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[InstCombine] Canonicalize xor with disjoint ops to or disjoint #133139

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[InstCombine] Canonicalize xor with disjoint ops to or disjoint #133139

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5 changes: 5 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4993,6 +4993,11 @@ Instruction *InstCombinerImpl::visitXor(BinaryOperator &I) {
if (Instruction *Abs = canonicalizeAbs(I, Builder))
return Abs;

if (KnownBits::haveNoCommonBitsSet(
computeKnownBits(I.getOperand(0), /*Depth=*/0, &I),
computeKnownBits(I.getOperand(1), /*Depth=*/0, &I)))
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@arsenm arsenm Mar 27, 2025

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Can try to short circuit the first operand query if the second is unknown

return BinaryOperator::CreateDisjointOr(I.getOperand(0), I.getOperand(1));

// Otherwise, if all else failed, try to hoist the xor-by-constant:
// (X ^ C) ^ Y --> (X ^ Y) ^ C
// Just like we do in other places, we completely avoid the fold
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49 changes: 49 additions & 0 deletions llvm/test/Transforms/InstCombine/xor.ll
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Expand Up @@ -1664,3 +1664,52 @@ entry:
%or = or <2 x i32> %add, %c
ret <2 x i32> %or
}

declare i32 @callee()

define i32 @xor_disjoint() {
; CHECK-LABEL: @xor_disjoint(
; CHECK-NEXT: [[CALL1:%.*]] = call i32 @callee(), !range [[RNG0:![0-9]+]]
; CHECK-NEXT: [[XOR:%.*]] = or disjoint i32 [[CALL1]], 4096
; CHECK-NEXT: ret i32 [[XOR]]
;
%call1 = call i32 @callee(), !range !0
%xor = xor i32 %call1, 4096
ret i32 %xor
}

define i32 @xor_disjoint2() {
; CHECK-LABEL: @xor_disjoint2(
; CHECK-NEXT: [[CALL1:%.*]] = call i32 @callee(), !range [[RNG1:![0-9]+]]
; CHECK-NEXT: [[XOR:%.*]] = or disjoint i32 [[CALL1]], 512
; CHECK-NEXT: ret i32 [[XOR]]
;
%call1 = call i32 @callee(), !range !1
%xor = xor i32 %call1, 512
ret i32 %xor
}

define i32 @xor_non_disjoint() {
; CHECK-LABEL: @xor_non_disjoint(
; CHECK-NEXT: [[CALL1:%.*]] = call i32 @callee(), !range [[RNG0]]
; CHECK-NEXT: [[XOR:%.*]] = xor i32 [[CALL1]], 1024
; CHECK-NEXT: ret i32 [[XOR]]
;
%call1 = call i32 @callee(), !range !0
%xor = xor i32 %call1, 1024
ret i32 %xor
}

define i32 @xor_non_disjoint2() {
; CHECK-LABEL: @xor_non_disjoint2(
; CHECK-NEXT: [[CALL1:%.*]] = call i32 @callee(), !range [[RNG1]]
; CHECK-NEXT: [[XOR:%.*]] = and i32 [[CALL1]], 511
; CHECK-NEXT: ret i32 [[XOR]]
;
%call1 = call i32 @callee(), !range !1
%xor = xor i32 %call1, 1024
ret i32 %xor
}

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@arsenm arsenm Mar 27, 2025

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Test a vector version. Also could use alive2 proof link

!0 = !{ i32 0, i32 2048 }
!1 = !{ i32 1024, i32 1536 }