[Mesa-dev] [PATCH 1/8] configure.ac: Use AX_GCC_BUILTIN to check availability of __builtin_bswap32

[Matt Turner]

On Thu, Feb 20, 2014 at 10:21 AM, Tom Stellard <thomas.stellard at amd.com> wrote:
> ---
>  configure.ac                        |   6 ++
>  m4/ax_gcc_builtin.m4                | 168 ++++++++++++++++++++++++++++++++++++
>  src/gallium/auxiliary/util/u_math.h |   3 +-
>  3 files changed, 176 insertions(+), 1 deletion(-)
>  create mode 100644 m4/ax_gcc_builtin.m4
>
> diff --git a/configure.ac b/configure.ac
> index 8390d27..75d345a 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -119,6 +119,12 @@ if test "x$GCC" = xyes -a "x$acv_mesa_CLANG" = xno; then
>          GEN_ASM_OFFSETS=yes
>      fi
>  fi
> +
> +dnl Check for compiler builtins
> +AX_GCC_BUILTIN([__builtin_bswap32])
> +
> +AC_SUBST(HAVE___BUILTIN_BSWAP32)
> +
>  AM_CONDITIONAL([GEN_ASM_OFFSETS], test "x$GEN_ASM_OFFSETS" = xyes)
>
>  dnl Make sure the pkg-config macros are defined
> diff --git a/src/gallium/auxiliary/util/u_math.h b/src/gallium/auxiliary/util/u_math.h
> index b5e0663..b0f0e3d 100644
> --- a/src/gallium/auxiliary/util/u_math.h
> +++ b/src/gallium/auxiliary/util/u_math.h
> @@ -731,7 +731,8 @@ util_bitcount(unsigned n)
>  static INLINE uint32_t
>  util_bswap32(uint32_t n)
>  {
> -#if defined(PIPE_CC_GCC) && (PIPE_CC_GCC_VERSION >= 403)
> +/* We need the gcc version checks for non-autoconf build system */
> +#if defined(HAVE___BUILTIN_BSWAP32) || (defined(PIPE_CC_GCC) && (PIPE_CC_GCC_VERSION >= 403))
>     return __builtin_bswap32(n);
>  #else
>     return (n >> 24) |

I don't think this will work. AC_SUBST substitutes into the files
listed in AC_OUTPUT. I think what you want is to add something to
DEFINES. But I don't know what the point is of this patch, since the
existing preprocessor check should be sufficient?