Re: [PATCH] C undefined behavior fix

jtv (
Mon, 7 Jan 2002 23:16:20 +0100

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;"?


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