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

[Balazs Benics via cfe-commits]

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@@ -6298,10 +6308,60 @@ 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;
+
+    auto *FD = CE->getDirectCallee();
+
+    if (!FD)
+      return false;
+
+    auto *CanCD = FD->getCanonicalDecl();
+    auto *DefFD = CanCD->getDefinition();
+    auto NoRetAttrOpt = CanCD->getAnalyzerNoReturn();
+    auto NoReturn = false;
+
+    if (!NoRetAttrOpt && DefFD && DefFD->getBody()) {
+      // HACK: we are gonna cache analysis result as implicit
+      // `analyzer_noreturn` attribute
+      auto *MutCD = const_cast<FunctionDecl *>(CanCD);
+
+      // Mark function as `analyzer_noreturn(false)` to:
+      //  * prevent infinite recursion in noreturn analysis
+      //  * indicate that we've already analyzed(-ing) this function
+      //  * serve as a safe default assumption (function may return)
+      MutCD->addAttr(AnalyzerNoReturnAttr::CreateImplicit(
+          CanCD->getASTContext(), false, CanCD->getLocation()));
+
+      auto CalleeCFG =
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steakhal wrote:

I've discussed this with @Xazax-hun and I agree with him that we should have a look at the performance of some warnings. I think they live under the [AnalysisBasedWarnings.cpp](https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/AnalysisBasedWarnings.cpp) file.
There could be many, but I can recall one which is the noreturn analysis, like `CheckFallThrough`.

Another problem with the use of this `analyzer_noreturn(bool)` attribute is that it will basically touch/pollute every FunctionDecl in the AST - if I understand it correctly.

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