[RegisterConfiguration] Streamline access to arch defaults, simplify Registers.

src/x64/code-stubs-x64.h

 // Copyright 2011 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.
 
 #ifndef V8_X64_CODE_STUBS_X64_H_
 #define V8_X64_CODE_STUBS_X64_H_
 
 namespace v8 {
 namespace internal {
 
@@ skipping 277 matching lines @@
     Register object_;
     Register address_;
     Register scratch0_;
     Register scratch1_;
     // Third scratch register is always rcx.
 
     Register GetRegThatIsNotRcxOr(Register r1,
                                   Register r2,
                                   Register r3) {
       for (int i = 0; i < Register::kNumRegisters; i++) {
-        Register candidate = Register::from_code(i);
-        if (candidate.IsAllocatable()) {
+        if (RegisterConfiguration::Crankshaft()->IsAllocatableGeneralCode(i)) {
+          Register candidate = Register::from_code(i);
           if (candidate.is(rcx)) continue;
           if (candidate.is(r1)) continue;
           if (candidate.is(r2)) continue;
           if (candidate.is(r3)) continue;
           return candidate;
         }
       }
       UNREACHABLE();
       return no_reg;
     }
@@ skipping 49 matching lines @@
   RegisterAllocation regs_;
 
   DISALLOW_COPY_AND_ASSIGN(RecordWriteStub);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_X64_CODE_STUBS_X64_H_