On 08/09/2012 01:22 PM, Kenneth Graunke wrote:
> On 08/09/2012 01:10 PM, Chad Versace wrote:
>> Add -Wno-narrowing to CXXFLAGS for gcc.
>>
>> 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 of the form. When building
>> i965, I observed no other difference in the build output.
>>
>> CC: Kenneth Graunke <kenn...@whitecape.org>
>> Signed-off-by: Chad Versace <chad.vers...@linux.intel.com>
>> ---
>> configure.ac | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/configure.ac b/configure.ac
>> index 89686b4..fa4fd71 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -228,6 +228,9 @@ if test "x$GXX" = xyes; then
>> # gcc's builtin memcmp is slower than glibc's
>> # http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43052
>> CXXFLAGS="$CXXFLAGS -fno-builtin-memcmp"
>> +
>> + # Silence C++11 warnings that we don't care about.
>> + CXXFLAGS="$CXXFLAGS -Wno-narrowing"
>> fi
>>
>> dnl even if the compiler appears to support it, using visibility attributes
>> isn't
>
> Nak. I believe this will break the build if using a g++ too old to
> recognize -Wno-narrowing. You'd need to do the whole rigamarole used in
> the compiler flag checks a bit earlier. Or import the handy m4 macro
> from xorg-util-macros which does all the rigamarole in one line.
It's safe to do this. If an old gcc encounters a -Wno option that it does not
recognize, then it will usually silently ignore it. I verified this by building
with -Wno-whatever, and the option was silently ignored, as expected.
>From the GCC Manual [http://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html],
emphasis mine:
When an unrecognized warning option is requested (e.g., -Wunknown-warning), GCC
emits a diagnostic stating that the option is not recognized. However, if the
-Wno- form is used, the behavior is slightly different: no diagnostic is
produced for -Wno-unknown-warning unless other diagnostics are being produced.
***This allows the use of new -Wno- options with old compilers***, but if
something goes wrong, the compiler warns that an unrecognized option is present.
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