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Apply "Instead of loading small c string constant, use integer constant directly" transformation while processing load instruction.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43070 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Devang Patel 2007-10-17 07:24:40 +00:00
parent a5bfc97da7
commit afc407ea51
2 changed files with 29 additions and 25 deletions
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53
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -7673,41 +7673,21 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
unsigned Size = MemOpLength->getZExtValue();
unsigned Align = cast<ConstantInt>(CI.getOperand(4))->getZExtValue();
PointerType *NewPtrTy = NULL;
unsigned numBits = Size << 3;
// Destination pointer type is always i8 *
// If Size is 8 then use Int64Ty
// If Size is 4 then use Int32Ty
// If Size is 2 then use Int16Ty
// If Size is 1 then use Int8Ty
if (Size && Size <=8 && !(Size&(Size-1)))
NewPtrTy = PointerType::get(IntegerType::get(numBits));
NewPtrTy = PointerType::get(IntegerType::get(Size<<3));
if (NewPtrTy) {
Value *L = NULL;
// If source is a null terminated constant c string then try to use immediate store.
if (Constant *C = dyn_cast<Constant>(CI.getOperand(2))) {
const std::string &Str = C->getStringValue();
if (!Str.empty()) {
APInt StrVal(numBits, 0);
unsigned len = Str.length();
APInt SingleChar(numBits, 0);
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;
L = ConstantInt::get(StrVal);
}
}
// Otherwise load source from memory.
if (L == NULL) {
Value *Src = InsertCastBefore(Instruction::BitCast, CI.getOperand(2), NewPtrTy, CI);
L = new LoadInst(Src, "tmp", false, Align, &CI);
}
Value *Src = InsertCastBefore(Instruction::BitCast, CI.getOperand(2), NewPtrTy, CI);
Value *Dest = InsertCastBefore(Instruction::BitCast, CI.getOperand(1), NewPtrTy, CI);
Value *L = new LoadInst(Src, "tmp", false, Align, &CI);
Value *NS = new StoreInst(L, Dest, false, Align, &CI);
AddToWorkList(cast<Instruction>(L));
AddToWorkList(cast<Instruction>(NS));
CI.replaceAllUsesWith(NS);
Changed = true;
return EraseInstFromFunction(CI);
@ -9136,6 +9116,29 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
}
} else if (CE->isCast()) {
// 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();
if ((numBits >> 3) == len + 1) {
// Replace LI with immediate integer store.
APInt StrVal(numBits, 0);
APInt SingleChar(numBits, 0);
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 ReplaceInstUsesWith(LI, NL);
}
}
if (Instruction *Res = InstCombineLoadCast(*this, LI))
return Res;
}

1
test/Transforms/InstCombine/2007-10-10-EliminateMemCpy.ll
View File

@ -1,4 +1,5 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep call
; RUN: llvm-as < %s | opt -std-compile-opts | llvm-dis | not grep xyz
@.str = internal constant [4 x i8] c"xyz\00" ; <[4 x i8]*> [#uses=1]
define void @foo(i8* %P) {