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1003 lines
39 KiB
1003 lines
39 KiB
//===- InstCombinePHI.cpp -------------------------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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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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//===----------------------------------------------------------------------===//
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//
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// This file implements the visitPHINode function.
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//
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//===----------------------------------------------------------------------===//
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#include "InstCombineInternal.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/PatternMatch.h"
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#include "llvm/Transforms/Utils/Local.h"
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using namespace llvm;
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using namespace llvm::PatternMatch;
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#define DEBUG_TYPE "instcombine"
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/// If we have something like phi [add (a,b), add(a,c)] and if a/b/c and the
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/// adds all have a single use, turn this into a phi 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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Type *LHSType = LHSVal->getType();
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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.
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I->getOperand(0)->getType() != LHSType ||
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I->getOperand(1)->getType() != RHSType)
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return nullptr;
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// If they are CmpInst instructions, check their predicates
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if (CmpInst *CI = dyn_cast<CmpInst>(I))
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if (CI->getPredicate() != cast<CmpInst>(FirstInst)->getPredicate())
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return nullptr;
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// Keep track of which operand needs a phi node.
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if (I->getOperand(0) != LHSVal) LHSVal = nullptr;
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if (I->getOperand(1) != RHSVal) RHSVal = nullptr;
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}
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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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return nullptr;
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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 = nullptr, *NewRHS = nullptr;
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if (!LHSVal) {
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NewLHS = PHINode::Create(LHSType, PN.getNumIncomingValues(),
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FirstInst->getOperand(0)->getName() + ".pn");
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NewLHS->addIncoming(InLHS, PN.getIncomingBlock(0));
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InsertNewInstBefore(NewLHS, PN);
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LHSVal = NewLHS;
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}
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if (!RHSVal) {
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NewRHS = PHINode::Create(RHSType, PN.getNumIncomingValues(),
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FirstInst->getOperand(1)->getName() + ".pn");
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NewRHS->addIncoming(InRHS, PN.getIncomingBlock(0));
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InsertNewInstBefore(NewRHS, PN);
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RHSVal = NewRHS;
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}
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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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if (NewLHS) {
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Value *NewInLHS = InInst->getOperand(0);
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NewLHS->addIncoming(NewInLHS, PN.getIncomingBlock(i));
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}
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if (NewRHS) {
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Value *NewInRHS = InInst->getOperand(1);
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NewRHS->addIncoming(NewInRHS, PN.getIncomingBlock(i));
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}
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}
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}
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if (CmpInst *CIOp = dyn_cast<CmpInst>(FirstInst)) {
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CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(),
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LHSVal, RHSVal);
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NewCI->setDebugLoc(FirstInst->getDebugLoc());
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return NewCI;
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}
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BinaryOperator *BinOp = cast<BinaryOperator>(FirstInst);
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BinaryOperator *NewBinOp =
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BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal);
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NewBinOp->copyIRFlags(PN.getIncomingValue(0));
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for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i)
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NewBinOp->andIRFlags(PN.getIncomingValue(i));
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NewBinOp->setDebugLoc(FirstInst->getDebugLoc());
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return NewBinOp;
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}
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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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// constants.
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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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bool AllInBounds = true;
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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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return nullptr;
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AllInBounds &= GEP->isInBounds();
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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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continue;
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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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return nullptr;
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if (FirstInst->getOperand(op)->getType() !=GEP->getOperand(op)->getType())
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return nullptr;
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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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// block.
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if (NeededPhi)
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return nullptr;
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FixedOperands[op] = nullptr; // Needs a PHI.
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NeededPhi = true;
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}
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}
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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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return nullptr;
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// Otherwise, this is safe to transform. Insert PHI nodes for each operand
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// that is variable.
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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(), e,
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FirstOp->getName()+".pn");
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InsertNewInstBefore(NewPN, PN);
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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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HasAnyPHIs = true;
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}
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// Add all operands to the new PHIs.
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if (HasAnyPHIs) {
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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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}
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}
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Value *Base = FixedOperands[0];
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GetElementPtrInst *NewGEP =
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GetElementPtrInst::Create(FirstInst->getSourceElementType(), Base,
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makeArrayRef(FixedOperands).slice(1));
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if (AllInBounds) NewGEP->setIsInBounds();
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NewGEP->setDebugLoc(FirstInst->getDebugLoc());
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return NewGEP;
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}
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/// Return true if we know that it is safe to sink the load out of the block
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/// that defines it. This means that it must be obvious the value of the load is
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/// not changed from the point of the load to the end of the block it is in.
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///
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/// Finally, it is safe, but not profitable, to sink a load targeting a
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/// non-address-taken alloca. Doing so will cause us to not promote the alloca
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/// to a register.
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static bool isSafeAndProfitableToSinkLoad(LoadInst *L) {
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BasicBlock::iterator BBI = L->getIterator(), E = L->getParent()->end();
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for (++BBI; BBI != E; ++BBI)
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if (BBI->mayWriteToMemory())
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return false;
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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 (User *U : AI->users()) {
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if (isa<LoadInst>(U)) continue;
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if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
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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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}
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isAddressTaken = true;
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break;
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}
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if (!isAddressTaken && AI->isStaticAlloca())
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return false;
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}
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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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return false;
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return true;
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}
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Instruction *InstCombiner::FoldPHIArgLoadIntoPHI(PHINode &PN) {
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LoadInst *FirstLI = cast<LoadInst>(PN.getIncomingValue(0));
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// FIXME: This is overconservative; this transform is allowed in some cases
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// for atomic operations.
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if (FirstLI->isAtomic())
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return nullptr;
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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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// load and the PHI.
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if (FirstLI->getParent() != PN.getIncomingBlock(0) ||
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!isSafeAndProfitableToSinkLoad(FirstLI))
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return nullptr;
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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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if (isVolatile &&
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FirstLI->getParent()->getTerminator()->getNumSuccessors() != 1)
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return nullptr;
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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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return nullptr;
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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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return nullptr;
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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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return nullptr;
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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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if (isVolatile &&
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LI->getParent()->getTerminator()->getNumSuccessors() != 1)
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return nullptr;
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}
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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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PN.getNumIncomingValues(),
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PN.getName()+".in");
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Value *InVal = FirstLI->getOperand(0);
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NewPN->addIncoming(InVal, PN.getIncomingBlock(0));
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LoadInst *NewLI = new LoadInst(NewPN, "", isVolatile, LoadAlignment);
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unsigned KnownIDs[] = {
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LLVMContext::MD_tbaa,
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LLVMContext::MD_range,
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LLVMContext::MD_invariant_load,
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LLVMContext::MD_alias_scope,
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LLVMContext::MD_noalias,
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LLVMContext::MD_nonnull,
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LLVMContext::MD_align,
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LLVMContext::MD_dereferenceable,
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LLVMContext::MD_dereferenceable_or_null,
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};
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for (unsigned ID : KnownIDs)
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NewLI->setMetadata(ID, FirstLI->getMetadata(ID));
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// Add all operands to the new PHI and combine TBAA metadata.
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for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
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LoadInst *LI = cast<LoadInst>(PN.getIncomingValue(i));
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combineMetadata(NewLI, LI, KnownIDs);
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Value *NewInVal = LI->getOperand(0);
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if (NewInVal != InVal)
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InVal = nullptr;
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NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i));
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}
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if (InVal) {
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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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NewLI->setOperand(0, InVal);
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delete NewPN;
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} else {
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InsertNewInstBefore(NewPN, PN);
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}
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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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if (isVolatile)
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for (Value *IncValue : PN.incoming_values())
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cast<LoadInst>(IncValue)->setVolatile(false);
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NewLI->setDebugLoc(FirstLI->getDebugLoc());
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return NewLI;
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}
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/// TODO: This function could handle other cast types, but then it might
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/// require special-casing a cast from the 'i1' type. See the comment in
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/// FoldPHIArgOpIntoPHI() about pessimizing illegal integer types.
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Instruction *InstCombiner::FoldPHIArgZextsIntoPHI(PHINode &Phi) {
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// We cannot create a new instruction after the PHI if the terminator is an
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// EHPad because there is no valid insertion point.
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if (TerminatorInst *TI = Phi.getParent()->getTerminator())
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if (TI->isEHPad())
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return nullptr;
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// Early exit for the common case of a phi with two operands. These are
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// handled elsewhere. See the comment below where we check the count of zexts
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// and constants for more details.
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unsigned NumIncomingValues = Phi.getNumIncomingValues();
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if (NumIncomingValues < 3)
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return nullptr;
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// Find the narrower type specified by the first zext.
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Type *NarrowType = nullptr;
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for (Value *V : Phi.incoming_values()) {
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if (auto *Zext = dyn_cast<ZExtInst>(V)) {
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NarrowType = Zext->getSrcTy();
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break;
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}
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}
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if (!NarrowType)
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return nullptr;
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// Walk the phi operands checking that we only have zexts or constants that
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// we can shrink for free. Store the new operands for the new phi.
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SmallVector<Value *, 4> NewIncoming;
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unsigned NumZexts = 0;
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unsigned NumConsts = 0;
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for (Value *V : Phi.incoming_values()) {
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if (auto *Zext = dyn_cast<ZExtInst>(V)) {
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// All zexts must be identical and have one use.
