On 11/09/2015 02:28 PM, Jason Merrill wrote:
> On 11/09/2015 04:08 AM, Richard Biener wrote:
>> On Mon, 9 Nov 2015, Jason Merrill wrote:
>>
>>> I'm planning to merge the C++ delayed folding branch this week, but I
>>> need to
>>> get approval of the back end changes (the first patch attached).
>>> Most of
>>> these are the introduction of non-folding variants of convert_to_*,
>>> but there
>>> are a few others.
>>>
>>> One question: The branch changes 'convert' to not fold its result,
>>> and it's
>>> not clear to me whether that's part of the expected behavior of a
>>> front end
>>> 'convert' function or not.
>>
>> History.  convert is purely frontend (but shared, unfortunately between
>> all frontends).  I would expect that FEs that do not do delayed folding
>> expect convert to fold.
>>
>>> Also, I'm a bit uncertain about merging this at the end of stage 1,
>>> since it's
>>> a large internal change with relatively small user impact; it just
>>> improves
>>> handling of constant expression corner cases.  I'm inclined to go
>>> ahead with
>>> it at this point, but I'm interested in contrary opinions.
>>
>> I welcome this change as it should allow cleaning up the FE-middle-end
>> interface a bit more.  It should be possible to remove all
>> NON_LVALUE_EXPR adding/removal from the middle-end folders.
>>
>> Looks like the backend patch included frontend parts but as far as I
>> skimmed it only
>>
>> diff --git a/gcc/fold-const.c b/gcc/fold-const.c
>> index 5e32901..d754a90 100644
>> --- a/gcc/fold-const.c
>> +++ b/gcc/fold-const.c
>> @@ -2091,6 +2091,17 @@ fold_convert_const (enum tree_code code, tree
>> type,
>> tree arg1)
>>         else if (TREE_CODE (arg1) == REAL_CST)
>>          return fold_convert_const_fixed_from_real (type, arg1);
>>       }
>> +  else if (TREE_CODE (type) == VECTOR_TYPE)
>> +    {
>> +      if (TREE_CODE (arg1) == VECTOR_CST
>> +         && TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (TREE_TYPE
>> (arg1))
>> +         && TYPE_VECTOR_SUBPARTS (type) == VECTOR_CST_NELTS (arg1))
>> +       {
>> +         tree r = copy_node (arg1);
>> +         TREE_TYPE (arg1) = type;
>> +         return r;
>> +       }
>> +    }
>>
>>
>> looks suspicious.  The issue here is that the vector elements will
>> have the wrong type after this simple handling.
>
> I was aiming to just handle simple cv-qualifier changes; that's why the
> TYPE_MAIN_VARIANT comparison is there.
>
>> If you fix that you can as well handle all kind of element type
>> changes via recursing to fold_convert_const (that includes
>> float to int / int to float changes).
>
> But I'll try this.

Like so?

Jason