[clang][dataflow] Add a transfer function for conditional operator

[sgatev]

Summary

This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.

clang/lib/Analysis/FlowSensitive/Transfer.cpp

if (S->getCastKind() == CK_NoOp) {
       auto *SubExprLoc = Env.getStorageLocation(*SubExpr, SkipPast::None);
       if (SubExprLoc == nullptr)
         return;
 
       Env.setStorageLocation(*S, *SubExprLoc);
     }
   }
 
+  void VisitConditionalOperator(const ConditionalOperator *S) {
+    // FIXME: Revisit this once flow conditions are added to the framework. For
+    // `a = b ? c : d` we can add `b => a == c && !b => a == d` to the flow
+    // condition.
+    auto &Loc = Env.createStorageLocation(*S);
+    Env.setStorageLocation(*S, Loc);
+    if (Value *Val = Env.createValue(S->getType()))
+      Env.setValue(Loc, *Val);
+  }
+
   // FIXME: Add support for:
   // - CXXBoolLiteralExpr
 
 private:
   Environment &Env;
 };
 
 void transfer(const Stmt &S, Environment &Env) {
   assert(!isa<ParenExpr>(&S));
   TransferVisitor(Env).Visit(&S);
 }
 
 } // namespace dataflow
 } // namespace clang

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

runDataflow(
         const auto *FooVal =
             cast<PointerValue>(Env.getValue(*FooDecl, SkipPast::None));
         const auto *BarVal =
             cast<ReferenceValue>(Env.getValue(*BarDecl, SkipPast::None));
         EXPECT_EQ(&BarVal->getPointeeLoc(), &FooVal->getPointeeLoc());
       });
 }
 
+TEST_F(TransferTest, VarDeclInitAssignConditionalOperator) {
+  std::string Code = R"(
+    struct A {};
+
+    void target(A Foo, A Bar, bool Cond) {
+      A Baz = Cond ?  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 *FooDecl = findValueDecl(ASTCtx, "Foo");
+        ASSERT_THAT(FooDecl, NotNull());
+
+        const ValueDecl *BarDecl = findValueDecl(ASTCtx, "Bar");
+        ASSERT_THAT(BarDecl, NotNull());
+
+        const ValueDecl *BazDecl = findValueDecl(ASTCtx, "Baz");
+        ASSERT_THAT(BazDecl, NotNull());
+
+        const auto *FooVal =
+            cast<StructValue>(Env.getValue(*FooDecl, SkipPast::None));
+        const auto *BarVal =
+            cast<StructValue>(Env.getValue(*BarDecl, SkipPast::None));
+
+        const auto *BazVal =
+            dyn_cast<StructValue>(Env.getValue(*BazDecl, SkipPast::None));
+        ASSERT_THAT(BazVal, NotNull());
+
+        EXPECT_NE(BazVal, FooVal);
+        EXPECT_NE(BazVal, BarVal);
+      });
+}
+
 } // namespace