Add full TurboFan support for accessing SeqString contents.

src/compiler/access-builder.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/compiler/access-builder.h"
 #include "src/types-inl.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
@@ skipping 98 matching lines @@
       return {taggedness, header_size, Type::Unsigned32(), kMachUint32};
     case kExternalFloat32Array:
       return {taggedness, header_size, Type::Number(), kMachFloat32};
     case kExternalFloat64Array:
       return {taggedness, header_size, Type::Number(), kMachFloat64};
   }
   UNREACHABLE();
   return {kUntaggedBase, 0, Type::None(), kMachNone};
 }
 
+
+// static
+ElementAccess AccessBuilder::ForSeqStringChar(String::Encoding encoding) {
+  switch (encoding) {
+    case String::ONE_BYTE_ENCODING:
+      return {kTaggedBase, SeqString::kHeaderSize, Type::Unsigned32(),
+              kMachUint8};
+    case String::TWO_BYTE_ENCODING:
+      return {kTaggedBase, SeqString::kHeaderSize, Type::Unsigned32(),
+              kMachUint16};
+  }
+  UNREACHABLE();
+  return {kUntaggedBase, 0, Type::None(), kMachNone};
+}
+
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8