Re: [PATCH/RFC 0/5] Add internationalization support to Git

On Sun, May 30, 2010 at 22:23, Jonathan Nieder [off-list ref] wrote:

[...]
It would seem that __attribute__((__pure__)) should let the compiler give
us the best of both worlds, but no luck.  Even __attribute__((__const__))
is ignored; the compiler inlines the body of _() before it has a chance
to notice.

We can fool the compiler into paying attention by making it not
inlinable: if gettext.h contains

| extern char *_(const char *s) __attribute__((__format_arg__(1), __const__));

and a separate gettext.c contains

| #include <libintl.h>
| #include "gettext.h"
| char *_(const char *s) { return gettext(s); }

we get the performance of B again:

 1.36user 0.01system 0:01.38elapsed 98%CPU (0avgtext+0avgdata 2304maxresident)k
 0inputs+0outputs (0major+180minor)pagefaults 0swaps

This amounts to lying to the compiler, since it is possible for the string
pointed to by a single address s to differ between calls to _.  The __pure__
attribute would be more honest, but for reasons I don’t understand it
suppresses the optimization.

Moral of the story: at least in simple cases, we can keep the performance
and the typechecking.  Phew.

Awesome, how portable is this? If it's just GCC I guess it can just be
wrapped in #ifdef __GNUC__.

Thanks for investingating this.