PIC register allocation by reload (Was: Re: egcs-1.2 stuff)

[Joern Rennecke <amylaar at cygnus dot co dot uk>]

> 
>   In message <199903281412.JAA02308@caip.rutgers.edu>you write:
>   > 	I think we should address the -fpic/-fPIC failures on the sparc. 
>   > This would affect glibc or really any shared library.  IIRC, Dave had a
>   > preliminary fix early last fall around the time we split the 1.1.x
>   > branch.  For some reason it never went in.  (?)
> If it's the problem I think it is then it's unlikely we'll have a general
> solution in time for egcs-1.2. 
> 
> Lazy allocation of the PIC register is a bad bad idea right now.  It's going
> to consistently lose.  If we want this to work 100% reliably for egcs-1.2, then
> the backend is going to need to pre-allocate the register early and take the
> performance hit.  This effects multiple ports that have tried to do lazy
> allocation of the PIC register (for example the ppc).
> 
> Then someone will need to block out some significant time post egcs-1.2 to fix
> the problem correctly.  It's not a simple problem to fix.

I think that, if no PIC register is preallocated and we find during
reload that we need one after all, we should just load it with a secondary
reload (by defining SECONDARY_RELOAD_INPUT_CLASS and reload_in[sd]i
appropriately).
We should check that reload inheritance works for the temporarily
allocated PIC register.  Then we should get actually better code than if
we allocated the PIC register for the entire function.