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We went through all that trouble to compute whether it was safe to transform

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this comparison, but never checked it.  Whoops, no wonder we miscompiled
177.mesa!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@30511 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-09-20 04:44:59 +00:00
parent 711762497c
commit b8456460cb
1 changed files with 46 additions and 6 deletions
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42
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -5713,12 +5713,51 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
return new CastInst(NotCond, SI.getType());
}
if (SetCondInst *IC = dyn_cast<SetCondInst>(SI.getCondition())) {
// (x <s 0) ? -1 : 0 -> sra x, 31
// (x >u 2147483647) ? -1 : 0 -> sra x, 31
if (TrueValC->isAllOnesValue() && FalseValC->isNullValue())
if (ConstantInt *CmpCst = dyn_cast<ConstantInt>(IC->getOperand(1))) {
bool CanXForm = false;
if (CmpCst->getType()->isSigned())
CanXForm = CmpCst->isNullValue() &&
IC->getOpcode() == Instruction::SetLT;
else {
unsigned Bits = CmpCst->getType()->getPrimitiveSizeInBits();
CanXForm = (CmpCst->getRawValue() == ~0ULL >> (64-Bits+1)) &&
IC->getOpcode() == Instruction::SetGT;
}
if (CanXForm) {
// The comparison constant and the result are not neccessarily the
// same width. In any case, the first step to do is make sure
// that X is signed.
Value *X = IC->getOperand(0);
if (!X->getType()->isSigned())
X = InsertCastBefore(X, X->getType()->getSignedVersion(), SI);
// Now that X is signed, we have to make the all ones value. Do
// this by inserting a new SRA.
unsigned Bits = X->getType()->getPrimitiveSizeInBits();
Constant *ShAmt = ConstantUInt::get(Type::UByteTy, Bits-1);
Instruction *SRA = new ShiftInst(Instruction::Shr, X,
ShAmt, "ones");
InsertNewInstBefore(SRA, SI);
// Finally, convert to the type of the select RHS. If this is
// smaller than the compare value, it will truncate the ones to
// fit. If it is larger, it will sext the ones to fit.
return new CastInst(SRA, SI.getType());
}
}
// If one of the constants is zero (we know they can't both be) and we
// have a setcc instruction with zero, and we have an 'and' with the
// non-constant value, eliminate this whole mess. This corresponds to
// cases like this: ((X & 27) ? 27 : 0)
if (TrueValC->isNullValue() || FalseValC->isNullValue())
if (SetCondInst *IC = dyn_cast<SetCondInst>(SI.getCondition()))
if (IC->isEquality() && isa<ConstantInt>(IC->getOperand(1)) &&
cast<Constant>(IC->getOperand(1))->isNullValue())
if (Instruction *ICA = dyn_cast<Instruction>(IC->getOperand(0)))
@ -5739,6 +5778,7 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
return ReplaceInstUsesWith(SI, V);
}
}
}
// See if we are selecting two values based on a comparison of the two values.
if (SetCondInst *SCI = dyn_cast<SetCondInst>(CondVal)) {