[Mesa-dev] [PATCH] clover: work around altivec build failure with GNU C++ and -std=c++

[Francisco Jerez]

Chí-Thanh Christopher Nguyễn <chithanh at gentoo.org> writes:

> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=68504
> Bugzilla: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58241
> CC: mesa-stable at lists.freedesktop.org
> ---
>  configure.ac                                  | 11 +++++++++++
>  src/gallium/state_trackers/clover/Makefile.am |  2 +-
>  2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/configure.ac b/configure.ac
> index 40e052c..15831fd 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -1390,6 +1390,17 @@ if test "x$enable_opencl" = xyes; then
>          AC_MSG_ERROR([pkg-config cannot use libclc.pc which is required to build clover])
>      fi
>  
> +dnl
> +dnl Workaround for altivec failure with GNU C++ and -std=c++0x, PR58241
> +dnl
> +
> +    if test "x${ac_cv_cxx_compiler_gnu}" = xyes ; then
> +        CLOVER_CXX_STD="gnu++0x"
> +    else
> +        CLOVER_CXX_STD="c++0x"
> +    fi
> +    AC_SUBST([CLOVER_CXX_STD])
> +
>      GALLIUM_STATE_TRACKERS_DIRS="$GALLIUM_STATE_TRACKERS_DIRS clover"
>      GALLIUM_TARGET_DIRS="$GALLIUM_TARGET_DIRS opencl"
>      enable_gallium_loader=yes
> diff --git a/src/gallium/state_trackers/clover/Makefile.am b/src/gallium/state_trackers/clover/Makefile.am
> index b4c197a..e339c1f 100644
> --- a/src/gallium/state_trackers/clover/Makefile.am
> +++ b/src/gallium/state_trackers/clover/Makefile.am
> @@ -30,7 +30,7 @@ libclllvm_la_SOURCES = \
>  	llvm/invocation.cpp
>  
>  libclover_la_CXXFLAGS = \
> -	-std=c++0x
> +	-std=$(CLOVER_CXX_STD)
>  
>  libclover_la_LIBADD = \
>  	libcltgsi.la libclllvm.la

How about disabling AltiVec code generation by adding "-mno-altivec" to
CXXFLAGS?  AFAICT what's going on is that the "-maltivec" option (which
is implied by your "-mcpu=7450") enables a number of language extensions
as a side effect that collide with the C++ standard, which is
exacerbated by GCC's seemingly broken implementation.

I wonder if they could have any undesirable side effects on components
other than clover: not including "altivec.h" doesn't seem to guarantee
that the problematic preprocessor definitions ("bool" and "vector")
aren't going to be present.

Switching the dialect we're compiling with to GNU C++ isn't especially
reassuring, clover doesn't need GNU's C++ extensions and we don't want
to start using any of them by accident -- we don't use the AltiVec
extensions either so disabling the latter seems like the most reasonable
solution to me.

Thank you.
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