
| 1171 | // is because we use the guards/assume to reason about the `Cond` value | |||
| 1172 | // at the end of block, but RAUW unconditionally replaces all uses | |||
| 1173 | // including the guards/assumes themselves and the uses before the | |||
| 1174 | // guard/assume. | |||
| 1175 | else if (CondCmp->getParent() == BB) { | |||
| 1176 | auto *CI = Ret == LazyValueInfo::True ? | |||
| 1177 | ConstantInt::getTrue(CondCmp->getType()) : | |||
| 1178 | ConstantInt::getFalse(CondCmp->getType()); | |||
| 1179 | ReplaceFoldableUses(CondCmp, CI); | |||
| 1180 | } | |||
| 1181 | DTU->applyUpdatesPermissive( | |||
| 1182 | {{DominatorTree::Delete, BB, ToRemoveSucc}}); | |||
| 1183 | return true; | |||
| 1184 | } | |||
| 1185 | ||||
| 1186 | // We did not manage to simplify this branch, try to see whether | |||
| 1187 | // CondCmp depends on a known phi-select pattern. | |||
| 1188 | if (TryToUnfoldSelect(CondCmp, BB)) | |||
| 1189 | return true; | |||
| 1190 | } | |||
| 1191 | } | |||
| 1192 | ||||
| 1193 | if (SwitchInst *SI
| |||
| 1194 | if (TryToUnfoldSelect(SI, BB)) | |||
| 1195 | return true; | |||
| 1196 | ||||
| 1197 | // Check for some cases that are worth simplifying. Right now we want to look | |||
| 1198 | // for loads that are used by a switch or by the condition for the branch. If | |||
| 1199 | // we see one, check to see if it's partially redundant. If so, insert a PHI | |||
| 1200 | // which can then be used to thread the values. | |||
| 1201 | Value *SimplifyValue = CondInst; | |||
| 1202 | if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue)) | |||
| 1203 | if (isa<Constant>(CondCmp->getOperand(1))) | |||
| 1204 | SimplifyValue = CondCmp->getOperand(0); | |||
| 1205 | ||||
| 1206 | // TODO: There are other places where load PRE would be profitable, such as | |||
| 1207 | // more complex comparisons. | |||
| 1208 | if (LoadInst *LoadI = dyn_cast<LoadInst>(SimplifyValue)) | |||
| 1209 | if (SimplifyPartiallyRedundantLoad(LoadI)) | |||
| 1210 | return true; | |||
| 1211 | ||||
| 1212 | // Before threading, try to propagate profile data backwards: | |||
| 1213 | if (PHINode *PN = dyn_cast<PHINode>(CondInst)) | |||
| 1214 | if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator())) | |||
| 1215 | updatePredecessorProfileMetadata(PN, BB); | |||
| 1216 | ||||
| 1217 | // Handle a variety of cases where we are branching on something derived from | |||
| 1218 | // a PHI node in the current block. If we can prove that any predecessors | |||
| 1219 | // compute a predictable value based on a PHI node, thread those predecessors. | |||
| 1220 | if (ProcessThreadableEdges(CondInst, BB, Preference, Terminator)) | |||
| 1221 | return true; | |||
| 1222 | ||||
| 1223 | // If this is an otherwise-unfoldable branch on a phi node in the current | |||
| 1224 | // block, see if we can simplify. | |||
| 1225 | if (PHINode *PN = dyn_cast<PHINode>(CondInst)) | |||
| 1226 | if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator())) | |||
| 1227 | return ProcessBranchOnPHI(PN); | |||
| 1228 | ||||
| 1229 | // If this is an otherwise-unfoldable branch on a XOR, see if we can simplify. | |||
| 1230 | if (CondInst->getOpcode() == Instruction::Xor && | |||
| 1231 | CondInst->getParent() == BB && isa<BranchInst>(BB->getTerminator())) | |||
| 1232 | return ProcessBranchOnXOR(cast<BinaryOperator>(CondInst)); | |||
| 1233 | ||||
| 1234 | // Search for a stronger dominating condition that can be used to simplify a | |||
| 1235 | // conditional branch leaving BB. | |||
| 1236 | if (ProcessImpliedCondition(BB)) | |||
| 1237 | return true; | |||
| 1238 | ||||
| 1239 | return false; | |||
| 1240 | } | |||
| 1241 | ||||
| 1242 | bool JumpThreadingPass::ProcessImpliedCondition(BasicBlock *BB) { | |||
| 1243 | auto *BI = dyn_cast<BranchInst>(BB->getTerminator()); | |||
| 1244 | if (!BI || !BI->isConditional()) | |||
| 1245 | return false; | |||
| 1246 | ||||
| 1247 | Value *Cond = BI->getCondition(); | |||
| 1248 | BasicBlock *CurrentBB = BB; | |||
| 1249 | BasicBlock *CurrentPred = BB->getSinglePredecessor(); | |||
| 1250 | unsigned Iter = 0; | |||
| 1251 | ||||
| 1252 | auto &DL = BB->getModule()->getDataLayout(); | |||
| 1253 | ||||
| 1254 | while (CurrentPred && Iter++ < ImplicationSearchThreshold) { | |||
| 1255 | auto *PBI = dyn_cast<BranchInst>(CurrentPred->getTerminator()); | |||
| 1256 | if (!PBI || !PBI->isConditional()) | |||
| 1257 | return false; | |||
| 1258 | if (PBI->getSuccessor(0) != CurrentBB && PBI->getSuccessor(1) != CurrentBB) | |||
| 1259 | return false; | |||
| 1260 | ||||
| 1261 | bool CondIsTrue = PBI->getSuccessor(0) == CurrentBB; | |||
| 1262 | Optional<bool> Implication = | |||
| 1263 | isImpliedCondition(PBI->getCondition(), Cond, DL, CondIsTrue); | |||
| 1264 | if (Implication) { | |||
| 1265 | BasicBlock *KeepSucc = BI->getSuccessor(*Implication ? 0 : 1); | |||
| 1266 | BasicBlock *RemoveSucc = BI->getSuccessor(*Implication ? 1 : 0); | |||
| 1267 | RemoveSucc->removePredecessor(BB); | |||
| 1268 | BranchInst *UncondBI = BranchInst::Create(KeepSucc, BI); | |||
| 1269 | UncondBI->setDebugLoc(BI->getDebugLoc()); | |||
| 1270 | BI->eraseFromParent(); | |||
| 1271 | DTU->applyUpdatesPermissive({{DominatorTree::Delete, BB, RemoveSucc}}); | |||
| 1272 | return true; | |||
| 1273 | } | |||
| 1274 | CurrentBB = CurrentPred; | |||
| 1275 | CurrentPred = CurrentBB->getSinglePredecessor(); | |||
| 1276 | } | |||
| 1277 | ||||
| 1278 | return false; | |||
| 1279 | } | |||
| 1280 | ||||
| 1281 | /// Return true if Op is an instruction defined in the given block. | |||
| 1282 | static bool isOpDefinedInBlock(Value *Op, BasicBlock *BB) { | |||
| 1283 | if (Instruction *OpInst = dyn_cast<Instruction>(Op)) | |||
| 1284 | if (OpInst->getParent() == BB) | |||
| 1285 | return true; | |||
| 1286 | return false; | |||
| 1287 | } | |||
| 1288 | ||||
| 1289 | /// SimplifyPartiallyRedundantLoad - If LoadI is an obviously partially | |||
| 1290 | /// redundant load instruction, eliminate it by replacing it with a PHI node. | |||
| 1291 | /// This is an important optimization that encourages jump threading, and needs | |||
| 1292 | /// to be run interlaced with other jump threading tasks. | |||
| 1293 | bool JumpThreadingPass::SimplifyPartiallyRedundantLoad(LoadInst *LoadI) { | |||
| 1294 | // Don't hack volatile and ordered loads. | |||
| 1295 | if (!LoadI->isUnordered()) return false; | |||
| 1296 | ||||
| 1297 | // If the load is defined in a block with exactly one predecessor, it can't be | |||
| 1298 | // partially redundant. | |||
| 1299 | BasicBlock *LoadBB = LoadI->getParent(); | |||
| 1300 | if (LoadBB->getSinglePredecessor()) | |||
| 1301 | return false; | |||
| 1302 | ||||
| 1303 | // If the load is defined in an EH pad, it can't be partially redundant, | |||
| 1304 | // because the edges between the invoke and the EH pad cannot have other | |||
| 1305 | // instructions between them. | |||
| 1306 | if (LoadBB->isEHPad()) | |||
| 1307 | return false; | |||
| 1308 | ||||
| 1309 | Value *LoadedPtr = LoadI->getOperand(0); | |||
| 1310 | ||||
| 1311 | // If the loaded operand is defined in the LoadBB and its not a phi, | |||
| 1312 | // it can't be available in predecessors. | |||
| 1313 | if (isOpDefinedInBlock(LoadedPtr, LoadBB) && !isa<PHINode>(LoadedPtr)) | |||
| 1314 | return false; | |||
| 1315 | ||||
| 1316 | // Scan a few instructions up from the load, to see if it is obviously live at | |||
| 1317 | // the entry to its block. | |||
| 1318 | BasicBlock::iterator BBIt(LoadI); | |||
| 1319 | bool IsLoadCSE; | |||
| 1320 | if (Value *AvailableVal = FindAvailableLoadedValue( | |||
| 1321 | LoadI, LoadBB, BBIt, DefMaxInstsToScan, AA, &IsLoadCSE)) { | |||
| 1322 | // If the value of the load is locally available within the block, just use | |||
| 1323 | // it. This frequently occurs for reg2mem'd allocas. | |||
| 1324 | ||||
| 1325 | if (IsLoadCSE) { | |||
| 1326 | LoadInst *NLoadI = cast<LoadInst>(AvailableVal); | |||
| 1327 | combineMetadataForCSE(NLoadI, LoadI, false); | |||
| 1328 | }; | |||
| 1329 | ||||
| 1330 | // If the returned value is the load itself, replace with an undef. This can | |||
| 1331 | // only happen in dead loops. | |||
| 1332 | if (AvailableVal == LoadI) | |||
| 1333 | AvailableVal = UndefValue::get(LoadI->getType()); | |||
| 1334 | if (AvailableVal->getType() != LoadI->getType()) | |||
| 1335 | AvailableVal = CastInst::CreateBitOrPointerCast( | |||
| 1336 | AvailableVal, LoadI->getType(), "", LoadI); | |||
| 1337 | LoadI->replaceAllUsesWith(AvailableVal); | |||
| 1338 | LoadI->eraseFromParent(); | |||
| 1339 | return true; | |||
| 1340 | } | |||
| 1341 | ||||
| 1342 | // Otherwise, if we scanned the whole block and got to the top of the block, | |||
| 1343 | // we know the block is locally transparent to the load. If not, something | |||
| 1344 | // might clobber its value. | |||
| 1345 | if (BBIt != LoadBB->begin()) | |||
| 1346 | return false; | |||
| 1347 | ||||
| 1348 | // If all of the loads and stores that feed the value have the same AA tags, | |||
| 1349 | // then we can propagate them onto any newly inserted loads. | |||
| 1350 | AAMDNodes AATags; | |||
| 1351 | LoadI->getAAMetadata(AATags); | |||
| 1352 | ||||
| 1353 | SmallPtrSet<BasicBlock*, 8> PredsScanned; | |||
| 1354 | ||||
| 1355 | using AvailablePredsTy = SmallVector<std::pair<BasicBlock *, Value *>, 8>; | |||
| 1356 | ||||
| 1357 | AvailablePredsTy AvailablePreds; | |||
| 1358 | BasicBlock *OneUnavailablePred = nullptr; | |||
| 1359 | SmallVector<LoadInst*, 8> CSELoads; | |||
| 1360 | ||||
| 1361 | // If we got here, the loaded value is transparent through to the start of the | |||
| 1362 | // block. Check to see if it is available in any of the predecessor blocks. | |||
| 1363 | for (BasicBlock *PredBB : predecessors(LoadBB)) { | |||
| 1364 | // If we already scanned this predecessor, skip it. | |||
| 1365 | if (!PredsScanned.insert(PredBB).second) | |||
| 1366 | continue; | |||
| 1367 | ||||
| 1368 | BBIt = PredBB->end(); | |||
| 1369 | unsigned NumScanedInst = 0; | |||
| 1370 | Value *PredAvailable = nullptr; | |||
| 1371 | // NOTE: We don't CSE load that is volatile or anything stronger than | |||
| 1372 | // unordered, that should have been checked when we entered the function. | |||
| 1373 | assert(LoadI->isUnordered() &&((LoadI->isUnordered() && "Attempting to CSE volatile or atomic loads" ) ? static_cast<void> (0) : __assert_fail ("LoadI->isUnordered() && \"Attempting to CSE volatile or atomic loads\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1374, __PRETTY_FUNCTION__)) | |||
| 1374 | "Attempting to CSE volatile or atomic loads")((LoadI->isUnordered() && "Attempting to CSE volatile or atomic loads" ) ? static_cast<void> (0) : __assert_fail ("LoadI->isUnordered() && \"Attempting to CSE volatile or atomic loads\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1374, __PRETTY_FUNCTION__)); | |||
