X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FJumpThreading.cpp;h=1a64b2cbad7c195c75883652043203188d665ba8;hb=1bfcd1f675919f7f6b669e171f65fe84db9d79a0;hp=21b6cebca56d8e330ed866a4c2032747ca98be2f;hpb=6776064d190701c5bae4d5403939eed2e480d1cd;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp index 21b6cebca56..83ac915e606 100644 --- a/lib/Transforms/Scalar/JumpThreading.cpp +++ b/lib/Transforms/Scalar/JumpThreading.cpp @@ -11,35 +11,56 @@ // //===----------------------------------------------------------------------===// -#define DEBUG_TYPE "jump-threading" #include "llvm/Transforms/Scalar.h" -#include "llvm/IntrinsicInst.h" -#include "llvm/LLVMContext.h" -#include "llvm/Pass.h" -#include "llvm/Analysis/ConstantFolding.h" -#include "llvm/Transforms/Utils/BasicBlockUtils.h" -#include "llvm/Transforms/Utils/Local.h" -#include "llvm/Target/TargetData.h" #include "llvm/ADT/DenseMap.h" -#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/DenseSet.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/CFG.h" +#include "llvm/Analysis/ConstantFolding.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/LazyValueInfo.h" +#include "llvm/Analysis/Loads.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/ValueHandle.h" +#include "llvm/Pass.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" -#include "llvm/Support/ValueHandle.h" #include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Transforms/Utils/SSAUpdater.h" using namespace llvm; +#define DEBUG_TYPE "jump-threading" + STATISTIC(NumThreads, "Number of jumps threaded"); STATISTIC(NumFolds, "Number of terminators folded"); +STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi"); static cl::opt -Threshold("jump-threading-threshold", +BBDuplicateThreshold("jump-threading-threshold", cl::desc("Max block size to duplicate for jump threading"), cl::init(6), cl::Hidden); namespace { + // These are at global scope so static functions can use them too. + typedef SmallVectorImpl > PredValueInfo; + typedef SmallVector, 8> PredValueInfoTy; + + // This is used to keep track of what kind of constant we're currently hoping + // to find. + enum ConstantPreference { + WantInteger, + WantBlockAddress + }; + /// This pass performs 'jump threading', which looks at blocks that have /// multiple predecessors and multiple successors. If one or more of the /// predecessors of the block can be proven to always jump to one of the @@ -57,82 +78,219 @@ namespace { /// revectored to the false side of the second if. /// class JumpThreading : public FunctionPass { - TargetData *TD; + TargetLibraryInfo *TLI; + LazyValueInfo *LVI; #ifdef NDEBUG SmallPtrSet LoopHeaders; #else SmallSet, 16> LoopHeaders; #endif + DenseSet > RecursionSet; + + unsigned BBDupThreshold; + + // RAII helper for updating the recursion stack. + struct RecursionSetRemover { + DenseSet > &TheSet; + std::pair ThePair; + + RecursionSetRemover(DenseSet > &S, + std::pair P) + : TheSet(S), ThePair(P) { } + + ~RecursionSetRemover() { + TheSet.erase(ThePair); + } + }; public: static char ID; // Pass identification - JumpThreading() : FunctionPass(&ID) {} + JumpThreading(int T = -1) : FunctionPass(ID) { + BBDupThreshold = (T == -1) ? BBDuplicateThreshold : unsigned(T); + initializeJumpThreadingPass(*PassRegistry::getPassRegistry()); + } - virtual void getAnalysisUsage(AnalysisUsage &AU) const { + bool runOnFunction(Function &F) override; + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.addRequired(); + AU.addPreserved(); + AU.addRequired(); } - bool runOnFunction(Function &F); void FindLoopHeaders(Function &F); - bool ProcessBlock(BasicBlock *BB); - bool ThreadEdge(BasicBlock *BB, BasicBlock *PredBB, BasicBlock *SuccBB, - unsigned JumpThreadCost); - BasicBlock *FactorCommonPHIPreds(PHINode *PN, Value *Val); - bool ProcessBranchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB); - bool ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB); - - bool ProcessJumpOnPHI(PHINode *PN); - bool ProcessBranchOnLogical(Value *V, BasicBlock *BB, bool isAnd); - bool ProcessBranchOnCompare(CmpInst *Cmp, BasicBlock *BB); - + bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl &PredBBs, + BasicBlock *SuccBB); + bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, + const SmallVectorImpl &PredBBs); + + bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB, + PredValueInfo &Result, + ConstantPreference Preference, + Instruction *CxtI = nullptr); + bool ProcessThreadableEdges(Value *Cond, BasicBlock *BB, + ConstantPreference Preference, + Instruction *CxtI = nullptr); + + bool ProcessBranchOnPHI(PHINode *PN); + bool ProcessBranchOnXOR(BinaryOperator *BO); + bool SimplifyPartiallyRedundantLoad(LoadInst *LI); + bool TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB); }; } char JumpThreading::ID = 0; -static RegisterPass -X("jump-threading", "Jump Threading"); +INITIALIZE_PASS_BEGIN(JumpThreading, "jump-threading", + "Jump Threading", false, false) +INITIALIZE_PASS_DEPENDENCY(LazyValueInfo) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) +INITIALIZE_PASS_END(JumpThreading, "jump-threading", + "Jump Threading", false, false) // Public interface to the Jump Threading pass -FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); } +FunctionPass *llvm::createJumpThreadingPass(int Threshold) { return new JumpThreading(Threshold); } /// runOnFunction - Top level algorithm. /// bool JumpThreading::runOnFunction(Function &F) { - DEBUG(errs() << "Jump threading on function '" << F.getName() << "'\n"); - TD = getAnalysisIfAvailable(); - + if (skipOptnoneFunction(F)) + return false; + + DEBUG(dbgs() << "Jump threading on function '" << F.getName() << "'\n"); + TLI = &getAnalysis().getTLI(); + LVI = &getAnalysis(); + + // Remove unreachable blocks from function as they may result in infinite + // loop. We do threading if we found something profitable. Jump threading a + // branch can create other opportunities. If these opportunities form a cycle + // i.e. if any jump treading is undoing previous threading in the path, then + // we will loop forever. We take care of this issue by not jump threading for + // back edges. This works for normal cases but not for unreachable blocks as + // they may have cycle with no back edge. + removeUnreachableBlocks(F); + FindLoopHeaders(F); - - bool AnotherIteration = true, EverChanged = false; - while (AnotherIteration) { - AnotherIteration = false; - bool Changed = false; + + bool Changed, EverChanged = false; + do { + Changed = false; for (Function::iterator I = F.begin(), E = F.end(); I != E;) { BasicBlock *BB = I; + // Thread all of the branches we can over this block. while (ProcessBlock(BB)) Changed = true; - + ++I; - + // If the block is trivially dead, zap it. This eliminates the successor // edges which simplifies the CFG. - if (pred_begin(BB) == pred_end(BB) && + if (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()) { - DEBUG(errs() << " JT: Deleting dead block '" << BB->getName() - << "' with terminator: " << *BB->getTerminator()); + DEBUG(dbgs() << " JT: Deleting dead block '" << BB->getName() + << "' with terminator: " << *BB->getTerminator() << '\n'); LoopHeaders.erase(BB); + LVI->eraseBlock(BB); DeleteDeadBlock(BB); Changed = true; + continue; + } + + BranchInst *BI = dyn_cast(BB->getTerminator()); + + // Can't thread an unconditional jump, but if the block is "almost + // empty", we can replace uses of it with uses of the successor and make + // this dead. + if (BI && BI->isUnconditional() && + BB != &BB->getParent()->getEntryBlock() && + // If the terminator is the only non-phi instruction, try to nuke it. + BB->getFirstNonPHIOrDbg()->isTerminator()) { + // Since TryToSimplifyUncondBranchFromEmptyBlock may delete the + // block, we have to make sure it isn't in the LoopHeaders set. We + // reinsert afterward if needed. + bool ErasedFromLoopHeaders = LoopHeaders.erase(BB); + BasicBlock *Succ = BI->getSuccessor(0); + + // FIXME: It is always conservatively correct to drop the info + // for a block even if it doesn't get erased. This isn't totally + // awesome, but it allows us to use AssertingVH to prevent nasty + // dangling pointer issues within LazyValueInfo. + LVI->eraseBlock(BB); + if (TryToSimplifyUncondBranchFromEmptyBlock(BB)) { + Changed = true; + // If we deleted BB and BB was the header of a loop, then the + // successor is now the header of the loop. + BB = Succ; + } + + if (ErasedFromLoopHeaders) + LoopHeaders.insert(BB); } } - AnotherIteration = Changed; EverChanged |= Changed; - } - + } while (Changed); + LoopHeaders.clear(); return EverChanged; } +/// getJumpThreadDuplicationCost - Return the cost of duplicating this block to +/// thread across it. Stop scanning the block when passing the threshold. +static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB, + unsigned Threshold) { + /// Ignore PHI nodes, these will be flattened when duplication happens. + BasicBlock::const_iterator I = BB->getFirstNonPHI(); + + // FIXME: THREADING will delete values that are just used to compute the + // branch, so they shouldn't count against the duplication cost. + + // Sum up the cost of each instruction until we get to the terminator. Don't + // include the terminator because the copy won't include it. + unsigned Size = 0; + for (; !isa(I); ++I) { + + // Stop scanning the block if we've reached the threshold. + if (Size > Threshold) + return Size; + + // Debugger intrinsics don't incur code size. + if (isa(I)) continue; + + // If this is a pointer->pointer bitcast, it is free. + if (isa(I) && I->getType()->isPointerTy()) + continue; + + // All other instructions count for at least one unit. + ++Size; + + // Calls are more expensive. If they are non-intrinsic calls, we model them + // as having cost of 4. If they are a non-vector intrinsic, we model them + // as having cost of 2 total, and if they are a vector intrinsic, we model + // them as having cost 1. + if (const CallInst *CI = dyn_cast(I)) { + if (CI->cannotDuplicate()) + // Blocks with NoDuplicate are modelled as having infinite cost, so they + // are never duplicated. + return ~0U; + else if (!isa(CI)) + Size += 3; + else if (!CI->getType()->isVectorTy()) + Size += 1; + } + } + + // Threading through a switch statement is particularly profitable. If this + // block ends in a switch, decrease its cost to make it more likely to