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Diffstat (limited to 'llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp')
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp | 1266 |
1 files changed, 1266 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp new file mode 100644 index 000000000000..e0376b7582f3 --- /dev/null +++ b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp @@ -0,0 +1,1266 @@ +//===- InstCombinePHI.cpp -------------------------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This file implements the visitPHINode function. +// +//===----------------------------------------------------------------------===// + +#include "InstCombineInternal.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/PatternMatch.h" +using namespace llvm; +using namespace llvm::PatternMatch; + +#define DEBUG_TYPE "instcombine" + +static cl::opt<unsigned> +MaxNumPhis("instcombine-max-num-phis", cl::init(512), + cl::desc("Maximum number phis to handle in intptr/ptrint folding")); + +/// The PHI arguments will be folded into a single operation with a PHI node +/// as input. The debug location of the single operation will be the merged +/// locations of the original PHI node arguments. +void InstCombiner::PHIArgMergedDebugLoc(Instruction *Inst, PHINode &PN) { + auto *FirstInst = cast<Instruction>(PN.getIncomingValue(0)); + Inst->setDebugLoc(FirstInst->getDebugLoc()); + // We do not expect a CallInst here, otherwise, N-way merging of DebugLoc + // will be inefficient. + assert(!isa<CallInst>(Inst)); + + for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) { + auto *I = cast<Instruction>(PN.getIncomingValue(i)); + Inst->applyMergedLocation(Inst->getDebugLoc(), I->getDebugLoc()); + } +} + +// Replace Integer typed PHI PN if the PHI's value is used as a pointer value. +// If there is an existing pointer typed PHI that produces the same value as PN, +// replace PN and the IntToPtr operation with it. Otherwise, synthesize a new +// PHI node: +// +// Case-1: +// bb1: +// int_init = PtrToInt(ptr_init) +// br label %bb2 +// bb2: +// int_val = PHI([int_init, %bb1], [int_val_inc, %bb2] +// ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2] +// ptr_val2 = IntToPtr(int_val) +// ... +// use(ptr_val2) +// ptr_val_inc = ... +// inc_val_inc = PtrToInt(ptr_val_inc) +// +// ==> +// bb1: +// br label %bb2 +// bb2: +// ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2] +// ... +// use(ptr_val) +// ptr_val_inc = ... +// +// Case-2: +// bb1: +// int_ptr = BitCast(ptr_ptr) +// int_init = Load(int_ptr) +// br label %bb2 +// bb2: +// int_val = PHI([int_init, %bb1], [int_val_inc, %bb2] +// ptr_val2 = IntToPtr(int_val) +// ... +// use(ptr_val2) +// ptr_val_inc = ... +// inc_val_inc = PtrToInt(ptr_val_inc) +// ==> +// bb1: +// ptr_init = Load(ptr_ptr) +// br label %bb2 +// bb2: +// ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2] +// ... +// use(ptr_val) +// ptr_val_inc = ... +// ... +// +Instruction *InstCombiner::FoldIntegerTypedPHI(PHINode &PN) { + if (!PN.getType()->isIntegerTy()) + return nullptr; + if (!PN.hasOneUse()) + return nullptr; + + auto *IntToPtr = dyn_cast<IntToPtrInst>(PN.user_back()); + if (!IntToPtr) + return nullptr; + + // Check if the pointer is actually used as pointer: + auto HasPointerUse = [](Instruction *IIP) { + for (User *U : IIP->users()) { + Value *Ptr = nullptr; + if (LoadInst *LoadI = dyn_cast<LoadInst>(U)) { + Ptr = LoadI->getPointerOperand(); + } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { + Ptr = SI->getPointerOperand(); + } else if (GetElementPtrInst *GI = dyn_cast<GetElementPtrInst>(U)) { + Ptr = GI->getPointerOperand(); + } + + if (Ptr && Ptr == IIP) + return true; + } + return false; + }; + + if (!HasPointerUse(IntToPtr)) + return nullptr; + + if (DL.getPointerSizeInBits(IntToPtr->getAddressSpace()) != + DL.getTypeSizeInBits(IntToPtr->getOperand(0)->getType())) + return nullptr; + + SmallVector<Value *, 4> AvailablePtrVals; + for (unsigned i = 0; i != PN.getNumIncomingValues(); ++i) { + Value *Arg = PN.getIncomingValue(i); + + // First look backward: + if (auto *PI = dyn_cast<PtrToIntInst>(Arg)) { + AvailablePtrVals.emplace_back(PI->getOperand(0)); + continue; + } + + // Next look forward: + Value *ArgIntToPtr = nullptr; + for (User *U : Arg->users()) { + if (isa<IntToPtrInst>(U) && U->getType() == IntToPtr->getType() && + (DT.dominates(cast<Instruction>(U), PN.getIncomingBlock(i)) || + cast<Instruction>(U)->getParent() == PN.getIncomingBlock(i))) { + ArgIntToPtr = U; + break; + } + } + + if (ArgIntToPtr) { + AvailablePtrVals.emplace_back(ArgIntToPtr); + continue; + } + + // If Arg is defined by a PHI, allow it. This will also create + // more opportunities iteratively. + if (isa<PHINode>(Arg)) { + AvailablePtrVals.emplace_back(Arg); + continue; + } + + // For a single use integer load: + auto *LoadI = dyn_cast<LoadInst>(Arg); + if (!LoadI) + return nullptr; + + if (!LoadI->hasOneUse()) + return nullptr; + + // Push the integer typed Load instruction into the available + // value set, and fix it up later when the pointer typed PHI + // is synthesized. + AvailablePtrVals.emplace_back(LoadI); + } + + // Now search for a matching PHI + auto *BB = PN.getParent(); + assert(AvailablePtrVals.size() == PN.getNumIncomingValues() && + "Not enough available ptr typed incoming values"); + PHINode *MatchingPtrPHI = nullptr; + unsigned NumPhis = 0; + for (auto II = BB->begin(), EI = BasicBlock::iterator(BB->getFirstNonPHI()); + II != EI; II++, NumPhis++) { + // FIXME: consider handling this in AggressiveInstCombine + if (NumPhis > MaxNumPhis) + return nullptr; + PHINode *PtrPHI = dyn_cast<PHINode>(II); + if (!PtrPHI || PtrPHI == &PN || PtrPHI->getType() != IntToPtr->getType()) + continue; + MatchingPtrPHI = PtrPHI; + for (unsigned i = 0; i != PtrPHI->getNumIncomingValues(); ++i) { + if (AvailablePtrVals[i] != + PtrPHI->getIncomingValueForBlock(PN.getIncomingBlock(i))) { + MatchingPtrPHI = nullptr; + break; + } + } + + if (MatchingPtrPHI) + break; + } + + if (MatchingPtrPHI) { + assert(MatchingPtrPHI->getType() == IntToPtr->getType() && + "Phi's Type does not match with IntToPtr"); + // The PtrToCast + IntToPtr will be simplified later + return CastInst::CreateBitOrPointerCast(MatchingPtrPHI, + IntToPtr->getOperand(0)->getType()); + } + + // If it requires a conversion for every PHI operand, do not do it. + if (all_of(AvailablePtrVals, [&](Value *V) { + return (V->getType() != IntToPtr->getType()) || isa<IntToPtrInst>(V); + })) + return nullptr; + + // If any of the operand that requires casting is a terminator + // instruction, do not do it. + if (any_of(AvailablePtrVals, [&](Value *V) { + if (V->getType() == IntToPtr->getType()) + return false; + + auto *Inst = dyn_cast<Instruction>(V); + return Inst && Inst->isTerminator(); + })) + return nullptr; + + PHINode *NewPtrPHI = PHINode::Create( + IntToPtr->getType(), PN.getNumIncomingValues(), PN.getName() + ".ptr"); + + InsertNewInstBefore(NewPtrPHI, PN); + SmallDenseMap<Value *, Instruction *> Casts; + for (unsigned i = 0; i != PN.getNumIncomingValues(); ++i) { + auto *IncomingBB = PN.getIncomingBlock(i); + auto *IncomingVal = AvailablePtrVals[i]; + + if (IncomingVal->getType() == IntToPtr->getType()) { + NewPtrPHI->addIncoming(IncomingVal, IncomingBB); + continue; + } + +#ifndef NDEBUG + LoadInst *LoadI = dyn_cast<LoadInst>(IncomingVal); + assert((isa<PHINode>(IncomingVal) || + IncomingVal->getType()->isPointerTy() || + (LoadI && LoadI->hasOneUse())) && + "Can not replace LoadInst with multiple uses"); +#endif + // Need to insert a BitCast. + // For an integer Load instruction with a single use, the load + IntToPtr + // cast will be simplified into a pointer load: + // %v = load i64, i64* %a.ip, align 8 + // %v.cast = inttoptr i64 %v to float ** + // ==> + // %v.ptrp = bitcast i64 * %a.ip to float ** + // %v.cast = load float *, float ** %v.ptrp, align 8 + Instruction *&CI = Casts[IncomingVal]; + if (!CI) { + CI = CastInst::CreateBitOrPointerCast(IncomingVal, IntToPtr->getType(), + IncomingVal->getName() + ".ptr"); + if (auto *IncomingI = dyn_cast<Instruction>(IncomingVal)) { + BasicBlock::iterator InsertPos(IncomingI); + InsertPos++; + if (isa<PHINode>(IncomingI)) + InsertPos = IncomingI->getParent()->getFirstInsertionPt(); + InsertNewInstBefore(CI, *InsertPos); + } else { + auto *InsertBB = &IncomingBB->getParent()->getEntryBlock(); + InsertNewInstBefore(CI, *InsertBB->getFirstInsertionPt()); + } + } + NewPtrPHI->addIncoming(CI, IncomingBB); + } + + // The PtrToCast + IntToPtr will be simplified later + return CastInst::CreateBitOrPointerCast(NewPtrPHI, + IntToPtr->getOperand(0)->getType()); +} + +/// If we have something like phi [add (a,b), add(a,c)] and if a/b/c and the +/// adds all have a single use, turn this into a phi and a single binop. +Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) { + Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0)); + assert(isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)); + unsigned Opc = FirstInst->getOpcode(); + Value *LHSVal = FirstInst->getOperand(0); + Value *RHSVal = FirstInst->getOperand(1); + + Type *LHSType = LHSVal->getType(); + Type *RHSType = RHSVal->getType(); + + // Scan to see if all operands are the same opcode, and all have one use. + for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) { + Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i)); + if (!I || I->getOpcode() != Opc || !I->hasOneUse() || + // Verify type of the LHS matches so we don't fold cmp's of different + // types. + I->getOperand(0)->getType() != LHSType || + I->getOperand(1)->getType() != RHSType) + return nullptr; + + // If they are CmpInst instructions, check their predicates + if (CmpInst *CI = dyn_cast<CmpInst>(I)) + if (CI->getPredicate() != cast<CmpInst>(FirstInst)->getPredicate()) + return nullptr; + + // Keep track of which operand needs a phi node. + if (I->getOperand(0) != LHSVal) LHSVal = nullptr; + if (I->getOperand(1) != RHSVal) RHSVal = nullptr; + } + + // If both LHS and RHS would need a PHI, don't do this transformation, + // because it would increase the number of PHIs entering the block, + // which leads to higher register pressure. This is especially + // bad when the PHIs are in the header of a loop. + if (!LHSVal && !RHSVal) + return nullptr; + + // Otherwise, this is safe to transform! + + Value *InLHS = FirstInst->getOperand(0); + Value *InRHS = FirstInst->getOperand(1); + PHINode *NewLHS = nullptr, *NewRHS = nullptr; + if (!LHSVal) { + NewLHS = PHINode::Create(LHSType, PN.getNumIncomingValues(), + FirstInst->getOperand(0)->getName() + ".pn"); + NewLHS->addIncoming(InLHS, PN.getIncomingBlock(0)); + InsertNewInstBefore(NewLHS, PN); + LHSVal = NewLHS; + } + + if (!RHSVal) { + NewRHS = PHINode::Create(RHSType, PN.getNumIncomingValues(), + FirstInst->getOperand(1)->getName() + ".pn"); + NewRHS->addIncoming(InRHS, PN.getIncomingBlock(0)); + InsertNewInstBefore(NewRHS, PN); + RHSVal = NewRHS; + } + + // Add all operands to the new PHIs. + if (NewLHS || NewRHS) { + for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { + Instruction *InInst = cast<Instruction>(PN.getIncomingValue(i)); + if (NewLHS) { + Value *NewInLHS = InInst->getOperand(0); + NewLHS->addIncoming(NewInLHS, PN.getIncomingBlock(i)); + } + if (NewRHS) { + Value *NewInRHS = InInst->getOperand(1); + NewRHS->addIncoming(NewInRHS, PN.getIncomingBlock(i)); + } + } + } + + if (CmpInst *CIOp = dyn_cast<CmpInst>(FirstInst)) { + CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), + LHSVal, RHSVal); + PHIArgMergedDebugLoc(NewCI, PN); + return NewCI; + } + + BinaryOperator *BinOp = cast<BinaryOperator>(FirstInst); + BinaryOperator *NewBinOp = + BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal); + + NewBinOp->copyIRFlags(PN.getIncomingValue(0)); + + for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) + NewBinOp->andIRFlags(PN.getIncomingValue(i)); + + PHIArgMergedDebugLoc(NewBinOp, PN); + return NewBinOp; +} + +Instruction *InstCombiner::FoldPHIArgGEPIntoPHI(PHINode &PN) { + GetElementPtrInst *FirstInst =cast<GetElementPtrInst>(PN.getIncomingValue(0)); + + SmallVector<Value*, 16> FixedOperands(FirstInst->op_begin(), + FirstInst->op_end()); + // This is true if all GEP bases are allocas and if all indices into them are + // constants. + bool AllBasePointersAreAllocas = true; + + // We don't want to replace this phi if the replacement would require + // more than one phi, which leads to higher register pressure. This is + // especially bad when the PHIs are in the header of a loop. + bool NeededPhi = false; + + bool AllInBounds = true; + + // Scan to see if all operands are the same opcode, and all have one use. + for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) { + GetElementPtrInst *GEP= dyn_cast<GetElementPtrInst>(PN.getIncomingValue(i)); + if (!GEP || !GEP->hasOneUse() || GEP->getType() != FirstInst->getType() || + GEP->getNumOperands() != FirstInst->getNumOperands()) + return nullptr; + + AllInBounds &= GEP->isInBounds(); + + // Keep track of whether or not all GEPs are of alloca pointers. + if (AllBasePointersAreAllocas && + (!isa<AllocaInst>(GEP->getOperand(0)) || + !GEP->hasAllConstantIndices())) + AllBasePointersAreAllocas = false; + + // Compare the operand lists. + for (unsigned op = 0, e = FirstInst->getNumOperands(); op != e; ++op) { + if (FirstInst->getOperand(op) == GEP->getOperand(op)) + continue; + + // Don't merge two GEPs when two operands differ (introducing phi nodes) + // if one of the PHIs has a constant for the index. The index may be + // substantially cheaper to compute for the constants, so making it a + // variable index could pessimize the path. This also handles the case + // for struct indices, which must always be constant. + if (isa<ConstantInt>(FirstInst->getOperand(op)) || + isa<ConstantInt>(GEP->getOperand(op))) + return nullptr; + + if (FirstInst->getOperand(op)->getType() !=GEP->getOperand(op)->getType()) + return nullptr; + + // If we already needed a PHI for an earlier operand, and another operand + // also requires a PHI, we'd be introducing more PHIs than we're + // eliminating, which increases register pressure on entry to the PHI's + // block. + if (NeededPhi) + return nullptr; + + FixedOperands[op] = nullptr; // Needs a PHI. + NeededPhi = true; + } + } + + // If all of the base pointers of the PHI'd GEPs are from allocas, don't + // bother doing this transformation. At best, this will just save a bit of + // offset calculation, but all the predecessors will have to materialize the + // stack address into a register anyway. We'd actually rather *clone* the + // load up into the predecessors so that we have a load of a gep of an alloca, + // which can usually all be folded into the load. + if (AllBasePointersAreAllocas) + return nullptr; + + // Otherwise, this is safe to transform. Insert PHI nodes for each operand + // that is variable. + SmallVector<PHINode*, 16> OperandPhis(FixedOperands.size()); + + bool HasAnyPHIs = false; + for (unsigned i = 0, e = FixedOperands.size(); i != e; ++i) { + if (FixedOperands[i]) continue; // operand doesn't need a phi. + Value *FirstOp = FirstInst->getOperand(i); + PHINode *NewPN = PHINode::Create(FirstOp->getType(), e, + FirstOp->getName()+".pn"); + InsertNewInstBefore(NewPN, PN); + + NewPN->addIncoming(FirstOp, PN.getIncomingBlock(0)); + OperandPhis[i] = NewPN; + FixedOperands[i] = NewPN; + HasAnyPHIs = true; + } + + + // Add all operands to the new PHIs. + if (HasAnyPHIs) { + for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { + GetElementPtrInst *InGEP =cast<GetElementPtrInst>(PN.getIncomingValue(i)); + BasicBlock *InBB = PN.getIncomingBlock(i); + + for (unsigned op = 0, e = OperandPhis.size(); op != e; ++op) + if (PHINode *OpPhi = OperandPhis[op]) + OpPhi->addIncoming(InGEP->getOperand(op), InBB); + } + } + + Value *Base = FixedOperands[0]; + GetElementPtrInst *NewGEP = + GetElementPtrInst::Create(FirstInst->getSourceElementType(), Base, + makeArrayRef(FixedOperands).slice(1)); + if (AllInBounds) NewGEP->setIsInBounds(); + PHIArgMergedDebugLoc(NewGEP, PN); + return NewGEP; +} + + +/// Return true if we know that it is safe to sink the load out of the block +/// that defines it. This means that it must be obvious the value of the load is +/// not changed from the point of the load to the end of the block it is in. +/// +/// Finally, it is safe, but not profitable, to sink a load targeting a +/// non-address-taken alloca. Doing so will cause us to not promote the alloca +/// to a register. +static bool isSafeAndProfitableToSinkLoad(LoadInst *L) { + BasicBlock::iterator BBI = L->getIterator(), E = L->getParent()->end(); + + for (++BBI; BBI != E; ++BBI) + if (BBI->mayWriteToMemory()) + return false; + + // Check for non-address taken alloca. If not address-taken already, it isn't + // profitable to do this xform. + if (AllocaInst *AI = dyn_cast<AllocaInst>(L->getOperand(0))) { + bool isAddressTaken = false; + for (User *U : AI->users()) { + if (isa<LoadInst>(U)) continue; + if (StoreInst *SI = dyn_cast<StoreInst>(U)) { + // If storing TO the alloca, then the address isn't taken. + if (SI->getOperand(1) == AI) continue; + } + isAddressTaken = true; + break; + } + + if (!isAddressTaken && AI->isStaticAlloca()) + return false; + } + + // If this load is a load from a GEP with a constant offset from an alloca, + // then we don't want to sink it. In its present form, it will be + // load [constant stack offset]. Sinking it will cause us to have to + // materialize the stack addresses in each predecessor in a register only to + // do a shared load from register in the successor. + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(L->getOperand(0))) + if (AllocaInst *AI = dyn_cast<AllocaInst>(GEP->getOperand(0))) + if (AI->isStaticAlloca() && GEP->hasAllConstantIndices()) + return false; + + return true; +} + +Instruction *InstCombiner::FoldPHIArgLoadIntoPHI(PHINode &PN) { + LoadInst *FirstLI = cast<LoadInst>(PN.getIncomingValue(0)); + + // FIXME: This is overconservative; this transform is allowed in some cases + // for atomic operations. + if (FirstLI->isAtomic()) + return nullptr; + + // When processing loads, we need to propagate two bits of information to the + // sunk load: whether it is volatile, and what its alignment is. We currently + // don't sink loads when some have their alignment specified and some don't. + // visitLoadInst will propagate an alignment onto the load when TD is around, + // and if TD isn't around, we can't handle the mixed case. + bool isVolatile = FirstLI->isVolatile(); + MaybeAlign LoadAlignment(FirstLI->getAlignment()); + unsigned LoadAddrSpace = FirstLI->getPointerAddressSpace(); + + // We can't sink the load if the loaded value could be modified between the + // load and the PHI. + if (FirstLI->getParent() != PN.getIncomingBlock(0) || + !isSafeAndProfitableToSinkLoad(FirstLI)) + return nullptr; + + // If the PHI is of volatile loads and the load block has multiple + // successors, sinking it would remove a load of the volatile value from + // the path through the other successor. + if (isVolatile && + FirstLI->getParent()->getTerminator()->getNumSuccessors() != 1) + return nullptr; + + // Check to see if all arguments are the same operation. + for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { + LoadInst *LI = dyn_cast<LoadInst>(PN.getIncomingValue(i)); + if (!LI || !LI->hasOneUse()) + return nullptr; + + // We can't sink the load if the loaded value could be modified between + // the load and the PHI. + if (LI->isVolatile() != isVolatile || + LI->getParent() != PN.getIncomingBlock(i) || + LI->getPointerAddressSpace() != LoadAddrSpace || + !isSafeAndProfitableToSinkLoad(LI)) + return nullptr; + + // If some of the loads have an alignment specified but not all of them, + // we can't do the transformation. + if ((LoadAlignment.hasValue()) != (LI->getAlignment() != 0)) + return nullptr; + + LoadAlignment = std::min(LoadAlignment, MaybeAlign(LI->getAlignment())); + + // If the PHI is of volatile loads and the load block has multiple + // successors, sinking it would remove a load of the volatile value from + // the path through the other successor. + if (isVolatile && + LI->getParent()->getTerminator()->getNumSuccessors() != 1) + return nullptr; + } + + // Okay, they are all the same operation. Create a new PHI node of the + // correct type, and PHI together all of the LHS's of the instructions. + PHINode *NewPN = PHINode::Create(FirstLI->getOperand(0)->getType(), + PN.getNumIncomingValues(), + PN.getName()+".in"); + + Value *InVal = FirstLI->getOperand(0); + NewPN->addIncoming(InVal, PN.getIncomingBlock(0)); + LoadInst *NewLI = + new LoadInst(FirstLI->getType(), NewPN, "", isVolatile, LoadAlignment); + + unsigned KnownIDs[] = { + LLVMContext::MD_tbaa, + LLVMContext::MD_range, + LLVMContext::MD_invariant_load, + LLVMContext::MD_alias_scope, + LLVMContext::MD_noalias, + LLVMContext::MD_nonnull, + LLVMContext::MD_align, + LLVMContext::MD_dereferenceable, + LLVMContext::MD_dereferenceable_or_null, + LLVMContext::MD_access_group, + }; + + for (unsigned ID : KnownIDs) + NewLI->setMetadata(ID, FirstLI->getMetadata(ID)); + + // Add all operands to the new PHI and combine TBAA metadata. + for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { + LoadInst *LI = cast<LoadInst>(PN.getIncomingValue(i)); + combineMetadata(NewLI, LI, KnownIDs, true); + Value *NewInVal = LI->getOperand(0); + if (NewInVal != InVal) + InVal = nullptr; + NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i)); + } + + if (InVal) { + // The new PHI unions all of the same values together. This is really + // common, so we handle it intelligently here for compile-time speed. + NewLI->setOperand(0, InVal); + delete NewPN; + } else { + InsertNewInstBefore(NewPN, PN); + } + + // If this was a volatile load that we are merging, make sure to loop through + // and mark all the input loads as non-volatile. If we don't do this, we will + // insert a new volatile load and the old ones will not be deletable. + if (isVolatile) + for (Value *IncValue : PN.incoming_values()) + cast<LoadInst>(IncValue)->setVolatile(false); + + PHIArgMergedDebugLoc(NewLI, PN); + return NewLI; +} + +/// TODO: This function could handle other cast types, but then it might +/// require special-casing a cast from the 'i1' type. See the comment in +/// FoldPHIArgOpIntoPHI() about pessimizing illegal integer types. +Instruction *InstCombiner::FoldPHIArgZextsIntoPHI(PHINode &Phi) { + // We cannot create a new instruction after the PHI if the terminator is an + // EHPad because there is no valid insertion point. + if (Instruction *TI = Phi.getParent()->getTerminator()) + if (TI->isEHPad()) + return nullptr; + + // Early exit for the common case of a phi with two operands. These are + // handled elsewhere. See the comment below where we check the count of zexts + // and constants for more details. + unsigned NumIncomingValues = Phi.getNumIncomingValues(); + if (NumIncomingValues < 3) + return nullptr; + + // Find the narrower type specified by the first zext. + Type *NarrowType = nullptr; + for (Value *V : Phi.incoming_values()) { + if (auto *Zext = dyn_cast<ZExtInst>(V)) { + NarrowType = Zext->getSrcTy(); + break; + } + } + if (!NarrowType) + return nullptr; + + // Walk the phi operands checking that we only have zexts or constants that + // we can shrink for free. Store the new operands for the new phi. + SmallVector<Value *, 4> NewIncoming; + unsigned NumZexts = 0; + unsigned NumConsts = 0; + for (Value *V : Phi.incoming_values()) { + if (auto *Zext = dyn_cast<ZExtInst>(V)) { + // All zexts must be identical and have one use. + if (Zext->getSrcTy() != NarrowType || !Zext->hasOneUse()) + return nullptr; + NewIncoming.push_back(Zext->getOperand(0)); + NumZexts++; + } else if (auto *C = dyn_cast<Constant>(V)) { + // Make sure that constants can fit in the new type. + Constant *Trunc = ConstantExpr::getTrunc(C, NarrowType); + if (ConstantExpr::getZExt(Trunc, C->getType()) != C) + return nullptr; + NewIncoming.push_back(Trunc); + NumConsts++; + } else { + // If it's not a cast or a constant, bail out. + return nullptr; + } + } + + // The more common cases of a phi with no constant operands or just one + // variable operand are handled by FoldPHIArgOpIntoPHI() and foldOpIntoPhi() + // respectively. foldOpIntoPhi() wants to do the opposite transform that is + // performed here. It tries to replicate a cast in the phi operand's basic + // block to expose other folding opportunities. Thus, InstCombine will + // infinite loop without this check. + if (NumConsts == 0 || NumZexts < 2) + return nullptr; + + // All incoming values are zexts or constants that are safe to truncate. + // Create a new phi node of the narrow type, phi together all of the new + // operands, and zext the result back to the original type. + PHINode *NewPhi = PHINode::Create(NarrowType, NumIncomingValues, + Phi.getName() + ".shrunk"); + for (unsigned i = 0; i != NumIncomingValues; ++i) + NewPhi->addIncoming(NewIncoming[i], Phi.getIncomingBlock(i)); + + InsertNewInstBefore(NewPhi, Phi); + return CastInst::CreateZExtOrBitCast(NewPhi, Phi.getType()); +} + +/// If all operands to a PHI node are the same "unary" operator and they all are +/// only used by the PHI, PHI together their inputs, and do the operation once, +/// to the result of the PHI. +Instruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) { + // We cannot create a new instruction after the PHI if the terminator is an + // EHPad because there is no valid insertion point. + if (Instruction *TI = PN.getParent()->getTerminator()) + if (TI->isEHPad()) + return nullptr; + + Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0)); + + if (isa<GetElementPtrInst>(FirstInst)) + return FoldPHIArgGEPIntoPHI(PN); + if (isa<LoadInst>(FirstInst)) + return FoldPHIArgLoadIntoPHI(PN); + + // Scan the instruction, looking for input operations that can be folded away. + // If all input operands to the phi are the same instruction (e.g. a cast from + // the same type or "+42") we can pull the operation through the PHI, reducing + // code size and simplifying code. + Constant *ConstantOp = nullptr; + Type *CastSrcTy = nullptr; + + if (isa<CastInst>(FirstInst)) { + CastSrcTy = FirstInst->getOperand(0)->getType(); + + // Be careful about transforming integer PHIs. We don't want to pessimize + // the code by turning an i32 into an i1293. + if (PN.getType()->isIntegerTy() && CastSrcTy->isIntegerTy()) { + if (!shouldChangeType(PN.getType(), CastSrcTy)) + return nullptr; + } + } else if (isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)) { + // Can fold binop, compare or shift here if the RHS is a constant, + // otherwise call FoldPHIArgBinOpIntoPHI. + ConstantOp = dyn_cast<Constant>(FirstInst->getOperand(1)); + if (!ConstantOp) + return FoldPHIArgBinOpIntoPHI(PN); + } else { + return nullptr; // Cannot fold this operation. + } + + // Check to see if all arguments are the same operation. + for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { + Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i)); + if (!I || !I->hasOneUse() || !I->isSameOperationAs(FirstInst)) + return nullptr; + if (CastSrcTy) { + if (I->getOperand(0)->getType() != CastSrcTy) + return nullptr; // Cast operation must match. + } else if (I->getOperand(1) != ConstantOp) { + return nullptr; + } + } + + // Okay, they are all the same operation. Create a new PHI node of the + // correct type, and PHI together all of the LHS's of the instructions. + PHINode *NewPN = PHINode::Create(FirstInst->getOperand(0)->getType(), + PN.getNumIncomingValues(), + PN.getName()+".in"); + + Value *InVal = FirstInst->getOperand(0); + NewPN->addIncoming(InVal, PN.getIncomingBlock(0)); + + // Add all operands to the new PHI. + for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { + Value *NewInVal = cast<Instruction>(PN.getIncomingValue(i))->getOperand(0); + if (NewInVal != InVal) + InVal = nullptr; + NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i)); + } + + Value *PhiVal; + if (InVal) { + // The new PHI unions all of the same values together. This is really + // common, so we handle it intelligently here for compile-time speed. + PhiVal = InVal; + delete NewPN; + } else { + InsertNewInstBefore(NewPN, PN); + PhiVal = NewPN; + } + + // Insert and return the new operation. + if (CastInst *FirstCI = dyn_cast<CastInst>(FirstInst)) { + CastInst *NewCI = CastInst::Create(FirstCI->getOpcode(), PhiVal, + PN.getType()); + PHIArgMergedDebugLoc(NewCI, PN); + return NewCI; + } + + if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) { + BinOp = BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp); + BinOp->copyIRFlags(PN.getIncomingValue(0)); + + for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) + BinOp->andIRFlags(PN.getIncomingValue(i)); + + PHIArgMergedDebugLoc(BinOp, PN); + return BinOp; + } + + CmpInst *CIOp = cast<CmpInst>(FirstInst); + CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), + PhiVal, ConstantOp); + PHIArgMergedDebugLoc(NewCI, PN); + return NewCI; +} + +/// Return true if this PHI node is only used by a PHI node cycle that is dead. +static bool DeadPHICycle(PHINode *PN, + SmallPtrSetImpl<PHINode*> &PotentiallyDeadPHIs) { + if (PN->use_empty()) return true; + if (!PN->hasOneUse()) return false; + + // Remember this node, and if we find the cycle, return. + if (!PotentiallyDeadPHIs.insert(PN).second) + return true; + + // Don't scan crazily complex things. + if (PotentiallyDeadPHIs.size() == 16) + return false; + + if (PHINode *PU = dyn_cast<PHINode>(PN->user_back())) + return DeadPHICycle(PU, PotentiallyDeadPHIs); + + return false; +} + +/// Return true if this phi node is always equal to NonPhiInVal. +/// This happens with mutually cyclic phi nodes like: +/// z = some value; x = phi (y, z); y = phi (x, z) +static bool PHIsEqualValue(PHINode *PN, Value *NonPhiInVal, + SmallPtrSetImpl<PHINode*> &ValueEqualPHIs) { + // See if we already saw this PHI node. + if (!ValueEqualPHIs.insert(PN).second) + return true; + + // Don't scan crazily complex things. + if (ValueEqualPHIs.size() == 16) + return false; + + // Scan the operands to see if they are either phi nodes or are equal to + // the value. + for (Value *Op : PN->incoming_values()) { + if (PHINode *OpPN = dyn_cast<PHINode>(Op)) { + if (!PHIsEqualValue(OpPN, NonPhiInVal, ValueEqualPHIs)) + return false; + } else if (Op != NonPhiInVal) + return false; + } + + return true; +} + +/// Return an existing non-zero constant if this phi node has one, otherwise +/// return constant 1. +static ConstantInt *GetAnyNonZeroConstInt(PHINode &PN) { + assert(isa<IntegerType>(PN.getType()) && "Expect only integer type phi"); + for (Value *V : PN.operands()) + if (auto *ConstVA = dyn_cast<ConstantInt>(V)) + if (!ConstVA->isZero()) + return ConstVA; + return ConstantInt::get(cast<IntegerType>(PN.getType()), 1); +} + +namespace { +struct PHIUsageRecord { + unsigned PHIId; // The ID # of the PHI (something determinstic to sort on) + unsigned Shift; // The amount shifted. + Instruction *Inst; // The trunc instruction. + + PHIUsageRecord(unsigned pn, unsigned Sh, Instruction *User) + : PHIId(pn), Shift(Sh), Inst(User) {} + + bool operator<(const PHIUsageRecord &RHS) const { + if (PHIId < RHS.PHIId) return true; + if (PHIId > RHS.PHIId) return false; + if (Shift < RHS.Shift) return true; + if (Shift > RHS.Shift) return false; + return Inst->getType()->getPrimitiveSizeInBits() < + RHS.Inst->getType()->getPrimitiveSizeInBits(); + } +}; + +struct LoweredPHIRecord { + PHINode *PN; // The PHI that was lowered. + unsigned Shift; // The amount shifted. + unsigned Width; // The width extracted. + + LoweredPHIRecord(PHINode *pn, unsigned Sh, Type *Ty) + : PN(pn), Shift(Sh), Width(Ty->getPrimitiveSizeInBits()) {} + + // Ctor form used by DenseMap. + LoweredPHIRecord(PHINode *pn, unsigned Sh) + : PN(pn), Shift(Sh), Width(0) {} +}; +} + +namespace llvm { + template<> + struct DenseMapInfo<LoweredPHIRecord> { + static inline LoweredPHIRecord getEmptyKey() { + return LoweredPHIRecord(nullptr, 0); + } + static inline LoweredPHIRecord getTombstoneKey() { + return LoweredPHIRecord(nullptr, 1); + } + static unsigned getHashValue(const LoweredPHIRecord &Val) { + return DenseMapInfo<PHINode*>::getHashValue(Val.PN) ^ (Val.Shift>>3) ^ + (Val.Width>>3); + } + static bool isEqual(const LoweredPHIRecord &LHS, + const LoweredPHIRecord &RHS) { + return LHS.PN == RHS.PN && LHS.Shift == RHS.Shift && + LHS.Width == RHS.Width; + } + }; +} + + +/// This is an integer PHI and we know that it has an illegal type: see if it is +/// only used by trunc or trunc(lshr) operations. If so, we split the PHI into +/// the various pieces being extracted. This sort of thing is introduced when +/// SROA promotes an aggregate to large integer values. +/// +/// TODO: The user of the trunc may be an bitcast to float/double/vector or an +/// inttoptr. We should produce new PHIs in the right type. +/// +Instruction *InstCombiner::SliceUpIllegalIntegerPHI(PHINode &FirstPhi) { + // PHIUsers - Keep track of all of the truncated values extracted from a set + // of PHIs, along with their offset. These are the things we want to rewrite. + SmallVector<PHIUsageRecord, 16> PHIUsers; + + // PHIs are often mutually cyclic, so we keep track of a whole set of PHI + // nodes which are extracted from. PHIsToSlice is a set we use to avoid + // revisiting PHIs, PHIsInspected is a ordered list of PHIs that we need to + // check the uses of (to ensure they are all extracts). + SmallVector<PHINode*, 8> PHIsToSlice; + SmallPtrSet<PHINode*, 8> PHIsInspected; + + PHIsToSlice.push_back(&FirstPhi); + PHIsInspected.insert(&FirstPhi); + + for (unsigned PHIId = 0; PHIId != PHIsToSlice.size(); ++PHIId) { + PHINode *PN = PHIsToSlice[PHIId]; + + // Scan the input list of the PHI. If any input is an invoke, and if the + // input is defined in the predecessor, then we won't