Some thoughts about steerring commitee work

[Ryan Hill]

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.

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.


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