[PATCH] D33262: [JumpThreading] Teach jump threading how to analyze (and (cmp A, C1), (cmp A, C2)) after InstCombine has turned it into (cmp (add A, C3), C4)

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

@reames   For 1. were you envisioning detecting the add at the time we're visiting the compare similar to what I do now? Or were you envisioning propagating the add result as we unwind CVKInP after visiting the directly. The latter I think would require us to make CVKInP work in ConstantRanges like suggestion 2. For the former I think I'd also have to replicate some of the compare handling from LVI to calculate the result for the range from the add?

For 2, I think our range solving capabilities are considerably weaker than our ConstantExpr handling so I think we'd still need to rely on ConstantExpr when we have single element ranges?

@Farhana for your suggestion of moving the logic into getPredicateOnEdge. We'd have to decide how far back to make getPredicateOnEdge search for a livein. One instruction? Multiple instructions? We'd also still need some check in jump threading to know whether we are looking at a livein or whether we should recurse into CVKInP like we do today. So we'd have to try getPredicateOnEdge and if it fails, recurse into CVKInP only if we aren't looking at a livein.


https://reviews.llvm.org/D33262