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if (Zext->getSrcTy() != NarrowType || !Zext->hasOneUse())
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return nullptr;
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NewIncoming.push_back(Zext->getOperand(0));
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NumZexts++;
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} else if (auto *C = dyn_cast<Constant>(V)) {
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// Make sure that constants can fit in the new type.
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Constant *Trunc = ConstantExpr::getTrunc(C, NarrowType);
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if (ConstantExpr::getZExt(Trunc, C->getType()) != C)
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return nullptr;
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NewIncoming.push_back(Trunc);
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NumConsts++;
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} else {
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// If it's not a cast or a constant, bail out.
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return nullptr;
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}
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}
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// The more common cases of a phi with no constant operands or just one
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// variable operand are handled by FoldPHIArgOpIntoPHI() and FoldOpIntoPhi()
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// respectively. FoldOpIntoPhi() wants to do the opposite transform that is
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// performed here. It tries to replicate a cast in the phi operand's basic
|
|
// block to expose other folding opportunities. Thus, InstCombine will
|
|
// infinite loop without this check.
|
|
if (NumConsts == 0 || NumZexts < 2)
|
|
return nullptr;
|
|
|
|
// All incoming values are zexts or constants that are safe to truncate.
|
|
// Create a new phi node of the narrow type, phi together all of the new
|
|
// operands, and zext the result back to the original type.
|
|
PHINode *NewPhi = PHINode::Create(NarrowType, NumIncomingValues,
|
|
Phi.getName() + ".shrunk");
|
|
for (unsigned i = 0; i != NumIncomingValues; ++i)
|
|
NewPhi->addIncoming(NewIncoming[i], Phi.getIncomingBlock(i));
|
|
|
|
InsertNewInstBefore(NewPhi, Phi);
|
|
return CastInst::CreateZExtOrBitCast(NewPhi, Phi.getType());
|
|
}
|
|
|
|
/// If all operands to a PHI node are the same "unary" operator and they all are
|
|
/// only used by the PHI, PHI together their inputs, and do the operation once,
|
|
/// to the result of the PHI.
|
|
Instruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) {
|
|
// We cannot create a new instruction after the PHI if the terminator is an
|
|
// EHPad because there is no valid insertion point.
|
|
if (TerminatorInst *TI = PN.getParent()->getTerminator())
|
|
if (TI->isEHPad())
|
|
return nullptr;
|
|
|
|
Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
|
|
|
|
if (isa<GetElementPtrInst>(FirstInst))
|
|
return FoldPHIArgGEPIntoPHI(PN);
|
|
if (isa<LoadInst>(FirstInst))
|
|
return FoldPHIArgLoadIntoPHI(PN);
|
|
|
|
// Scan the instruction, looking for input operations that can be folded away.
|
|
// If all input operands to the phi are the same instruction (e.g. a cast from
|
|
// the same type or "+42") we can pull the operation through the PHI, reducing
|
|
// code size and simplifying code.
|
|
Constant *ConstantOp = nullptr;
|
|
Type *CastSrcTy = nullptr;
|
|
|
|
if (isa<CastInst>(FirstInst)) {
|
|
CastSrcTy = FirstInst->getOperand(0)->getType();
|
|
|
|
// Be careful about transforming integer PHIs. We don't want to pessimize
|
|
// the code by turning an i32 into an i1293.
|
|
if (PN.getType()->isIntegerTy() && CastSrcTy->isIntegerTy()) {
|
|
if (!ShouldChangeType(PN.getType(), CastSrcTy))
|
|
return nullptr;
|
|
}
|
|
} else if (isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)) {
|
|
// Can fold binop, compare or shift here if the RHS is a constant,
|
|
// otherwise call FoldPHIArgBinOpIntoPHI.
|
|
ConstantOp = dyn_cast<Constant>(FirstInst->getOperand(1));
|
|
if (!ConstantOp)
|
|
return FoldPHIArgBinOpIntoPHI(PN);
|
|
} else {
|
|
return nullptr; // Cannot fold this operation.
|
|
}
|
|
|
|
// Check to see if all arguments are the same operation.
|
|
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
|
|
Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
|
|
if (!I || !I->hasOneUse() || !I->isSameOperationAs(FirstInst))
|
|
return nullptr;
|
|
if (CastSrcTy) {
|
|
if (I->getOperand(0)->getType() != CastSrcTy)
|
|
return nullptr; // Cast operation must match.
|
|
} else if (I->getOperand(1) != ConstantOp) {
|
|
return nullptr;
|
|
}
|
|
}
|
|
|
|
// Okay, they are all the same operation. Create a new PHI node of the
|
|
// correct type, and PHI together all of the LHS's of the instructions.
