X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FLoopUnswitch.cpp;h=95d7f8a3beda23b180d350f3835f2e2c187e639e;hp=ef43483772020a1e985c8ba0b3dc65dcc932634b;hb=2027fcbfdaea79a5486db80a4da7407f50f7f4ec;hpb=3d03d60ca8ad1f1b4e76cd5af024e31a1aed5b6d diff --git a/lib/Transforms/Scalar/LoopUnswitch.cpp b/lib/Transforms/Scalar/LoopUnswitch.cpp index ef434837720..95d7f8a3bed 100644 --- a/lib/Transforms/Scalar/LoopUnswitch.cpp +++ b/lib/Transforms/Scalar/LoopUnswitch.cpp @@ -30,18 +30,25 @@ #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/Statistic.h" -#include "llvm/Analysis/AssumptionTracker.h" +#include "llvm/Analysis/GlobalsModRef.h" +#include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/CodeMetrics.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/LoopPass.h" #include "llvm/Analysis/ScalarEvolution.h" #include "llvm/Analysis/TargetTransformInfo.h" +#include "llvm/Analysis/BlockFrequencyInfoImpl.h" +#include "llvm/Analysis/BlockFrequencyInfo.h" +#include "llvm/Analysis/BranchProbabilityInfo.h" +#include "llvm/Support/BranchProbability.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Function.h" #include "llvm/IR/Instructions.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/MDBuilder.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" @@ -68,6 +75,19 @@ static cl::opt Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"), cl::init(100), cl::Hidden); +static cl::opt +LoopUnswitchWithBlockFrequency("loop-unswitch-with-block-frequency", + cl::init(false), cl::Hidden, + cl::desc("Enable the use of the block frequency analysis to access PGO " + "heuristics to minimize code growth in cold regions.")); + +static cl::opt +ColdnessThreshold("loop-unswitch-coldness-threshold", cl::init(1), cl::Hidden, + cl::desc("Coldness threshold in percentage. The loop header frequency " + "(relative to the entry frequency) is compared with this " + "threshold to determine if non-trivial unswitching should be " + "enabled.")); + namespace { class LUAnalysisCache { @@ -79,6 +99,7 @@ namespace { struct LoopProperties { unsigned CanBeUnswitchedCount; + unsigned WasUnswitchedCount; unsigned SizeEstimation; UnswitchedValsMap UnswitchedVals; }; @@ -92,50 +113,72 @@ namespace { UnswitchedValsMap *CurLoopInstructions; LoopProperties *CurrentLoopProperties; - // Max size of code we can produce on remained iterations. + // A loop unswitching with an estimated cost above this threshold + // is not performed. MaxSize is turned into unswitching quota for + // the current loop, and reduced correspondingly, though note that + // the quota is returned by releaseMemory() when the loop has been + // processed, so that MaxSize will return to its previous + // value. So in most cases MaxSize will equal the Threshold flag + // when a new loop is processed. An exception to that is that + // MaxSize will have a smaller value while processing nested loops + // that were introduced due to loop unswitching of an outer loop. + // + // FIXME: The way that MaxSize works is subtle and depends on the + // pass manager processing loops and calling releaseMemory() in a + // specific order. It would be good to find a more straightforward + // way of doing what MaxSize does. unsigned MaxSize; - public: - - LUAnalysisCache() : - CurLoopInstructions(nullptr), CurrentLoopProperties(nullptr), - MaxSize(Threshold) - {} - - // Analyze loop. Check its size, calculate is it possible to unswitch - // it. Returns true if we can unswitch this loop. - bool countLoop(const Loop *L, const TargetTransformInfo &TTI, - AssumptionTracker *AT); - - // Clean all data related to given loop. - void forgetLoop(const Loop *L); - - // Mark case value as unswitched. - // Since SI instruction can be partly unswitched, in order to avoid - // extra unswitching in cloned loops keep track all unswitched values. - void setUnswitched(const SwitchInst *SI, const Value *V); - - // Check was this case value unswitched before or not. - bool isUnswitched(const SwitchInst *SI, const Value *V); - - // Clone all loop-unswitch related loop properties. - // Redistribute unswitching quotas. - // Note, that new loop data is stored inside the VMap. - void cloneData(const Loop *NewLoop, const Loop *OldLoop, - const ValueToValueMapTy &VMap); + public: + LUAnalysisCache() + : CurLoopInstructions(nullptr), CurrentLoopProperties(nullptr), + MaxSize(Threshold) {} + + // Analyze loop. Check its size, calculate is it possible to unswitch + // it. Returns true if we can unswitch this loop. + bool countLoop(const Loop *L, const TargetTransformInfo &TTI, + AssumptionCache *AC); + + // Clean all data related to given loop. + void forgetLoop(const Loop *L); + + // Mark case value as unswitched. + // Since SI instruction can be partly unswitched, in order to avoid + // extra unswitching in cloned loops keep track all unswitched values. + void setUnswitched(const SwitchInst *SI, const Value *V); + + // Check was this case value unswitched before or not. + bool isUnswitched(const SwitchInst *SI, const Value *V); + + // Returns true if another unswitching could be done within the cost + // threshold. + bool CostAllowsUnswitching(); + + // Clone all loop-unswitch related loop properties. + // Redistribute unswitching quotas. + // Note, that new loop data is stored inside the VMap. + void cloneData(const Loop *NewLoop, const Loop *OldLoop, + const