[patch][version5]add -ftrivial-auto-var-init and variable attribute "uninitialized" to gcc

[Qing Zhao]

> On Jul 26, 2021, at 11:09 AM, Martin Jambor <mjambor@suse.cz> wrote:
> 
> Hi,
> 
>>> So you either need to change build_access_from_expr like I described in
>>> my email
>> 
>> Is the following the change you suggested previously:
>> 
>> [opc@qinzhao-ol8u3-x86 gcc]$ git diff tree-sra.c
>> diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
>> index d1280e5f8848..c2597b705169 100644
>> --- a/gcc/tree-sra.c
>> +++ b/gcc/tree-sra.c
>> @@ -1195,8 +1195,10 @@ build_access_from_expr (tree expr, gimple *stmt, bool write)
>>     {
>>       /* This means the aggregate is accesses as a whole in a way other than an
>>         assign statement and thus cannot be removed even if we had a scalar
>> -        replacement for everything.  */
>> -      if (cannot_scalarize_away_bitmap)
>> +        replacement for everything. However, when the STMT is a call to
>> +        DEFERRED_INIT, we should not set this bit.  */
>> +      if (cannot_scalarize_away_bitmap 
>> +         && !gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
>>        bitmap_set_bit (cannot_scalarize_away_bitmap, DECL_UID (access->base));
>>       return true;
>>     }
>> 
> 
> Yes, although I think that the one I wrote today is more efficient as it
> tests for IFN_DEFERRED_INIT only if we already know stmt is a call and
> also philosophically more correct as the test is performed only for the
> LHS of the statement (I don't think either reason matters much in
> practice, though).

Okay, I will use the patch you wrote today instead.
> 
>> 
>>> or add the following to your patch, which is probably slightly
>>> mor efficient (but it has been only very mildly tested).
>>> 
>>> 
>>> diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
>>> index d1280e5f884..602b0fb3a2d 100644
>>> --- a/gcc/tree-sra.c
>>> +++ b/gcc/tree-sra.c
>>> @@ -1395,7 +1395,12 @@ scan_function (void)
>>> 
>>>             t = gimple_call_lhs (stmt);
>>>             if (t && !disqualify_if_bad_bb_terminating_stmt (stmt, t, NULL))
>>> -               ret |= build_access_from_expr (t, stmt, true);
>>> +               {
>>> +                 if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
>>> +                   ret |= !!build_access_from_expr_1 (t, stmt, true);
>>> +                 else
>>> +                   ret |= build_access_from_expr (t, stmt, true);
>>> +               }
>>>             break;
>> 
>> Thanks for the patch, but I don’t quite understand the above change:
>> 
>> When the call is IFN_DEFERRED_INIT, you used build_access_from_expr_1 instead of build_access_from_expr to avoid setting “cannot_scalarize_away_bitmap” bit.
>>    But why adding “!” To this call?
> 
> Note that it is a double !! which is basically a fancy way to convert a
> test for non-NULL to a bool.  It is equivalent to:
> 
> +                 if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
> +                   ret |= (build_access_from_expr_1 (t, stmt, true) != NULL);
> +                 else
> +                   ret |= build_access_from_expr (t, stmt, true);
> 
> use whichever variant you like better.  But the !! trick is used
> throughout the gcc source already.

Okay, I see. thanks.

Qing
> 
> Martin