[LLVMdev] TargetRegisterInfo and "infinite" register files

[Jakob Stoklund Olesen]

On May 17, 2011, at 9:18 AM, Andrew Clinton wrote:

> I have faced this same problem in my backend, and I'm working around it by providing a large physical register set.  There are two problems with this:
> 
> 1. There's a chance that the register allocator will run out of registers to assign, in which case the allocation will fail - making it necessary to retry with a larger register set
> 2. The code generator consumes storage proportional to the number of registers that could be assigned
> 
> I'd be interested in an improvement to the code generator that makes it possible to specify an infinite register set without the need to store the registers explicitly.

As I explained to Justin, allocating against an infinite register file doesn't really do anything. It's a quadratic time no-op.

What you can do instead is:

1) Just use virtual registers and skip register allocation, or

2) Allocate to a small register file, implement memory operand folding, and pretend that spill slots are registers.

/jakob