C++: Introduce new predicate for better performance in models.

geoffw0 · geoffw0 · commit b8e6ad892214 · 2021-01-19T08:46:52.000Z
diff --git a/cpp/ql/src/semmle/code/cpp/Function.qll b/cpp/ql/src/semmle/code/cpp/Function.qll
@@ -334,6 +334,18 @@ class Function extends Declaration, ControlFlowNode, AccessHolder, @function {
     )
   }
 
+  /**
+   * Gets the class of which this function, called `name`, is a member.
+   *
+   * Prefer to use `getDeclaringType()` or `getName()` directly if you do not
+   * need to reason about both.
+   */
+  pragma[nomagic]
+  Class getClassAndName(string myName) {
+    this.hasName(myName) and
+    this.getDeclaringType() = result
+  }
+
   /**
    * Implements `ControlFlowNode.getControlFlowScope`. The `Function` is
    * used to represent the exit node of the control flow graph, so it is
diff --git a/cpp/ql/src/semmle/code/cpp/models/implementations/StdString.qll b/cpp/ql/src/semmle/code/cpp/models/implementations/StdString.qll
@@ -69,7 +69,7 @@ private class StdStringConstructor extends Constructor, TaintFunction {
  * The `std::string` function `c_str`.
  */
 private class StdStringCStr extends TaintFunction {
-  StdStringCStr() { this.getDeclaringType() instanceof StdBasicString and this.hasName("c_str") }
+  StdStringCStr() { this.getClassAndName("c_str") instanceof StdBasicString }
 
   override predicate hasTaintFlow(FunctionInput input, FunctionOutput output) {
     // flow from string itself (qualifier) to return value
