GNU bug report logs - #36370
27.0.50; XFIXNAT called on negative numbers

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Message #81 received at 36370 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Pip Cet <pipcet <at> gmail.com>
Cc: 36370 <at> debbugs.gnu.org, bug-gnulib <at> gnu.org, Bruno Haible <bruno <at> clisp.org>
Subject: Re: bug#36370: 27.0.50; XFIXNAT called on negative numbers
Date: Fri, 28 Jun 2019 22:41:02 -0700

Pip Cet wrote:
>    eassume (global == 0);
>    eassume (f ());
> #else
>    eassume (global == 0 && f ());
> ...
> extern int global;
> 
> int f(void)
> {
>    return ++global;
> }


This is not a valid use of 'assume'. It's documented that assume's argument 
should be free of side effects.

It would be nice if 'assume (R)' reported an error if R has side effects, and 
generated a warning unless the compiler can verify that R is free of side 
effects. However, these niceties would require better support from the compiler.

> If you want your program to behave predictably, in the strict sense,
> you cannot ever use the current assume() API.

I'm not sure what you mean by "in the strict sense". It's true that programs can 
misuse 'assume' and get undefined behavior, but that's kind of the point....

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