[clang][dataflow] Assign aggregate storage locations to union stmts

This patch ensures that the dataflow analysis framework does not crash when it encounters access to members of union types. This is part of the implementation of the dataflow analysis framework. See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev. Reviewed-by: xazax.hun Differential Revision: https://reviews.llvm.org/D118226
llvm · Jan 26, 2022 · 188d28f · 188d28f
1 parent e9b4239
commit 188d28f
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diff --git a/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp b/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
@@ -100,7 +100,7 @@ LatticeJoinEffect Environment::join(const Environment &Other) {
 
 StorageLocation &Environment::createStorageLocation(QualType Type) {
   assert(!Type.isNull());
-  if (Type->isStructureOrClassType()) {
+  if (Type->isStructureOrClassType() || Type->isUnionType()) {
     // FIXME: Explore options to avoid eager initialization of fields as some of
     // them might not be needed for a particular analysis.
     llvm::DenseMap<const ValueDecl *, StorageLocation *> FieldLocs;

diff --git a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
@@ -1952,4 +1952,37 @@ TEST_F(TransferTest, AggregateInitialization) {
   }
 }
 
+TEST_F(TransferTest, AssignToUnionMember) {
+  std::string Code = R"(
+    union A {
+      int Foo;
+    };
+
+    void target(int Bar) {
+      A Baz;
+      Baz.Foo = Bar;
+      // [[p]]
+    }
+  )";
+  runDataflow(Code,
+              [](llvm::ArrayRef<
+                     std::pair<std::string, DataflowAnalysisState<NoopLattice>>>
+                     Results,
+                 ASTContext &ASTCtx) {
+                ASSERT_THAT(Results, ElementsAre(Pair("p", _)));
+                const Environment &Env = Results[0].second.Env;
+
+                const ValueDecl *BazDecl = findValueDecl(ASTCtx, "Baz");
+                ASSERT_THAT(BazDecl, NotNull());
+                ASSERT_TRUE(BazDecl->getType()->isUnionType());
+
+                const auto *BazLoc = dyn_cast_or_null<AggregateStorageLocation>(
+                    Env.getStorageLocation(*BazDecl, SkipPast::None));
+                ASSERT_THAT(BazLoc, NotNull());
+
+                // FIXME: Add support for union types.
+                EXPECT_THAT(Env.getValue(*BazLoc), IsNull());
+              });
+}
+
 } // namespace