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Re: bug#36370: 27.0.50; XFIXNAT called on negative numbers

From: Paul Eggert
Subject: Re: bug#36370: 27.0.50; XFIXNAT called on negative numbers
Date: Fri, 28 Jun 2019 22:41:02 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.1

Pip Cet wrote:
   eassume (global == 0);
   eassume (f ());
   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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