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//===- InstCombinePHI.cpp -------------------------------------------------===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// This file implements the visitPHINode function.
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//===----------------------------------------------------------------------===//
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#include "InstCombine.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/STLExtras.h"
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/// FoldPHIArgBinOpIntoPHI - If we have something like phi [add (a,b), add(a,c)]
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/// and if a/b/c and the add's all have a single use, turn this into a phi
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/// and a single binop.
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Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) {
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Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
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assert(isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst));
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unsigned Opc = FirstInst->getOpcode();
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Value *LHSVal = FirstInst->getOperand(0);
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Value *RHSVal = FirstInst->getOperand(1);
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const Type *LHSType = LHSVal->getType();
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const Type *RHSType = RHSVal->getType();
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// Scan to see if all operands are the same opcode, and all have one use.
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for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
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Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
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if (!I || I->getOpcode() != Opc || !I->hasOneUse() ||
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// Verify type of the LHS matches so we don't fold cmp's of different
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// types or GEP's with different index types.
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I->getOperand(0)->getType() != LHSType ||
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I->getOperand(1)->getType() != RHSType)
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// If they are CmpInst instructions, check their predicates
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if (Opc == Instruction::ICmp || Opc == Instruction::FCmp)
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if (cast<CmpInst>(I)->getPredicate() !=
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cast<CmpInst>(FirstInst)->getPredicate())
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// Keep track of which operand needs a phi node.
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if (I->getOperand(0) != LHSVal) LHSVal = 0;
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if (I->getOperand(1) != RHSVal) RHSVal = 0;
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// If both LHS and RHS would need a PHI, don't do this transformation,
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// because it would increase the number of PHIs entering the block,
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// which leads to higher register pressure. This is especially
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// bad when the PHIs are in the header of a loop.
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if (!LHSVal && !RHSVal)
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// Otherwise, this is safe to transform!
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Value *InLHS = FirstInst->getOperand(0);
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Value *InRHS = FirstInst->getOperand(1);
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PHINode *NewLHS = 0, *NewRHS = 0;
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NewLHS = PHINode::Create(LHSType,
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FirstInst->getOperand(0)->getName() + ".pn");
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NewLHS->reserveOperandSpace(PN.getNumOperands()/2);
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NewLHS->addIncoming(InLHS, PN.getIncomingBlock(0));
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InsertNewInstBefore(NewLHS, PN);
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NewRHS = PHINode::Create(RHSType,
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FirstInst->getOperand(1)->getName() + ".pn");
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NewRHS->reserveOperandSpace(PN.getNumOperands()/2);
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NewRHS->addIncoming(InRHS, PN.getIncomingBlock(0));
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InsertNewInstBefore(NewRHS, PN);
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// Add all operands to the new PHIs.
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if (NewLHS || NewRHS) {
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for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
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Instruction *InInst = cast<Instruction>(PN.getIncomingValue(i));
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Value *NewInLHS = InInst->getOperand(0);
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NewLHS->addIncoming(NewInLHS, PN.getIncomingBlock(i));
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Value *NewInRHS = InInst->getOperand(1);
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NewRHS->addIncoming(NewInRHS, PN.getIncomingBlock(i));
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if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst))
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return BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal);
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CmpInst *CIOp = cast<CmpInst>(FirstInst);
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return CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(),
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Instruction *InstCombiner::FoldPHIArgGEPIntoPHI(PHINode &PN) {
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GetElementPtrInst *FirstInst =cast<GetElementPtrInst>(PN.getIncomingValue(0));
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SmallVector<Value*, 16> FixedOperands(FirstInst->op_begin(),
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FirstInst->op_end());
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// This is true if all GEP bases are allocas and if all indices into them are
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bool AllBasePointersAreAllocas = true;
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// We don't want to replace this phi if the replacement would require
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// more than one phi, which leads to higher register pressure. This is
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// especially bad when the PHIs are in the header of a loop.
