C++/C#/Java: Split localFlowStep predicate in two

There's now a `localFlowStep` predicate for use directly in queries and
other libraries and a `simpleLocalFlowStep` for use only by the global
data flow library. The former predicate is intended to include field
flow, but the latter may not.

This will let Java and C# (and possibly C++ IR) avoid getting two kinds
of field flow at the same time, both from SSA and from the global data
flow library. It should let C++ AST add some form of field flow to
`localFlowStep` without making it an input to the global data flow
library.

Author: jbj

cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowImpl.qll

@@ -162,7 +162,7 @@ private predicate isAdditionalFlowStep(
  * Holds if data can flow in one local step from `node1` to `node2`.
  */
 private predicate localFlowStep(Node node1, Node node2, Configuration config) {
-  localFlowStep(node1, node2) and
+  simpleLocalFlowStep(node1, node2) and
   not outBarrier(node1, config) and
   not inBarrier(node2, config) and
   not fullBarrier(node1, config) and

cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowImpl2.qll

@@ -162,7 +162,7 @@ private predicate isAdditionalFlowStep(
  * Holds if data can flow in one local step from `node1` to `node2`.
  */
 private predicate localFlowStep(Node node1, Node node2, Configuration config) {
-  localFlowStep(node1, node2) and
+  simpleLocalFlowStep(node1, node2) and
   not outBarrier(node1, config) and
   not inBarrier(node2, config) and
   not fullBarrier(node1, config) and

cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowImpl3.qll

@@ -162,7 +162,7 @@ private predicate isAdditionalFlowStep(
  * Holds if data can flow in one local step from `node1` to `node2`.
  */
 private predicate localFlowStep(Node node1, Node node2, Configuration config) {
-  localFlowStep(node1, node2) and
+  simpleLocalFlowStep(node1, node2) and
   not outBarrier(node1, config) and
   not inBarrier(node2, config) and
   not fullBarrier(node1, config) and

cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowImpl4.qll

@@ -162,7 +162,7 @@ private predicate isAdditionalFlowStep(
  * Holds if data can flow in one local step from `node1` to `node2`.
  */
 private predicate localFlowStep(Node node1, Node node2, Configuration config) {
-  localFlowStep(node1, node2) and
+  simpleLocalFlowStep(node1, node2) and
   not outBarrier(node1, config) and
   not inBarrier(node2, config) and
   not fullBarrier(node1, config) and

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

@@ -422,8 +422,18 @@ private module ThisFlow {
  * Holds if data flows from `nodeFrom` to `nodeTo` in exactly one local
  * (intra-procedural) step.
  */
-cached
 predicate localFlowStep(Node nodeFrom, Node nodeTo) {
+  simpleLocalFlowStep(nodeFrom, nodeTo)
+}
+
+/**
+ * INTERNAL: do not use.
+ *
+ * This is the local flow predicate that's used as a building block in global
+ * data flow. It may have less flow than the `localFlowStep` predicate.
+ */
+cached
+predicate simpleLocalFlowStep(Node nodeFrom, Node nodeTo) {
   // Expr -> Expr
   exprToExprStep_nocfg(nodeFrom.asExpr(), nodeTo.asExpr())
   or

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

@@ -162,7 +162,7 @@ private predicate isAdditionalFlowStep(
  * Holds if data can flow in one local step from `node1` to `node2`.
  */
 private predicate localFlowStep(Node node1, Node node2, Configuration config) {
-  localFlowStep(node1, node2) and
+  simpleLocalFlowStep(node1, node2) and
   not outBarrier(node1, config) and
   not inBarrier(node2, config) and
   not fullBarrier(node1, config) and

cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowImpl2.qll

@@ -162,7 +162,7 @@ private predicate isAdditionalFlowStep(
  * Holds if data can flow in one local step from `node1` to `node2`.
  */
 private predicate localFlowStep(Node node1, Node node2, Configuration config) {
-  localFlowStep(node1, node2) and
+  simpleLocalFlowStep(node1, node2) and
   not outBarrier(node1, config) and
   not inBarrier(node2, config) and
   not fullBarrier(node1, config) and

cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowImpl3.qll

@@ -162,7 +162,7 @@ private predicate isAdditionalFlowStep(
  * Holds if data can flow in one local step from `node1` to `node2`.
  */
 private predicate localFlowStep(Node node1, Node node2, Configuration config) {
-  localFlowStep(node1, node2) and
+  simpleLocalFlowStep(node1, node2) and
   not outBarrier(node1, config) and
   not inBarrier(node2, config) and
   not fullBarrier(node1, config) and

cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowImpl4.qll

@@ -162,7 +162,7 @@ private predicate isAdditionalFlowStep(
  * Holds if data can flow in one local step from `node1` to `node2`.
  */
 private predicate localFlowStep(Node node1, Node node2, Configuration config) {
-  localFlowStep(node1, node2) and
+  simpleLocalFlowStep(node1, node2) and
   not outBarrier(node1, config) and
   not inBarrier(node2, config) and
   not fullBarrier(node1, config) and

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

@@ -156,6 +156,16 @@ UninitializedNode uninitializedNode(LocalVariable v) { result.getLocalVariable()
  * (intra-procedural) step.
  */
 predicate localFlowStep(Node nodeFrom, Node nodeTo) {
+  simpleLocalFlowStep(nodeFrom, nodeTo)
+}
+
+/**
+ * INTERNAL: do not use.
+ *
+ * This is the local flow predicate that's used as a building block in global
+ * data flow. It may have less flow than the `localFlowStep` predicate.
+ */
+predicate simpleLocalFlowStep(Node nodeFrom, Node nodeTo) {
   nodeTo.(CopyInstruction).getSourceValue() = nodeFrom or
   nodeTo.(PhiInstruction).getAnOperand().getDef() = nodeFrom or
   // Treat all conversions as flow, even conversions between different numeric types.