From e2d4bac51e15407ecd2572e493a4106c451fa10b Mon Sep 17 00:00:00 2001
From: Luke Cartey <lcartey@github.com>
Date: Fri, 28 Apr 2023 11:48:53 +0100
Subject: [PATCH 1/2] DCL56-CPP: Improve performance

Frequent use of getAChild*() was causing slow performance, as it
attempted to specialize it for different contexts. We instead replace
getAChild*() with a getAnInitializerExpr predicate, which uses explicit
recursion which experimentally gave better performance.
---
 .../cpp/StaticInitialization.qll              | 23 ++++++++++++-------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/cpp/common/src/codingstandards/cpp/StaticInitialization.qll b/cpp/common/src/codingstandards/cpp/StaticInitialization.qll
index 0a8f5811e0..34c353726d 100644
--- a/cpp/common/src/codingstandards/cpp/StaticInitialization.qll
+++ b/cpp/common/src/codingstandards/cpp/StaticInitialization.qll
@@ -27,6 +27,15 @@ module StaticInitializationGraph {
    *  - Create a `Node` instance for each injector type.
    */
 
+  /**
+   * Gets an Expr directly or indirectly included in an initializer.
+   */
+  private Expr getAnInitializerExpr(Initializer i) {
+    result = i.getExpr()
+    or
+    result = getAnInitializerExpr(i).getAChild()
+  }
+
   newtype TNode =
     TInitializerNode(Initializer i) {
       // This is the initializer of a static storage duration variable
@@ -48,7 +57,7 @@ module StaticInitializationGraph {
     } or
     TFunctionCallNode(FunctionCall fc) {
       // This is a function call that occurs in an initializer called during static initialization
-      exists(TInitializerNode(any(Initializer i | i.getExpr().getAChild*() = fc)))
+      exists(TInitializerNode(any(Initializer i | getAnInitializerExpr(i) = fc)))
       or
       // This is a function call that occurs in a function called during static initialization
       exists(
@@ -56,13 +65,13 @@ module StaticInitializationGraph {
             f = fc.getEnclosingFunction() and
             // Not in an initializer of a local variable, where the desired flow is instead:
             // function -> initializer -> fc
-            not exists(Initializer i | i.getExpr().getAChild*() = fc)
+            not exists(Initializer i | getAnInitializerExpr(i) = fc)
           ))
       )
     } or
     TVariableAccessNode(VariableAccess va) {
       // This is a variable that is accessed in an initializer called during static initialization
-      exists(TInitializerNode(any(Initializer i | i.getExpr().getAChild*() = va)))
+      exists(TInitializerNode(any(Initializer i | getAnInitializerExpr(i) = va)))
       or
       // This is a variable that is accessed in a function called during static initialization
       exists(
@@ -70,7 +79,7 @@ module StaticInitializationGraph {
             f = va.getEnclosingFunction() and
             // Not in an initializer of a local variable, where the desired flow is instead:
             // function -> initializer -> va
-            not exists(Initializer i | i.getExpr().getAChild*() = va)
+            not exists(Initializer i | getAnInitializerExpr(i) = va)
           ))
       )
     }
@@ -149,9 +158,7 @@ module StaticInitializationGraph {
     or
     // Initializer steps
     exists(Initializer i | i = n1.(InitializerNode).getInitializer() |
-      i.getExpr().getAChild*() = n2.(FunctionCallNode).getFunctionCall()
-      or
-      i.getExpr().getAChild*() = n2.(VariableAccessNode).getVariableAccess()
+      getAnInitializerExpr(i) = n2.getExpr()
     )
     or
     // FunctionCall steps
@@ -169,7 +176,7 @@ module StaticInitializationGraph {
       f = n2.getExpr().getEnclosingFunction() and
       // But not in an initializer of a local variable, where the desired flow is instead:
       // function -> initializer -> expression
-      not exists(Initializer i | i.getExpr().getAChild*() = n2.getExpr())
+      not exists(Initializer i | getAnInitializerExpr(i) = n2.getExpr())
       or
       // `n2` is an initializer of a local scope variable within function `f`
       n2.(InitializerNode).getInitializer().getDeclaration().(LocalScopeVariable).getFunction() = f

From 73cc3a4aad6c8d5cf6d7f67671a5bf27a2711240 Mon Sep 17 00:00:00 2001
From: Luke Cartey <lcartey@github.com>
Date: Fri, 28 Apr 2023 12:01:25 +0100
Subject: [PATCH 2/2] Add change note

---
 change_notes/2023-04-28-dcl56-cpp-perf.md | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 change_notes/2023-04-28-dcl56-cpp-perf.md

diff --git a/change_notes/2023-04-28-dcl56-cpp-perf.md b/change_notes/2023-04-28-dcl56-cpp-perf.md
new file mode 100644
index 0000000000..61ce45b133
--- /dev/null
+++ b/change_notes/2023-04-28-dcl56-cpp-perf.md
@@ -0,0 +1 @@
+ * `DCL56-CPP` - performance has been improved for databases with complex initializers.
\ No newline at end of file