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Re: IBM z13 support for older GCCs


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?

-Andreas-



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