Created attachment 11731 [details]
test case

This test case should fail to assemble.  Yet it does at -O1 or higher.

      __asm__ ("choke_me %0 %1 %2" : "+m" (*p1), "+m" (*p2), "+m" (*p3));
      *p1 = val0;
      *p2 = val0;
      *p3 = val0;

Actually I don't think so since the asm is dead code as the stores to *p1, *p2, and *p3 are dead by the next couple of statements.

(In reply to comment #2)
>       __asm__ ("choke_me %0 %1 %2" : "+m" (*p1), "+m" (*p2), "+m" (*p3));
>       *p1 = val0;
>       *p2 = val0;
>       *p3 = val0;
> 
> Actually I don't think so since the asm is dead code as the stores to *p1, *p2,
> and *p3 are dead by the next couple of statements.
Hmm, that's true.