[llvm] [InstCombine] Change (add x, c) to (xor x, c) (PR #75129)

[Fujun Han via llvm-commits]

================
@@ -2711,3 +2711,36 @@ define i32 @canonicalize_and_sub_power2_or_zero_multiuse_nofold(i32 %x, i32 %y)
   %and = and i32 %val, %p2
   ret i32 %and
 }
+
+define i32 @add_constant_equal_with_the_top_bit_of_demandedbits_pass(i32 %x) {
+; CHECK-LABEL: @add_constant_equal_with_the_top_bit_of_demandedbits_pass(
+; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[X:%.*]], 24
+; CHECK-NEXT:    [[AND:%.*]] = xor i32 [[TMP1]], 16
+; CHECK-NEXT:    ret i32 [[AND]]
+;
+  %add = add i32 %x, 16
+  %and = and i32 %add, 24
+  ret i32 %and
+}
+
+define i32 @add_constant_equal_with_the_top_bit_of_demandedbits_fail1(i32 %x) {
+; CHECK-LABEL: @add_constant_equal_with_the_top_bit_of_demandedbits_fail1(
+; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[X:%.*]], 8
+; CHECK-NEXT:    [[AND:%.*]] = and i32 [[ADD]], 24
+; CHECK-NEXT:    ret i32 [[AND]]
+;
+  %add = add i32 %x, 8
+  %and = and i32 %add, 24
+  ret i32 %and
+}
+
+define i32 @add_constant_equal_with_the_top_bit_of_demandedbits_fail2(i32 %x) {
+; CHECK-LABEL: @add_constant_equal_with_the_top_bit_of_demandedbits_fail2(
+; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[X:%.*]], 24
+; CHECK-NEXT:    [[AND:%.*]] = and i32 [[ADD]], 24
+; CHECK-NEXT:    ret i32 [[AND]]
+;
+  %add = add i32 %x, 24
+  %and = and i32 %add, 24
+  ret i32 %and
+}
----------------
Peter9606 wrote:

original case appended.

https://github.com/llvm/llvm-project/pull/75129