mips: omit initialization of $gp and stack allocation when possible

[Richard Sandiford]

Alexandre Oliva <aoliva@redhat.com> writes:
> This is an updated version of the patch, such that it applies cleanly
> after the merged from mips-rewrite-branch.  No changes other than
> patch context.

Sorry Alex, feel like I'm giving you a really hard time today ;(.
But it is worth having mips_rtx_may_use_gp_p now that every use
of $gp is explicit?  Couldn't you just rely on regs_ever_live[28]
and disable the optimisation if !TARGET_EXPLICIT_RELOCS?

> Tested by bootstrapping on mips-sgi-irix6.5 with
> native as and ld, and mips-sgi-irix6.5o32 with GNU as (for some reason
> the native as didn't seem to like some %got expressions introduced
> with the rewrite when assembling for -32).

Yikes!  Thanks for the heads-up.  I guess configure was testing the n32
assembler rather than the o32 one.  I'll try to come up with something.

Richard