[PATCH] X86-64: Add _dl_runtime_resolve_avx[512]_opt [BZ #20508]

[H.J. Lu]

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?


-- 
H.J.
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