[clang] [clang-tools-extra] [clang]: Propagate `*noreturn` attributes in `CFG` (PR #146355)

[Andrey Karlov via cfe-commits]

================
@@ -6298,10 +6334,43 @@ static bool isImmediateSinkBlock(const CFGBlock *Blk) {
   // at least for now, but once we have better support for exceptions,
   // we'd need to carefully handle the case when the throw is being
   // immediately caught.
-  if (llvm::any_of(*Blk, [](const CFGElement &Elm) {
+  if (llvm::any_of(*Blk, [](const CFGElement &Elm) -> bool {
+        if (std::optional<CFGStmt> StmtElm = Elm.getAs<CFGStmt>())
+          return isa<CXXThrowExpr>(StmtElm->getStmt());
+        return false;
+      }))
+    return true;
+
+  auto HasNoReturnCall = [](const CallExpr *CE) {
+    if (!CE)
+      return false;
+
+    static thread_local llvm::SmallPtrSet<const FunctionDecl *, 32> InProgress;
+
+    auto *FD = CE->getDirectCallee();
+
+    if (!FD || InProgress.count(FD))
+      return false;
+
+    InProgress.insert(FD);
+    auto DoCleanup = llvm::make_scope_exit([&]() { InProgress.erase(FD); });
+
+    auto NoReturnFromCFG = [FD]() {
+      if (!FD->getBody())
+        return false;
+
+      auto CalleeCFG =
+          CFG::buildCFG(FD, FD->getBody(), &FD->getASTContext(), {});
----------------
negativ wrote:

As I understand it (please correct me if I'm wrong), `FunctionDecl*` instances within the constructed `AS`T will be reused when building the `CFG` - if so, we could do something like:
```cpp
if( FD->isAnalyzerNoReturn() || NoReturnFromCFG() ) {
     const_cast<FunctionDecl *>(FD)->addAttr(AnalyzerNoReturnAttr::Create(
      FD->getASTContext(), FD->getLocation()));
     return true;
   }
```

https://github.com/llvm/llvm-project/pull/146355