[PATCH] LoongArch: Add new relocation R_LARCH_CALL36

[WANG Xuerui]

On 11/7/23 20:16, Xi Ruoyao wrote:
> I'd like to have some pseudo instructions:
>
> - call36 r0, t0, func -> pcaddu18i t0, func + jirl r0, t0, func
> - call36 t0, func -> pcaddu18i t0, func + jirl t0, t0, func
> - call36 func -> pcaddu18i ra, func + jirl ra, ra, func
>
> These will make the work of the compiler (or assembly programmer)
> easier.  Anyway with R_LARCH_CALL36 the pcaddu18i instruction and the
> jirl instruction must be adjacent, so there is no benefit for the
> compiler or programmer to use them separately to make a function call.
>
> And the last one can be annotated with R_LARCH_RELAX so we may relax it
> into a bl instruction if possible.

The suggestion sounds reasonable! Although IMO a name like "call.36" 
might look better, the name "call36" also works for me.

And regarding the proposed "call36 func" reusing the $ra for the 
temporary -- IIUC this will break the subroutine return prediction. I 
think we've been hit by similar regalloc in GCC and have since fixed 
that: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=11013. So maybe it's 
necessary to specify a different temp register after all...