| 1375 | // If this is a load on a phi pointer, phi-translate it and search | |||
| 1376 | // for available load/store to the pointer in predecessors. | |||
| 1377 | Value *Ptr = LoadedPtr->DoPHITranslation(LoadBB, PredBB); | |||
| 1378 | PredAvailable = FindAvailablePtrLoadStore( | |||
| 1379 | Ptr, LoadI->getType(), LoadI->isAtomic(), PredBB, BBIt, | |||
| 1380 | DefMaxInstsToScan, AA, &IsLoadCSE, &NumScanedInst); | |||
| 1381 | ||||
| 1382 | // If PredBB has a single predecessor, continue scanning through the | |||
| 1383 | // single predecessor. | |||
| 1384 | BasicBlock *SinglePredBB = PredBB; | |||
| 1385 | while (!PredAvailable && SinglePredBB && BBIt == SinglePredBB->begin() && | |||
| 1386 | NumScanedInst < DefMaxInstsToScan) { | |||
| 1387 | SinglePredBB = SinglePredBB->getSinglePredecessor(); | |||
| 1388 | if (SinglePredBB) { | |||
| 1389 | BBIt = SinglePredBB->end(); | |||
| 1390 | PredAvailable = FindAvailablePtrLoadStore( | |||
| 1391 | Ptr, LoadI->getType(), LoadI->isAtomic(), SinglePredBB, BBIt, | |||
| 1392 | (DefMaxInstsToScan - NumScanedInst), AA, &IsLoadCSE, | |||
| 1393 | &NumScanedInst); | |||
| 1394 | } | |||
| 1395 | } | |||
| 1396 | ||||
| 1397 | if (!PredAvailable) { | |||
| 1398 | OneUnavailablePred = PredBB; | |||
| 1399 | continue; | |||
| 1400 | } | |||
| 1401 | ||||
| 1402 | if (IsLoadCSE) | |||
| 1403 | CSELoads.push_back(cast<LoadInst>(PredAvailable)); | |||
| 1404 | ||||
| 1405 | // If so, this load is partially redundant. Remember this info so that we | |||
| 1406 | // can create a PHI node. | |||
| 1407 | AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable)); | |||
| 1408 | } | |||
| 1409 | ||||
| 1410 | // If the loaded value isn't available in any predecessor, it isn't partially | |||
| 1411 | // redundant. | |||
| 1412 | if (AvailablePreds.empty()) return false; | |||
| 1413 | ||||
| 1414 | // Okay, the loaded value is available in at least one (and maybe all!) | |||
| 1415 | // predecessors. If the value is unavailable in more than one unique | |||
| 1416 | // predecessor, we want to insert a merge block for those common predecessors. | |||
| 1417 | // This ensures that we only have to insert one reload, thus not increasing | |||
| 1418 | // code size. | |||
| 1419 | BasicBlock *UnavailablePred = nullptr; | |||
| 1420 | ||||
| 1421 | // If the value is unavailable in one of predecessors, we will end up | |||
| 1422 | // inserting a new instruction into them. It is only valid if all the | |||
| 1423 | // instructions before LoadI are guaranteed to pass execution to its | |||
| 1424 | // successor, or if LoadI is safe to speculate. | |||
| 1425 | // TODO: If this logic becomes more complex, and we will perform PRE insertion | |||
| 1426 | // farther than to a predecessor, we need to reuse the code from GVN's PRE. | |||
| 1427 | // It requires domination tree analysis, so for this simple case it is an | |||
| 1428 | // overkill. | |||
| 1429 | if (PredsScanned.size() != AvailablePreds.size() && | |||
| 1430 | !isSafeToSpeculativelyExecute(LoadI)) | |||
| 1431 | for (auto I = LoadBB->begin(); &*I != LoadI; ++I) | |||
| 1432 | if (!isGuaranteedToTransferExecutionToSuccessor(&*I)) | |||
| 1433 | return false; | |||
| 1434 | ||||
| 1435 | // If there is exactly one predecessor where the value is unavailable, the | |||
| 1436 | // already computed 'OneUnavailablePred' block is it. If it ends in an | |||
| 1437 | // unconditional branch, we know that it isn't a critical edge. | |||
| 1438 | if (PredsScanned.size() == AvailablePreds.size()+1 && | |||
| 1439 | OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) { | |||
| 1440 | UnavailablePred = OneUnavailablePred; | |||
| 1441 | } else if (PredsScanned.size() != AvailablePreds.size()) { | |||
| 1442 | // Otherwise, we had multiple unavailable predecessors or we had a critical | |||
| 1443 | // edge from the one. | |||
| 1444 | SmallVector<BasicBlock*, 8> PredsToSplit; | |||
| 1445 | SmallPtrSet<BasicBlock*, 8> AvailablePredSet; | |||
| 1446 | ||||
| 1447 | for (const auto &AvailablePred : AvailablePreds) | |||
| 1448 | AvailablePredSet.insert(AvailablePred.first); | |||
| 1449 | ||||
| 1450 | // Add all the unavailable predecessors to the PredsToSplit list. | |||
| 1451 | for (BasicBlock *P : predecessors(LoadBB)) { | |||
| 1452 | // If the predecessor is an indirect goto, we can't split the edge. | |||
| 1453 | // Same for CallBr. | |||
| 1454 | if (isa<IndirectBrInst>(P->getTerminator()) || | |||
| 1455 | isa<CallBrInst>(P->getTerminator())) | |||
| 1456 | return false; | |||
| 1457 | ||||
| 1458 | if (!AvailablePredSet.count(P)) | |||
| 1459 | PredsToSplit.push_back(P); | |||
| 1460 | } | |||
| 1461 | ||||
| 1462 | // Split them out to their own block. | |||
| 1463 | UnavailablePred = SplitBlockPreds(LoadBB, PredsToSplit, "thread-pre-split"); | |||
| 1464 | } | |||
| 1465 | ||||
| 1466 | // If the value isn't available in all predecessors, then there will be | |||
| 1467 | // exactly one where it isn't available. Insert a load on that edge and add | |||
| 1468 | // it to the AvailablePreds list. | |||
| 1469 | if (UnavailablePred) { | |||
| 1470 | assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&((UnavailablePred->getTerminator()->getNumSuccessors() == 1 && "Can't handle critical edge here!") ? static_cast <void> (0) : __assert_fail ("UnavailablePred->getTerminator()->getNumSuccessors() == 1 && \"Can't handle critical edge here!\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1471, __PRETTY_FUNCTION__)) | |||
| 1471 | "Can't handle critical edge here!")((UnavailablePred->getTerminator()->getNumSuccessors() == 1 && "Can't handle critical edge here!") ? static_cast <void> (0) : __assert_fail ("UnavailablePred->getTerminator()->getNumSuccessors() == 1 && \"Can't handle critical edge here!\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1471, __PRETTY_FUNCTION__)); | |||
| 1472 | LoadInst *NewVal = new LoadInst( | |||
| 1473 | LoadI->getType(), LoadedPtr->DoPHITranslation(LoadBB, UnavailablePred), | |||
| 1474 | LoadI->getName() + ".pr", false, LoadI->getAlignment(), | |||
| 1475 | LoadI->getOrdering(), LoadI->getSyncScopeID(), | |||
| 1476 | UnavailablePred->getTerminator()); | |||
| 1477 | NewVal->setDebugLoc(LoadI->getDebugLoc()); | |||
| 1478 | if (AATags) | |||
| 1479 | NewVal->setAAMetadata(AATags); | |||
| 1480 | ||||
| 1481 | AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal)); | |||
| 1482 | } | |||
| 1483 | ||||
| 1484 | // Now we know that each predecessor of this block has a value in | |||
| 1485 | // AvailablePreds, sort them for efficient access as we're walking the preds. | |||
| 1486 | array_pod_sort(AvailablePreds.begin(), AvailablePreds.end()); | |||
| 1487 | ||||
| 1488 | // Create a PHI node at the start of the block for the PRE'd load value. | |||
| 1489 | pred_iterator PB = pred_begin(LoadBB), PE = pred_end(LoadBB); | |||
| 1490 | PHINode *PN = PHINode::Create(LoadI->getType(), std::distance(PB, PE), "", | |||
| 1491 | &LoadBB->front()); | |||
| 1492 | PN->takeName(LoadI); | |||
| 1493 | PN->setDebugLoc(LoadI->getDebugLoc()); | |||
| 1494 | ||||
| 1495 | // Insert new entries into the PHI for each predecessor. A single block may | |||
| 1496 | // have multiple entries here. | |||
| 1497 | for (pred_iterator PI = PB; PI != PE; ++PI) { | |||
| 1498 | BasicBlock *P = *PI; | |||
| 1499 | AvailablePredsTy::iterator I = | |||
| 1500 | llvm::lower_bound(AvailablePreds, std::make_pair(P, (Value *)nullptr)); | |||
| 1501 | ||||
| 1502 | assert(I != AvailablePreds.end() && I->first == P &&((I != AvailablePreds.end() && I->first == P && "Didn't find entry for predecessor!") ? static_cast<void> (0) : __assert_fail ("I != AvailablePreds.end() && I->first == P && \"Didn't find entry for predecessor!\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1503, __PRETTY_FUNCTION__)) | |||
| 1503 | "Didn't find entry for predecessor!")((I != AvailablePreds.end() && I->first == P && "Didn't find entry for predecessor!") ? static_cast<void> (0) : __assert_fail ("I != AvailablePreds.end() && I->first == P && \"Didn't find entry for predecessor!\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1503, __PRETTY_FUNCTION__)); | |||
| 1504 | ||||
| 1505 | // If we have an available predecessor but it requires casting, insert the | |||
| 1506 | // cast in the predecessor and use the cast. Note that we have to update the | |||
| 1507 | // AvailablePreds vector as we go so that all of the PHI entries for this | |||
| 1508 | // predecessor use the same bitcast. | |||
| 1509 | Value *&PredV = I->second; | |||
| 1510 | if (PredV->getType() != LoadI->getType()) | |||
| 1511 | PredV = CastInst::CreateBitOrPointerCast(PredV, LoadI->getType(), "", | |||
| 1512 | P->getTerminator()); | |||
| 1513 | ||||
| 1514 | PN->addIncoming(PredV, I->first); | |||
| 1515 | } | |||
| 1516 | ||||
| 1517 | for (LoadInst *PredLoadI : CSELoads) { | |||
| 1518 | combineMetadataForCSE(PredLoadI, LoadI, true); | |||
| 1519 | } | |||
| 1520 | ||||
| 1521 | LoadI->replaceAllUsesWith(PN); | |||
| 1522 | LoadI->eraseFromParent(); | |||
| 1523 | ||||
| 1524 | return true; | |||
| 1525 | } | |||
| 1526 | ||||
| 1527 | /// FindMostPopularDest - The specified list contains multiple possible | |||
| 1528 | /// threadable destinations. Pick the one that occurs the most frequently in | |||
| 1529 | /// the list. | |||
| 1530 | static BasicBlock * | |||
| 1531 | FindMostPopularDest(BasicBlock *BB, | |||
| 1532 | const SmallVectorImpl<std::pair<BasicBlock *, | |||
| 1533 | BasicBlock *>> &PredToDestList) { | |||
| 1534 | assert(!PredToDestList.empty())((!PredToDestList.empty()) ? static_cast<void> (0) : __assert_fail ("!PredToDestList.empty()", "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1534, __PRETTY_FUNCTION__)); | |||
| 1535 | ||||
| 1536 | // Determine popularity. If there are multiple possible destinations, we | |||
| 1537 | // explicitly choose to ignore 'undef' destinations. We prefer to thread | |||
| 1538 | // blocks with known and real destinations to threading undef. We'll handle | |||
| 1539 | // them later if interesting. | |||
| 1540 | DenseMap<BasicBlock*, unsigned> DestPopularity; | |||
| 1541 | for (const auto &PredToDest : PredToDestList) | |||
| 1542 | if (PredToDest.second) | |||
| 1543 | DestPopularity[PredToDest.second]++; | |||
| 1544 | ||||
| 1545 | if (DestPopularity.empty()) | |||
| 1546 | return nullptr; | |||
| 1547 | ||||
| 1548 | // Find the most popular dest. | |||
| 1549 | DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin(); | |||
| 1550 | BasicBlock *MostPopularDest = DPI->first; | |||
| 1551 | unsigned Popularity = DPI->second; | |||
| 1552 | SmallVector<BasicBlock*, 4> SamePopularity; | |||
| 1553 | ||||
| 1554 | for (++DPI; DPI != DestPopularity.end(); ++DPI) { | |||
| 1555 | // If the popularity of this entry isn't higher than the popularity we've | |||
| 1556 | // seen so far, ignore it. | |||
| 1557 | if (DPI->second < Popularity) | |||
| 1558 | ; // ignore. | |||
| 1559 | else if (DPI->second == Popularity) { | |||
| 1560 | // If it is the same as what we've seen so far, keep track of it. | |||
| 1561 | SamePopularity.push_back(DPI->first); | |||
| 1562 | } else { | |||
| 1563 | // If it is more popular, remember it. | |||
| 1564 | SamePopularity.clear(); | |||
| 1565 | MostPopularDest = DPI->first; | |||
| 1566 | Popularity = DPI->second; | |||
| 1567 | } | |||
| 1568 | } | |||
| 1569 | ||||
| 1570 | // Okay, now we know the most popular destination. If there is more than one | |||
| 1571 | // destination, we need to determine one. This is arbitrary, but we need | |||
| 1572 | // to make a deterministic decision. Pick the first one that appears in the | |||
| 1573 | // successor list. | |||
| 1574 | if (!SamePopularity.empty()) { | |||
| 1575 | SamePopularity.push_back(MostPopularDest); | |||
| 1576 | Instruction *TI = BB->getTerminator(); | |||
| 1577 | for (unsigned i = 0; ; ++i) { | |||
| 1578 | assert(i != TI->getNumSuccessors() && "Didn't find any successor!")((i != TI->getNumSuccessors() && "Didn't find any successor!" ) ? static_cast<void> (0) : __assert_fail ("i != TI->getNumSuccessors() && \"Didn't find any successor!\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1578, __PRETTY_FUNCTION__)); | |||
| 1579 | ||||
| 1580 | if (!is_contained(SamePopularity, TI->getSuccessor(i))) | |||
| 1581 | continue; | |||
| 1582 | ||||
| 1583 | MostPopularDest = TI->getSuccessor(i); | |||
| 1584 | break; | |||
| 1585 | } | |||
| 1586 | } | |||
| 1587 | ||||
| 1588 | // Okay, we have finally picked the most popular destination. | |||
| 1589 | return MostPopularDest; | |||
| 1590 | } | |||
| 1591 | ||||
| 1592 | bool JumpThreadingPass::ProcessThreadableEdges(Value *Cond, BasicBlock *BB, | |||
| 1593 | ConstantPreference Preference, | |||
| 1594 | Instruction *CxtI) { | |||
| 1595 | // If threading this would thread across a loop header, don't even try to | |||
| 1596 | // thread the edge. | |||
| 1597 | if (LoopHeaders.count(BB)) | |||
| 1598 | return false; | |||
| 1599 | ||||
| 1600 | PredValueInfoTy PredValues; | |||
| 1601 | if (!ComputeValueKnownInPredecessors(Cond, BB, PredValues, Preference, CxtI)) | |||
| 1602 | return false; | |||
| 1603 | ||||
| 1604 | assert(!PredValues.empty() &&((!PredValues.empty() && "ComputeValueKnownInPredecessors returned true with no values" ) ? static_cast<void> (0) : __assert_fail ("!PredValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1605, __PRETTY_FUNCTION__)) | |||
| 1605 | "ComputeValueKnownInPredecessors returned true with no values")((!PredValues.empty() && "ComputeValueKnownInPredecessors returned true with no values" ) ? static_cast<void> (0) : __assert_fail ("!PredValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1605, __PRETTY_FUNCTION__)); | |||
| 1606 | ||||
| 1607 | 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) | |||
| 1608 | 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) | |||
| 1609 | 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) | |||
| 1610 | << "': 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) | |||
| 1611 | << " 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) | |||
| 1612 | })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); | |||
| 1613 | ||||
| 1614 | // Decide what we want to thread through. Convert our list of known values to | |||
| 1615 | // a list of known destinations for each pred. This also discards duplicate | |||
| 1616 | // predecessors and keeps track of the undefined inputs (which are represented | |||
| 1617 | // as a null dest in the PredToDestList). | |||
| 1618 | SmallPtrSet<BasicBlock*, 16> SeenPreds; | |||
| 1619 | SmallVector<std::pair<BasicBlock*, BasicBlock*>, 16> PredToDestList; | |||
| 1620 | ||||
| 1621 | BasicBlock *OnlyDest = nullptr; | |||
| 1622 | BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL; | |||
| 1623 | Constant *OnlyVal = nullptr; | |||
| 1624 | Constant *MultipleVal = (Constant *)(intptr_t)~0ULL; | |||
| 1625 | ||||
| 1626 | for (const auto &PredValue : PredValues) { | |||
| 1627 | BasicBlock *Pred = PredValue.second; | |||
| 1628 | if (!SeenPreds.insert(Pred).second) | |||
| 1629 | continue; // Duplicate predecessor entry. | |||
| 1630 | ||||
| 1631 | Constant *Val = PredValue.first; | |||
| 1632 | ||||
| 1633 | BasicBlock *DestBB; | |||
| 1634 | if (isa<UndefValue>(Val)) | |||
| 1635 | DestBB = nullptr; | |||
| 1636 | else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { | |||
| 1637 | assert(isa<ConstantInt>(Val) && "Expecting a constant integer")((isa<ConstantInt>(Val) && "Expecting a constant integer" ) ? static_cast<void> (0) : __assert_fail ("isa<ConstantInt>(Val) && \"Expecting a constant integer\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1637, __PRETTY_FUNCTION__)); | |||
| 1638 | DestBB = BI->getSuccessor(cast<ConstantInt>(Val)->isZero()); | |||
| 1639 | } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { | |||
| 1640 | assert(isa<ConstantInt>(Val) && "Expecting a constant integer")((isa<ConstantInt>(Val) && "Expecting a constant integer" ) ? static_cast<void> (0) : __assert_fail ("isa<ConstantInt>(Val) && \"Expecting a constant integer\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1640, __PRETTY_FUNCTION__)); | |||
| 1641 | DestBB = SI->findCaseValue(cast<ConstantInt>(Val))->getCaseSuccessor(); | |||
| 1642 | } else { | |||
| 1643 | assert(isa<IndirectBrInst>(BB->getTerminator())((isa<IndirectBrInst>(BB->getTerminator()) && "Unexpected terminator") ? static_cast<void> (0) : __assert_fail ("isa<IndirectBrInst>(BB->getTerminator()) && \"Unexpected terminator\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1644, __PRETTY_FUNCTION__)) | |||
| 1644 | && "Unexpected terminator")((isa<IndirectBrInst>(BB->getTerminator()) && "Unexpected terminator") ? static_cast<void> (0) : __assert_fail ("isa<IndirectBrInst>(BB->getTerminator()) && \"Unexpected terminator\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1644, __PRETTY_FUNCTION__)); | |||
| 1645 | assert(isa<BlockAddress>(Val) && "Expecting a constant blockaddress")((isa<BlockAddress>(Val) && "Expecting a constant blockaddress" ) ? static_cast<void> (0) : __assert_fail ("isa<BlockAddress>(Val) && \"Expecting a constant blockaddress\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1645, __PRETTY_FUNCTION__)); | |||
| 1646 | DestBB = cast<BlockAddress>(Val)->getBasicBlock(); | |||
| 1647 | } | |||
| 1648 | ||||
| 1649 | // If we have exactly one destination, remember it for efficiency below. | |||
| 1650 | if (PredToDestList.empty()) { | |||
| 1651 | OnlyDest = DestBB; | |||
| 1652 | OnlyVal = Val; | |||
| 1653 | } else { | |||
| 1654 | if (OnlyDest != DestBB) | |||
| 1655 | OnlyDest = MultipleDestSentinel; | |||
| 1656 | // It possible we have same destination, but different value, e.g. default | |||
| 1657 | // case in switchinst. | |||
| 1658 | if (Val != OnlyVal) | |||
| 1659 | OnlyVal = MultipleVal; | |||
| 1660 | } | |||
| 1661 | ||||
| 1662 | // If the predecessor ends with an indirect goto, we can't change its | |||
| 1663 | // destination. Same for CallBr. | |||
| 1664 | if (isa<IndirectBrInst>(Pred->getTerminator()) || | |||
| 1665 | isa<CallBrInst>(Pred->getTerminator())) | |||
| 1666 | continue; | |||
| 1667 | ||||
| 1668 | PredToDestList.push_back(std::make_pair(Pred, DestBB)); | |||
| 1669 | } | |||
| 1670 | ||||
| 1671 | // If all edges were unthreadable, we fail. | |||
| 1672 | if (PredToDestList.empty()) | |||
| 1673 | return false; | |||
| 1674 | ||||
| 1675 | // If all the predecessors go to a single known successor, we want to fold, | |||
| 1676 | // not thread. By doing so, we do not need to duplicate the current block and | |||
| 1677 | // also miss potential opportunities in case we dont/cant duplicate. | |||
| 1678 | if (OnlyDest && OnlyDest != MultipleDestSentinel) { | |||
| 1679 | if (BB->hasNPredecessors(PredToDestList.size())) { | |||
| 1680 | bool SeenFirstBranchToOnlyDest = false; | |||
| 1681 | std::vector <DominatorTree::UpdateType> Updates; | |||
| 1682 | Updates.reserve(BB->getTerminator()->getNumSuccessors() - 1); | |||
| 1683 | for (BasicBlock *SuccBB : successors(BB)) { | |||
| 1684 | if (SuccBB == OnlyDest && !SeenFirstBranchToOnlyDest) { | |||
| 1685 | SeenFirstBranchToOnlyDest = true; // Don't modify the first branch. | |||
| 1686 | } else { | |||
| 1687 | SuccBB->removePredecessor(BB, true); // This is unreachable successor. | |||
| 1688 | Updates.push_back({DominatorTree::Delete, BB, SuccBB}); | |||
| 1689 | } | |||
| 1690 | } | |||
| 1691 | ||||
| 1692 | // Finally update the terminator. | |||
| 1693 | Instruction *Term = BB->getTerminator(); | |||
| 1694 | BranchInst::Create(OnlyDest, Term); | |||
| 1695 | Term->eraseFromParent(); | |||
| 1696 | DTU->applyUpdatesPermissive(Updates); | |||
| 1697 | ||||
| 1698 | // If the condition is now dead due to the removal of the old terminator, | |||
| 1699 | // erase it. | |||
| 1700 | if (auto *CondInst = dyn_cast<Instruction>(Cond)) { | |||
| 1701 | if (CondInst->use_empty() && !CondInst->mayHaveSideEffects()) | |||
| 1702 | CondInst->eraseFromParent(); | |||
| 1703 | // We can safely replace *some* uses of the CondInst if it has | |||
| 1704 | // exactly one value as returned by LVI. RAUW is incorrect in the | |||
| 1705 | // presence of guards and assumes, that have the `Cond` as the use. This | |||
| 1706 | // is because we use the guards/assume to reason about the `Cond` value | |||
| 1707 | // at the end of block, but RAUW unconditionally replaces all uses | |||
| 1708 | // including the guards/assumes themselves and the uses before the | |||
| 1709 | // guard/assume. | |||
| 1710 | else if (OnlyVal && OnlyVal != MultipleVal && | |||
| 1711 | CondInst->getParent() == BB) | |||
| 1712 | ReplaceFoldableUses(CondInst, OnlyVal); | |||
| 1713 | } | |||
| 1714 | return true; | |||
| 1715 | } | |||
| 1716 | } | |||
| 1717 | ||||
| 1718 | // Determine which is the most common successor. If we have many inputs and | |||
| 1719 | // this block is a switch, we want to start by threading the batch that goes | |||
| 1720 | // to the most popular destination first. If we only know about one | |||
| 1721 | // threadable destination (the common case) we can avoid this. | |||
| 1722 | BasicBlock *MostPopularDest = OnlyDest; | |||
| 1723 | ||||
| 1724 | if (MostPopularDest == MultipleDestSentinel) { | |||
| 1725 | // Remove any loop headers from the Dest list, ThreadEdge conservatively | |||
| 1726 | // won't process them, but we might have other destination that are eligible | |||
| 1727 | // and we still want to process. | |||
| 1728 | erase_if(PredToDestList, | |||
| 1729 | [&](const std::pair<BasicBlock *, BasicBlock *> &PredToDest) { | |||
| 1730 | return LoopHeaders.count(PredToDest.second) != 0; | |||
| 1731 | }); | |||
| 1732 | ||||
| 1733 | if (PredToDestList.empty()) | |||
