C++: Add field flow through single-field structs and accept tests

cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowPrivate.qll

@@ -180,12 +180,16 @@ private class ArrayContent extends Content, TArrayContent {
   override Type getType() { none() }
 }
 
-/**
- * Holds if data can flow from `node1` to `node2` via an assignment to `f`.
- * Thus, `node2` references an object with a field `f` that contains the
- * value of `node1`.
- */
-predicate storeStep(Node node1, Content f, PostUpdateNode node2) {
+private predicate storeStepNoChi(Node node1, Content f, PostUpdateNode node2) {
+  exists(FieldAddressInstruction fa, StoreInstruction store |
+    store = node2.asInstruction() and
+    store.getDestinationAddress() = fa and
+    store.getSourceValue() = node1.asInstruction() and
+    f.(FieldContent).getField() = fa.getField()
+  )
+}
+
+private predicate storeStepChi(Node node1, Content f, PostUpdateNode node2) {
   exists(FieldAddressInstruction fa, StoreInstruction store |
     node1.asInstruction() = store and
     store.getDestinationAddress() = fa and
@@ -194,6 +198,16 @@ predicate storeStep(Node node1, Content f, PostUpdateNode node2) {
   )
 }
 
+/**
+ * Holds if data can flow from `node1` to `node2` via an assignment to `f`.
+ * Thus, `node2` references an object with a field `f` that contains the
+ * value of `node1`.
+ */
+predicate storeStep(Node node1, Content f, PostUpdateNode node2) {
+  storeStepNoChi(node1, f, node2) or
+  storeStepChi(node1, f, node2)
+}
+
 /**
  * Holds if data can flow from `node1` to `node2` via a read of `f`.
  * Thus, `node1` references an object with a field `f` whose value ends up in

cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowUtil.qll

@@ -270,6 +270,19 @@ private class ExplicitFieldStoreQualifierNode extends PartialDefinitionNode {
   override Node getPreUpdateNode() { result.asInstruction() = instr.getTotal() }
 }
 
+private class ExplicitSingleFieldStoreQualifierNode extends PartialDefinitionNode {
+  override StoreInstruction instr;
+
+  ExplicitSingleFieldStoreQualifierNode() {
+    exists(FieldAddressInstruction field |
+      field = instr.getDestinationAddress() and
+      not exists(ChiInstruction chi | chi.getPartial() = instr)
+    )
+  }
+
+  override Node getPreUpdateNode() { none() }
+}
+
 /**
  * A node that represents the value of a variable after a function call that
  * may have changed the variable because it's passed by reference.
@@ -404,6 +417,8 @@ predicate simpleLocalFlowStep(Node nodeFrom, Node nodeTo) {
   simpleInstructionLocalFlowStep(nodeFrom.asInstruction(), nodeTo.asInstruction())
 }
 
+private predicate hasSize(Type t, int size) { t.getSize() = size }
+
 cached
 private predicate simpleInstructionLocalFlowStep(Instruction iFrom, Instruction iTo) {
   iTo.(CopyInstruction).getSourceValue() = iFrom
@@ -452,6 +467,13 @@ private predicate simpleInstructionLocalFlowStep(Instruction iFrom, Instruction
     iTo.(LoadInstruction).getSourceValueOperand().getAnyDef() = chi
   )
   or
+  iTo.(CopyInstruction).getSourceValueOperand().getAnyDef() = iFrom and
+  exists(Class c, int size |
+    c = iTo.getResultType() and
+    hasSize(c, size) and
+    hasSize(iFrom.getResultType(), size)
+  )
+  or
   // Flow through modeled functions
   modelFlow(iFrom, iTo)
 }

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

@@ -19,6 +19,7 @@ unreachableNodeCCtx
 localCallNodes
 postIsNotPre
 postHasUniquePre
+| simple.cpp:65:5:65:22 | Store | PostUpdateNode should have one pre-update node but has 0. |
 uniquePostUpdate
 postIsInSameCallable
 reverseRead

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

@@ -25,6 +25,9 @@ edges
 | aliasing.cpp:79:11:79:20 | call to user_input | aliasing.cpp:80:12:80:13 | m1 |
 | aliasing.cpp:86:10:86:19 | call to user_input | aliasing.cpp:87:12:87:13 | m1 |
 | aliasing.cpp:92:12:92:21 | call to user_input | aliasing.cpp:93:12:93:13 | m1 |
+| simple.cpp:65:5:65:22 | Store [i] | simple.cpp:66:12:66:12 | Store [i] |
+| simple.cpp:65:11:65:20 | call to user_input | simple.cpp:65:5:65:22 | Store [i] |
+| simple.cpp:66:12:66:12 | Store [i] | simple.cpp:67:13:67:13 | i |
 | struct_init.c:20:20:20:29 | call to user_input | struct_init.c:22:11:22:11 | a |
 | struct_init.c:27:7:27:16 | call to user_input | struct_init.c:31:23:31:23 | a |
 nodes
@@ -63,6 +66,10 @@ nodes
 | aliasing.cpp:87:12:87:13 | m1 | semmle.label | m1 |
 | aliasing.cpp:92:12:92:21 | call to user_input | semmle.label | call to user_input |
 | aliasing.cpp:93:12:93:13 | m1 | semmle.label | m1 |
+| simple.cpp:65:5:65:22 | Store [i] | semmle.label | Store [i] |
+| simple.cpp:65:11:65:20 | call to user_input | semmle.label | call to user_input |
+| simple.cpp:66:12:66:12 | Store [i] | semmle.label | Store [i] |
+| simple.cpp:67:13:67:13 | i | semmle.label | i |
 | struct_init.c:20:20:20:29 | call to user_input | semmle.label | call to user_input |
 | struct_init.c:22:11:22:11 | a | semmle.label | a |
 | struct_init.c:27:7:27:16 | call to user_input | semmle.label | call to user_input |
@@ -78,5 +85,6 @@ nodes
 | aliasing.cpp:80:12:80:13 | m1 | aliasing.cpp:79:11:79:20 | call to user_input | aliasing.cpp:80:12:80:13 | m1 | m1 flows from $@ | aliasing.cpp:79:11:79:20 | call to user_input | call to user_input |
 | aliasing.cpp:87:12:87:13 | m1 | aliasing.cpp:86:10:86:19 | call to user_input | aliasing.cpp:87:12:87:13 | m1 | m1 flows from $@ | aliasing.cpp:86:10:86:19 | call to user_input | call to user_input |
 | aliasing.cpp:93:12:93:13 | m1 | aliasing.cpp:92:12:92:21 | call to user_input | aliasing.cpp:93:12:93:13 | m1 | m1 flows from $@ | aliasing.cpp:92:12:92:21 | call to user_input | call to user_input |
+| simple.cpp:67:13:67:13 | i | simple.cpp:65:11:65:20 | call to user_input | simple.cpp:67:13:67:13 | i | i flows from $@ | simple.cpp:65:11:65:20 | call to user_input | call to user_input |
 | struct_init.c:22:11:22:11 | a | struct_init.c:20:20:20:29 | call to user_input | struct_init.c:22:11:22:11 | a | a flows from $@ | struct_init.c:20:20:20:29 | call to user_input | call to user_input |
 | struct_init.c:31:23:31:23 | a | struct_init.c:27:7:27:16 | call to user_input | struct_init.c:31:23:31:23 | a | a flows from $@ | struct_init.c:27:7:27:16 | call to user_input | call to user_input |