local-alloc update_equiv_regs and moving register initialization

Joern Rennecke amylaar@cygnus.co.uk
Thu Sep 14 16:22:00 GMT 2000


> > Because then you might change the semantics of the program.
> 
> That's a good reason, however I'm feeling a bit dense.  How could it
> change the semantics of the program?  If it's safe to change:
> 
>   a = 3;
>   ...
>   c = a + b;
> 
> to
> 
>   ...
>   a = 3;
>   c = a + b;
> 
> when a = 3 and c = a + b are outside a loop, why isn't it safe to make
> the same change when both are inside the same loop?

consider

    if (i)
      c = a + b;
    a = i * 3;


More information about the Gcc mailing list