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Re: [PATCH] X86-64: Add _dl_runtime_resolve_avx[512]_opt [BZ #20508]
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Richard Henderson <rth at twiddle dot net>
- Cc: Florian Weimer <fweimer at redhat dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Thu, 1 Sep 2016 14:52:42 -0700
- Subject: Re: [PATCH] X86-64: Add _dl_runtime_resolve_avx[512]_opt [BZ #20508]
- Authentication-results: sourceware.org; auth=none
- References: <CAMe9rOojpuFz1jTbMpNcqZK1KVDqaWozNuEuS3E67dvD3Rh=hw@mail.gmail.com> <c6e21847-bc95-3c75-ed54-798c62194072@redhat.com> <CAMe9rOp=bvrk0MBF8SrP4JqLHembRdeyfGNqNkcVWvoEs3R=tA@mail.gmail.com> <CAMe9rOo7MmGNPKct=AzzbtR564yH1P96tUcLD7pFv7GtxF3-Ng@mail.gmail.com> <48eeea78-99e8-f255-bd26-b6d28929b4f0@twiddle.net> <CAMe9rOqXhVLVbT90JBfkJnCLzZBrkUHtkO4Ddfk9HPH7jiyEzw@mail.gmail.com> <CAMe9rOoDp7XYwLdDetFNghAdDo_zj-4342LKV4i0zCH36aBWtw@mail.gmail.com>
On Tue, Aug 30, 2016 at 1:30 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Aug 29, 2016 at 5:01 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Mon, Aug 29, 2016 at 4:07 PM, Richard Henderson <rth@twiddle.net> wrote:
>>> On 08/26/2016 10:18 AM, H.J. Lu wrote:
>>>>
>>>> + vpcmpeqd %xmm8, %xmm8, %xmm8
>>>> + vorpd %ymm9, %ymm10, %ymm10
>>>> + vptest %ymm10, %ymm8
>>>
>>>
>>> No need to create a mask of all -1; use vptest ymm10, ymm10.
>>>
>>
>> ymm8 isn't all -1. Only the lower 128 bis are all -1:
>>
>>
>> (gdb) p/x $ymm8
>> $4 = {v8_float = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, v4_double = {
>> 0x8000000000000000, 0x8000000000000000, 0x0, 0x0}, v32_int8 = {
>> 0xff <repeats 16 times>, 0x0 <repeats 16 times>}, v16_int16 = {0xffff,
>> 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0x0, 0x0, 0x0,
>> 0x0, 0x0, 0x0, 0x0, 0x0}, v8_int32 = {0xffffffff, 0xffffffff, 0xffffffff,
>> 0xffffffff, 0x0, 0x0, 0x0, 0x0}, v4_int64 = {0xffffffffffffffff,
>> 0xffffffffffffffff, 0x0, 0x0}, v2_int128 = {
>> 0xffffffffffffffffffffffffffffffff, 0x00000000000000000000000000000000}}
>> (gdb)
>>
>> ymm10 (ymm0|..|ymm7) has
>>
>> (gdb) p/x $ymm10
>> $2 = {v8_float = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, v4_double = {
>> 0x8000000000000000, 0x8000000000000000, 0x0, 0x0}, v32_int8 = {0x6d,
>> 0x79, 0x72, 0x6f, 0x7f, 0x74, 0x6f, 0x73, 0x77, 0x6f, 0x6f, 0x67, 0x6f,
>> 0xff, 0x6f, 0xff, 0x0 <repeats 16 times>}, v16_int16 = {0x796d, 0x6f72,
>> 0x747f, 0x736f, 0x6f77, 0x676f, 0xff6f, 0xff6f, 0x0, 0x0, 0x0, 0x0, 0x0,
>> 0x0, 0x0, 0x0}, v8_int32 = {0x6f72796d, 0x736f747f, 0x676f6f77,
>> 0xff6fff6f, 0x0, 0x0, 0x0, 0x0}, v4_int64 = {0x736f747f6f72796d,
>> 0xff6fff6f676f6f77, 0x0, 0x0}, v2_int128 = {
>> 0xff6fff6f676f6f77736f747f6f72796d, 0x00000000000000000000000000000000}}
>>
>> Since
>>
>> vptest %ymm10, %ymm8
>>
>> IF (SRC[255:0] BITWISE AND NOT DEST[255:0] = 0)
>> THEN CF = 1;
>> ELSE CF = 0;
>>
>> this ignores the lower 128 bits of ymm10 and sets CF = 0
>> only if the upper 128 bits of ymm10 aren't zero. If we use
>>
>> vptest ymm10, ymm10
>>
>> CF is always 1 and we will always preserve ymm0-ymm7 even
>> when the upper 128 bits are zero.
>>
>
> Here is the updated patch to add PRESERVE_BND_REGS_PREFIX
> before branches. Otherwise bound registers will be cleared. OK
> for master?
>
Any comments? I will check it in next week if there is no objection.
--
H.J.