Add JSFunction -> CodeBlock edge in heap snapshot

Summary: Adds a "shortcut" edge ( = internal, non-retaining, named) from each `JSFunction` to its `CodeBlock`.

Reviewed By: dulinriley

Differential Revision: D26583520

fbshipit-source-id: 81220f6d24ac9828abee348c12e3416a9876f121

include/hermes/VM/Callable.h

@@ -1037,6 +1037,7 @@ class JSFunction : public Callable {
   static std::string _snapshotNameImpl(GCCell *cell, GC *gc);
   static void
   _snapshotAddLocationsImpl(GCCell *cell, GC *gc, HeapSnapshot &snap);
+  static void _snapshotAddEdgesImpl(GCCell *cell, GC *gc, HeapSnapshot &snap);
 };
 
 /// A function which interprets code and returns a Async Function when called.

lib/VM/Callable.cpp

@@ -1311,6 +1311,21 @@ std::string JSFunction::_snapshotNameImpl(GCCell *cell, GC *gc) {
   return self->codeBlock_->getNameString(gc->getCallbacks());
 }
 
+void JSFunction::_snapshotAddEdgesImpl(
+    GCCell *cell,
+    GC *gc,
+    HeapSnapshot &snap) {
+  auto *const self = vmcast<JSFunction>(cell);
+  // Add the super type's edges too.
+  Callable::_snapshotAddEdgesImpl(self, gc, snap);
+
+  // A node for the code block will be added as part of the RuntimeModule.
+  snap.addNamedEdge(
+      HeapSnapshot::EdgeType::Shortcut,
+      "codeBlock",
+      gc->getIDTracker().getNativeID(self->codeBlock_));
+}
+
 void JSFunction::_snapshotAddLocationsImpl(
     GCCell *cell,
     GC *gc,

unittests/VMRuntime/HeapSnapshotTest.cpp

@@ -771,7 +771,7 @@ TEST_F(HeapSnapshotRuntimeTest, FunctionLocationForLazyCode) {
       "myGlobal",
       funcID,
       func->getAllocatedSize(),
-      6};
+      7};
   EXPECT_EQ(node, expected);
   // Edges aren't tested in this test.
 
@@ -814,7 +814,7 @@ TEST_F(HeapSnapshotRuntimeTest, FunctionLocationAndNameTest) {
       "foo",
       funcID,
       func->getAllocatedSize(),
-      6};
+      7};
   EXPECT_EQ(node, expected);
   // Edges aren't tested in this test.
 
@@ -858,7 +858,7 @@ TEST_F(HeapSnapshotRuntimeTest, FunctionDisplayNameTest) {
       "bar",
       funcID,
       func->getAllocatedSize(),
-      11};
+      12};
   EXPECT_EQ(node, expected);
 }