Convert String array index/length hash to BitField

src/x64/macro-assembler-x64.cc

 // Copyright 2012 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_X64
 
 #include "bootstrapper.h"
 #include "codegen.h"
@@ skipping 530 matching lines @@
   return has_frame_ || !stub->SometimesSetsUpAFrame();
 }
 
 
 void MacroAssembler::IndexFromHash(Register hash, Register index) {
   // 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. Even if we subsequently go to
-  // the slow case, converting the key to a smi is always valid.
-  // key: string key
-  // hash: key's hash field, including its array index value.
-  andp(hash, Immediate(String::kArrayIndexValueMask));
-  shrp(hash, Immediate(String::kHashShift));
-  // Here we actually clobber the key which will be used if calling into
-  // runtime later. However as the new key is the numeric value of a string key
-  // there is no difference in using either key.
-  Integer32ToSmi(index, hash);
+  if (!hash.is(index)) {
+    movl(index, hash);
+  }
+  DecodeFieldToSmi<String::ArrayIndexValueBits>(index);
 }
 
 
 void MacroAssembler::CallRuntime(const Runtime::Function* f,
                                  int num_arguments,
                                  SaveFPRegsMode save_doubles) {
   // If the expected number of arguments of the runtime function is
   // constant, we check that the actual number of arguments match the
   // expectation.
   CHECK(f->nargs < 0 || f->nargs == num_arguments);
@@ skipping 4646 matching lines @@
   if (ms.shift() > 0) sarl(rdx, Immediate(ms.shift()));
   movl(rax, dividend);
   shrl(rax, Immediate(31));
   addl(rdx, rax);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64