ValueToValueMapTy &VMap); }; class LoopUnswitch : public LoopPass { LoopInfo *LI; // Loop information LPPassManager *LPM; - AssumptionTracker *AT; + AssumptionCache *AC; - // LoopProcessWorklist - Used to check if second loop needs processing - // after RewriteLoopBodyWithConditionConstant rewrites first loop. + // Used to check if second loop needs processing after + // RewriteLoopBodyWithConditionConstant rewrites first loop. std::vector LoopProcessWorklist; LUAnalysisCache BranchesInfo; + bool EnabledPGO; + + // BFI and ColdEntryFreq are only used when PGO and + // LoopUnswitchWithBlockFrequency are enabled. + BlockFrequencyInfo BFI; + BlockFrequency ColdEntryFreq; + bool OptimizeForSize; bool redoLoop; @@ -167,16 +210,18 @@ namespace { /// loop preheaders be inserted into the CFG. /// void getAnalysisUsage(AnalysisUsage &AU) const override { - AU.addRequired(); + AU.addRequired(); AU.addRequiredID(LoopSimplifyID); AU.addPreservedID(LoopSimplifyID); - AU.addRequired(); - AU.addPreserved(); + AU.addRequired(); + AU.addPreserved(); AU.addRequiredID(LCSSAID); AU.addPreservedID(LCSSAID); + AU.addRequired(); AU.addPreserved(); - AU.addPreserved(); - AU.addRequired(); + AU.addPreserved(); + AU.addRequired(); + AU.addPreserved(); } private: @@ -192,12 +237,17 @@ namespace { /// Split all of the edges from inside the loop to their exit blocks. /// Update the appropriate Phi nodes as we do so. - void SplitExitEdges(Loop *L, const SmallVectorImpl &ExitBlocks); + void SplitExitEdges(Loop *L, + const SmallVectorImpl &ExitBlocks); + + bool TryTrivialLoopUnswitch(bool &Changed); - bool UnswitchIfProfitable(Value *LoopCond, Constant *Val); + bool UnswitchIfProfitable(Value *LoopCond, Constant *Val, + TerminatorInst *TI = nullptr); void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, - BasicBlock *ExitBlock); - void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L); + BasicBlock *ExitBlock, TerminatorInst *TI); + void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L, + TerminatorInst *TI); void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, Constant *Val, bool isEqual); @@ -205,19 +255,17 @@ namespace { void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, BasicBlock *TrueDest, BasicBlock *FalseDest, - Instruction *InsertPt); + Instruction *InsertPt, + TerminatorInst *TI); void SimplifyCode(std::vector &Worklist, Loop *L); - bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = nullptr, - BasicBlock **LoopExit = nullptr); - }; } // Analyze loop. Check its size, calculate is it possible to unswitch // it. Returns true if we can unswitch this loop. bool LUAnalysisCache::countLoop(const Loop *L, const TargetTransformInfo &TTI, - AssumptionTracker *AT) { + AssumptionCache *AC) { LoopPropsMapIt PropsIt; bool Inserted; @@ -235,18 +283,19 @@ bool LUAnalysisCache::countLoop(const Loop *L, const TargetTransformInfo &TTI, // This is a very ad-hoc heuristic. SmallPtrSet EphValues; - CodeMetrics::collectEphemeralValues(L, AT, EphValues); + CodeMetrics::collectEphemeralValues(L, AC, EphValues); // FIXME: This is overly conservative because it does not take into // consideration code simplification opportunities and code that can // be shared by the resultant unswitched loops. CodeMetrics Metrics; - for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); - I != E; ++I) + for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); I != E; + ++I) Metrics.analyzeBasicBlock(*I, TTI, EphValues); - Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5); + Props.SizeEstimation = Metrics.NumInsts; Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation); + Props.WasUnswitchedCount = 0; MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount; if (Metrics.notDuplicatable) { @@ -257,13 +306,6 @@ bool LUAnalysisCache::countLoop(const Loop *L, const TargetTransformInfo &TTI, } } - if (!Props.CanBeUnswitchedCount) { - DEBUG(dbgs() << "NOT unswitching loop %" - << L->getHeader()->getName() << ", cost too high: " - << L->getBlocks().size() << "\n"); - return false; - } - // Be careful. This links are good only before new loop addition. CurrentLoopProperties = &Props; CurLoopInstructions = &Props.UnswitchedVals; @@ -278,7 +320,8 @@ void LUAnalysisCache::forgetLoop(const Loop *L) { if (LIt != LoopsProperties.end()) { LoopProperties &Props = LIt->second; - MaxSize += Props.CanBeUnswitchedCount * Props.SizeEstimation; + MaxSize += (Props.CanBeUnswitchedCount + Props.WasUnswitchedCount) * + Props.SizeEstimation; LoopsProperties.erase(LIt); } @@ -298,6 +341,10 @@ bool LUAnalysisCache::isUnswitched(const SwitchInst *SI, const Value *V) { return (*CurLoopInstructions)[SI].count(V); } +bool LUAnalysisCache::CostAllowsUnswitching() { + return CurrentLoopProperties->CanBeUnswitchedCount > 0; +} + // Clone all loop-unswitch related loop properties. // Redistribute unswitching quotas. // Note, that new loop data is stored inside the VMap. @@ -311,6 +358,8 @@ void LUAnalysisCache::cloneData(const Loop *NewLoop, const Loop *OldLoop, // Reallocate "can-be-unswitched quota" --OldLoopProps.CanBeUnswitchedCount; + ++OldLoopProps.WasUnswitchedCount; + NewLoopProps.WasUnswitchedCount = 0; unsigned Quota = OldLoopProps.CanBeUnswitchedCount; NewLoopProps.CanBeUnswitchedCount = Quota / 2; OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2; @@ -333,10 +382,10 @@ void