Merge the locally-scoped and globally-scoped local memory stacks

[GoogleCodeExporter]

I think that the right way of doing this would be to lay out the stack like 
this:

[ globally scoped local memory ] low
[ frame 0                                ]
[   frame 0 locally scoped local  ]
[ frame 1                                ]
[   frame 1 locally scoped local  ]
[ frame 2                                ]
[   frame 2 locally scoped local  ]
[ frame 3                                ]
[   frame 3 locally scoped local  ] high

Then a mov from a globally-scoped local variable would move the offset 
directly, and
a mov from a locally-scoped local variable would move the offset plus the
stack frame pointer.  Then all ld.local operations would be relative to the 
base of the stack,
rather than the current frame as it is done now.

This is a pretty major change though.

Original issue reported on code.google.com by SolusStu...@gmail.com on 26 Jul 2011 at 9:47