SH5 compact register numbering in gcc -> gdb interface

[Andrew Cagney]

> 
> I was proposing only to change the SHcompact mapping, so that code
> compiled with the default options won't be affected.  Moreover, there
> are still a number of bugs in gcc 3.1 that affect the SH5 port, some
> of which can only be fixed with changes to the machine-independent sources.
> I am working on this, but it is not feasible to finish this work in time
> for gcc 3.1 .  Hence, I'd expect some gcc 3.2 snapshots to be better
> for SH5 than gcc 3.1 for production code.
> 
> Another reason to switch to a post 3.1 compiler will be debugging speed.
> The prologue-disassembling slows backtraces considerably when debugging
> on real hardware.  We are currently working on SH gcc emitting proper
> cfi information, and gdb making use of it.  For SH4 this has already
> proved to make quite an improvement, and the gcc bug fixes for this
> are among the next patches I intend to put into the FSF gcc repository.

Humor me here.

How do you use dwarf2 cfi to unwind a compact register (saved on the 
stack) back to a media register?  In addition to the address of the 
saved register you'll need to know that only part of the register was 
saved. Does CFI describe this?

Andrew