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[InstSimpify] Simplifying (xor (sub C_Mask, X), C_Mask) -> X #122552

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Jan 11, 2025
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[InstSimpify] Simplifying (xor (sub C_Mask, X), C_Mask) -> X #122552

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62adb89
[InstSimpify] Add tests for simplifying `(xor (sub C_Mask, X), C_Mask…
goldsteinn Jan 10, 2025
5916041
[InstSimpify] Simplifying `(xor (sub C_Mask, X), C_Mask)` -> `X`
goldsteinn Jan 10, 2025
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goldsteinn Jan 11, 2025
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16 changes: 16 additions & 0 deletions llvm/lib/Analysis/InstructionSimplify.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -871,6 +871,14 @@ static Value *simplifySubInst(Value *Op0, Value *Op1, bool IsNSW, bool IsNUW,
if (Value *V = simplifyByDomEq(Instruction::Sub, Op0, Op1, Q, MaxRecurse))
return V;

// (sub nuw C_Mask, (xor X, C_Mask)) -> X
if (IsNUW) {
Value *X;
if (match(Op1, m_Xor(m_Value(X), m_Specific(Op0))) &&
match(Op0, m_LowBitMask()))
return X;
}

return nullptr;
}

Expand Down Expand Up @@ -2540,6 +2548,14 @@ static Value *simplifyXorInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
if (Value *V = simplifyByDomEq(Instruction::Xor, Op0, Op1, Q, MaxRecurse))
return V;

// (xor (sub nuw C_Mask, X), C_Mask) -> X
{
Value *X;
if (match(Op0, m_NUWSub(m_Specific(Op1), m_Value(X))) &&
match(Op1, m_LowBitMask()))
return X;
}

return nullptr;
}

Expand Down
118 changes: 118 additions & 0 deletions llvm/test/Transforms/InstSimplify/subnuw-with-xor.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,118 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt < %s -passes=instsimplify -S | FileCheck %s

define i8 @xor_w_sub_fail_missing_nuw(i8 range(i8 0, 16) %x) {
; CHECK-LABEL: define i8 @xor_w_sub_fail_missing_nuw(
; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[X]], 15
; CHECK-NEXT: [[R:%.*]] = sub nsw i8 15, [[XOR]]
; CHECK-NEXT: ret i8 [[R]]
;
%xor = xor i8 %x, 15
%r = sub nsw i8 15, %xor
ret i8 %r
}

define i8 @xor_w_sub_fail_diff_values(i8 range(i8 0, 16) %x) {
; CHECK-LABEL: define i8 @xor_w_sub_fail_diff_values(
; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[X]], 15
; CHECK-NEXT: [[R:%.*]] = sub nuw nsw i8 31, [[XOR]]
; CHECK-NEXT: ret i8 [[R]]
;
%xor = xor i8 %x, 15
%r = sub nsw nuw i8 31, %xor
ret i8 %r
}

define i8 @xor_w_sub_fail_diff_values2(i8 range(i8 0, 16) %x) {
; CHECK-LABEL: define i8 @xor_w_sub_fail_diff_values2(
; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[X]], 31
; CHECK-NEXT: [[R:%.*]] = sub nuw nsw i8 15, [[XOR]]
; CHECK-NEXT: ret i8 [[R]]
;
%xor = xor i8 %x, 31
%r = sub nsw nuw i8 15, %xor
ret i8 %r
}

define i8 @xor_w_sub_fail_not_mask(i8 range(i8 0, 16) %x) {
; CHECK-LABEL: define i8 @xor_w_sub_fail_not_mask(
; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[X]], 30
; CHECK-NEXT: [[R:%.*]] = sub nuw nsw i8 30, [[XOR]]
; CHECK-NEXT: ret i8 [[R]]
;
%xor = xor i8 %x, 30
%r = sub nsw nuw i8 30, %xor
ret i8 %r
}

define i8 @xor_w_sub_okay(i8 range(i8 0, 16) %x) {
; CHECK-LABEL: define i8 @xor_w_sub_okay(
; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
; CHECK-NEXT: ret i8 [[X]]
;
%xor = xor i8 %x, 31
%r = sub nsw nuw i8 31, %xor
ret i8 %r
}

define i8 @sub_w_xor_fail_missing_nuw(i8 range(i8 0, 16) %x) {
; CHECK-LABEL: define i8 @sub_w_xor_fail_missing_nuw(
; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 15, [[X]]
; CHECK-NEXT: [[R:%.*]] = xor i8 [[SUB]], 15
; CHECK-NEXT: ret i8 [[R]]
;
%sub = sub nsw i8 15, %x
%r = xor i8 %sub, 15
ret i8 %r
}

define i8 @sub_w_xor_fail_diff_values(i8 range(i8 0, 16) %x) {
; CHECK-LABEL: define i8 @sub_w_xor_fail_diff_values(
; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
; CHECK-NEXT: [[SUB:%.*]] = sub nuw nsw i8 15, [[X]]
; CHECK-NEXT: [[R:%.*]] = xor i8 [[SUB]], 31
; CHECK-NEXT: ret i8 [[R]]
;
%sub = sub nsw nuw i8 15, %x
%r = xor i8 %sub, 31
ret i8 %r
}

define i8 @sub_w_sub_fail_diff_values2(i8 range(i8 0, 16) %x) {
; CHECK-LABEL: define i8 @sub_w_sub_fail_diff_values2(
; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
; CHECK-NEXT: [[SUB:%.*]] = sub nuw nsw i8 31, [[X]]
; CHECK-NEXT: [[R:%.*]] = xor i8 [[SUB]], 15
; CHECK-NEXT: ret i8 [[R]]
;
%sub = sub nsw nuw i8 31, %x
%r = xor i8 %sub, 15
ret i8 %r
}

define i8 @sub_w_sub_fail_not_mask(i8 range(i8 0, 16) %x) {
; CHECK-LABEL: define i8 @sub_w_sub_fail_not_mask(
; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
; CHECK-NEXT: [[SUB:%.*]] = sub nuw nsw i8 30, [[X]]
; CHECK-NEXT: [[R:%.*]] = xor i8 [[SUB]], 30
; CHECK-NEXT: ret i8 [[R]]
;
%sub = sub nsw nuw i8 30, %x
%r = xor i8 %sub, 30
ret i8 %r
}

define i8 @sub_w_sub_okay(i8 range(i8 0, 16) %x) {
; CHECK-LABEL: define i8 @sub_w_sub_okay(
; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
; CHECK-NEXT: ret i8 [[X]]
;
%sub = sub nsw nuw i8 31, %x
%r = xor i8 %sub, 31
ret i8 %r
}
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