LUAnalysisCache::cloneData(const Loop *NewLoop, const Loop *OldLoop, char LoopUnswitch::ID = 0; INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops", false, false) -INITIALIZE_AG_DEPENDENCY(TargetTransformInfo) -INITIALIZE_PASS_DEPENDENCY(AssumptionTracker) +INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) +INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) INITIALIZE_PASS_DEPENDENCY(LoopSimplify) -INITIALIZE_PASS_DEPENDENCY(LoopInfo) +INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) INITIALIZE_PASS_DEPENDENCY(LCSSA) INITIALIZE_PASS_END(LoopUnswitch, "loop-unswitch", "Unswitch loops", false, false) @@ -345,9 +394,8 @@ Pass *llvm::createLoopUnswitchPass(bool Os) { return new LoopUnswitch(Os); } -/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is -/// invariant in the loop, or has an invariant piece, return the invariant. -/// Otherwise, return null. +/// Cond is a condition that occurs in L. If it is invariant in the loop, or has +/// an invariant piece, return the invariant. Otherwise, return null. static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) { // We started analyze new instruction, increment scanned instructions counter. @@ -385,14 +433,27 @@ bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) { if (skipOptnoneFunction(L)) return false; - AT = &getAnalysis(); - LI = &getAnalysis(); + AC = &getAnalysis().getAssumptionCache( + *L->getHeader()->getParent()); + LI = &getAnalysis().getLoopInfo(); LPM = &LPM_Ref; - DominatorTreeWrapperPass *DTWP = - getAnalysisIfAvailable(); - DT = DTWP ? &DTWP->getDomTree() : nullptr; + DT = &getAnalysis().getDomTree(); currentLoop = L; Function *F = currentLoop->getHeader()->getParent(); + + EnabledPGO = F->getEntryCount().hasValue(); + + if (LoopUnswitchWithBlockFrequency && EnabledPGO) { + BranchProbabilityInfo BPI(*F, *LI); + BFI.calculate(*L->getHeader()->getParent(), BPI, *LI); + + // Use BranchProbability to compute a minimum frequency based on + // function entry baseline frequency. Loops with headers below this + // frequency are considered as cold. + const BranchProbability ColdProb(ColdnessThreshold, 100); + ColdEntryFreq = BlockFrequency(BFI.getEntryFreq()) * ColdProb; + } + bool Changed = false; do { assert(currentLoop->isLCSSAForm(*DT)); @@ -400,16 +461,13 @@ bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) { Changed |= processCurrentLoop(); } while(redoLoop); - if (Changed) { - // FIXME: Reconstruct dom info, because it is not preserved properly. - if (DT) - DT->recalculate(*F); - } + // FIXME: Reconstruct dom info, because it is not preserved properly. + if (Changed) + DT->recalculate(*F); return Changed; } -/// processCurrentLoop - Do actual work and unswitch loop if possible -/// and profitable. +/// Do actual work and unswitch loop if possible and profitable. bool LoopUnswitch::processCurrentLoop() { bool Changed = false; @@ -429,12 +487,48 @@ bool LoopUnswitch::processCurrentLoop() { LLVMContext &Context = loopHeader->getContext(); - // Probably we reach the quota of branches for this loop. If so - // stop unswitching. - if (!BranchesInfo.countLoop(currentLoop, getAnalysis(), - AT)) + // Analyze loop cost, and stop unswitching if loop content can not be duplicated. + if (!BranchesInfo.countLoop( + currentLoop, getAnalysis().getTTI( + *currentLoop->getHeader()->getParent()), + AC)) return false; + // Try trivial unswitch first before loop over other basic blocks in the loop. + if (TryTrivialLoopUnswitch(Changed)) { + return true; + } + + // Do not unswitch loops containing convergent operations, as we might be + // making them control dependent on the unswitch value when they were not + // before. + // FIXME: This could be refined to only bail if the convergent operation is + // not already control-dependent on the unswitch value. + for (const auto BB : currentLoop->blocks()) { + for (auto &I : *BB) { + auto CS = CallSite(&I); + if (!CS) continue; + if (CS.hasFnAttr(Attribute::Convergent)) + return false; + } + } + + // Do not do non-trivial unswitch while optimizing for size. + // FIXME: Use Function::optForSize(). + if (OptimizeForSize || + loopHeader->getParent()->hasFnAttribute(Attribute::OptimizeForSize)) + return false; + + if (LoopUnswitchWithBlockFrequency && EnabledPGO) { + // Compute the weighted frequency of the hottest block in the + // loop (loopHeader in this case since inner loops should be + // processed before outer loop). If it is less than ColdFrequency, + // we should not unswitch. + BlockFrequency LoopEntryFreq = BFI.getBlockFreq(loopHeader); + if (LoopEntryFreq < ColdEntryFreq) + return false; + } + // Loop over all of the basic blocks in the loop. If we find an interior // block that is branching on a loop-invariant condition, we can unswitch this // loop. @@ -449,8 +543,8 @@ bool LoopUnswitch::processCurrentLoop() { // unswitch on it if we desire. Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), currentLoop, Changed); - if (LoopCond && UnswitchIfProfitable(LoopCond, - ConstantInt::getTrue(Context))) { + if (LoopCond && + UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(Context), TI)) { ++NumBranches; return true; } @@ -503,8 +597,8 @@ bool LoopUnswitch::processCurrentLoop() { return Changed; } -/// isTrivialLoopExitBlock - Check to see if all paths from BB exit the -/// loop with no side effects (including infinite loops). +/// Check to see if all paths from BB exit the loop with no side effects +/// (including infinite loops). /// /// If true, we return true and set ExitBB to the block we /// exit through. @@ -541,9 +635,9 @@ static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB, return true; } -/// isTrivialLoopExitBlock - Return true if the specified block unconditionally -/// leads to an exit from the specified loop, and has no side-effects in the -/// process. If so, return the block that is exited to, otherwise return null. +/// Return true if the specified block unconditionally leads to an exit from +/// the specified loop, and has no side-effects in the process. If so, return +/// the block that is exited to, otherwise return null. static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) { std::set Visited; Visited.insert(L->getHeader()); // Branches to header make infinite loops. @@ -553,179 +647,129 @@ static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) { return nullptr; } -/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is -/// trivial: that is, that the condition controls whether or not the loop does -/// anything at all. If this is a trivial condition, unswitching produces no -/// code duplications (equivalently, it produces a simpler loop and a new empty -/// loop, which gets deleted). -/// -/// If this is a trivial condition, return true, otherwise return false. When -/// returning true, this sets Cond and Val to the condition that controls the -/// trivial condition: when Cond dynamically equals Val, the loop is known to -/// exit. Finally, this sets LoopExit to the BB that the loop exits to when -/// Cond == Val. -/// -bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val, - BasicBlock **LoopExit) { - BasicBlock *Header = currentLoop->getHeader(); - TerminatorInst *HeaderTerm = Header->getTerminator(); - LLVMContext &Context = Header->getContext(); - - BasicBlock *LoopExitBB = nullptr; - if (BranchInst *BI = dyn_cast(HeaderTerm)) { - // If the header block doesn't end with a conditional branch on Cond, we - // can't handle it. - if (!BI->isConditional() || BI->getCondition() != Cond) - return false; - - // Check to see if a successor of the branch is guaranteed to - // exit through a unique exit block without having any - // side-effects. If so, determine the value of Cond that causes it to do - // this. - if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop, - BI->getSuccessor(0)))) { - if (Val) *Val = ConstantInt::getTrue(Context); - } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop, - BI->getSuccessor(1)))) { - if (Val) *Val = ConstantInt::getFalse(Context); - } - } else if (SwitchInst *SI = dyn_cast(HeaderTerm)) { - // If this isn't a switch on Cond, we can't handle it. - if (SI->getCondition() != Cond) return false; - - // Check to see if a successor of the switch is guaranteed to go to the - // latch block or exit through a one exit block without having any - // side-effects. If so, determine the value of Cond that causes it to do - // this. - // Note that we can't trivially unswitch on the default case or - // on already unswitched cases. - for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); - i != e; ++i) { - BasicBlock *LoopExitCandidate; - if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop, - i.getCaseSuccessor()))) { - // Okay, we found a trivial case, remember the value that is trivial. - ConstantInt *CaseVal = i.getCaseValue(); - - // Check that it was not unswitched before, since already unswitched - // trivial vals are looks trivial too. - if (BranchesInfo.isUnswitched(SI, CaseVal)) - continue; - LoopExitBB = LoopExitCandidate; - if (Val) *Val = CaseVal; - break; - } - } - } - - // If we didn't find a single unique LoopExit block, or if the loop exit block - // contains phi nodes, this isn't trivial. - if (!LoopExitBB || isa(LoopExitBB->begin())) - return false; // Can't handle this. - - if (LoopExit) *LoopExit = LoopExitBB; - - // We already know that nothing uses any scalar values defined inside of this - // loop. As such, we just have to check to see if this loop will execute any - // side-effecting instructions (e.g. stores, calls, volatile loads) in the - // part of the loop that the code *would* execute. We already checked the - // tail, check the header now. - for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I) - if (I->mayHaveSideEffects()) - return false; - return true; -} - -/// UnswitchIfProfitable - We have found that we can unswitch currentLoop when -/// LoopCond == Val to simplify the loop. If we decide that this is profitable, +/// We have found that we can unswitch currentLoop when LoopCond == Val to +/// simplify the loop. If we decide that this is profitable, /// unswitch the loop, reprocess the pieces, then return true. -bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) { - Function *F = loopHeader->getParent(); - Constant *CondVal = nullptr; - BasicBlock *ExitBlock = nullptr; - - if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) { - // If the condition is trivial, always unswitch. There is no code growth - // for this case. - UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock); - return true; - } - +bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val, + TerminatorInst *TI) { // Check to see if it would be profitable to unswitch current loop. - - // Do not do non-trivial unswitch while optimizing for size. - if (OptimizeForSize || - F->getAttributes().hasAttribute(AttributeSet::FunctionIndex, - Attribute::OptimizeForSize)) + if (!BranchesInfo.CostAllowsUnswitching()) { + DEBUG(dbgs() << "NOT unswitching loop %" + << currentLoop->getHeader()->getName() + << " at non-trivial condition '" << *Val + << "' == " << *LoopCond << "\n" + << ". Cost too high.