operating on individual register bits

[Doug Evans <dje@transmeta.com>]

Ben Elliston writes:
 > Frequently, I find myself wanting to set and clear individual bits of
 > hardware registers in rtl.  Perhaps such a mechanism already exists.
 > If it does, I'm not aware of it.  Here is the canonical example:
 > 
 > 	 (set cc.z 1)
 > 
 > versus:
 > 
 > 	(set cc (or cc (sll SI 1 10))),
 > 
 > which makes much less sense to the reader.
 > 
 > Is it sensible to extend cgen to give names to individual bits of a
 > register such that operands on registers can adopt this C/Pascal-style
 > syntax for accessing individual bits?

There's comments regarding this in the code and/or docs.
I wasn't sure how I wanted to go (e.g. follow gcc's rtl support
for this or not) so I punted until there was a need and more thought
could be put in.

It's a reasonable thing to add but it needs to be thought about
(try to find lots of architectures with such support and see what
works best to describe them).