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Re: [Emacs-diffs] master 74f54af: Use eassume (false) for branch that's

From: Paul Eggert
Subject: Re: [Emacs-diffs] master 74f54af: Use eassume (false) for branch that's never taken.
Date: Fri, 19 Apr 2019 12:04:51 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

On 4/19/19 3:08 AM, Eli Zaretskii wrote:
> When ENABLE_CHECKING is not defined, which happens in every production
> build, eassume expands to code that has no side effects, so the
> function will return a random value to its caller.  I don't think this
> is desired.

It looks OK to me. The default branch is impossible, so the function
cannot return a random value to its caller. Although GCC is not smart
enough to deduce this fact, eassume lets the programmer communicate it
to GCC so that GCC doesn't issue a false-alarm diagnostic (and GCC also
can generate better code). When ENABLE_CHECKING is defined, there's also
a runtime check that the impossible does not happen, but this extra
check isn't needed in ordinary production.

This would all be simpler if we replaced 'enum nonlocal_exit' with a
simple boolean. The enum seems to be more trouble than it's worth, if
it's causing this sort of bikeshedding. Not every boolean deserves an
enum just for it.

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