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bool NeededPhi = false;
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// Scan to see if all operands are the same opcode, and all have one use.
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for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
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GetElementPtrInst *GEP= dyn_cast<GetElementPtrInst>(PN.getIncomingValue(i));
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if (!GEP || !GEP->hasOneUse() || GEP->getType() != FirstInst->getType() ||
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GEP->getNumOperands() != FirstInst->getNumOperands())
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// Keep track of whether or not all GEPs are of alloca pointers.
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if (AllBasePointersAreAllocas &&
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(!isa<AllocaInst>(GEP->getOperand(0)) ||
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!GEP->hasAllConstantIndices()))
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AllBasePointersAreAllocas = false;
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// Compare the operand lists.
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for (unsigned op = 0, e = FirstInst->getNumOperands(); op != e; ++op) {
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if (FirstInst->getOperand(op) == GEP->getOperand(op))
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// Don't merge two GEPs when two operands differ (introducing phi nodes)
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// if one of the PHIs has a constant for the index. The index may be
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// substantially cheaper to compute for the constants, so making it a
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// variable index could pessimize the path. This also handles the case
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// for struct indices, which must always be constant.
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if (isa<ConstantInt>(FirstInst->getOperand(op)) ||
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isa<ConstantInt>(GEP->getOperand(op)))
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if (FirstInst->getOperand(op)->getType() !=GEP->getOperand(op)->getType())
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// If we already needed a PHI for an earlier operand, and another operand
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// also requires a PHI, we'd be introducing more PHIs than we're
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// eliminating, which increases register pressure on entry to the PHI's
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FixedOperands[op] = 0; // Needs a PHI.
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// If all of the base pointers of the PHI'd GEPs are from allocas, don't
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// bother doing this transformation. At best, this will just save a bit of
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// offset calculation, but all the predecessors will have to materialize the
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// stack address into a register anyway. We'd actually rather *clone* the
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// load up into the predecessors so that we have a load of a gep of an alloca,
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// which can usually all be folded into the load.
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if (AllBasePointersAreAllocas)
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// Otherwise, this is safe to transform. Insert PHI nodes for each operand
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SmallVector<PHINode*, 16> OperandPhis(FixedOperands.size());
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bool HasAnyPHIs = false;
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for (unsigned i = 0, e = FixedOperands.size(); i != e; ++i) {
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if (FixedOperands[i]) continue; // operand doesn't need a phi.
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Value *FirstOp = FirstInst->getOperand(i);
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PHINode *NewPN = PHINode::Create(FirstOp->getType(),
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FirstOp->getName()+".pn");
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InsertNewInstBefore(NewPN, PN);
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NewPN->reserveOperandSpace(e);
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NewPN->addIncoming(FirstOp, PN.getIncomingBlock(0));
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OperandPhis[i] = NewPN;
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FixedOperands[i] = NewPN;
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// Add all operands to the new PHIs.
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for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
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GetElementPtrInst *InGEP =cast<GetElementPtrInst>(PN.getIncomingValue(i));
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BasicBlock *InBB = PN.getIncomingBlock(i);
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for (unsigned op = 0, e = OperandPhis.size(); op != e; ++op)
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if (PHINode *OpPhi = OperandPhis[op])
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OpPhi->addIncoming(InGEP->getOperand(op), InBB);
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Value *Base = FixedOperands[0];
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return cast<GEPOperator>(FirstInst)->isInBounds() ?
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GetElementPtrInst::CreateInBounds(Base, FixedOperands.begin()+1,
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FixedOperands.end()) :
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GetElementPtrInst::Create(Base, FixedOperands.begin()+1,
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FixedOperands.end());
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/// isSafeAndProfitableToSinkLoad - Return true if we know that it is safe to
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/// sink the load out of the block that defines it. This means that it must be
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/// obvious the value of the load is not changed from the point of the load to
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/// the end of the block it is in.