|
|
PHINode *NewPN = PHINode::Create(FirstInst->getOperand(0)->getType(),
|
|
PN.getNumIncomingValues(),
|
|
PN.getName()+".in");
|
|
|
|
Value *InVal = FirstInst->getOperand(0);
|
|
NewPN->addIncoming(InVal, PN.getIncomingBlock(0));
|
|
|
|
// Add all operands to the new PHI.
|
|
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
|
|
Value *NewInVal = cast<Instruction>(PN.getIncomingValue(i))->getOperand(0);
|
|
if (NewInVal != InVal)
|
|
InVal = nullptr;
|
|
NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i));
|
|
}
|
|
|
|
Value *PhiVal;
|
|
if (InVal) {
|
|
// The new PHI unions all of the same values together. This is really
|
|
// common, so we handle it intelligently here for compile-time speed.
|
|
PhiVal = InVal;
|
|
delete NewPN;
|
|
} else {
|
|
InsertNewInstBefore(NewPN, PN);
|
|
PhiVal = NewPN;
|
|
}
|
|
|
|
// Insert and return the new operation.
|
|
if (CastInst *FirstCI = dyn_cast<CastInst>(FirstInst)) {
|
|
CastInst *NewCI = CastInst::Create(FirstCI->getOpcode(), PhiVal,
|
|
PN.getType());
|
|
NewCI->setDebugLoc(FirstInst->getDebugLoc());
|
|
return NewCI;
|
|
}
|
|
|
|
if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) {
|
|
BinOp = BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp);
|
|
BinOp->copyIRFlags(PN.getIncomingValue(0));
|
|
|
|
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i)
|
|
BinOp->andIRFlags(PN.getIncomingValue(i));
|
|
|
|
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;
|
|
}
|
|
|
|
/// Return true if this PHI node is only used by a PHI node cycle that is dead.
|
|
static bool DeadPHICycle(PHINode *PN,
|
|
SmallPtrSetImpl<PHINode*> &PotentiallyDeadPHIs) {
|
|
if (PN->use_empty()) return true;
|
|
if (!PN->hasOneUse()) return false;
|
|
|
|
// Remember this node, and if we find the cycle, return.
|
|
if (!PotentiallyDeadPHIs.insert(PN).second)
|
|
return true;
|
|
|
|
// Don't scan crazily complex things.
|
|
if (PotentiallyDeadPHIs.size() == 16)
|
|
return false;
|
|
|
|
if (PHINode *PU = dyn_cast<PHINode>(PN->user_back()))
|
|
return DeadPHICycle(PU, PotentiallyDeadPHIs);
|
|
|
|
return false;
|
|
}
|
|
|
|
/// Return true if this phi node is always equal to NonPhiInVal.
|
|
/// This happens with mutually cyclic phi nodes like:
|
|
/// z = some value; x = phi (y, z); y = phi (x, z)
|
|
static bool PHIsEqualValue(PHINode *PN, Value *NonPhiInVal,
|
|
SmallPtrSetImpl<PHINode*> &ValueEqualPHIs) {
|
|
// See if we already saw this PHI node.
|
|
if (!ValueEqualPHIs.insert(PN).second)
|
|
return true;
|
|
|
|
// Don't scan crazily complex things.
|
|
if (ValueEqualPHIs.size() == 16)
|
|
return false;
|
|
|
|
// Scan the operands to see if they are either phi nodes or are equal to
|
|
// the value.
|
|
for (Value *Op : PN->incoming_values()) {
|
|
if (PHINode *OpPN = dyn_cast<PHINode>(Op)) {
|
|
if (!PHIsEqualValue(OpPN, NonPhiInVal, ValueEqualPHIs))
|
|
return false;
|
|
} else if (Op != NonPhiInVal)
|
|
return false;
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/// Return an existing non-zero constant if this phi node has one, otherwise
|
|
/// return constant 1.
|
|
static ConstantInt *GetAnyNonZeroConstInt(PHINode &PN) {
|
|
assert(isa<IntegerType>(PN.getType()) && "Expect only intger type phi");
|
|
for (Value *V : PN.operands())
|
|
if (auto *ConstVA = dyn_cast<ConstantInt>(V))
|
|
if (!ConstVA->isZeroValue())
|
|
return ConstVA;
|
|
return ConstantInt::get(cast<IntegerType>(PN.getType()), 1);
|
|
}
|
|
|
|
namespace {
|
|
struct PHIUsageRecord {
|
|
unsigned PHIId; // The ID # of the PHI (something determinstic to sort on)
|
|
unsigned Shift; // The amount shifted.
|
|
Instruction *Inst; // The trunc instruction.
