[dataflow] CXXForRangeStmt should extend flow condition

This is needed in order to correctly assume implicit iterator validity
in the iterator checker.

Author: paulsemel

clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp

@@ -103,9 +103,12 @@ class TerminatorVisitor
     return {nullptr, false};
   }
 
-  TerminatorVisitorRetTy VisitCXXForRangeStmt(const CXXForRangeStmt *) {
-    // Don't do anything special for CXXForRangeStmt, because the condition
-    // (being implicitly generated) isn't visible from the loop body.
+  TerminatorVisitorRetTy VisitCXXForRangeStmt(const CXXForRangeStmt *S) {
+    // Even though the condition isn't visible from the loop body, analysis
+    // might depend on the implicit implicit statements implied by the loop.
+    auto *Cond = S->getCond();
+    if (Cond != nullptr)
+      return extendFlowCondition(*Cond);
     return {nullptr, false};
   }
 

clang/unittests/Analysis/FlowSensitive/TypeErasedDataflowAnalysisTest.cpp

@@ -1710,4 +1710,25 @@ TEST_F(TopTest, ForRangeStmtConverges) {
                 // analysis converged.
               });
 }
+
+TEST_F(TopTest, ForRangeStmtHasFlowCondition) {
+  std::string Code = R"(
+    #include <array>
+    void target(bool Foo) {
+      std::array<int, 5> t;
+      for (auto& i : t) {
+        (void)0;
+        /*[[p1]]*/
+      }
+    }
+  )";
+  runDataflow(Code,
+              [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+                 const AnalysisOutputs &AO) {
+                  ASSERT_THAT(Results.keys(), UnorderedElementsAre("p1"));
+                  const Environment &Env1 = getEnvironmentAtAnnotation(Results, "p1");
+                  ASSERT_TRUE(Env1.proves(Env1.arena().makeAtomRef(Env1.getFlowConditionToken())));
+              });
+}
+
 } // namespace