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/// Finally, it is safe, but not profitable, to sink a load targetting a
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/// non-address-taken alloca. Doing so will cause us to not promote the alloca
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static bool isSafeAndProfitableToSinkLoad(LoadInst *L) {
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BasicBlock::iterator BBI = L, E = L->getParent()->end();
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for (++BBI; BBI != E; ++BBI)
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if (BBI->mayWriteToMemory())
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// Check for non-address taken alloca. If not address-taken already, it isn't
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// profitable to do this xform.
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if (AllocaInst *AI = dyn_cast<AllocaInst>(L->getOperand(0))) {
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bool isAddressTaken = false;
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for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
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if (isa<LoadInst>(UI)) continue;
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if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
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// If storing TO the alloca, then the address isn't taken.
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if (SI->getOperand(1) == AI) continue;
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isAddressTaken = true;
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if (!isAddressTaken && AI->isStaticAlloca())
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// If this load is a load from a GEP with a constant offset from an alloca,
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// then we don't want to sink it. In its present form, it will be
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// load [constant stack offset]. Sinking it will cause us to have to
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// materialize the stack addresses in each predecessor in a register only to
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// do a shared load from register in the successor.
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if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(L->getOperand(0)))
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if (AllocaInst *AI = dyn_cast<AllocaInst>(GEP->getOperand(0)))
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if (AI->isStaticAlloca() && GEP->hasAllConstantIndices())
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Instruction *InstCombiner::FoldPHIArgLoadIntoPHI(PHINode &PN) {
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LoadInst *FirstLI = cast<LoadInst>(PN.getIncomingValue(0));
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// When processing loads, we need to propagate two bits of information to the
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// sunk load: whether it is volatile, and what its alignment is. We currently
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// don't sink loads when some have their alignment specified and some don't.
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// visitLoadInst will propagate an alignment onto the load when TD is around,
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// and if TD isn't around, we can't handle the mixed case.
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bool isVolatile = FirstLI->isVolatile();
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unsigned LoadAlignment = FirstLI->getAlignment();
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unsigned LoadAddrSpace = FirstLI->getPointerAddressSpace();
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// We can't sink the load if the loaded value could be modified between the
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if (FirstLI->getParent() != PN.getIncomingBlock(0) ||
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!isSafeAndProfitableToSinkLoad(FirstLI))
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// If the PHI is of volatile loads and the load block has multiple
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// successors, sinking it would remove a load of the volatile value from
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// the path through the other successor.
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FirstLI->getParent()->getTerminator()->getNumSuccessors() != 1)
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// Check to see if all arguments are the same operation.
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for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
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LoadInst *LI = dyn_cast<LoadInst>(PN.getIncomingValue(i));
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if (!LI || !LI->hasOneUse())
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// We can't sink the load if the loaded value could be modified between
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// the load and the PHI.
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if (LI->isVolatile() != isVolatile ||
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LI->getParent() != PN.getIncomingBlock(i) ||
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LI->getPointerAddressSpace() != LoadAddrSpace ||
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!isSafeAndProfitableToSinkLoad(LI))
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// If some of the loads have an alignment specified but not all of them,
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// we can't do the transformation.
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if ((LoadAlignment != 0) != (LI->getAlignment() != 0))
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LoadAlignment = std::min(LoadAlignment, LI->getAlignment());
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// If the PHI is of volatile loads and the load block has multiple
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// successors, sinking it would remove a load of the volatile value from
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// the path through the other successor.
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LI->getParent()->getTerminator()->getNumSuccessors() != 1)
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// Okay, they are all the same operation. Create a new PHI node of the
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// correct type, and PHI together all of the LHS's of the instructions.
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PHINode *NewPN = PHINode::Create(FirstLI->getOperand(0)->getType(),
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NewPN->reserveOperandSpace(PN.getNumOperands()/2);
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Value *InVal = FirstLI->getOperand(0);
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NewPN->addIncoming(InVal, PN.getIncomingBlock(0));
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// Add all operands to the new PHI.
