[llvm] [SimplifyCFG] Improve reduceSwitchRange to avoid unnecessary subtractions (PR #198374)

[Hans Wennborg via llvm-commits]

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@@ -317,6 +317,109 @@ three:
   ret i32 99783
 }
 
+; Base=0 is profitable here: shifting out the common low zero bits produces a
+; dense range without subtracting the local minimum first.
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zmodem wrote:

In the end, will this get lowered without the subtraction, or does that reappear in a range check like in test9 above?

https://github.com/llvm/llvm-project/pull/198374