be split the critical + // edge which is required to insert a truncate. Because of this, we have to + // bail out. + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + InvokeInst *II = dyn_cast<InvokeInst>(PN->getIncomingValue(i)); + if (!II) continue; + if (II->getParent() != PN->getIncomingBlock(i)) + continue; + + // If we have a phi, and if it's directly in the predecessor, then we have + // a critical edge where we need to put the truncate. Since we can't + // split the edge in instcombine, we have to bail out. + return nullptr; + } + + for (User *U : PN->users()) { + Instruction *UserI = cast<Instruction>(U); + + // If the user is a PHI, inspect its uses recursively. + if (PHINode *UserPN = dyn_cast<PHINode>(UserI)) { + if (PHIsInspected.insert(UserPN).second) + PHIsToSlice.push_back(UserPN); + continue; + } + + // Truncates are always ok. + if (isa<TruncInst>(UserI)) { + PHIUsers.push_back(PHIUsageRecord(PHIId, 0, UserI)); + continue; + } + + // Otherwise it must be a lshr which can only be used by one trunc. + if (UserI->getOpcode() != Instruction::LShr || + !UserI->hasOneUse() || !isa<TruncInst>(UserI->user_back()) || + !isa<ConstantInt>(UserI->getOperand(1))) + return nullptr; + + // Bail on out of range shifts. + unsigned SizeInBits = UserI->getType()->getScalarSizeInBits(); + if (cast<ConstantInt>(UserI->getOperand(1))->getValue().uge(SizeInBits)) + return nullptr; + + unsigned Shift = cast<ConstantInt>(UserI->getOperand(1))->getZExtValue(); + PHIUsers.push_back(PHIUsageRecord(PHIId, Shift, UserI->user_back())); + } + } + + // If we have no users, they must be all self uses, just nuke the PHI. + if (PHIUsers.empty()) + return replaceInstUsesWith(FirstPhi, UndefValue::get(FirstPhi.getType())); + + // If this phi node is transformable, create new PHIs for all the pieces + // extracted out of it. First, sort the users by their offset and size. + array_pod_sort(PHIUsers.begin(), PHIUsers.end()); + + LLVM_DEBUG(dbgs() << "SLICING UP PHI: " << FirstPhi << '\n'; + for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i) dbgs() + << "AND USER PHI #" << i << ": " << *PHIsToSlice[i] << '\n';); + + // PredValues - This is a temporary used when rewriting PHI nodes. It is + // hoisted out here to avoid construction/destruction thrashing. + DenseMap<BasicBlock*, Value*> PredValues; + + // ExtractedVals - Each new PHI we introduce is saved here so we don't + // introduce redundant PHIs. + DenseMap<LoweredPHIRecord, PHINode*> ExtractedVals; + + for (unsigned UserI = 0, UserE = PHIUsers.size(); UserI != UserE; ++UserI) { + unsigned PHIId = PHIUsers[UserI].PHIId; + PHINode *PN = PHIsToSlice[PHIId]; + unsigned Offset = PHIUsers[UserI].Shift; + Type *Ty = PHIUsers[UserI].Inst->getType(); + + PHINode *EltPHI; + + // If we've already lowered a user like this, reuse the previously lowered + // value. + if ((EltPHI = ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)]) == nullptr) { + + // Otherwise, Create the new PHI node for this user. + EltPHI = PHINode::Create(Ty, PN->getNumIncomingValues(), + PN->getName()+".off"+Twine(Offset), PN); + assert(EltPHI->getType() != PN->getType() && + "Truncate didn't shrink phi?"); + + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + BasicBlock *Pred = PN->getIncomingBlock(i); + Value *&PredVal = PredValues[Pred]; + + // If we already have a value for this predecessor, reuse it. + if (PredVal) { + EltPHI->addIncoming(PredVal, Pred); + continue; + } + + // Handle the PHI self-reuse case. + Value *InVal = PN->getIncomingValue(i); + if (InVal == PN) { + PredVal = EltPHI; + EltPHI->addIncoming(PredVal, Pred); + continue; + } + + if (PHINode *InPHI = dyn_cast<PHINode>(PN)) { + // If the incoming value was a PHI, and if it was one of the PHIs we + // already rewrote it, just use the lowered value. + if (Value *Res = ExtractedVals[LoweredPHIRecord(InPHI, Offset, Ty)]) { + PredVal = Res; + EltPHI->addIncoming(PredVal, Pred); + continue; + } + } + + // Otherwise, do an extract in the predecessor. + Builder.SetInsertPoint(Pred->getTerminator()); + Value *Res = InVal; + if (Offset) + Res = Builder.CreateLShr(Res, ConstantInt::get(InVal->getType(), + Offset), "extract"); + Res = Builder.CreateTrunc(Res, Ty, "extract.t"); + PredVal = Res; + EltPHI->addIncoming(Res, Pred); + + // If the incoming value was a PHI, and if it was one of the PHIs we are + // rewriting, we will ultimately delete the code we inserted. This + // means we need to revisit that PHI to make sure we extract out the + // needed piece. + if (PHINode *OldInVal = dyn_cast<PHINode>(PN->getIncomingValue(i))) + if (PHIsInspected.count(OldInVal)) { + unsigned RefPHIId = + find(PHIsToSlice, OldInVal) - PHIsToSlice.begin(); + PHIUsers.push_back(PHIUsageRecord(RefPHIId, Offset, + cast<Instruction>(Res))); + ++UserE; + } + } + PredValues.clear(); + + LLVM_DEBUG(dbgs() << " Made element PHI for offset " << Offset << ": " + << *EltPHI << '\n'); + ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)] = EltPHI; + } + + // Replace the use of this piece with the PHI node. + replaceInstUsesWith(*PHIUsers[UserI].Inst, EltPHI); + } + + // Replace all the remaining uses of the PHI nodes (self uses and the lshrs) + // with undefs. + Value *Undef = UndefValue::get(FirstPhi.getType()); + for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i) + replaceInstUsesWith(*PHIsToSlice[i], Undef); + return replaceInstUsesWith(FirstPhi, Undef); +} + +// PHINode simplification +// +Instruction *InstCombiner::visitPHINode(PHINode &PN) { + if (Value *V = SimplifyInstruction(&PN, SQ.getWithInstruction(&PN))) + return replaceInstUsesWith(PN, V); + + if (Instruction *Result = FoldPHIArgZextsIntoPHI(PN)) + return