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?
> Richard.
>
>> Uros.
