Is there a builtin macro defined when optimisation is enabled in clang?

Question

When compiling with gcc, the __OPTIMIZE__ macro is defined when optimisations are turned on (see here). This enables runtime warnings like the following:

#ifndef __OPTIMIZE__
  printf("[WARNING] COMPILED WITHOUT OPTIMISATIONS\n");
#endif

Is there a similar macro for clang? I wasn't able to find one in the documentation here.

Or, even better, is there a way to do this that will work across all compilers?

Answer 1

The __OPTIMIZE__ macro also exists on clang and seems to work the same way as in gcc (your example code works fine).

I've not yet found specific documentation about this but I suspect the page you linked lists some clang-specific macros not adopted by gcc. Edit: that's not strictly true as __COUNTER__ also exists in gcc.

I guess this matter falls into clang's "mission" to be as compatible with gcc as possible:

The Clang driver and language features are intentionally designed to be as compatible with the GNU GCC compiler as reasonably possible, easing migration from GCC to Clang. In most cases, code “just works”.

source: http://clang.llvm.org/docs/UsersManual.html#id4

Also, this little command is useful to list macros used by the compiler:

cc -dM -E -x c [options] /dev/null

It works with gcc, clang and maybe some other compilers.

Edit: looks like it's documented after all... in the code :)

__OPTIMIZE__ is a GNU extension that Clang implements but MSVC does not. Is there a good equivalent there?

source: https://github.com/llvm-mirror/clang/blob/master/include/clang/StaticAnalyzer/Core/PathSensitive/ConstraintManager.h#L84