Revert of Remove register index/code indirection

test/cctest/test-code-stubs-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Rrdistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Rrdistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Rrdistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 54 matching lines @@
 
   // Push the double argument.
   __ Push(d0);
   __ Mov(source_reg, jssp);
 
   MacroAssembler::PushPopQueue queue(&masm);
 
   // Save registers make sure they don't get clobbered.
   int source_reg_offset = kDoubleSize;
   int reg_num = 0;
-  for (; reg_num < Register::kNumRegisters; ++reg_num) {
+  for (;reg_num < Register::NumAllocatableRegisters(); ++reg_num) {
     Register reg = Register::from_code(reg_num);
-    if (reg.IsAllocatable()) {
-      if (!reg.is(destination_reg)) {
-        queue.Queue(reg);
-        source_reg_offset += kPointerSize;
-      }
+    if (!reg.is(destination_reg)) {
+      queue.Queue(reg);
+      source_reg_offset += kPointerSize;
     }
   }
   // Re-push the double argument.
   queue.Queue(d0);
 
   queue.PushQueued();
 
   // Call through to the actual stub
   if (inline_fastpath) {
     __ Ldr(d0, MemOperand(source_reg));
     __ TryConvertDoubleToInt64(destination_reg, d0, &done);
     if (destination_reg.is(source_reg)) {
       // Restore clobbered source_reg.
       __ add(source_reg, jssp, Operand(source_reg_offset));
     }
   }
   __ Call(start, RelocInfo::EXTERNAL_REFERENCE);
   __ bind(&done);
 
   __ Drop(1, kDoubleSize);
 
   // // Make sure no registers have been unexpectedly clobbered
   for (--reg_num; reg_num >= 0; --reg_num) {
     Register reg = Register::from_code(reg_num);
-    if (reg.IsAllocatable()) {
-      if (!reg.is(destination_reg)) {
-        __ Pop(ip0);
-        __ cmp(reg, ip0);
-        __ Assert(eq, kRegisterWasClobbered);
-      }
+    if (!reg.is(destination_reg)) {
+      __ Pop(ip0);
+      __ cmp(reg, ip0);
+      __ Assert(eq, kRegisterWasClobbered);
     }
   }
 
   __ Drop(1, kDoubleSize);
 
   if (!destination_reg.is(x0))
     __ Mov(x0, destination_reg);
 
   // Restore callee save registers.
   __ Mov(csp, jssp);
@@ skipping 62 matching lines @@
                                         false));
       RunAllTruncationTests(
           RunGeneratedCodeCallWrapper,
           MakeConvertDToIFuncTrampoline(isolate,
                                         source_registers[s],
                                         dest_registers[d],
                                         true));
     }
   }
 }