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Re: TODO_rebuild_alias and -O0


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.

Richard.

> Ludo’.


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