|
|
|
|
PHIUsageRecord(unsigned pn, unsigned Sh, Instruction *User)
|
|
: PHIId(pn), Shift(Sh), Inst(User) {}
|
|
|
|
bool operator<(const PHIUsageRecord &RHS) const {
|
|
if (PHIId < RHS.PHIId) return true;
|
|
if (PHIId > RHS.PHIId) return false;
|
|
if (Shift < RHS.Shift) return true;
|
|
if (Shift > RHS.Shift) return false;
|
|
return Inst->getType()->getPrimitiveSizeInBits() <
|
|
RHS.Inst->getType()->getPrimitiveSizeInBits();
|
|
}
|
|
};
|
|
|
|
struct LoweredPHIRecord {
|
|
PHINode *PN; // The PHI that was lowered.
|
|
unsigned Shift; // The amount shifted.
|
|
unsigned Width; // The width extracted.
|
|
|
|
LoweredPHIRecord(PHINode *pn, unsigned Sh, Type *Ty)
|
|
: PN(pn), Shift(Sh), Width(Ty->getPrimitiveSizeInBits()) {}
|
|
|
|
// Ctor form used by DenseMap.
|
|
LoweredPHIRecord(PHINode *pn, unsigned Sh)
|
|
: PN(pn), Shift(Sh), Width(0) {}
|
|
};
|
|
}
|
|
|
|
namespace llvm {
|
|
template<>
|
|
struct DenseMapInfo<LoweredPHIRecord> {
|
|
static inline LoweredPHIRecord getEmptyKey() {
|
|
return LoweredPHIRecord(nullptr, 0);
|
|
}
|
|
static inline LoweredPHIRecord getTombstoneKey() {
|
|
return LoweredPHIRecord(nullptr, 1);
|
|
}
|
|
static unsigned getHashValue(const LoweredPHIRecord &Val) {
|
|
return DenseMapInfo<PHINode*>::getHashValue(Val.PN) ^ (Val.Shift>>3) ^
|
|
(Val.Width>>3);
|
|
}
|
|
static bool isEqual(const LoweredPHIRecord &LHS,
|
|
const LoweredPHIRecord &RHS) {
|
|
return LHS.PN == RHS.PN && LHS.Shift == RHS.Shift &&
|
|
LHS.Width == RHS.Width;
|
|
}
|
|
};
|
|
}
|
|
|
|
|
|
/// This is an integer PHI and we know that it has an illegal type: see if it is
|
|
/// only used by trunc or trunc(lshr) operations. If so, we split the PHI into
|
|
/// the various pieces being extracted. This sort of thing is introduced when
|
|
/// SROA promotes an aggregate to large integer values.
|
|
///
|
|
/// TODO: The user of the trunc may be an bitcast to float/double/vector or an
|
|
/// inttoptr. We should produce new PHIs in the right type.
|
|
///
|
|
Instruction *InstCombiner::SliceUpIllegalIntegerPHI(PHINode &FirstPhi) {
|
|
// PHIUsers - Keep track of all of the truncated values extracted from a set
|
|
// of PHIs, along with their offset. These are the things we want to rewrite.
|
|
SmallVector<PHIUsageRecord, 16> PHIUsers;
|
|
|
|
// PHIs are often mutually cyclic, so we keep track of a whole set of PHI
|
|
// nodes which are extracted from. PHIsToSlice is a set we use to avoid
|
|
// revisiting PHIs, PHIsInspected is a ordered list of PHIs that we need to
|
|
// check the uses of (to ensure they are all extracts).
|
|
SmallVector<PHINode*, 8> PHIsToSlice;
|
|
SmallPtrSet<PHINode*, 8> PHIsInspected;
|
|
|
|
PHIsToSlice.push_back(&FirstPhi);
|
|
PHIsInspected.insert(&FirstPhi);
|
|
|
|
for (unsigned PHIId = 0; PHIId != PHIsToSlice.size(); ++PHIId) {
|
|
PHINode *PN = PHIsToSlice[PHIId];
|
|
|
|
// Scan the input list of the PHI. If any input is an invoke, and if the
|
|
// input is defined in the predecessor, then we won't be split the critical
|
|
// edge which is required to insert a truncate. Because of this, we have to
|
|
// bail out.
