Internalize strings in-place

src/runtime/runtime-internal.cc

 // Copyright 2014 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/runtime/runtime-utils.h"
 
 #include <memory>
 
 #include "src/arguments.h"
 #include "src/ast/prettyprinter.h"
@@ skipping 281 matching lines @@
   bool double_align = AllocateDoubleAlignFlag::decode(flags);
   AllocationSpace space = AllocateTargetSpace::decode(flags);
   CHECK(size <= kMaxRegularHeapObjectSize || space == LO_SPACE);
   return *isolate->factory()->NewFillerObject(size, double_align, space);
 }
 
 RUNTIME_FUNCTION(Runtime_AllocateSeqOneByteString) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_SMI_ARG_CHECKED(length, 0);
+  if (length == 0) return isolate->heap()->empty_string();
   Handle<SeqOneByteString> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result, isolate->factory()->NewRawOneByteString(length));
   return *result;
 }
 
 RUNTIME_FUNCTION(Runtime_AllocateSeqTwoByteString) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_SMI_ARG_CHECKED(length, 0);
+  if (length == 0) return isolate->heap()->empty_string();
   Handle<SeqTwoByteString> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result, isolate->factory()->NewRawTwoByteString(length));
   return *result;
 }
 
 
 RUNTIME_FUNCTION(Runtime_IS_VAR) {
   UNREACHABLE();  // implemented as macro in the parser
   return NULL;
@@ skipping 169 matching lines @@
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_ARG_HANDLE_CHECKED(JSFunction, target, 0);
   Handle<JSObject> global_proxy(target->global_proxy(), isolate);
   return *isolate->factory()->ToBoolean(
       Builtins::AllowDynamicFunction(isolate, target, global_proxy));
 }
 
 }  // namespace internal
 }  // namespace v8