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[InstCombine] Use a more targeted fix instead of r235544

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Only clear out the NSW/NUW flags if we are optimizing 'add'/'sub' while
taking advantage that the sign bit is not set.  We do this optimization
to further shrink the mask but shrinking the mask isn't NSW/NUW
preserving in this case.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235558 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2015-04-22 22:42:05 +00:00
parent d9b72fea11
commit f9c92b069a
2 changed files with 20 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

17
lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
View File

@ -88,13 +88,6 @@ bool InstCombiner::SimplifyDemandedBits(Use &U, APInt DemandedMask,
KnownOne, Depth, UserI); KnownOne, Depth, UserI);
if (!NewVal) return false; if (!NewVal) return false;
U = NewVal; U = NewVal;
// Shrinking a constant might cause a nsw/nuw violation to occur in
// instructions which are themselves demanded.
if (auto *UserOBO = dyn_cast<OverflowingBinaryOperator>(UserI)) {
cast<BinaryOperator>(UserOBO)->setHasNoSignedWrap(false);
cast<BinaryOperator>(UserOBO)->setHasNoUnsignedWrap(false);
}
return true; return true;
} }
@ -607,10 +600,13 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
if (SimplifyDemandedBits(I->getOperandUse(0), DemandedFromOps, if (SimplifyDemandedBits(I->getOperandUse(0), DemandedFromOps,
LHSKnownZero, LHSKnownOne, Depth + 1) || LHSKnownZero, LHSKnownOne, Depth + 1) ||
SimplifyDemandedBits(I->getOperandUse(1), DemandedFromOps, SimplifyDemandedBits(I->getOperandUse(1), DemandedFromOps,
LHSKnownZero, LHSKnownOne, Depth + 1)) LHSKnownZero, LHSKnownOne, Depth + 1)) {
cast<BinaryOperator>(I)->setHasNoSignedWrap(false);
cast<BinaryOperator>(I)->setHasNoUnsignedWrap(false);
return I; return I;
} }
} }
}
break; break;
} }
case Instruction::Sub: case Instruction::Sub:
@ -624,9 +620,12 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
if (SimplifyDemandedBits(I->getOperandUse(0), DemandedFromOps, if (SimplifyDemandedBits(I->getOperandUse(0), DemandedFromOps,
LHSKnownZero, LHSKnownOne, Depth + 1) || LHSKnownZero, LHSKnownOne, Depth + 1) ||
SimplifyDemandedBits(I->getOperandUse(1), DemandedFromOps, SimplifyDemandedBits(I->getOperandUse(1), DemandedFromOps,
LHSKnownZero, LHSKnownOne, Depth + 1)) LHSKnownZero, LHSKnownOne, Depth + 1)) {
cast<BinaryOperator>(I)->setHasNoSignedWrap(false);
cast<BinaryOperator>(I)->setHasNoUnsignedWrap(false);
return I; return I;
} }
}
// Otherwise just hand the sub off to computeKnownBits to fill in // Otherwise just hand the sub off to computeKnownBits to fill in
// the known zeros and ones. // the known zeros and ones.

12
test/Transforms/InstCombine/cast.ll
View File

@ -1125,3 +1125,15 @@ define i1 @PR23309(i32 %A, i32 %B) {
%trunc = trunc i32 %sub to i1 %trunc = trunc i32 %sub to i1
ret i1 %trunc ret i1 %trunc
} }
define i1 @PR23309v2(i32 %A, i32 %B) {
; CHECK-LABEL: @PR23309v2(
; CHECK-NEXT: %[[sub:.*]] = add i32 %A, %B
; CHECK-NEXT: %[[and:.*]] = and i32 %[[sub]], 1
; CHECK-NEXT: %[[cmp:.*]] = icmp ne i32 %[[and]], 0
; CHECK-NEXT: ret i1 %[[cmp]]
%add = add i32 %A, -4
%sub = add nuw i32 %add, %B
%trunc = trunc i32 %sub to i1
ret i1 %trunc
}