Revert of Remove register index/code indirection

test/cctest/test-code-stubs-ia32.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions 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 52 matching lines @@
   __ push(esi);
   __ push(edi);
 
   if (!source_reg.is(esp)) {
     __ lea(source_reg, MemOperand(esp, 6 * kPointerSize - offset));
   }
 
   int param_offset = 7 * kPointerSize;
   // Save registers make sure they don't get clobbered.
   int reg_num = 0;
-  for (; reg_num < Register::kNumRegisters; ++reg_num) {
-    Register reg = Register::from_code(reg_num);
-    if (reg.IsAllocatable()) {
-      if (!reg.is(esp) && !reg.is(ebp) && !reg.is(destination_reg)) {
-        __ push(reg);
-        param_offset += kPointerSize;
-      }
+  for (;reg_num < Register::NumAllocatableRegisters(); ++reg_num) {
+    Register reg = Register::FromAllocationIndex(reg_num);
+    if (!reg.is(esp) && !reg.is(ebp) && !reg.is(destination_reg)) {
+      __ push(reg);
+      param_offset += kPointerSize;
     }
   }
 
   // Re-push the double argument
   __ push(MemOperand(esp, param_offset));
   __ push(MemOperand(esp, param_offset));
 
   // Call through to the actual stub
   __ call(start, RelocInfo::EXTERNAL_REFERENCE);
 
   __ add(esp, Immediate(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(esp) && !reg.is(ebp) && !reg.is(destination_reg)) {
-        __ cmp(reg, MemOperand(esp, 0));
-        __ Assert(equal, kRegisterWasClobbered);
-        __ add(esp, Immediate(kPointerSize));
-      }
+    Register reg = Register::FromAllocationIndex(reg_num);
+    if (!reg.is(esp) && !reg.is(ebp) && !reg.is(destination_reg)) {
+      __ cmp(reg, MemOperand(esp, 0));
+      __ Assert(equal, kRegisterWasClobbered);
+      __ add(esp, Immediate(kPointerSize));
     }
   }
 
   __ mov(eax, destination_reg);
 
   __ pop(edi);
   __ pop(esi);
   __ pop(edx);
   __ pop(ecx);
   __ pop(ebx);
@@ skipping 32 matching lines @@
 
   for (size_t s = 0; s < sizeof(source_registers) / sizeof(Register); s++) {
     for (size_t d = 0; d < sizeof(dest_registers) / sizeof(Register); d++) {
       RunAllTruncationTests(
           MakeConvertDToIFuncTrampoline(isolate,
                                         source_registers[s],
                                         dest_registers[d]));
     }
   }
 }