[CVP] Add additional tests for undef check (NFC)

Author: nikic

llvm/test/Transforms/CorrelatedValuePropagation/cond-at-use.ll

@@ -567,3 +567,33 @@ define i16 @cond_value_may_not_well_defined(i16 %x) {
   %sel = select i1 %cmp, i16 %and, i16 24
   ret i16 %sel
 }
+
+define i16 @and_elide_poison_flags(i16 noundef %a) {
+; CHECK-LABEL: @and_elide_poison_flags(
+; CHECK-NEXT:    [[X:%.*]] = add nuw i16 [[A:%.*]], 1
+; CHECK-NEXT:    [[AND:%.*]] = and i16 [[X]], 7
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i16 [[X]], 8
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i16 [[AND]], i16 24
+; CHECK-NEXT:    ret i16 [[SEL]]
+;
+  %x = add nuw i16 %a, 1
+  %and = and i16 %x, 7
+  %cmp = icmp ult i16 %x, 8
+  %sel = select i1 %cmp, i16 %and, i16 24
+  ret i16 %sel
+}
+
+define i16 @and_elide_poison_flags_missing_noundef(i16 %a) {
+; CHECK-LABEL: @and_elide_poison_flags_missing_noundef(
+; CHECK-NEXT:    [[X:%.*]] = add nuw i16 [[A:%.*]], 1
+; CHECK-NEXT:    [[AND:%.*]] = and i16 [[X]], 7
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i16 [[X]], 8
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i16 [[AND]], i16 24
+; CHECK-NEXT:    ret i16 [[SEL]]
+;
+  %x = add nuw i16 %a, 1
+  %and = and i16 %x, 7
+  %cmp = icmp ult i16 %x, 8
+  %sel = select i1 %cmp, i16 %and, i16 24
+  ret i16 %sel
+}