Re: [PATCH v7 1/2] x86: Add defines / utilities for making ISA specific x86 builds

[Noah Goldstein <goldstein.w.n@gmail.com>]

On Wed, Jun 22, 2022 at 7:20 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Tue, Jun 21, 2022 at 9:48 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > 1. Factor out some of the ISA level defines in isa-level.c to
> >    standalone header isa-level.h
> >
> > 2. Add new headers with ISA level dependent macros for handling
> >    ifuncs.
> >
> > Note, this file does not change any code.
> >
> > Tested with and without multiarch on x86_64 for ISA levels:
> > {generic, x86-64-v2, x86-64-v3, x86-64-v4}
> > ---
> >  sysdeps/x86/init-arch.h           |   4 +-
> >  sysdeps/x86/isa-ifunc-macros.h    | 111 ++++++++++++++++++++++++++++++
> >  sysdeps/x86/isa-level.c           |  17 ++---
> >  sysdeps/x86/isa-level.h           |  99 ++++++++++++++++++++++++++
> >  sysdeps/x86_64/isa-default-impl.h |  49 +++++++++++++
> >  5 files changed, 267 insertions(+), 13 deletions(-)
> >  create mode 100644 sysdeps/x86/isa-ifunc-macros.h
> >  create mode 100644 sysdeps/x86/isa-level.h
> >  create mode 100644 sysdeps/x86_64/isa-default-impl.h
> >
> > diff --git a/sysdeps/x86/init-arch.h b/sysdeps/x86/init-arch.h
> > index 277c15f116..a2886a2532 100644
> > --- a/sysdeps/x86/init-arch.h
> > +++ b/sysdeps/x86/init-arch.h
> > @@ -19,7 +19,9 @@
> >  #include <ifunc-init.h>
> >  #include <isa.h>
> >
> > -#ifndef __x86_64__
> > +#ifdef __x86_64__
> > +# include <isa-ifunc-macros.h>
> > +#else
> >  /* Due to the reordering and the other nifty extensions in i686, it is
> >     not really good to use heavily i586 optimized code on an i686.  It's
> >     better to use i486 code if it isn't an i586.  */
> > diff --git a/sysdeps/x86/isa-ifunc-macros.h b/sysdeps/x86/isa-ifunc-macros.h
> > new file mode 100644
> > index 0000000000..2aa8fab000
> > --- /dev/null
> > +++ b/sysdeps/x86/isa-ifunc-macros.h
> > @@ -0,0 +1,111 @@
> > +/* Common ifunc selection utils
> > +   All versions must be listed in ifunc-impl-list.c.
> > +   Copyright (C) 2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _ISA_IFUNC_MACROS_H
> > +#define _ISA_IFUNC_MACROS_H 1
> > +
> > +#include <isa-level.h>
> > +#include <sys/cdefs.h>
> > +#include <stdlib.h>
> > +
> > +/* Only include at the level of the minimum build ISA or higher. I.e
> > +   if built with ISA=V1, then include all implementations. On the
> > +   other hand if built with ISA=V3 only include V3/V4
> > +   implementations. If there is no implementation at or above the
> > +   minimum build ISA level, then include the highest ISA level
> > +   implementation.  */
> > +#if MINIMUM_X86_ISA_LEVEL <= 4
> > +# define X86_IFUNC_IMPL_ADD_V4(...) IFUNC_IMPL_ADD (__VA_ARGS__)
> > +# define return_X86_OPTIMIZE_V4(...) return OPTIMIZE (__VA_ARGS__)
> > +# define return_X86_OPTIMIZE1_V4(...) return OPTIMIZE1 (__VA_ARGS__)
> > +#endif
> > +#if MINIMUM_X86_ISA_LEVEL <= 3
> > +# define X86_IFUNC_IMPL_ADD_V3(...) IFUNC_IMPL_ADD (__VA_ARGS__)
> > +# define return_X86_OPTIMIZE_V3(...) return OPTIMIZE (__VA_ARGS__)
> > +# define return_X86_OPTIMIZE1_V3(...) return OPTIMIZE1 (__VA_ARGS__)
> > +#endif
> > +#if MINIMUM_X86_ISA_LEVEL <= 2
> > +# define X86_IFUNC_IMPL_ADD_V2(...) IFUNC_IMPL_ADD (__VA_ARGS__)
> > +# define return_X86_OPTIMIZE_V2(...) return OPTIMIZE (__VA_ARGS__)
> > +# define return_X86_OPTIMIZE1_V2(...) return OPTIMIZE1 (__VA_ARGS__)
> > +#endif
> > +#if MINIMUM_X86_ISA_LEVEL <= 1
> > +# define X86_IFUNC_IMPL_ADD_V1(...) IFUNC_IMPL_ADD (__VA_ARGS__)
> > +# define return_X86_OPTIMIZE_V1(...) return OPTIMIZE (__VA_ARGS__)
> > +# define return_X86_OPTIMIZE1_V1(...) return OPTIMIZE1 (__VA_ARGS__)
> > +#endif
> > +
> > +#ifndef return_X86_OPTIMIZE_V4
> > +# define X86_IFUNC_IMPL_ADD_V4(...)
