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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: UB in asm
Date: Thu, 28 Dec 2017 09:25:15 -0800
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Richard Damon <Richard@Damon-Family.org> writes:
> On 12/28/17 11:46 AM, David Brown wrote:
>> Or use:
>> 
>>              a = (uint32_t) a + 1u;
>> 
>> for code that is simpler, and portable to all practical systems (that
>> support int32_t).
>
> The one problem with this is that the conversion of an unsigned number 
> greater that INT_MAX to a signed integer still invokes undefined 
> behavior, so an aggressively optimizing compiler might still assume that 
> a can't equal INT_MIN.

No, such a conversion yields an implementation-defined result (or raises
an implementation-defined signal).

Raising an implementation-defined signal could, I suppose, lead to
undefined behavior, but I don't know of any compiler that takes
advantage of that permission (added in C99 IIRC).

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"