Re: [PATCH] Don't override user alignment with the same value

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Aug 21, 2017 at 12:59 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Sat, Aug 19, 2017 at 10:18 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> Don't override alignment specified by user with the same value to
>> preserve TYPE_USER_ALIGN.  This fixes PR 53037 tests on Sparc.
>>
>> Does it look right?
>
> Doesn't match do_type_align so it introduces inconsistencies.  The documentation
> for TYPE_USER_ALIGN doesn't specify when both cases conflict:
>
> /* 1 if the alignment for this type was requested by "aligned" attribute,
>    0 if it is the default for this type.  */
>
> Note that for example the vectorizer looks at DECL_USER_ALIGN  (for
> non-field-decls)
> to decide whether it can increase alignment.
>
> Richard.
>
>>
>> H.J.
>> --
>>         * stor-layout.c (finalize_type_size): Don't override alignment
>>         specified by user with the same value.
>> ---
>>  gcc/stor-layout.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c
>> index 3028d55773a..6dd605810ac 100644
>> --- a/gcc/stor-layout.c
>> +++ b/gcc/stor-layout.c
>> @@ -1784,7 +1784,7 @@ finalize_type_size (tree type)
>>
>>        /* Don't override a larger alignment requirement coming from a user
>>          alignment of one of the fields.  */
>> -      if (mode_align >= TYPE_ALIGN (type))
>> +      if (mode_align > TYPE_ALIGN (type))
>>         {
>>           SET_TYPE_ALIGN (type, mode_align);
>>           TYPE_USER_ALIGN (type) = 0;
>> --
>> 2.13.5
>>

According to Eric:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53037#c32

"if (mode_align >= TYPE_ALIGN (type))" was intentional.  I am
not familiar with STRICT_ALIGNMENT target and there is no
testcase to show why it is needed.


-- 
H.J.