[PATCH] D15559: [LoopUnrollRuntime] Do unroll when IV's setp is one or minus one

[Sanjoy Das via llvm-commits]

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I'd rather have this sort of logic live in `SCEVExpander::isHighCostExpansion` than be scattered throughout the codebase.  I think the "increment by one" case is covered by `findExistingExpansion` already; and the "decrement by one" case can be added there as well by teaching it to look at the initial values for the induction phi nodes.


http://reviews.llvm.org/D15559