Loop safepoints and backedge copies

[Tom Rodriguez]

> That's interesting, what is it that determines whether a backedge is
> cloned or not?  And also, out of interest, what benefit does having
> the backedge copies bring?

The cloning in ciTypeFLow is really just a helper to get loop shapes  
nicer at the beginning of parse.  It's converting relatively simply  
loops into what's often called a zero trip loop, which is basically a  
guarded do/while.  So this, which is just a translation of a for loop:

int i = 0;
while (i < n) {
   body();
   i++;
}

becomes:

int i = 0;
if (i < n) {
   do {
     body();
     i++;
   while (i < n);
}

The nice thing about this is that it provide a place for loop  
invariant values to be computed where it's guaranteed that you will  
execute the body at least one.

In ciTypeFlow this is don't for simply loops only.  Check out  
is_clonable_exit.

tom

>
>
> Cheers,
> Gary
>
> -- 
> http://gbenson.net/