Proposed doc update for Explicit Reg Vars 3/3

[Andrew Haley]

On 10/20/2015 05:00 PM, Jeff Law wrote:
> But the technical reality is I can't see a use outside the extended asm. 

I can.  In the past (and probably still today) GCC did an awful job of
allocating registers in a large function.  This was visible in a
bytecode interpreter, where the programmer knows that the virtual PC
and SP should live in a register.  GCC does not know this and is
forever spilling them.  Explicit local reg vars fixed this nicely.

Andrew.