> > +# define return_X86_OPTIMIZE_V4(...) (void) (0)
> > +# define return_X86_OPTIMIZE1_V4(...) (void) (0)
> > +#endif
> > +#ifndef return_X86_OPTIMIZE_V3
> > +# define X86_IFUNC_IMPL_ADD_V3(...)
> > +# define return_X86_OPTIMIZE_V3(...) (void) (0)
> > +# define return_X86_OPTIMIZE1_V3(...) (void) (0)
> > +#endif
> > +#ifndef return_X86_OPTIMIZE_V2
> > +# define X86_IFUNC_IMPL_ADD_V2(...)
> > +# define return_X86_OPTIMIZE_V2(...) (void) (0)
> > +# define return_X86_OPTIMIZE1_V2(...) (void) (0)
> > +#endif
> > +#ifndef return_X86_OPTIMIZE_V1
> > +# define X86_IFUNC_IMPL_ADD_V1(...)
> > +# define return_X86_OPTIMIZE_V1(...) (void) (0)
> > +# define return_X86_OPTIMIZE1_V1(...) (void) (0)
> > +#endif
> > +
> > +#if MINIMUM_X86_ISA_LEVEL >= 4
> > +__errordecl (
> > +    __unreachable_isa_above_4,
> > +    "This code should be unreachable if ISA level >= 4 build ");
> > +# define X86_ERROR_IF_REACHABLE_V4() __unreachable_isa_above_4 ();
> > +#else
> > +# define X86_ERROR_IF_REACHABLE_V4()
> > +#endif
> > +
> > +#if MINIMUM_X86_ISA_LEVEL >= 3
> > +__errordecl (__unreachable_isa_above_3,
> > +            "This code should be unreachable if ISA level >= 3 build");
> > +# define X86_ERROR_IF_REACHABLE_V3() __unreachable_isa_above_3 ();
> > +#else
> > +# define X86_ERROR_IF_REACHABLE_V3()
> > +#endif
> > +
> > +#if MINIMUM_X86_ISA_LEVEL >= 2
> > +__errordecl (__unreachable_isa_above_2,
> > +            "This code should be unreachable if ISA level >= 2 build");
> > +# define X86_ERROR_IF_REACHABLE_V2() __unreachable_isa_above_2 ();
> > +#else
> > +# define X86_ERROR_IF_REACHABLE_V2()
> > +#endif
>
> No need for return_X86_OPTIMIZE nor X86_ERROR_IF_REACHABLE.
> When the minimum ISA level is v3, we will get undefined
> symbol linker error if compiler doesn't optimize out references
> to v1 and v2 symbols.

Prefer to keep both.

Think in this case there is a meaningful clarity argument. If build fails
because undefined reference to sse2 its a less meaningfully error
than if it fails on the exact attr warning.

