provides a mechanism for optimizing compilers to select the different Register configuration.

src/compiler/register-allocator.cc

 // Copyright 2014 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 "src/base/adapters.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/register-allocator.h"
 #include "src/string-stream.h"
 
 namespace v8 {
@@ skipping 17 matching lines @@
 
 int GetRegisterCount(const RegisterConfiguration* cfg, RegisterKind kind) {
   return kind == DOUBLE_REGISTERS ? cfg->num_double_registers()
                                   : cfg->num_general_registers();
 }
 
 
 int GetAllocatableRegisterCount(const RegisterConfiguration* cfg,
                                 RegisterKind kind) {
   return kind == DOUBLE_REGISTERS
-             ? cfg->num_allocatable_aliased_double_registers()
+             ? cfg->num_allocatable_aliased_double_registers(true)
              : cfg->num_allocatable_general_registers();
 }
 
 
 const int* GetAllocatableRegisterCodes(const RegisterConfiguration* cfg,
                                        RegisterKind kind) {
   return kind == DOUBLE_REGISTERS ? cfg->allocatable_double_codes()
                                   : cfg->allocatable_general_codes();
 }
 
@@ skipping 1900 matching lines @@
         int code = config()->GetAllocatableGeneralCode(i);
         if (!IsOutputRegisterOf(instr, Register::from_code(code))) {
           auto range = FixedLiveRangeFor(code);
           range->AddUseInterval(curr_position, curr_position.End(),
                                 allocation_zone());
         }
       }
     }
 
     if (instr->ClobbersDoubleRegisters()) {
-      for (int i = 0; i < config()->num_allocatable_aliased_double_registers();
-           ++i) {
+      for (int i = 0;
+           i < config()->num_allocatable_aliased_double_registers(true); ++i) {
         int code = config()->GetAllocatableDoubleCode(i);
         if (!IsOutputDoubleRegisterOf(instr, DoubleRegister::from_code(code))) {
           auto range = FixedDoubleLiveRangeFor(code);
           range->AddUseInterval(curr_position, curr_position.End(),
                                 allocation_zone());
         }
       }
     }
 
     for (size_t i = 0; i < instr->InputCount(); i++) {
@@ skipping 1422 matching lines @@
     auto eliminate = moves->PrepareInsertAfter(move);
     to_insert.push_back(move);
     if (eliminate != nullptr) to_eliminate.push_back(eliminate);
   }
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8