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Diffstat (limited to 'contrib/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp | 843 |
1 files changed, 843 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp b/contrib/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp new file mode 100644 index 0000000..65f0393 --- /dev/null +++ b/contrib/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp @@ -0,0 +1,843 @@ +//===- 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/Target/TargetData.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/STLExtras.h" +using namespace llvm; + +/// 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); + + const Type *LHSType = LHSVal->getType(); + const 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 or GEP's with different index types. + I->getOperand(0)->getType() != LHSType || + I->getOperand(1)->getType() != RHSType) + return 0; + + // If they are CmpInst instructions, check their predicates + if (Opc == Instruction::ICmp || Opc == Instruction::FCmp) + if (cast<CmpInst>(I)->getPredicate() != + cast<CmpInst>(FirstInst)->getPredicate()) + return 0; + + // Keep track of which operand needs a phi node. + if (I->getOperand(0) != LHSVal) LHSVal = 0; + if (I->getOperand(1) != RHSVal) RHSVal = 0; + } + + // 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 0; + + // Otherwise, this is safe to transform! + + Value *InLHS = FirstInst->getOperand(0); + Value *InRHS = FirstInst->getOperand(1); + PHINode *NewLHS = 0, *NewRHS = 0; + if (LHSVal == 0) { + NewLHS = PHINode::Create(LHSType, + FirstInst->getOperand(0)->getName() + ".pn"); + NewLHS->reserveOperandSpace(PN.getNumOperands()/2); + NewLHS->addIncoming(InLHS, PN.getIncomingBlock(0)); + InsertNewInstBefore(NewLHS, PN); + LHSVal = NewLHS; + } + + if (RHSVal == 0) { + NewRHS = PHINode::Create(RHSType, + FirstInst->getOperand(1)->getName() + ".pn"); + NewRHS->reserveOperandSpace(PN.getNumOperands()/2); + 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 (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) + return BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal); + CmpInst *CIOp = cast<CmpInst>(FirstInst); + return CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), + LHSVal, RHSVal); +} + +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; + + // 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 0; + + // 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 0; + + if (FirstInst->getOperand(op)->getType() !=GEP->getOperand(op)->getType()) + return 0; + + // 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 0; + + FixedOperands[op] = 0; // 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 0; + + // 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(), + FirstOp->getName()+".pn"); + InsertNewInstBefore(NewPN, PN); + + NewPN->reserveOperandSpace(e); + 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]; + return cast<GEPOperator>(FirstInst)->isInBounds() ? + GetElementPtrInst::CreateInBounds(Base, FixedOperands.begin()+1, + FixedOperands.end()) : + GetElementPtrInst::Create(Base, FixedOperands.begin()+1, + FixedOperands.end()); +} + + +/// 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 targetting 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 (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); + UI != E; ++UI) { + if (isa<LoadInst>(UI)) continue; + if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) { + // 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)); + + // 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 0; + + // 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 0; + + // 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 0; + + // 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 0; + + // 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 0; + + 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 0; + } + + // 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.getName()+".in"); + NewPN->reserveOperandSpace(PN.getNumOperands()/2); + + 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 = 0; + 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); + + return new LoadInst(PhiVal, "", isVolatile, LoadAlignment); +} + + + +/// 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 = 0; + const Type *CastSrcTy = 0; + + 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 0; + } + } 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 == 0) + return FoldPHIArgBinOpIntoPHI(PN); + } else { + return 0; // 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 == 0 || !I->hasOneUse() || !I->isSameOperationAs(FirstInst)) + return 0; + if (CastSrcTy) { + if (I->getOperand(0)->getType() != CastSrcTy) + return 0; // Cast operation must match. + } else if (I->getOperand(1) != ConstantOp) { + return 0; + } + } + + // 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.getName()+".in"); + NewPN->reserveOperandSpace(PN.getNumOperands()/2); + + 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 = 0; + 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)) + return CastInst::Create(FirstCI->getOpcode(), PhiVal, PN.getType()); + + if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) + return BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp); + + CmpInst *CIOp = cast<CmpInst>(FirstInst); + return CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), + PhiVal, ConstantOp); +} + +/// 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->use_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, const 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(0, 0); + } + static inline LoweredPHIRecord getTombstoneKey() { + return LoweredPHIRecord(0, 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; + } + }; + template <> + struct isPodLike<LoweredPHIRecord> { static const bool value = true; }; +} + + +/// 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 == 0) 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 0; + } + + + for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); + UI != E; ++UI) { + Instruction *User = cast<Instruction>(*UI); + + // If the user is a PHI, inspect its uses recursively. + if (PHINode *UserPN = dyn_cast<PHINode>(User)) { + if (PHIsInspected.insert(UserPN)) + PHIsToSlice.push_back(UserPN); + continue; + } + + // Truncates are always ok. + if (isa<TruncInst>(User)) { + PHIUsers.push_back(PHIUsageRecord(PHIId, 0, User)); + continue; + } + + // Otherwise it must be a lshr which can only be used by one trunc. + if (User->getOpcode() != Instruction::LShr || + !User->hasOneUse() || !isa<TruncInst>(User->use_back()) || + !isa<ConstantInt>(User->getOperand(1))) + return 0; + + unsigned Shift = cast<ConstantInt>(User->getOperand(1))->getZExtValue(); + PHIUsers.push_back(PHIUsageRecord(PHIId, Shift, User->use_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(errs() << "SLICING UP PHI: " << FirstPhi << '\n'; + for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i) + errs() << "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; + const 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)]) == 0) { + + // Otherwise, Create the new PHI node for this user. + EltPHI = PHINode::Create(Ty, 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(errs() << " 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 LCSSA is around, don't mess with Phi nodes + if (MustPreserveLCSSA) return 0; + + if (Value *V = PN.hasConstantValue()) + 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.use_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->use_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, NumOperandVals = PN.getNumIncomingValues(); + // Scan for the first non-phi operand. + while (InValNo != NumOperandVals && + isa<PHINode>(PN.getIncomingValue(InValNo))) + ++InValNo; + + if (InValNo != NumOperandVals) { + Value *NonPhiInVal = PN.getOperand(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 != NumOperandVals; ++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 == NumOperandVals) { + 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() && TD && + !TD->isLegalInteger(PN.getType()->getPrimitiveSizeInBits())) + if (Instruction *Res = SliceUpIllegalIntegerPHI(PN)) + return Res; + + return 0; +} |
