[Mesa-dev] [PATCH 1/2] util: Make unreachable at least be an assert

[Ian Romanick]

On 12/05/2014 01:42 PM, Matt Turner wrote:
> On Fri, Dec 5, 2014 at 1:25 PM, Ian Romanick <idr at freedesktop.org> wrote:
>> On 12/05/2014 01:17 PM, Carl Worth wrote:
>>> Previously, if __builtin_unreachable() was unavailable, the
>>> unreachable macro was defined to do nothing. We do better here, by at
>>> least still making it an assert.
>>> ---
>>>  src/util/macros.h | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/src/util/macros.h b/src/util/macros.h
>>> index 5fc6729..eec8b93 100644
>>> --- a/src/util/macros.h
>>> +++ b/src/util/macros.h
>>> @@ -82,7 +82,7 @@ do {                        \
>>>  #endif
>>>
>>>  #ifndef unreachable
>>> -#define unreachable(str)
>>> +#define unreachable(str) assert(!str)
>>
>> I'd make this ASSERT.  In Mesa, ASSERT only exists if DEBUG is defined.
>>  It seems that many distros build without -DDEBUG and without -DNDEBUG.
>>  I'd rather have no code for these cases in all release builds.
> 
> I'm surprised by that.
> 
> I see that we add -DDEBUG with --enable-debug, but from experience
> assert() does nothing in my regular release build (without
> --enable-debug). Where is NDEBUG coming from in that case? I don't see
> it in the macros gcc automatically defines (gcc -g -dM -E - <
> /dev/null).

Right... and you need NDEBUG to no-op assert.  It has to be added by
hand, and it seems that the distros don't.