[llvm] [InstCombine] When -A + B both have nsw flag, set nsw flag. (PR #72127)

[Nikita Popov via llvm-commits]

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@@ -120,6 +120,36 @@ define i32 @test5(i32 %A, i32 %B) {
   ret i32 %D
 }
 
+define i32 @test5_2(i32 %A, i32 %B) {
+; CHECK-LABEL: @test5_2(
+; CHECK-NEXT:    [[D:%.*]] = sub nsw i32 [[B:%.*]], [[A:%.*]]
+; CHECK-NEXT:    ret i32 [[D]]
+;
+  %C = sub nsw i32 0, %A
+  %D = add nsw i32 %C, %B
+  ret i32 %D
+}
+
+define i32 @test5_3(i32 %A, i32 %B) {
+; CHECK-LABEL: @test5_3(
+; CHECK-NEXT:    [[D:%.*]] = sub i32 [[B:%.*]], [[A:%.*]]
+; CHECK-NEXT:    ret i32 [[D]]
+;
+  %C = sub nsw i32 0, %A
+  %D = add i32 %C, %B
+  ret i32 %D
+}
+
+define i32 @test5_4(i32 %A, i32 %B) {
----------------
nikic wrote:

```suggestion
define i32 @test5_add_nsw(i32 %A, i32 %B) {
```

https://github.com/llvm/llvm-project/pull/72127