------- Comment #15 from rakdver at kam dot mff dot cuni dot cz 2010-07-07
09:37 -------
Subject: Re: [4.6 regression] RTL loop
unrolling causes FAIL: gcc.dg/pr39794.c
> ------- Comment #14 from rguenth at gcc dot gnu dot org 2010-07-07 09:01
> -------
> Huh. Unrolling preserves MEM_ATTRs even though it re-writes the RTXen. That
> causes scheduling to see just a bunch of repeated
>
>
> where there is obviously no conflicts between the above patterns during
> different unrolled copies.
>
> Who is supposed to magically deal with that? (or what is supposed to prevent
> this from happening?)
I am not sure what you mean -- I may be misunderstanding how rtl alias analysis
works, but as far as I can tell, what unroller does (just preserving the
MEM_ATTRs) is conservatively correct (so, potentially it may make us believe
that there are dependences that are not really present, but it should not cause
a wrong-code bug).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44838
