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

[Andrey Karlov via cfe-commits]

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@@ -6298,10 +6304,43 @@ 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;
----------------
negativ wrote:

> The use of static locals is a red-flag. Consider running gtests, where multiple clang instances will be created in sequence, slowly filling up the static cache with decl pointer that will get dangling after each test. Once in a while after a long running unittest you would get a cache hit for a dangling pointer and the disaster happens.

I've revisited the approach I initially took, so now we don't need any cache to collect visited functions as I added an implicit bool argument to the `analyzer_noreturn` attribute. These declarations are now considered equivalent:

```cpp
void foo() __attribute__((analyzer_noreturn));
void foo() __attribute__((analyzer_noreturn(true)));
```
...and I can add implicit `__attribute__((analyzer_noreturn(false)))` to functions that I've already checked. This gives us the following benefits:

- We don't need to revisit function calls repeatedly since the result of the previous check is saved in the analyzer_noreturn attribute
- Simplifies DFS search (nodes we're currently visiting are marked with` analyzer_noreturn(false)`)

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