Re: Feature request: ability to describe x86 register halves as contraints.

[Jeffrey A Law <law at cygnus dot com>]

  In message <35996BF7.5474@tssc.co.nz>you write:
  > I'm not sure what you mean. I'm starting to think that this comment is
  > related to your comment above about the constant reffering to word sized
  > objects.  I just had the thought of defining a whole new varian of
  > subreg, BUT then I realized there's still the problem of what to do with
  > it (as in getting the compiler to us it at the right times).
You need something similar to a SUBREG, but with semantics to describe
the situation you want to address.

Seems to me it would need an expression and two integer args -- the
expresion is the data item (ie a register) that we want to operate
on, then start offset (in bits) and width (in bits).

Hmmm, I think we just described the bitfield support :-)

Maybe you could make it handle the stuff you're trying to do.


  > Does egcs not support the upper half of ANY register size (<=word, I
  > know DI upper half is accessable) on any machine?
Not that I'm aware of.

jeff