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* Further cleanup.

Browse Source 
* Test for whether bits are shifted out during the optzn.

If so, the fold is illegal, though it can be handled explicitly for setne/seteq

This fixes the miscompilation of 254.gap last night, which was a latent bug
exposed by other optimizer improvements.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@15085 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-07-21 20:14:10 +00:00
parent 97a296f743
commit f0cacc0ae7
1 changed files with 27 additions and 9 deletions
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36
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -1471,22 +1471,40 @@ Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
if (ShAmt) {
bool CanFold = Shift->getOpcode() != Instruction::Shr ||
Shift->getType()->isUnsigned();
if (!CanFold &&
if (!CanFold) {
// To test for the bad case of the signed shr, see if any
// of the bits shifted in could be tested after the mask.
ConstantExpr::getAnd(ConstantExpr::getShl(ConstantInt::getAllOnesValue(Ty), ConstantUInt::get(Type::UByteTy, Ty->getPrimitiveSize()*8-ShAmt->getValue())), AndCST)->isNullValue()) {
CanFold = true;
Constant *OShAmt = ConstantUInt::get(Type::UByteTy,
Ty->getPrimitiveSize()*8-ShAmt->getValue());
Constant *ShVal =
ConstantExpr::getShl(ConstantInt::getAllOnesValue(Ty), OShAmt);
if (ConstantExpr::getAnd(ShVal, AndCST)->isNullValue())
CanFold = true;
}
if (CanFold) {
unsigned ShiftOp = Shift->getOpcode() == Instruction::Shl
? Instruction::Shr : Instruction::Shl;
I.setOperand(1, ConstantExpr::get(ShiftOp, CI, ShAmt));
LHSI->setOperand(1,ConstantExpr::get(ShiftOp,AndCST,ShAmt));
LHSI->setOperand(0, Shift->getOperand(0));
WorkList.push_back(Shift); // Shift is dead.
AddUsesToWorkList(I);
return &I;
Constant *NewCst = ConstantExpr::get(ShiftOp, CI, ShAmt);
// Check to see if we are shifting out any of the bits being
// compared.
if (ConstantExpr::get(Shift->getOpcode(), NewCst, ShAmt) != CI){
// If we shifted bits out, the fold is not going to work out.
// As a special case, check to see if this means that the
// result is always true or false now.
if (I.getOpcode() == Instruction::SetEQ)
return ReplaceInstUsesWith(I, ConstantBool::False);
if (I.getOpcode() == Instruction::SetNE)
return ReplaceInstUsesWith(I, ConstantBool::True);
} else {
I.setOperand(1, NewCst);
LHSI->setOperand(1, ConstantExpr::get(ShiftOp, AndCST,ShAmt));
LHSI->setOperand(0, Shift->getOperand(0));
WorkList.push_back(Shift); // Shift is dead.
AddUsesToWorkList(I);
return &I;
}
}
}
}