mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-31 12:30:06 +00:00
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92685 91177308-0d34-0410-b5e6-96231b3b80d8
614 lines
23 KiB
C++
614 lines
23 KiB
C++
//===- InstCombineLoadStoreAlloca.cpp -------------------------------------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file implements the visit functions for load, store and alloca.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "InstCombine.h"
|
|
#include "llvm/IntrinsicInst.h"
|
|
#include "llvm/Target/TargetData.h"
|
|
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
|
|
#include "llvm/Transforms/Utils/Local.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
using namespace llvm;
|
|
|
|
STATISTIC(NumDeadStore, "Number of dead stores eliminated");
|
|
|
|
Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
|
|
// Convert: alloca Ty, C - where C is a constant != 1 into: alloca [C x Ty], 1
|
|
if (AI.isArrayAllocation()) { // Check C != 1
|
|
if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) {
|
|
const Type *NewTy =
|
|
ArrayType::get(AI.getAllocatedType(), C->getZExtValue());
|
|
assert(isa<AllocaInst>(AI) && "Unknown type of allocation inst!");
|
|
AllocaInst *New = Builder->CreateAlloca(NewTy, 0, AI.getName());
|
|
New->setAlignment(AI.getAlignment());
|
|
|
|
// Scan to the end of the allocation instructions, to skip over a block of
|
|
// allocas if possible...also skip interleaved debug info
|
|
//
|
|
BasicBlock::iterator It = New;
|
|
while (isa<AllocaInst>(*It) || isa<DbgInfoIntrinsic>(*It)) ++It;
|
|
|
|
// Now that I is pointing to the first non-allocation-inst in the block,
|
|
// insert our getelementptr instruction...
|
|
//
|
|
Value *NullIdx =Constant::getNullValue(Type::getInt32Ty(AI.getContext()));
|
|
Value *Idx[2];
|
|
Idx[0] = NullIdx;
|
|
Idx[1] = NullIdx;
|
|
Value *V = GetElementPtrInst::CreateInBounds(New, Idx, Idx + 2,
|
|
New->getName()+".sub", It);
|
|
|
|
// Now make everything use the getelementptr instead of the original
|
|
// allocation.
|
|
return ReplaceInstUsesWith(AI, V);
|
|
} else if (isa<UndefValue>(AI.getArraySize())) {
|
|
return ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
|
|
}
|
|
}
|
|
|
|
if (TD && isa<AllocaInst>(AI) && AI.getAllocatedType()->isSized()) {
|
|
// If alloca'ing a zero byte object, replace the alloca with a null pointer.
|
|
// Note that we only do this for alloca's, because malloc should allocate
|
|
// and return a unique pointer, even for a zero byte allocation.
|
|
if (TD->getTypeAllocSize(AI.getAllocatedType()) == 0)
|
|
return ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
|
|
|
|
// If the alignment is 0 (unspecified), assign it the preferred alignment.
|
|
if (AI.getAlignment() == 0)
|
|
AI.setAlignment(TD->getPrefTypeAlignment(AI.getAllocatedType()));
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
|
|
/// InstCombineLoadCast - Fold 'load (cast P)' -> cast (load P)' when possible.
|
|
static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI,
|
|
const TargetData *TD) {
|
|
User *CI = cast<User>(LI.getOperand(0));
|
|
Value *CastOp = CI->getOperand(0);
|
|
|
|
const PointerType *DestTy = cast<PointerType>(CI->getType());
|
|
const Type *DestPTy = DestTy->getElementType();
|
|
if (const PointerType *SrcTy = dyn_cast<PointerType>(CastOp->getType())) {
|
|
|
|
// If the address spaces don't match, don't eliminate the cast.
|
|
if (DestTy->getAddressSpace() != SrcTy->getAddressSpace())
|
|
return 0;
|
|
|
|
const Type *SrcPTy = SrcTy->getElementType();
|
|
|
|
if (DestPTy->isInteger() || isa<PointerType>(DestPTy) ||
|
|
isa<VectorType>(DestPTy)) {
|
|
// If the source is an array, the code below will not succeed. Check to
|
|
// see if a trivial 'gep P, 0, 0' will help matters. Only do this for
|
|
// constants.
