Shrink SmallPtrSet. It gets swapped a lot which copies the whole small part.
Shrink SmallPtrSet. It gets swapped a lot which copies the whole small part.

Testing shows that it's empty in >99% of the cases and I couldn't find a case
where it contained more than 2 elements.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@175967 91177308-0d34-0410-b5e6-96231b3b80d8

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