[PATCH] Speed up creation of live ranges for physical registers by using a segment set

[Matthias Braun]

Sorry for coming so late to the review, no need to address these issues before commit.

- Why is the SegmentSet part of the LiveRange? My understanding is that you only use it during initial live calculation anyway, and these calculations are done one another for each live range. So I'd assume it is enough to have the set as a member of the LiveRangeCalc class and not having an extra pointer in each LiveRange.
- for the createDeadDefs() part it may be interesting to simply append the new segments to the vector in any order and later run a sorting algorithm which also eliminates duplicates on the vector. This should reduce the O(n**2) complexity to O(n log n) and I'd imagine it to perform well in the case where only a few segments are used.
- It would be nice if the decision on whether to use the set or sorted vector based techniques could be based on the actual number of Defs/Uses of a register (deciding on whether it is a physreg seems a bit arbitrary to me although it's probably a good heuristic in practice). Unfortunately I don't see an easy way to determine the actual number of defs/uses for a vreg as that is only maintained as a double linked list without a counter at the moment, so it is probably okay as is.


http://reviews.llvm.org/D6013

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