Re: Some thoughts about steerring commitee work

[Dorit Nuzman <DORIT at il dot ibm dot com>]

> Dorit Nuzman wrote:
> >> H. J. Lu wrote:
> >>
> >>> Why don't we turn on vectorizer at -O3 or even -O2, depending on
> >>> ISA? I added -ftree-vectorize to BOOT_CFLAGS on x86-64. According to
> >>> -ftree-vectorizer-verbose=1, there are 82 loops vectorized in
> >>> gcc source. There are no regressions. There are not much changes
> >>> in bootstrap time as well as "make check" time.
> >> We have about two dozen cases of packages that break when
> >> -ftree-vectorize is used.  I'm sure there are several more as we tend
to
> >> discourage such bug reports.
> >>
> > If you could take the time to find the reduced testcases and file PRs
for
> > these, that would be most appreciated.
>
> I believe the majority of them can be traced back to PR 25413.  For
> example building zlib with -O2 -march=pentium4 -ftree-vectorize will
> cause several apps that link to it (firefox, openoffice, poppler, etc.)
> to segfault.  The vectorizer generates movdqa instructions with datarefs
> that are not aligned on a 16 byte boundary.
>

there is an old patch floating around by Devang to address this problem (as
mentioned in the PR). we should push this forward, it's really a simple
fix. I'll try to get to it soonish

> Other than that, I went through the rest of our -ftree-vectorize bugs
> this morning and found that many of them have been fixed in 4.2, so the
> situation is much better than I originally thought.
>

cool!

thanks,
dorit

>
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