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for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
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Value *NewInVal = cast<LoadInst>(PN.getIncomingValue(i))->getOperand(0);
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if (NewInVal != InVal)
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NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i));
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// The new PHI unions all of the same values together. This is really
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// common, so we handle it intelligently here for compile-time speed.
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InsertNewInstBefore(NewPN, PN);
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// If this was a volatile load that we are merging, make sure to loop through
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// and mark all the input loads as non-volatile. If we don't do this, we will
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// insert a new volatile load and the old ones will not be deletable.
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for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
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cast<LoadInst>(PN.getIncomingValue(i))->setVolatile(false);
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return new LoadInst(PhiVal, "", isVolatile, LoadAlignment);
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/// FoldPHIArgOpIntoPHI - If all operands to a PHI node are the same "unary"
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/// operator and they all are only used by the PHI, PHI together their
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/// inputs, and do the operation once, to the result of the PHI.
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Instruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) {
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Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
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if (isa<GetElementPtrInst>(FirstInst))
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return FoldPHIArgGEPIntoPHI(PN);
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if (isa<LoadInst>(FirstInst))
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return FoldPHIArgLoadIntoPHI(PN);
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// Scan the instruction, looking for input operations that can be folded away.
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// If all input operands to the phi are the same instruction (e.g. a cast from
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// the same type or "+42") we can pull the operation through the PHI, reducing
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// code size and simplifying code.
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Constant *ConstantOp = 0;
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const Type *CastSrcTy = 0;
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if (isa<CastInst>(FirstInst)) {
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CastSrcTy = FirstInst->getOperand(0)->getType();
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// Be careful about transforming integer PHIs. We don't want to pessimize
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// the code by turning an i32 into an i1293.
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if (PN.getType()->isIntegerTy() && CastSrcTy->isIntegerTy()) {
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if (!ShouldChangeType(PN.getType(), CastSrcTy))
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} else if (isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)) {
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// Can fold binop, compare or shift here if the RHS is a constant,
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// otherwise call FoldPHIArgBinOpIntoPHI.
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ConstantOp = dyn_cast<Constant>(FirstInst->getOperand(1));
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return FoldPHIArgBinOpIntoPHI(PN);
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return 0; // Cannot fold this operation.
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// Check to see if all arguments are the same operation.
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for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
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Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
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if (I == 0 || !I->hasOneUse() || !I->isSameOperationAs(FirstInst))
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if (I->getOperand(0)->getType() != CastSrcTy)
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return 0; // Cast operation must match.
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} else if (I->getOperand(1) != ConstantOp) {
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// Okay, they are all the same operation. Create a new PHI node of the
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// correct type, and PHI together all of the LHS's of the instructions.
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PHINode *NewPN = PHINode::Create(FirstInst->getOperand(0)->getType(),
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NewPN->reserveOperandSpace(PN.getNumOperands()/2);
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Value *InVal = FirstInst->getOperand(0);
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NewPN->addIncoming(InVal, PN.getIncomingBlock(0));
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// Add all operands to the new PHI.
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for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
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Value *NewInVal = cast<Instruction>(PN.getIncomingValue(i))->getOperand(0);
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if (NewInVal != InVal)
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NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i));
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// The new PHI unions all of the same values together. This is really
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// common, so we handle it intelligently here for compile-time speed.
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InsertNewInstBefore(NewPN, PN);
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// Insert and return the new operation.
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if (CastInst *FirstCI = dyn_cast<CastInst>(FirstInst))
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return CastInst::Create(FirstCI->getOpcode(), PhiVal, PN.getType());
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if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst))
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return BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp);
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CmpInst *CIOp = cast<CmpInst>(FirstInst);
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return CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(),
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/// DeadPHICycle - Return true if this PHI node is only used by a PHI node cycle
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static bool DeadPHICycle(PHINode *PN,
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SmallPtrSet<PHINode*, 16> &PotentiallyDeadPHIs) {
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if (PN->use_empty()) return true;
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if (!PN->hasOneUse()) return false;
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// Remember this node, and if we find the cycle, return.
