Make maps in monomorphic IC stubs weak.

src/objects.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 11517 matching lines @@
 
 
 void Map::AddDependentCode(DependentCode::DependencyGroup group,
                            Handle<Code> code) {
   Handle<DependentCode> codes = DependentCode::Insert(
       Handle<DependentCode>(dependent_code()), group, code);
   if (*codes != dependent_code()) set_dependent_code(*codes);
 }
 
 
+void Map::AddDependentIC(Handle<Code> stub) {
+  ASSERT(stub->next_code_link()->IsUndefined());
+  int n = dependent_code()->number_of_entries(DependentCode::kWeakICGroup);
+  if (n == 0) {
+    // Slow path: insert the head of the list with possible heap allocation.
+    AddDependentCode(DependentCode::kWeakICGroup, stub);
+  } else {
+    // Fast path: link the stub to the existing head of the list without any
+    // heap allocation.
+    ASSERT(n == 1);
+    dependent_code()->AddToDependentICList(stub);
+  }
+}
+
+
 DependentCode::GroupStartIndexes::GroupStartIndexes(DependentCode* entries) {
   Recompute(entries);
 }
 
 
 void DependentCode::GroupStartIndexes::Recompute(DependentCode* entries) {
   start_indexes_[0] = 0;
   for (int g = 1; g <= kGroupCount; g++) {
     int count = entries->number_of_entries(static_cast<DependencyGroup>(g - 1));
     start_indexes_[g] = start_indexes_[g - 1] + count;
@@ skipping 110 matching lines @@
   set_number_of_entries(group, end - start - 1);
 
 #ifdef DEBUG
   for (int i = start; i < end - 1; i++) {
     ASSERT(is_code_at(i) || compilation_info_at(i) != info);
   }
 #endif
 }
 
 
+static bool CodeListContains(Object* head, Code* code) {
+  while (!head->IsUndefined()) {
+    if (head == code) return true;
+    head = Code::cast(head)->next_code_link();
+  }
+  return false;
+}
+
+
 bool DependentCode::Contains(DependencyGroup group, Code* code) {
   GroupStartIndexes starts(this);
   int start = starts.at(group);
   int end = starts.at(group + 1);
+  if (group == kWeakICGroup) {
+    return CodeListContains(object_at(start), code);
+  }
   for (int i = start; i < end; i++) {
     if (object_at(i) == code) return true;
   }
   return false;
 }
 
 
 bool DependentCode::MarkCodeForDeoptimization(
     Isolate* isolate,
     DependentCode::DependencyGroup group) {
@@ skipping 36 matching lines @@
     Isolate* isolate,
     DependentCode::DependencyGroup group) {
   ASSERT(AllowCodeDependencyChange::IsAllowed());
   DisallowHeapAllocation no_allocation_scope;
   bool marked = MarkCodeForDeoptimization(isolate, group);
 
   if (marked) Deoptimizer::DeoptimizeMarkedCode(isolate);
 }
 
 
+void DependentCode::AddToDependentICList(Handle<Code> stub) {
+  DisallowHeapAllocation no_heap_allocation;
+  GroupStartIndexes starts(this);
+  int i = starts.at(kWeakICGroup);
+  stub->set_next_code_link(object_at(i));
+  set_object_at(i, *stub);
+}
+
+
 Handle<Object> JSObject::SetPrototype(Handle<JSObject> object,
                                       Handle<Object> value,
                                       bool skip_hidden_prototypes) {
 #ifdef DEBUG
   int size = object->Size();
 #endif
 
   Isolate* isolate = object->GetIsolate();
   Heap* heap = isolate->heap();
   // Silently ignore the change if value is not a JSObject or null.
@@ skipping 4723 matching lines @@
 #define ERROR_MESSAGES_TEXTS(C, T) T,
   static const char* error_messages_[] = {
       ERROR_MESSAGES_LIST(ERROR_MESSAGES_TEXTS)
   };
 #undef ERROR_MESSAGES_TEXTS
   return error_messages_[reason];
 }
 
 
 } }  // namespace v8::internal