The m_objects store in this class is only used to check whether
this ClusterManager already owns this pointer. With a SmallVector
the is_contained call was non-linear in number of children, and for
instance printing all the elements of a 16M element std::vector
didn't complete in the time I was willing to wait for it (hours).
Since we are only doing insert & contains, some kind of set is a
better data structure. In this patch I used SmallPtrSet. With
that, the same array prints out in 30 seconds. I also tried a
std::unordered_set but that was slightly slower and used a fair bit
more memory.
Other than performance, this is NFC.
Differential Revision: https://reviews.llvm.org/D131996
33722848fc