[PATCH] [SDAG] Make the DAGCombine worklist not grow endlessly due to duplicate insertions.

[Philip Reames]

Chandler,

Overall, this seems quite reasonable.  My only minor comment would be 
that you should improve the naming and documentation of 
recursivelyDeleteUnusedNodes.  It is not currently clear from the 
interface that items are added to the worklist at all, or that it is the 
frontier of used nodes which are added.  Given this seems to be 
important from your description, it should be documented.

LGTM -- Mind you, I'm not particularly familiar with this code. So take 
my LGTM with a grain or two of salt.  :)

Philip

http://reviews.llvm.org/D4616