//===- InstCombinePHI.cpp -------------------------------------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file implements the visitPHINode function. // //===----------------------------------------------------------------------===// #include "InstCombine.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/IR/DataLayout.h" using namespace llvm; #define DEBUG_TYPE "instcombine" /// FoldPHIArgBinOpIntoPHI - If we have something like phi [add (a,b), add(a,c)] /// and if a/b/c and the add's 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(); bool isNUW = false, isNSW = false, isExact = false; if (OverflowingBinaryOperator *BO = dyn_cast<OverflowingBinaryOperator>(FirstInst)) { isNUW = BO->hasNoUnsignedWrap(); isNSW = BO->hasNoSignedWrap(); } else if (PossiblyExactOperator *PEO = dyn_cast<PossiblyExactOperator>(FirstInst)) isExact = PEO->isExact(); // 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; if (isNUW) isNUW = cast<OverflowingBinaryOperator>(I)->hasNoUnsignedWrap(); if (isNSW) isNSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap(); if (isExact) isExact = cast<PossiblyExactOperator>(I)->isExact(); // 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); NewCI->setDebugLoc(FirstInst->getDebugLoc()); return NewCI; } BinaryOperator *BinOp = cast<BinaryOperator>(FirstInst); BinaryOperator *NewBinOp = BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal); if (isNUW) NewBinOp->setHasNoUnsignedWrap(); if (isNSW) NewBinOp->setHasNoSignedWrap(); if (isExact) NewBinOp->setIsExact(); NewBinOp->setDebugLoc(FirstInst->getDebugLoc()); 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(Base, makeArrayRef(FixedOperands).slice(1)); if (AllInBounds) NewGEP->setIsInBounds(); NewGEP->setDebugLoc(FirstInst->getDebugLoc()); return NewGEP; } /// isSafeAndProfitableToSinkLoad - 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, 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(); unsigned 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 != 0) != (LI->getAlignment() != 0)) return nullptr; LoadAlignment = std::min(LoadAlignment, 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)); // Add all operands to the new PHI. for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { Value *NewInVal = cast<LoadInst>(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; } // 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 (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) cast<LoadInst>(PN.getIncomingValue(i))->setVolatile(false); LoadInst *NewLI = new LoadInst(PhiVal, "", isVolatile, LoadAlignment); NewLI->setDebugLoc(FirstLI->getDebugLoc()); return NewLI; } /// FoldPHIArgOpIntoPHI - 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) { 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; bool isNUW = false, isNSW = false, isExact = false; 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); if (OverflowingBinaryOperator *BO = dyn_cast<OverflowingBinaryOperator>(FirstInst)) { isNUW = BO->hasNoUnsignedWrap(); isNSW = BO->hasNoSignedWrap(); } else if (PossiblyExactOperator *PEO = dyn_cast<PossiblyExactOperator>(FirstInst)) isExact = PEO->isExact(); } 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; } if (isNUW) isNUW = cast<OverflowingBinaryOperator>(I)->hasNoUnsignedWrap(); if (isNSW) isNSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap(); if (isExact) isExact = cast<PossiblyExactOperator>(I)->isExact(); } // 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()); NewCI->setDebugLoc(FirstInst->getDebugLoc()); return NewCI; } if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) { BinOp = BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp); if (isNUW) BinOp->setHasNoUnsignedWrap(); if (isNSW) BinOp->setHasNoSignedWrap(); if (isExact) BinOp->setIsExact(); BinOp->setDebugLoc(FirstInst->getDebugLoc()); return BinOp; } CmpInst *CIOp = cast<CmpInst>(FirstInst); CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), PhiVal, ConstantOp); NewCI->setDebugLoc(FirstInst->getDebugLoc()); return NewCI; } /// DeadPHICycle - Return true if this PHI node is only used by a PHI node cycle /// that is dead. static bool DeadPHICycle(PHINode *PN, SmallPtrSet<PHINode*, 16> &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)) 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; } /// PHIsEqualValue - 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, SmallPtrSet<PHINode*, 16> &ValueEqualPHIs) { // See if we already saw this PHI node. if (!ValueEqualPHIs.insert(PN)) 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 (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { Value *Op = PN->getIncomingValue(i); if (PHINode *OpPN = dyn_cast<PHINode>(Op)) { if (!PHIsEqualValue(OpPN, NonPhiInVal, ValueEqualPHIs)) return false; } else if (Op != NonPhiInVal) return false; } return true; } 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; } }; } /// SliceUpIllegalIntegerPHI - 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)) 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; 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()); 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, 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 = std::find(PHIsToSlice.begin(),PHIsToSlice.end(), OldInVal)-PHIsToSlice.begin(); PHIUsers.push_back(PHIUsageRecord(RefPHIId, Offset, cast<Instruction>(Res))); ++UserE; } } PredValues.clear(); 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, DL, TLI)) return ReplaceInstUsesWith(PN, V); // 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()) { 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())); } } // 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 && !DL->isLegalInteger(PN.getType()->getPrimitiveSizeInBits())) if (Instruction *Res = SliceUpIllegalIntegerPHI(PN)) return Res; return nullptr; }