[PATCH] [PR20893] Change SelectionDAG's DbgValueMap to have set semantics (NFC)

[Dimitry Andric]

Just as a remark, this patch seems to work for fixing the OOM issue occuring in certain FreeBSD ports here: http://docs.freebsd.org/cgi/mid.cgi?542105A3.4090507

So it would be nice if it can go in. :-)

http://reviews.llvm.org/D5451