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if (!PotentiallyDeadPHIs.insert(PN))
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// Don't scan crazily complex things.
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if (PotentiallyDeadPHIs.size() == 16)
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if (PHINode *PU = dyn_cast<PHINode>(PN->use_back()))
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return DeadPHICycle(PU, PotentiallyDeadPHIs);
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/// PHIsEqualValue - Return true if this phi node is always equal to
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/// NonPhiInVal. This happens with mutually cyclic phi nodes like:
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/// z = some value; x = phi (y, z); y = phi (x, z)
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static bool PHIsEqualValue(PHINode *PN, Value *NonPhiInVal,
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SmallPtrSet<PHINode*, 16> &ValueEqualPHIs) {
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// See if we already saw this PHI node.
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if (!ValueEqualPHIs.insert(PN))
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// Don't scan crazily complex things.
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if (ValueEqualPHIs.size() == 16)
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// Scan the operands to see if they are either phi nodes or are equal to
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
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Value *Op = PN->getIncomingValue(i);
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if (PHINode *OpPN = dyn_cast<PHINode>(Op)) {
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if (!PHIsEqualValue(OpPN, NonPhiInVal, ValueEqualPHIs))
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} else if (Op != NonPhiInVal)
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struct PHIUsageRecord {
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unsigned PHIId; // The ID # of the PHI (something determinstic to sort on)
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unsigned Shift; // The amount shifted.
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Instruction *Inst; // The trunc instruction.
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PHIUsageRecord(unsigned pn, unsigned Sh, Instruction *User)
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: PHIId(pn), Shift(Sh), Inst(User) {}
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bool operator<(const PHIUsageRecord &RHS) const {
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if (PHIId < RHS.PHIId) return true;
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if (PHIId > RHS.PHIId) return false;
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if (Shift < RHS.Shift) return true;
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if (Shift > RHS.Shift) return false;
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return Inst->getType()->getPrimitiveSizeInBits() <
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RHS.Inst->getType()->getPrimitiveSizeInBits();
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struct LoweredPHIRecord {
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PHINode *PN; // The PHI that was lowered.
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unsigned Shift; // The amount shifted.
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unsigned Width; // The width extracted.
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LoweredPHIRecord(PHINode *pn, unsigned Sh, const Type *Ty)
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: PN(pn), Shift(Sh), Width(Ty->getPrimitiveSizeInBits()) {}
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// Ctor form used by DenseMap.
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LoweredPHIRecord(PHINode *pn, unsigned Sh)
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: PN(pn), Shift(Sh), Width(0) {}
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struct DenseMapInfo<LoweredPHIRecord> {
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static inline LoweredPHIRecord getEmptyKey() {
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return LoweredPHIRecord(0, 0);
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static inline LoweredPHIRecord getTombstoneKey() {
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return LoweredPHIRecord(0, 1);
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static unsigned getHashValue(const LoweredPHIRecord &Val) {
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return DenseMapInfo<PHINode*>::getHashValue(Val.PN) ^ (Val.Shift>>3) ^
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static bool isEqual(const LoweredPHIRecord &LHS,
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const LoweredPHIRecord &RHS) {
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return LHS.PN == RHS.PN && LHS.Shift == RHS.Shift &&
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LHS.Width == RHS.Width;
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struct isPodLike<LoweredPHIRecord> { static const bool value = true; };
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/// SliceUpIllegalIntegerPHI - This is an integer PHI and we know that it has an
550
/// illegal type: see if it is only used by trunc or trunc(lshr) operations. If
551
/// so, we split the PHI into the various pieces being extracted. This sort of
552
/// thing is introduced when SROA promotes an aggregate to large integer values.
554
/// TODO: The user of the trunc may be an bitcast to float/double/vector or an
555
/// inttoptr. We should produce new PHIs in the right type.
