[clang][dataflow] Propagate storage location of compound assignment operators. (llvm#94332)

To avoid generating unnecessary values, we don't create a new value but
instead
leave it to the specific analysis to do this if desired.

Author: martinboehme

clang/lib/Analysis/FlowSensitive/Transfer.cpp

@@ -147,6 +147,13 @@ class TransferVisitor : public ConstStmtVisitor<TransferVisitor> {
     const Expr *RHS = S->getRHS();
     assert(RHS != nullptr);
 
+    // Do compound assignments up-front, as there are so many of them and we
+    // don't want to list all of them in the switch statement below.
+    // To avoid generating unnecessary values, we don't create a new value but
+    // instead leave it to the specific analysis to do this if desired.
+    if (S->isCompoundAssignmentOp())
+      propagateStorageLocation(*S->getLHS(), *S, Env);
+
     switch (S->getOpcode()) {
     case BO_Assign: {
       auto *LHSLoc = Env.getStorageLocation(*LHS);

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

@@ -3796,6 +3796,26 @@ TEST(TransferTest, Postincrement) {
       });
 }
 
+// We test just one of the compound assignment operators because we know the
+// code for propagating the storage location is shared among all of them.
+TEST(TransferTest, AddAssign) {
+  std::string Code = R"(
+    void target(int I) {
+      int &IRef = (I += 1);
+      // [[p]]
+    }
+  )";
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        const Environment &Env = getEnvironmentAtAnnotation(Results, "p");
+
+        EXPECT_EQ(&getLocForDecl(ASTCtx, Env, "IRef"),
+                  &getLocForDecl(ASTCtx, Env, "I"));
+      });
+}
+
 TEST(TransferTest, CannotAnalyzeFunctionTemplate) {
   std::string Code = R"(
     template <typename T>