Question about register allocation (GCC 4.1)

[Thomas Bernard <tbernard at science dot uva dot nl>]

Hello all,

I have a question about retargeting the back-end of GCC 4.1.
Our targeted architecture uses four classes of registers: global ($RG), 
locals ($RL), dependents ($RD), shareds ($RS). In total 31 hard 
registers available for the all previous classes.
The amount of each register is only known at compile-time depending on 
the needs of the program.

Normally I would have to specify the number of registers for each class 
in the .md and .h files which describe the targeted architecture.
But is it possible to have an arbitrary number of register in each class 
and the number would be given by the compiler depending on the needs of 
registers at compile-time (when the compiler discovers how many 
registers of each class are needed) ???

Let's take an example...
A source file A needs 10 registers for the globals, 11 for the locals, 5 
for dependents and 5 for shareds (10RG+11RL+5RD+5RS<=31). And for a 
program B needs 11 globals, 13 for the locals, 3 for dependents and 4 
for shareds (11RG+13RL+3RD+4RS<=31). Finally the program C needs 3 
globals and 10 locals (3RG+10RL<<31).

So basically this is known at compile-time. Such as "dynamic" register 
allocator.
Is it that possible and what are the implications on the register 
allocator ???



Thanks in advance,
Regards,
T.