Re: An unusual Performance approach using Synthetic registers

[Daniel Berlin <dberlin@dberlin.org>]

>
> My goal is that the generated code with Synthetic registers will be
> significantly better (looking just at the instruction count).  If the 
> fields
> have individual values, in your example, then Reload imposes an 
> overhead.  It
> is a two step process: move the spilled data back into a register, 
> then use
> it.  With a Synthetic, you get to just use it.
>
If the new allocator determines the data in question is cheaper to 
recalculate than it would be to reload it from memory, it'll do so 
(though it might be a bit limited in what it *can* recalculate right 
now, this is fixable. I don't have numbers on how often it would have 
wanted to remat but couldn't due to these problems). It's known as 
"rematerialization".
Thus, in the example of vtable pointers, it'll simply recalculate the 
value into the new register, rather than reload it from memory.

> Andy