On 20 June 2007 11:36, Bokhanko, Andrey S wrote:
> Hi,
>
> As I learned from experience, gcc always assume independence between memory
> references in the following program:
>
> typedef struct {
> int m1;
> int m2;
> } S1;
>
> void foo(S1 *p1, S1 *p2) {
> ... = p1->m1;
> ... = p2->m2;
> }
>
> ...even if -fno-strict-aliasing (an option disabling ansi-aliasing rules)
> supplied.
>
> I wonder, is there a way to force gcc not to assume independence in the
> example shown above?
Just maybe if you give the struct definition __attribute__ ((packed)) gcc
will no longer assume that all struct S1s are naturally aligned and therefore
know that they might overlap? (But it's also quite possible that it won't...
I haven't been through the sources to determine how much aliasing information
it infers from alignment.)
cheers,
DaveK
--
Can't think of a witty .sigline today....
