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From: Richard Biener <>
To: Marc Glisse <>
Cc: GCC Patches <>
Subject: Re: [i386] __builtin_ia32_stmxcsr could be pure
Date: Fri, 26 May 2017 09:13:00 -0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Fri, May 26, 2017 at 10:55 AM, Marc Glisse <> 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


> Bootstrap+testsuite on x86_64-pc-linux-gnu with default languages.
> 2017-05-29  Marc Glisse  <>
> 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/
>         * New file.
> --
> Marc Glisse

  reply	other threads:[~2017-05-26  9:06 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-05-26  8:57 Marc Glisse
2017-05-26  9:13 ` Richard Biener [this message]
2017-06-03 19:05   ` Marc Glisse
2017-06-20 21:34     ` Marc Glisse
2017-06-21  7:43 Uros Bizjak

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