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
InvokeInst *II = dyn_cast<InvokeInst>(PN->getIncomingValue(i));
|
|
if (!II) continue;
|
|
if (II->getParent() != PN->getIncomingBlock(i))
|
|
continue;
|
|
|
|
// If we have a phi, and if it's directly in the predecessor, then we have
|
|
// a critical edge where we need to put the truncate. Since we can't
|
|
// split the edge in instcombine, we have to bail out.
|
|
return nullptr;
|
|
}
|
|
|
|
for (User *U : PN->users()) {
|
|
Instruction *UserI = cast<Instruction>(U);
|
|
|
|
// If the user is a PHI, inspect its uses recursively.
|
|
if (PHINode *UserPN = dyn_cast<PHINode>(UserI)) {
|
|
if (PHIsInspected.insert(UserPN).second)
|
|
PHIsToSlice.push_back(UserPN);
|
|
continue;
|
|
}
|
|
|
|
// Truncates are always ok.
|
|
if (isa<TruncInst>(UserI)) {
|
|
PHIUsers.push_back(PHIUsageRecord(PHIId, 0, UserI));
|
|
continue;
|
|
}
|
|
|
|
// Otherwise it must be a lshr which can only be used by one trunc.
|
|
if (UserI->getOpcode() != Instruction::LShr ||
|
|
!UserI->hasOneUse() || !isa<TruncInst>(UserI->user_back()) ||
|
|
!isa<ConstantInt>(UserI->getOperand(1)))
|
|
return nullptr;
|
|
|
|
unsigned Shift = cast<ConstantInt>(UserI->getOperand(1))->getZExtValue();
|
|
PHIUsers.push_back(PHIUsageRecord(PHIId, Shift, UserI->user_back()));
|
|
}
|
|
}
|
|
|
|
// If we have no users, they must be all self uses, just nuke the PHI.
|
|
if (PHIUsers.empty())
|
|
return replaceInstUsesWith(FirstPhi, UndefValue::get(FirstPhi.getType()));
|
|
|
|
// If this phi node is transformable, create new PHIs for all the pieces
|
|
// extracted out of it. First, sort the users by their offset and size.
|
|
array_pod_sort(PHIUsers.begin(), PHIUsers.end());
|
|
|
|
DEBUG(dbgs() << "SLICING UP PHI: " << FirstPhi << '\n';
|
|
for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i)
|
|
dbgs() << "AND USER PHI #" << i << ": " << *PHIsToSlice[i] << '\n';
|
|
);
|
|
|
|
// PredValues - This is a temporary used when rewriting PHI nodes. It is
|
|
// hoisted out here to avoid construction/destruction thrashing.
|
|
DenseMap<BasicBlock*, Value*> PredValues;
|
|
|
|
// ExtractedVals - Each new PHI we introduce is saved here so we don't
|
|
// introduce redundant PHIs.
|
|
DenseMap<LoweredPHIRecord, PHINode*> ExtractedVals;
|
|
|
|
for (unsigned UserI = 0, UserE = PHIUsers.size(); UserI != UserE; ++UserI) {
|
|
unsigned PHIId = PHIUsers[UserI].PHIId;
|
|
PHINode *PN = PHIsToSlice[PHIId];
|
|
unsigned Offset = PHIUsers[UserI].Shift;
|
|
Type *Ty = PHIUsers[UserI].Inst->getType();
|
|
|
|
PHINode *EltPHI;
|
|
|
|
// If we've already lowered a user like this, reuse the previously lowered
|
|
// value.
|
|
if ((EltPHI = ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)]) == nullptr) {
|
|
|
|
// Otherwise, Create the new PHI node for this user.
|
|
EltPHI = PHINode::Create(Ty, PN->getNumIncomingValues(),
|
|
PN->getName()+".off"+Twine(Offset), PN);
|
|
assert(EltPHI->getType() != PN->getType() &&
|
|
"Truncate didn't shrink phi?");
|
|
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
BasicBlock *Pred = PN->getIncomingBlock(i);
|
|
Value *&PredVal = PredValues[Pred];
|
|
|
|
// If we already have a value for this predecessor, reuse it.
|
|
if (PredVal) {
|
|
EltPHI->addIncoming(PredVal, Pred);
|
|
continue;
|
|
}
|
|
|
|
// Handle the PHI self-reuse case.
|
|
Value *InVal = PN->getIncomingValue(i);
|
|
if (InVal == PN) {
|
|
PredVal = EltPHI;
|
|
EltPHI->addIncoming(PredVal, Pred);
|
|
continue;
|
|
}
|
|
|
|
if (PHINode *InPHI = dyn_cast<PHINode>(PN)) {
|
|
// If the incoming value was a PHI, and if it was one of the PHIs we
|
|
// already rewrote it, just use the lowered value.
|
|
if (Value *Res = ExtractedVals[LoweredPHIRecord(InPHI, Offset, Ty)]) {
|
|
PredVal = Res;
|
|
EltPHI->addIncoming(PredVal, Pred);
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// Otherwise, do an extract in the predecessor.
|
|
Builder->SetInsertPoint(Pred->getTerminator());
|
|
Value *Res = InVal;
|
|
if (Offset)
|
|
Res = Builder->CreateLShr(Res, ConstantInt::get(InVal->getType(),
|
|
Offset), "extract");
|
|
Res = Builder->CreateTrunc(Res, Ty, "extract.t");
|
|
PredVal = Res;
|
|
EltPHI->addIncoming(Res, Pred);
|
|
|
|
// If the incoming value was a PHI, and if it was one of the PHIs we are
|
|
// rewriting, we will ultimately delete the code we inserted. This
|
|
// means we need to revisit that PHI to make sure we extract out the
|
|
// needed piece.
|
|
if (PHINode *OldInVal = dyn_cast<PHINode>(PN->getIncomingValue(i)))
|
|
if (PHIsInspected.count(OldInVal)) {
|
|
unsigned RefPHIId = std::find(PHIsToSlice.begin(),PHIsToSlice.end(),
|
|
OldInVal)-PHIsToSlice.begin();
|
|
PHIUsers.push_back(PHIUsageRecord(RefPHIId, Offset,
|
|
cast<Instruction>(Res)));
|
|
++UserE;
|
|
}
|
|
}
|
|
PredValues.clear();
|
|
|
|
DEBUG(dbgs() << " Made element PHI for offset " << Offset << ": "
|
|
<< *EltPHI << '\n');
|
|
ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)] = EltPHI;
|
|
}
|
|
|
|
// Replace the use of this piece with the PHI node.
|
|
replaceInstUsesWith(*PHIUsers[UserI].Inst, EltPHI);
|
|
}
|
|
|
|
// Replace all the remaining uses of the PHI nodes (self uses and the lshrs)
|
|
// with undefs.
|
|
Value *Undef = UndefValue::get(FirstPhi.getType());
|
|
for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i)
|
|
replaceInstUsesWith(*PHIsToSlice[i], Undef);
|
|
return replaceInstUsesWith(FirstPhi, Undef);
|
|
}
|
|
|
|
// PHINode simplification
|
|
//
|
|
Instruction *InstCombiner::visitPHINode(PHINode &PN) {
|
|
if (Value *V = SimplifyInstruction(&PN, DL, TLI, DT, AC))
|
|
return replaceInstUsesWith(PN, V);
|
|
|
|
if (Instruction *Result = FoldPHIArgZextsIntoPHI(PN))
|
|
return Result;
|
|
|
|
// If all PHI operands are the same operation, pull them through the PHI,
|
|
// reducing code size.
|
|
if (isa<Instruction>(PN.getIncomingValue(0)) &&
|
|
isa<Instruction>(PN.getIncomingValue(1)) &&
|
|
cast<Instruction>(PN.getIncomingValue(0))->getOpcode() ==
|
|
cast<Instruction>(PN.getIncomingValue(1))->getOpcode() &&
|
|
// FIXME: The hasOneUse check will fail for PHIs that use the value more
|
|
// than themselves more than once.
|
|
PN.getIncomingValue(0)->hasOneUse())
|
|
if (Instruction *Result = FoldPHIArgOpIntoPHI(PN))
|
|
return Result;
|
|
|
|
// If this is a trivial cycle in the PHI node graph, remove it. Basically, if
|
|
// this PHI only has a single use (a PHI), and if that PHI only has one use (a
|
|
// PHI)... break the cycle.
|
|
if (PN.hasOneUse()) {
|
|
Instruction *PHIUser = cast<Instruction>(PN.user_back());
|
|
if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) {
|
|
SmallPtrSet<PHINode*, 16> PotentiallyDeadPHIs;
|
|
PotentiallyDeadPHIs.insert(&PN);
|
|
if (DeadPHICycle(PU, PotentiallyDeadPHIs))
|
|
return replaceInstUsesWith(PN, UndefValue::get(PN.getType()));
|
|
}
|
|
|
|
// If this phi has a single use, and if that use just computes a value for
|
|
// the next iteration of a loop, delete the phi. This occurs with unused
|
|
// induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this
|
|
// common case here is good because the only other things that catch this
|
|
// are induction variable analysis (sometimes) and ADCE, which is only run
|
|
// late.
|
|
if (PHIUser->hasOneUse() &&
|
|
(isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) &&
|
|
PHIUser->user_back() == &PN) {
|
|
return replaceInstUsesWith(PN, UndefValue::get(PN.getType()));
|
|
}
|
|
// When a PHI is used only to be compared with zero, it is safe to replace
|
|
// an incoming value proved as known nonzero with any non-zero constant.
|
|
// For example, in the code below, the incoming value %v can be replaced
|
|
// with any non-zero constant based on the fact that the PHI is only used to
|
|
// be compared with zero and %v is a known non-zero value:
|
|
// %v = select %cond, 1, 2
|
|
// %p = phi [%v, BB] ...
