Re: [i386] __builtin_ia32_stmxcsr could be pure

[Marc Glisse <marc.glisse@inria.fr>]

Hello,

I don't think Richard's "sounds good" was meant as "ok to commit". Does an 
x86 maintainer want to approve or criticize the patch?

https://gcc.gnu.org/ml/gcc-patches/2017-05/msg02009.html

On Fri, 26 May 2017, Richard Biener wrote:

> On Fri, May 26, 2017 at 10:55 AM, Marc Glisse <marc.glisse@inria.fr> wrote:
>> Hello,
>>
>> glibc marks fegetround as a pure function. On x86, people tend to use
>> _MM_GET_ROUNDING_MODE instead, which could benefit from the same. I think it
>> is safe, but a second opinion would be welcome.
>
> Sounds good.  The important part is to keep the dependency to SET_ROUNDING_MODE
> which is done via claiming both touch global memory.
>
>> I could have handled just this builtin, but it seemed better to provide
>> def_builtin_pure (like "const" already has) since there should be other
>> builtins that can be marked this way (maybe the gathers?).
>
> Should work for gathers.  They could even use stronger guarantees,
> namely a fnspec with "..R" (the pointer argument is only read from directly).
> Similarly scatter can use ".W" (the pointer argument is only written to
> directly).
>
> Richard.
>
>> Bootstrap+testsuite on x86_64-pc-linux-gnu with default languages.
>>
>> 2017-05-29  Marc Glisse  <marc.glisse@inria.fr>
>>
>> gcc/
>>         * config/i386/i386.c (struct builtin_isa): New field pure_p.
>>         Reorder for compactness.
>>         (def_builtin, def_builtin2, ix86_add_new_builtins): Handle pure_p.
>>         (def_builtin_pure, def_builtin_pure2): New functions.
>>         (ix86_init_mmx_sse_builtins) [__builtin_ia32_stmxcsr]: Mark as pure.
>>
>> gcc/testsuite/
>>         * gcc.target/i386/getround.c: New file.
>>
>> --
>> Marc Glisse
>

-- 
Marc Glisse