\n"); return false; + } - UnswitchNontrivialCondition(LoopCond, Val, currentLoop); + UnswitchNontrivialCondition(LoopCond, Val, currentLoop, TI); return true; } -/// CloneLoop - Recursively clone the specified loop and all of its children, +/// Recursively clone the specified loop and all of its children, /// mapping the blocks with the specified map. static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM, LoopInfo *LI, LPPassManager *LPM) { - Loop *New = new Loop(); - LPM->insertLoop(New, PL); + Loop &New = LPM->addLoop(PL); // Add all of the blocks in L to the new loop. for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); I != E; ++I) if (LI->getLoopFor(*I) == L) - New->addBasicBlockToLoop(cast(VM[*I]), LI->getBase()); + New.addBasicBlockToLoop(cast(VM[*I]), *LI); // Add all of the subloops to the new loop. for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) - CloneLoop(*I, New, VM, LI, LPM); + CloneLoop(*I, &New, VM, LI, LPM); - return New; + return &New; +} + +static void copyMetadata(Instruction *DstInst, const Instruction *SrcInst, + bool Swapped) { + if (!SrcInst || !SrcInst->hasMetadata()) + return; + + SmallVector, 4> MDs; + SrcInst->getAllMetadata(MDs); + for (auto &MD : MDs) { + switch (MD.first) { + default: + break; + case LLVMContext::MD_prof: + if (Swapped && MD.second->getNumOperands() == 3 && + isa(MD.second->getOperand(0))) { + MDString *MDName = cast(MD.second->getOperand(0)); + if (MDName->getString() == "branch_weights") { + auto *ValT = cast_or_null( + MD.second->getOperand(1))->getValue(); + auto *ValF = cast_or_null( + MD.second->getOperand(2))->getValue(); + assert(ValT && ValF && "Invalid Operands of branch_weights"); + auto NewMD = + MDBuilder(DstInst->getParent()->getContext()) + .createBranchWeights(cast(ValF)->getZExtValue(), + cast(ValT)->getZExtValue()); + MD.second = NewMD; + } + } + // fallthrough. + case LLVMContext::MD_make_implicit: + case LLVMContext::MD_dbg: + DstInst->setMetadata(MD.first, MD.second); + } + } } -/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values -/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the -/// code immediately before InsertPt. +/// Emit a conditional branch on two values if LIC == Val, branch to TrueDst, +/// otherwise branch to FalseDest. Insert the code immediately before InsertPt. void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, BasicBlock *TrueDest, BasicBlock *FalseDest, - Instruction *InsertPt) { + Instruction *InsertPt, + TerminatorInst *TI) { // Insert a conditional branch on LIC to the two preheaders. The original // code is the true version and the new code is the false version. Value *BranchVal = LIC; + bool Swapped = false; if (!isa(Val) || Val->getType() != Type::getInt1Ty(LIC->getContext())) BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val); - else if (Val != ConstantInt::getTrue(Val->getContext())) + else if (Val != ConstantInt::getTrue(Val->getContext())) { // We want to enter the new loop when the condition is true. std::swap(TrueDest, FalseDest); + Swapped = true; + } // Insert the new branch. BranchInst *BI = BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt); + copyMetadata(BI, TI, Swapped); // If either edge is critical, split it. This helps preserve LoopSimplify // form for enclosing loops. - SplitCriticalEdge(BI, 0, this, false, false, true); - SplitCriticalEdge(BI, 1, this, false, false, true); + auto Options = CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA(); + SplitCriticalEdge(BI, 0, Options); + SplitCriticalEdge(BI, 1, Options); } -/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable -/// condition in it (a cond branch from its header block to its latch block, -/// where the path through the loop that doesn't execute its body has no -/// side-effects), unswitch it. This doesn't involve any code duplication, just -/// moving the conditional branch outside of the loop and updating loop info. -void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, - Constant *Val, - BasicBlock *ExitBlock) { +/// Given a loop that has a trivial unswitchable condition in it (a cond branch +/// from its header block to its latch block, where the path through the loop +/// that doesn't execute its body has no side-effects), unswitch it. This +/// doesn't involve any code duplication, just moving the conditional branch +/// outside of the loop and updating loop info. +void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, + BasicBlock *ExitBlock, + TerminatorInst *TI) { DEBUG(dbgs() << "loop-unswitch: Trivial-Unswitch loop %" - << loopHeader->getName() << " [" << L->getBlocks().size() - << " blocks] in Function " << L->getHeader()->getParent()->getName() - << " on cond: " << *Val << " == " << *Cond << "\n"); + << loopHeader->getName() << " [" << L->getBlocks().size() + << " blocks] in Function " + << L->getHeader()->getParent()->getName() << " on cond: " << *Val + << " == " << *Cond << "\n"); // First step, split the preheader, so that we know that there is a safe place // to insert the conditional branch. We will change loopPreheader to have a // conditional branch on Cond. - BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, this); + BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, DT, LI); // Now that we have a place to insert the conditional branch, create a place // to branch to: this is the exit block out of the loop that we should @@ -736,12 +780,12 @@ void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, // without actually branching to it (the exit block should be dominated by the // loop header, not the preheader). assert(!L->contains(ExitBlock) && "Exit block is in the loop?"); - BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this); + BasicBlock *NewExit = SplitBlock(ExitBlock, &ExitBlock->front(), DT, LI); // Okay, now we have a position to branch from and a position to branch to, // insert the new conditional branch. EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH, - loopPreheader->getTerminator()); + loopPreheader->getTerminator(), TI); LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L); loopPreheader->getTerminator()->eraseFromParent(); @@ -755,8 +799,155 @@ void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, ++NumTrivial; } -/// SplitExitEdges - Split all of the edges from inside the loop to their exit -/// blocks. Update the appropriate Phi nodes as we do so. +/// Check if the first non-constant condition starting from the loop header is +/// a trivial unswitch condition: that is, a condition controls whether or not +/// the loop does anything at all. If it is a trivial condition, unswitching +/// produces no code duplications (equivalently, it produces a simpler loop and +/// a new empty loop, which gets deleted). Therefore always unswitch trivial +/// condition. +bool LoopUnswitch::TryTrivialLoopUnswitch(bool &Changed) { + BasicBlock *CurrentBB = currentLoop->getHeader(); + TerminatorInst *CurrentTerm = CurrentBB->getTerminator(); + LLVMContext &Context = CurrentBB->getContext(); + + // If loop header has only one reachable successor (currently via an + // unconditional branch or constant foldable conditional branch, but + // should also consider adding constant foldable switch instruction in + // future), we should keep looking for trivial condition candidates in + // the successor as well. An alternative is to constant fold conditions + // and merge successors into loop header (then we only need to check header's + // terminator). The reason for not doing this in LoopUnswitch pass is that + // it could potentially break LoopPassManager's invariants. Folding dead + // branches could either eliminate the current loop or make other loops + // unreachable. LCSSA form might also not be preserved after deleting + // branches. The following code keeps traversing loop header's successors + // until it finds the trivial condition candidate (condition that is not a + // constant). Since unswitching generates branches with constant conditions, + // this scenario could be very common in practice. + SmallSet Visited; + + while (true) { + // If we exit loop or reach a previous visited block, then + // we can not reach any trivial condition candidates (unfoldable + // branch instructions or switch instructions) and no unswitch + // can happen. Exit and return false. + if (!currentLoop->contains(CurrentBB) || !Visited.insert(CurrentBB).second) + return false; + + // Check if this loop will execute any side-effecting instructions (e.g. + // stores, calls, volatile loads) in the part of the loop that the code + // *would* execute. Check the header first. + for (Instruction &I : *CurrentBB) + if (I.mayHaveSideEffects()) + return false; + + // FIXME: add check for constant foldable switch instructions. + if (BranchInst *BI = dyn_cast(CurrentTerm)) { + if (BI->isUnconditional()) { + CurrentBB = BI->getSuccessor(0); + } else if (BI->getCondition() == ConstantInt::getTrue(Context)) { + CurrentBB = BI->getSuccessor(0); + } else if (BI->getCondition() == ConstantInt::getFalse(Context)) { + CurrentBB = BI->getSuccessor(1); + } else { + // Found a trivial condition candidate: non-foldable conditional branch. + break; + } + } else { + break; + } + + CurrentTerm = CurrentBB->getTerminator(); + } + + // CondVal is the condition that controls the trivial condition. + // LoopExitBB is the BasicBlock that loop exits when meets trivial condition. + Constant *CondVal = nullptr; + BasicBlock *LoopExitBB = nullptr; + + if (BranchInst *BI = dyn_cast(CurrentTerm)) { + // If this isn't branching on an invariant condition, we can't unswitch it. + if (!BI->isConditional()) + return false; + + Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), + currentLoop, Changed); + + // Unswitch only if the trivial condition itself is an LIV (not + // partial LIV which could occur in and/or) + if (!LoopCond || LoopCond != BI->getCondition()) + return false; + + // Check to see if a successor of the branch is guaranteed to + // exit through a unique exit block without having any + // side-effects. If so, determine the value of Cond that causes + // it to do this. + if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop, + BI->getSuccessor(0)))) { + CondVal = ConstantInt::getTrue(Context); + } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop, + BI->getSuccessor(1)))) { + CondVal = ConstantInt::getFalse(Context); + } + + // If we didn't find a single unique LoopExit block, or if the loop exit + // block contains phi nodes, this isn't trivial. + if (!LoopExitBB || isa(LoopExitBB->begin())) + return false; // Can't handle this. + + UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB, + CurrentTerm); + ++NumBranches; + return true; + } else if (SwitchInst *SI = dyn_cast(CurrentTerm)) { + // If this isn't switching on an invariant condition, we can't unswitch it. + Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), + currentLoop, Changed); + + // Unswitch only if the trivial condition itself is an LIV (not + // partial LIV which could occur in and/or) + if (!LoopCond || LoopCond != SI->getCondition()) + return false; + + // Check to see if a successor of the switch is guaranteed to go to the + // latch block or exit through a one exit block without having any + // side-effects. If so, determine the value of Cond that causes it to do + // this. + // Note that we can't trivially unswitch on the default case or + // on already unswitched cases. + for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); + i != e; ++i) { + BasicBlock *LoopExitCandidate; + if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop, + i.getCaseSuccessor()))) { + // Okay, we found a trivial case, remember the value that is trivial. + ConstantInt *CaseVal = i.getCaseValue(); + + // Check that it was not unswitched before, since already unswitched + // trivial vals are looks trivial too. + if (BranchesInfo.isUnswitched(SI, CaseVal)) + continue; + LoopExitBB = LoopExitCandidate; + CondVal = CaseVal; + break; + } + } + + // If we didn't find a single unique LoopExit block, or if the loop exit + // block contains phi nodes, this isn't trivial. + if (!LoopExitBB || isa(LoopExitBB->begin())) + return false; // Can't handle this. + + UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB, + nullptr); + ++NumSwitches; + return true; + } + return false; +} + +/// Split all of the edges from inside the loop to their exit blocks. +/// Update the appropriate Phi nodes as we do so. void LoopUnswitch::SplitExitEdges(Loop *L, const SmallVectorImpl &ExitBlocks){ @@ -767,36 +958,31 @@ void LoopUnswitch::SplitExitEdges(Loop *L, // Although SplitBlockPredecessors doesn't preserve loop-simplify in // general, if we call it on all predecessors of all exits then it does. - if (!ExitBlock->isLandingPad()) { - SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", this); - } else { - SmallVector NewBBs; - SplitLandingPadPredecessors(ExitBlock, Preds, ".us-lcssa", ".us-lcssa", - this, NewBBs); - } + SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", DT, LI, + /*PreserveLCSSA*/ true); } } -/// UnswitchNontrivialCondition - We determined that the loop is profitable -/// to unswitch when LIC equal Val. Split it into loop versions and test the -/// condition outside of either loop. Return the loops created as Out1/Out2. +/// We determined that the loop is profitable to unswitch when LIC equal Val. +/// Split it into loop versions and test the condition outside of either loop. +/// Return the loops created as Out1/Out2. void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, - Loop *L) { + Loop *L, TerminatorInst *TI) { Function *F = loopHeader->getParent(); DEBUG(dbgs() << "loop-unswitch: Unswitching loop %" << loopHeader->getName() << " [" << L->getBlocks().size() << " blocks] in Function " << F->getName() << " when '" << *Val << "' == " << *LIC << "\n"); - if (ScalarEvolution *SE = getAnalysisIfAvailable()) - SE->forgetLoop(L); + if (auto *SEWP = getAnalysisIfAvailable()) + SEWP->getSE().forgetLoop(L); LoopBlocks.clear(); NewBlocks.clear(); // First step, split the preheader and exit blocks, and add these blocks to // the LoopBlocks list. - BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, this); + BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, DT, LI); LoopBlocks.push_back(NewPreheader); // We want the loop to come after the preheader, but before the exit blocks. @@ -831,12 +1017,13 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, // Splice the newly inserted blocks into the function right before the // original preheader. - F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(), - NewBlocks[0], F->end()); + F->getBasicBlockList().splice(NewPreheader->getIterator(), + F->getBasicBlockList(), + NewBlocks[0]->getIterator(), F->end()); // FIXME: We could register any cloned assumptions instead of clearing the // whole function's cache. - AT->forgetCachedAssumptions(F); + AC->clear(); // Now we create the new Loop object for the versioned loop. Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM); @@ -849,14 +1036,14 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, if (ParentLoop) { // Make sure to add the cloned preheader and exit blocks to the parent loop // as well. - ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase()); + ParentLoop->addBasicBlockToLoop(NewBlocks[0], *LI); } for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { BasicBlock *NewExit = cast(VMap[ExitBlocks[i]]); // The new exit block should be in the same loop as the old one. if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i])) - ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase()); + ExitBBLoop->addBasicBlockToLoop(NewExit, *LI); assert(NewExit->getTerminator()->getNumSuccessors() == 1 && "Exit block should have been split to have one successor!"); @@ -874,7 +1061,7 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, if (LandingPadInst *LPad = NewExit->getLandingPadInst()) { PHINode *PN = PHINode::Create(LPad->getType(), 0, "", - ExitSucc->getFirstInsertionPt()); + &*ExitSucc->getFirstInsertionPt()); for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc); I != E; ++I) { @@ -890,7 +1077,8 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i) for (BasicBlock::iterator I = NewBlocks[i]->begin(), E = NewBlocks[i]->end(); I != E; ++I) - RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries); + RemapInstruction(&*I, VMap, + RF_NoModuleLevelChanges | RF_IgnoreMissingEntries); // Rewrite the original preheader to select between versions of the loop. BranchInst *OldBR = cast(loopPreheader->getTerminator()); @@ -898,7 +1086,8 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, "Preheader splitting did not work correctly!"); // Emit the new branch that selects between the two versions of this loop. - EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR); + EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR, + TI); LPM->deleteSimpleAnalysisValue(OldBR, L); OldBR->eraseFromParent(); @@ -923,8 +1112,7 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true); } -/// RemoveFromWorklist - Remove all instances of I from the worklist vector -/// specified. +/// Remove all instances of I from the worklist vector specified. static void RemoveFromWorklist(Instruction *I, std::vector &Worklist) { @@ -932,7 +1120,7 @@ static void RemoveFromWorklist(Instruction *I, Worklist.end()); } -/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the +/// When we find that I really equals V, remove I from the /// program, replacing all uses with V and update the worklist. static void ReplaceUsesOfWith(Instruction *I, Value *V, std::vector &Worklist, @@ -954,9 +1142,9 @@ static void ReplaceUsesOfWith(Instruction *I, Value *V, ++NumSimplify; } -// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has -// the value specified by Val in the specified loop, or we know it does NOT have -// that value. Rewrite any uses of LIC or of properties correlated to it. +/// We know either that the value LIC has the value specified by Val in the +/// specified loop, or we know it does NOT have that value. +/// Rewrite any uses of LIC or of properties correlated to it. void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, Constant *Val, bool IsEqual) { @@ -1042,7 +1230,7 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, // and hooked up so as to preserve the loop structure, because // trying to update it is complicated. So instead we preserve the // loop structure and put the block on a dead code path. - SplitEdge(Switch, SISucc, this); + SplitEdge(Switch, SISucc, DT, LI); // Compute the successors instead of relying on the return value // of SplitEdge, since it may have split the switch successor // after PHI nodes. @@ -1067,23 +1255,22 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, // domtree here -- instead we force it to do a full recomputation // after the pass is complete -- but we do need to inform it of // new blocks. - if (DT) - DT->addNewBlock(Abort, NewSISucc); + DT->addNewBlock(Abort, NewSISucc); } SimplifyCode(Worklist, L); } -/// SimplifyCode - Okay, now that we have simplified some instructions in the -/// loop, walk over it and constant prop, dce, and fold control flow where -/// possible. Note that this is effectively a very simple loop-structure-aware -/// optimizer. During processing of this loop, L could very well be deleted, so -/// it must not be used. +/// Now that we have simplified some instructions in the loop, walk over it and +/// constant prop, dce, and fold control flow where possible. Note that this is +/// effectively a very simple loop-structure-aware optimizer. During processing +/// of this loop, L could very well be deleted, so it must not be used. /// /// FIXME: When the loop optimizer is more mature, separate this out to a new /// pass. /// void LoopUnswitch::SimplifyCode(std::vector &Worklist, Loop *L) { + const DataLayout &DL = L->getHeader()->getModule()->getDataLayout(); while (!Worklist.empty()) { Instruction *I = Worklist.back(); Worklist.pop_back(); @@ -1106,7 +1293,7 @@ void LoopUnswitch::SimplifyCode(std::vector &Worklist, Loop *L) { // See if instruction simplification can hack this up. This is common for // things like "select false, X, Y" after unswitching made the condition be // 'false'. TODO: update the domtree properly so we can pass it here. - if (Value *V = SimplifyInstruction(I)) + if (Value *V = SimplifyInstruction(I, DL)) if (LI->replacementPreservesLCSSAForm(I, V)) { ReplaceUsesOfWith(I, V, Worklist, L, LPM); continue; @@ -1135,8 +1322,8 @@ void LoopUnswitch::SimplifyCode(std::vector &Worklist, Loop *L) { Succ->replaceAllUsesWith(Pred); // Move all of the successor contents from Succ to Pred. - Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(), - Succ->end()); + Pred->getInstList().splice(BI->getIterator(), Succ->getInstList(), + Succ->begin(), Succ->end()); LPM->deleteSimpleAnalysisValue(BI, L); BI->eraseFromParent(); RemoveFromWorklist(BI, Worklist);