[tree-ssa] Too conservative optimization with global variables??

[Diego Novillo]

On Mon, 2003-06-16 at 06:59, Steven Bosscher wrote:

> extern int c;
> 
> fubar()
> {
>   int T.1;
>   int a;
>   int b;
> 
>   c = 3;
>   c = c * 2;
> }
> 
> Why can't this just be folded to "c = 6;"?
> 
Because we do not rename global nor local static variables anymore. 
This is to avoid problems in the SSA->normal pass.  If two versions of
the same global were live at the same time, we would need to have
copy-in/copy-out operations at entry/exit points to update the original
object.

Adding copy-in/copy-out ops are somewhere in the todo list, but it's not
a priority yet.  Inserting those operations blindly seems expensive.


Diego.