Re: register allocation questions

Dan Sugalski wrote:
> At 11:09 AM +0200 10/26/04, Leopold Toetsch wrote:

> > So, if you want that really super efficient, you would allocate
> > registers around function calls directly to that wanted register number,
> > which should be in the SymReg's want_regno.
>
> While true, in the general case leaving 0-15 as non-preferred registers 
> will probably make things easier. Those registers, especially the PMC 
> ones, are going to see a lot of thrash as function calls are made, and 
> it'll probably be easier to have them as scratch registers.

Yep, that's the easy part ;) OTOH when the register allocator is doing 
register renaming anyway, the most inner loop with a function call 
should get registers assigned already matching the calling convemtions. 
With more then one call at that loop level, you have to move around 
registers anyway.

> It's distinctly possible, of course, that there'll be very little 
> pressure to actually *use* them for most code, as we've got plenty of 
> registers in general. That's the hope, at least.

Yes, 16 regs are plenty and do suffice for all "normal"[1] code. 
Assigning to wanted reg numbers for a function is a nice optimization.

[1] all except Dan's 6000 lines subroutines :) Did you start creating 
real subs for your code already?

leo