[PATCH] Save and restore xmm0-xmm7 in _dl_runtime_resolve

[H.J. Lu]

On Mon, Jul 27, 2015 at 6:37 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Jul 27, 2015 at 6:26 AM, Ondřej Bílka <neleai@seznam.cz> wrote:
>> On Mon, Jul 27, 2015 at 06:14:07AM -0700, H.J. Lu wrote:
>>> >>
>>> >> There is a potential performance issue.  This won't change parameters
>>> >> passed in S256-bit/512-bit vector registers because SSE load will only
>>> >> update the lower 128 bits of 256-bit/512-bit vector registers while
>>> >> preserving the upper bits.  But these SSE load operations may not be
>>> >> fast on all current and future processors.  To load the entire
>>> >> 256-bit/512-bit vector registers, we need to check CPU feature in
>>> >> each symbol lookup.  On the other hand, we can compile x86-64 ld.so
>>> >> with -msse2.  I don't know what the final performance impact is.
>>> >>
>>> > Yes, these should be saved due problems with modes. There could be
>>> > problem that saving these takes longer. You don't need
>>> > check cpu features on each call.
>>> > Make _dl_runtime_resolve a function pointer and on
>>> > startup initialize it to correct variant.
>>>
>>> One more indirect call.
>>>
>> no, my proposal is different, we could do this:
>>
>> void *_dl_runtime_resolve;
>> int startup()
>> {
>>   if (has_avx())
>>     _dl_runtime_resolve = _dl_runtime_resolve_avx;
>>   else
>>     _dl_runtime_resolve = _dl_runtime_resolve_sse;
>> }
>>
>> Then we will assign correct variant.
>
> Yes, this may work for both _dl_runtime_profile and
>  _dl_runtime_resolve.  I will see what I can do.
>

Please try hjl/pr18661 branch.  I implemented:

0000000000016fd0 t _dl_runtime_profile_avx
0000000000016b50 t _dl_runtime_profile_avx512
0000000000017450 t _dl_runtime_profile_sse
00000000000168d0 t _dl_runtime_resolve_avx
0000000000016780 t _dl_runtime_resolve_avx512
0000000000016a20 t _dl_runtime_resolve_sse

-- 
H.J.