[tree-ssa][ GC, Virtual operands, and GCing between passes

[law@redhat.com]

In message <1071199658.5712.571.camel@p4>, Andrew MacLeod writes:
 >If it was just tree *def, we would have access to read the defs and
 >uses, but if we wanted to actually change the value of the def or use
 >operands in the originating stmt, you dont have a handle on the pointer
 >in the stmt which points at that operand, so you cant change it without
 >structure copying the tree structure.And we dont want to do that :-)
 >tree **def lets us get a tthe things which points at the operand.
Then how did it work previously with use_ops & def_ops?  I'm pretty sure
we can replace uses & defs within that framework and my recollection was
that it simply used a varray of tree *.

vuses and vdefs are varrays of trees.

I think you've got one too many levels of indirection.

jeff