happen. + if (isa(I)) + Size = Size > 6 ? Size-6 : 0; + + // The same holds for indirect branches, but slightly more so. + if (isa(I)) + Size = Size > 8 ? Size-8 : 0; + + return Size; +} + /// FindLoopHeaders - We do not want jump threading to turn proper loop /// structures into irreducible loops. Doing this breaks up the loop nesting /// hierarchy and pessimizes later transformations. To prevent this from @@ -151,226 +309,511 @@ bool JumpThreading::runOnFunction(Function &F) { void JumpThreading::FindLoopHeaders(Function &F) { SmallVector, 32> Edges; FindFunctionBackedges(F, Edges); - + for (unsigned i = 0, e = Edges.size(); i != e; ++i) LoopHeaders.insert(const_cast(Edges[i].second)); } +/// getKnownConstant - Helper method to determine if we can thread over a +/// terminator with the given value as its condition, and if so what value to +/// use for that. What kind of value this is depends on whether we want an +/// integer or a block address, but an undef is always accepted. +/// Returns null if Val is null or not an appropriate constant. +static Constant *getKnownConstant(Value *Val, ConstantPreference Preference) { + if (!Val) + return nullptr; + + // Undef is "known" enough. + if (UndefValue *U = dyn_cast(Val)) + return U; + + if (Preference == WantBlockAddress) + return dyn_cast(Val->stripPointerCasts()); -/// FactorCommonPHIPreds - If there are multiple preds with the same incoming -/// value for the PHI, factor them together so we get one block to thread for -/// the whole group. -/// This is important for things like "phi i1 [true, true, false, true, x]" -/// where we only need to clone the block for the true blocks once. + return dyn_cast(Val); +} + +/// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see +/// if we can infer that the value is a known ConstantInt/BlockAddress or undef +/// in any of our predecessors. If so, return the known list of value and pred +/// BB in the result vector. /// -BasicBlock *JumpThreading::FactorCommonPHIPreds(PHINode *PN, Value *Val) { - SmallVector CommonPreds; - for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) - if (PN->getIncomingValue(i) == Val) - CommonPreds.push_back(PN->getIncomingBlock(i)); - - if (CommonPreds.size() == 1) - return CommonPreds[0]; - - DEBUG(errs() << " Factoring out " << CommonPreds.size() - << " common predecessors.\n"); - return SplitBlockPredecessors(PN->getParent(), - &CommonPreds[0], CommonPreds.size(), - ".thr_comm", this); +/// This returns true if there were any known values. +/// +bool JumpThreading:: +ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB, PredValueInfo &Result, + ConstantPreference Preference, + Instruction *CxtI) { + // This method walks up use-def chains recursively. Because of this, we could + // get into an infinite loop going around loops in the use-def chain. To + // prevent this, keep track of what (value, block) pairs we've already visited + // and terminate the search if we loop back to them + if (!RecursionSet.insert(std::make_pair(V, BB)).second) + return false; + + // An RAII help to remove this pair from the recursion set once the recursion + // stack pops back out again. + RecursionSetRemover remover(RecursionSet, std::make_pair(V, BB)); + + // If V is a constant, then it is known in all predecessors. + if (Constant *KC = getKnownConstant(V, Preference)) { + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) + Result.push_back(std::make_pair(KC, *PI)); + + return true; + } + + // If V is a non-instruction value, or an instruction in a different block, + // then it can't be derived from a PHI. + Instruction *I = dyn_cast(V); + if (!I || I->getParent() != BB) { + + // Okay, if this is a live-in value, see if it has a known value at the end + // of any of our predecessors. + // + // FIXME: This should be an edge property, not a block end property. + /// TODO: Per PR2563, we could infer value range information about a + /// predecessor based on its terminator. + // + // FIXME: change this to use the more-rich 'getPredicateOnEdge' method if + // "I" is a non-local compare-with-a-constant instruction. This would be + // able to handle value inequalities better, for example if the compare is + // "X < 4" and "X < 3" is known true but "X < 4" itself is not available. + // Perhaps getConstantOnEdge should be smart enough to do this? + + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { + BasicBlock *P = *PI; + // If the value is known by LazyValueInfo to be a constant in a + // predecessor, use that information to try to thread this block. + Constant *PredCst = LVI->getConstantOnEdge(V, P, BB, CxtI); + if (Constant *KC = getKnownConstant(PredCst, Preference)) + Result.push_back(std::make_pair(KC, P)); + } + + return !Result.empty(); + } + + /// If I is a PHI node, then we know the incoming values for any constants. + if (PHINode *PN = dyn_cast(I)) { + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + Value *InVal = PN->getIncomingValue(i); + if (Constant *KC = getKnownConstant(InVal, Preference)) { + Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i))); + } else { + Constant *CI = LVI->getConstantOnEdge(InVal, + PN->getIncomingBlock(i), + BB, CxtI); + if (Constant *KC = getKnownConstant(CI, Preference)) + Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i))); + } + } + + return !Result.empty(); + } + + PredValueInfoTy LHSVals, RHSVals; + + // Handle some boolean conditions. + if (I->getType()->getPrimitiveSizeInBits() == 1) { + assert(Preference == WantInteger && "One-bit non-integer type?"); + // X | true -> true + // X & false -> false + if (I->getOpcode() == Instruction::Or || + I->getOpcode() == Instruction::And) { + ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals, + WantInteger, CxtI); + ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals, + WantInteger, CxtI); + + if (LHSVals.empty() && RHSVals.empty()) + return false; + + ConstantInt *InterestingVal; + if (I->getOpcode() == Instruction::Or) + InterestingVal = ConstantInt::getTrue(I->getContext()); + else + InterestingVal = ConstantInt::getFalse(I->getContext()); + + SmallPtrSet LHSKnownBBs; + + // Scan for the sentinel. If we find an undef, force it to the + // interesting value: x|undef -> true and x&undef -> false. + for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) + if (LHSVals[i].first == InterestingVal || + isa(LHSVals[i].first)) { + Result.push_back(LHSVals[i]); + Result.back().first = InterestingVal; + LHSKnownBBs.insert(LHSVals[i].second); + } + for (unsigned i = 0, e = RHSVals.size(); i != e; ++i) + if (RHSVals[i].first == InterestingVal || + isa(RHSVals[i].first)) { + // If we already inferred a value for this block on the LHS, don't + // re-add it. + if (!LHSKnownBBs.count(RHSVals[i].second)) { + Result.push_back(RHSVals[i]); + Result.back().first = InterestingVal; + } + } + + return !Result.empty(); + } + + // Handle the NOT form of XOR. + if (I->getOpcode() == Instruction::Xor && + isa(I->getOperand(1)) && + cast(I->getOperand(1))->isOne()) { + ComputeValueKnownInPredecessors(I->getOperand(0), BB, Result, + WantInteger, CxtI); + if (Result.empty()) + return false; + + // Invert the known values. + for (unsigned i = 0, e = Result.size(); i != e; ++i) + Result[i].first = ConstantExpr::getNot(Result[i].first); + + return true; + } + + // Try to simplify some other binary operator values. + } else if (BinaryOperator *BO = dyn_cast(I)) { + assert(Preference != WantBlockAddress + && "A binary operator creating a block address?"); + if (ConstantInt *CI = dyn_cast(BO->getOperand(1))) { + PredValueInfoTy LHSVals; + ComputeValueKnownInPredecessors(BO->getOperand(0), BB, LHSVals, + WantInteger, CxtI); + + // Try to use constant folding to simplify the binary operator. + for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) { + Constant *V = LHSVals[i].first; + Constant *Folded = ConstantExpr::get(BO->getOpcode(), V, CI); + + if (Constant *KC = getKnownConstant(Folded, WantInteger)) + Result.push_back(std::make_pair(KC, LHSVals[i].second)); + } + } + + return !Result.empty(); + } + + // Handle compare with phi operand, where the PHI is defined in this block. + if (CmpInst *Cmp = dyn_cast(I)) { + assert(Preference == WantInteger && "Compares only produce integers"); + PHINode *PN = dyn_cast(Cmp->getOperand(0)); + if (PN && PN->getParent() == BB) { + const DataLayout &DL = PN->getModule()->getDataLayout(); + // We can do this simplification if any comparisons fold to true or false. + // See if any do. + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + BasicBlock *PredBB = PN->getIncomingBlock(i); + Value *LHS = PN->getIncomingValue(i); + Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB); + + Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, DL); + if (!Res) { + if (!isa(RHS)) + continue; + + LazyValueInfo::Tristate + ResT = LVI->getPredicateOnEdge(Cmp->getPredicate(), LHS, + cast(RHS), PredBB, BB, + CxtI ? CxtI : Cmp); + if (ResT == LazyValueInfo::Unknown) + continue; + Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT); + } + + if (Constant *KC = getKnownConstant(Res, WantInteger)) + Result.push_back(std::make_pair(KC, PredBB)); + } + + return !Result.empty(); + } + + // If comparing a live-in value against a constant, see if we know the + // live-in value on any predecessors. + if (isa(Cmp->getOperand(1)) && Cmp->getType()->isIntegerTy()) { + if (!isa(Cmp->getOperand(0)) || + cast(Cmp->getOperand(0))->getParent() != BB) { + Constant *RHSCst = cast(Cmp->getOperand(1)); + + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB);PI != E; ++PI){ + BasicBlock *P = *PI; + // If the value is known by LazyValueInfo to be a constant in a + // predecessor, use that information to try to thread this block. + LazyValueInfo::Tristate Res = + LVI->getPredicateOnEdge(Cmp->getPredicate(), Cmp->getOperand(0), + RHSCst, P, BB, CxtI ? CxtI : Cmp); + if (Res == LazyValueInfo::Unknown) + continue; + + Constant *ResC = ConstantInt::get(Cmp->getType(), Res); + Result.push_back(std::make_pair(ResC, P)); + } + + return !Result.empty(); + } + + // Try to find a constant value for the LHS of a comparison, + // and evaluate it statically if we can. + if (Constant *CmpConst = dyn_cast(Cmp->getOperand(1))) { + PredValueInfoTy LHSVals; + ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals, + WantInteger, CxtI); + + for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) { + Constant *V = LHSVals[i].first; + Constant *Folded = ConstantExpr::getCompare(Cmp->getPredicate(), + V, CmpConst); + if (Constant *KC = getKnownConstant(Folded, WantInteger)) + Result.push_back(std::make_pair(KC, LHSVals[i].second)); + } + + return !Result.empty(); + } + } + } + + if (SelectInst *SI = dyn_cast(I)) { + // Handle select instructions where at least one operand is a known constant + // and we can figure out the condition value for any predecessor block. + Constant *TrueVal = getKnownConstant(SI->getTrueValue(), Preference); + Constant *FalseVal = getKnownConstant(SI->getFalseValue(), Preference); + PredValueInfoTy Conds; + if ((TrueVal || FalseVal) && + ComputeValueKnownInPredecessors(SI->getCondition(), BB, Conds, + WantInteger, CxtI)) { + for (unsigned i = 0, e = Conds.size(); i != e; ++i) { + Constant *Cond = Conds[i].first; + + // Figure out what value to use for the condition. + bool KnownCond; + if (ConstantInt *CI = dyn_cast(Cond)) { + // A known boolean. + KnownCond = CI->isOne(); + } else { + assert(isa(Cond) && "Unexpected condition value"); + // Either operand will do, so be sure to pick the one that's a known + // constant. + // FIXME: Do this more cleverly if both values are known constants? + KnownCond = (TrueVal != nullptr); + } + + // See if the select has a known constant value for this predecessor. + if (Constant *Val = KnownCond ? TrueVal : FalseVal) + Result.push_back(std::make_pair(Val, Conds[i].second)); + } + + return !Result.empty(); + } + } + + // If all else fails, see if LVI can figure out a constant value for us. + Constant *CI = LVI->getConstant(V, BB, CxtI); + if (Constant *KC = getKnownConstant(CI, Preference)) { + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) + Result.push_back(std::make_pair(KC, *PI)); + } + + return !Result.empty(); } - -/// getJumpThreadDuplicationCost - Return the cost of duplicating this block to -/// thread across it. -static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) { - /// Ignore PHI nodes, these will be flattened when duplication happens. - BasicBlock::const_iterator I = BB->getFirstNonPHI(); - // Sum up the cost of each instruction until we get to the terminator. Don't - // include the terminator because the copy won't include it. - unsigned Size = 0; - for (; !isa(I); ++I) { - // Debugger intrinsics don't incur code size. - if (isa(I)) continue; - - // If this is a pointer->pointer bitcast, it is free. - if (isa(I) && isa(I->getType())) - continue; - - // All other instructions count for at least one unit. - ++Size; - - // Calls are more expensive. If they are non-intrinsic calls, we model them - // as having cost of 4. If they are a non-vector intrinsic, we model them - // as having cost of 2 total, and if they are a vector intrinsic, we model - // them as having cost 1. - if (const CallInst *CI = dyn_cast(I)) { - if (!isa(CI)) - Size += 3; - else if (!isa(CI->getType())) - Size += 1; + +/// GetBestDestForBranchOnUndef - If we determine that the specified block ends +/// in an undefined jump, decide which block is best to revector to. +/// +/// Since we can pick an arbitrary destination, we pick the successor with the +/// fewest predecessors. This should reduce the in-degree of the others. +/// +static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) { + TerminatorInst *BBTerm = BB->getTerminator(); + unsigned MinSucc = 0; + BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc); + // Compute the successor with the minimum number of predecessors. + unsigned MinNumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB)); + for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) { + TestBB = BBTerm->getSuccessor(i); + unsigned NumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB)); + if (NumPreds < MinNumPreds) { + MinSucc = i; + MinNumPreds = NumPreds; } } - - // Threading through a switch statement is particularly profitable. If this - // block ends in a switch, decrease its cost to make it more likely to happen. - if (isa(I)) - Size = Size > 6 ? Size-6 : 0; - - return Size; + + return MinSucc; +} + +static bool hasAddressTakenAndUsed(BasicBlock *BB) { + if (!BB->hasAddressTaken()) return false; + + // If the block has its address taken, it may be a tree of dead constants + // hanging off of it. These shouldn't keep the block alive. + BlockAddress *BA = BlockAddress::get(BB); + BA->removeDeadConstantUsers(); + return !BA->use_empty(); } /// ProcessBlock - If there are any predecessors whose control can be threaded /// through to a successor, transform them now. bool JumpThreading::ProcessBlock(BasicBlock *BB) { + // If the block is trivially dead, just return and let the caller nuke it. + // This simplifies other transformations. + if (pred_empty(BB) && + BB != &BB->getParent()->getEntryBlock()) + return false; + // If this block has a single predecessor, and if that pred has a single // successor, merge the blocks. This encourages recursive jump threading // because now the condition in this block can be threaded through // predecessors of our predecessor block. - if (BasicBlock *SinglePred = BB->getSinglePredecessor()) + if (BasicBlock *SinglePred = BB->getSinglePredecessor()) { if (SinglePred->getTerminator()->getNumSuccessors() == 1 && - SinglePred != BB) { + SinglePred != BB && !hasAddressTakenAndUsed(BB)) { // If SinglePred was a loop header, BB becomes one. if (LoopHeaders.erase(SinglePred)) LoopHeaders.insert(BB); - - // Remember if SinglePred was the entry block of the function. If so, we - // will need to move BB back to the entry position. - bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock(); + + LVI->eraseBlock(SinglePred); MergeBasicBlockIntoOnlyPred(BB); - - if (isEntry && BB != &BB->getParent()->getEntryBlock()) - BB->moveBefore(&BB->getParent()->getEntryBlock()); + return true; } - - // See if this block ends with a branch or switch. If so, see if the - // condition is a phi node. If so, and if an entry of the phi node is a - // constant, we can thread the block. + } + + // What kind of constant we're looking for. + ConstantPreference Preference = WantInteger; + + // Look to see if the terminator is a conditional branch, switch or indirect + // branch, if not we can't thread it. Value *Condition; - if (BranchInst *BI = dyn_cast(BB->getTerminator())) { + Instruction *Terminator = BB->getTerminator(); + if (BranchInst *BI = dyn_cast(Terminator)) { // Can't thread an unconditional jump. if (BI->isUnconditional()) return false; Condition = BI->getCondition(); - } else if (SwitchInst *SI = dyn_cast(BB->getTerminator())) + } else if (SwitchInst *SI = dyn_cast(Terminator)) { Condition = SI->getCondition(); - else + } else if (IndirectBrInst *IB = dyn_cast(Terminator)) { + // Can't thread indirect branch with no successors. + if (IB->getNumSuccessors() == 0) return false; + Condition = IB->getAddress()->stripPointerCasts(); + Preference = WantBlockAddress; + } else { return false; // Must be an invoke. - - // If the terminator of this block is branching on a constant, simplify the - // terminator to an unconditional branch. This can occur due to threading in - // other blocks. - if (isa(Condition)) { - DEBUG(errs() << " In block '" << BB->getName() - << "' folding terminator: " << *BB->getTerminator()); - ++NumFolds; - ConstantFoldTerminator(BB); - return true; } - + + // Run constant folding to see if we can reduce the condition to a simple + // constant. + if (Instruction *I = dyn_cast(Condition)) { + Value *SimpleVal = + ConstantFoldInstruction(I, BB->getModule()->getDataLayout(), TLI); + if (SimpleVal) { + I->replaceAllUsesWith(SimpleVal); + I->eraseFromParent(); + Condition = SimpleVal; + } + } + // If the terminator is branching on an undef, we can pick any of the - // successors to branch to. Since this is arbitrary, we pick the successor - // with the fewest predecessors. This should reduce the in-degree of the - // others. + // successors to branch to. Let GetBestDestForJumpOnUndef decide. if (isa(Condition)) { - TerminatorInst *BBTerm = BB->getTerminator(); - unsigned MinSucc = 0; - BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc); - // Compute the successor with the minimum number of predecessors. - unsigned MinNumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB)); - for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) { - TestBB = BBTerm->getSuccessor(i); - unsigned NumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB)); - if (NumPreds < MinNumPreds) - MinSucc = i; - } - + unsigned BestSucc = GetBestDestForJumpOnUndef(BB); + // Fold the branch/switch. + TerminatorInst *BBTerm = BB->getTerminator(); for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) { - if (i == MinSucc) continue; - BBTerm->getSuccessor(i)->removePredecessor(BB); + if (i == BestSucc) continue; + BBTerm->getSuccessor(i)->removePredecessor(BB, true); } - - DEBUG(errs() << " In block '" << BB->getName() - << "' folding undef terminator: " << *BBTerm); - BranchInst::Create(BBTerm->getSuccessor(MinSucc), BBTerm); + + DEBUG(dbgs() << " In block '" << BB->getName() + << "' folding undef terminator: " << *BBTerm << '\n'); + BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm); BBTerm->eraseFromParent(); return true; } - - Instruction *CondInst = dyn_cast(Condition); - // If the condition is an instruction defined in another block, see if a - // predecessor has the same condition: - // br COND, BBX, BBY - // BBX: - // br COND, BBZ, BBW - if (!Condition->hasOneUse() && // Multiple uses. - (CondInst == 0 || CondInst->getParent() != BB)) { // Non-local definition. - pred_iterator PI = pred_begin(BB), E = pred_end(BB); - if (isa(BB->getTerminator())) { - for (; PI != E; ++PI) - if (BranchInst *PBI = dyn_cast((*PI)->getTerminator())) - if (PBI->isConditional() && PBI->getCondition() == Condition && - ProcessBranchOnDuplicateCond(*PI, BB)) - return true; - } else { - assert(isa(BB->getTerminator()) && "Unknown jump terminator"); - for (; PI != E; ++PI) - if (SwitchInst *PSI = dyn_cast((*PI)->getTerminator())) - if (PSI->getCondition() == Condition && - ProcessSwitchOnDuplicateCond(*PI, BB)) - return true; - } + // If the terminator of this block is branching on a constant, simplify the + // terminator to an unconditional branch. This can occur due to threading in + // other blocks. + if (getKnownConstant(Condition, Preference)) { + DEBUG(dbgs() << " In block '" << BB->getName() + << "' folding terminator: " << *BB->getTerminator() << '\n'); + ++NumFolds; + ConstantFoldTerminator(BB, true); + return true; } + Instruction *CondInst = dyn_cast(Condition); + // All the rest of our checks depend on the condition being an instruction. - if (CondInst == 0) + if (!CondInst) { + // FIXME: Unify this with code below. + if (ProcessThreadableEdges(Condition, BB, Preference, Terminator)) + return true; return false; - - // See if this is a phi node in the current block. - if (PHINode *PN = dyn_cast(CondInst)) - if (PN->getParent() == BB) - return ProcessJumpOnPHI(PN); - - // If this is a conditional branch whose condition is and/or of a phi, try to - // simplify it. - if ((CondInst->getOpcode() == Instruction::And || - CondInst->getOpcode() == Instruction::Or) && - isa(BB->getTerminator()) && - ProcessBranchOnLogical(CondInst, BB, - CondInst->getOpcode() == Instruction::And)) - return true; - + } + + if (CmpInst *CondCmp = dyn_cast(CondInst)) { - if (isa(CondCmp->getOperand(0))) { - // If we have "br (phi != 42)" and the phi node has any constant values - // as operands, we can thread through this block. - // - // If we have "br (cmp phi, x)" and the phi node contains x such that the - // comparison uniquely identifies the branch target, we can thread - // through this block. - - if (ProcessBranchOnCompare(CondCmp, BB)) - return true; - } - - // If we have a comparison, loop over the predecessors to see if there is - // a condition with the same value. - pred_iterator PI = pred_begin(BB), E = pred_end(BB); - for (; PI != E; ++PI) - if (BranchInst *PBI = dyn_cast((*PI)->getTerminator())) - if (PBI->isConditional() && *PI != BB) { - if (CmpInst *CI = dyn_cast(PBI->getCondition())) { - if (CI->getOperand(0) == CondCmp->getOperand(0) && - CI->getOperand(1) == CondCmp->getOperand(1) && - CI->getPredicate() == CondCmp->getPredicate()) { - // TODO: Could handle things like (x != 4) --> (x == 17) - if (ProcessBranchOnDuplicateCond(*PI, BB)) - return true; - } - } + // For a comparison where the LHS is outside this block, it's possible + // that we've branched on it before. Used LVI to see if we can simplify + // the branch based on that. + BranchInst *CondBr = dyn_cast(BB->getTerminator()); + Constant *CondConst = dyn_cast(CondCmp->getOperand(1)); + pred_iterator PI = pred_begin(BB), PE = pred_end(BB); + if (CondBr && CondConst && CondBr->isConditional() && PI != PE && + (!isa(CondCmp->getOperand(0)) || + cast(CondCmp->getOperand(0))->getParent() != BB)) { + // For predecessor edge, determine if the comparison is true or false + // on that edge. If they're all true or all false, we can simplify the + // branch. + // FIXME: We could handle mixed true/false by duplicating code. + LazyValueInfo::Tristate Baseline = + LVI->getPredicateOnEdge(CondCmp->getPredicate(), CondCmp->getOperand(0), + CondConst, *PI, BB, CondCmp); + if (Baseline != LazyValueInfo::Unknown) { + // Check that all remaining incoming values match the first one. + while (++PI != PE) { + LazyValueInfo::Tristate Ret = + LVI->getPredicateOnEdge(CondCmp->getPredicate(), + CondCmp->getOperand(0), CondConst, *PI, BB, + CondCmp); + if (Ret != Baseline) break; + } + + // If we terminated early, then one of the values didn't match. + if (PI == PE) { + unsigned ToRemove = Baseline == LazyValueInfo::True ? 1 : 0; + unsigned ToKeep = Baseline == LazyValueInfo::True ? 0 : 1; + CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true); + BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr); + CondBr->eraseFromParent(); + return true; } + } + + } else if (CondBr && CondConst && CondBr->isConditional()) { + // There might be an invariant in the same block with the conditional + // that can determine the predicate. + + LazyValueInfo::Tristate Ret = + LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0), + CondConst, CondCmp); + if (Ret != LazyValueInfo::Unknown) { + unsigned ToRemove = Ret == LazyValueInfo::True ? 1 : 0; + unsigned ToKeep = Ret == LazyValueInfo::True ? 0 : 1; + CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true); + BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr); + CondBr->eraseFromParent(); + return true; + } + } + + if (CondBr && CondConst && TryToUnfoldSelect(CondCmp, BB)) + return true; } // Check for some cases that are worth simplifying. Right now we want to look @@ -378,193 +821,88 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) { // we see one, check to see if it's partially redundant. If so, insert a PHI // which can then be used to thread the values. // - // This is particularly important because reg2mem inserts loads and stores all - // over the place, and this blocks jump threading if we don't zap them. Value *SimplifyValue = CondInst; if (CmpInst *CondCmp = dyn_cast(SimplifyValue)) if (isa(CondCmp->getOperand(1))) SimplifyValue = CondCmp->getOperand(0); - + + // TODO: There are other places where load PRE would be profitable, such as + // more complex comparisons. if (LoadInst *LI = dyn_cast(SimplifyValue)) if (SimplifyPartiallyRedundantLoad(LI)) return true; - - // TODO: If we have: "br (X > 0)" and we have a predecessor where we know - // "(X == 4)" thread through this block. - - return false; -} -/// ProcessBranchOnDuplicateCond - We found a block and a predecessor of that -/// block that jump on exactly the same condition. This means that we almost -/// always know the direction of the edge in the DESTBB: -/// PREDBB: -/// br COND, DESTBB, BBY -/// DESTBB: -/// br COND, BBZ, BBW -/// -/// If DESTBB has multiple predecessors, we can't just constant fold the branch -/// in DESTBB, we have to thread over it. -bool JumpThreading::ProcessBranchOnDuplicateCond(BasicBlock *PredBB, - BasicBlock *BB) { - BranchInst *PredBI = cast(PredBB->getTerminator()); - - // If both successors of PredBB go to DESTBB, we don't know anything. We can - // fold the branch to an unconditional one, which allows other recursive - // simplifications. - bool BranchDir; - if (PredBI->getSuccessor(1) != BB) - BranchDir = true; - else if (PredBI->getSuccessor(0) != BB) - BranchDir = false; - else { - DEBUG(errs() << " In block '" << PredBB->getName() - << "' folding terminator: " << *PredBB->getTerminator()); - ++NumFolds; - ConstantFoldTerminator(PredBB); - return true; - } - - BranchInst *DestBI = cast(BB->getTerminator()); - // If the dest block has one predecessor, just fix the branch condition to a - // constant and fold it. - if (BB->getSinglePredecessor()) { - DEBUG(errs() << " In block '" << BB->getName() - << "' folding condition to '" << BranchDir << "': " - << *BB->getTerminator()); - ++NumFolds; - DestBI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()), - BranchDir)); - ConstantFoldTerminator(BB); + // Handle a variety of cases where we are branching on something derived from + // a PHI node in the current block. If we can prove that any predecessors + // compute a predictable value based on a PHI node, thread those predecessors. + // + if (ProcessThreadableEdges(CondInst, BB, Preference, Terminator)) return true; - } - - // Otherwise we need to thread from PredBB to DestBB's successor which - // involves code duplication. Check to see if it is worth it. - unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB); - if (JumpThreadCost > Threshold) { - DEBUG(errs() << " Not threading BB '" << BB->getName() - << "' - Cost is too high: " << JumpThreadCost << "\n"); - return false; - } - - // Next, figure out which successor we are threading to. - BasicBlock *SuccBB = DestBI->getSuccessor(!BranchDir); - - // Ok, try to thread it! - return ThreadEdge(BB, PredBB, SuccBB, JumpThreadCost); -} -/// ProcessSwitchOnDuplicateCond - We found a block and a predecessor of that -/// block that switch on exactly the same condition. This means that we almost -/// always know the direction of the edge in the DESTBB: -/// PREDBB: -/// switch COND [... DESTBB, BBY ... ] -/// DESTBB: -/// switch COND [... BBZ, BBW ] -/// -/// Optimizing switches like this is very important, because simplifycfg builds -/// switches out of repeated 'if' conditions. -bool JumpThreading::ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, - BasicBlock *DestBB) { - // Can't thread edge to self. - if (PredBB == DestBB) - return false; - - - SwitchInst *PredSI = cast(PredBB->getTerminator()); - SwitchInst *DestSI = cast(DestBB->getTerminator()); - - // There are a variety of optimizations that we can potentially do on these - // blocks: we order them from most to least preferable. - - // If DESTBB *just* contains the switch, then we can forward edges from PREDBB - // directly to their destination. This does not introduce *any* code size - // growth. Skip debug info first. - BasicBlock::iterator BBI = DestBB->begin(); - while (isa(BBI)) - BBI++; - - // FIXME: Thread if it just contains a PHI. - if (isa(BBI)) { - bool MadeChange = false; - // Ignore the default edge for now. - for (unsigned i = 1, e = DestSI->getNumSuccessors(); i != e; ++i) { - ConstantInt *DestVal = DestSI->getCaseValue(i); - BasicBlock *DestSucc = DestSI->getSuccessor(i); - - // Okay, DestSI has a case for 'DestVal' that goes to 'DestSucc'. See if - // PredSI has an explicit case for it. If so, forward. If it is covered - // by the default case, we can't update PredSI. - unsigned PredCase = PredSI->findCaseValue(DestVal); - if (PredCase == 0) continue; - - // If PredSI doesn't go to DestBB on this value, then it won't reach the - // case on this condition. - if (PredSI->getSuccessor(PredCase) != DestBB && - DestSI->getSuccessor(i) != DestBB) - continue; + // If this is an otherwise-unfoldable branch on a phi node in the current + // block, see if we can simplify. + if (PHINode *PN = dyn_cast(CondInst)) + if (PN->getParent() == BB && isa(BB->getTerminator())) + return ProcessBranchOnPHI(PN); - // Otherwise, we're safe to make the change. Make sure that the edge from - // DestSI to DestSucc is not critical and has no PHI nodes. - DEBUG(errs() << "FORWARDING EDGE " << *DestVal << " FROM: " << *PredSI); - DEBUG(errs() << "THROUGH: " << *DestSI); - // If the destination has PHI nodes, just split the edge for updating - // simplicity. - if (isa(DestSucc->begin()) && !DestSucc->getSinglePredecessor()){ - SplitCriticalEdge(DestSI, i, this); - DestSucc = DestSI->getSuccessor(i); - } - FoldSingleEntryPHINodes(DestSucc); - PredSI->setSuccessor(PredCase, DestSucc); - MadeChange = true; - } - - if (MadeChange) - return true; - } - + // If this is an otherwise-unfoldable branch on a XOR, see if we can simplify. + if (CondInst->getOpcode() == Instruction::Xor && + CondInst->getParent() == BB && isa(BB->getTerminator())) + return ProcessBranchOnXOR(cast(CondInst)); + + + // TODO: If we have: "br (X > 0)" and we have a predecessor where we know + // "(X == 4)", thread through this block. + return false; } - /// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant /// load instruction, eliminate it by replacing it with a PHI node. This is an /// important optimization that encourages jump threading, and needs to be run /// interlaced with other jump threading tasks. bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) { - // Don't hack volatile loads. - if (LI->isVolatile()) return false; - + // Don't hack volatile/atomic loads. + if (!LI->isSimple()) return false; + // If the load is defined in a block with exactly one predecessor, it can't be // partially redundant. BasicBlock *LoadBB = LI->getParent(); if (LoadBB->getSinglePredecessor()) return false; - + + // If the load is defined in a landing pad, it can't be partially redundant, + // because the edges between the invoke and the landing pad cannot have other + // instructions between them. + if (LoadBB->isLandingPad()) + return false; + Value *LoadedPtr = LI->getOperand(0); // If the loaded operand is defined in the LoadBB, it can't be available. - // FIXME: Could do PHI translation, that would be fun :) + // TODO: Could do simple PHI translation, that would be fun :) if (Instruction *PtrOp = dyn_cast(LoadedPtr)) if (PtrOp->getParent() == LoadBB) return false; - + // Scan a few instructions up from the load, to see if it is obviously live at // the entry to its block. BasicBlock::iterator BBIt = LI; - if (Value *AvailableVal = FindAvailableLoadedValue(LoadedPtr, LoadBB, - BBIt, 6)) { + if (Value *AvailableVal = + FindAvailableLoadedValue(LoadedPtr, LoadBB, BBIt, 6)) { // If the value if the load is locally available within the block, just use // it. This frequently occurs for reg2mem'd allocas. //cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n"; - + // If the returned value is the load itself, replace with an undef. This can // only happen in dead loops. if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType()); + if (AvailableVal->getType() != LI->getType()) + AvailableVal = + CastInst::CreateBitOrPointerCast(AvailableVal, LI->getType(), "", LI); LI->replaceAllUsesWith(AvailableVal); LI->eraseFromParent(); return true; @@ -575,13 +913,17 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) { // might clobber its value. if (BBIt != LoadBB->begin()) return false; - - + + // If all of the loads and stores that feed the value have the same AA tags, + // then we can propagate them onto any newly inserted loads. + AAMDNodes AATags; + LI->getAAMetadata(AATags); + SmallPtrSet PredsScanned; typedef SmallVector, 8> AvailablePredsTy; AvailablePredsTy AvailablePreds; - BasicBlock *OneUnavailablePred = 0; - + BasicBlock *OneUnavailablePred = nullptr; + // If we got here, the loaded value is transparent through to the start of the // block. Check to see if it is available in any of the predecessor blocks. for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB); @@ -589,33 +931,38 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) { BasicBlock *PredBB = *PI; // If we already scanned this predecessor, skip it. - if (!PredsScanned.insert(PredBB)) + if (!PredsScanned.insert(PredBB).second) continue; // Scan the predecessor to see if the value is available in the pred. BBIt = PredBB->end(); - Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6); + AAMDNodes ThisAATags; + Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6, + nullptr, &ThisAATags); if (!PredAvailable) { OneUnavailablePred = PredBB; continue; } - + + // If AA tags disagree or are not present, forget about them. + if (AATags != ThisAATags) AATags = AAMDNodes(); + // If so, this load is partially redundant. Remember this info so that we // can create a PHI node. AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable)); } - + // If the loaded value isn't available in any predecessor, it isn't partially // redundant. if (AvailablePreds.empty()) return false; - + // Okay, the loaded value is available in at least one (and maybe all!) // predecessors. If the value is unavailable in more than one unique // predecessor, we want to insert a merge block for those common predecessors. // This ensures that we only have to insert one reload, thus not increasing // code size. - BasicBlock *UnavailablePred = 0; - + BasicBlock *UnavailablePred = nullptr; + // If there is exactly one predecessor where the value is unavailable, the // already computed 'OneUnavailablePred' block is it. If it ends in an // unconditional branch, we know that it isn't a critical edge. @@ -633,304 +980,468 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) { // Add all the unavailable predecessors to the PredsToSplit list. for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB); - PI != PE; ++PI) - if (!AvailablePredSet.count(*PI)) - PredsToSplit.push_back(*PI); - + PI != PE; ++PI) { + BasicBlock *P = *PI; + // If the predecessor is an indirect goto, we can't split the edge. + if (isa(P->getTerminator())) + return false; + + if (!AvailablePredSet.count(P)) + PredsToSplit.push_back(P); + } + // Split them out to their own block. UnavailablePred = - SplitBlockPredecessors(LoadBB, &PredsToSplit[0], PredsToSplit.size(), - "thread-split", this); + SplitBlockPredecessors(LoadBB, PredsToSplit, "thread-pre-split"); } - + // If the value isn't available in all predecessors, then there will be // exactly one where it isn't available. Insert a load on that edge and add // it to the AvailablePreds list. if (UnavailablePred) { assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 && "Can't handle critical edge here!"); - Value *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr", + LoadInst *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr", false, + LI->getAlignment(), UnavailablePred->getTerminator()); + NewVal->setDebugLoc(LI->getDebugLoc()); + if (AATags) + NewVal->setAAMetadata(AATags); + AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal)); } - + // Now we know that each predecessor of this block has a value in // AvailablePreds, sort them for efficient access as we're walking the preds. array_pod_sort(AvailablePreds.begin(), AvailablePreds.end()); - + // Create a PHI node at the start of the block for the PRE'd load value. - PHINode *PN = PHINode::Create(LI->getType(), "", LoadBB->begin()); + pred_iterator PB = pred_begin(LoadBB), PE = pred_end(LoadBB); + PHINode *PN = PHINode::Create(LI->getType(), std::distance(PB, PE), "", + LoadBB->begin()); PN->takeName(LI); - + PN->setDebugLoc(LI->getDebugLoc()); + // Insert new entries into the PHI for each predecessor. A single block may // have multiple entries here. - for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); PI != E; - ++PI) { - AvailablePredsTy::iterator I = + for (pred_iterator PI = PB; PI != PE; ++PI) { + BasicBlock *P = *PI; + AvailablePredsTy::iterator I = std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(), - std::make_pair(*PI, (Value*)0)); - - assert(I != AvailablePreds.end() && I->first == *PI && + std::make_pair(P, (Value*)nullptr)); + + assert(I != AvailablePreds.end() && I->first == P && "Didn't find entry for predecessor!"); - - PN->addIncoming(I->second, I->first); + + // If we have an available predecessor but it requires casting, insert the + // cast in the predecessor and use the cast. Note that we have to update the + // AvailablePreds vector as we go so that all of the PHI entries for this + // predecessor use the same bitcast. + Value *&PredV = I->second; + if (PredV->getType() != LI->getType()) + PredV = CastInst::CreateBitOrPointerCast(PredV, LI->getType(), "", + P->getTerminator()); + + PN->addIncoming(PredV, I->first); } - + //cerr << "PRE: " << *LI << *PN << "\n"; - + LI->replaceAllUsesWith(PN); LI->eraseFromParent(); - + return true; } +/// FindMostPopularDest - The specified list contains multiple possible +/// threadable destinations. Pick the one that occurs the most frequently in +/// the list. +static BasicBlock * +FindMostPopularDest(BasicBlock *BB, + const SmallVectorImpl > &PredToDestList) { + assert(!PredToDestList.empty()); + + // Determine popularity. If there are multiple possible destinations, we + // explicitly choose to ignore 'undef' destinations. We prefer to thread + // blocks with known and real destinations to threading undef. We'll handle + // them later if interesting. + DenseMap DestPopularity; + for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i) + if (PredToDestList[i].second) + DestPopularity[PredToDestList[i].second]++; + + // Find the most popular dest. + DenseMap::iterator DPI = DestPopularity.begin(); + BasicBlock *MostPopularDest = DPI->first; + unsigned Popularity = DPI->second; + SmallVector SamePopularity; + + for (++DPI; DPI != DestPopularity.end(); ++DPI) { + // If the popularity of this entry isn't higher than the popularity we've + // seen so far, ignore it. + if (DPI->second < Popularity) + ; // ignore. + else if (DPI->second == Popularity) { + // If it is the same as what we've seen so far, keep track of it. + SamePopularity.push_back(DPI->first); + } else { + // If it is more popular, remember it. + SamePopularity.clear(); + MostPopularDest = DPI->first; + Popularity = DPI->second; + } + } + + // Okay, now we know the most popular destination. If there is more than one + // destination, we need to determine one. This is arbitrary, but we need + // to make a deterministic decision. Pick the first one that appears in the + // successor list. + if (!SamePopularity.empty()) { + SamePopularity.push_back(MostPopularDest); + TerminatorInst *TI = BB->getTerminator(); + for (unsigned i = 0; ; ++i) { + assert(i != TI->getNumSuccessors() && "Didn't find any successor!"); + + if (std::find(SamePopularity.begin(), SamePopularity.end(), + TI->getSuccessor(i)) == SamePopularity.end()) + continue; -/// ProcessJumpOnPHI - We have a conditional branch of switch