[clang][dataflow] Fix getResultObjectLocation() on CXXDefaultArgExpr. (llvm#85072)

This patch includes a test that causes an assertion failure without the
other
changes in this patch.

Author: martinboehme

clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp

@@ -771,6 +771,7 @@ static bool isOriginalRecordConstructor(const Expr &RecordPRValue) {
     return !Init->isSemanticForm() || !Init->isTransparent();
   return isa<CXXConstructExpr>(RecordPRValue) || isa<CallExpr>(RecordPRValue) ||
          isa<LambdaExpr>(RecordPRValue) ||
+         isa<CXXDefaultArgExpr>(RecordPRValue) ||
          isa<CXXDefaultInitExpr>(RecordPRValue) ||
          // The framework currently does not propagate the objects created in
          // the two branches of a `ConditionalOperator` because there is no way

clang/lib/Analysis/FlowSensitive/Transfer.cpp

@@ -450,6 +450,25 @@ class TransferVisitor : public ConstStmtVisitor<TransferVisitor> {
     Env.setStorageLocation(*S, *MemberLoc);
   }
 
+  void VisitCXXDefaultArgExpr(const CXXDefaultArgExpr *S) {
+    const Expr *ArgExpr = S->getExpr();
+    assert(ArgExpr != nullptr);
+    propagateValueOrStorageLocation(*ArgExpr, *S, Env);
+
+    // If this is a prvalue of record type, we consider it to be an "original
+    // record constructor", which we always require to have a `RecordValue`.
+    // So make sure we have a value if we didn't propagate one above.
+    if (S->isPRValue() && S->getType()->isRecordType()) {
+      if (Env.getValue(*S) == nullptr) {
+        Value *Val = Env.createValue(S->getType());
+        // We're guaranteed to always be able to create a value for record
+        // types.
+        assert(Val != nullptr);
+        Env.setValue(*S, *Val);
+      }
+    }
+  }
+
   void VisitCXXDefaultInitExpr(const CXXDefaultInitExpr *S) {
     const Expr *InitExpr = S->getExpr();
     assert(InitExpr != nullptr);

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

@@ -2924,6 +2924,36 @@ TEST(TransferTest, ResultObjectLocation) {
       });
 }
 
+TEST(TransferTest, ResultObjectLocationForDefaultArgExpr) {
+  std::string Code = R"(
+    struct S {};
+    void funcWithDefaultArg(S s = S());
+    void target() {
+      funcWithDefaultArg();
+      // [[p]]
+    }
+  )";
+
+  using ast_matchers::cxxDefaultArgExpr;
+  using ast_matchers::match;
+  using ast_matchers::selectFirst;
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        const Environment &Env = getEnvironmentAtAnnotation(Results, "p");
+
+        auto *DefaultArg = selectFirst<CXXDefaultArgExpr>(
+            "default_arg",
+            match(cxxDefaultArgExpr().bind("default_arg"), ASTCtx));
+        ASSERT_NE(DefaultArg, nullptr);
+
+        // The values for default arguments aren't modeled; we merely verify
+        // that we can get a result object location for a default arg.
+        Env.getResultObjectLocation(*DefaultArg);
+      });
+}
+
 TEST(TransferTest, ResultObjectLocationForDefaultInitExpr) {
   std::string Code = R"(
     struct S {};