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Instruction *InstCombiner::SliceUpIllegalIntegerPHI(PHINode &FirstPhi) {
558
// PHIUsers - Keep track of all of the truncated values extracted from a set
559
// of PHIs, along with their offset. These are the things we want to rewrite.
560
SmallVector<PHIUsageRecord, 16> PHIUsers;
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// PHIs are often mutually cyclic, so we keep track of a whole set of PHI
563
// nodes which are extracted from. PHIsToSlice is a set we use to avoid
564
// revisiting PHIs, PHIsInspected is a ordered list of PHIs that we need to
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// check the uses of (to ensure they are all extracts).
566
SmallVector<PHINode*, 8> PHIsToSlice;
567
SmallPtrSet<PHINode*, 8> PHIsInspected;
569
PHIsToSlice.push_back(&FirstPhi);
570
PHIsInspected.insert(&FirstPhi);
572
for (unsigned PHIId = 0; PHIId != PHIsToSlice.size(); ++PHIId) {
573
PHINode *PN = PHIsToSlice[PHIId];
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// Scan the input list of the PHI. If any input is an invoke, and if the
576
// input is defined in the predecessor, then we won't be split the critical
577
// edge which is required to insert a truncate. Because of this, we have to
579
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
580
InvokeInst *II = dyn_cast<InvokeInst>(PN->getIncomingValue(i));
581
if (II == 0) continue;
582
if (II->getParent() != PN->getIncomingBlock(i))
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// If we have a phi, and if it's directly in the predecessor, then we have
586
// a critical edge where we need to put the truncate. Since we can't
587
// split the edge in instcombine, we have to bail out.
592
for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end();
594
Instruction *User = cast<Instruction>(*UI);
596
// If the user is a PHI, inspect its uses recursively.
597
if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
598
if (PHIsInspected.insert(UserPN))
599
PHIsToSlice.push_back(UserPN);
603
// Truncates are always ok.
604
if (isa<TruncInst>(User)) {
605
PHIUsers.push_back(PHIUsageRecord(PHIId, 0, User));
609
// Otherwise it must be a lshr which can only be used by one trunc.
610
if (User->getOpcode() != Instruction::LShr ||
611
!User->hasOneUse() || !isa<TruncInst>(User->use_back()) ||
612
!isa<ConstantInt>(User->getOperand(1)))
615
unsigned Shift = cast<ConstantInt>(User->getOperand(1))->getZExtValue();
616
PHIUsers.push_back(PHIUsageRecord(PHIId, Shift, User->use_back()));
620
// If we have no users, they must be all self uses, just nuke the PHI.
621
if (PHIUsers.empty())
622
return ReplaceInstUsesWith(FirstPhi, UndefValue::get(FirstPhi.getType()));
624
// If this phi node is transformable, create new PHIs for all the pieces
625
// extracted out of it. First, sort the users by their offset and size.
626
array_pod_sort(PHIUsers.begin(), PHIUsers.end());
628
DEBUG(errs() << "SLICING UP PHI: " << FirstPhi << '\n';
629
for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i)
630
errs() << "AND USER PHI #" << i << ": " << *PHIsToSlice[i] <<'\n';
633
// PredValues - This is a temporary used when rewriting PHI nodes. It is
634
// hoisted out here to avoid construction/destruction thrashing.
635
DenseMap<BasicBlock*, Value*> PredValues;
637
// ExtractedVals - Each new PHI we introduce is saved here so we don't
638
// introduce redundant PHIs.
639
DenseMap<LoweredPHIRecord, PHINode*> ExtractedVals;
641
for (unsigned UserI = 0, UserE = PHIUsers.size(); UserI != UserE; ++UserI) {
642
unsigned PHIId = PHIUsers[UserI].PHIId;
643
PHINode *PN = PHIsToSlice[PHIId];
644
unsigned Offset = PHIUsers[UserI].Shift;
645
const Type *Ty = PHIUsers[UserI].Inst->getType();
649
// If we've already lowered a user like this, reuse the previously lowered
651
if ((EltPHI = ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)]) == 0) {
653
// Otherwise, Create the new PHI node for this user.