on a PHI node in -/// the current block. See if there are any simplifications we can do based on -/// inputs to the phi node. -/// -bool JumpThreading::ProcessJumpOnPHI(PHINode *PN) { - // See if the phi node has any constant values. If so, we can determine where - // the corresponding predecessor will branch. - ConstantInt *PredCst = 0; - for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) - if ((PredCst = dyn_cast(PN->getIncomingValue(i)))) + MostPopularDest = TI->getSuccessor(i); break; - - // If no incoming value has a constant, we don't know the destination of any - // predecessors. - if (PredCst == 0) + } + } + + // Okay, we have finally picked the most popular destination. + return MostPopularDest; +} + +bool JumpThreading::ProcessThreadableEdges(Value *Cond, BasicBlock *BB, + ConstantPreference Preference, + Instruction *CxtI) { + // If threading this would thread across a loop header, don't even try to + // thread the edge. + if (LoopHeaders.count(BB)) return false; - - // See if the cost of duplicating this block is low enough. - BasicBlock *BB = PN->getParent(); - unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB); - if (JumpThreadCost > Threshold) { - DEBUG(errs() << " Not threading BB '" << BB->getName() - << "' - Cost is too high: " << JumpThreadCost << "\n"); + + PredValueInfoTy PredValues; + if (!ComputeValueKnownInPredecessors(Cond, BB, PredValues, Preference, CxtI)) return false; + + assert(!PredValues.empty() && + "ComputeValueKnownInPredecessors returned true with no values"); + + DEBUG(dbgs() << "IN BB: " << *BB; + for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { + dbgs() << " BB '" << BB->getName() << "': FOUND condition = " + << *PredValues[i].first + << " for pred '" << PredValues[i].second->getName() << "'.\n"; + }); + + // Decide what we want to thread through. Convert our list of known values to + // a list of known destinations for each pred. This also discards duplicate + // predecessors and keeps track of the undefined inputs (which are represented + // as a null dest in the PredToDestList). + SmallPtrSet SeenPreds; + SmallVector, 16> PredToDestList; + + BasicBlock *OnlyDest = nullptr; + BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL; + + for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { + BasicBlock *Pred = PredValues[i].second; + if (!SeenPreds.insert(Pred).second) + continue; // Duplicate predecessor entry. + + // If the predecessor ends with an indirect goto, we can't change its + // destination. + if (isa(Pred->getTerminator())) + continue; + + Constant *Val = PredValues[i].first; + + BasicBlock *DestBB; + if (isa(Val)) + DestBB = nullptr; + else if (BranchInst *BI = dyn_cast(BB->getTerminator())) + DestBB = BI->getSuccessor(cast(Val)->isZero()); + else if (SwitchInst *SI = dyn_cast(BB->getTerminator())) { + DestBB = SI->findCaseValue(cast(Val)).getCaseSuccessor(); + } else { + assert(isa(BB->getTerminator()) + && "Unexpected terminator"); + DestBB = cast(Val)->getBasicBlock(); + } + + // If we have exactly one destination, remember it for efficiency below. + if (PredToDestList.empty()) + OnlyDest = DestBB; + else if (OnlyDest != DestBB) + OnlyDest = MultipleDestSentinel; + + PredToDestList.push_back(std::make_pair(Pred, DestBB)); } - - // If so, we can actually do this threading. Merge any common predecessors - // that will act the same. - BasicBlock *PredBB = FactorCommonPHIPreds(PN, PredCst); - - // Next, figure out which successor we are threading to. - BasicBlock *SuccBB; - if (BranchInst *BI = dyn_cast(BB->getTerminator())) - SuccBB = BI->getSuccessor(PredCst == - ConstantInt::getFalse(PredBB->getContext())); - else { - SwitchInst *SI = cast(BB->getTerminator()); - SuccBB = SI->getSuccessor(SI->findCaseValue(PredCst)); - } - + + // If all edges were unthreadable, we fail. + if (PredToDestList.empty()) + return false; + + // Determine which is the most common successor. If we have many inputs and + // this block is a switch, we want to start by threading the batch that goes + // to the most popular destination first. If we only know about one + // threadable destination (the common case) we can avoid this. + BasicBlock *MostPopularDest = OnlyDest; + + if (MostPopularDest == MultipleDestSentinel) + MostPopularDest = FindMostPopularDest(BB, PredToDestList); + + // Now that we know what the most popular destination is, factor all + // predecessors that will jump to it into a single predecessor. + SmallVector PredsToFactor; + for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i) + if (PredToDestList[i].second == MostPopularDest) { + BasicBlock *Pred = PredToDestList[i].first; + + // This predecessor may be a switch or something else that has multiple + // edges to the block. Factor each of these edges by listing them + // according to # occurrences in PredsToFactor. + TerminatorInst *PredTI = Pred->getTerminator(); + for (unsigned i = 0, e = PredTI->getNumSuccessors(); i != e; ++i) + if (PredTI->getSuccessor(i) == BB) + PredsToFactor.push_back(Pred); + } + + // If the threadable edges are branching on an undefined value, we get to pick + // the destination that these predecessors should get to. + if (!MostPopularDest) + MostPopularDest = BB->getTerminator()-> + getSuccessor(GetBestDestForJumpOnUndef(BB)); + // Ok, try to thread it! - return ThreadEdge(BB, PredBB, SuccBB, JumpThreadCost); + return ThreadEdge(BB, PredsToFactor, MostPopularDest); } -/// ProcessJumpOnLogicalPHI - PN's basic block contains a conditional branch -/// whose condition is an AND/OR where one side is PN. If PN has constant -/// operands that permit us to evaluate the condition for some operand, thread -/// through the block. For example with: -/// br (and X, phi(Y, Z, false)) -/// the predecessor corresponding to the 'false' will always jump to the false -/// destination of the branch. +/// ProcessBranchOnPHI - We have an otherwise unthreadable conditional branch on +/// a PHI node in the current block. See if there are any simplifications we +/// can do based on inputs to the phi node. /// -bool JumpThreading::ProcessBranchOnLogical(Value *V, BasicBlock *BB, - bool isAnd) { - // If this is a binary operator tree of the same AND/OR opcode, check the - // LHS/RHS. - if (BinaryOperator *BO = dyn_cast(V)) - if ((isAnd && BO->getOpcode() == Instruction::And) || - (!isAnd && BO->getOpcode() == Instruction::Or)) { - if (ProcessBranchOnLogical(BO->getOperand(0), BB, isAnd)) - return true; - if (ProcessBranchOnLogical(BO->getOperand(1), BB, isAnd)) - return true; - } - - // If this isn't a PHI node, we can't handle it. - PHINode *PN = dyn_cast(V); - if (!PN || PN->getParent() != BB) return false; - - // We can only do the simplification for phi nodes of 'false' with AND or - // 'true' with OR. See if we have any entries in the phi for this. - unsigned PredNo = ~0U; - ConstantInt *PredCst = ConstantInt::get(Type::getInt1Ty(BB->getContext()), - !isAnd); +bool JumpThreading::ProcessBranchOnPHI(PHINode *PN) { + BasicBlock *BB = PN->getParent(); + + // TODO: We could make use of this to do it once for blocks with common PHI + // values. + SmallVector PredBBs; + PredBBs.resize(1); + + // If any of the predecessor blocks end in an unconditional branch, we can + // *duplicate* the conditional branch into that block in order to further + // encourage jump threading and to eliminate cases where we have branch on a + // phi of an icmp (branch on icmp is much better). for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { - if (PN->getIncomingValue(i) == PredCst) { - PredNo = i; - break; - } + BasicBlock *PredBB = PN->getIncomingBlock(i); + if (BranchInst *PredBr = dyn_cast(PredBB->getTerminator())) + if (PredBr->isUnconditional()) { + PredBBs[0] = PredBB; + // Try to duplicate BB into PredBB. + if (DuplicateCondBranchOnPHIIntoPred(BB, PredBBs)) + return true; + } } - - // If no match, bail out. - if (PredNo == ~0U) + + return false; +} + +/// ProcessBranchOnXOR - We have an otherwise unthreadable conditional branch on +/// a xor instruction in the current block. See if there are any +/// simplifications we can do based on inputs to the xor. +/// +bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) { + BasicBlock *BB = BO->getParent(); + + // If either the LHS or RHS of the xor is a constant, don't do this + // optimization. + if (isa(BO->getOperand(0)) || + isa(BO->getOperand(1))) return false; - - // See if the cost of duplicating this block is low enough. - unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB); - if (JumpThreadCost > Threshold) { - DEBUG(errs() << " Not threading BB '" << BB->getName() - << "' - Cost is too high: " << JumpThreadCost << "\n"); + + // If the first instruction in BB isn't a phi, we won't be able to infer + // anything special about any particular predecessor. + if (!isa(BB->front())) return false; + + // If we have a xor as the branch input to this block, and we know that the + // LHS or RHS of the xor in any predecessor is true/false, then we can clone + // the condition into the predecessor and fix that value to true, saving some + // logical ops on that path and encouraging other paths to simplify. + // + // This copies something like this: + // + // BB: + // %X = phi i1 [1], [%X'] + // %Y = icmp eq i32 %A, %B + // %Z = xor i1 %X, %Y + // br i1 %Z, ... + // + // Into: + // BB': + // %Y = icmp ne i32 %A, %B + // br i1 %Z, ... + + PredValueInfoTy XorOpValues; + bool isLHS = true; + if (!ComputeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues, + WantInteger, BO)) { + assert(XorOpValues.empty()); + if (!ComputeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues, + WantInteger, BO)) + return false; + isLHS = false; } - // If so, we can actually do this threading. Merge any common predecessors - // that will act the same. - BasicBlock *PredBB = FactorCommonPHIPreds(PN, PredCst); - - // Next, figure out which successor we are threading to. If this was an AND, - // the constant must be FALSE, and we must be targeting the 'false' block. - // If this is an OR, the constant must be TRUE, and we must be targeting the - // 'true' block. - BasicBlock *SuccBB = BB->getTerminator()->getSuccessor(isAnd); - - // Ok, try to thread it! - return ThreadEdge(BB, PredBB, SuccBB, JumpThreadCost); -} + assert(!XorOpValues.empty() && + "ComputeValueKnownInPredecessors returned true