Convert String array index/length hash to BitField

src/arm64/macro-assembler-arm64.cc

 // Copyright 2013 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 "v8.h"
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "bootstrapper.h"
 #include "codegen.h"
@@ skipping 3957 matching lines @@
 }
 
 
 void MacroAssembler::IndexFromHash(Register hash, Register index) {
   // If the hash field contains an array index pick it out. The assert checks
   // that the constants for the maximum number of digits for an array index
   // cached in the hash field and the number of bits reserved for it does not
   // conflict.
   ASSERT(TenToThe(String::kMaxCachedArrayIndexLength) <
          (1 << String::kArrayIndexValueBits));
-  // We want the smi-tagged index in key.  kArrayIndexValueMask has zeros in
-  // the low kHashShift bits.
-  STATIC_ASSERT(kSmiTag == 0);
-  Ubfx(hash, hash, String::kHashShift, String::kArrayIndexValueBits);
-  SmiTag(index, hash);
+  DecodeField<String::ArrayIndexValueBits>(index, hash);
+  SmiTag(index, index);
 }
 
 
 void MacroAssembler::EmitSeqStringSetCharCheck(
     Register string,
     Register index,
     SeqStringSetCharCheckIndexType index_type,
     Register scratch,
     uint32_t encoding_mask) {
   ASSERT(!AreAliased(string, index, scratch));
@@ skipping 1267 matching lines @@
   }
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM64