[PATCH] D36486: [InstCombine] Don't fall back to only calling computeKnownBits if the upper bit of Add/Sub is demanded.
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Fri Aug 25 11:43:09 PDT 2017
This revision was automatically updated to reflect the committed changes.
Closed by commit rL311789: [InstCombine] Don't fall back to only calling computeKnownBits if the upper bit… (authored by ctopper).
Changed prior to commit:
https://reviews.llvm.org/D36486?vs=110271&id=112724#toc
Repository:
rL LLVM
https://reviews.llvm.org/D36486
Files:
llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -396,38 +396,39 @@
/// If the high-bits of an ADD/SUB are not demanded, then we do not care
/// about the high bits of the operands.
unsigned NLZ = DemandedMask.countLeadingZeros();
- if (NLZ > 0) {
- // Right fill the mask of bits for this ADD/SUB to demand the most
- // significant bit and all those below it.
- APInt DemandedFromOps(APInt::getLowBitsSet(BitWidth, BitWidth-NLZ));
- if (ShrinkDemandedConstant(I, 0, DemandedFromOps) ||
- SimplifyDemandedBits(I, 0, DemandedFromOps, LHSKnown, Depth + 1) ||
- ShrinkDemandedConstant(I, 1, DemandedFromOps) ||
- SimplifyDemandedBits(I, 1, DemandedFromOps, RHSKnown, Depth + 1)) {
+ // Right fill the mask of bits for this ADD/SUB to demand the most
+ // significant bit and all those below it.
+ APInt DemandedFromOps(APInt::getLowBitsSet(BitWidth, BitWidth-NLZ));
+ if (ShrinkDemandedConstant(I, 0, DemandedFromOps) ||
+ SimplifyDemandedBits(I, 0, DemandedFromOps, LHSKnown, Depth + 1) ||
+ ShrinkDemandedConstant(I, 1, DemandedFromOps) ||
+ SimplifyDemandedBits(I, 1, DemandedFromOps, RHSKnown, Depth + 1)) {
+ if (NLZ > 0) {
// Disable the nsw and nuw flags here: We can no longer guarantee that
// we won't wrap after simplification. Removing the nsw/nuw flags is
// legal here because the top bit is not demanded.
BinaryOperator &BinOP = *cast<BinaryOperator>(I);
BinOP.setHasNoSignedWrap(false);
BinOP.setHasNoUnsignedWrap(false);
- return I;
}
-
- // If we are known to be adding/subtracting zeros to every bit below
- // the highest demanded bit, we just return the other side.
- if (DemandedFromOps.isSubsetOf(RHSKnown.Zero))
- return I->getOperand(0);
- // We can't do this with the LHS for subtraction, unless we are only
- // demanding the LSB.
- if ((I->getOpcode() == Instruction::Add ||
- DemandedFromOps.isOneValue()) &&
- DemandedFromOps.isSubsetOf(LHSKnown.Zero))
- return I->getOperand(1);
+ return I;
}
- // Otherwise just hand the add/sub off to computeKnownBits to fill in
- // the known zeros and ones.
- computeKnownBits(V, Known, Depth, CxtI);
+ // If we are known to be adding/subtracting zeros to every bit below
+ // the highest demanded bit, we just return the other side.
+ if (DemandedFromOps.isSubsetOf(RHSKnown.Zero))
+ return I->getOperand(0);
+ // We can't do this with the LHS for subtraction, unless we are only
+ // demanding the LSB.
+ if ((I->getOpcode() == Instruction::Add ||
+ DemandedFromOps.isOneValue()) &&
+ DemandedFromOps.isSubsetOf(LHSKnown.Zero))
+ return I->getOperand(1);
+
+ // Otherwise just compute the known bits of the result.
+ bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoUnsignedWrap();
+ Known = KnownBits::computeForAddSub(I->getOpcode() == Instruction::Add,
+ NSW, LHSKnown, RHSKnown);
break;
}
case Instruction::Shl: {
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