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From: "Alexei A. Frounze" <alexfru AT chat DOT ru>
Newsgroups: comp.os.msdos.djgpp
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Subject: Re: gcc bug?
Date: Wed, 18 Apr 2007 19:14:11 -0700
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To: djgpp AT delorie DOT com
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Alexei A. Frounze wrote:
> DJ Delorie wrote:
>> Part of the problem may be that your volatile variable is on the
>> stack, rather than being a global or static variable.  You've also
>> defined it as "pointer to volatile T" not "volatile pointer to T".
>
> But from where did gcc get the idea of the variable (to which the
> pointer points, at address 0) being zero?

Oh, I see. If in f1() I assign the pointer to 1, then the asm output 
(obtained with -O2 optimization switch) is this:
_f1:
        pushl   %ebp
        movl    %esp, %ebp
        .p2align 4,,7
L2:
        movb    1, %al
        testb   %al, %al
        jne     L2
        popl    %ebp
        ret
For some reason the compiler decides that the pointer to the variable and 
that variable are the same thing.

Alex