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* Add ability to eliminate a bunch of different cascading cast variations

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* Allow elimination of getelementptr X, uint 0 (which is a noop)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2428 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2002-05-02 17:06:02 +00:00
parent fa49f810c2
commit a1be566213
1 changed files with 60 additions and 2 deletions
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62
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -61,6 +61,7 @@ namespace {
Instruction *visitSub(BinaryOperator *I);
Instruction *visitMul(BinaryOperator *I);
Instruction *visitCastInst(CastInst *CI);
Instruction *visitGetElementPtrInst(GetElementPtrInst *GEP);
Instruction *visitMemAccessInst(MemAccessInst *MAI);
// visitInstruction - Specify what to return for unhandled instructions...
@ -163,18 +164,75 @@ Instruction *InstCombiner::visitMul(BinaryOperator *I) {
}
// CastInst simplification - If the user is casting a value to the same type,
// eliminate this cast instruction...
// isEliminableCastOfCast - Return true if it is valid to eliminate the CI
// instruction.
//
static inline bool isEliminableCastOfCast(const CastInst *CI,
const CastInst *CSrc) {
assert(CI->getOperand(0) == CSrc);
const Type *SrcTy = CSrc->getOperand(0)->getType();
const Type *MidTy = CSrc->getType();
const Type *DstTy = CI->getType();
// It is legal to eliminate the instruction if casting A->B->A
if (SrcTy == DstTy) return true;
// Allow free casting and conversion of sizes as long as the sign doesn't
// change...
if (SrcTy->isSigned() == MidTy->isSigned() &&
MidTy->isSigned() == DstTy->isSigned())
return true;
// Otherwise, we cannot succeed. Specifically we do not want to allow things
// like: short -> ushort -> uint, because this can create wrong results if
// the input short is negative!
//
return false;
}
// CastInst simplification
//
Instruction *InstCombiner::visitCastInst(CastInst *CI) {
// If the user is casting a value to the same type, eliminate this cast
// instruction...
if (CI->getType() == CI->getOperand(0)->getType() && !CI->use_empty()) {
AddUsesToWorkList(CI); // Add all modified instrs to worklist
CI->replaceAllUsesWith(CI->getOperand(0));
return CI;
}
// If casting the result of another cast instruction, try to eliminate this
// one!
//
if (CastInst *CSrc = dyn_cast<CastInst>(CI->getOperand(0)))
if (isEliminableCastOfCast(CI, CSrc)) {
// This instruction now refers directly to the cast's src operand. This
// has a good chance of making CSrc dead.
CI->setOperand(0, CSrc->getOperand(0));
return CI;
}
return 0;
}
Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst *GEP) {
// Is it getelementptr %P, uint 0
// If so, elminate the noop.
if (GEP->getNumOperands() == 2 && !GEP->use_empty() &&
GEP->getOperand(1) == Constant::getNullValue(Type::UIntTy)) {
AddUsesToWorkList(GEP); // Add all modified instrs to worklist
GEP->replaceAllUsesWith(GEP->getOperand(0));
return GEP;
}
return visitMemAccessInst(GEP);
}
// Combine Indices - If the source pointer to this mem access instruction is a
// getelementptr instruction, combine the indices of the GEP into this
// instruction