[InstCombine] Fold (sub (xor X, (sext C)), (sext C)) => (select C (neg X), X)

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -2448,6 +2448,21 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
     }
   }
 
+  {
+    // (sub (xor X, (sext C)), (sext C)) => (select C, (neg X), X)
+    // (sub (sext C), (xor X, (sext C))) => (select C, X, (neg X))
+    Value *C, *X;
+    auto m_SubXorCmp = [&C, &X](Value *LHS, Value *RHS) {
+      return match(LHS, m_OneUse(m_c_Xor(m_Value(X), m_Specific(RHS)))) &&
+             match(RHS, m_SExt(m_Value(C))) &&
+             (C->getType()->getScalarSizeInBits() == 1);
+    };
+    if (m_SubXorCmp(Op0, Op1))
+      return SelectInst::Create(C, Builder.CreateNeg(X), X);
+    if (m_SubXorCmp(Op1, Op0))
+      return SelectInst::Create(C, X, Builder.CreateNeg(X));
+  }
+
   if (Instruction *R = tryFoldInstWithCtpopWithNot(&I))
     return R;
 

llvm/test/Transforms/InstCombine/sub-xor-cmp.ll

@@ -0,0 +1,205 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define i64 @sext_xor_sub(i64 %a, i1 %b) {
+; CHECK-LABEL: define i64 @sext_xor_sub(
+; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i64 0, [[A]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[B]], i64 [[TMP1]], i64 [[A]]
+; CHECK-NEXT:    ret i64 [[R]]
+;
+  %c = sext i1 %b to i64
+  %d = xor i64 %a, %c
+  %r = sub i64 %d, %c
+  ret i64 %r
+}
+
+define i64 @sext_xor_sub_1(i64 %a, i1 %b) {
+; CHECK-LABEL: define i64 @sext_xor_sub_1(
+; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i64 0, [[A]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[B]], i64 [[TMP1]], i64 [[A]]
+; CHECK-NEXT:    ret i64 [[R]]
+;
+  %c = sext i1 %b to i64
+  %d = xor i64 %c, %a
+  %r = sub i64 %d, %c
+  ret i64 %r
+}
+
+define i64 @sext_xor_sub_2(i64 %a, i1 %b) {
+; CHECK-LABEL: define i64 @sext_xor_sub_2(
+; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i64 0, [[A]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[B]], i64 [[A]], i64 [[TMP1]]
+; CHECK-NEXT:    ret i64 [[R]]
+;
+  %c = sext i1 %b to i64
+  %d = xor i64 %a, %c
+  %r = sub i64 %c, %d
+  ret i64 %r
+}
+
+define i64 @sext_xor_sub_3(i64 %a, i1 %b) {
+; CHECK-LABEL: define i64 @sext_xor_sub_3(
+; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i64 0, [[A]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[B]], i64 [[A]], i64 [[TMP1]]
+; CHECK-NEXT:    ret i64 [[R]]
+;
+  %c = sext i1 %b to i64
+  %d = xor i64 %c, %a
+  %r = sub i64 %c, %d
+  ret i64 %r
+}
+
+; Sext non boolean type.
+define i64 @sext_non_bool_xor_sub(i64 %a, i8 %b) {
+; CHECK-LABEL: define i64 @sext_non_bool_xor_sub(
+; CHECK-SAME: i64 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT:    [[C:%.*]] = sext i8 [[B]] to i64
+; CHECK-NEXT:    [[D:%.*]] = xor i64 [[C]], [[A]]
+; CHECK-NEXT:    [[R:%.*]] = sub i64 [[D]], [[C]]
+; CHECK-NEXT:    ret i64 [[R]]
+;
+  %c = sext i8 %b to i64
+  %d = xor i64 %a, %c
+  %r = sub i64 %d, %c
+  ret i64 %r
+}
+
+define i64 @sext_non_bool_xor_sub_1(i64 %a, i8 %b) {
+; CHECK-LABEL: define i64 @sext_non_bool_xor_sub_1(
+; CHECK-SAME: i64 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT:    [[C:%.*]] = sext i8 [[B]] to i64
+; CHECK-NEXT:    [[D:%.*]] = xor i64 [[C]], [[A]]
+; CHECK-NEXT:    [[R:%.*]] = sub i64 [[D]], [[C]]
+; CHECK-NEXT:    ret i64 [[R]]
+;
+  %c = sext i8 %b to i64
+  %d = xor i64 %c, %a
+  %r = sub i64 %d, %c
+  ret i64 %r
+}
+
+; Different boolean values.
+define i64 @sext_diff_i1_xor_sub(i64 %a, i1 %b, i1 %c) {
+; CHECK-LABEL: define i64 @sext_diff_i1_xor_sub(
+; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]], i1 [[C:%.*]]) {
+; CHECK-NEXT:    [[D:%.*]] = sext i1 [[B]] to i64
+; CHECK-NEXT:    [[E_NEG:%.*]] = zext i1 [[C]] to i64
+; CHECK-NEXT:    [[R:%.*]] = add nsw i64 [[E_NEG]], [[D]]
+; CHECK-NEXT:    ret i64 [[R]]
+;
