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Subject: [Bug c/44555] Pointer evalutions, is that expected ?
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From: "zilvinas dot valinskas at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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------- Comment #2 from zilvinas dot valinskas at gmail dot com  2010-06-16 10:29 -------
I don't agree. This is an optimizer bug ("dead code elimination" don't know
much of GCC). Consider that there is a function like this:


$ cat ptr.h
struct a {
        char    b[100];
        int     a;
};

$ cat ptr.c

$ cat ptr.c 
#include <stdio.h>
#include "ptr.h"

int main(int argc, char *argv[])
{
        struct a *a = NULL;

        function(a);
        return 0;
}


$ cat func.c 
#include <stdio.h>
#include "ptr.h"

void function(struct a *a)
{
        void *ptr;

        if (&a->b)
                puts("ok, not null #1");

        if (&a->b == NULL)
                puts("ok, null ? #1");

        ptr = &a->b;
        if (ptr)
                puts("ok, not null #2");

        if (ptr == NULL)
                puts("ok, null ? #2");
}

$ gcc ptr.c func.c -o ptr
$ ./ptr

$ ./ptr 
ok, not null #1
ok, null ? #1
ok, null ? #2


Still the same problem (maybe not a problem). But how does GCC is able to tell
that in this particular case func() is invoked with a NULL pointer as parameter
(not valid pointer) and eliminates code just like that ???

Mind you this code is an approximation of bug I was tracking not so long time
ago.


-- 

zilvinas dot valinskas at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44555