[Mesa-dev] [PATCH] mesa: Remove C++11 narrowing warnings

[Chad Versace]

On 08/20/2012 02:17 PM, Matt Turner wrote:
> On Mon, Aug 20, 2012 at 1:52 PM, Chad Versace
> <chad.versace at linux.intel.com> wrote:
>> Add -Wno-narrowing to CXXFLAGS if gcc supports it.
>>
>> This removes warnings of the form
>>     warning: narrowing conversion of X from 'int' to 'float' inside { } is
>>     ill-formed in C++11 [-Wnarrowing]
>> in ff_fragment_shader.cpp and gen6_blorp.cpp. When building i965,
>> I observed no other difference in the build output.
>>
>> CC: Kenneth Graunke <kenneth at whitecape.org>
>> CC: Matthew Turner <matts88 at gmail.com>
>> Signed-off-by: Chad Versace <chad.versace at linux.intel.com>
>> ---
>>  configure.ac | 13 ++++++++++++-
>>  1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/configure.ac b/configure.ac
>> index fcfe085..89b8fe7 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -219,7 +219,17 @@ if test "x$GXX" = xyes; then
>>                    [VISIBILITY_CXXFLAGS="" ; AC_MSG_RESULT([no])]);
>>      AC_LANG_POP([C++])
>>
>> -    # Restore CXXFLAGS; VISIBILITY_CXXFLAGS are added to it where needed.
>> +    # Enable -Wno-narrowing if using a gcc that supports it.
>> +    save_CXXFLAGS="$CXXFLAGS"
>> +    WNO_NARROWING_CXXFLAGS="-Wno-narrowing"
>> +    AC_MSG_CHECKING([whether $CXX supports $WNO_NARROWING_CXXFLAGS])
>> +    CXXFLAGS="$CXXFLAGS $WNO_NARROWING_CXXFLAGS"
>> +    AC_LANG_PUSH([C++])
>> +    AC_LINK_IFELSE([AC_LANG_PROGRAM()], AC_MSG_RESULT([yes]),
>> +                  [WNO_NARROWING_CXXFLAGS="" ; AC_MSG_RESULT([no])]);
>> +    AC_LANG_POP([C++])
>> +
>> +    # Restore CXXFLAGS. The flags probed above are added where needed.
>>      CXXFLAGS=$save_CXXFLAGS
>>
>>      # Work around aliasing bugs - developers should comment this out
>> @@ -244,6 +254,7 @@ esac
>>
>>  AC_SUBST([VISIBILITY_CFLAGS])
>>  AC_SUBST([VISIBILITY_CXXFLAGS])
>> +AC_SUBST([WNO_NARROWING_CXXFLAGS])
>>
>>  dnl
>>  dnl Hacks to enable 32 or 64 bit build
>> --
>> 1.7.11.4
> 
> I can't see how the VISIBILITY_CFLAGS are getting added to the build.
> It looks like we somehow lost their uses -- which means the narrowing
> flag also isn't being added to the build. To do this you either add it
> to the Makefile.am's (via AM_CXXFLAGS) or directly to CXXFLAGS.

I also don't see how the VISIBILITY_CFLAGS are getting added, but that's just
due to me not understanding autoconf at all. However, I've verified by building
with `env V=1 make` that -fivisibility=hidden and -Wno-narrowing do appear in
the gcc invocations.

> I think we're doing the right thing here and setting the flags in
> their own variables (as opposed to appending to C(XX)FLAGS). The
> automake manual recommends this:
> http://www.gnu.org/software/automake/manual/automake.html#User-Variables