Re: Help with lra

[shmeel gutl <shmeelgutl at shmuelhome dot mine dot nu>]

On 03-Aug-16 12:10 AM, Vladimir Makarov wrote:
> On 08/02/2016 04:41 PM, shmeel gutl wrote:
> > I am trying to enable lra for a propriety backend. I ran into one 
> > problem that I can't solve. In lra-constraints.c:split_reg 
> > lra_create_new_reg can be called with a hard code rclass of NO_REGS. 
> > It then queues a move instruction of the type
> >
> >  set TYPE:new_reg  TYPE:old_reg
> >
> > But the NO_REGS rclass stops new_reg from matching a register 
> > constraint and forces a reload. But the reload will have the same 
> > problem. This recurses until the recursion limit is hit.
> >
> > What is my backend missing that will allow a register assignment to 
> > new_reg?
> NO_REGS in this case means memory and the generated RTL move insn 
> finally should be a target load or store insn.  It is hard to say w/o 
> looking at the code but, probably, your move insn descriptions do not 
> have memory constraints (or these constraints are quite specific).
Currently our memory constraints only match memory operands. I assume 
that you are suggesting that pseudo registers should match memory 
constraints. Is this true only for lra, or, would reload also benefit 
from such a change? Would other passes gain by such a change? Is any 
extra support needed in patterns or hooks?

Thanks,

Shmeel