Why are BLOCK_HEAD/BLOCK_END not used?

[Steven Bosscher]

Hello,

For tree-ssa I would like to make the basic block head/end a union because we 
now have a head and end for both RTL and trees, and obviously we only can use 
one at a time so one field at least is redundant.

Problem is, everything uses bb->head instead of BLOCK_HEAD (bb), and bb->end 
instead of BLOCK_END (bb).  Is there a reason for this?  Would a patch to 
update _all_ of these to use the macro be acceptable in stage3 if it prevents 
merge trouble for the tree-ssa branch maintainers?

Gr.
Steven