Hi Chuck,
On 28 June 2016 at 20:50, Chuck Atkins <chuck.atk...@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 part should have been a separate patch. Please try to keep things
separate for the future.
> 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.row...@intel.com>
> Signed-off-by: Chuck Atkins <chuck.atk...@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
Esp with the IFS override this looks rather nasty imho.
Just a suggestion: An approach similar to LIBDRM_CC_TRY_FLAG in [1] is
a lot more readable imho.
-Emil
[1] https://cgit.freedesktop.org/mesa/drm/tree/configure.ac
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