| 1734 | return false; | |||
| 1735 | ||||
| 1736 | MostPopularDest = FindMostPopularDest(BB, PredToDestList); | |||
| 1737 | } | |||
| 1738 | ||||
| 1739 | // Now that we know what the most popular destination is, factor all | |||
| 1740 | // predecessors that will jump to it into a single predecessor. | |||
| 1741 | SmallVector<BasicBlock*, 16> PredsToFactor; | |||
| 1742 | for (const auto &PredToDest : PredToDestList) | |||
| 1743 | if (PredToDest.second == MostPopularDest) { | |||
| 1744 | BasicBlock *Pred = PredToDest.first; | |||
| 1745 | ||||
| 1746 | // This predecessor may be a switch or something else that has multiple | |||
| 1747 | // edges to the block. Factor each of these edges by listing them | |||
| 1748 | // according to # occurrences in PredsToFactor. | |||
| 1749 | for (BasicBlock *Succ : successors(Pred)) | |||
| 1750 | if (Succ == BB) | |||
| 1751 | PredsToFactor.push_back(Pred); | |||
| 1752 | } | |||
| 1753 | ||||
| 1754 | // If the threadable edges are branching on an undefined value, we get to pick | |||
| 1755 | // the destination that these predecessors should get to. | |||
| 1756 | if (!MostPopularDest) | |||
| 1757 | MostPopularDest = BB->getTerminator()-> | |||
| 1758 | getSuccessor(GetBestDestForJumpOnUndef(BB)); | |||
| 1759 | ||||
| 1760 | // Ok, try to thread it! | |||
| 1761 | return ThreadEdge(BB, PredsToFactor, MostPopularDest); | |||
| 1762 | } | |||
| 1763 | ||||
| 1764 | /// ProcessBranchOnPHI - We have an otherwise unthreadable conditional branch on | |||
| 1765 | /// a PHI node in the current block. See if there are any simplifications we | |||
| 1766 | /// can do based on inputs to the phi node. | |||
| 1767 | bool JumpThreadingPass::ProcessBranchOnPHI(PHINode *PN) { | |||
| 1768 | BasicBlock *BB = PN->getParent(); | |||
| 1769 | ||||
| 1770 | // TODO: We could make use of this to do it once for blocks with common PHI | |||
| 1771 | // values. | |||
| 1772 | SmallVector<BasicBlock*, 1> PredBBs; | |||
| 1773 | PredBBs.resize(1); | |||
| 1774 | ||||
| 1775 | // If any of the predecessor blocks end in an unconditional branch, we can | |||
| 1776 | // *duplicate* the conditional branch into that block in order to further | |||
| 1777 | // encourage jump threading and to eliminate cases where we have branch on a | |||
| 1778 | // phi of an icmp (branch on icmp is much better). | |||
| 1779 | for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { | |||
| 1780 | BasicBlock *PredBB = PN->getIncomingBlock(i); | |||
| 1781 | if (BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator())) | |||
| 1782 | if (PredBr->isUnconditional()) { | |||
| 1783 | PredBBs[0] = PredBB; | |||
| 1784 | // Try to duplicate BB into PredBB. | |||
| 1785 | if (DuplicateCondBranchOnPHIIntoPred(BB, PredBBs)) | |||
| 1786 | return true; | |||
| 1787 | } | |||
| 1788 | } | |||
| 1789 | ||||
| 1790 | return false; | |||
| 1791 | } | |||
| 1792 | ||||
| 1793 | /// ProcessBranchOnXOR - We have an otherwise unthreadable conditional branch on | |||
| 1794 | /// a xor instruction in the current block. See if there are any | |||
| 1795 | /// simplifications we can do based on inputs to the xor. | |||
| 1796 | bool JumpThreadingPass::ProcessBranchOnXOR(BinaryOperator *BO) { | |||
| 1797 | BasicBlock *BB = BO->getParent(); | |||
| 1798 | ||||
| 1799 | // If either the LHS or RHS of the xor is a constant, don't do this | |||
| 1800 | // optimization. | |||
| 1801 | if (isa<ConstantInt>(BO->getOperand(0)) || | |||
| 1802 | isa<ConstantInt>(BO->getOperand(1))) | |||
| 1803 | return false; | |||
| 1804 | ||||
| 1805 | // If the first instruction in BB isn't a phi, we won't be able to infer | |||
| 1806 | // anything special about any particular predecessor. | |||
| 1807 | if (!isa<PHINode>(BB->front())) | |||
| 1808 | return false; | |||
| 1809 | ||||
| 1810 | // If this BB is a landing pad, we won't be able to split the edge into it. | |||
| 1811 | if (BB->isEHPad()) | |||
| 1812 | return false; | |||
| 1813 | ||||
| 1814 | // If we have a xor as the branch input to this block, and we know that the | |||
| 1815 | // LHS or RHS of the xor in any predecessor is true/false, then we can clone | |||
| 1816 | // the condition into the predecessor and fix that value to true, saving some | |||
| 1817 | // logical ops on that path and encouraging other paths to simplify. | |||
| 1818 | // | |||
| 1819 | // This copies something like this: | |||
| 1820 | // | |||
| 1821 | // BB: | |||
| 1822 | // %X = phi i1 [1], [%X'] | |||
| 1823 | // %Y = icmp eq i32 %A, %B | |||
| 1824 | // %Z = xor i1 %X, %Y | |||
| 1825 | // br i1 %Z, ... | |||
| 1826 | // | |||
| 1827 | // Into: | |||
| 1828 | // BB': | |||
| 1829 | // %Y = icmp ne i32 %A, %B | |||
| 1830 | // br i1 %Y, ... | |||
| 1831 | ||||
| 1832 | PredValueInfoTy XorOpValues; | |||
| 1833 | bool isLHS = true; | |||
| 1834 | if (!ComputeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues, | |||
| 1835 | WantInteger, BO)) { | |||
| 1836 | assert(XorOpValues.empty())((XorOpValues.empty()) ? static_cast<void> (0) : __assert_fail ("XorOpValues.empty()", "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1836, __PRETTY_FUNCTION__)); | |||
| 1837 | if (!ComputeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues, | |||
| 1838 | WantInteger, BO)) | |||
| 1839 | return false; | |||
| 1840 | isLHS = false; | |||
| 1841 | } | |||
| 1842 | ||||
| 1843 | assert(!XorOpValues.empty() &&((!XorOpValues.empty() && "ComputeValueKnownInPredecessors returned true with no values" ) ? static_cast<void> (0) : __assert_fail ("!XorOpValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1844, __PRETTY_FUNCTION__)) | |||
| 1844 | "ComputeValueKnownInPredecessors returned true with no values")((!XorOpValues.empty() && "ComputeValueKnownInPredecessors returned true with no values" ) ? static_cast<void> (0) : __assert_fail ("!XorOpValues.empty() && \"ComputeValueKnownInPredecessors returned true with no values\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 1844, __PRETTY_FUNCTION__)); | |||
| 1845 | ||||
| 1846 | // Scan the information to see which is most popular: true or false. The | |||
| 1847 | // predecessors can be of the set true, false, or undef. | |||
| 1848 | unsigned NumTrue = 0, NumFalse = 0; | |||
| 1849 | for (const auto &XorOpValue : XorOpValues) { | |||
| 1850 | if (isa<UndefValue>(XorOpValue.first)) | |||
| 1851 | // Ignore undefs for the count. | |||
| 1852 | continue; | |||
| 1853 | if (cast<ConstantInt>(XorOpValue.first)->isZero()) | |||
| 1854 | ++NumFalse; | |||
| 1855 | else | |||
| 1856 | ++NumTrue; | |||
| 1857 | } | |||
| 1858 | ||||
| 1859 | // Determine which value to split on, true, false, or undef if neither. | |||
| 1860 | ConstantInt *SplitVal = nullptr; | |||
| 1861 | if (NumTrue > NumFalse) | |||
| 1862 | SplitVal = ConstantInt::getTrue(BB->getContext()); | |||
| 1863 | else if (NumTrue != 0 || NumFalse != 0) | |||
| 1864 | SplitVal = ConstantInt::getFalse(BB->getContext()); | |||
| 1865 | ||||
| 1866 | // Collect all of the blocks that this can be folded into so that we can | |||
| 1867 | // factor this once and clone it once. | |||
| 1868 | SmallVector<BasicBlock*, 8> BlocksToFoldInto; | |||
| 1869 | for (const auto &XorOpValue : XorOpValues) { | |||
| 1870 | if (XorOpValue.first != SplitVal && !isa<UndefValue>(XorOpValue.first)) | |||
| 1871 | continue; | |||
| 1872 | ||||
| 1873 | BlocksToFoldInto.push_back(XorOpValue.second); | |||
| 1874 | } | |||
| 1875 | ||||
| 1876 | // If we inferred a value for all of the predecessors, then duplication won't | |||
| 1877 | // help us. However, we can just replace the LHS or RHS with the constant. | |||
| 1878 | if (BlocksToFoldInto.size() == | |||
| 1879 | cast<PHINode>(BB->front()).getNumIncomingValues()) { | |||
| 1880 | if (!SplitVal) { | |||
| 1881 | // If all preds provide undef, just nuke the xor, because it is undef too. | |||
| 1882 | BO->replaceAllUsesWith(UndefValue::get(BO->getType())); | |||
| 1883 | BO->eraseFromParent(); | |||
| 1884 | } else if (SplitVal->isZero()) { | |||
| 1885 | // If all preds provide 0, replace the xor with the other input. | |||
| 1886 | BO->replaceAllUsesWith(BO->getOperand(isLHS)); | |||
| 1887 | BO->eraseFromParent(); | |||
| 1888 | } else { | |||
| 1889 | // If all preds provide 1, set the computed value to 1. | |||
| 1890 | BO->setOperand(!isLHS, SplitVal); | |||
| 1891 | } | |||
| 1892 | ||||
| 1893 | return true; | |||
| 1894 | } | |||
| 1895 | ||||
| 1896 | // Try to duplicate BB into PredBB. | |||
| 1897 | return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto); | |||
| 1898 | } | |||
| 1899 | ||||
| 1900 | /// AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new | |||
| 1901 | /// predecessor to the PHIBB block. If it has PHI nodes, add entries for | |||
| 1902 | /// NewPred using the entries from OldPred (suitably mapped). | |||
| 1903 | static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB, | |||
| 1904 | BasicBlock *OldPred, | |||
| 1905 | BasicBlock *NewPred, | |||
| 1906 | DenseMap<Instruction*, Value*> &ValueMap) { | |||
| 1907 | for (PHINode &PN : PHIBB->phis()) { | |||
| 1908 | // Ok, we have a PHI node. Figure out what the incoming value was for the | |||
| 1909 | // DestBlock. | |||
| 1910 | Value *IV = PN.getIncomingValueForBlock(OldPred); | |||
| 1911 | ||||
| 1912 | // Remap the value if necessary. | |||
| 1913 | if (Instruction *Inst = dyn_cast<Instruction>(IV)) { | |||
| 1914 | DenseMap<Instruction*, Value*>::iterator I = ValueMap.find(Inst); | |||
| 1915 | if (I != ValueMap.end()) | |||
| 1916 | IV = I->second; | |||
| 1917 | } | |||
| 1918 | ||||
| 1919 | PN.addIncoming(IV, NewPred); | |||
| 1920 | } | |||
| 1921 | } | |||
| 1922 | ||||
| 1923 | /// ThreadEdge - We have decided that it is safe and profitable to factor the | |||
| 1924 | /// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB | |||
| 1925 | /// across BB. Transform the IR to reflect this change. | |||
| 1926 | bool JumpThreadingPass::ThreadEdge(BasicBlock *BB, | |||
| 1927 | const SmallVectorImpl<BasicBlock *> &PredBBs, | |||
| 1928 | BasicBlock *SuccBB) { | |||
| 1929 | // If threading to the same block as we come from, we would infinite loop. | |||
| 1930 | if (SuccBB == BB) { | |||
| 1931 | 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) | |||
| 1932 | << "' - 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); | |||
| 1933 | return false; | |||
| 1934 | } | |||
| 1935 | ||||
| 1936 | // If threading this would thread across a loop header, don't thread the edge. | |||
| 1937 | // See the comments above FindLoopHeaders for justifications and caveats. | |||
| 1938 | if (LoopHeaders.count(BB) || LoopHeaders.count(SuccBB)) { | |||
| 1939 | 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) | |||
| 1940 | 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) | |||
| 1941 | 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) | |||
| 1942 | 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) | |||
| 1943 | << (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) | |||
| 1944 | << "' 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) | |||
| 1945 | << 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) | |||
| 1946 | })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); | |||
| 1947 | return false; | |||
| 1948 | } | |||
| 1949 | ||||
| 1950 | unsigned JumpThreadCost = | |||
| 1951 | getJumpThreadDuplicationCost(BB, BB->getTerminator(), BBDupThreshold); | |||
| 1952 | if (JumpThreadCost > BBDupThreshold) { | |||
| 1953 | 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) | |||
| 1954 | << "' - 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); | |||
| 1955 | return false; | |||
| 1956 | } | |||
| 1957 | ||||
| 1958 | // And finally, do it! Start by factoring the predecessors if needed. | |||
| 1959 | BasicBlock *PredBB; | |||
| 1960 | if (PredBBs.size() == 1) | |||
| 1961 | PredBB = PredBBs[0]; | |||
| 1962 | else { | |||
| 1963 | 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) | |||
| 1964 | << " common predecessors.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("jump-threading")) { dbgs() << " Factoring out " << PredBBs.size() << " common predecessors.\n"; } } while (false); | |||
| 1965 | PredBB = SplitBlockPreds(BB, PredBBs, ".thr_comm"); | |||
| 1966 | } | |||
| 1967 | ||||
| 1968 | // And finally, do it! | |||
| 1969 | 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) | |||
| 1970 | << "' 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) | |||
| 1971 | << "' 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) | |||
| 1972 | << ", 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); | |||
| 1973 | ||||
| 1974 | if (DTU->hasPendingDomTreeUpdates()) | |||
| 1975 | LVI->disableDT(); | |||
| 1976 | else | |||
| 1977 | LVI->enableDT(); | |||
| 1978 | LVI->threadEdge(PredBB, BB, SuccBB); | |||
| 1979 | ||||
| 1980 | // We are going to have to map operands from the original BB block to the new | |||
| 1981 | // copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to | |||
| 1982 | // account for entry from PredBB. | |||
| 1983 | DenseMap<Instruction*, Value*> ValueMapping; | |||
| 1984 | ||||
| 1985 | BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), | |||
| 1986 | BB->getName()+".thread", | |||
| 1987 | BB->getParent(), BB); | |||
| 1988 | NewBB->moveAfter(PredBB); | |||
| 1989 | ||||
| 1990 | // Set the block frequency of NewBB. | |||
| 1991 | if (HasProfileData) { | |||
| 1992 | auto NewBBFreq = | |||
| 1993 | BFI->getBlockFreq(PredBB) * BPI->getEdgeProbability(PredBB, BB); | |||
| 1994 | BFI->setBlockFreq(NewBB, NewBBFreq.getFrequency()); | |||
| 1995 | } | |||
| 1996 | ||||
| 1997 | BasicBlock::iterator BI = BB->begin(); | |||
| 1998 | // Clone the phi nodes of BB into NewBB. The resulting phi nodes are trivial, | |||
| 1999 | // since NewBB only has one predecessor, but SSAUpdater might need to rewrite | |||
| 2000 | // the operand of the cloned phi. | |||
| 2001 | for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI) { | |||
| 2002 | PHINode *NewPN = PHINode::Create(PN->getType(), 1, PN->getName(), NewBB); | |||
| 2003 | NewPN->addIncoming(PN->getIncomingValueForBlock(PredBB), PredBB); | |||
| 2004 | ValueMapping[PN] = NewPN; | |||
| 2005 | } | |||
| 2006 | ||||
| 2007 | // Clone the non-phi instructions of BB into NewBB, keeping track of the | |||
| 2008 | // mapping and using it to remap operands in the cloned instructions. | |||
| 2009 | for (; !BI->isTerminator(); ++BI) { | |||
| 2010 | Instruction *New = BI->clone(); | |||
| 2011 | New->setName(BI->getName()); | |||
| 2012 | NewBB->getInstList().push_back(New); | |||
| 2013 | ValueMapping[&*BI] = New; | |||
| 2014 | ||||
| 2015 | // Remap operands to patch up intra-block references. | |||
| 2016 | for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i) | |||
| 2017 | if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) { | |||
| 2018 | DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst); | |||
| 2019 | if (I != ValueMapping.end()) | |||
| 2020 | New->setOperand(i, I->second); | |||
| 2021 | } | |||
| 2022 | } | |||
| 2023 | ||||
| 2024 | // We didn't copy the terminator from BB over to NewBB, because there is now | |||
| 2025 | // an unconditional jump to SuccBB. Insert the unconditional jump. | |||
| 2026 | BranchInst *NewBI = BranchInst::Create(SuccBB, NewBB); | |||
| 2027 | NewBI->setDebugLoc(BB->getTerminator()->getDebugLoc()); | |||
| 2028 | ||||
| 2029 | // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the | |||
| 2030 | // PHI nodes for NewBB now. | |||
| 2031 | AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping); | |||
| 2032 | ||||
| 2033 | // Update the terminator of PredBB to jump to NewBB instead of BB. This | |||
| 2034 | // eliminates predecessors from BB, which requires us to simplify any PHI | |||
| 2035 | // nodes in BB. | |||
| 2036 | Instruction *PredTerm = PredBB->getTerminator(); | |||
| 2037 | for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i) | |||
| 2038 | if (PredTerm->getSuccessor(i) == BB) { | |||
| 2039 | BB->removePredecessor(PredBB, true); | |||
| 2040 | PredTerm->setSuccessor(i, NewBB); | |||
| 2041 | } | |||
| 2042 | ||||
| 2043 | // Enqueue required DT updates. | |||
| 2044 | DTU->applyUpdatesPermissive({{DominatorTree::Insert, NewBB, SuccBB}, | |||
| 2045 | {DominatorTree::Insert, PredBB, NewBB}, | |||
| 2046 | {DominatorTree::Delete, PredBB, BB}}); | |||
| 2047 | ||||
| 2048 | // If there were values defined in BB that are used outside the block, then we | |||
| 2049 | // now have to update all uses of the value to use either the original value, | |||
| 2050 | // the cloned value, or some PHI derived value. This can require arbitrary | |||
| 2051 | // PHI insertion, of which we are prepared to do, clean these up now. | |||
| 2052 | SSAUpdater SSAUpdate; | |||
| 2053 | SmallVector<Use*, 16> UsesToRename; | |||
| 2054 | ||||
| 2055 | for (Instruction &I : *BB) { | |||
| 2056 | // Scan all uses of this instruction to see if their uses are no longer | |||
| 2057 | // dominated by the previous def and if so, record them in UsesToRename. | |||
| 2058 | // Also, skip phi operands from PredBB - we'll remove them anyway. | |||
| 2059 | for (Use &U : I.uses()) { | |||
| 2060 | Instruction *User = cast<Instruction>(U.getUser()); | |||
| 2061 | if (PHINode *UserPN = dyn_cast<PHINode>(User)) { | |||
| 2062 | if (UserPN->getIncomingBlock(U) == BB) | |||
| 2063 | continue; | |||
| 2064 | } else if (User->getParent() == BB) | |||
| 2065 | continue; | |||
| 2066 | ||||
| 2067 | UsesToRename.push_back(&U); | |||
| 2068 | } | |||
| 2069 | ||||
| 2070 | // If there are no uses outside the block, we're done with this instruction. | |||
| 2071 | if (UsesToRename.empty()) | |||
| 2072 | continue; | |||
| 2073 | 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); | |||
| 2074 | ||||
| 2075 | // We found a use of I outside of BB. Rename all uses of I that are outside | |||
| 2076 | // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks | |||
| 2077 | // with the two values we know. | |||
| 2078 | SSAUpdate.Initialize(I.getType(), I.getName()); | |||
| 2079 | SSAUpdate.AddAvailableValue(BB, &I); | |||
| 2080 | SSAUpdate.AddAvailableValue(NewBB, ValueMapping[&I]); | |||
| 2081 | ||||
| 2082 | while (!UsesToRename.empty()) | |||
| 2083 | SSAUpdate.RewriteUse(*UsesToRename.pop_back_val()); | |||
| 2084 | LLVM_DEBUG(dbgs() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("jump-threading")) { dbgs() << "\n"; } } while (false); | |||
| 2085 | } | |||
| 2086 | ||||
| 2087 | // At this point, the IR is fully up to date and consistent. Do a quick scan | |||
| 2088 | // over the new instructions and zap any that are constants or dead. This | |||
| 2089 | // frequently happens because of phi translation. | |||
| 2090 | SimplifyInstructionsInBlock(NewBB, TLI); | |||
| 2091 | ||||
| 2092 | // Update the edge weight from BB to SuccBB, which should be less than before. | |||
| 2093 | UpdateBlockFreqAndEdgeWeight(PredBB, BB, NewBB, SuccBB); | |||
| 2094 | ||||
| 2095 | // Threaded an edge! | |||
| 2096 | ++NumThreads; | |||
| 2097 | return true; | |||
| 2098 | } | |||
| 2099 | ||||
| 2100 | /// Create a new basic block that will be the predecessor of BB and successor of | |||
| 2101 | /// all blocks in Preds. When profile data is available, update the frequency of | |||
| 2102 | /// this new block. | |||
| 2103 | BasicBlock *JumpThreadingPass::SplitBlockPreds(BasicBlock *BB, | |||
| 2104 | ArrayRef<BasicBlock *> Preds, | |||
| 2105 | const char *Suffix) { | |||
| 2106 | SmallVector<BasicBlock *, 2> NewBBs; | |||
| 2107 | ||||
| 2108 | // Collect the frequencies of all predecessors of BB, which will be used to | |||
| 2109 | // update the edge weight of the result of splitting predecessors. | |||
| 2110 | DenseMap<BasicBlock *, BlockFrequency> FreqMap; | |||
| 2111 | if (HasProfileData) | |||
| 2112 | for (auto Pred : Preds) | |||
| 2113 | FreqMap.insert(std::make_pair( | |||
| 2114 | Pred, BFI->getBlockFreq(Pred) * BPI->getEdgeProbability(Pred, BB))); | |||
| 2115 | ||||
| 2116 | // In the case when BB is a LandingPad block we create 2 new predecessors | |||
| 2117 | // instead of just one. | |||
| 2118 | if (BB->isLandingPad()) { | |||
| 2119 | std::string NewName = std::string(Suffix) + ".split-lp"; | |||
| 2120 | SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(), NewBBs); | |||
| 2121 | } else { | |||
| 2122 | NewBBs.push_back(SplitBlockPredecessors(BB, Preds, Suffix)); | |||
| 2123 | } | |||
| 2124 | ||||
| 2125 | std::vector<DominatorTree::UpdateType> Updates; | |||
| 2126 | Updates.reserve((2 * Preds.size()) + NewBBs.size()); | |||
| 2127 | for (auto NewBB : NewBBs) { | |||
| 2128 | BlockFrequency NewBBFreq(0); | |||
| 2129 | Updates.push_back({DominatorTree::Insert, NewBB, BB}); | |||
| 2130 | for (auto Pred : predecessors(NewBB)) { | |||
| 2131 | Updates.push_back({DominatorTree::Delete, Pred, BB}); | |||
| 2132 | Updates.push_back({DominatorTree::Insert, Pred, NewBB}); | |||
| 2133 | if (HasProfileData) // Update frequencies between Pred -> NewBB. | |||
| 2134 | NewBBFreq += FreqMap.lookup(Pred); | |||
| 2135 | } | |||
| 2136 | if (HasProfileData) // Apply the summed frequency to NewBB. | |||
| 2137 | BFI->setBlockFreq(NewBB, NewBBFreq.getFrequency()); | |||
| 2138 | } | |||
| 2139 | ||||
| 2140 | DTU->applyUpdatesPermissive(Updates); | |||
| 2141 | return NewBBs[0]; | |||
| 2142 | } | |||
| 2143 | ||||
| 2144 | bool JumpThreadingPass::doesBlockHaveProfileData(BasicBlock *BB) { | |||
| 2145 | const Instruction *TI = BB->getTerminator(); | |||
| 2146 | assert(TI->getNumSuccessors() > 1 && "not a split")((TI->getNumSuccessors() > 1 && "not a split") ? static_cast<void> (0) : __assert_fail ("TI->getNumSuccessors() > 1 && \"not a split\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 2146, __PRETTY_FUNCTION__)); | |||
