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From: | Paul Eggert |
Subject: | Re: Using __builtin_expect (likely/unlikely macros) |
Date: | Mon, 15 Apr 2019 20:42:56 -0700 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 |
Alex Gramiak wrote:
These macro calls would not help near calls to emacs_abort, as it should already be obvious to a careful human reader that the jump to emacs_abort is the road less traveled. (That's also obvious to GCC, since emacs_abort is _Noreturn.)
To human readers, yes, but from what I can tell, GCC is mixed on this.
Then we should fix GCC, if the code it generates has a performance problem (whatever it is, it's quite small). That'd be better than littering the Emacs source code with __builtin_expect or UNLIKELY calls. The GCC manual recommends against manually inserting such calls; performance nerds are supposed to use -fprofile-arcs instead. In my experience the calls are typically more trouble than they're worth.
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