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Implement new transforms: 

Replace (cast (sub A, B) to bool) -> (setne A, B)
  Replace (cast (add A, B) to bool) -> (setne A, -B)

llvm-svn: 6873
This commit is contained in:
Chris Lattner 2003-06-23 21:59:52 +00:00
parent eea63a519a
commit 55d4bda861
1 changed files with 33 additions and 4 deletions
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37
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
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@ -898,15 +898,17 @@ static inline bool isEliminableCastOfCast(const CastInst &CI,
// CastInst simplification
//
Instruction *InstCombiner::visitCastInst(CastInst &CI) {
Value *Src = CI.getOperand(0);
// If the user is casting a value to the same type, eliminate this cast
// instruction...
if (CI.getType() == CI.getOperand(0)->getType())
return ReplaceInstUsesWith(CI, CI.getOperand(0));
if (CI.getType() == Src->getType())
return ReplaceInstUsesWith(CI, Src);
// If casting the result of another cast instruction, try to eliminate this
// one!
//
if (CastInst *CSrc = dyn_cast<CastInst>(CI.getOperand(0))) {
if (CastInst *CSrc = dyn_cast<CastInst>(Src)) {
if (isEliminableCastOfCast(CI, CSrc)) {
// This instruction now refers directly to the cast's src operand. This
// has a good chance of making CSrc dead.
@ -933,7 +935,7 @@ Instruction *InstCombiner::visitCastInst(CastInst &CI) {
// If casting the result of a getelementptr instruction with no offset, turn
// this into a cast of the original pointer!
//
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CI.getOperand(0))) {
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Src)) {
bool AllZeroOperands = true;
for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i)
if (!isa<Constant>(GEP->getOperand(i)) ||
@ -947,6 +949,33 @@ Instruction *InstCombiner::visitCastInst(CastInst &CI) {
}
}
// If this is a cast to bool (which is effectively a "!=0" test), then we can
// perform a few optimizations...
//
if (CI.getType() == Type::BoolTy) {
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Src)) {
Value *Op0 = BO->getOperand(0), *Op1 = BO->getOperand(1);
// Replace (cast (sub A, B) to bool) with (setne A, B)
if (BO->getOpcode() == Instruction::Sub)
return new SetCondInst(Instruction::SetNE, Op0, Op1);
// Replace (cast (add A, B) to bool) with (setne A, -B) if B is
// efficiently invertible, or if the add has just this one use.
if (BO->getOpcode() == Instruction::Add)
if (Value *NegVal = dyn_castNegVal(Op1))
return new SetCondInst(Instruction::SetNE, Op0, NegVal);
else if (Value *NegVal = dyn_castNegVal(Op0))
return new SetCondInst(Instruction::SetNE, NegVal, Op1);
else if (BO->use_size() == 1) {
Instruction *Neg = BinaryOperator::createNeg(Op1, BO->getName());
BO->setName("");
InsertNewInstBefore(Neg, CI);
return new SetCondInst(Instruction::SetNE, Op0, Neg);
}
}
}
return 0;
}