Re: Add option for whether ceil etc. can raise "inexact", adjust x86 conditions

[Uros Bizjak <ubizjak at gmail dot com>]

On Wed, Aug 16, 2017 at 12:48 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
> On Wed, Aug 16, 2017 at 12:43 PM, Richard Biener
> <richard.guenther@gmail.com> wrote:
>> On Tue, Aug 15, 2017 at 9:21 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
>>> On Tue, Aug 15, 2017 at 4:59 PM, Richard Biener
>>> <richard.guenther@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.