Re: [PATCH] x86: Compile CPUID functions with -mgeneral-regs-only

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Jun 24, 2021 at 2:13 PM H.J. Lu via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> CPUID functions are used to detect CPU features.  If vector ISAs
> are enabled, compiler is free to use them in these functions.  Add
> __attribute__ ((target("general-regs-only"))) to CPUID functions
> to avoid vector instructions.

But there are GPR instructions not in x86_64, so shouldn't
we use target("march=x86_64") or so?  Note doing either will
of course prevent inlining of those "inlines".

So I'm not sure how much of a fix this is ... the error will almost
always be visible in the caller as well.

> gcc/
>
>         PR target/101185
>         * config/i386/cpuid.h (__get_cpuid_max): Add
>         __attribute__ ((target("general-regs-only"))).
>         (__get_cpuid): Likewise.
>         (__get_cpuid_count): Likewise.
>         (__cpuidex): Likewise.
>
> gcc/testsuite/
>
>         PR target/101185
>         * gcc.target/i386/avx512-check.h (check_osxsave): Add
>         __attribute__ ((target("general-regs-only"))).
>         (main): Likewise.
> ---
>  gcc/config/i386/cpuid.h                      | 4 ++++
>  gcc/testsuite/gcc.target/i386/avx512-check.h | 2 ++
>  2 files changed, 6 insertions(+)
>
> diff --git a/gcc/config/i386/cpuid.h b/gcc/config/i386/cpuid.h
> index aebc17c6827..74881ee91e5 100644
> --- a/gcc/config/i386/cpuid.h
> +++ b/gcc/config/i386/cpuid.h
> @@ -243,6 +243,7 @@
>     pointer is non-null, then first four bytes of the signature
>     (as found in ebx register) are returned in location pointed by sig.  */
>
> +__attribute__ ((target("general-regs-only")))
>  static __inline unsigned int
>  __get_cpuid_max (unsigned int __ext, unsigned int *__sig)
>  {
> @@ -298,6 +299,7 @@ __get_cpuid_max (unsigned int __ext, unsigned int *__sig)
>     supported and returns 1 for valid cpuid information or 0 for
>     unsupported cpuid leaf.  All pointers are required to be non-null.  */
>
> +__attribute__ ((target("general-regs-only")))
>  static __inline int
>  __get_cpuid (unsigned int __leaf,
>              unsigned int *__eax, unsigned int *__ebx,
> @@ -315,6 +317,7 @@ __get_cpuid (unsigned int __leaf,
>
>  /* Same as above, but sub-leaf can be specified.  */
>
> +__attribute__ ((target("general-regs-only")))
>  static __inline int
>  __get_cpuid_count (unsigned int __leaf, unsigned int __subleaf,
>                    unsigned int *__eax, unsigned int *__ebx,
> @@ -330,6 +333,7 @@ __get_cpuid_count (unsigned int __leaf, unsigned int __subleaf,
>    return 1;
>  }
>
> +__attribute__ ((target("general-regs-only")))
>  static __inline void
>  __cpuidex (int __cpuid_info[4], int __leaf, int __subleaf)
>  {
> diff --git a/gcc/testsuite/gcc.target/i386/avx512-check.h b/gcc/testsuite/gcc.target/i386/avx512-check.h
> index 0a377dba1d5..406faf8fe03 100644
> --- a/gcc/testsuite/gcc.target/i386/avx512-check.h
> +++ b/gcc/testsuite/gcc.target/i386/avx512-check.h
> @@ -25,6 +25,7 @@ do_test (void)
>  }
>  #endif
>
> +__attribute__ ((target("general-regs-only")))
>  static int
>  check_osxsave (void)
>  {
> @@ -34,6 +35,7 @@ check_osxsave (void)
>    return (ecx & bit_OSXSAVE) != 0;
>  }
>
> +__attribute__ ((target("general-regs-only")))
>  int
>  main ()
>  {
> --
> 2.31.1
>