[llvm] [CodeExtractor] Terminate callsite blocks to new `noreturn` functions with `unreachable` (PR #84682)

[Matt Arsenault via llvm-commits]

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@@ -1390,12 +1402,16 @@ CallInst *CodeExtractor::emitCallAndSwitchStatement(Function *newFunction,
   Type *OldFnRetTy = TheSwitch->getParent()->getParent()->getReturnType();
   switch (NumExitBlocks) {
   case 0:
+    // If fn is no return, end with an unreachable terminator.
+    if (newFunction->doesNotReturn()) {
+      (void)new UnreachableInst(Context, TheSwitch->getIterator());
+    }
     // There are no successors (the block containing the switch itself), which
     // means that previously this was the last part of the function, and hence
     // this should be rewritten as a `ret'
 
     // Check if the function should return a value
-    if (OldFnRetTy->isVoidTy()) {
+    else if (OldFnRetTy->isVoidTy()) {
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arsenm wrote:

I think this formatting is extremely misleading. The else needs to be on the same line as the closing brace. Can you move the comment before the whole chain? 

https://github.com/llvm/llvm-project/pull/84682