Re: aliasing with char*

[Wouter Vermaelen <wouter.vermaelen@xxxxxxxxx>]

John Love-Jensen wrote:
> Hi Wouter,
>
> What happens if you tell the compiler than the two cannot alias?  I think
> this is sufficient to do that...
>
> -----------------------
> /* -DT=short or -DT=char */
>
> int count;
>
> T f(T* restrict p) {
>     count += 2;
>     T t = *p;
>     count += 3;
>     return t;
> }
> -----------------------
>
> gcc -std=iso9899:1999 -DT=char -O3 -S test.c -o test-char.s
> gcc -std=iso9899:1999 -DT=short -O3 -S test.c -o test-short.s
> vi -d test-char.s test-short.s

I already tried this, but unfortunately it doesn't work for me :(

> gcc -std=iso9899:1999 -DT=char -O3 -S test.c -o test-char.s
> cat test-char.s
        ...
        movl    count(%rip), %edx
        leal    2(%rdx), %eax
        addl    $5, %edx
        movl    %eax, count(%rip)
        movzbl  (%rdi), %eax
        movl    %edx, count(%rip)
        ret
        ...
> gcc --version
gcc (GCC) 4.3.0 20071119 (experimental)
...
> uname -a
Linux argon 2.6.22-3-amd64 #1 SMP Sun Nov 4 18:18:09 UTC 2007 x86_64 GNU/Linux

But thanks anyway.


Wouter