with no values"); -/// GetResultOfComparison - Given an icmp/fcmp predicate and the left and right -/// hand sides of the compare instruction, try to determine the result. If the -/// result can not be determined, a null pointer is returned. -static Constant *GetResultOfComparison(CmpInst::Predicate pred, - Value *LHS, Value *RHS, - LLVMContext &Context) { - if (Constant *CLHS = dyn_cast(LHS)) - if (Constant *CRHS = dyn_cast(RHS)) - return ConstantExpr::getCompare(pred, CLHS, CRHS); - - if (LHS == RHS) - if (isa(LHS->getType()) || isa(LHS->getType())) - return ICmpInst::isTrueWhenEqual(pred) ? - ConstantInt::getTrue(Context) : ConstantInt::getFalse(Context); - - return 0; -} + // Scan the information to see which is most popular: true or false. The + // predecessors can be of the set true, false, or undef. + unsigned NumTrue = 0, NumFalse = 0; + for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) { + if (isa(XorOpValues[i].first)) + // Ignore undefs for the count. + continue; + if (cast(XorOpValues[i].first)->isZero()) + ++NumFalse; + else + ++NumTrue; + } -/// ProcessBranchOnCompare - We found a branch on a comparison between a phi -/// node and a value. If we can identify when the comparison is true between -/// the phi inputs and the value, we can fold the compare for that edge and -/// thread through it. -bool JumpThreading::ProcessBranchOnCompare(CmpInst *Cmp, BasicBlock *BB) { - PHINode *PN = cast(Cmp->getOperand(0)); - Value *RHS = Cmp->getOperand(1); - - // If the phi isn't in the current block, an incoming edge to this block - // doesn't control the destination. - if (PN->getParent() != BB) - return false; - - // We can do this simplification if any comparisons fold to true or false. - // See if any do. - Value *PredVal = 0; - bool TrueDirection = false; - for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { - PredVal = PN->getIncomingValue(i); - - Constant *Res = GetResultOfComparison(Cmp->getPredicate(), PredVal, - RHS, Cmp->getContext()); - if (!Res) { - PredVal = 0; + // Determine which value to split on, true, false, or undef if neither. + ConstantInt *SplitVal = nullptr; + if (NumTrue > NumFalse) + SplitVal = ConstantInt::getTrue(BB->getContext()); + else if (NumTrue != 0 || NumFalse != 0) + SplitVal = ConstantInt::getFalse(BB->getContext()); + + // Collect all of the blocks that this can be folded into so that we can + // factor this once and clone it once. + SmallVector BlocksToFoldInto; + for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) { + if (XorOpValues[i].first != SplitVal && + !isa(XorOpValues[i].first)) continue; - } - - // If this folded to a constant expr, we can't do anything. - if (ConstantInt *ResC = dyn_cast(Res)) { - TrueDirection = ResC->getZExtValue(); - break; - } - // If this folded to undef, just go the false way. - if (isa(Res)) { - TrueDirection = false; - break; - } - - // Otherwise, we can't fold this input. - PredVal = 0; + + BlocksToFoldInto.push_back(XorOpValues[i].second); } - - // If no match, bail out. - if (PredVal == 0) - return false; - - // See if the cost of duplicating this block is low enough. - unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB); - if (JumpThreadCost > Threshold) { - DEBUG(errs() << " Not threading BB '" << BB->getName() - << "' - Cost is too high: " << JumpThreadCost << "\n"); - return false; + + // If we inferred a value for all of the predecessors, then duplication won't + // help us. However, we can just replace the LHS or RHS with the constant. + if (BlocksToFoldInto.size() == + cast(BB->front()).getNumIncomingValues()) { + if (!SplitVal) { + // If all preds provide undef, just nuke the xor, because it is undef too. + BO->replaceAllUsesWith(UndefValue::get(BO->getType())); + BO->eraseFromParent(); + } else if (SplitVal->isZero()) { + // If all preds provide 0, replace the xor with the other input. + BO->replaceAllUsesWith(BO->getOperand(isLHS)); + BO->eraseFromParent(); + } else { + // If all preds provide 1, set the computed value to 1. + BO->setOperand(!isLHS, SplitVal); + } + + return true; } - - // If so, we can actually do this threading. Merge any common predecessors - // that will act the same. - BasicBlock *PredBB = FactorCommonPHIPreds(PN, PredVal); - - // Next, get our successor. - BasicBlock *SuccBB = BB->getTerminator()->getSuccessor(!TrueDirection); - - // Ok, try to thread it! - return ThreadEdge(BB, PredBB, SuccBB, JumpThreadCost); + + // Try to duplicate BB into PredBB. + return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto); } -/// ThreadEdge - We have decided that it is safe and profitable to thread an -/// edge from PredBB to SuccBB across BB. Transform the IR to reflect this -/// change. -bool JumpThreading::ThreadEdge(BasicBlock *BB, BasicBlock *PredBB, - BasicBlock *SuccBB, unsigned JumpThreadCost) { +/// AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new +/// predecessor to the PHIBB block. If it has PHI nodes, add entries for +/// NewPred using the entries from OldPred (suitably mapped). +static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB, + BasicBlock *OldPred, + BasicBlock *NewPred, + DenseMap &ValueMap) { + for (BasicBlock::iterator PNI = PHIBB->begin(); + PHINode *PN = dyn_cast(PNI); ++PNI) { + // Ok, we have a PHI node. Figure out what the incoming value was for the + // DestBlock. + Value *IV = PN->getIncomingValueForBlock(OldPred); + + // Remap the value if necessary. + if (Instruction *Inst = dyn_cast(IV)) { + DenseMap::iterator I = ValueMap.find(Inst); + if (I != ValueMap.end()) + IV = I->second; + } + + PN->addIncoming(IV, NewPred); + } +} +/// ThreadEdge - We have decided that it is safe and profitable to factor the +/// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB +/// across BB. Transform the IR to reflect this change. +bool JumpThreading::ThreadEdge(BasicBlock *BB, + const SmallVectorImpl &PredBBs, + BasicBlock *SuccBB) { // If threading to the same block as we come from, we would infinite loop. if (SuccBB == BB) { - DEBUG(errs() << " Not threading across BB '" << BB->getName() + DEBUG(dbgs() << " Not threading across BB '" << BB->getName() << "' - would thread to self!\n"); return false; } - + // If threading this would thread across a loop header, don't thread the edge. // See the comments above FindLoopHeaders for justifications and caveats. if (LoopHeaders.count(BB)) { - DEBUG(errs() << " Not threading from '" << PredBB->getName() - << "' across loop header BB '" << BB->getName() + DEBUG(dbgs() << " Not threading across loop header BB '" << BB->getName() << "' to dest BB '" << SuccBB->getName() << "' - it might create an irreducible loop!\n"); return false; } + unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB, BBDupThreshold); + if (JumpThreadCost > BBDupThreshold) { + DEBUG(dbgs() << " Not threading BB '" << BB->getName() + << "' - Cost is too high: " << JumpThreadCost << "\n"); + return false; + } + + // And finally, do it! Start by factoring the predecessors is needed. + BasicBlock *PredBB; + if (PredBBs.size() == 1) + PredBB = PredBBs[0]; + else { + DEBUG(dbgs() << " Factoring out " << PredBBs.size() + << " common predecessors.\n"); + PredBB = SplitBlockPredecessors(BB, PredBBs, ".thr_comm"); + } + // And finally, do it! - DEBUG(errs() << " Threading edge from '" << PredBB->getName() << "' to '" + DEBUG(dbgs() << " Threading edge from '" << PredBB->getName() << "' to '" << SuccBB->getName() << "' with cost: " << JumpThreadCost << ", across block:\n " << *BB << "\n"); - - // Jump Threading can not update SSA properties correctly if the values - // defined in the duplicated block are used outside of the block itself. For - // this reason, we spill all values that are used outside of BB to the stack. - for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) { - if (!I->isUsedOutsideOfBlock(BB)) - continue; - - // We found a use of I outside of BB. Create a new stack slot to - // break this inter-block usage pattern. - DemoteRegToStack(*I); - } - + + LVI->threadEdge(PredBB, BB, SuccBB); + // We are going to have to map operands from the original BB block to the new // copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to // account for entry from PredBB. DenseMap ValueMapping; - - BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), - BB->getName()+".thread", + + BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), + BB->getName()+".thread", BB->getParent(), BB); NewBB->moveAfter(PredBB); - + BasicBlock::iterator BI = BB->begin(); for (; PHINode *PN = dyn_cast(BI); ++BI) ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB); - + // Clone the non-phi instructions of BB into NewBB, keeping track of the // mapping and using it to remap operands in the cloned instructions. for (; !isa(BI); ++BI) { @@ -938,7 +1449,7 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB, BasicBlock *PredBB, New->setName(BI->getName()); NewBB->getInstList().push_back(New); ValueMapping[BI] = New; - + // Remap operands to patch up intra-block references. for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i) if (Instruction *Inst = dyn_cast(New->getOperand(i))) { @@ -947,54 +1458,292 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB, BasicBlock *PredBB, New->setOperand(i, I->second); } } - + // We didn't copy the terminator from BB over to NewBB, because there is now // an unconditional jump to SuccBB. Insert the unconditional jump. - BranchInst::Create(SuccBB, NewBB); - + BranchInst *NewBI =BranchInst::Create(SuccBB, NewBB); + NewBI->setDebugLoc(BB->getTerminator()->getDebugLoc()); + // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the // PHI nodes for NewBB now. - for (BasicBlock::iterator PNI = SuccBB->begin(); isa(PNI); ++PNI) { - PHINode *PN = cast(PNI); - // Ok, we have a PHI node. Figure out what the incoming value was for the - // DestBlock. - Value *IV = PN->getIncomingValueForBlock(BB); - - // Remap the value if necessary. - if (Instruction *Inst = dyn_cast(IV)) { - DenseMap::iterator I = ValueMapping.find(Inst); - if (I != ValueMapping.end()) - IV = I->second; + AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping); + + // If there were values defined in BB that are used outside the block, then we + // now have to update all uses of the value to use either the original value, + // the cloned value, or some PHI derived value. This can require