On 07.01.2019 13:35, Florian Weimer wrote:
* Marc Glisse:
On Mon, 7 Jan 2019, Konstantin Kharlamov wrote:
In most projects a definite pattern that's unlikely to be executed
is a PRINT_ERR macro which is basically a wrapper around fprintf()
call. E.g.
if (some_error) {
PRINT_ERR("ERR");
// do cleanup
return;
}
I wonder, is there a way to hint GCC that, whenever that code
appears, whatever branch was prior to that is unlikely to be
executed?
Make PRINT_ERR a function with __attribute__((cold)).
But this does something completely differently. On some targets, it
produces unbearably slow code because GCC expects the code to never run
in practice. __builtin_expect does not have this effect.
So, you would not recommend using that attribute for functions-loggers?
Ultimately I was asking because I was thinking of contributing such
optimization to arbitrary projects I happen to use, such as libinput,
wine, etc (list is completely offhand, I didn't look at wine code in
particular, and they're on feature-freeze ATM anyway).
