Speed up the inner loop of free register allocation.

src/register-allocator.cc

 // Copyright 2009 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 65 matching lines @@
   }
 }
 
 
 // -------------------------------------------------------------------------
 // RegisterAllocator implementation.
 
 
 Result RegisterAllocator::AllocateWithoutSpilling() {
   // Return the first free register, if any.
-  for (int i = 0; i < kNumRegisters; i++) {
-    if (!is_used(i)) {
-      Register free_reg = { i };
-      return Result(free_reg, cgen_);
-    }
+  int free_reg = registers_.ScanForFreeRegister();
+  if (free_reg < kNumRegisters) {
+    Register free_result = { free_reg };
+    return Result(free_result, cgen_);
   }
   return Result(cgen_);
 }
 
 
 Result RegisterAllocator::Allocate() {
   Result result = AllocateWithoutSpilling();
   if (!result.is_valid()) {
     // Ask the current frame to spill a register.
     ASSERT(cgen_->has_valid_frame());
@@ skipping 19 matching lines @@
     cgen_->frame()->Spill(target);
     ASSERT(!is_used(target));
     return Result(target, cgen_);
   }
   // Otherwise (if it's referenced outside the frame) we cannot allocate it.
   return Result(cgen_);
 }
 
 
 } }  // namespace v8::internal