Skip to content

[ValueTracking] Have sub and xor in KnownNonZero take the same exact path #146975

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 2 commits into from
Jul 7, 2025
Merged

[ValueTracking] Have sub and xor in KnownNonZero take the same exact path #146975

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
aa21780
Pre-commit test (NFC)
AZero13 Jul 5, 2025
217a937
[ValueTracking] Have sub and xor in KnownNonZero take the same exact …
AZero13 Jul 3, 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
8 changes: 3 additions & 5 deletions llvm/lib/Analysis/ValueTracking.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -3036,14 +3036,12 @@ static bool isKnownNonZeroFromOperator(const Operator *I,
return isKnownNonZero(TI->getOperand(0), DemandedElts, Q, Depth);
break;

// Iff x - y != 0, then x ^ y != 0
// Therefore we can do the same exact checks
case Instruction::Xor:
case Instruction::Sub:
return isNonZeroSub(DemandedElts, Q, BitWidth, I->getOperand(0),
I->getOperand(1), Depth);
case Instruction::Xor:
// (X ^ (X != 0)) is non zero
if (matchOpWithOpEqZero(I->getOperand(0), I->getOperand(1)))
return true;
break;
case Instruction::Or:
// (X | (X != 0)) is non zero
if (matchOpWithOpEqZero(I->getOperand(0), I->getOperand(1)))
Expand Down
21 changes: 21 additions & 0 deletions llvm/test/Transforms/InstCombine/ctpop-cttz.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -127,3 +127,24 @@ define <2 x i32> @ctpop3v_poison(<2 x i32> %0) {
%5 = tail call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> %4)
ret <2 x i32> %5
}

define i32 @ctpop_xor(i32 %x, i32 %y) {
; CHECK-LABEL: @ctpop_xor(
; CHECK-NEXT: [[CMP_NOT:%.*]] = icmp eq i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: br i1 [[CMP_NOT]], label [[FALSE:%.*]], label [[TRUE:%.*]]
; CHECK: true:
; CHECK-NEXT: [[XOR:%.*]] = xor i32 [[X]], [[Y]]
; CHECK-NEXT: [[RET:%.*]] = call range(i32 1, 33) i32 @llvm.ctpop.i32(i32 [[XOR]])
; CHECK-NEXT: ret i32 [[RET]]
; CHECK: false:
; CHECK-NEXT: ret i32 0
;
%cmp = icmp ne i32 %x, %y
br i1 %cmp, label %true, label %false
true:
%xor = xor i32 %x, %y
%ret = call i32 @llvm.ctpop.i32(i32 %xor)
ret i32 %ret
false:
ret i32 0
}
Loading