654
EltPHI = PHINode::Create(Ty, PN->getName()+".off"+Twine(Offset), PN);
655
assert(EltPHI->getType() != PN->getType() &&
656
"Truncate didn't shrink phi?");
658
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
659
BasicBlock *Pred = PN->getIncomingBlock(i);
660
Value *&PredVal = PredValues[Pred];
662
// If we already have a value for this predecessor, reuse it.
664
EltPHI->addIncoming(PredVal, Pred);
668
// Handle the PHI self-reuse case.
669
Value *InVal = PN->getIncomingValue(i);
672
EltPHI->addIncoming(PredVal, Pred);
676
if (PHINode *InPHI = dyn_cast<PHINode>(PN)) {
677
// If the incoming value was a PHI, and if it was one of the PHIs we
678
// already rewrote it, just use the lowered value.
679
if (Value *Res = ExtractedVals[LoweredPHIRecord(InPHI, Offset, Ty)]) {
681
EltPHI->addIncoming(PredVal, Pred);
686
// Otherwise, do an extract in the predecessor.
687
Builder->SetInsertPoint(Pred, Pred->getTerminator());
690
Res = Builder->CreateLShr(Res, ConstantInt::get(InVal->getType(),
692
Res = Builder->CreateTrunc(Res, Ty, "extract.t");
694
EltPHI->addIncoming(Res, Pred);
696
// If the incoming value was a PHI, and if it was one of the PHIs we are
697
// rewriting, we will ultimately delete the code we inserted. This
698
// means we need to revisit that PHI to make sure we extract out the
700
if (PHINode *OldInVal = dyn_cast<PHINode>(PN->getIncomingValue(i)))
701
if (PHIsInspected.count(OldInVal)) {
702
unsigned RefPHIId = std::find(PHIsToSlice.begin(),PHIsToSlice.end(),
703
OldInVal)-PHIsToSlice.begin();
704
PHIUsers.push_back(PHIUsageRecord(RefPHIId, Offset,
705
cast<Instruction>(Res)));
711
DEBUG(errs() << " Made element PHI for offset " << Offset << ": "
713
ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)] = EltPHI;
716
// Replace the use of this piece with the PHI node.
717
ReplaceInstUsesWith(*PHIUsers[UserI].Inst, EltPHI);
720
// Replace all the remaining uses of the PHI nodes (self uses and the lshrs)
722
Value *Undef = UndefValue::get(FirstPhi.getType());
723
for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i)
724
ReplaceInstUsesWith(*PHIsToSlice[i], Undef);
725
return ReplaceInstUsesWith(FirstPhi, Undef);
728
// PHINode simplification
730
Instruction *InstCombiner::visitPHINode(PHINode &PN) {
731
// If LCSSA is around, don't mess with Phi nodes
732
if (MustPreserveLCSSA) return 0;
734
if (Value *V = PN.hasConstantValue())
735
return ReplaceInstUsesWith(PN, V);
737
// If all PHI operands are the same operation, pull them through the PHI,
738
// reducing code size.
739
if (isa<Instruction>(PN.getIncomingValue(0)) &&
740
isa<Instruction>(PN.getIncomingValue(1)) &&
741
cast<Instruction>(PN.getIncomingValue(0))->getOpcode() ==
742
cast<Instruction>(PN.getIncomingValue(1))->getOpcode() &&
743
// FIXME: The hasOneUse check will fail for PHIs that use the value more
744
// than themselves more than once.
745
PN.getIncomingValue(0)->hasOneUse())
746
if (Instruction *Result = FoldPHIArgOpIntoPHI(PN))
749
// If this is a trivial cycle in the PHI node graph, remove it. Basically, if
750
// this PHI only has a single use (a PHI), and if that PHI only has one use (a
751
// PHI)... break the cycle.
752
if (PN.hasOneUse()) {
753
Instruction *PHIUser = cast<Instruction>(PN.use_back());
754
if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) {
755
SmallPtrSet<PHINode*, 16> PotentiallyDeadPHIs;
756
PotentiallyDeadPHIs.insert(&PN);
757
if (DeadPHICycle(PU, PotentiallyDeadPHIs))
758
return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
761
// If this phi has a single use, and if that use just computes a value for
762
// the next iteration of a loop, delete the phi. This occurs with unused
763
// induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this
764
// common case here is good because the only other things that catch this
765
// are induction variable analysis (sometimes) and ADCE, which is only run
767
if (PHIUser->hasOneUse() &&
768
(isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) &&
769
PHIUser->use_back() == &PN) {
770
return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
774
// We sometimes end up with phi cycles that non-obviously end up being the
775
// same value, for example:
776
// z = some value; x = phi (y, z); y = phi (x, z)
777
// where the phi nodes don't necessarily need to be in the same block. Do a
778
// quick check to see if the PHI node only contains a single non-phi value, if
779
// so, scan to see if the phi cycle is actually equal to that value.
781
unsigned InValNo = 0, NumOperandVals = PN.getNumIncomingValues();
782
// Scan for the first non-phi operand.
783
while (InValNo != NumOperandVals &&
784
isa<PHINode>(PN.getIncomingValue(InValNo)))
787
if (InValNo != NumOperandVals) {
788
Value *NonPhiInVal = PN.getOperand(InValNo);
790
// Scan the rest of the operands to see if there are any conflicts, if so
791
// there is no need to recursively scan other phis.
792
for (++InValNo; InValNo != NumOperandVals; ++InValNo) {
793
Value *OpVal = PN.getIncomingValue(InValNo);
794
if (OpVal != NonPhiInVal && !isa<PHINode>(OpVal))
798
// If we scanned over all operands, then we have one unique value plus
799
// phi values. Scan PHI nodes to see if they all merge in each other or
801
if (InValNo == NumOperandVals) {
802
SmallPtrSet<PHINode*, 16> ValueEqualPHIs;
803
if (PHIsEqualValue(&PN, NonPhiInVal, ValueEqualPHIs))
804
return ReplaceInstUsesWith(PN, NonPhiInVal);
809
// If there are multiple PHIs, sort their operands so that they all list
810
// the blocks in the same order. This will help identical PHIs be eliminated
811
// by other passes. Other passes shouldn't depend on this for correctness
813
PHINode *FirstPN = cast<PHINode>(PN.getParent()->begin());
815
for (unsigned i = 0, e = FirstPN->getNumIncomingValues(); i != e; ++i) {
816
BasicBlock *BBA = PN.getIncomingBlock(i);
817
BasicBlock *BBB = FirstPN->getIncomingBlock(i);
819
Value *VA = PN.getIncomingValue(i);
820
unsigned j = PN.getBasicBlockIndex(BBB);
821
Value *VB = PN.getIncomingValue(j);
822
PN.setIncomingBlock(i, BBB);
823
PN.setIncomingValue(i, VB);
824
PN.setIncomingBlock(j, BBA);
825
PN.setIncomingValue(j, VA);
826
// NOTE: Instcombine normally would want us to "return &PN" if we
827
// modified any of the operands of an instruction. However, since we
828
// aren't adding or removing uses (just rearranging them) we don't do
829
// this in this case.
833
// If this is an integer PHI and we know that it has an illegal type, see if
834
// it is only used by trunc or trunc(lshr) operations. If so, we split the
835
// PHI into the various pieces being extracted. This sort of thing is
836
// introduced when SROA promotes an aggregate to a single large integer type.
837
if (PN.getType()->isIntegerTy() && TD &&
838
!TD->isLegalInteger(PN.getType()->getPrimitiveSizeInBits()))
839
if (Instruction *Res = SliceUpIllegalIntegerPHI(PN))