Register allocation cost question

[Segher Boessenkool]

Hi Andrew,

On Tue, Oct 10, 2023 at 04:11:18PM +0100, Andrew Stubbs wrote:
> I'm also seeing wrong-code bugs when I allow more than 32 new registers, 
> but that might be an unrelated problem. Or the allocation is broken? I'm 
> still analyzing this.

It could be connected.  both things should not happen.

> If it matters, ... the new registers can't be used for general purposes, 

What does this mean?  I think you mean they *can* be used for anything,
you just don't want to (maybe it is slow)?  If you make it allocatable
registers, they *will* be allocated for anythin the compilers deems a
good idea.

> so I'm trying to set them up as a temporary spill destination. This 
> means they're typically not busy. It feels like it shouldn't be this 
> hard... :(

So what did you do, put them later in the allocation order?  Make their
register_move_cost higher than for normal registers (but still below
memory_move_cost)?  Or what?  TARGEt_SPILL_CLASS maybe?


Segher