A number of LSR fixes: - ChangeCompareStride only reuse stride that is larger than current stride. It   will let the general reuse mechanism to try to reuse a smaller stride. - Watch out for multiplication overflow in ChangeCompareStride. - Replace std::set with SmallPtrSet.
A number of LSR fixes:
- ChangeCompareStride only reuse stride that is larger than current stride. It
  will let the general reuse mechanism to try to reuse a smaller stride.
- Watch out for multiplication overflow in ChangeCompareStride.
- Replace std::set with SmallPtrSet.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@43408 91177308-0d34-0410-b5e6-96231b3b80d8

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