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[Reassociate] Use disjoint flag to convert Or to Add. #72772

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Merged
merged 1 commit into from
Dec 6, 2023
Merged

[Reassociate] Use disjoint flag to convert Or to Add. #72772

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7 changes: 4 additions & 3 deletions llvm/lib/Transforms/Scalar/Reassociate.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2256,9 +2256,10 @@ void ReassociatePass::OptimizeInst(Instruction *I) {
// with no common bits set, convert it to X+Y.
if (I->getOpcode() == Instruction::Or &&
shouldConvertOrWithNoCommonBitsToAdd(I) && !isLoadCombineCandidate(I) &&
haveNoCommonBitsSet(I->getOperand(0), I->getOperand(1),
SimplifyQuery(I->getModule()->getDataLayout(),
/*DT=*/nullptr, /*AC=*/nullptr, I))) {
(I->isDisjoint() ||
haveNoCommonBitsSet(I->getOperand(0), I->getOperand(1),
SimplifyQuery(I->getModule()->getDataLayout(),
/*DT=*/nullptr, /*AC=*/nullptr, I)))) {
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I think we should instead infer disjoint in InstCombine and then replace all existing haveNoCommonBitsSet() checks with only a isDisjoint() check, not both.

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I looked at this some more. When we reassociate a set of Ors we lose the flag, but then we revisit them to try more reassociation that may want to treat them as Adds. But we've lost the flag. So I think we need to call haveNoCommonBitsSet again somewhere to recover it.

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Okay, in that case keeping the haveNoCommonBitsSet calls makes sense.

Instruction *NI = convertOrWithNoCommonBitsToAdd(I);
RedoInsts.insert(I);
MadeChange = true;
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12 changes: 12 additions & 0 deletions llvm/test/Transforms/Reassociate/add-like-or.ll
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Expand Up @@ -59,6 +59,18 @@ define i32 @test3(i32 %x, i32 %bit) {
ret i32 %res
}

; Test that disjoint allow reassociation.
define i32 @test4(i32 %a, i32 %b) {
; CHECK-LABEL: @test4(
; CHECK-NEXT: [[C:%.*]] = add i32 [[A:%.*]], 1
; CHECK-NEXT: [[C_PLUS_ONE:%.*]] = add i32 [[C]], [[B:%.*]]
; CHECK-NEXT: ret i32 [[C_PLUS_ONE]]
;
%c = or disjoint i32 %a, %b
%c.plus.one = add i32 %c, 1
ret i32 %c.plus.one
}

declare i32 @llvm.ctlz.i32(i32, i1 immarg) #2

!0 = !{i32 0, i32 33}