[clang][dataflow] Handle `for` statements without conditions

[sgatev]

Summary

Handle for statements without conditions.

clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp

public:
   void VisitDoStmt(const DoStmt *S) {
     auto *Cond = S->getCond();
     assert(Cond != nullptr);
     extendFlowCondition(*Cond);
   }
 
   void VisitForStmt(const ForStmt *S) {
     auto *Cond = S->getCond();
-    assert(Cond != nullptr);
+    if (Cond != nullptr)
       extendFlowCondition(*Cond);
   }
 
   void VisitBinaryOperator(const BinaryOperator *S) {
     assert(S->getOpcode() == BO_LAnd || S->getOpcode() == BO_LOr);
     auto *LHS = S->getLHS();
     assert(LHS != nullptr);
     extendFlowCondition(*LHS);
   }

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

runDataflow(
 
         BoolValue &AfterLoopFooVal =
             *cast<BoolValue>(AfterLoopEnv.getValue(*FooDecl, SkipPast::None));
         EXPECT_TRUE(AfterLoopEnv.flowConditionImplies(
             AfterLoopEnv.makeNot(AfterLoopFooVal)));
       });
 }
 
+TEST_F(TransferTest, ForStmtBranchWithoutConditionDoesNotExtendFlowCondition) {
+  std::string Code = R"(
+    void target(bool Foo) {
+      for (;;) {
+        (void)0;
+        // [[loop_body]]
+      }
+    }
+  )";
+  runDataflow(
+      Code, [](llvm::ArrayRef<
+                   std::pair<std::string, DataflowAnalysisState<NoopLattice>>>
+                   Results,
+               ASTContext &ASTCtx) {
+        ASSERT_THAT(Results, ElementsAre(Pair("loop_body", _)));
+        const Environment &LoopBodyEnv = Results[0].second.Env;
+
+        const ValueDecl *FooDecl = findValueDecl(ASTCtx, "Foo");
+        ASSERT_THAT(FooDecl, NotNull());
+
+        BoolValue &LoopBodyFooVal =
+            *cast<BoolValue>(LoopBodyEnv.getValue(*FooDecl, SkipPast::None));
+        EXPECT_FALSE(LoopBodyEnv.flowConditionImplies(LoopBodyFooVal));
+      });
+}
+
 } // namespace