[RFA] Use correct register names for MIPS n32/n64 ABIs

[Andrew Cagney]

> For an Irix 6 target, when debugging an o32 program, gdb does not
> provide the correct register names when using "info registers".
> It does however, use the correct names for n32/n64.  Conversely, for
> all other MIPS targets, o32 register names are always used regardless
> of the ABI.

+  if (i < 32 && (abi == MIPS_ABI_N32 || abi == MIPS_ABI_N64))
+    return mips_n32_n64_gpr_names[i];
+  else
+    return mips_processor_reg_names[i];

Having mips_register_name() only handle half the ABIs (n32/n64) is, I 
think, weird.


> The patch below causes the correct ABI-dependent register names to be
> used.
> 
> I considered at least one other approach for fixing this problem.  I
> considered providing new register name arrays for each of the ABIs,
> but that seemed unwieldy, and quite unnecessary too since the GPR
> register numbers are always 0-31.  Also, all mips cores (that gdb
> knows about) agree on what these names should be for the o32 ABI.  As
> such, it seemed easier to remap just the names of the GPRs in
> mips_register_name(). 
> 
> Another follow on patch to this one would be to encode the knowledge
> of what the GPRs should be entirely within mips_register_name() and
> relegate the register name arrays to describing (only) the names of
> registers whose numbers are 32 or greater.  (I'll wait to do this
> until I find out the reaction to the patch below.)

Can you please just do this, and consider it pre-approved.  When (regnum 
< 32) have mips_register_name() always generate the name directly, only 
refering to mips_processor_reg_names[] when i>=32.

A bounds check on mips_processor_reg_names[i] probably wouldn't hurt.

Andrew