[clang][dataflow] Add two repros for non-convergence involving pointers in loops.

[mboehme]

Summary

These are broken out from https://reviews.llvm.org/D156658, which it now seems obvious isn't the right way to solve the non-convergence.

Instead, my plan is to address the non-convergence through pointer value widening, but the exact way this should be implemented is TBD. In the meantime, I think there's value in getting these repros submitted to record the current undesirable behavior.

[mboehme]

pre-merge failure appears to be unrelated to this patch.

clang/unittests/Analysis/FlowSensitive/TestingSupport.h

 
 /// Runs dataflow on `Code` with a `NoopAnalysis` and calls `VerifyResults` to
 /// verify the results.
 llvm::Error checkDataflowWithNoopAnalysis(
     llvm::StringRef Code,
     std::function<
         void(const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &,
              ASTContext &)>
-        VerifyResults,
-    DataflowAnalysisOptions Options,
+        VerifyResults = [](const auto &, auto &) {},
+    DataflowAnalysisOptions Options = {BuiltinOptions()},
     LangStandard::Kind Std = LangStandard::lang_cxx17,
     llvm::StringRef TargetFun = "target");
 
 /// Returns the `ValueDecl` for the given identifier.
 ///
 /// Requirements:
 ///
 ///   `Name` must be unique in `ASTCtx`.

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

 }
 
 TEST(TransferTest, CannotAnalyzeFunctionTemplate) {
   std::string Code = R"(
     template <typename T>
     void target() {}
   )";
   ASSERT_THAT_ERROR(
-      checkDataflowWithNoopAnalysis(
-          Code,
-          [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
-             ASTContext &ASTCtx) {},
-          {BuiltinOptions()}),
+      checkDataflowWithNoopAnalysis(Code),
       llvm::FailedWithMessage("Cannot analyze templated declarations"));
 }
 
 TEST(TransferTest, CannotAnalyzeMethodOfClassTemplate) {
   std::string Code = R"(
     template <typename T>
     struct A {
       void target() {}
     };
   )";
   ASSERT_THAT_ERROR(
-      checkDataflowWithNoopAnalysis(
-          Code,
-          [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
-             ASTContext &ASTCtx) {},
-          {BuiltinOptions()}),
+      checkDataflowWithNoopAnalysis(Code),
       llvm::FailedWithMessage("Cannot analyze templated declarations"));
 }
 
 TEST(TransferTest, VarDeclInitAssignConditionalOperator) {
   std::string Code = R"(
     struct A {};
 
     void target(A Foo, A Bar, bool Cond) {
runDataflow(
 
         // The loop body may not have been executed, so we should not conclude
         // that `l` points to `val`.
         EXPECT_NE(&LVal->getPointeeLoc(),
                   OuterEnv.getStorageLocation(*ValDecl));
       });
 }
 
+TEST(TransferTest, LoopDereferencingChangingPointerConverges) {
+  std::string Code = R"cc(
+    bool some_condition();
+
+    void target(int i1, int i2) {
+      int *p = &i1;
+      while (true) {
+        (void)*p;
+        if (some_condition())
+          p = &i1;
+        else
+          p = &i2;
+      }
+    }
+  )cc";
+  // FIXME: Implement pointer value widening to make analysis converge.
+  ASSERT_THAT_ERROR(
+      checkDataflowWithNoopAnalysis(Code),
+      llvm::FailedWithMessage("maximum number of iterations reached"));
+}
+
+TEST(TransferTest, LoopDereferencingChangingRecordPointerConverges) {
+  std::string Code = R"cc(
+    struct Lookup {
+      int x;
+    };
+
+    bool some_condition();
+
+    void target(Lookup l1, Lookup l2) {
+      Lookup *l = &l1;
+      while (true) {
+        (void)l->x;
+        if (some_condition())
+          l = &l1;
+        else
+          l = &l2;
+      }
+    }
+  )cc";
+  // FIXME: Implement pointer value widening to make analysis converge.
+  ASSERT_THAT_ERROR(
+      checkDataflowWithNoopAnalysis(Code),
+      llvm::FailedWithMessage("maximum number of iterations reached"));
+}
+
 TEST(TransferTest, DoesNotCrashOnUnionThisExpr) {
   std::string Code = R"(
     union Union {
       int A;
       float B;
     };
 
     void foo() {