From: "Mattias Engdegård" <mattiase@acm.org>
To: Paul Eggert <eggert@cs.ucla.edu>
Cc: emacs-devel <emacs-devel@gnu.org>
Subject: Re: __builtin_assume warnings
Date: Wed, 19 Aug 2020 10:01:04 +0200 [thread overview]
Message-ID: <538D98E3-DCE7-4A6C-B1AC-B00253E1CCA1@acm.org> (raw)
In-Reply-To: <25e394e9-0e6e-7794-3e90-5fbab3951678@cs.ucla.edu>
19 aug. 2020 kl. 00.53 skrev Paul Eggert <eggert@cs.ucla.edu>:
> No, it's the other way around at least for me: having 'assume' use Clang's __builtin_assume makes 'assume' slower. Without __builtin_assume, 'assume' falls back on __builtin_unreachable, and Clang generates better code for __builtin_unreachable than it does __builtin_assume.
Right you are; as far as I can tell, __builtin_assume is strictly less useful. There does not seem to be any point in using it at this time. The only advantage over if(!x)__builtin_unreachable() appears to be that the argument isn't actually evaluated, but I'm not sure when that property would be useful.
Thank you for clearing that up.
prev parent reply other threads:[~2020-08-19 8:01 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-12 9:38 __builtin_assume warnings Mattias Engdegård
2020-08-15 2:32 ` Paul Eggert
2020-08-16 8:23 ` Mattias Engdegård
2020-08-17 14:05 ` Mattias Engdegård
2020-08-17 22:11 ` Paul Eggert
2020-08-18 7:11 ` Mattias Engdegård
2020-08-18 22:53 ` Paul Eggert
2020-08-19 8:01 ` Mattias Engdegård [this message]
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