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

["H.J. Lu" <hjl.tools@gmail.com>]

On Thu, Jun 24, 2021 at 5:35 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> 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".

Does -march=x86_64, which enables CMOV and other GPR
ISAs,  work for -m32?

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

I think _attribute__ ((target("general-regs-only"))) is a step
forward.

> > 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
> >



-- 
H.J.