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?
Richard.
> Uros.
