[tree-ssa, RFC] CFG transparent RTL expansion

[law@redhat.com]

In message <1071801428.21456.162.camel@p4>, Andrew MacLeod writes:
 >This implements something which isnt actually used yet (ie, no
 >collection emitted/done). If I read it correctly, just a proof of
 >concept of a persistant CFG. So lets skip to how it would actually be
 >used. And excuse my lackof knowledge about how gcc collects profile info
 >:-)
Another potential use would be to detect when the tree->rtl lowering
process creates new blocks.  This _may_ be interesting in that it may
be an indication that rather than a block-local CSE we may want to run
something a little more extensive.  

If it's not obvious, I'm thinking about how we start trimming down the
first stage RTL optimizers -- knowing if new blocks were created may be
useful in determining which early RTL optimizers to run or what mode to
run them in (block-local or extended-basic-blocks).

jeff