>
> > +#define X86_ISA_CPU_FEATURE_CONST_CHECK_ENABLED(name)                  \
> > +  ((name##_X86_ISA_LEVEL) <= MINIMUM_X86_ISA_LEVEL)
> > +
> > +#define X86_ISA_CPU_FEATURE_USABLE_P(ptr, name)                        \
> > +  (X86_ISA_CPU_FEATURE_CONST_CHECK_ENABLED (name)                      \
> > +   || CPU_FEATURE_USABLE_P (ptr, name))
> > +
> > +#define X86_ISA_CPU_FEATURES_ARCH_P(ptr, name)                         \
> > +  (X86_ISA_CPU_FEATURE_CONST_CHECK_ENABLED (name)                      \
> > +   || CPU_FEATURES_ARCH_P (ptr, name))
> > +
> > +#endif
> > diff --git a/sysdeps/x86/isa-level.c b/sysdeps/x86/isa-level.c
> > index 09cd72ab20..5b7a2da870 100644
> > --- a/sysdeps/x86/isa-level.c
> > +++ b/sysdeps/x86/isa-level.c
> > @@ -26,38 +26,31 @@
> >     <https://www.gnu.org/licenses/>.  */
> >
> >  #include <elf.h>
> > -
> > +#include <sysdeps/x86/isa-level.h>
> >  /* ELF program property for x86 ISA level.  */
> >  #ifdef INCLUDE_X86_ISA_LEVEL
> > -# if defined __SSE__ && defined __SSE2__
> > +# if MINIMUM_X86_ISA_LEVEL >= 1
> >  /* NB: ISAs, excluding MMX, in x86-64 ISA level baseline are used.  */
> >  #  define ISA_BASELINE GNU_PROPERTY_X86_ISA_1_BASELINE
> >  # else
> >  #  define ISA_BASELINE 0
> >  # endif
> >
> > -# if ISA_BASELINE && defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 \
> > -     && defined HAVE_X86_LAHF_SAHF && defined __POPCNT__ \
> > -     && defined __SSE3__ && defined __SSSE3__ && defined __SSE4_1__ \
> > -     && defined __SSE4_2__
> > +# if MINIMUM_X86_ISA_LEVEL >= 2
> >  /* NB: ISAs in x86-64 ISA level v2 are used.  */
> >  #  define ISA_V2       GNU_PROPERTY_X86_ISA_1_V2
> >  # else
> >  #  define ISA_V2       0
> >  # endif
> >
> > -# if ISA_V2 && defined __AVX__ && defined __AVX2__ && defined __F16C__ \
> > -     && defined __FMA__ && defined __LZCNT__ && defined HAVE_X86_MOVBE \
> > -     && defined __BMI__ && defined __BMI2__
> > +# if MINIMUM_X86_ISA_LEVEL >= 3
> >  /* NB: ISAs in x86-64 ISA level v3 are used.  */
> >  #  define ISA_V3       GNU_PROPERTY_X86_ISA_1_V3
> >  # else
> >  #  define ISA_V3       0
> >  # endif
> >
> > -# if ISA_V3 && defined __AVX512F__ && defined __AVX512BW__ \
> > -     && defined __AVX512CD__ && defined __AVX512DQ__ \
> > -     && defined __AVX512VL__
> > +# if MINIMUM_X86_ISA_LEVEL >= 4
> >  /* NB: ISAs in x86-64 ISA level v4 are used.  */
> >  #  define ISA_V4       GNU_PROPERTY_X86_ISA_1_V4
> >  # else
> > diff --git a/sysdeps/x86/isa-level.h b/sysdeps/x86/isa-level.h
> > new file mode 100644
> > index 0000000000..21366b3132
> > --- /dev/null
> > +++ b/sysdeps/x86/isa-level.h
> > @@ -0,0 +1,99 @@
> > +/* Header defining the minimum x86 ISA level
> > +   Copyright (C) 2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   In addition to the permissions in the GNU Lesser General Public
> > +   License, the Free Software Foundation gives you unlimited
> > +   permission to link the compiled version of this file with other
> > +   programs, and to distribute those programs without any restriction
> > +   coming from the use of this file.  (The Lesser General Public
> > +   License restrictions do apply in other respects; for example, they
> > +   cover modification of the file, and distribution when not linked
> > +   into another program.)
