[llvm] [InstCombine] Fold (sub (xor X, (sext C)), (sext C)) => (select C (neg X), X) (PR #79417)

[Yingwei Zheng via llvm-commits]

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@@ -0,0 +1,45 @@
+; 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 @foo(i64 %a, i1 %b) {
+; CHECK-LABEL: define i64 @foo(
+; 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 @bar(i64 %a, i1 %b) {
+; CHECK-LABEL: define i64 @bar(
+; 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
+}
+
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dtcxzyw wrote:

Please add some negative tests:
+ mismatched type: (sub (xor X, (sext i8 C)), (sext i8 C))
+ mismatched C: (sub (xor X, (sext C1)), (sext C2))
+ (xor X, (sext C)) has multiple uses
+ (sext C) has multiple uses


https://github.com/llvm/llvm-project/pull/79417