switch ConstantFP's from ValueMap to DenseMap, which is much faster to query and is more memory efficient.
switch ConstantFP's from ValueMap to DenseMap, which is much faster to query
and is more memory efficient.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@34446 91177308-0d34-0410-b5e6-96231b3b80d8

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