Fix allocations of SmallVector and SmallPtrSet so they are more prone to
being power-of-two sized.

llvm-svn: 178332

SmallPtrSet: Provide a more efficient implementation of swap than the default triple-copy std::swap.

This currently assumes that both sets have the same SmallSize to keep the implementation simple,

SmallPtrSet: Provide a more efficient implementation of swap than the default triple-copy std::swap.

This currently assumes that both sets have the same SmallSize to keep the implementation simple,
a limitation that can be lifted if someone cares.

llvm-svn: 152143

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