On Wed, Aug 16, 2017 at 12:48 PM, Uros Bizjak <ubiz...@gmail.com> wrote:
> On Wed, Aug 16, 2017 at 12:43 PM, Richard Biener
> <richard.guent...@gmail.com> wrote:
>> On Tue, Aug 15, 2017 at 9:21 PM, Uros Bizjak <ubiz...@gmail.com> wrote:
>>> On Tue, Aug 15, 2017 at 4:59 PM, Richard Biener
>>> <richard.guent...@gmail.com> wrote:
>>>
>>>> So I'd try the "easy" way of expanding if (__builtin_cpu_supports
>>>> ("sse4.1"))
>>>> as the sse4.1 sequence is just a single instruction. The interesting part
>>>> of the story will be to make sure we can emit that even if ! TARGET_ROUND
>>>> ...
>>>>
>>>> Uros, any idea how to accomplish this? Or is the idea of a "local" ifunc
>>>> better? Note the ABI boundary will be expensive but I guess the
>>>> conditional
>>>> sequence as well (and it will disturb RA even if predicted to have SSE
>>>> 4.1).
>>>
>>> TARGET_ROUND is just:
>>>
>>> /* SSE4.1 defines round instructions */
>>> #define OPTION_MASK_ISA_ROUND OPTION_MASK_ISA_SSE4_1
>>> #define TARGET_ISA_ROUND ((ix86_isa_flags & OPTION_MASK_ISA_ROUND) !=
>>> 0)
>>>
>>> I don't remember the history around the #define, once upon a time
>>> probably made sense, but nowadays it looks that it can be simply
>>> substituted with TARGET_SSE4_1.
>>
>> Sure but we want the backend to use a TARGET_ROUND guarded define_insn
>> when TARGET_ROUND is false but inside a runtime conditional ensuring that
>> TARGET_ROUND is satisfied. With doing this with ifuncs we'd mark the
>> function
>> with a proper target attribute but within a function?
>
> How about something intrinsic headers are using?
(... somehow managed to press send too early ...)
There we use GCC_push_options and GCC_target pragmas. Maybe we also
need corresponding __ROUND__ define defined by the compiler.
Uros.
