Avoid creating weak cells for literal arrays that are empty of literals.

src/objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 11592 matching lines @@
   } else {
     Handle<FixedArray> old_code_map(shared->optimized_code_map(), isolate);
     entry = shared->SearchOptimizedCodeMapEntry(*native_context, osr_ast_id);
     if (entry > kSharedCodeIndex) {
       // Just set the code and literals of the entry.
       if (!code.is_null()) {
         Handle<WeakCell> code_cell =
             isolate->factory()->NewWeakCell(code.ToHandleChecked());
         old_code_map->set(entry + kCachedCodeOffset, *code_cell);
       }
-      Handle<WeakCell> literals_cell =
-          isolate->factory()->NewWeakCell(literals);
-      old_code_map->set(entry + kLiteralsOffset, *literals_cell);
+      if (literals->literals_count() == 0) {
+        old_code_map->set(entry + kLiteralsOffset, *literals);
+      } else {
+        Handle<WeakCell> literals_cell =
+            isolate->factory()->NewWeakCell(literals);
+        old_code_map->set(entry + kLiteralsOffset, *literals_cell);
+      }
       return;
     }
 
     // Can we reuse an entry?
     DCHECK(entry < kEntriesStart);
     int length = old_code_map->length();
     for (int i = kEntriesStart; i < length; i += kEntryLength) {
       if (WeakCell::cast(old_code_map->get(i + kContextOffset))->cleared()) {
         new_code_map = old_code_map;
         entry = i;
@@ skipping 10 matching lines @@
       // holes. For now we just give up on adding the entry and pretend it got
       // flushed.
       if (shared->OptimizedCodeMapIsCleared()) return;
       entry = old_code_map->length();
     }
   }
 
   Handle<WeakCell> code_cell =
       code.is_null() ? isolate->factory()->empty_weak_cell()
                      : isolate->factory()->NewWeakCell(code.ToHandleChecked());
-  Handle<WeakCell> literals_cell = isolate->factory()->NewWeakCell(literals);
   WeakCell* context_cell = native_context->self_weak_cell();
 
   new_code_map->set(entry + kContextOffset, context_cell);
   new_code_map->set(entry + kCachedCodeOffset, *code_cell);
-  new_code_map->set(entry + kLiteralsOffset, *literals_cell);
+
+  if (literals->literals_count() == 0) {
+    new_code_map->set(entry + kLiteralsOffset, *literals);
+  } else {
+    Handle<WeakCell> literals_cell = isolate->factory()->NewWeakCell(literals);
+    new_code_map->set(entry + kLiteralsOffset, *literals_cell);
+  }
+
   new_code_map->set(entry + kOsrAstIdOffset, Smi::FromInt(osr_ast_id.ToInt()));
 
 #ifdef DEBUG
   for (int i = kEntriesStart; i < new_code_map->length(); i += kEntryLength) {
     WeakCell* cell = WeakCell::cast(new_code_map->get(i + kContextOffset));
     DCHECK(cell->cleared() || cell->value()->IsNativeContext());
     cell = WeakCell::cast(new_code_map->get(i + kCachedCodeOffset));
     DCHECK(cell->cleared() ||
            (cell->value()->IsCode() &&
             Code::cast(cell->value())->kind() == Code::OPTIMIZED_FUNCTION));
-    cell = WeakCell::cast(new_code_map->get(i + kLiteralsOffset));
-    DCHECK(cell->cleared() || cell->value()->IsFixedArray());
+    Object* lits = new_code_map->get(i + kLiteralsOffset);
+    if (lits->IsWeakCell()) {
+      cell = WeakCell::cast(lits);
+      DCHECK(cell->cleared() ||
+             (cell->value()->IsLiteralsArray() &&
+              LiteralsArray::cast(cell->value())->literals_count() > 0));
+    } else {
+      DCHECK(lits->IsLiteralsArray() &&
+             LiteralsArray::cast(lits)->literals_count() == 0);
+    }
     DCHECK(new_code_map->get(i + kOsrAstIdOffset)->IsSmi());
   }
 #endif
 
   FixedArray* old_code_map = shared->optimized_code_map();
   if (old_code_map != *new_code_map) {
     shared->set_optimized_code_map(*new_code_map);
   }
 }
 
@@ skipping 1597 matching lines @@
     if (entry == kSharedCodeIndex) {
       // We know the weak cell isn't cleared because we made sure of it in
       // SearchOptimizedCodeMapEntry and performed no allocations since that
       // call.
       result = {
           Code::cast(WeakCell::cast(code_map->get(kSharedCodeIndex))->value()),
           nullptr};
     } else {
       DCHECK_LE(entry + kEntryLength, code_map->length());
       WeakCell* cell = WeakCell::cast(code_map->get(entry + kCachedCodeOffset));
-      WeakCell* literals_cell =
-          WeakCell::cast(code_map->get(entry + kLiteralsOffset));
-
+      Object* lits = code_map->get(entry + kLiteralsOffset);
+      LiteralsArray* literals = nullptr;
+      if (lits->IsWeakCell()) {
+        WeakCell* literal_cell = WeakCell::cast(lits);
+        if (!literal_cell->cleared()) {
+          literals = LiteralsArray::cast(literal_cell->value());
+        }
+      } else {
+        literals = LiteralsArray::cast(lits);
+      }
       result = {cell->cleared() ? nullptr : Code::cast(cell->value()),
-                literals_cell->cleared()
-                    ? nullptr
-                    : LiteralsArray::cast(literals_cell->value())};
+                literals};
     }
   }
   return result;
 }
 
 
 #define DECLARE_TAG(ignore1, name, ignore2) name,
 const char* const VisitorSynchronization::kTags[
     VisitorSynchronization::kNumberOfSyncTags] = {
   VISITOR_SYNCHRONIZATION_TAGS_LIST(DECLARE_TAG)
@@ skipping 5488 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8