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Add some simple folds that occur in bitfield cases. Fix a minor bug in 

isHighOnes, where it would consider 0 to have high ones.

llvm-svn: 22693
This commit is contained in:
Chris Lattner 2005-08-07 07:03:10 +00:00
parent 134ebd0801
commit 2c14cf7b74
1 changed files with 32 additions and 0 deletions
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32
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
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@ -1215,6 +1215,7 @@ static bool isLowOnes(const ConstantInt *CI) {
// This is the same as lowones(~X).
static bool isHighOnes(const ConstantInt *CI) {
uint64_t V = ~CI->getRawValue();
if (~V == 0) return false; // 0's does not match "1+"
// There won't be bits set in parts that the type doesn't contain.
V &= ConstantInt::getAllOnesValue(CI->getType())->getRawValue();
@ -1636,6 +1637,37 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
} else if (CastInst *CI = dyn_cast<CastInst>(Op0)) {
const Type *SrcTy = CI->getOperand(0)->getType();
// If this is an integer truncation or change from signed-to-unsigned, and
// if the source is an and/or with immediate, transform it. This
// frequently occurs for bitfield accesses.
if (Instruction *CastOp = dyn_cast<Instruction>(CI->getOperand(0))) {
if (SrcTy->getPrimitiveSizeInBits() >=
I.getType()->getPrimitiveSizeInBits() &&
CastOp->getNumOperands() == 2)
if (ConstantInt *AndCI =dyn_cast<ConstantInt>(CastOp->getOperand(1)))
if (CastOp->getOpcode() == Instruction::And) {
// Change: and (cast (and X, C1) to T), C2
// into : and (cast X to T), trunc(C1)&C2
// This will folds the two ands together, which may allow other
// simplifications.
Instruction *NewCast =
new CastInst(CastOp->getOperand(0), I.getType(),
CastOp->getName()+".shrunk");
NewCast = InsertNewInstBefore(NewCast, I);
Constant *C3=ConstantExpr::getCast(AndCI, I.getType());//trunc(C1)
C3 = ConstantExpr::getAnd(C3, AndRHS); // trunc(C1)&C2
return BinaryOperator::createAnd(NewCast, C3);
} else if (CastOp->getOpcode() == Instruction::Or) {
// Change: and (cast (or X, C1) to T), C2
// into : trunc(C1)&C2 iff trunc(C1)&C2 == C2
Constant *C3=ConstantExpr::getCast(AndCI, I.getType());//trunc(C1)
if (ConstantExpr::getAnd(C3, AndRHS) == AndRHS) // trunc(C1)&C2
return ReplaceInstUsesWith(I, AndRHS);
}
}
// If this is an integer sign or zero extension instruction.
if (SrcTy->isIntegral() &&
SrcTy->getPrimitiveSizeInBits() <