C++: Add an example with missing flow.

Author: MathiasVP

cpp/ql/test/library-tests/dataflow/fields/dataflow-consistency.expected

@@ -142,6 +142,7 @@ postWithInFlow
 | simple.cpp:92:7:92:7 | i [post update] | PostUpdateNode should not be the target of local flow. |
 | simple.cpp:118:7:118:7 | i [post update] | PostUpdateNode should not be the target of local flow. |
 | simple.cpp:124:5:124:6 | * ... [post update] | PostUpdateNode should not be the target of local flow. |
+| simple.cpp:167:9:167:9 | x [post update] | PostUpdateNode should not be the target of local flow. |
 viableImplInCallContextTooLarge
 uniqueParameterNodeAtPosition
 uniqueParameterNodePosition

cpp/ql/test/library-tests/dataflow/fields/partial-definition-diff.expected

@@ -308,3 +308,5 @@ WARNING: module 'DataFlow' has been deprecated and may be removed in future (par
 | simple.cpp:124:5:124:6 | * ... | AST only |
 | simple.cpp:131:14:131:14 | a | IR only |
 | simple.cpp:136:10:136:10 | a | IR only |
+| simple.cpp:167:9:167:9 | x | AST only |
+| simple.cpp:168:8:168:12 | u_int | IR only |

cpp/ql/test/library-tests/dataflow/fields/partial-definition-ir.expected

@@ -670,6 +670,8 @@
 | simple.cpp:131:14:131:14 | a |
 | simple.cpp:135:20:135:20 | q |
 | simple.cpp:136:10:136:10 | a |
+| simple.cpp:167:3:167:7 | u_int |
+| simple.cpp:168:8:168:12 | u_int |
 | struct_init.c:15:8:15:9 | ab |
 | struct_init.c:15:12:15:12 | a |
 | struct_init.c:16:8:16:9 | ab |

cpp/ql/test/library-tests/dataflow/fields/partial-definition.expected

@@ -597,6 +597,8 @@ WARNING: module 'DataFlow' has been deprecated and may be removed in future (par
 | simple.cpp:118:7:118:7 | i |
 | simple.cpp:124:5:124:6 | * ... |
 | simple.cpp:135:20:135:20 | q |
+| simple.cpp:167:3:167:7 | u_int |
+| simple.cpp:167:9:167:9 | x |
 | struct_init.c:15:8:15:9 | ab |
 | struct_init.c:15:12:15:12 | a |
 | struct_init.c:16:8:16:9 | ab |

cpp/ql/test/library-tests/dataflow/fields/simple.cpp

@@ -136,4 +136,36 @@ void alias_with_fields(bool b) {
     sink(a.i); // $ MISSING: ast,ir
 }
 
+template<typename T>
+union U_with_two_instantiations_of_different_size {
+  int x;
+  T y;
+};
+
+struct LargeStruct {
+  int data[64];
+};
+
+void test_union_with_two_instantiations_of_different_sizes() {
+  // A union's fields is partitioned into "chunks" for field-flow in order to
+  // improve performance (so that a write to a field of a union does not flow
+  // to too many reads that don't happen at runtime). The partitioning is based
+  // the size of the types in the union. So a write to a field of size k only
+  // flows to a read of size k.
+  // Since field-flow is based on uninstantiated types a field can have
+  // multiple sizes if the union is instantiated with types of
+  // different sizes. So to compute the partition we pick the maximum size.
+  // Because of this there are `Content`s corresponding to the union
+  // `U_with_two_instantiations_of_different_size<T>`: The one for size
+  // `sizeof(int)`, and the one for size `sizeof(LargeStruct)` (because
+  // `LargeStruct` is larger than `int`). So the write to `x` writes to the
+  // `Content` for size `sizeof(int)`, and the read of `y` reads from the
+  // `Content` for size `sizeof(LargeStruct)`.
+  U_with_two_instantiations_of_different_size<int> u_int;
+  U_with_two_instantiations_of_different_size<LargeStruct> u_very_large;
+
+  u_int.x = user_input();
+  sink(u_int.y); // $ MISSING: ir
+}
+
 } // namespace Simple