Index: llvm/test/Transforms/InstCombine/add.ll
===================================================================
--- llvm/test/Transforms/InstCombine/add.ll
+++ llvm/test/Transforms/InstCombine/add.ll
@@ -357,6 +357,28 @@
   ret i8 %C
 }
 
+; ~X + -127 and (-128) - X with nsw are equally poisonous
+define i8 @test18_nsw(i8 %A) {
+; CHECK-LABEL: @test18_nsw(
+; CHECK-NEXT:    [[C:%.*]] = sub i8 -128, [[A:%.*]]
+; CHECK-NEXT:    ret i8 [[C]]
+;
+  %B = xor i8 %A, -1
+  %C = add nsw i8 %B, -127
+  ret i8 %C
+}
+
+; 127 - X with nsw will be more poisonous than ~X + -128 with nsw. (see X = -1)
+define i8 @test18_nsw_overflow(i8 %A) {
+; CHECK-LABEL: @test18_nsw_overflow(
+; CHECK-NEXT:    [[C:%.*]] = sub i8 127, [[A:%.*]]
+; CHECK-NEXT:    ret i8 [[C]]
+;
+  %B = xor i8 %A, -1
+  %C = add nsw i8 %B, -128
+  ret i8 %C
+}
+
 define <2 x i64> @test18vec(<2 x i64> %A) {
 ; CHECK-LABEL: @test18vec(
 ; CHECK-NEXT:    [[ADD:%.*]] = sub <2 x i64> <i64 1, i64 2>, [[A:%.*]]