|
|
// icmp eq, %p, 0
|
|
auto *CmpInst = dyn_cast<ICmpInst>(PHIUser);
|
|
// FIXME: To be simple, handle only integer type for now.
|
|
if (CmpInst && isa<IntegerType>(PN.getType()) && CmpInst->isEquality() &&
|
|
match(CmpInst->getOperand(1), m_Zero())) {
|
|
ConstantInt *NonZeroConst = nullptr;
|
|
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
|
|
Instruction *CtxI = PN.getIncomingBlock(i)->getTerminator();
|
|
Value *VA = PN.getIncomingValue(i);
|
|
if (isKnownNonZero(VA, DL, 0, AC, CtxI, DT)) {
|
|
if (!NonZeroConst)
|
|
NonZeroConst = GetAnyNonZeroConstInt(PN);
|
|
PN.setIncomingValue(i, NonZeroConst);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// We sometimes end up with phi cycles that non-obviously end up being the
|
|
// same value, for example:
|
|
// z = some value; x = phi (y, z); y = phi (x, z)
|
|
// where the phi nodes don't necessarily need to be in the same block. Do a
|
|
// quick check to see if the PHI node only contains a single non-phi value, if
|
|
// so, scan to see if the phi cycle is actually equal to that value.
|
|
{
|
|
unsigned InValNo = 0, NumIncomingVals = PN.getNumIncomingValues();
|
|
// Scan for the first non-phi operand.
|
|
while (InValNo != NumIncomingVals &&
|
|
isa<PHINode>(PN.getIncomingValue(InValNo)))
|
|
++InValNo;
|
|
|
|
if (InValNo != NumIncomingVals) {
|
|
Value *NonPhiInVal = PN.getIncomingValue(InValNo);
|
|
|
|
// Scan the rest of the operands to see if there are any conflicts, if so
|
|
// there is no need to recursively scan other phis.
|
|
for (++InValNo; InValNo != NumIncomingVals; ++InValNo) {
|
|
Value *OpVal = PN.getIncomingValue(InValNo);
|
|
if (OpVal != NonPhiInVal && !isa<PHINode>(OpVal))
|
|
break;
|
|
}
|
|
|
|
// If we scanned over all operands, then we have one unique value plus
|
|
// phi values. Scan PHI nodes to see if they all merge in each other or
|
|
// the value.
|
|
if (InValNo == NumIncomingVals) {
|
|
SmallPtrSet<PHINode*, 16> ValueEqualPHIs;
|
|
if (PHIsEqualValue(&PN, NonPhiInVal, ValueEqualPHIs))
|
|
return replaceInstUsesWith(PN, NonPhiInVal);
|
|
}
|
|
}
|
|
}
|
|
|
|
// If there are multiple PHIs, sort their operands so that they all list
|
|
// the blocks in the same order. This will help identical PHIs be eliminated
|
|
// by other passes. Other passes shouldn't depend on this for correctness
|
|
// however.
|
|
PHINode *FirstPN = cast<PHINode>(PN.getParent()->begin());
|
|
if (&PN != FirstPN)
|
|
for (unsigned i = 0, e = FirstPN->getNumIncomingValues(); i != e; ++i) {
|
|
BasicBlock *BBA = PN.getIncomingBlock(i);
|
|
BasicBlock *BBB = FirstPN->getIncomingBlock(i);
|
|
if (BBA != BBB) {
|
|
Value *VA = PN.getIncomingValue(i);
|
|
unsigned j = PN.getBasicBlockIndex(BBB);
|
|
Value *VB = PN.getIncomingValue(j);
|
|
PN.setIncomingBlock(i, BBB);
|
|
PN.setIncomingValue(i, VB);
|
|
PN.setIncomingBlock(j, BBA);
|
|
PN.setIncomingValue(j, VA);
|
|
// NOTE: Instcombine normally would want us to "return &PN" if we
|
|
// modified any of the operands of an instruction. However, since we
|
|
// aren't adding or removing uses (just rearranging them) we don't do
|
|
// this in this case.
|
|
}
|
|
}
|
|
|
|
// If this is an integer PHI and we know that it has an illegal type, see if
|
|
// it is only used by trunc or trunc(lshr) operations. If so, we split the
|
|
// PHI into the various pieces being extracted. This sort of thing is
|
|
// introduced when SROA promotes an aggregate to a single large integer type.
|
|
if (PN.getType()->isIntegerTy() &&
|
|
!DL.isLegalInteger(PN.getType()->getPrimitiveSizeInBits()))
|
|
if (Instruction *Res = SliceUpIllegalIntegerPHI(PN))
|
|
return Res;
|
|
|
|
return nullptr;
|
|
}
|