Fast allocation of block contexts.

src/full-codegen.cc

 // Copyright 2011 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 800 matching lines @@
 void FullCodeGenerator::VisitBlock(Block* stmt) {
   Comment cmnt(masm_, "[ Block");
   NestedBlock nested_block(this, stmt);
   SetStatementPosition(stmt);
 
   Scope* saved_scope = scope();
   // Push a block context when entering a block with block scoped variables.
   if (stmt->block_scope() != NULL) {
     { Comment cmnt(masm_, "[ Extend block context");
       scope_ = stmt->block_scope();
-      __ Push(scope_->GetSerializedScopeInfo());
+      Handle<SerializedScopeInfo> scope_info = scope_->GetSerializedScopeInfo();
+      int heap_slots =
+          scope_info->NumberOfContextSlots() - Context::MIN_CONTEXT_SLOTS;
+      __ Push(scope_info);
       PushFunctionArgumentForContextAllocation();
-      __ CallRuntime(Runtime::kPushBlockContext, 2);
+      if (heap_slots <= FastNewBlockContextStub::kMaximumSlots) {
+        FastNewBlockContextStub stub(heap_slots);
+        __ CallStub(&stub);
+      } else {
+        __ CallRuntime(Runtime::kPushBlockContext, 2);
+      }
+
+      // Replace the context stored in the frame.
       StoreToFrameField(StandardFrameConstants::kContextOffset,
                         context_register());
     }
     { Comment cmnt(masm_, "[ Declarations");
       VisitDeclarations(scope_->declarations());
     }
   }
   PrepareForBailoutForId(stmt->EntryId(), NO_REGISTERS);
   VisitStatements(stmt->statements());
   scope_ = saved_scope;
@@ skipping 501 matching lines @@
   }
 
   return false;
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal