[PATCH v2] c++: Implement -Wuninitialized for mem-initializers (redux) [PR19808]

[Martin Sebor]

On 11/18/21 6:56 PM, Jason Merrill via Gcc-patches wrote:
> On 11/18/21 19:24, Marek Polacek wrote:
>> On Thu, Nov 18, 2021 at 05:10:47PM -0500, Jason Merrill wrote:
>>> On 11/8/21 18:41, Marek Polacek wrote:
>>>> @@ -1311,13 +1462,25 @@ emit_mem_initializers (tree mem_inits)
>>>>      if (!COMPLETE_TYPE_P (current_class_type))
>>>>        return;
>>>> +  /* Keep a set holding fields that are not initialized.  */
>>>> +  hash_set<tree> uninitialized;
>>>> +
>>>> +  /* Initially that is all of them.  */
>>>> +  if (warn_uninitialized)
>>>> +    for (tree f = next_initializable_field (TYPE_FIELDS 
>>>> (current_class_type));
>>>> +     f != NULL_TREE;
>>>> +     f = next_initializable_field (DECL_CHAIN (f)))
>>>> +      if (!DECL_ARTIFICIAL (f))
>>>> +    uninitialized.add (f);
>>>
>>> I wonder about flipping the sense of the set, so that it tracks 
>>> fields that
>>> have been initialized rather than those that haven't; then you 
>>> wouldn't need
>>> this loop.
>>
>> True, but then I'd have to figure out a new way to signal that we 
>> don't want
>> to warn about the current member-initializer-list.  What I mean by 
>> that is
>> that when I see e.g. a MODIFY_EXPR or something else with side-effects in
>> a mem-init, I can just empty the set:
>>
>>      case MODIFY_EXPR:
>>      /* Don't attempt to handle statement-expressions, either.  */
>>      case STATEMENT_LIST:
>>        uninitialized->empty ();
>>
>> and then we won't even bother walking the other mem-inits, because
>> find_uninit_fields has:
>>
>>    if (!uninitialized->is_empty ())
>>      {
>>        // walk_tree ()
>>      }
>>
>> and I thought that was pretty elegant.  Of course, I could just add a new
>> bool member into find_uninit_data and then do what you suggest...  Up to
>> you, I'm happy to do that too.
> 
> No need, the patch is OK as is.

Awesome!  Thank you both and especially Marek for finally making
it happen (after no less than 15 years)! :)

Martin

> 
> Jason
>