[ES6 modules] UninstantiatedInclusiveDescendants: skip recursion for instantiated sub-trees.

third_party/WebKit/Source/core/loader/modulescript/ModuleTreeLinker.cpp

Index: third_party/WebKit/Source/core/loader/modulescript/ModuleTreeLinker.cpp
diff --git a/third_party/WebKit/Source/core/loader/modulescript/ModuleTreeLinker.cpp b/third_party/WebKit/Source/core/loader/modulescript/ModuleTreeLinker.cpp
index baceb7eedd23f10e52a9ea52e7ffd19e0cf300e0..b4400f988a3a5b7feee76b8800aa953144895064 100644
--- a/third_party/WebKit/Source/core/loader/modulescript/ModuleTreeLinker.cpp
+++ b/third_party/WebKit/Source/core/loader/modulescript/ModuleTreeLinker.cpp
@@ -451,6 +451,14 @@ ModuleTreeLinker::UninstantiatedInclusiveDescendants() {
     // or null).
     DCHECK(current);
 
+    // [nospec, optimization]
+    // We can safely skip recursing into the descendants if the module graph
+    // node status is "instantiated". The sub-graph is guaranteed to be all
+    // "instantiated", thus never would end up in the "uninstantiated set".
+    if (current->InstantiationState() ==
+        ModuleInstantiationState::kInstantiated)
+      continue;
+
     // Step 4.3. If inclusive descendants and stack both do not contain current,
     // then:
     if (inclusive_descendants.Contains(current))