[clang][dataflow] Consider CXXDefaultInitExpr to be an "original record ctor". (#78423)

The CFG doesn't contain a CFGElement for the
`CXXDefaultInitExpr::getInit()`, so
it makes sense to consider the `CXXDefaultInitExpr` to be the expression
that
originally constructs the object.

Author: martinboehme

clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp

@@ -747,6 +747,7 @@ static bool isOriginalRecordConstructor(const Expr &RecordPRValue) {
     return !Init->isSemanticForm() || !Init->isTransparent();
   return isa<CXXConstructExpr>(RecordPRValue) || isa<CallExpr>(RecordPRValue) ||
          isa<LambdaExpr>(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
          // to reconcile their storage locations, which are different. We

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

@@ -2684,6 +2684,48 @@ TEST(TransferTest, ResultObjectLocation) {
       });
 }
 
+TEST(TransferTest, ResultObjectLocationForDefaultInitExpr) {
+  std::string Code = R"(
+    struct S {};
+    struct target {
+      target () {
+        (void)0;
+        // [[p]]
+      }
+      S s = {};
+    };
+  )";
+
+  using ast_matchers::cxxCtorInitializer;
+  using ast_matchers::match;
+  using ast_matchers::selectFirst;
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        const Environment &Env = getEnvironmentAtAnnotation(Results, "p");
+
+        const ValueDecl *SField = findValueDecl(ASTCtx, "s");
+
+        auto *CtorInit = selectFirst<CXXCtorInitializer>(
+            "ctor_initializer",
+            match(cxxCtorInitializer().bind("ctor_initializer"), ASTCtx));
+        ASSERT_NE(CtorInit, nullptr);
+
+        auto *DefaultInit = cast<CXXDefaultInitExpr>(CtorInit->getInit());
+
+        RecordStorageLocation &Loc = Env.getResultObjectLocation(*DefaultInit);
+
+        // FIXME: The result object location for the `CXXDefaultInitExpr` should
+        // be the location of the member variable being initialized, but we
+        // don't do this correctly yet; see also comments in
+        // `builtinTransferInitializer()`.
+        // For the time being, we just document the current erroneous behavior
+        // here (this should be `EXPECT_EQ` when the behavior is fixed).
+        EXPECT_NE(&Loc, Env.getThisPointeeStorageLocation()->getChild(*SField));
+      });
+}
+
 TEST(TransferTest, StaticCast) {
   std::string Code = R"(
     void target(int Foo) {