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Re: __builtin_assume warnings

From: Mattias Engdegård
Subject: Re: __builtin_assume warnings
Date: Wed, 19 Aug 2020 10:01:04 +0200

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.

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