Re: [PATCH] tilegx: work around vector insn bug in gcc

[Chris Metcalf <cmetcalf at mellanox dot com>]

On 12/5/2017 11:22 AM, Joseph Myers wrote:
> On Tue, 5 Dec 2017, Adhemerval Zanella wrote:
>
> > On 04/12/2017 13:56, Chris Metcalf wrote:
> > > Avoid an issue in gcc where some of the vector (aka SIMD) ops will
> > > sometimes end up getting wrongly optimized out.  We use these
> > > instructions in many of the string implementations.  If/when we
> > > have an upstreamed fix for this problem in gcc we can conditionalize
> > > the use of the extended assembly workaround in glibc.
> > Do you the conditions to trigger this issue (compiler option, gcc
> > version, etc.)?
> It would seem appropriate for the comment saying "buggy in current
> compiler versions" to link to a corresponding bug report in GCC Bugzilla.

Good point.  A bug was filed for this a year ago (78117) and I added a
comment with my small use case, and pushed a tweak to the comment
in sysdeps/tile/tilegx/string-endian.h referencing the bug.

--
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com