More precise typing at the C-- and Mach level:
- Register type "Addr" is split into
    . "Val" (well-formed OCaml values, appropriate as GC roots)
    . "Addr" (derived pointers within the heap, must not survive a GC)
- memory_chunk "Word" is split into
    . "Word_val" (OCaml value)
    . "Word_int" (native-sized integer, not a pointer into the heap)

Cmmgen was updated to use Word_val or Word_int as appropriate.

Application #1: fail at compile-time if a derived pointer within the heap
survives a GC point (cf. PR#6484).

Application #2: CSE can do a better job across allocation points
(keep factoring expressions of type Int, Val, Float, but not Addr).


git-svn-id: http://caml.inria.fr/svn/ocaml/branches/cmm-mach-types@15568 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02