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _ISA_LEVEL_H
> > +#define _ISA_LEVEL_H
> > +
> > +#if defined __SSE__ && defined __SSE2__
> > +/* NB: ISAs, excluding MMX, in x86-64 ISA level baseline are used.  */
> > +# define __X86_ISA_V1 1
> > +#else
> > +# define __X86_ISA_V1 0
> > +#endif
> > +
> > +#if __X86_ISA_V1 && defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16               \
> > +    && defined HAVE_X86_LAHF_SAHF && defined __POPCNT__ && defined __SSE3__   \
> > +    && defined __SSSE3__ && defined __SSE4_1__ && defined __SSE4_2__
> > +/* NB: ISAs in x86-64 ISA level v2 are used.  */
> > +# define __X86_ISA_V2 1
> > +#else
> > +# define __X86_ISA_V2 0
> > +#endif
> > +
> > +#if __X86_ISA_V2 && defined __AVX__ && defined __AVX2__ && defined __F16C__   \
> > +    && defined __FMA__ && defined __LZCNT__ && defined HAVE_X86_MOVBE         \
> > +    && defined __BMI__ && defined __BMI2__
> > +/* NB: ISAs in x86-64 ISA level v3 are used.  */
> > +# define __X86_ISA_V3 1
> > +#else
> > +# define __X86_ISA_V3 0
> > +#endif
> > +
> > +#if __X86_ISA_V3 && defined __AVX512F__ && defined __AVX512BW__               \
> > +    && defined __AVX512CD__ && defined __AVX512DQ__ && defined __AVX512VL__
> > +/* NB: ISAs in x86-64 ISA level v4 are used.  */
> > +# define __X86_ISA_V4 1
> > +#else
> > +# define __X86_ISA_V4 0
> > +#endif
> > +
> > +#define MINIMUM_X86_ISA_LEVEL                                                 \
> > +  (__X86_ISA_V1 + __X86_ISA_V2 + __X86_ISA_V3 + __X86_ISA_V4)
> > +
> > +
> > +/*
> > + * CPU Features that are hard coded as enabled depending on ISA build
> > + *   level.
> > + *    - Values > 0 features are always ENABLED if:
> > + *          Value >= MINIMUM_X86_ISA_LEVEL
> > + */
> > +
> > +
> > +/* ISA level >= 4 guaranteed includes.  */
> > +#define AVX512VL_X86_ISA_LEVEL 4
> > +#define AVX512BW_X86_ISA_LEVEL 4
> > +
> > +/* ISA level >= 3 guaranteed includes.  */
> > +#define AVX2_X86_ISA_LEVEL 3
> > +#define BMI2_X86_ISA_LEVEL 3
> > +
> > +/*
> > + * NB: This may not be fully assumable for ISA level >= 3. From
> > + * looking over the architectures supported in cpu-features.h the
> > + * following CPUs may have an issue with this being default set:
> > + *      - AMD Excavator
> > + */
> > +#define AVX_Fast_Unaligned_Load_X86_ISA_LEVEL 3
> > +
> > +/*
> > + * KNL (the only cpu that sets this supported in cpu-features.h)
> > + * builds with ISA V1 so this shouldn't harm any architectures.
> > + */
> > +#define Prefer_No_VZEROUPPER_X86_ISA_LEVEL 3
> > +
> > +
> > +#endif
> > diff --git a/sysdeps/x86_64/isa-default-impl.h b/sysdeps/x86_64/isa-default-impl.h
> > new file mode 100644
> > index 0000000000..34634668e5
> > --- /dev/null
> > +++ b/sysdeps/x86_64/isa-default-impl.h
> > @@ -0,0 +1,49 @@
> > +/* Utility for including proper default function based on ISA level
> > +   Copyright (C) 2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#include <isa-level.h>
> > +
> > +#ifndef DEFAULT_IMPL_V1
> > +# error "Must have at least ISA V1 Version"
> > +#endif
> > +
> > +#ifndef DEFAULT_IMPL_V2
> > +# define DEFAULT_IMPL_V2 DEFAULT_IMPL_V1
> > +#endif
> > +
> > +#ifndef DEFAULT_IMPL_V3
> > +# define DEFAULT_IMPL_V3 DEFAULT_IMPL_V2
> > +#endif
> > +
> > +#ifndef DEFAULT_IMPL_V4
> > +# define DEFAULT_IMPL_V4 DEFAULT_IMPL_V3
> > +#endif
> > +
> > +#if MINIMUM_X86_ISA_LEVEL == 1
> > +# define ISA_DEFAULT_IMPL DEFAULT_IMPL_V1
> > +#elif MINIMUM_X86_ISA_LEVEL == 2
> > +# define ISA_DEFAULT_IMPL DEFAULT_IMPL_V2
> > +#elif MINIMUM_X86_ISA_LEVEL == 3
> > +# define ISA_DEFAULT_IMPL DEFAULT_IMPL_V3
> > +#elif MINIMUM_X86_ISA_LEVEL == 4
> > +# define ISA_DEFAULT_IMPL DEFAULT_IMPL_V4
> > +#else
> > +# error "Unsupported ISA Level!"
> > +#endif
> > +
> > +#include ISA_DEFAULT_IMPL
> > --
> > 2.34.1
> >
>
>
> --
> H.J.