[clang][dataflow] Fix initializing a reference field with an `InitListExpr`.

[mboehme]

Summary

I added a test for this as the ongoing migration to strict handling of value categories (see https://discourse.llvm.org/t/70086) will change the code that handles this case. It turns out we already didn't handle this correctly, so I fixed the existing implementation.

Depends On D154961

[xazax.hun]

clang/lib/Analysis/FlowSensitive/Transfer.cpp

719–722

[mboehme]

Changes in response to review comments

clang/lib/Analysis/FlowSensitive/Transfer.cpp

void VisitInitListExpr(const InitListExpr *S) {
     auto *Val = Env.createValue(Type);
     if (Val == nullptr)
       return;
 
     Env.setValue(Loc, *Val);
 
     if (Type->isStructureOrClassType()) {
       std::vector<FieldDecl *> Fields =
           getFieldsForInitListExpr(Type->getAsRecordDecl());
-      for (auto It : llvm::zip(Fields, S->inits())) {
-        const FieldDecl *Field = std::get<0>(It);
+      for (auto [Field, Init] : llvm::zip(Fields, S->inits())) {
         assert(Field != nullptr);
-
-        const Expr *Init = std::get<1>(It);
         assert(Init != nullptr);
 
-        if (Value *InitVal = Env.getValue(*Init, SkipPast::None))
+        if (Field->getType()->isReferenceType()) {
+          if (StorageLocation *Loc = Env.getStorageLocationStrict(*Init))
+            cast<StructValue>(Val)->setChild(*Field,
+                                             Env.create<ReferenceValue>(*Loc));
+        } else if (Value *InitVal = Env.getValue(*Init, SkipPast::None))
           cast<StructValue>(Val)->setChild(*Field, *InitVal);
       }
     }
     // FIXME: Implement array initialization.
   }
 
   void VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *S) {
     Env.setValueStrict(*S, Env.getBoolLiteralValue(S->getValue()));

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

runDataflow(
               getValueForDecl<StructValue>(ASTCtx, Env, "OtherB");
           EXPECT_THAT(OtherBVal.getChild(*BarDecl), NotNull());
           EXPECT_THAT(OtherBVal.getChild(*BazDecl), NotNull());
           EXPECT_THAT(OtherBVal.getChild(*QuxDecl), NotNull());
         });
   }
 }
 
+TEST(TransferTest, AggregateInitializationReferenceField) {
+  std::string Code = R"(
+    struct S {
+      int &RefField;
+    };
+
+    void target(int i) {
+      S s = { i };
+      /*[[p]]*/
+    }
+  )";
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        const Environment &Env = getEnvironmentAtAnnotation(Results, "p");
+
+        const ValueDecl *RefFieldDecl = findValueDecl(ASTCtx, "RefField");
+
+        auto &ILoc = getLocForDecl<StorageLocation>(ASTCtx, Env, "i");
+        auto &SLoc = getLocForDecl<AggregateStorageLocation>(ASTCtx, Env, "s");
+
+        auto &RefValue =
+            *cast<ReferenceValue>(getFieldValue(&SLoc, *RefFieldDecl, Env));
+        EXPECT_EQ(&RefValue.getReferentLoc(), &ILoc);
+      });
+}
+
 TEST(TransferTest, AssignToUnionMember) {
   std::string Code = R"(
     union A {
       int Foo;
     };
 
     void target(int Bar) {
       A Baz;