[Mesa-dev] [PATCH v4] swr: Refactor checks for compiler feature flags

[Rowley, Timothy O]

Tested on gcc-5.3.1, clang-3.8, icc-16.0.3

Reviewed-by: Tim Rowley <timothy.o.rowley at intel.com>
Tested-by: Tim Rowley <timothy.o.rowley at Intel.com>

> On Jun 28, 2016, at 2:50 PM, Chuck Atkins <chuck.atkins at kitware.com> wrote:
> 
> Encapsulate the test for which flags are needed to get a compiler to
> support certain features.  Along with this, give various options to try
> for AVX and AVX2 support.  Ideally we want to use specific instruction
> set feature flags, like -mavx2 for instance instead of -march=haswell,
> but the flags required for certain compilers are different.  This
> allows, for AVX2 for instance, GCC to use -mavx2 -mfma -mbmi2 -mf16c
> while the Intel compiler which doesn't support those flags can fall
> back to using -march=core-avx2.
> 
> This addresses a bug where the Intel compiler will silently ignore the
> AVX2 instruction feature flags and then potentially fail to build.
> 
> v2: Pass preprocessor-check argument as true-state instead of
>    false-state for clarity.
> v3: Reduce AVX2 define test to just __AVX2__.  Additional defines suchas
>    __FMA__, __BMI2__, and __F16C__ appear to be inconsistently defined
>    w.r.t thier availability.
> v4: Fix C++11 flags being added globally and add more logic to
>    swr_require_cxx_feature_flags
> 
> Cc: Tim Rowley <timothy.o.rowley at intel.com>
> Signed-off-by: Chuck Atkins <chuck.atkins at kitware.com>
> ---
> configure.ac                        | 73 +++++++++++++++++++++++++------------
> src/gallium/drivers/swr/Makefile.am |  4 +-
> 2 files changed, 52 insertions(+), 25 deletions(-)
> 
> diff --git a/configure.ac b/configure.ac
> index cc9bc47..8321e8e 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -2330,6 +2330,45 @@ swr_llvm_check() {
>     fi
> }
> 
> +swr_require_cxx_feature_flags() {
> +    feature_name="$1"
> +    preprocessor_test="$2"
> +    option_list="$3"
> +    output_var="$4"
> +
> +    AC_MSG_CHECKING([whether $CXX supports $feature_name])
> +    AC_LANG_PUSH([C++])
> +    save_CXXFLAGS="$CXXFLAGS"
> +    save_IFS="$IFS"
> +    IFS=","
> +    found=0
> +    for opts in $option_list
> +    do
> +        unset IFS
> +        CXXFLAGS="$opts $save_CXXFLAGS"
> +        AC_COMPILE_IFELSE(
> +            [AC_LANG_PROGRAM(
> +                [   #if !($preprocessor_test)
> +                    #error
> +                    #endif
> +                ])],
> +            [found=1; break],
> +            [])
> +        IFS=","
> +    done
> +    IFS="$save_IFS"
> +    CXXFLAGS="$save_CXXFLAGS"
> +    AC_LANG_POP([C++])
> +    if test $found -eq 1; then
> +        AC_MSG_RESULT([$opts])
> +        eval "$output_var=\$opts"
> +        return 0
> +    fi
> +    AC_MSG_RESULT([no])
> +    AC_MSG_ERROR([swr requires $feature_name support])
> +    return 1
> +}
> +
> dnl Duplicates in GALLIUM_DRIVERS_DIRS are removed by sorting it after this block
> if test -n "$with_gallium_drivers"; then
>     gallium_drivers=`IFS=', '; echo $with_gallium_drivers`
> @@ -2399,31 +2438,19 @@ if test -n "$with_gallium_drivers"; then
>         xswr)
>             swr_llvm_check "swr"
> 
> -            AC_MSG_CHECKING([whether $CXX supports c++11/AVX/AVX2])
> -            SWR_AVX_CXXFLAGS="-mavx"
> -            SWR_AVX2_CXXFLAGS="-mavx2 -mfma -mbmi2 -mf16c"
> -
> -            AC_LANG_PUSH([C++])
> -            save_CXXFLAGS="$CXXFLAGS"
> -            CXXFLAGS="-std=c++11 $CXXFLAGS"
> -            AC_COMPILE_IFELSE([AC_LANG_PROGRAM()],[],
> -                              [AC_MSG_ERROR([c++11 compiler support not detected])])
> -            CXXFLAGS="$save_CXXFLAGS"
> -
> -            save_CXXFLAGS="$CXXFLAGS"
> -            CXXFLAGS="$SWR_AVX_CXXFLAGS $CXXFLAGS"
> -            AC_COMPILE_IFELSE([AC_LANG_PROGRAM()],[],
> -                              [AC_MSG_ERROR([AVX compiler support not detected])])
> -            CXXFLAGS="$save_CXXFLAGS"
> -
> -            save_CFLAGS="$CXXFLAGS"
> -            CXXFLAGS="$SWR_AVX2_CXXFLAGS $CXXFLAGS"
> -            AC_COMPILE_IFELSE([AC_LANG_PROGRAM()],[],
> -                              [AC_MSG_ERROR([AVX2 compiler support not detected])])
> -            CXXFLAGS="$save_CXXFLAGS"
> -            AC_LANG_POP([C++])
> +            swr_require_cxx_feature_flags "C++11" "__cplusplus >= 201103L" \
> +                ",-std=c++11" \
> +                SWR_CXX11_CXXFLAGS
> +            AC_SUBST([SWR_CXX11_CXXFLAGS])
> 
> +            swr_require_cxx_feature_flags "AVX" "defined(__AVX__)" \
> +                ",-mavx,-march=core-avx" \
> +                SWR_AVX_CXXFLAGS
>             AC_SUBST([SWR_AVX_CXXFLAGS])
> +
> +            swr_require_cxx_feature_flags "AVX2" "defined(__AVX2__)" \
> +                ",-mavx2 -mfma -mbmi2 -mf16c,-march=core-avx2" \
> +                SWR_AVX2_CXXFLAGS
>             AC_SUBST([SWR_AVX2_CXXFLAGS])
> 
>             HAVE_GALLIUM_SWR=yes
> diff --git a/src/gallium/drivers/swr/Makefile.am b/src/gallium/drivers/swr/Makefile.am
> index d896154..210b203 100644
> --- a/src/gallium/drivers/swr/Makefile.am
> +++ b/src/gallium/drivers/swr/Makefile.am
> @@ -22,7 +22,7 @@
> include Makefile.sources
> include $(top_srcdir)/src/gallium/Automake.inc
> 
> -AM_CXXFLAGS = $(GALLIUM_DRIVER_CFLAGS) -std=c++11
> +AM_CXXFLAGS = $(GALLIUM_DRIVER_CFLAGS) $(SWR_CXX11_CXXFLAGS)
> 
> noinst_LTLIBRARIES = libmesaswr.la
> 
> @@ -31,7 +31,7 @@ libmesaswr_la_SOURCES = $(LOADER_SOURCES)
> COMMON_CXXFLAGS = \
> 	$(GALLIUM_DRIVER_CFLAGS) \
> 	$(LLVM_CXXFLAGS) \
> -	-std=c++11 \
> +	$(SWR_CXX11_CXXFLAGS) \
> 	-I$(builddir)/rasterizer/scripts \
> 	-I$(builddir)/rasterizer/jitter \
> 	-I$(srcdir)/rasterizer \
> -- 
> 2.5.5
>