[Bug tree-optimization/64541] FRE pass optimization failure
rguenther at suse dot de
gcc-bugzilla@gcc.gnu.org
Wed Jan 14 12:00:00 GMT 2015
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64541
--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> ---
On Wed, 14 Jan 2015, skvadrik at gmail dot com wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64541
>
> --- Comment #2 from Ulya <skvadrik at gmail dot com> ---
> > we have to assume that p == q and thus the store to *q invalidates the previously load *p
>
> I see.
> It seemed to me from GIMPLE dumps that both cases are equally easy to optimize,
> perhaps I'm missing something.
1:
_6 = *p_2(D);
*q_7(D) = _6;
_9 = *q_7(D);
_10 = *_9;
it's easy to see that the load _9 = *q_7(D) results in _6.
2:
*p_2(D) = _4;
_6 = *p_2(D);
*q_7(D) = _6;
_9 = *p_2(D);
_10 = *_9;
not so much here for the load _9 = *p_2(D) as I explained
(the store *q_7(D) = _6 aliases it)
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