[PATCH] D119854: [SimplifyCFG][PhaseOrdering] Defer lowering switch into an integer range comparison and branch until after at least the IPSCCP

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


================
Comment at: llvm/include/llvm/Transforms/Utils/SimplifyCFGOptions.h:26
   bool ForwardSwitchCondToPhi = false;
+  bool ConvertSwitchRangeToICmp = false;
   bool ConvertSwitchToLookupTable = false;
----------------
As we want to disable this essentially only for the first SimplifyCFG run, may make the default true?


================
Comment at: llvm/lib/Transforms/Utils/SimplifyCFG.cpp:6566
+  // CVP. Therefore, only apply this transformation during late stages of the
+  // optimisation pipeline.
+  if (Options.ConvertSwitchRangeToICmp && TurnSwitchRangeIntoICmp(SI, Builder))
----------------
This copy&pasted description doesn't sound quite right for this case. What we're losing here is information on values that branch to unreachable.

```
// The conversion from switch to comparison may lose information on
// impossible switch values, so disable it early in the pipeline.
```


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D119854