Skip to content

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

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 4 commits into from
Mar 14, 2025
Merged

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

Show file tree
Hide file tree
Changes from 2 commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
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
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
13 changes: 8 additions & 5 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View file
Open in desktop
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,
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 +149,13 @@ 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, 0, SQ.getWithInstruction(Cmp));
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 +1960,7 @@ 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
10 changes: 10 additions & 0 deletions llvm/test/Transforms/InstCombine/select-icmp-and.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -912,3 +912,13 @@ 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
}