[llvm] [SimplifyCFG] Convert switch to cmp/select sequence (PR #82795)

[Thomas Symalla via llvm-commits]

================
@@ -6197,6 +6197,268 @@ static bool trySwitchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
   return true;
 }
 
+// The first field contains the value that the switch produces when a certain
+// case group is selected, and the second field is a vector containing the
+// cases composing the case group.
+using SwitchCaseResultVectorTy2 =
+    SmallVector<std::pair<Value *, SmallVector<Value *, 4>>, 2>;
+
+// The first field contains the phi node that generates a result of the switch
+// and the second field contains the value generated for a certain case in the
+// switch for that PHI.
+using SwitchCaseResultsTy2 = SmallVector<std::pair<PHINode *, Value *>, 4>;
+
+using PHINodeToCaseEntryValueMapTy =
+    std::map<PHINode *, SmallVector<std::pair<ConstantInt *, Value *>, 4>>;
+
+// Helper function that checks if all PHI Nodes have default value
+bool allPHINodesHaveDefaultValue(const SwitchCaseResultsTy2 &Results) {
+  for (const auto &Pair : Results)
+    if (Pair.second == nullptr)
+      return false;
+  return true;
+}
+
+static bool getCaseResultsWithoutConstants(
+    SwitchInst *SI, BasicBlock *CaseDest, BasicBlock **CommonDest,
----------------
tsymalla wrote:

```suggestion
    SwitchInst *SI, BasicBlock *CaseDest, BasicBlock *&CommonDest,
```

https://github.com/llvm/llvm-project/pull/82795