arbitrary + // PHI insertion, of which we are prepared to do, clean these up now. + SSAUpdater SSAUpdate; + SmallVector UsesToRename; + for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) { + // Scan all uses of this instruction to see if it is used outside of its + // block, and if so, record them in UsesToRename. + for (Use &U : I->uses()) { + Instruction *User = cast(U.getUser()); + if (PHINode *UserPN = dyn_cast(User)) { + if (UserPN->getIncomingBlock(U) == BB) + continue; + } else if (User->getParent() == BB) + continue; + + UsesToRename.push_back(&U); } - PN->addIncoming(IV, NewBB); + + // If there are no uses outside the block, we're done with this instruction. + if (UsesToRename.empty()) + continue; + + DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n"); + + // We found a use of I outside of BB. Rename all uses of I that are outside + // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks + // with the two values we know. + SSAUpdate.Initialize(I->getType(), I->getName()); + SSAUpdate.AddAvailableValue(BB, I); + SSAUpdate.AddAvailableValue(NewBB, ValueMapping[I]); + + while (!UsesToRename.empty()) + SSAUpdate.RewriteUse(*UsesToRename.pop_back_val()); + DEBUG(dbgs() << "\n"); } - + + // Ok, NewBB is good to go. Update the terminator of PredBB to jump to // NewBB instead of BB. This eliminates predecessors from BB, which requires // us to simplify any PHI nodes in BB. TerminatorInst *PredTerm = PredBB->getTerminator(); for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i) if (PredTerm->getSuccessor(i) == BB) { - BB->removePredecessor(PredBB); + BB->removePredecessor(PredBB, true); PredTerm->setSuccessor(i, NewBB); } - + // At this point, the IR is fully up to date and consistent. Do a quick scan // over the new instructions and zap any that are constants or dead. This // frequently happens because of phi translation. - BI = NewBB->begin(); - for (BasicBlock::iterator E = NewBB->end(); BI != E; ) { - Instruction *Inst = BI++; - if (Constant *C = ConstantFoldInstruction(Inst, BB->getContext(), TD)) { - Inst->replaceAllUsesWith(C); - Inst->eraseFromParent(); - continue; - } - - RecursivelyDeleteTriviallyDeadInstructions(Inst); - } - + SimplifyInstructionsInBlock(NewBB, TLI); + // Threaded an edge! ++NumThreads; return true; } + +/// DuplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch +/// to BB which contains an i1 PHI node and a conditional branch on that PHI. +/// If we can duplicate the contents of BB up into PredBB do so now, this +/// improves the odds that the branch will be on an analyzable instruction like +/// a compare. +bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, + const SmallVectorImpl &PredBBs) { + assert(!PredBBs.empty() && "Can't handle an empty set"); + + // If BB is a loop header, then duplicating this block outside the loop would + // cause us to transform this into an irreducible loop, don't do this. + // See the comments above FindLoopHeaders for justifications and caveats. + if (LoopHeaders.count(BB)) { + DEBUG(dbgs() << " Not duplicating loop header '" << BB->getName() + << "' into predecessor block '" << PredBBs[0]->getName() + << "' - it might create an irreducible loop!\n"); + return false; + } + + unsigned DuplicationCost = getJumpThreadDuplicationCost(BB, BBDupThreshold); + if (DuplicationCost > BBDupThreshold) { + DEBUG(dbgs() << " Not duplicating BB '" << BB->getName() + << "' - Cost is too high: " << DuplicationCost << "\n"); + return false; + } + + // And finally, do it! Start by factoring the predecessors is needed. + BasicBlock *PredBB; + if (PredBBs.size() == 1) + PredBB = PredBBs[0]; + else { + DEBUG(dbgs() << " Factoring out " << PredBBs.size() + << " common predecessors.\n"); + PredBB = SplitBlockPredecessors(BB, PredBBs, ".thr_comm"); + } + + // Okay, we decided to do this! Clone all the instructions in BB onto the end + // of PredBB. + DEBUG(dbgs() << " Duplicating block '" << BB->getName() << "' into end of '" + << PredBB->getName() << "' to eliminate branch on phi. Cost: " + << DuplicationCost << " block is:" << *BB << "\n"); + + // Unless PredBB ends with an unconditional branch, split the edge so that we + // can just clone the bits from BB into the end of the new PredBB. + BranchInst *OldPredBranch = dyn_cast(PredBB->getTerminator()); + + if (!OldPredBranch || !OldPredBranch->isUnconditional()) { + PredBB = SplitEdge(PredBB, BB); + OldPredBranch = cast(PredBB->getTerminator()); + } + + // We are going to have to map operands from the original BB block into the + // PredBB block. Evaluate PHI nodes in BB. + DenseMap ValueMapping; + + BasicBlock::iterator BI = BB->begin(); + for (; PHINode *PN = dyn_cast(BI); ++BI) + ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB); + // Clone the non-phi instructions of BB into PredBB, keeping track of the + // mapping and using it to remap operands in the cloned instructions. + for (; BI != BB->end(); ++BI) { + Instruction *New = BI->clone(); + + // Remap operands to patch up intra-block references. + for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i) + if (Instruction *Inst = dyn_cast(New->getOperand(i))) { + DenseMap::iterator I = ValueMapping.find(Inst); + if (I != ValueMapping.end()) + New->setOperand(i, I->second); + } + + // If this instruction can be simplified after the operands are updated, + // just use the simplified value instead. This frequently happens due to + // phi translation. + if (Value *IV = + SimplifyInstruction(New, BB->getModule()->getDataLayout())) { + delete New; + ValueMapping[BI] = IV; + } else { + // Otherwise, insert the new instruction into the block. + New->setName(BI->getName()); + PredBB->getInstList().insert(OldPredBranch, New); + ValueMapping[BI] = New; + } + } + + // Check to see if the targets of the branch had PHI nodes. If so, we need to + // add entries to the PHI nodes for branch from PredBB now. + BranchInst *BBBranch = cast(BB->getTerminator()); + AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB, + ValueMapping); + AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB, + ValueMapping); + + // If there were values defined in BB that are used outside the block, then we + // now have to update all uses of the value to use either the original value, + // the cloned value, or some PHI derived value. This can require arbitrary + // PHI insertion, of which we are prepared to do, clean these up now. + SSAUpdater SSAUpdate; + SmallVector UsesToRename; + for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) { + // Scan all uses of this instruction to see if it is used outside of its + // block, and if so, record them in UsesToRename. + for (Use &U : I->uses()) { + Instruction *User = cast(U.getUser()); + if (PHINode *UserPN = dyn_cast(User)) { + if (UserPN->getIncomingBlock(U) == BB) + continue; + } else if (User->getParent() == BB) + continue; + + UsesToRename.push_back(&U); + } + + // If there are no uses outside the block, we're done with this instruction. + if (UsesToRename.empty()) + continue; + + DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n"); + + // We found a use of I outside of BB. Rename all uses of I that are outside + // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks + // with the two values we know. + SSAUpdate.Initialize(I->getType(), I->getName()); + SSAUpdate.AddAvailableValue(BB, I); + SSAUpdate.AddAvailableValue(PredBB, ValueMapping[I]); + + while (!UsesToRename.empty()) + SSAUpdate.RewriteUse(*UsesToRename.pop_back_val()); + DEBUG(dbgs() << "\n"); + } + + // PredBB no longer jumps to BB, remove entries in the PHI node for the edge + // that we nuked. + BB->removePredecessor(PredBB, true); + + // Remove the unconditional branch at the end of the PredBB block. + OldPredBranch->eraseFromParent(); + + ++NumDupes; + return true; +} + +/// TryToUnfoldSelect - Look for blocks of the form +/// bb1: +/// %a = select +/// br bb +/// +/// bb2: +/// %p = phi [%a, %bb] ... +/// %c = icmp %p +/// br i1 %c +/// +/// And expand the select into a branch structure if one of its arms allows %c +/// to be folded. This later enables threading from bb1 over bb2. +bool JumpThreading::TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB) { + BranchInst *CondBr = dyn_cast(BB->getTerminator()); + PHINode *CondLHS = dyn_cast(CondCmp->getOperand(0)); + Constant *CondRHS = cast(CondCmp->getOperand(1)); + + if (!CondBr || !CondBr->isConditional() || !CondLHS || + CondLHS->getParent() != BB) + return false; + + for (unsigned I = 0, E = CondLHS->getNumIncomingValues(); I != E; ++I) { + BasicBlock *Pred = CondLHS->getIncomingBlock(I); + SelectInst *SI = dyn_cast(CondLHS->getIncomingValue(I)); + + // Look if one of the incoming values is a select in the corresponding + // predecessor. + if (!SI || SI->getParent() != Pred || !SI->hasOneUse()) + continue; + + BranchInst *PredTerm = dyn_cast(Pred->getTerminator()); + if (!PredTerm || !PredTerm->isUnconditional()) + continue; + + // Now check if one of the select values would allow us to constant fold the + // terminator in BB. We don't do the transform if both sides fold, those + // cases will be threaded in any case. + LazyValueInfo::Tristate LHSFolds = + LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(1), + CondRHS, Pred, BB, CondCmp); + LazyValueInfo::Tristate RHSFolds = + LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(2), + CondRHS, Pred, BB, CondCmp); + if ((LHSFolds != LazyValueInfo::Unknown || + RHSFolds != LazyValueInfo::Unknown) && + LHSFolds != RHSFolds) { + // Expand the select. + // + // Pred -- + // | v + // | NewBB + // | | + // |----- + // v + // BB + BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "select.unfold", + BB->getParent(), BB); + // Move the unconditional branch to NewBB. + PredTerm->removeFromParent(); + NewBB->getInstList().insert(NewBB->end(), PredTerm); + // Create a conditional branch and update PHI nodes. + BranchInst::Create(NewBB, BB, SI->getCondition(), Pred); + CondLHS->setIncomingValue(I, SI->getFalseValue()); + CondLHS->addIncoming(SI->getTrueValue(), NewBB); + // The select is now dead. + SI->eraseFromParent(); + + // Update any other PHI nodes in BB. + for (BasicBlock::iterator BI = BB->begin(); + PHINode *Phi = dyn_cast(BI); ++BI) + if (Phi != CondLHS) + Phi->addIncoming(Phi->getIncomingValueForBlock(Pred), NewBB); + return true; + } + } + return false; +}