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

[via llvm-commits]

================
@@ -6166,6 +6166,279 @@ 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>;
+
+using PHINodeToCaseEntryValueMapTy = std::map<
+    llvm::PHINode *,
+    llvm::SmallVector<std::pair<llvm::ConstantInt *, llvm::Value *>, 4>>;
+
+// 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>;
+
+static void mapCaseToResultWithMap(SwitchCaseResultsTy2 &Results,
+                                   PHINodeToCaseEntryValueMapTy &Map,
+                                   ConstantInt *CaseVal,
+                                   SwitchCaseResultVectorTy2 &UniqueResults,
+                                   Value *Result) {
+  // fill in PHINodeToCaseEntryValueMapTy &Map
+  for (const auto &Pair : Results) {
+    PHINode *PHI = Pair.first;
+    Value *ReturnValue = Pair.second;
+    Map[PHI].emplace_back(std::make_pair(CaseVal, ReturnValue));
+  }
+
+  // fill in SwitchCaseResultVectorTy2 &UniqueResults
+  for (auto &I : UniqueResults) {
+    if (I.first == Result) {
+      I.second.push_back(CaseVal);
+      return;
+    }
+  }
+  UniqueResults.push_back(
+      std::make_pair(Result, SmallVector<Value *, 4>(1, CaseVal)));
+}
+
+static bool getCaseResultsWithoutConstants(
+    SwitchInst *SI, BasicBlock *CaseDest, BasicBlock **CommonDest,
+    SmallVectorImpl<std::pair<PHINode *, Value *>> &Res,
+    bool IsDefault = false) {
+  BasicBlock *Pred = SI->getParent();
+  int NumOfInsts = 0;
+  // Check if there is only one instruction per block, excepet from default
+  // block
+  if (!IsDefault) {
+    for (Instruction &I : CaseDest->instructionsWithoutDebug(false)) {
+
+      if (I.isTerminator()) {
+        // If the terminator is a simple branch, continue to the next block.
+        if (I.getNumSuccessors() != 1 || I.isSpecialTerminator())
----------------
XChy wrote:

```suggestion
      if (BranchInst* BI = dyn_cast<BranchInst>(&I)) {
        // If the terminator is a simple branch, continue to the next block.
        if (!BI->isUnconditional())
```

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