|
|
if (const ArrayType *ASrcTy = dyn_cast<ArrayType>(SrcPTy))
|
|
if (Constant *CSrc = dyn_cast<Constant>(CastOp))
|
|
if (ASrcTy->getNumElements() != 0) {
|
|
Value *Idxs[2];
|
|
Idxs[0] = Constant::getNullValue(Type::getInt32Ty(LI.getContext()));
|
|
Idxs[1] = Idxs[0];
|
|
CastOp = ConstantExpr::getGetElementPtr(CSrc, Idxs, 2);
|
|
SrcTy = cast<PointerType>(CastOp->getType());
|
|
SrcPTy = SrcTy->getElementType();
|
|
}
|
|
|
|
if (IC.getTargetData() &&
|
|
(SrcPTy->isInteger() || isa<PointerType>(SrcPTy) ||
|
|
isa<VectorType>(SrcPTy)) &&
|
|
// Do not allow turning this into a load of an integer, which is then
|
|
// casted to a pointer, this pessimizes pointer analysis a lot.
|
|
(isa<PointerType>(SrcPTy) == isa<PointerType>(LI.getType())) &&
|
|
IC.getTargetData()->getTypeSizeInBits(SrcPTy) ==
|
|
IC.getTargetData()->getTypeSizeInBits(DestPTy)) {
|
|
|
|
// Okay, we are casting from one integer or pointer type to another of
|
|
// the same size. Instead of casting the pointer before the load, cast
|
|
// the result of the loaded value.
|
|
Value *NewLoad =
|
|
IC.Builder->CreateLoad(CastOp, LI.isVolatile(), CI->getName());
|
|
// Now cast the result of the load.
|
|
return new BitCastInst(NewLoad, LI.getType());
|
|
}
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
|
|
Value *Op = LI.getOperand(0);
|
|
|
|
// Attempt to improve the alignment.
|
|
if (TD) {
|
|
unsigned KnownAlign =
|
|
GetOrEnforceKnownAlignment(Op, TD->getPrefTypeAlignment(LI.getType()));
|
|
if (KnownAlign >
|
|
(LI.getAlignment() == 0 ? TD->getABITypeAlignment(LI.getType()) :
|
|
LI.getAlignment()))
|
|
LI.setAlignment(KnownAlign);
|
|
}
|
|
|
|
// load (cast X) --> cast (load X) iff safe.
|
|
if (isa<CastInst>(Op))
|
|
if (Instruction *Res = InstCombineLoadCast(*this, LI, TD))
|
|
return Res;
|
|
|
|
// None of the following transforms are legal for volatile loads.
|
|
if (LI.isVolatile()) return 0;
|
|
|
|
// Do really simple store-to-load forwarding and load CSE, to catch cases
|
|
// where there are several consequtive memory accesses to the same location,
|
|
// separated by a few arithmetic operations.
|
|
BasicBlock::iterator BBI = &LI;
|
|
if (Value *AvailableVal = FindAvailableLoadedValue(Op, LI.getParent(), BBI,6))
|
|
return ReplaceInstUsesWith(LI, AvailableVal);
|
|
|
|
// load(gep null, ...) -> unreachable
|
|
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) {
|
|
const Value *GEPI0 = GEPI->getOperand(0);
|
|
// TODO: Consider a target hook for valid address spaces for this xform.
|
|
if (isa<ConstantPointerNull>(GEPI0) && GEPI->getPointerAddressSpace() == 0){
|
|
// Insert a new store to null instruction before the load to indicate
|
|
// that this code is not reachable. We do this instead of inserting
|
|
// an unreachable instruction directly because we cannot modify the
|
|
// CFG.
|
|
new StoreInst(UndefValue::get(LI.getType()),
|
|
Constant::getNullValue(Op->getType()), &LI);
|
|
return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType()));
|
|
}
|
|
}
|
|
|
|
// load null/undef -> unreachable
|
|
// TODO: Consider a target hook for valid address spaces for this xform.
|
|
if (isa<UndefValue>(Op) ||
|
|
(isa<ConstantPointerNull>(Op) && LI.getPointerAddressSpace() == 0)) {
|
|
// Insert a new store to null instruction before the load to indicate that
|
|
// this code is not reachable. We do this instead of inserting an
|
|
// unreachable instruction directly because we cannot modify the CFG.
|
|
new StoreInst(UndefValue::get(LI.getType()),
|
|
Constant::getNullValue(Op->getType()), &LI);
|
|
return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType()));
|
|
}
|
|
|
|
// Instcombine load (constantexpr_cast global) -> cast (load global)
|
|
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Op))
|
|
if (CE->isCast())
|
|
if (Instruction *Res = InstCombineLoadCast(*this, LI, TD))
|
|
return Res;
|
|
|
|
if (Op->hasOneUse()) {
|
|
// Change select and PHI nodes to select values instead of addresses: this
|
|
// helps alias analysis out a lot, allows many others simplifications, and
|
|
// exposes redundancy in the code.
|
|
//
|
|
// Note that we cannot do the transformation unless we know that the
|
|
// introduced loads cannot trap! Something like this is valid as long as
|
|
// the condition is always false: load (select bool %C, int* null, int* %G),
|
|
// but it would not be valid if we transformed it to load from null
|
|
// unconditionally.
|
|
//
|
|
if (SelectInst *SI = dyn_cast<SelectInst>(Op)) {
|
|
// load (select (Cond, &V1, &V2)) --> select(Cond, load &V1, load &V2).
|
|
if (isSafeToLoadUnconditionally(SI->getOperand(1), SI) &&
|
|
isSafeToLoadUnconditionally(SI->getOperand(2), SI)) {
|
|
Value *V1 = Builder->CreateLoad(SI->getOperand(1),
|
|
SI->getOperand(1)->getName()+".val");
|
|
Value *V2 = Builder->CreateLoad(SI->getOperand(2),
|
|
SI->getOperand(2)->getName()+".val");
|
|
return SelectInst::Create(SI->getCondition(), V1, V2);
|
|
}
|
|
|
|
// load (select (cond, null, P)) -> load P
|
|
if (Constant *C = dyn_cast<Constant>(SI->getOperand(1)))
|
|
if (C->isNullValue()) {
|
|
LI.setOperand(0, SI->getOperand(2));
|
|
return &LI;
|
|
}
|
|
|
|
// load (select (cond, P, null)) -> load P
|
|
if (Constant *C = dyn_cast<Constant>(SI->getOperand(2)))
|
|
if (C->isNullValue()) {
|
|
LI.setOperand(0, SI->getOperand(1));
|
|
return &LI;
|
|
}
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/// InstCombineStoreToCast - Fold store V, (cast P) -> store (cast V), P
|
|
/// when possible. This makes it generally easy to do alias analysis and/or
|
|
/// SROA/mem2reg of the memory object.
|
|
static Instruction *InstCombineStoreToCast(InstCombiner &IC, StoreInst &SI) {
|
|
User *CI = cast<User>(SI.getOperand(1));
|
|
Value *CastOp = CI->getOperand(0);
|
|
|
|
const Type *DestPTy = cast<PointerType>(CI->getType())->getElementType();
|
|
const PointerType *SrcTy = dyn_cast<PointerType>(CastOp->getType());
|
|
if (SrcTy == 0) return 0;
|
|
|
|
const Type *SrcPTy = SrcTy->getElementType();
|
|
|
|
if (!DestPTy->isInteger() && !isa<PointerType>(DestPTy))
|
|
return 0;
|
|
|
|
/// NewGEPIndices - If SrcPTy is an aggregate type, we can emit a "noop gep"
|
|
/// to its first element. This allows us to handle things like:
|
|
/// store i32 xxx, (bitcast {foo*, float}* %P to i32*)
|
|
/// on 32-bit hosts.
|
|
SmallVector<Value*, 4> NewGEPIndices;
|
|
|
|
// If the source is an array, the code below will not succeed. Check to
|
|
// see if a trivial 'gep P, 0, 0' will help matters. Only do this for
|
|
// constants.
|
|
if (isa<ArrayType>(SrcPTy) || isa<StructType>(SrcPTy)) {
|
|
// Index through pointer.
|
|
Constant *Zero = Constant::getNullValue(Type::getInt32Ty(SI.getContext()));
|
|
NewGEPIndices.push_back(Zero);
|
|
|
|
while (1) {
|
|
if (const StructType *STy = dyn_cast<StructType>(SrcPTy)) {
|
|
if (!STy->getNumElements()) /* Struct can be empty {} */
|
|
break;
|
|
NewGEPIndices.push_back(Zero);
|
|
SrcPTy = STy->getElementType(0);
|
|
} else if (const ArrayType *ATy = dyn_cast<ArrayType>(SrcPTy)) {
|
|
NewGEPIndices.push_back(Zero);
|
|
SrcPTy = ATy->getElementType();
|
|
} else {
|
|
break;
|
|
}
|
|
}
|
|
|
|
SrcTy = PointerType::get(SrcPTy, SrcTy->getAddressSpace());
|
|
}
|
|
|
|
if (!SrcPTy->isInteger() && !isa<PointerType>(SrcPTy))
|
|
return 0;
|
|
|
|
// If the pointers point into different address spaces or if they point to
|
|
// values with different sizes, we can't do the transformation.
|
|
if (!IC.getTargetData() ||
|
|
SrcTy->getAddressSpace() !=
|
|
cast<PointerType>(CI->getType())->getAddressSpace() ||
|
|
IC.getTargetData()->getTypeSizeInBits(SrcPTy) !=
|
|
IC.getTargetData()->getTypeSizeInBits(DestPTy))
|
|
return 0;
|
|
|
|
// Okay, we are casting from one integer or pointer type to another of
|
|
// the same size. Instead of casting the pointer before
|
|
// the store, cast the value to be stored.
|
|
Value *NewCast;
|
|
Value *SIOp0 = SI.getOperand(0);
|
|
Instruction::CastOps opcode = Instruction::BitCast;
|
|
const Type* CastSrcTy = SIOp0->getType();
|
|
const Type* CastDstTy = SrcPTy;
|
|
if (isa<PointerType>(CastDstTy)) {
|
|
if (CastSrcTy->isInteger())
|
|
opcode = Instruction::IntToPtr;
|
|
} else if (isa<IntegerType>(CastDstTy)) {
|
|
if (isa<PointerType>(SIOp0->getType()))
|
|
opcode = Instruction::PtrToInt;
|
|
}
|
|
|
|
// SIOp0 is a pointer to aggregate and this is a store to the first field,
|
|
// emit a GEP to index into its first field.
|
|
if (!NewGEPIndices.empty())
|
|
CastOp = IC.Builder->CreateInBoundsGEP(CastOp, NewGEPIndices.begin(),
|
|
NewGEPIndices.end());
|
|
|
|
NewCast = IC.Builder->CreateCast(opcode, SIOp0, CastDstTy,
|
|
SIOp0->getName()+".c");
|
|
return new StoreInst(NewCast, CastOp);
|
|
}
|
|
|
|
/// equivalentAddressValues - Test if A and B will obviously have the same
|
|
/// value. This includes recognizing that %t0 and %t1 will have the same
|
|
/// value in code like this:
|
|
/// %t0 = getelementptr \@a, 0, 3
|
|
/// store i32 0, i32* %t0
|
|
/// %t1 = getelementptr \@a, 0, 3
|
|
/// %t2 = load i32* %t1
|
|
///
|
|
static bool equivalentAddressValues(Value *A, Value *B) {
|
|
// Test if the values are trivially equivalent.
|
|
if (A == B) return true;
|
|
|
|
// Test if the values come form identical arithmetic instructions.
|
|
// This uses isIdenticalToWhenDefined instead of isIdenticalTo because
|
|
// its only used to compare two uses within the same basic block, which
|
|
// means that they'll always either have the same value or one of them
|
|
// will have an undefined value.
|
|
if (isa<BinaryOperator>(A) ||
|
|
isa<CastInst>(A) ||
|
|
isa<PHINode>(A) ||
|
|
isa<GetElementPtrInst>(A))
|
|
if (Instruction *BI = dyn_cast<Instruction>(B))
|
|
if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI))
|
|
return true;
|
|
|
|
// Otherwise they may not be equivalent.
|
|
return false;
|
|
}
|
|
|
|
// If this instruction has two uses, one of which is a llvm.dbg.declare,
|
|
// return the llvm.dbg.declare.
|
|
DbgDeclareInst *InstCombiner::hasOneUsePlusDeclare(Value *V) {
|
|
if (!V->hasNUses(2))
|
|
return 0;
|
|
for (Value::use_iterator UI = V->use_begin(), E = V->use_end();
|
|
UI != E; ++UI) {
|
|
if (DbgDeclareInst *DI = dyn_cast<DbgDeclareInst>(UI))
|
|
return DI;
|
|
if (isa<BitCastInst>(UI) && UI->hasOneUse()) {
|
|
if (DbgDeclareInst *DI = dyn_cast<DbgDeclareInst>(UI->use_begin()))
|
|
return DI;
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
|
|
Value *Val = SI.getOperand(0);
|
|
Value *Ptr = SI.getOperand(1);
|
|
|
|
// If the RHS is an alloca with a single use, zapify the store, making the
|
|
// alloca dead.
|
|
// If the RHS is an alloca with a two uses, the other one being a
|
|
// llvm.dbg.declare, zapify the store and the declare, making the
|
|
// alloca dead. We must do this to prevent declare's from affecting
|
|
// codegen.
|
|
if (!SI.isVolatile()) {
|
|
if (Ptr->hasOneUse()) {
|
|
if (isa<AllocaInst>(Ptr))
|
|
return EraseInstFromFunction(SI);
|
|
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) {
|
|
if (isa<AllocaInst>(GEP->getOperand(0))) {
|
|
if (GEP->getOperand(0)->hasOneUse())
|
|
return EraseInstFromFunction(SI);
|
|
if (DbgDeclareInst *DI = hasOneUsePlusDeclare(GEP->getOperand(0))) {
|
|
EraseInstFromFunction(*DI);
|
|
return EraseInstFromFunction(SI);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
if (DbgDeclareInst *DI = hasOneUsePlusDeclare(Ptr)) {
|
|
EraseInstFromFunction(*DI);
|
|
return EraseInstFromFunction(SI);
|
|
}
|
|
}
|
|
|
|
// Attempt to improve the alignment.
|
|
if (TD) {
|
|
unsigned KnownAlign =
|
|
GetOrEnforceKnownAlignment(Ptr, TD->getPrefTypeAlignment(Val->getType()));
|
|
if (KnownAlign >
|
|
(SI.getAlignment() == 0 ? TD->getABITypeAlignment(Val->getType()) :
|
|
SI.getAlignment()))
|
|
SI.setAlignment(KnownAlign);
|
|
}
|
|
|
|
// Do really simple DSE, to catch cases where there are several consecutive
|
|
// stores to the same location, separated by a few arithmetic operations. This
|
|
// situation often occurs with bitfield accesses.
|
|
BasicBlock::iterator BBI = &SI;
|
|
for (unsigned ScanInsts = 6; BBI != SI.getParent()->begin() && ScanInsts;
|
|
--ScanInsts) {
|
|
--BBI;
|
|
// Don't count debug info directives, lest they affect codegen,
|
|
// and we skip pointer-to-pointer bitcasts, which are NOPs.
|
|
// It is necessary for correctness to skip those that feed into a
|
|
// llvm.dbg.declare, as these are not present when debugging is off.
|
|
if (isa<DbgInfoIntrinsic>(BBI) ||
|
|
(isa<BitCastInst>(BBI) && isa<PointerType>(BBI->getType()))) {
|
|
ScanInsts++;
|
|
continue;
|
|
}
|
|
|
|
if (StoreInst *PrevSI = dyn_cast<StoreInst>(BBI)) {
|
|
// Prev store isn't volatile, and stores to the same location?
|
|
if (!PrevSI->isVolatile() &&equivalentAddressValues(PrevSI->getOperand(1),
|
|
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 the pointer bitcasts that feed
|
|
// into them), 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) && isa<PointerType>(BBI->getType())));
|
|
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 *OtherBB = 0;
|
|
if (*PI != StoreBB)
|
|
OtherBB = *PI;
|
|
++PI;
|
|
if (PI == pred_end(DestBB))
|
|
return false;
|
|
|
|
if (*PI != StoreBB) {
|
|
if (OtherBB)
|
|
return false;
|
|
OtherBB = *PI;
|
|
}
|
|
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) && isa<PointerType>(BBI->getType()))) {
|
|
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;
|
|
}
|