Improve RangeSet union performance #74963
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The existing implementation of `RangeSet.formUnion` performs a naive insertion of each range of one range set into the other. This requires shuffling the array of ranges down with each insertion, which can have quadratic performance. This change uses the known invariants of the ranges array to instead perform the merge in linear time. Each range in the resulting array is determined by finding the next lowest bound between the two range sets, and then searching for the first upper bound that isn't included in the merged range set contents. rdar://129296438
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The existing implementation of
RangeSet.formUnionperforms a naive insertion of each range of one range set into the other. This requires shuffling the array of ranges down with each insertion, which can have quadratic performance.This change uses the known invariants of the ranges array to instead perform the merge in linear time. Each range in the resulting array is determined by finding the next lowest bound between the two range sets, and then searching for the first upper bound that isn't included in the merged range set contents.
rdar://129296438