+  %d = sext i1 %b to i64
+  %e = sext i1 %c to i64
+  %f = xor i64 %a, %d
+  %r = sub i64 %d, %e
+  ret i64 %r
+}
+
+define i64 @sext_diff_i1_xor_sub_1(i64 %a, i1 %b, i1 %c) {
+; CHECK-LABEL: define i64 @sext_diff_i1_xor_sub_1(
+; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]], i1 [[C:%.*]]) {
+; CHECK-NEXT:    [[D:%.*]] = sext i1 [[B]] to i64
+; CHECK-NEXT:    [[E_NEG:%.*]] = zext i1 [[C]] to i64
+; CHECK-NEXT:    [[R:%.*]] = add nsw i64 [[E_NEG]], [[D]]
+; CHECK-NEXT:    ret i64 [[R]]
+;
+  %d = sext i1 %b to i64
+  %e = sext i1 %c to i64
+  %f = xor i64 %d, %a
+  %r = sub i64 %d, %e
+  ret i64 %r
+}
+
+; (sext C) has multiple uses.
+define i64 @sext_multi_uses(i64 %a, i1 %b, i64 %x) {
+; CHECK-LABEL: define i64 @sext_multi_uses(
+; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]], i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[C:%.*]] = sext i1 [[B]] to i64
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i64 0, [[A]]
+; CHECK-NEXT:    [[E:%.*]] = select i1 [[B]], i64 [[TMP1]], i64 [[A]]
+; CHECK-NEXT:    [[F:%.*]] = mul i64 [[C]], [[X]]
+; CHECK-NEXT:    [[R:%.*]] = add i64 [[F]], [[E]]
+; CHECK-NEXT:    ret i64 [[R]]
+;
+  %c = sext i1 %b to i64
+  %d = xor i64 %a, %c
+  %e = sub i64 %d, %c
+  %f = mul i64 %x, %c
+  %r = add i64 %f, %e
+  ret i64 %r
+}
+
+; (xor X, (sext C)) has multiple uses.
+define i64 @xor_multi_uses(i64 %a, i1 %b, i64 %x) {
+; CHECK-LABEL: define i64 @xor_multi_uses(
+; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]], i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[C:%.*]] = sext i1 [[B]] to i64
+; CHECK-NEXT:    [[D:%.*]] = xor i64 [[C]], [[A]]
+; CHECK-NEXT:    [[E:%.*]] = sub i64 [[D]], [[C]]
+; CHECK-NEXT:    [[F:%.*]] = mul i64 [[D]], [[X]]
+; CHECK-NEXT:    [[R:%.*]] = add i64 [[F]], [[E]]
+; CHECK-NEXT:    ret i64 [[R]]
+;
+  %c = sext i1 %b to i64
+  %d = xor i64 %a, %c
+  %e = sub i64 %d, %c
+  %f = mul i64 %x, %d
+  %r = add i64 %f, %e
+  ret i64 %r
+}
+
+define i64 @absdiff(i64 %a, i64 %b) {
+; CHECK-LABEL: define i64 @absdiff(
+; CHECK-SAME: i64 [[A:%.*]], i64 [[B:%.*]]) {
+; CHECK-NEXT:    [[C:%.*]] = icmp ult i64 [[A]], [[B]]
+; CHECK-NEXT:    [[D:%.*]] = sub i64 [[A]], [[B]]
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i64 0, [[D]]
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C]], i64 [[TMP1]], i64 [[D]]
+; CHECK-NEXT:    ret i64 [[RES]]
+;
+  %c = icmp ult i64 %a, %b
+  %c.ext = sext i1 %c to i64
+  %d = sub i64 %a, %b
+  %may.rev = xor i64 %c.ext, %d
+  %res = sub i64 %may.rev, %c.ext
+  ret i64 %res
+}
+
+; Commuted xor operands compared to absdiff.
+define i64 @absdiff1(i64 %a, i64 %b) {
+; CHECK-LABEL: define i64 @absdiff1(
+; CHECK-SAME: i64 [[A:%.*]], i64 [[B:%.*]]) {
+; CHECK-NEXT:    [[C:%.*]] = icmp ult i64 [[A]], [[B]]
+; CHECK-NEXT:    [[D:%.*]] = sub i64 [[A]], [[B]]
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i64 0, [[D]]
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C]], i64 [[TMP1]], i64 [[D]]
+; CHECK-NEXT:    ret i64 [[RES]]
+;
+  %c = icmp ult i64 %a, %b
+  %c.ext = sext i1 %c to i64
+  %d = sub i64 %a, %b
+  %may.rev = xor i64 %d, %c.ext
+  %res = sub i64 %may.rev, %c.ext
+  ret i64 %res
+}
+
+; Use ugt as compare cond.
+define i64 @absdiff2(i64 %a, i64 %b) {
+; CHECK-LABEL: define i64 @absdiff2(
+; CHECK-SAME: i64 [[A:%.*]], i64 [[B:%.*]]) {
+; CHECK-NEXT:    [[C:%.*]] = icmp ugt i64 [[A]], [[B]]
+; CHECK-NEXT:    [[D:%.*]] = sub i64 [[B]], [[A]]
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i64 0, [[D]]
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[C]], i64 [[TMP1]], i64 [[D]]
+; CHECK-NEXT:    ret i64 [[RES]]
+;
+  %c = icmp ugt i64 %a, %b
+  %c.ext = sext i1 %c to i64
+  %d = sub i64 %b, %a
+  %may.rev = xor i64 %d, %c.ext
+  %res = sub i64 %may.rev, %c.ext
+  ret i64 %res
+}