Re: IBM z13 support for older GCCs

[Richard Biener <rguenther at suse dot de>]

On Fri, 22 May 2015, Andreas Krebbel wrote:

> On 05/22/2015 10:22 AM, Richard Biener wrote:
> > On Fri, 22 May 2015, Andreas Krebbel wrote:
> > 
> >> Hi,
> >>
> >> in order to get the IBM z13 support into present distros the Linux distributors asked me to get this
> >> stuff upstream into the older GCC branches first. This would ease the whole backporting efforts,
> >> interactions with other patches and would make sure that everybody uses the same code level.
> >>
> >> This would affect at least the GCC 4.8 and 5 branches but for continuity reasons it probably also
> >> should go into 4.9 then.
> >>
> >> The patchset requires only very minor common code changes and therefore imposes only a low risk for
> >> other platforms:
> >>
> >> recog: Increased max number of alternatives - v2
> >> https://gcc.gnu.org/ml/gcc-patches/2015-05/msg02059.html
> > 
> > On branches you'd have to use unsigned HOST_WIDE_INT (where that might
> > be 32bits on some hosts!).  We still support hosts without uint64_t
> > here.  So this might already be a no-go.
> > 
> >> optabs: Fix vec_perm -> V16QI middle end lowering.
> >> https://gcc.gnu.org/ml/gcc-patches/2015-05/msg02058.html
> >>
> >> There is definitely some risk for S/390 but this again should be 
> >> relatively low when compiling for CPU levels prio to z13.
> >>
> >> For the z13 support itself I've added a bunch of testcases but I've also 
> >> run checks with about 10000 automatically generated testcases not part 
> >> of the patchset.
> >>
> >> We also ran the ABI comparison testsuite to compare the GCC and LLVM 
> >> implementations regarding vector data types.
> >>
> >> Is it ok to apply the patchset to GCC 4.8, 4.9, and 5 branches as well?
> > 
> > I'm somewhat missing the point of backporting z13 support.  ppc64le
> > enablement was a different story (IBM basically saying ppc64-linux
> > is dead), but surely all z13 machines can run non-z13 code just fine.
> > 
> > s390x-linux-gnu is a secondary platform so I don't think we'd want
> > to destabilize it (esp. on the 4.8 branch where I expect only one
> > more release around the end of June with no chance to fix things up).
> > 
> > So that's a "no" from me basically.  But I'm willing to be convinced
> > otherwise (not having looked into the z13 backend patches at all).
> 
> Ok. What about GCC 5 branch?

All arguments still apply apart from the fact that we'll have plenty
of releases from the GCC 5 branch (and the alternatives patch is
safe there).

So for GCC 5 I'm willing to leave it to the architecture maintainers,
but please wait for other RMs to chime in.

Thanks,
Richard.

> 
> -Andreas-
> 
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Dilip Upmanyu, Graham Norton, HRB 21284 (AG Nuernberg)