[RFC] LRA: Carrying hard registers around

[Alexander Monakov]

On Wed, 24 Jun 2026, Michael Matz via Gcc wrote:

> > Due to register asm, hard register r18 is live across the division.
> 
> And that's the bogosity.  The register variable r18 can live in a pseudo 
> during that division, and _should_ live in a pseudo outside of the 
> specific setup/teardown sequences of the two inline asms.
> 
> In normal situations the register allocator will then do its best to 
> allocate that pseudo to r18 again (and hence remove the copy insns), 
> whereas in _this_ situation it won't (the pseudo conflicts with r18), so 
> the copies remain, and everything will work out automatically leading to 
> exactly the situation that you'd like to create after the fact by 
> extending live range splitting.

Great to finally hear this, fwiw. I tried to ask for saner register var
implementation back in 2018 unsuccessfully:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87984

Alexander