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[InstSimpify] Simplifying (xor (sub C_Mask, X), C_Mask) -> X (#122552)
- **[InstSimpify] Add tests for simplifying `(xor (sub C_Mask, X), C_Mask)`; NFC** - **[InstSimpify] Simplifying `(xor (sub C_Mask, X), C_Mask)` -> `X`** Helps address regressions with folding `clz(Pow2)`. Proof: https://alive2.llvm.org/ce/z/zGwUBp
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‎llvm/lib/Analysis/InstructionSimplify.cpp

Lines changed: 16 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -871,6 +871,14 @@ static Value *simplifySubInst(Value *Op0, Value *Op1, bool IsNSW, bool IsNUW,
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if (Value *V = simplifyByDomEq(Instruction::Sub, Op0, Op1, Q, MaxRecurse))
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return V;
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// (sub nuw C_Mask, (xor X, C_Mask)) -> X
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if (IsNUW) {
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Value *X;
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if (match(Op1, m_Xor(m_Value(X), m_Specific(Op0))) &&
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match(Op0, m_LowBitMask()))
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return X;
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}
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return nullptr;
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}
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@@ -2540,6 +2548,14 @@ static Value *simplifyXorInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
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if (Value *V = simplifyByDomEq(Instruction::Xor, Op0, Op1, Q, MaxRecurse))
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return V;
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// (xor (sub nuw C_Mask, X), C_Mask) -> X
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{
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Value *X;
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if (match(Op0, m_NUWSub(m_Specific(Op1), m_Value(X))) &&
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match(Op1, m_LowBitMask()))
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return X;
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}
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return nullptr;
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}
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‎llvm/test/Transforms/InstSimplify/subnuw-with-xor.ll

Lines changed: 118 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,118 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
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; RUN: opt < %s -passes=instsimplify -S | FileCheck %s
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define i8 @xor_w_sub_fail_missing_nuw(i8 range(i8 0, 16) %x) {
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; CHECK-LABEL: define i8 @xor_w_sub_fail_missing_nuw(
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; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
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; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[X]], 15
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; CHECK-NEXT: [[R:%.*]] = sub nsw i8 15, [[XOR]]
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; CHECK-NEXT: ret i8 [[R]]
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;
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%xor = xor i8 %x, 15
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%r = sub nsw i8 15, %xor
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ret i8 %r
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}
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define i8 @xor_w_sub_fail_diff_values(i8 range(i8 0, 16) %x) {
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; CHECK-LABEL: define i8 @xor_w_sub_fail_diff_values(
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; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
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; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[X]], 15
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; CHECK-NEXT: [[R:%.*]] = sub nuw nsw i8 31, [[XOR]]
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; CHECK-NEXT: ret i8 [[R]]
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;
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%xor = xor i8 %x, 15
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%r = sub nsw nuw i8 31, %xor
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ret i8 %r
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}
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define i8 @xor_w_sub_fail_diff_values2(i8 range(i8 0, 16) %x) {
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; CHECK-LABEL: define i8 @xor_w_sub_fail_diff_values2(
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; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
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; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[X]], 31
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; CHECK-NEXT: [[R:%.*]] = sub nuw nsw i8 15, [[XOR]]
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; CHECK-NEXT: ret i8 [[R]]
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;
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%xor = xor i8 %x, 31
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%r = sub nsw nuw i8 15, %xor
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ret i8 %r
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}
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define i8 @xor_w_sub_fail_not_mask(i8 range(i8 0, 16) %x) {
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; CHECK-LABEL: define i8 @xor_w_sub_fail_not_mask(
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; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
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; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[X]], 30
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; CHECK-NEXT: [[R:%.*]] = sub nuw nsw i8 30, [[XOR]]
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; CHECK-NEXT: ret i8 [[R]]
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;
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%xor = xor i8 %x, 30
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%r = sub nsw nuw i8 30, %xor
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ret i8 %r
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}
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define i8 @xor_w_sub_okay(i8 range(i8 0, 16) %x) {
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; CHECK-LABEL: define i8 @xor_w_sub_okay(
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; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
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; CHECK-NEXT: ret i8 [[X]]
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;
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%xor = xor i8 %x, 31
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%r = sub nsw nuw i8 31, %xor
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ret i8 %r
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}
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define i8 @sub_w_xor_fail_missing_nuw(i8 range(i8 0, 16) %x) {
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; CHECK-LABEL: define i8 @sub_w_xor_fail_missing_nuw(
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; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
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; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 15, [[X]]
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; CHECK-NEXT: [[R:%.*]] = xor i8 [[SUB]], 15
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; CHECK-NEXT: ret i8 [[R]]
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;
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%sub = sub nsw i8 15, %x
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%r = xor i8 %sub, 15
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ret i8 %r
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}
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define i8 @sub_w_xor_fail_diff_values(i8 range(i8 0, 16) %x) {
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; CHECK-LABEL: define i8 @sub_w_xor_fail_diff_values(
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; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
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; CHECK-NEXT: [[SUB:%.*]] = sub nuw nsw i8 15, [[X]]
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; CHECK-NEXT: [[R:%.*]] = xor i8 [[SUB]], 31
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; CHECK-NEXT: ret i8 [[R]]
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;
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%sub = sub nsw nuw i8 15, %x
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%r = xor i8 %sub, 31
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ret i8 %r
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}
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define i8 @sub_w_sub_fail_diff_values2(i8 range(i8 0, 16) %x) {
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; CHECK-LABEL: define i8 @sub_w_sub_fail_diff_values2(
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; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
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; CHECK-NEXT: [[SUB:%.*]] = sub nuw nsw i8 31, [[X]]
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; CHECK-NEXT: [[R:%.*]] = xor i8 [[SUB]], 15
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; CHECK-NEXT: ret i8 [[R]]
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;
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%sub = sub nsw nuw i8 31, %x
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%r = xor i8 %sub, 15
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ret i8 %r
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}
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define i8 @sub_w_sub_fail_not_mask(i8 range(i8 0, 16) %x) {
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; CHECK-LABEL: define i8 @sub_w_sub_fail_not_mask(
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; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
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; CHECK-NEXT: [[SUB:%.*]] = sub nuw nsw i8 30, [[X]]
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; CHECK-NEXT: [[R:%.*]] = xor i8 [[SUB]], 30
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; CHECK-NEXT: ret i8 [[R]]
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;
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%sub = sub nsw nuw i8 30, %x
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%r = xor i8 %sub, 30
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ret i8 %r
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}
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define i8 @sub_w_sub_okay(i8 range(i8 0, 16) %x) {
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; CHECK-LABEL: define i8 @sub_w_sub_okay(
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; CHECK-SAME: i8 range(i8 0, 16) [[X:%.*]]) {
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; CHECK-NEXT: ret i8 [[X]]
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;
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%sub = sub nsw nuw i8 31, %x
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%r = xor i8 %sub, 31
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ret i8 %r
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}

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