Use cmov instructions to avoid some conditional branches in stub code....

src/x64/stub-cache-x64.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 1809 matching lines @@
 
   // rax: argc
   // rcx: first argument
   // rdx: JSObject (untagged)
   // r8: undefined
   // r9: first in-object property of the JSObject
   // Fill the initialized properties with a constant value or a passed argument
   // depending on the this.x = ...; assignment in the function.
   for (int i = 0; i < shared->this_property_assignments_count(); i++) {
     if (shared->IsThisPropertyAssignmentArgument(i)) {
-      Label not_passed;
-      // Set the property to undefined.
-      __ movq(Operand(r9, i * kPointerSize), r8);
       // Check if the argument assigned to the property is actually passed.
+      // If argument is not passed the property is set to undefined,
+      // otherwise find it on the stack.
       int arg_number = shared->GetThisPropertyAssignmentArgument(i);
+      __ movq(rbx, r8);
       __ cmpq(rax, Immediate(arg_number));
-      __ j(below_equal, &not_passed);
-      // Argument passed - find it on the stack.
-      __ movq(rbx, Operand(rcx, arg_number * -kPointerSize));
+      __ cmovq(above, rbx, Operand(rcx, arg_number * -kPointerSize));
+      // Store value in the property.
       __ movq(Operand(r9, i * kPointerSize), rbx);
-      __ bind(&not_passed);
     } else {
       // Set the property to the constant value.
       Handle<Object> constant(shared->GetThisPropertyAssignmentConstant(i));
       __ Move(Operand(r9, i * kPointerSize), constant);
     }
   }
 
   // Fill the unused in-object property fields with undefined.
   for (int i = shared->this_property_assignments_count();
        i < shared->CalculateInObjectProperties();
@@ skipping 26 matching lines @@
   __ Jump(generic_construct_stub, RelocInfo::CODE_TARGET);
 
   // Return the generated code.
   return GetCode();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal