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Instead of loading small global string from memory, use
integer constant.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43148 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Devang Patel 2007-10-18 19:52:32 +00:00
parent b388ca9544
commit 99db6add3d
1 changed files with 36 additions and 3 deletions
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39
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -8941,10 +8941,43 @@ Instruction *InstCombiner::visitFreeInst(FreeInst &FI) {
/// InstCombineLoadCast - Fold 'load (cast P)' -> cast (load P)' when possible.
static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI) {
static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI,
const TargetData *TD) {
User *CI = cast<User>(LI.getOperand(0));
Value *CastOp = CI->getOperand(0);
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(CI)) {
// Instead of loading constant c string, use corresponding integer value
// directly if string length is small enough.
const std::string &Str = CE->getOperand(0)->getStringValue();
if (!Str.empty()) {
unsigned len = Str.length();
const Type *Ty = cast<PointerType>(CE->getType())->getElementType();
unsigned numBits = Ty->getPrimitiveSizeInBits();
// Replace LI with immediate integer store.
if ((numBits >> 3) == len + 1) {
APInt StrVal(numBits, 0);
APInt SingleChar(numBits, 0);
if (TD->isLittleEndian()) {
for (signed i = len-1; i >= 0; i--) {
SingleChar = (uint64_t) Str[i];
StrVal = (StrVal << 8) | SingleChar;
}
} else {
for (unsigned i = 0; i < len; i++) {
SingleChar = (uint64_t) Str[i];
StrVal = (StrVal << 8) | SingleChar;
}
// Append NULL at the end.
SingleChar = 0;
StrVal = (StrVal << 8) | SingleChar;
}
Value *NL = ConstantInt::get(StrVal);
return IC.ReplaceInstUsesWith(LI, NL);
}
}
}
const Type *DestPTy = cast<PointerType>(CI->getType())->getElementType();
if (const PointerType *SrcTy = dyn_cast<PointerType>(CastOp->getType())) {
const Type *SrcPTy = SrcTy->getElementType();
@ -9050,7 +9083,7 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
// load (cast X) --> cast (load X) iff safe
if (isa<CastInst>(Op))
if (Instruction *Res = InstCombineLoadCast(*this, LI))
if (Instruction *Res = InstCombineLoadCast(*this, LI, TD))
return Res;
// None of the following transforms are legal for volatile loads.
@ -9114,7 +9147,7 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
}
} else if (CE->isCast()) {
if (Instruction *Res = InstCombineLoadCast(*this, LI))
if (Instruction *Res = InstCombineLoadCast(*this, LI, TD))
return Res;
}
}