This series will aim at introducing a DIE_REF tree node which we can use to carry references to debug entities in places like DECL_ABSTRACT_ORIGIN or BLOCK_ABSTRACT_ORIGIN. The main motivation is to cut down the amount of trees we stream for LTO but in principle it should also allow for more GCing of trees for non-LTO operation.
I have prototyped the DIE_REF part already but will start the series with some (obvious?) cleanups which make the fallout easier to deal with. Richard.
