| //===- 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/Analysis/InstructionSimplify.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); |
| |
| 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 0; |
| |
| // If they are CmpInst instructions, check their predicates |
| if (CmpInst *CI = dyn_cast<CmpInst>(I)) |
| if (CI->getPredicate() != cast<CmpInst>(FirstInst)->getPredicate()) |
| return 0; |
| |
| 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 = 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, PN.getNumIncomingValues(), |
| FirstInst->getOperand(0)->getName() + ".pn"); |
| NewLHS->addIncoming(InLHS, PN.getIncomingBlock(0)); |
| InsertNewInstBefore(NewLHS, PN); |
| LHSVal = NewLHS; |
| } |
| |
| if (RHSVal == 0) { |
| 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 0; |
| |
| 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 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(), 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 (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); |
| UI != E; ++UI) { |
| User *U = *UI; |
| 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 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.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 = 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); |
| |
| 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 = 0; |
| Type *CastSrcTy = 0; |
| 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 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); |
| |
| 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 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; |
| } |
| |
| 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 = 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)) { |
| 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->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, 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; |
| 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->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(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 (Value *V = SimplifyInstruction(&PN, TD)) |
| 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, 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() && TD && |
| !TD->isLegalInteger(PN.getType()->getPrimitiveSizeInBits())) |
| if (Instruction *Res = SliceUpIllegalIntegerPHI(PN)) |
| return Res; |
| |
| return 0; |
| } |