Result; + + // If all PHI operands are the same operation, pull them through the PHI, + // reducing code size. + if (isa<Instruction>(PN.getIncomingValue(0)) && + isa<Instruction>(PN.getIncomingValue(1)) && + cast<Instruction>(PN.getIncomingValue(0))->getOpcode() == + cast<Instruction>(PN.getIncomingValue(1))->getOpcode() && + // FIXME: The hasOneUse check will fail for PHIs that use the value more + // than themselves more than once. + PN.getIncomingValue(0)->hasOneUse()) + if (Instruction *Result = FoldPHIArgOpIntoPHI(PN)) + return Result; + + // If this is a trivial cycle in the PHI node graph, remove it. Basically, if + // this PHI only has a single use (a PHI), and if that PHI only has one use (a + // PHI)... break the cycle. + if (PN.hasOneUse()) { + if (Instruction *Result = FoldIntegerTypedPHI(PN)) + return Result; + + Instruction *PHIUser = cast<Instruction>(PN.user_back()); + if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) { + SmallPtrSet<PHINode*, 16> PotentiallyDeadPHIs; + PotentiallyDeadPHIs.insert(&PN); + if (DeadPHICycle(PU, PotentiallyDeadPHIs)) + return replaceInstUsesWith(PN, UndefValue::get(PN.getType())); + } + + // If this phi has a single use, and if that use just computes a value for + // the next iteration of a loop, delete the phi. This occurs with unused + // induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this + // common case here is good because the only other things that catch this + // are induction variable analysis (sometimes) and ADCE, which is only run + // late. + if (PHIUser->hasOneUse() && + (isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) && + PHIUser->user_back() == &PN) { + return replaceInstUsesWith(PN, UndefValue::get(PN.getType())); + } + // When a PHI is used only to be compared with zero, it is safe to replace + // an incoming value proved as known nonzero with any non-zero constant. + // For example, in the code below, the incoming value %v can be replaced + // with any non-zero constant based on the fact that the PHI is only used to + // be compared with zero and %v is a known non-zero value: + // %v = select %cond, 1, 2 + // %p = phi [%v, BB] ... + // icmp eq, %p, 0 + auto *CmpInst = dyn_cast<ICmpInst>(PHIUser); + // FIXME: To be simple, handle only integer type for now. + if (CmpInst && isa<IntegerType>(PN.getType()) && CmpInst->isEquality() && + match(CmpInst->getOperand(1), m_Zero())) { + ConstantInt *NonZeroConst = nullptr; + for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) { + Instruction *CtxI = PN.getIncomingBlock(i)->getTerminator(); + Value *VA = PN.getIncomingValue(i); + if (isKnownNonZero(VA, DL, 0, &AC, CtxI, &DT)) { + if (!NonZeroConst) + NonZeroConst = GetAnyNonZeroConstInt(PN); + PN.setIncomingValue(i, NonZeroConst); + } + } + } + } + + // We sometimes end up with phi cycles that non-obviously end up being the + // same value, for example: + // z = some value; x = phi (y, z); y = phi (x, z) + // where the phi nodes don't necessarily need to be in the same block. Do a + // quick check to see if the PHI node only contains a single non-phi value, if + // so, scan to see if the phi cycle is actually equal to that value. + { + unsigned InValNo = 0, NumIncomingVals = PN.getNumIncomingValues(); + // Scan for the first non-phi operand. + while (InValNo != NumIncomingVals && + isa<PHINode>(PN.getIncomingValue(InValNo))) + ++InValNo; + + if (InValNo != NumIncomingVals) { + Value *NonPhiInVal = PN.getIncomingValue(InValNo); + + // Scan the rest of the operands to see if there are any conflicts, if so + // there is no need to recursively scan other phis. + for (++InValNo; InValNo != NumIncomingVals; ++InValNo) { + Value *OpVal = PN.getIncomingValue(InValNo); + if (OpVal != NonPhiInVal && !isa<PHINode>(OpVal)) + break; + } + + // If we scanned over all operands, then we have one unique value plus + // phi values. Scan PHI nodes to see if they all merge in each other or + // the value. + if (InValNo == NumIncomingVals) { + SmallPtrSet<PHINode*, 16> ValueEqualPHIs; + if (PHIsEqualValue(&PN, NonPhiInVal, ValueEqualPHIs)) + return replaceInstUsesWith(PN, NonPhiInVal); + } + } + } + + // If there are multiple PHIs, sort their operands so that they all list + // the blocks in the same order. This will help identical PHIs be eliminated + // by other passes. Other passes shouldn't depend on this for correctness + // however. + PHINode *FirstPN = cast<PHINode>(PN.getParent()->begin()); + if (&PN != FirstPN) + for (unsigned i = 0, e = FirstPN->getNumIncomingValues(); i != e; ++i) { + BasicBlock *BBA = PN.getIncomingBlock(i); + BasicBlock *BBB = FirstPN->getIncomingBlock(i); + if (BBA != BBB) { + Value *VA = PN.getIncomingValue(i); + unsigned j = PN.getBasicBlockIndex(BBB); + Value *VB = PN.getIncomingValue(j); + PN.setIncomingBlock(i, BBB); + PN.setIncomingValue(i, VB); + PN.setIncomingBlock(j, BBA); + PN.setIncomingValue(j, VA); + // NOTE: Instcombine normally would want us to "return &PN" if we + // modified any of the operands of an instruction. However, since we + // aren't adding or removing uses (just rearranging them) we don't do + // this in this case. + } + } + + // If this is an integer PHI and we know that it has an illegal type, see if + // it is only used by trunc or trunc(lshr) operations. If so, we split the + // PHI into the various pieces being extracted. This sort of thing is + // introduced when SROA promotes an aggregate to a single large integer type. + if (PN.getType()->isIntegerTy() && + !DL.isLegalInteger(PN.getType()->getPrimitiveSizeInBits())) + if (Instruction *Res = SliceUpIllegalIntegerPHI(PN)) + return Res; + + return nullptr; +} |