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642 lines
24 KiB
C++
642 lines
24 KiB
C++
//===- InstCombineLoadStoreAlloca.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 visit functions for load, store and alloca.
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//
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//===----------------------------------------------------------------------===//
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#include "InstCombine.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Analysis/Loads.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/ADT/Statistic.h"
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using namespace llvm;
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STATISTIC(NumDeadStore, "Number of dead stores eliminated");
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Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
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// Ensure that the alloca array size argument has type intptr_t, so that
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// any casting is exposed early.
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if (TD) {
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const Type *IntPtrTy = TD->getIntPtrType(AI.getContext());
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if (AI.getArraySize()->getType() != IntPtrTy) {
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Value *V = Builder->CreateIntCast(AI.getArraySize(),
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IntPtrTy, false);
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AI.setOperand(0, V);
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return &AI;
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}
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}
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// Convert: alloca Ty, C - where C is a constant != 1 into: alloca [C x Ty], 1
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if (AI.isArrayAllocation()) { // Check C != 1
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if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) {
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const Type *NewTy =
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ArrayType::get(AI.getAllocatedType(), C->getZExtValue());
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assert(isa<AllocaInst>(AI) && "Unknown type of allocation inst!");
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AllocaInst *New = Builder->CreateAlloca(NewTy, 0, AI.getName());
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New->setAlignment(AI.getAlignment());
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// Scan to the end of the allocation instructions, to skip over a block of
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// allocas if possible...also skip interleaved debug info
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//
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BasicBlock::iterator It = New;
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while (isa<AllocaInst>(*It) || isa<DbgInfoIntrinsic>(*It)) ++It;
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// Now that I is pointing to the first non-allocation-inst in the block,
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// insert our getelementptr instruction...
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//
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Value *NullIdx =Constant::getNullValue(Type::getInt32Ty(AI.getContext()));
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Value *Idx[2];
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Idx[0] = NullIdx;
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Idx[1] = NullIdx;
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Value *V = GetElementPtrInst::CreateInBounds(New, Idx, Idx + 2,
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New->getName()+".sub", It);
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// Now make everything use the getelementptr instead of the original
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// allocation.
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return ReplaceInstUsesWith(AI, V);
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} else if (isa<UndefValue>(AI.getArraySize())) {
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return ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
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}
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}
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if (TD && isa<AllocaInst>(AI) && AI.getAllocatedType()->isSized()) {
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// If alloca'ing a zero byte object, replace the alloca with a null pointer.
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// Note that we only do this for alloca's, because malloc should allocate
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// and return a unique pointer, even for a zero byte allocation.
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if (TD->getTypeAllocSize(AI.getAllocatedType()) == 0)
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return ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
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// If the alignment is 0 (unspecified), assign it the preferred alignment.
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if (AI.getAlignment() == 0)
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AI.setAlignment(TD->getPrefTypeAlignment(AI.getAllocatedType()));
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}
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return 0;
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}
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/// InstCombineLoadCast - Fold 'load (cast P)' -> cast (load P)' when possible.
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static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI,
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const TargetData *TD) {
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User *CI = cast<User>(LI.getOperand(0));
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Value *CastOp = CI->getOperand(0);
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const PointerType *DestTy = cast<PointerType>(CI->getType());
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const Type *DestPTy = DestTy->getElementType();
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if (const PointerType *SrcTy = dyn_cast<PointerType>(CastOp->getType())) {
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// If the address spaces don't match, don't eliminate the cast.
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if (DestTy->getAddressSpace() != SrcTy->getAddressSpace())
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return 0;
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const Type *SrcPTy = SrcTy->getElementType();
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if (DestPTy->isIntegerTy() || DestPTy->isPointerTy() ||
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DestPTy->isVectorTy()) {
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// If the source is an array, the code below will not succeed. Check to
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// see if a trivial 'gep P, 0, 0' will help matters. Only do this for
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// constants.
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if (const ArrayType *ASrcTy = dyn_cast<ArrayType>(SrcPTy))
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if (Constant *CSrc = dyn_cast<Constant>(CastOp))
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if (ASrcTy->getNumElements() != 0) {
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Value *Idxs[2];
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Idxs[0] = Constant::getNullValue(Type::getInt32Ty(LI.getContext()));
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Idxs[1] = Idxs[0];
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CastOp = ConstantExpr::getGetElementPtr(CSrc, Idxs, 2);
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SrcTy = cast<PointerType>(CastOp->getType());
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SrcPTy = SrcTy->getElementType();
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}
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if (IC.getTargetData() &&
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(SrcPTy->isIntegerTy() || SrcPTy->isPointerTy() ||
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SrcPTy->isVectorTy()) &&
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// Do not allow turning this into a load of an integer, which is then
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// casted to a pointer, this pessimizes pointer analysis a lot.
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(SrcPTy->isPointerTy() == LI.getType()->isPointerTy()) &&
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IC.getTargetData()->getTypeSizeInBits(SrcPTy) ==
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IC.getTargetData()->getTypeSizeInBits(DestPTy)) {
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// Okay, we are casting from one integer or pointer type to another of
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// the same size. Instead of casting the pointer before the load, cast
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// the result of the loaded value.
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LoadInst *NewLoad =
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IC.Builder->CreateLoad(CastOp, LI.isVolatile(), CI->getName());
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NewLoad->setAlignment(LI.getAlignment());
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// Now cast the result of the load.
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return new BitCastInst(NewLoad, LI.getType());
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}
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}
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}
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return 0;
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}
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Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
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Value *Op = LI.getOperand(0);
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// Attempt to improve the alignment.
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if (TD) {
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unsigned KnownAlign =
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GetOrEnforceKnownAlignment(Op, TD->getPrefTypeAlignment(LI.getType()));
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unsigned LoadAlign = LI.getAlignment();
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unsigned EffectiveLoadAlign = LoadAlign != 0 ? LoadAlign :
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TD->getABITypeAlignment(LI.getType());
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if (KnownAlign > EffectiveLoadAlign)
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LI.setAlignment(KnownAlign);
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else if (LoadAlign == 0)
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LI.setAlignment(EffectiveLoadAlign);
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}
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// load (cast X) --> cast (load X) iff safe.
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if (isa<CastInst>(Op))
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if (Instruction *Res = InstCombineLoadCast(*this, LI, TD))
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return Res;
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// None of the following transforms are legal for volatile loads.
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if (LI.isVolatile()) return 0;
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// Do really simple store-to-load forwarding and load CSE, to catch cases
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// where there are several consequtive memory accesses to the same location,
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// separated by a few arithmetic operations.
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BasicBlock::iterator BBI = &LI;
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if (Value *AvailableVal = FindAvailableLoadedValue(Op, LI.getParent(), BBI,6))
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return ReplaceInstUsesWith(LI, AvailableVal);
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// load(gep null, ...) -> unreachable
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if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) {
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const Value *GEPI0 = GEPI->getOperand(0);
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// TODO: Consider a target hook for valid address spaces for this xform.
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if (isa<ConstantPointerNull>(GEPI0) && GEPI->getPointerAddressSpace() == 0){
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// Insert a new store to null instruction before the load to indicate
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// that this code is not reachable. We do this instead of inserting
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// an unreachable instruction directly because we cannot modify the
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// CFG.
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new StoreInst(UndefValue::get(LI.getType()),
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Constant::getNullValue(Op->getType()), &LI);
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return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType()));
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}
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}
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// load null/undef -> unreachable
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// TODO: Consider a target hook for valid address spaces for this xform.
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if (isa<UndefValue>(Op) ||
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(isa<ConstantPointerNull>(Op) && LI.getPointerAddressSpace() == 0)) {
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// Insert a new store to null instruction before the load to indicate that
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// this code is not reachable. We do this instead of inserting an
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// unreachable instruction directly because we cannot modify the CFG.
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new StoreInst(UndefValue::get(LI.getType()),
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Constant::getNullValue(Op->getType()), &LI);
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return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType()));
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}
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// Instcombine load (constantexpr_cast global) -> cast (load global)
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if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Op))
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if (CE->isCast())
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if (Instruction *Res = InstCombineLoadCast(*this, LI, TD))
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return Res;
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if (Op->hasOneUse()) {
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// Change select and PHI nodes to select values instead of addresses: this
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// helps alias analysis out a lot, allows many others simplifications, and
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// exposes redundancy in the code.
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//
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// Note that we cannot do the transformation unless we know that the
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// introduced loads cannot trap! Something like this is valid as long as
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// the condition is always false: load (select bool %C, int* null, int* %G),
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// but it would not be valid if we transformed it to load from null
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// unconditionally.
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//
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if (SelectInst *SI = dyn_cast<SelectInst>(Op)) {
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// load (select (Cond, &V1, &V2)) --> select(Cond, load &V1, load &V2).
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unsigned Align = LI.getAlignment();
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if (isSafeToLoadUnconditionally(SI->getOperand(1), SI, Align, TD) &&
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isSafeToLoadUnconditionally(SI->getOperand(2), SI, Align, TD)) {
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LoadInst *V1 = Builder->CreateLoad(SI->getOperand(1),
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SI->getOperand(1)->getName()+".val");
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LoadInst *V2 = Builder->CreateLoad(SI->getOperand(2),
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SI->getOperand(2)->getName()+".val");
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V1->setAlignment(Align);
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V2->setAlignment(Align);
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return SelectInst::Create(SI->getCondition(), V1, V2);
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}
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// load (select (cond, null, P)) -> load P
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if (Constant *C = dyn_cast<Constant>(SI->getOperand(1)))
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if (C->isNullValue()) {
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LI.setOperand(0, SI->getOperand(2));
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return &LI;
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}
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// load (select (cond, P, null)) -> load P
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if (Constant *C = dyn_cast<Constant>(SI->getOperand(2)))
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if (C->isNullValue()) {
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LI.setOperand(0, SI->getOperand(1));
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return &LI;
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}
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}
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}
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return 0;
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}
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/// InstCombineStoreToCast - Fold store V, (cast P) -> store (cast V), P
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/// when possible. This makes it generally easy to do alias analysis and/or
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/// SROA/mem2reg of the memory object.
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static Instruction *InstCombineStoreToCast(InstCombiner &IC, StoreInst &SI) {
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User *CI = cast<User>(SI.getOperand(1));
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Value *CastOp = CI->getOperand(0);
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const Type *DestPTy = cast<PointerType>(CI->getType())->getElementType();
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const PointerType *SrcTy = dyn_cast<PointerType>(CastOp->getType());
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if (SrcTy == 0) return 0;
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const Type *SrcPTy = SrcTy->getElementType();
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if (!DestPTy->isIntegerTy() && !DestPTy->isPointerTy())
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return 0;
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/// NewGEPIndices - If SrcPTy is an aggregate type, we can emit a "noop gep"
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/// to its first element. This allows us to handle things like:
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/// store i32 xxx, (bitcast {foo*, float}* %P to i32*)
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/// on 32-bit hosts.
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SmallVector<Value*, 4> NewGEPIndices;
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// If the source is an array, the code below will not succeed. Check to
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// see if a trivial 'gep P, 0, 0' will help matters. Only do this for
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// constants.
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if (SrcPTy->isArrayTy() || SrcPTy->isStructTy()) {
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// Index through pointer.
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Constant *Zero = Constant::getNullValue(Type::getInt32Ty(SI.getContext()));
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NewGEPIndices.push_back(Zero);
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while (1) {
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if (const StructType *STy = dyn_cast<StructType>(SrcPTy)) {
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if (!STy->getNumElements()) /* Struct can be empty {} */
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break;
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NewGEPIndices.push_back(Zero);
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SrcPTy = STy->getElementType(0);
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} else if (const ArrayType *ATy = dyn_cast<ArrayType>(SrcPTy)) {
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NewGEPIndices.push_back(Zero);
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SrcPTy = ATy->getElementType();
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} else {
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break;
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}
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}
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SrcTy = PointerType::get(SrcPTy, SrcTy->getAddressSpace());
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}
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if (!SrcPTy->isIntegerTy() && !SrcPTy->isPointerTy())
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return 0;
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// If the pointers point into different address spaces or if they point to
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// values with different sizes, we can't do the transformation.
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if (!IC.getTargetData() ||
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SrcTy->getAddressSpace() !=
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cast<PointerType>(CI->getType())->getAddressSpace() ||
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IC.getTargetData()->getTypeSizeInBits(SrcPTy) !=
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IC.getTargetData()->getTypeSizeInBits(DestPTy))
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return 0;
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// Okay, we are casting from one integer or pointer type to another of
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// the same size. Instead of casting the pointer before
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// the store, cast the value to be stored.
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Value *NewCast;
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Value *SIOp0 = SI.getOperand(0);
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Instruction::CastOps opcode = Instruction::BitCast;
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const Type* CastSrcTy = SIOp0->getType();
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const Type* CastDstTy = SrcPTy;
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if (CastDstTy->isPointerTy()) {
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if (CastSrcTy->isIntegerTy())
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opcode = Instruction::IntToPtr;
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} else if (CastDstTy->isIntegerTy()) {
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if (SIOp0->getType()->isPointerTy())
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opcode = Instruction::PtrToInt;
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}
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// SIOp0 is a pointer to aggregate and this is a store to the first field,
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// emit a GEP to index into its first field.
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if (!NewGEPIndices.empty())
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CastOp = IC.Builder->CreateInBoundsGEP(CastOp, NewGEPIndices.begin(),
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NewGEPIndices.end());
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NewCast = IC.Builder->CreateCast(opcode, SIOp0, CastDstTy,
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SIOp0->getName()+".c");
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SI.setOperand(0, NewCast);
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SI.setOperand(1, CastOp);
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return &SI;
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}
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/// equivalentAddressValues - Test if A and B will obviously have the same
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/// value. This includes recognizing that %t0 and %t1 will have the same
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/// value in code like this:
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/// %t0 = getelementptr \@a, 0, 3
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/// store i32 0, i32* %t0
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/// %t1 = getelementptr \@a, 0, 3
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/// %t2 = load i32* %t1
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///
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static bool equivalentAddressValues(Value *A, Value *B) {
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// Test if the values are trivially equivalent.
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if (A == B) return true;
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// Test if the values come form identical arithmetic instructions.
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// This uses isIdenticalToWhenDefined instead of isIdenticalTo because
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// its only used to compare two uses within the same basic block, which
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// means that they'll always either have the same value or one of them
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// will have an undefined value.
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if (isa<BinaryOperator>(A) ||
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isa<CastInst>(A) ||
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isa<PHINode>(A) ||
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isa<GetElementPtrInst>(A))
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if (Instruction *BI = dyn_cast<Instruction>(B))
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if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI))
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return true;
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// Otherwise they may not be equivalent.
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return false;
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}
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// If this instruction has two uses, one of which is a llvm.dbg.declare,
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// return the llvm.dbg.declare.
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DbgDeclareInst *InstCombiner::hasOneUsePlusDeclare(Value *V) {
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if (!V->hasNUses(2))
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return 0;
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for (Value::use_iterator UI = V->use_begin(), E = V->use_end();
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UI != E; ++UI) {
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User *U = *UI;
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if (DbgDeclareInst *DI = dyn_cast<DbgDeclareInst>(U))
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return DI;
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if (isa<BitCastInst>(U) && U->hasOneUse()) {
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if (DbgDeclareInst *DI = dyn_cast<DbgDeclareInst>(*U->use_begin()))
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return DI;
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}
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}
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return 0;
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}
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Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
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Value *Val = SI.getOperand(0);
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Value *Ptr = SI.getOperand(1);
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// If the RHS is an alloca with a single use, zapify the store, making the
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// alloca dead.
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// If the RHS is an alloca with a two uses, the other one being a
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// llvm.dbg.declare, zapify the store and the declare, making the
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// alloca dead. We must do this to prevent declares from affecting
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// codegen.
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if (!SI.isVolatile()) {
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if (Ptr->hasOneUse()) {
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if (isa<AllocaInst>(Ptr))
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return EraseInstFromFunction(SI);
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if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) {
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if (isa<AllocaInst>(GEP->getOperand(0))) {
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if (GEP->getOperand(0)->hasOneUse())
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return EraseInstFromFunction(SI);
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if (DbgDeclareInst *DI = hasOneUsePlusDeclare(GEP->getOperand(0))) {
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EraseInstFromFunction(*DI);
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return EraseInstFromFunction(SI);
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}
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}
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}
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}
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if (DbgDeclareInst *DI = hasOneUsePlusDeclare(Ptr)) {
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EraseInstFromFunction(*DI);
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return EraseInstFromFunction(SI);
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}
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}
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// Attempt to improve the alignment.
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if (TD) {
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unsigned KnownAlign =
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GetOrEnforceKnownAlignment(Ptr, TD->getPrefTypeAlignment(Val->getType()));
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unsigned StoreAlign = SI.getAlignment();
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unsigned EffectiveStoreAlign = StoreAlign != 0 ? StoreAlign :
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TD->getABITypeAlignment(Val->getType());
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if (KnownAlign > EffectiveStoreAlign)
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SI.setAlignment(KnownAlign);
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else if (StoreAlign == 0)
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SI.setAlignment(EffectiveStoreAlign);
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}
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// Do really simple DSE, to catch cases where there are several consecutive
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// stores to the same location, separated by a few arithmetic operations. This
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// situation often occurs with bitfield accesses.
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BasicBlock::iterator BBI = &SI;
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for (unsigned ScanInsts = 6; BBI != SI.getParent()->begin() && ScanInsts;
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--ScanInsts) {
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--BBI;
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// Don't count debug info directives, lest they affect codegen,
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// and we skip pointer-to-pointer bitcasts, which are NOPs.
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if (isa<DbgInfoIntrinsic>(BBI) ||
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(isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
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ScanInsts++;
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continue;
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}
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if (StoreInst *PrevSI = dyn_cast<StoreInst>(BBI)) {
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// Prev store isn't volatile, and stores to the same location?
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if (!PrevSI->isVolatile() &&equivalentAddressValues(PrevSI->getOperand(1),
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SI.getOperand(1))) {
|
|
++NumDeadStore;
|
|
++BBI;
|
|
EraseInstFromFunction(*PrevSI);
|
|
continue;
|
|
}
|
|
break;
|
|
}
|
|
|
|
// If this is a load, we have to stop. However, if the loaded value is from
|
|
// the pointer we're loading and is producing the pointer we're storing,
|
|
// then *this* store is dead (X = load P; store X -> P).
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
|
|
if (LI == Val && equivalentAddressValues(LI->getOperand(0), Ptr) &&
|
|
!SI.isVolatile())
|
|
return EraseInstFromFunction(SI);
|
|
|
|
// Otherwise, this is a load from some other location. Stores before it
|
|
// may not be dead.
|
|
break;
|
|
}
|
|
|
|
// Don't skip over loads or things that can modify memory.
|
|
if (BBI->mayWriteToMemory() || BBI->mayReadFromMemory())
|
|
break;
|
|
}
|
|
|
|
|
|
if (SI.isVolatile()) return 0; // Don't hack volatile stores.
|
|
|
|
// store X, null -> turns into 'unreachable' in SimplifyCFG
|
|
if (isa<ConstantPointerNull>(Ptr) && SI.getPointerAddressSpace() == 0) {
|
|
if (!isa<UndefValue>(Val)) {
|
|
SI.setOperand(0, UndefValue::get(Val->getType()));
|
|
if (Instruction *U = dyn_cast<Instruction>(Val))
|
|
Worklist.Add(U); // Dropped a use.
|
|
}
|
|
return 0; // Do not modify these!
|
|
}
|
|
|
|
// store undef, Ptr -> noop
|
|
if (isa<UndefValue>(Val))
|
|
return EraseInstFromFunction(SI);
|
|
|
|
// If the pointer destination is a cast, see if we can fold the cast into the
|
|
// source instead.
|
|
if (isa<CastInst>(Ptr))
|
|
if (Instruction *Res = InstCombineStoreToCast(*this, SI))
|
|
return Res;
|
|
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
|
|
if (CE->isCast())
|
|
if (Instruction *Res = InstCombineStoreToCast(*this, SI))
|
|
return Res;
|
|
|
|
|
|
// If this store is the last instruction in the basic block (possibly
|
|
// excepting debug info instructions), and if the block ends with an
|
|
// unconditional branch, try to move it to the successor block.
|
|
BBI = &SI;
|
|
do {
|
|
++BBI;
|
|
} while (isa<DbgInfoIntrinsic>(BBI) ||
|
|
(isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy()));
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(BBI))
|
|
if (BI->isUnconditional())
|
|
if (SimplifyStoreAtEndOfBlock(SI))
|
|
return 0; // xform done!
|
|
|
|
return 0;
|
|
}
|
|
|
|
/// SimplifyStoreAtEndOfBlock - Turn things like:
|
|
/// if () { *P = v1; } else { *P = v2 }
|
|
/// into a phi node with a store in the successor.
|
|
///
|
|
/// Simplify things like:
|
|
/// *P = v1; if () { *P = v2; }
|
|
/// into a phi node with a store in the successor.
|
|
///
|
|
bool InstCombiner::SimplifyStoreAtEndOfBlock(StoreInst &SI) {
|
|
BasicBlock *StoreBB = SI.getParent();
|
|
|
|
// Check to see if the successor block has exactly two incoming edges. If
|
|
// so, see if the other predecessor contains a store to the same location.
|
|
// if so, insert a PHI node (if needed) and move the stores down.
|
|
BasicBlock *DestBB = StoreBB->getTerminator()->getSuccessor(0);
|
|
|
|
// Determine whether Dest has exactly two predecessors and, if so, compute
|
|
// the other predecessor.
|
|
pred_iterator PI = pred_begin(DestBB);
|
|
BasicBlock *P = *PI;
|
|
BasicBlock *OtherBB = 0;
|
|
|
|
if (P != StoreBB)
|
|
OtherBB = P;
|
|
|
|
if (++PI == pred_end(DestBB))
|
|
return false;
|
|
|
|
P = *PI;
|
|
if (P != StoreBB) {
|
|
if (OtherBB)
|
|
return false;
|
|
OtherBB = P;
|
|
}
|
|
if (++PI != pred_end(DestBB))
|
|
return false;
|
|
|
|
// Bail out if all the relevant blocks aren't distinct (this can happen,
|
|
// for example, if SI is in an infinite loop)
|
|
if (StoreBB == DestBB || OtherBB == DestBB)
|
|
return false;
|
|
|
|
// Verify that the other block ends in a branch and is not otherwise empty.
|
|
BasicBlock::iterator BBI = OtherBB->getTerminator();
|
|
BranchInst *OtherBr = dyn_cast<BranchInst>(BBI);
|
|
if (!OtherBr || BBI == OtherBB->begin())
|
|
return false;
|
|
|
|
// If the other block ends in an unconditional branch, check for the 'if then
|
|
// else' case. there is an instruction before the branch.
|
|
StoreInst *OtherStore = 0;
|
|
if (OtherBr->isUnconditional()) {
|
|
--BBI;
|
|
// Skip over debugging info.
|
|
while (isa<DbgInfoIntrinsic>(BBI) ||
|
|
(isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
|
|
if (BBI==OtherBB->begin())
|
|
return false;
|
|
--BBI;
|
|
}
|
|
// If this isn't a store, isn't a store to the same location, or if the
|
|
// alignments differ, bail out.
|
|
OtherStore = dyn_cast<StoreInst>(BBI);
|
|
if (!OtherStore || OtherStore->getOperand(1) != SI.getOperand(1) ||
|
|
OtherStore->getAlignment() != SI.getAlignment())
|
|
return false;
|
|
} else {
|
|
// Otherwise, the other block ended with a conditional branch. If one of the
|
|
// destinations is StoreBB, then we have the if/then case.
|
|
if (OtherBr->getSuccessor(0) != StoreBB &&
|
|
OtherBr->getSuccessor(1) != StoreBB)
|
|
return false;
|
|
|
|
// Okay, we know that OtherBr now goes to Dest and StoreBB, so this is an
|
|
// if/then triangle. See if there is a store to the same ptr as SI that
|
|
// lives in OtherBB.
|
|
for (;; --BBI) {
|
|
// Check to see if we find the matching store.
|
|
if ((OtherStore = dyn_cast<StoreInst>(BBI))) {
|
|
if (OtherStore->getOperand(1) != SI.getOperand(1) ||
|
|
OtherStore->getAlignment() != SI.getAlignment())
|
|
return false;
|
|
break;
|
|
}
|
|
// If we find something that may be using or overwriting the stored
|
|
// value, or if we run out of instructions, we can't do the xform.
|
|
if (BBI->mayReadFromMemory() || BBI->mayWriteToMemory() ||
|
|
BBI == OtherBB->begin())
|
|
return false;
|
|
}
|
|
|
|
// In order to eliminate the store in OtherBr, we have to
|
|
// make sure nothing reads or overwrites the stored value in
|
|
// StoreBB.
|
|
for (BasicBlock::iterator I = StoreBB->begin(); &*I != &SI; ++I) {
|
|
// FIXME: This should really be AA driven.
|
|
if (I->mayReadFromMemory() || I->mayWriteToMemory())
|
|
return false;
|
|
}
|
|
}
|
|
|
|
// Insert a PHI node now if we need it.
|
|
Value *MergedVal = OtherStore->getOperand(0);
|
|
if (MergedVal != SI.getOperand(0)) {
|
|
PHINode *PN = PHINode::Create(MergedVal->getType(), "storemerge");
|
|
PN->reserveOperandSpace(2);
|
|
PN->addIncoming(SI.getOperand(0), SI.getParent());
|
|
PN->addIncoming(OtherStore->getOperand(0), OtherBB);
|
|
MergedVal = InsertNewInstBefore(PN, DestBB->front());
|
|
}
|
|
|
|
// Advance to a place where it is safe to insert the new store and
|
|
// insert it.
|
|
BBI = DestBB->getFirstNonPHI();
|
|
InsertNewInstBefore(new StoreInst(MergedVal, SI.getOperand(1),
|
|
OtherStore->isVolatile(),
|
|
SI.getAlignment()), *BBI);
|
|
|
|
// Nuke the old stores.
|
|
EraseInstFromFunction(SI);
|
|
EraseInstFromFunction(*OtherStore);
|
|
return true;
|
|
}
|