[clang]: Support analyzer_noreturn attribute in CFG (#150952)

## Problem

Currently, functions with `analyzer_noreturn` attribute aren't
recognized as `no-return` by `CFG`:

```cpp
void assertion_handler() __attribute__((analyzer_noreturn)) {
    log(...);
}

void handle_error(const std::optional<int> opt) {
    if (!opt) {
        fatal_error(); // Static analyzer doesn't know this never returns
    }
    *opt = 1;          // False-positive `unchecked-optional-access` warning as analyzer thinks this is reachable
}
```

## Solution
1. Extend the `FunctionDecl` class by adding an `isAnalyzerNoReturn()`
function
2. Update `CFGBuilder::VisitCallExpr` to check both `FD->isNoReturn()`
and `FD->isAnalyzerNoReturn()` properties

## Comments
This PR incorporates part of the work done in
#146355

Author: negativ

clang-tools-extra/test/clang-tidy/checkers/bugprone/unchecked-optional-access.cpp

@@ -141,6 +141,17 @@ void nullable_value_after_swap(BloombergLP::bdlb::NullableValue<int> &opt1, Bloo
   }
 }
 
+void assertion_handler() __attribute__((analyzer_noreturn));
+
+void function_calling_analyzer_noreturn(const bsl::optional<int>& opt)
+{
+  if (!opt) {
+      assertion_handler();
+  }
+
+  *opt; // no-warning: The previous condition guards this dereference.
+}
+
 template <typename T>
 void function_template_without_user(const absl::optional<T> &opt) {
   opt.value(); // no-warning

clang/include/clang/AST/Decl.h

@@ -2668,6 +2668,10 @@ class FunctionDecl : public DeclaratorDecl,
   /// an attribute on its declaration or its type.
   bool isNoReturn() const;
 
+  /// Determines whether this function is known to be 'noreturn' for analyzer,
+  /// through an `analyzer_noreturn` attribute on its declaration.
+  bool isAnalyzerNoReturn() const;
+
   /// True if the function was a definition but its body was skipped.
   bool hasSkippedBody() const { return FunctionDeclBits.HasSkippedBody; }
   void setHasSkippedBody(bool Skipped = true) {

clang/lib/AST/Decl.cpp

@@ -3600,6 +3600,10 @@ bool FunctionDecl::isNoReturn() const {
   return false;
 }
 
+bool FunctionDecl::isAnalyzerNoReturn() const {
+  return hasAttr<AnalyzerNoReturnAttr>();
+}
+
 bool FunctionDecl::isMemberLikeConstrainedFriend() const {
   // C++20 [temp.friend]p9:
   //   A non-template friend declaration with a requires-clause [or]

clang/lib/Analysis/CFG.cpp

@@ -2833,7 +2833,8 @@ CFGBlock *CFGBuilder::VisitCallExpr(CallExpr *C, AddStmtChoice asc) {
     if (!FD->isVariadic())
       findConstructionContextsForArguments(C);
 
-    if (FD->isNoReturn() || C->isBuiltinAssumeFalse(*Context))
+    if (FD->isNoReturn() || FD->isAnalyzerNoReturn() ||
+        C->isBuiltinAssumeFalse(*Context))
       NoReturn = true;
     if (FD->hasAttr<NoThrowAttr>())
       AddEHEdge = false;

clang/unittests/Analysis/FlowSensitive/TypeErasedDataflowAnalysisTest.cpp

@@ -693,6 +693,80 @@ TEST_F(NoreturnDestructorTest, ConditionalOperatorNestedBranchReturns) {
   // FIXME: Called functions at point `p` should contain only "foo".
 }
 
+class AnalyzerNoreturnTest : public Test {
+protected:
+  template <typename Matcher>
+  void runDataflow(llvm::StringRef Code, Matcher Expectations) {
+    tooling::FileContentMappings FilesContents;
+    FilesContents.push_back(
+        std::make_pair<std::string, std::string>("noreturn_test_defs.h", R"(
+      void assertionHandler() __attribute__((analyzer_noreturn));
+
+      void trap() {}
+    )"));
+
+    ASSERT_THAT_ERROR(
+        test::checkDataflow<FunctionCallAnalysis>(
+            AnalysisInputs<FunctionCallAnalysis>(
+                Code, ast_matchers::hasName("target"),
+                [](ASTContext &C, Environment &) {
+                  return FunctionCallAnalysis(C);
+                })
+                .withASTBuildArgs({"-fsyntax-only", "-std=c++17"})
+                .withASTBuildVirtualMappedFiles(std::move(FilesContents)),
+            /*VerifyResults=*/
+            [&Expectations](
+                const llvm::StringMap<
+                    DataflowAnalysisState<FunctionCallLattice>> &Results,
+                const AnalysisOutputs &) {
+              EXPECT_THAT(Results, Expectations);
+            }),
+        llvm::Succeeded());
+  }
+};
+
+TEST_F(AnalyzerNoreturnTest, Breathing) {
+  std::string Code = R"(
+    #include "noreturn_test_defs.h"
+
+    void target() {
+      trap();
+      // [[p]]
+    }
+  )";
+  runDataflow(Code, UnorderedElementsAre(IsStringMapEntry(
+                        "p", HoldsFunctionCallLattice(HasCalledFunctions(
+                                 UnorderedElementsAre("trap"))))));
+}
+
+TEST_F(AnalyzerNoreturnTest, DirectNoReturnCall) {
+  std::string Code = R"(
+    #include "noreturn_test_defs.h"
+
+    void target() {
+      assertionHandler();
+      trap();
+      // [[p]]
+    }
+  )";
+  runDataflow(Code, IsEmpty());
+}
+
+TEST_F(AnalyzerNoreturnTest, CanonicalDeclCallCheck) {
+  std::string Code = R"(
+    #include "noreturn_test_defs.h"
+    
+    extern void assertionHandler();
+
+    void target() {
+      assertionHandler();
+      trap();
+      // [[p]]
+    }
+  )";
+  runDataflow(Code, IsEmpty());
+}
+
 // Models an analysis that uses flow conditions.
 class SpecialBoolAnalysis final
     : public DataflowAnalysis<SpecialBoolAnalysis, NoopLattice> {