[InstCombine] Add test for isKnownNonZero() undef miscompile (NFC)

Author: nikic

llvm/test/Transforms/InstCombine/add.ll

@@ -3093,6 +3093,32 @@ define <2 x i32> @dec_zext_add_nonzero_vec(<2 x i8> %x) {
   ret <2 x i32> %c
 }
 
+define <2 x i32> @dec_zext_add_nonzero_vec_undef0(<2 x i8> %x) {
+; CHECK-LABEL: @dec_zext_add_nonzero_vec_undef0(
+; CHECK-NEXT:    [[O:%.*]] = or <2 x i8> [[X:%.*]], <i8 8, i8 undef>
+; CHECK-NEXT:    [[C:%.*]] = zext <2 x i8> [[O]] to <2 x i32>
+; CHECK-NEXT:    ret <2 x i32> [[C]]
+;
+  %o = or <2 x i8> %x, <i8 8, i8 undef>
+  %a = add <2 x i8> %o, <i8 -1, i8 -1>
+  %b = zext <2 x i8> %a to <2 x i32>
+  %c = add <2 x i32> %b, <i32 1, i32 1>
+  ret <2 x i32> %c
+}
+
+define <2 x i32> @dec_zext_add_nonzero_poison0(<2 x i8> %x) {
+; CHECK-LABEL: @dec_zext_add_nonzero_poison0(
+; CHECK-NEXT:    [[O:%.*]] = or <2 x i8> [[X:%.*]], <i8 8, i8 poison>
+; CHECK-NEXT:    [[C:%.*]] = zext <2 x i8> [[O]] to <2 x i32>
+; CHECK-NEXT:    ret <2 x i32> [[C]]
+;
+  %o = or <2 x i8> %x, <i8 8, i8 poison>
+  %a = add <2 x i8> %o, <i8 -1, i8 -1>
+  %b = zext <2 x i8> %a to <2 x i32>
+  %c = add <2 x i32> %b, <i32 1, i32 1>
+  ret <2 x i32> %c
+}
+
 define <2 x i32> @dec_zext_add_nonzero_vec_poison1(<2 x i8> %x) {
 ; CHECK-LABEL: @dec_zext_add_nonzero_vec_poison1(
 ; CHECK-NEXT:    [[O:%.*]] = or <2 x i8> [[X:%.*]], <i8 8, i8 8>