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Re: [PATCH] C undefined behavior fix

From: jtv <jtv at xs4all dot nl>
To: Tim Hollebeek <tim at hollebeek dot com>
Cc: Bernard Dautrevaux <Dautrevaux at microprocess dot com>, "'dewar at gnat dot com'" <dewar at gnat dot com>, paulus at samba dot org, gcc at gcc dot gnu dot org, linux-kernel at vger dot kernel dot org, trini at kernel dot crashing dot org, velco at fadata dot bg
Date: Mon, 7 Jan 2002 23:16:20 +0100
Subject: Re: [PATCH] C undefined behavior fix
References: <17B78BDF120BD411B70100500422FC6309E402@IIS000> <20020107224907.D8157@xs4all.nl> <20020107172832.A1728@cj44686-b.reston1.va.home.com>

On Mon, Jan 07, 2002 at 05:28:32PM -0500, Tim Hollebeek wrote:
> 
> You're not allowed to be that smart wrt volatile.  If the programmer
> says the value might change unpredictably and should not be optimized,
> then It Is So and the compiler must respect that even if it determines
> It Cannot Possibly Happen.

Naturally I hope you're right.  But how does that follow from the Standard?
I have to admit I don't have a copy handy.  :(

Let's say we have this simplified version of the problem:

	int a = 3;
	{
		volatile int b = 10;
		a += b;
	}

Is there really language in the Standard preventing the compiler from
constant-folding this code to "int a = 13;"?

Jeroen

Follow-Ups:
- Re: [PATCH] C undefined behavior fix
  - From: J.A. Magallon

References:
- RE: [PATCH] C undefined behavior fix
  - From: Bernard Dautrevaux
- Re: [PATCH] C undefined behavior fix
  - From: jtv
- Re: [PATCH] C undefined behavior fix
  - From: Tim Hollebeek

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