| 2147 | ||||
| 2148 | MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof); | |||
| 2149 | if (!WeightsNode) | |||
| 2150 | return false; | |||
| 2151 | ||||
| 2152 | MDString *MDName = cast<MDString>(WeightsNode->getOperand(0)); | |||
| 2153 | if (MDName->getString() != "branch_weights") | |||
| 2154 | return false; | |||
| 2155 | ||||
| 2156 | // Ensure there are weights for all of the successors. Note that the first | |||
| 2157 | // operand to the metadata node is a name, not a weight. | |||
| 2158 | return WeightsNode->getNumOperands() == TI->getNumSuccessors() + 1; | |||
| 2159 | } | |||
| 2160 | ||||
| 2161 | /// Update the block frequency of BB and branch weight and the metadata on the | |||
| 2162 | /// edge BB->SuccBB. This is done by scaling the weight of BB->SuccBB by 1 - | |||
| 2163 | /// Freq(PredBB->BB) / Freq(BB->SuccBB). | |||
| 2164 | void JumpThreadingPass::UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB, | |||
| 2165 | BasicBlock *BB, | |||
| 2166 | BasicBlock *NewBB, | |||
| 2167 | BasicBlock *SuccBB) { | |||
| 2168 | if (!HasProfileData) | |||
| 2169 | return; | |||
| 2170 | ||||
| 2171 | assert(BFI && BPI && "BFI & BPI should have been created here")((BFI && BPI && "BFI & BPI should have been created here" ) ? static_cast<void> (0) : __assert_fail ("BFI && BPI && \"BFI & BPI should have been created here\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 2171, __PRETTY_FUNCTION__)); | |||
| 2172 | ||||
| 2173 | // As the edge from PredBB to BB is deleted, we have to update the block | |||
| 2174 | // frequency of BB. | |||
| 2175 | auto BBOrigFreq = BFI->getBlockFreq(BB); | |||
| 2176 | auto NewBBFreq = BFI->getBlockFreq(NewBB); | |||
| 2177 | auto BB2SuccBBFreq = BBOrigFreq * BPI->getEdgeProbability(BB, SuccBB); | |||
| 2178 | auto BBNewFreq = BBOrigFreq - NewBBFreq; | |||
| 2179 | BFI->setBlockFreq(BB, BBNewFreq.getFrequency()); | |||
| 2180 | ||||
| 2181 | // Collect updated outgoing edges' frequencies from BB and use them to update | |||
| 2182 | // edge probabilities. | |||
| 2183 | SmallVector<uint64_t, 4> BBSuccFreq; | |||
| 2184 | for (BasicBlock *Succ : successors(BB)) { | |||
| 2185 | auto SuccFreq = (Succ == SuccBB) | |||
| 2186 | ? BB2SuccBBFreq - NewBBFreq | |||
| 2187 | : BBOrigFreq * BPI->getEdgeProbability(BB, Succ); | |||
| 2188 | BBSuccFreq.push_back(SuccFreq.getFrequency()); | |||
| 2189 | } | |||
| 2190 | ||||
| 2191 | uint64_t MaxBBSuccFreq = | |||
| 2192 | *std::max_element(BBSuccFreq.begin(), BBSuccFreq.end()); | |||
| 2193 | ||||
| 2194 | SmallVector<BranchProbability, 4> BBSuccProbs; | |||
| 2195 | if (MaxBBSuccFreq == 0) | |||
| 2196 | BBSuccProbs.assign(BBSuccFreq.size(), | |||
| 2197 | {1, static_cast<unsigned>(BBSuccFreq.size())}); | |||
| 2198 | else { | |||
| 2199 | for (uint64_t Freq : BBSuccFreq) | |||
| 2200 | BBSuccProbs.push_back( | |||
| 2201 | BranchProbability::getBranchProbability(Freq, MaxBBSuccFreq)); | |||
| 2202 | // Normalize edge probabilities so that they sum up to one. | |||
| 2203 | BranchProbability::normalizeProbabilities(BBSuccProbs.begin(), | |||
| 2204 | BBSuccProbs.end()); | |||
| 2205 | } | |||
| 2206 | ||||
| 2207 | // Update edge probabilities in BPI. | |||
| 2208 | for (int I = 0, E = BBSuccProbs.size(); I < E; I++) | |||
| 2209 | BPI->setEdgeProbability(BB, I, BBSuccProbs[I]); | |||
| 2210 | ||||
| 2211 | // Update the profile metadata as well. | |||
| 2212 | // | |||
| 2213 | // Don't do this if the profile of the transformed blocks was statically | |||
| 2214 | // estimated. (This could occur despite the function having an entry | |||
| 2215 | // frequency in completely cold parts of the CFG.) | |||
| 2216 | // | |||
| 2217 | // In this case we don't want to suggest to subsequent passes that the | |||
| 2218 | // calculated weights are fully consistent. Consider this graph: | |||
| 2219 | // | |||
| 2220 | // check_1 | |||
| 2221 | // 50% / | | |||
| 2222 | // eq_1 | 50% | |||
| 2223 | // \ | | |||
| 2224 | // check_2 | |||
| 2225 | // 50% / | | |||
| 2226 | // eq_2 | 50% | |||
| 2227 | // \ | | |||
| 2228 | // check_3 | |||
| 2229 | // 50% / | | |||
| 2230 | // eq_3 | 50% | |||
| 2231 | // \ | | |||
| 2232 | // | |||
| 2233 | // Assuming the blocks check_* all compare the same value against 1, 2 and 3, | |||
| 2234 | // the overall probabilities are inconsistent; the total probability that the | |||
| 2235 | // value is either 1, 2 or 3 is 150%. | |||
| 2236 | // | |||
| 2237 | // As a consequence if we thread eq_1 -> check_2 to check_3, check_2->check_3 | |||
| 2238 | // becomes 0%. This is even worse if the edge whose probability becomes 0% is | |||
| 2239 | // the loop exit edge. Then based solely on static estimation we would assume | |||
| 2240 | // the loop was extremely hot. | |||
| 2241 | // | |||
| 2242 | // FIXME this locally as well so that BPI and BFI are consistent as well. We | |||
| 2243 | // shouldn't make edges extremely likely or unlikely based solely on static | |||
| 2244 | // estimation. | |||
| 2245 | if (BBSuccProbs.size() >= 2 && doesBlockHaveProfileData(BB)) { | |||
| 2246 | SmallVector<uint32_t, 4> Weights; | |||
| 2247 | for (auto Prob : BBSuccProbs) | |||
| 2248 | Weights.push_back(Prob.getNumerator()); | |||
| 2249 | ||||
| 2250 | auto TI = BB->getTerminator(); | |||
| 2251 | TI->setMetadata( | |||
| 2252 | LLVMContext::MD_prof, | |||
| 2253 | MDBuilder(TI->getParent()->getContext()).createBranchWeights(Weights)); | |||
| 2254 | } | |||
| 2255 | } | |||
| 2256 | ||||
| 2257 | /// DuplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch | |||
| 2258 | /// to BB which contains an i1 PHI node and a conditional branch on that PHI. | |||
| 2259 | /// If we can duplicate the contents of BB up into PredBB do so now, this | |||
| 2260 | /// improves the odds that the branch will be on an analyzable instruction like | |||
| 2261 | /// a compare. | |||
| 2262 | bool JumpThreadingPass::DuplicateCondBranchOnPHIIntoPred( | |||
| 2263 | BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs) { | |||
| 2264 | assert(!PredBBs.empty() && "Can't handle an empty set")((!PredBBs.empty() && "Can't handle an empty set") ? static_cast <void> (0) : __assert_fail ("!PredBBs.empty() && \"Can't handle an empty set\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 2264, __PRETTY_FUNCTION__)); | |||
| 2265 | ||||
| 2266 | // If BB is a loop header, then duplicating this block outside the loop would | |||
| 2267 | // cause us to transform this into an irreducible loop, don't do this. | |||
| 2268 | // See the comments above FindLoopHeaders for justifications and caveats. | |||
| 2269 | if (LoopHeaders.count(BB)) { | |||
| 2270 | 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) | |||
| 2271 | << "' 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) | |||
| 2272 | << "' - 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); | |||
| 2273 | return false; | |||
| 2274 | } | |||
| 2275 | ||||
| 2276 | unsigned DuplicationCost = | |||
| 2277 | getJumpThreadDuplicationCost(BB, BB->getTerminator(), BBDupThreshold); | |||
| 2278 | if (DuplicationCost > BBDupThreshold) { | |||
| 2279 | 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) | |||
| 2280 | << "' - 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); | |||
| 2281 | return false; | |||
| 2282 | } | |||
| 2283 | ||||
| 2284 | // And finally, do it! Start by factoring the predecessors if needed. | |||
| 2285 | std::vector<DominatorTree::UpdateType> Updates; | |||
| 2286 | BasicBlock *PredBB; | |||
| 2287 | if (PredBBs.size() == 1) | |||
| 2288 | PredBB = PredBBs[0]; | |||
| 2289 | else { | |||
| 2290 | 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) | |||
| 2291 | << " common predecessors.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("jump-threading")) { dbgs() << " Factoring out " << PredBBs.size() << " common predecessors.\n"; } } while (false); | |||
| 2292 | PredBB = SplitBlockPreds(BB, PredBBs, ".thr_comm"); | |||
| 2293 | } | |||
| 2294 | Updates.push_back({DominatorTree::Delete, PredBB, BB}); | |||
| 2295 | ||||
| 2296 | // Okay, we decided to do this! Clone all the instructions in BB onto the end | |||
| 2297 | // of PredBB. | |||
| 2298 | 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) | |||
| 2299 | << "' 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) | |||
| 2300 | << "' 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) | |||
| 2301 | << 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); | |||
| 2302 | ||||
| 2303 | // Unless PredBB ends with an unconditional branch, split the edge so that we | |||
| 2304 | // can just clone the bits from BB into the end of the new PredBB. | |||
| 2305 | BranchInst *OldPredBranch = dyn_cast<BranchInst>(PredBB->getTerminator()); | |||
| 2306 | ||||
| 2307 | if (!OldPredBranch || !OldPredBranch->isUnconditional()) { | |||
| 2308 | BasicBlock *OldPredBB = PredBB; | |||
| 2309 | PredBB = SplitEdge(OldPredBB, BB); | |||
| 2310 | Updates.push_back({DominatorTree::Insert, OldPredBB, PredBB}); | |||
| 2311 | Updates.push_back({DominatorTree::Insert, PredBB, BB}); | |||
| 2312 | Updates.push_back({DominatorTree::Delete, OldPredBB, BB}); | |||
| 2313 | OldPredBranch = cast<BranchInst>(PredBB->getTerminator()); | |||
| 2314 | } | |||
| 2315 | ||||
| 2316 | // We are going to have to map operands from the original BB block into the | |||
| 2317 | // PredBB block. Evaluate PHI nodes in BB. | |||
| 2318 | DenseMap<Instruction*, Value*> ValueMapping; | |||
| 2319 | ||||
| 2320 | BasicBlock::iterator BI = BB->begin(); | |||
| 2321 | for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI) | |||
| 2322 | ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB); | |||
| 2323 | // Clone the non-phi instructions of BB into PredBB, keeping track of the | |||
| 2324 | // mapping and using it to remap operands in the cloned instructions. | |||
| 2325 | for (; BI != BB->end(); ++BI) { | |||
| 2326 | Instruction *New = BI->clone(); | |||
| 2327 | ||||
| 2328 | // Remap operands to patch up intra-block references. | |||
| 2329 | for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i) | |||
| 2330 | if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) { | |||
| 2331 | DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst); | |||
| 2332 | if (I != ValueMapping.end()) | |||
| 2333 | New->setOperand(i, I->second); | |||
| 2334 | } | |||
| 2335 | ||||
| 2336 | // If this instruction can be simplified after the operands are updated, | |||
| 2337 | // just use the simplified value instead. This frequently happens due to | |||
| 2338 | // phi translation. | |||
| 2339 | if (Value *IV = SimplifyInstruction( | |||
| 2340 | New, | |||
| 2341 | {BB->getModule()->getDataLayout(), TLI, nullptr, nullptr, New})) { | |||
| 2342 | ValueMapping[&*BI] = IV; | |||
| 2343 | if (!New->mayHaveSideEffects()) { | |||
| 2344 | New->deleteValue(); | |||
| 2345 | New = nullptr; | |||
| 2346 | } | |||
| 2347 | } else { | |||
| 2348 | ValueMapping[&*BI] = New; | |||
| 2349 | } | |||
| 2350 | if (New) { | |||
| 2351 | // Otherwise, insert the new instruction into the block. | |||
| 2352 | New->setName(BI->getName()); | |||
| 2353 | PredBB->getInstList().insert(OldPredBranch->getIterator(), New); | |||
| 2354 | // Update Dominance from simplified New instruction operands. | |||
| 2355 | for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i) | |||
| 2356 | if (BasicBlock *SuccBB = dyn_cast<BasicBlock>(New->getOperand(i))) | |||
| 2357 | Updates.push_back({DominatorTree::Insert, PredBB, SuccBB}); | |||
| 2358 | } | |||
| 2359 | } | |||
| 2360 | ||||
| 2361 | // Check to see if the targets of the branch had PHI nodes. If so, we need to | |||
| 2362 | // add entries to the PHI nodes for branch from PredBB now. | |||
| 2363 | BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator()); | |||
| 2364 | AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB, | |||
| 2365 | ValueMapping); | |||
| 2366 | AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB, | |||
| 2367 | ValueMapping); | |||
| 2368 | ||||
| 2369 | // If there were values defined in BB that are used outside the block, then we | |||
| 2370 | // now have to update all uses of the value to use either the original value, | |||
| 2371 | // the cloned value, or some PHI derived value. This can require arbitrary | |||
| 2372 | // PHI insertion, of which we are prepared to do, clean these up now. | |||
| 2373 | SSAUpdater SSAUpdate; | |||
| 2374 | SmallVector<Use*, 16> UsesToRename; | |||
| 2375 | for (Instruction &I : *BB) { | |||
| 2376 | // Scan all uses of this instruction to see if it is used outside of its | |||
| 2377 | // block, and if so, record them in UsesToRename. | |||
| 2378 | for (Use &U : I.uses()) { | |||
| 2379 | Instruction *User = cast<Instruction>(U.getUser()); | |||
| 2380 | if (PHINode *UserPN = dyn_cast<PHINode>(User)) { | |||
| 2381 | if (UserPN->getIncomingBlock(U) == BB) | |||
| 2382 | continue; | |||
| 2383 | } else if (User->getParent() == BB) | |||
| 2384 | continue; | |||
| 2385 | ||||
| 2386 | UsesToRename.push_back(&U); | |||
| 2387 | } | |||
| 2388 | ||||
| 2389 | // If there are no uses outside the block, we're done with this instruction. | |||
| 2390 | if (UsesToRename.empty()) | |||
| 2391 | continue; | |||
| 2392 | ||||
| 2393 | 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); | |||
| 2394 | ||||
| 2395 | // We found a use of I outside of BB. Rename all uses of I that are outside | |||
| 2396 | // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks | |||
| 2397 | // with the two values we know. | |||
| 2398 | SSAUpdate.Initialize(I.getType(), I.getName()); | |||
| 2399 | SSAUpdate.AddAvailableValue(BB, &I); | |||
| 2400 | SSAUpdate.AddAvailableValue(PredBB, ValueMapping[&I]); | |||
| 2401 | ||||
| 2402 | while (!UsesToRename.empty()) | |||
| 2403 | SSAUpdate.RewriteUse(*UsesToRename.pop_back_val()); | |||
| 2404 | LLVM_DEBUG(dbgs() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("jump-threading")) { dbgs() << "\n"; } } while (false); | |||
| 2405 | } | |||
| 2406 | ||||
| 2407 | // PredBB no longer jumps to BB, remove entries in the PHI node for the edge | |||
| 2408 | // that we nuked. | |||
| 2409 | BB->removePredecessor(PredBB, true); | |||
| 2410 | ||||
| 2411 | // Remove the unconditional branch at the end of the PredBB block. | |||
| 2412 | OldPredBranch->eraseFromParent(); | |||
| 2413 | DTU->applyUpdatesPermissive(Updates); | |||
| 2414 | ||||
| 2415 | ++NumDupes; | |||
| 2416 | return true; | |||
| 2417 | } | |||
| 2418 | ||||
| 2419 | // Pred is a predecessor of BB with an unconditional branch to BB. SI is | |||
| 2420 | // a Select instruction in Pred. BB has other predecessors and SI is used in | |||
| 2421 | // a PHI node in BB. SI has no other use. | |||
| 2422 | // A new basic block, NewBB, is created and SI is converted to compare and | |||
| 2423 | // conditional branch. SI is erased from parent. | |||
| 2424 | void JumpThreadingPass::UnfoldSelectInstr(BasicBlock *Pred, BasicBlock *BB, | |||
| 2425 | SelectInst *SI, PHINode *SIUse, | |||
| 2426 | unsigned Idx) { | |||
| 2427 | // Expand the select. | |||
| 2428 | // | |||
| 2429 | // Pred -- | |||
| 2430 | // | v | |||
| 2431 | // | NewBB | |||
| 2432 | // | | | |||
| 2433 | // |----- | |||
| 2434 | // v | |||
| 2435 | // BB | |||
| 2436 | BranchInst *PredTerm = dyn_cast<BranchInst>(Pred->getTerminator()); | |||
| 2437 | BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "select.unfold", | |||
| 2438 | BB->getParent(), BB); | |||
| 2439 | // Move the unconditional branch to NewBB. | |||
| 2440 | PredTerm->removeFromParent(); | |||
| ||||
| 2441 | NewBB->getInstList().insert(NewBB->end(), PredTerm); | |||
| 2442 | // Create a conditional branch and update PHI nodes. | |||
| 2443 | BranchInst::Create(NewBB, BB, SI->getCondition(), Pred); | |||
| 2444 | SIUse->setIncomingValue(Idx, SI->getFalseValue()); | |||
| 2445 | SIUse->addIncoming(SI->getTrueValue(), NewBB); | |||
| 2446 | ||||
| 2447 | // The select is now dead. | |||
| 2448 | SI->eraseFromParent(); | |||
| 2449 | DTU->applyUpdatesPermissive({{DominatorTree::Insert, NewBB, BB}, | |||
| 2450 | {DominatorTree::Insert, Pred, NewBB}}); | |||
| 2451 | ||||
| 2452 | // Update any other PHI nodes in BB. | |||
| 2453 | for (BasicBlock::iterator BI = BB->begin(); | |||
| 2454 | PHINode *Phi = dyn_cast<PHINode>(BI); ++BI) | |||
| 2455 | if (Phi != SIUse) | |||
| 2456 | Phi->addIncoming(Phi->getIncomingValueForBlock(Pred), NewBB); | |||
| 2457 | } | |||
| 2458 | ||||
| 2459 | bool JumpThreadingPass::TryToUnfoldSelect(SwitchInst *SI, BasicBlock *BB) { | |||
| 2460 | PHINode *CondPHI = dyn_cast<PHINode>(SI->getCondition()); | |||
| 2461 | ||||
| 2462 | if (!CondPHI || CondPHI->getParent() != BB) | |||
| 2463 | return false; | |||
| 2464 | ||||
| 2465 | for (unsigned I = 0, E = CondPHI->getNumIncomingValues(); I != E; ++I) { | |||
| 2466 | BasicBlock *Pred = CondPHI->getIncomingBlock(I); | |||
| 2467 | SelectInst *PredSI = dyn_cast<SelectInst>(CondPHI->getIncomingValue(I)); | |||
| 2468 | ||||
| 2469 | // The second and third condition can be potentially relaxed. Currently | |||
| 2470 | // the conditions help to simplify the code and allow us to reuse existing | |||
| 2471 | // code, developed for TryToUnfoldSelect(CmpInst *, BasicBlock *) | |||
| 2472 | if (!PredSI || PredSI->getParent() != Pred || !PredSI->hasOneUse()) | |||
| 2473 | continue; | |||
| 2474 | ||||
| 2475 | BranchInst *PredTerm = dyn_cast<BranchInst>(Pred->getTerminator()); | |||
| 2476 | if (!PredTerm
| |||
| 2477 | continue; | |||
| 2478 | ||||
| 2479 | UnfoldSelectInstr(Pred, BB, PredSI, CondPHI, I); | |||
| 2480 | return true; | |||
| 2481 | } | |||
| 2482 | return false; | |||
| 2483 | } | |||
| 2484 | ||||
| 2485 | /// TryToUnfoldSelect - Look for blocks of the form | |||
| 2486 | /// bb1: | |||
| 2487 | /// %a = select | |||
| 2488 | /// br bb2 | |||
| 2489 | /// | |||
| 2490 | /// bb2: | |||
| 2491 | /// %p = phi [%a, %bb1] ... | |||
| 2492 | /// %c = icmp %p | |||
| 2493 | /// br i1 %c | |||
| 2494 | /// | |||
| 2495 | /// And expand the select into a branch structure if one of its arms allows %c | |||
| 2496 | /// to be folded. This later enables threading from bb1 over bb2. | |||
| 2497 | bool JumpThreadingPass::TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB) { | |||
| 2498 | BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator()); | |||
| 2499 | PHINode *CondLHS = dyn_cast<PHINode>(CondCmp->getOperand(0)); | |||
| 2500 | Constant *CondRHS = cast<Constant>(CondCmp->getOperand(1)); | |||
| 2501 | ||||
| 2502 | if (!CondBr || !CondBr->isConditional() || !CondLHS || | |||
| 2503 | CondLHS->getParent() != BB) | |||
| 2504 | return false; | |||
| 2505 | ||||
| 2506 | for (unsigned I = 0, E = CondLHS->getNumIncomingValues(); I != E; ++I) { | |||
| 2507 | BasicBlock *Pred = CondLHS->getIncomingBlock(I); | |||
| 2508 | SelectInst *SI = dyn_cast<SelectInst>(CondLHS->getIncomingValue(I)); | |||
| 2509 | ||||
| 2510 | // Look if one of the incoming values is a select in the corresponding | |||
| 2511 | // predecessor. | |||
| 2512 | if (!SI || SI->getParent() != Pred || !SI->hasOneUse()) | |||
| 2513 | continue; | |||
| 2514 | ||||
| 2515 | BranchInst *PredTerm = dyn_cast<BranchInst>(Pred->getTerminator()); | |||
| 2516 | if (!PredTerm || !PredTerm->isUnconditional()) | |||
| 2517 | continue; | |||
| 2518 | ||||
| 2519 | // Now check if one of the select values would allow us to constant fold the | |||
| 2520 | // terminator in BB. We don't do the transform if both sides fold, those | |||
| 2521 | // cases will be threaded in any case. | |||
| 2522 | if (DTU->hasPendingDomTreeUpdates()) | |||
| 2523 | LVI->disableDT(); | |||
| 2524 | else | |||
| 2525 | LVI->enableDT(); | |||
| 2526 | LazyValueInfo::Tristate LHSFolds = | |||
| 2527 | LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(1), | |||
| 2528 | CondRHS, Pred, BB, CondCmp); | |||
| 2529 | LazyValueInfo::Tristate RHSFolds = | |||
| 2530 | LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(2), | |||
| 2531 | CondRHS, Pred, BB, CondCmp); | |||
| 2532 | if ((LHSFolds != LazyValueInfo::Unknown || | |||
| 2533 | RHSFolds != LazyValueInfo::Unknown) && | |||
| 2534 | LHSFolds != RHSFolds) { | |||
| 2535 | UnfoldSelectInstr(Pred, BB, SI, CondLHS, I); | |||
| 2536 | return true; | |||
| 2537 | } | |||
| 2538 | } | |||
| 2539 | return false; | |||
| 2540 | } | |||
| 2541 | ||||
| 2542 | /// TryToUnfoldSelectInCurrBB - Look for PHI/Select or PHI/CMP/Select in the | |||
| 2543 | /// same BB in the form | |||
| 2544 | /// bb: | |||
| 2545 | /// %p = phi [false, %bb1], [true, %bb2], [false, %bb3], [true, %bb4], ... | |||
| 2546 | /// %s = select %p, trueval, falseval | |||
| 2547 | /// | |||
| 2548 | /// or | |||
| 2549 | /// | |||
| 2550 | /// bb: | |||
| 2551 | /// %p = phi [0, %bb1], [1, %bb2], [0, %bb3], [1, %bb4], ... | |||
| 2552 | /// %c = cmp %p, 0 | |||
| 2553 | /// %s = select %c, trueval, falseval | |||
| 2554 | /// | |||
| 2555 | /// And expand the select into a branch structure. This later enables | |||
| 2556 | /// jump-threading over bb in this pass. | |||
| 2557 | /// | |||
| 2558 | /// Using the similar approach of SimplifyCFG::FoldCondBranchOnPHI(), unfold | |||
| 2559 | /// select if the associated PHI has at least one constant. If the unfolded | |||
| 2560 | /// select is not jump-threaded, it will be folded again in the later | |||
| 2561 | /// optimizations. | |||
| 2562 | bool JumpThreadingPass::TryToUnfoldSelectInCurrBB(BasicBlock *BB) { | |||
| 2563 | // If threading this would thread across a loop header, don't thread the edge. | |||
| 2564 | // See the comments above FindLoopHeaders for justifications and caveats. | |||
| 2565 | if (LoopHeaders.count(BB)) | |||
| 2566 | return false; | |||
| 2567 | ||||
| 2568 | for (BasicBlock::iterator BI = BB->begin(); | |||
| 2569 | PHINode *PN = dyn_cast<PHINode>(BI); ++BI) { | |||
| 2570 | // Look for a Phi having at least one constant incoming value. | |||
| 2571 | if (llvm::all_of(PN->incoming_values(), | |||
| 2572 | [](Value *V) { return !isa<ConstantInt>(V); })) | |||
| 2573 | continue; | |||
| 2574 | ||||
| 2575 | auto isUnfoldCandidate = [BB](SelectInst *SI, Value *V) { | |||
| 2576 | // Check if SI is in BB and use V as condition. | |||
| 2577 | if (SI->getParent() != BB) | |||
| 2578 | return false; | |||
| 2579 | Value *Cond = SI->getCondition(); | |||
| 2580 | return (Cond && Cond == V && Cond->getType()->isIntegerTy(1)); | |||
| 2581 | }; | |||
| 2582 | ||||
| 2583 | SelectInst *SI = nullptr; | |||
| 2584 | for (Use &U : PN->uses()) { | |||
| 2585 | if (ICmpInst *Cmp = dyn_cast<ICmpInst>(U.getUser())) { | |||
| 2586 | // Look for a ICmp in BB that compares PN with a constant and is the | |||
| 2587 | // condition of a Select. | |||
| 2588 | if (Cmp->getParent() == BB && Cmp->hasOneUse() && | |||
| 2589 | isa<ConstantInt>(Cmp->getOperand(1 - U.getOperandNo()))) | |||
| 2590 | if (SelectInst *SelectI = dyn_cast<SelectInst>(Cmp->user_back())) | |||
| 2591 | if (isUnfoldCandidate(SelectI, Cmp->use_begin()->get())) { | |||
| 2592 | SI = SelectI; | |||
| 2593 | break; | |||
| 2594 | } | |||
| 2595 | } else if (SelectInst *SelectI = dyn_cast<SelectInst>(U.getUser())) { | |||
| 2596 | // Look for a Select in BB that uses PN as condition. | |||
| 2597 | if (isUnfoldCandidate(SelectI, U.get())) { | |||
| 2598 | SI = SelectI; | |||
| 2599 | break; | |||
| 2600 | } | |||
| 2601 | } | |||
| 2602 | } | |||
| 2603 | ||||
| 2604 | if (!SI) | |||
| 2605 | continue; | |||
| 2606 | // Expand the select. | |||
| 2607 | Instruction *Term = | |||
| 2608 | SplitBlockAndInsertIfThen(SI->getCondition(), SI, false); | |||
| 2609 | BasicBlock *SplitBB = SI->getParent(); | |||
| 2610 | BasicBlock *NewBB = Term->getParent(); | |||
| 2611 | PHINode *NewPN = PHINode::Create(SI->getType(), 2, "", SI); | |||
| 2612 | NewPN->addIncoming(SI->getTrueValue(), Term->getParent()); | |||
| 2613 | NewPN->addIncoming(SI->getFalseValue(), BB); | |||
| 2614 | SI->replaceAllUsesWith(NewPN); | |||
| 2615 | SI->eraseFromParent(); | |||
| 2616 | // NewBB and SplitBB are newly created blocks which require insertion. | |||
| 2617 | std::vector<DominatorTree::UpdateType> Updates; | |||
| 2618 | Updates.reserve((2 * SplitBB->getTerminator()->getNumSuccessors()) + 3); | |||
| 2619 | Updates.push_back({DominatorTree::Insert, BB, SplitBB}); | |||
| 2620 | Updates.push_back({DominatorTree::Insert, BB, NewBB}); | |||
| 2621 | Updates.push_back({DominatorTree::Insert, NewBB, SplitBB}); | |||
| 2622 | // BB's successors were moved to SplitBB, update DTU accordingly. | |||
| 2623 | for (auto *Succ : successors(SplitBB)) { | |||
| 2624 | Updates.push_back({DominatorTree::Delete, BB, Succ}); | |||
| 2625 | Updates.push_back({DominatorTree::Insert, SplitBB, Succ}); | |||
| 2626 | } | |||
| 2627 | DTU->applyUpdatesPermissive(Updates); | |||
| 2628 | return true; | |||
| 2629 | } | |||
| 2630 | return false; | |||
| 2631 | } | |||
| 2632 | ||||
| 2633 | /// Try to propagate a guard from the current BB into one of its predecessors | |||
| 2634 | /// in case if another branch of execution implies that the condition of this | |||
| 2635 | /// guard is always true. Currently we only process the simplest case that | |||
| 2636 | /// looks like: | |||
| 2637 | /// | |||
| 2638 | /// Start: | |||
| 2639 | /// %cond = ... | |||
| 2640 | /// br i1 %cond, label %T1, label %F1 | |||
| 2641 | /// T1: | |||
| 2642 | /// br label %Merge | |||
| 2643 | /// F1: | |||
| 2644 | /// br label %Merge | |||
| 2645 | /// Merge: | |||
| 2646 | /// %condGuard = ... | |||
| 2647 | /// call void(i1, ...) @llvm.experimental.guard( i1 %condGuard )[ "deopt"() ] | |||
| 2648 | /// | |||
| 2649 | /// And cond either implies condGuard or !condGuard. In this case all the | |||
| 2650 | /// instructions before the guard can be duplicated in both branches, and the | |||
| 2651 | /// guard is then threaded to one of them. | |||
| 2652 | bool JumpThreadingPass::ProcessGuards(BasicBlock *BB) { | |||
| 2653 | using namespace PatternMatch; | |||
| 2654 | ||||
| 2655 | // We only want to deal with two predecessors. | |||
| 2656 | BasicBlock *Pred1, *Pred2; | |||
| 2657 | auto PI = pred_begin(BB), PE = pred_end(BB); | |||
| 2658 | if (PI == PE) | |||
| 2659 | return false; | |||
| 2660 | Pred1 = *PI++; | |||
| 2661 | if (PI == PE) | |||
| 2662 | return false; | |||
| 2663 | Pred2 = *PI++; | |||
| 2664 | if (PI != PE) | |||
| 2665 | return false; | |||
| 2666 | if (Pred1 == Pred2) | |||
| 2667 | return false; | |||
| 2668 | ||||
| 2669 | // Try to thread one of the guards of the block. | |||
| 2670 | // TODO: Look up deeper than to immediate predecessor? | |||
| 2671 | auto *Parent = Pred1->getSinglePredecessor(); | |||
| 2672 | if (!Parent || Parent != Pred2->getSinglePredecessor()) | |||
| 2673 | return false; | |||
| 2674 | ||||
| 2675 | if (auto *BI = dyn_cast<BranchInst>(Parent->getTerminator())) | |||
| 2676 | for (auto &I : *BB) | |||
| 2677 | if (isGuard(&I) && ThreadGuard(BB, cast<IntrinsicInst>(&I), BI)) | |||
| 2678 | return true; | |||
| 2679 | ||||
| 2680 | return false; | |||
| 2681 | } | |||
| 2682 | ||||
| 2683 | /// Try to propagate the guard from BB which is the lower block of a diamond | |||
| 2684 | /// to one of its branches, in case if diamond's condition implies guard's | |||
| 2685 | /// condition. | |||
| 2686 | bool JumpThreadingPass::ThreadGuard(BasicBlock *BB, IntrinsicInst *Guard, | |||
| 2687 | BranchInst *BI) { | |||
| 2688 | assert(BI->getNumSuccessors() == 2 && "Wrong number of successors?")((BI->getNumSuccessors() == 2 && "Wrong number of successors?" ) ? static_cast<void> (0) : __assert_fail ("BI->getNumSuccessors() == 2 && \"Wrong number of successors?\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 2688, __PRETTY_FUNCTION__)); | |||
| 2689 | assert(BI->isConditional() && "Unconditional branch has 2 successors?")((BI->isConditional() && "Unconditional branch has 2 successors?" ) ? static_cast<void> (0) : __assert_fail ("BI->isConditional() && \"Unconditional branch has 2 successors?\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 2689, __PRETTY_FUNCTION__)); | |||
| 2690 | Value *GuardCond = Guard->getArgOperand(0); | |||
| 2691 | Value *BranchCond = BI->getCondition(); | |||
| 2692 | BasicBlock *TrueDest = BI->getSuccessor(0); | |||
| 2693 | BasicBlock *FalseDest = BI->getSuccessor(1); | |||
| 2694 | ||||
| 2695 | auto &DL = BB->getModule()->getDataLayout(); | |||
| 2696 | bool TrueDestIsSafe = false; | |||
| 2697 | bool FalseDestIsSafe = false; | |||
| 2698 | ||||
| 2699 | // True dest is safe if BranchCond => GuardCond. | |||
| 2700 | auto Impl = isImpliedCondition(BranchCond, GuardCond, DL); | |||
| 2701 | if (Impl && *Impl) | |||
| 2702 | TrueDestIsSafe = true; | |||
| 2703 | else { | |||
| 2704 | // False dest is safe if !BranchCond => GuardCond. | |||
| 2705 | Impl = isImpliedCondition(BranchCond, GuardCond, DL, /* LHSIsTrue */ false); | |||
| 2706 | if (Impl && *Impl) | |||
| 2707 | FalseDestIsSafe = true; | |||
| 2708 | } | |||
| 2709 | ||||
| 2710 | if (!TrueDestIsSafe && !FalseDestIsSafe) | |||
| 2711 | return false; | |||
| 2712 | ||||
| 2713 | BasicBlock *PredUnguardedBlock = TrueDestIsSafe ? TrueDest : FalseDest; | |||
| 2714 | BasicBlock *PredGuardedBlock = FalseDestIsSafe ? TrueDest : FalseDest; | |||
| 2715 | ||||
| 2716 | ValueToValueMapTy UnguardedMapping, GuardedMapping; | |||
| 2717 | Instruction *AfterGuard = Guard->getNextNode(); | |||
| 2718 | unsigned Cost = getJumpThreadDuplicationCost(BB, AfterGuard, BBDupThreshold); | |||
| 2719 | if (Cost > BBDupThreshold) | |||
| 2720 | return false; | |||
| 2721 | // Duplicate all instructions before the guard and the guard itself to the | |||
| 2722 | // branch where implication is not proved. | |||
| 2723 | BasicBlock *GuardedBlock = DuplicateInstructionsInSplitBetween( | |||
| 2724 | BB, PredGuardedBlock, AfterGuard, GuardedMapping, *DTU); | |||
| 2725 | assert(GuardedBlock && "Could not create the guarded block?")((GuardedBlock && "Could not create the guarded block?" ) ? static_cast<void> (0) : __assert_fail ("GuardedBlock && \"Could not create the guarded block?\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 2725, __PRETTY_FUNCTION__)); | |||
| 2726 | // Duplicate all instructions before the guard in the unguarded branch. | |||
| 2727 | // Since we have successfully duplicated the guarded block and this block | |||
| 2728 | // has fewer instructions, we expect it to succeed. | |||
| 2729 | BasicBlock *UnguardedBlock = DuplicateInstructionsInSplitBetween( | |||
| 2730 | BB, PredUnguardedBlock, Guard, UnguardedMapping, *DTU); | |||
| 2731 | assert(UnguardedBlock && "Could not create the unguarded block?")((UnguardedBlock && "Could not create the unguarded block?" ) ? static_cast<void> (0) : __assert_fail ("UnguardedBlock && \"Could not create the unguarded block?\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 2731, __PRETTY_FUNCTION__)); | |||
| 2732 | 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) | |||
| 2733 | << GuardedBlock->getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType ("jump-threading")) { dbgs() << "Moved guard " << *Guard << " to block " << GuardedBlock->getName () << "\n"; } } while (false); | |||
| 2734 | // Some instructions before the guard may still have uses. For them, we need | |||
| 2735 | // to create Phi nodes merging their copies in both guarded and unguarded | |||
| 2736 | // branches. Those instructions that have no uses can be just removed. | |||
| 2737 | SmallVector<Instruction *, 4> ToRemove; | |||
| 2738 | for (auto BI = BB->begin(); &*BI != AfterGuard; ++BI) | |||
| 2739 | if (!isa<PHINode>(&*BI)) | |||
| 2740 | ToRemove.push_back(&*BI); | |||
| 2741 | ||||
| 2742 | Instruction *InsertionPoint = &*BB->getFirstInsertionPt(); | |||
| 2743 | assert(InsertionPoint && "Empty block?")((InsertionPoint && "Empty block?") ? static_cast< void> (0) : __assert_fail ("InsertionPoint && \"Empty block?\"" , "/build/llvm-toolchain-snapshot-10~svn374877/lib/Transforms/Scalar/JumpThreading.cpp" , 2743, __PRETTY_FUNCTION__)); | |||
| 2744 | // Substitute with Phis & remove. | |||
| 2745 | for (auto *Inst : reverse(ToRemove)) { | |||
| 2746 | if (!Inst->use_empty()) { | |||
| 2747 | PHINode *NewPN = PHINode::Create(Inst->getType(), 2); | |||
| 2748 | NewPN->addIncoming(UnguardedMapping[Inst], UnguardedBlock); | |||
| 2749 | NewPN->addIncoming(GuardedMapping[Inst], GuardedBlock); | |||
| 2750 | NewPN->insertBefore(InsertionPoint); | |||
| 2751 | Inst->replaceAllUsesWith(NewPN); | |||
| 2752 | } | |||
| 2753 | Inst->eraseFromParent(); | |||
| 2754 | } | |||
| 2755 | return true; | |||
| 2756 | } |