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[InstCombine] Use known bits to simplify mask in foldSelectICmpAnd #128741

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Merged
merged 4 commits into from
Mar 14, 2025
Merged

[InstCombine] Use known bits to simplify mask in foldSelectICmpAnd #128741

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7f78ed9
[InstCombine] Add test showing bittest which uses range attribute
juliannagele Feb 25, 2025
ffd7298
[InstCombine] Use known bits to simplify mask in foldSelectICmpAnd
juliannagele Feb 25, 2025
17c8b66
fixup! [InstCombine] Use known bits to simplify mask in foldSelectICm…
juliannagele Mar 7, 2025
036445d
fixup! [InstCombine] Use known bits to simplify mask in foldSelectICm…
juliannagele Mar 13, 2025
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14 changes: 9 additions & 5 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -120,7 +120,8 @@ static Instruction *foldSelectBinOpIdentity(SelectInst &Sel,
/// With some variations depending if FC is larger than TC, or the shift
/// isn't needed, or the bit widths don't match.
static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,
InstCombiner::BuilderTy &Builder) {
InstCombiner::BuilderTy &Builder,
const SimplifyQuery &SQ) {
const APInt *SelTC, *SelFC;
if (!match(Sel.getTrueValue(), m_APInt(SelTC)) ||
!match(Sel.getFalseValue(), m_APInt(SelFC)))
Expand Down Expand Up @@ -148,11 +149,14 @@ static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,
} else if (auto Res = decomposeBitTestICmp(Cmp->getOperand(0),
Cmp->getOperand(1), Pred)) {
assert(ICmpInst::isEquality(Res->Pred) && "Not equality test?");
if (!Res->Mask.isPowerOf2())
AndMask = Res->Mask;
V = Res->X;
KnownBits Known =
computeKnownBits(V, /*Depth=*/0, SQ.getWithInstruction(&Sel));
AndMask &= Known.getMaxValue();
if (!AndMask.isPowerOf2())
return nullptr;

V = Res->X;
AndMask = Res->Mask;
Pred = Res->Pred;
CreateAnd = true;
} else {
Expand Down Expand Up @@ -1957,7 +1961,7 @@ Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
tryToReuseConstantFromSelectInComparison(SI, *ICI, *this))
return NewSel;

if (Value *V = foldSelectICmpAnd(SI, ICI, Builder))
if (Value *V = foldSelectICmpAnd(SI, ICI, Builder, SQ))
return replaceInstUsesWith(SI, V);

// NOTE: if we wanted to, this is where to detect integer MIN/MAX
Expand Down
32 changes: 32 additions & 0 deletions llvm/test/Transforms/InstCombine/select-icmp-and.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -912,3 +912,35 @@ define i16 @select_trunc_nuw_bittest_or(i8 %x) {
%res = or i16 4, %select
ret i16 %res
}

define i16 @select_icmp_bittest_range(i16 range (i16 0, 512) %a) {
; CHECK-LABEL: @select_icmp_bittest_range(
; CHECK-NEXT: [[RES:%.*]] = and i16 [[A:%.*]], 256
; CHECK-NEXT: ret i16 [[RES]]
;
%cmp = icmp ult i16 %a, 256
%res = select i1 %cmp, i16 0, i16 256
ret i16 %res
}

define i16 @select_icmp_bittest_range_negative_test(i16 range (i16 0, 513) %a) {
; CHECK-LABEL: @select_icmp_bittest_range_negative_test(
; CHECK-NEXT: [[CMP:%.*]] = icmp samesign ult i16 [[A:%.*]], 256
; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i16 0, i16 256
; CHECK-NEXT: ret i16 [[RES]]
;
%cmp = icmp ult i16 %a, 256
%res = select i1 %cmp, i16 0, i16 256
ret i16 %res
}

define i16 @select_icmp_bittest_range_negative_test2(i16 range (i16 0, 512) %a) {
; CHECK-LABEL: @select_icmp_bittest_range_negative_test2(
; CHECK-NEXT: [[CMP:%.*]] = icmp samesign ult i16 [[A:%.*]], 255
; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i16 0, i16 255
; CHECK-NEXT: ret i16 [[RES]]
;
%cmp = icmp ult i16 %a, 255
%res = select i1 %cmp, i16 0, i16 255
ret i16 %res
}
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