[PATCH] D156612: [SimplifyCFG] Add unsigned max-min comparison to `switchToLookupTable`.

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


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Comment at: llvm/lib/Transforms/Utils/SimplifyCFG.cpp:6440
+        MaxCaseVal = CaseVal;
+    }
 
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I don't like that the whole fold gets invoked twice with this flag flipped. Can we just pick the Min/Max that result in the smallest table size (i.e. Max-Min) here?

Ideally we would not even base this on signed/unsigned at all, because the smallest range might be both signed *and* unsigned wrapping. Consider something like -128, -1, 0, 127. This would pick [-128, 127] as the signed range, [0, -1] as the unsigned range, but a minimal range would be [127, 0] or [-1, -128]. This would be based around the largest gap between the case value. Though just signed/unsigned is probably the main useful case.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D156612/new/

https://reviews.llvm.org/D156612