TODO_rebuild_alias and -O0

[Ludovic Courtès]

Richard Guenther <richard.guenther@gmail.com> skribis:

> On Mon, Oct 8, 2012 at 1:42 PM, Ludovic Courtès <ludo@gnu.org> wrote:
>> Richard Guenther <richard.guenther@gmail.com> skribis:
>>
>>> On Mon, Oct 8, 2012 at 11:58 AM, Ludovic Courtès <ludo@gnu.org> wrote:
>>>> Richard Guenther <richard.guenther@gmail.com> skribis:
>>>>
>>>>> At -O0 no virtual operands are produced.  TODO_rebuild_alias only computes
>>>>> points-to sets which are in itself not useful.
>>>>>
>>>>> What do you want to achieve with TODO_rebuild_alias?
>>>>
>>>> I basically want to use ‘ptr_derefs_may_alias_p’ in this particular pass.
>>>
>>> That should work.
>>
>> It actually does, except that ‘ptr_derefs_may_alias_p’ returns true for
>> two SSA names in cases like this:
>>
>>   double *p, *q;
>>   p = malloc (123);
>>   q = malloc (234);
>>
>> (Where ‘malloc’ has the ‘malloc’ attribute.)
>>
>> For some reason, there’s no such false positive when using TODO_rebuild_alias.
>
> Well, "that should work" means it works non-conservatively with
> TODO_rebuild_alias, of course.

Right.  :-)  So how can I get maximum accuracy, while avoid the assertion
failure on -O0?

Thanks,
Ludo’.