PHINode::getBasicBlockIndex is O(n) in the number of inputs to a PHI, avoid it in the common case where the BB occurs in the same index for multiple phis.  This speeds up CGP on an insane testcase from 8.35 to 3.58s.
PHINode::getBasicBlockIndex is O(n) in the number of inputs
to a PHI, avoid it in the common case where the BB occurs
in the same index for multiple phis.  This speeds up CGP on
an insane testcase from 8.35 to 3.58s.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@96080 91177308-0d34-0410-b5e6-96231b3b80d8

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