How to supress a specific kind of ansi-aliasing rules?

[Diego Novillo]

On 6/20/07 6:35 AM, Bokhanko, Andrey S wrote:

> 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.

No, it doesn't.  Both p1->m1 and p2->m2 will use the same memory tag in
GIMPLE and the same alias set during RTL.  Notice how a store between
the two loads affects the second load:

  # VUSE <SMT.4_7(D)>
  x_2 = p1_1(D)->m1;

  # SMT.4_8 = VDEF <SMT.4_7(D)>
  p1_1(D)->m1 = 32;

  # VUSE <SMT.4_8>
  y_4 = p2_3(D)->m2;


Or did you mean that p1 and p2 should *not* interfere with each other?