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

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
===================================================================
--- src/x64/codegen-x64.cc	(revision 3528)
+++ src/x64/codegen-x64.cc	(working copy)
@@ -6598,16 +6598,13 @@
   __ movq(rdx, Operand(rbp, StandardFrameConstants::kCallerFPOffset));
   __ SmiCompare(Operand(rdx, StandardFrameConstants::kContextOffset),
                 Smi::FromInt(StackFrame::ARGUMENTS_ADAPTOR));
-  __ j(equal, &adaptor);
 
-  // Nothing to do: The formal number of parameters has already been
-  // passed in register rax by calling function. Just return it.
-  __ ret(0);
-
   // Arguments adaptor case: Read the arguments length from the
   // adaptor frame and return it.
-  __ bind(&adaptor);
-  __ movq(rax, Operand(rdx, ArgumentsAdaptorFrameConstants::kLengthOffset));
+  // Otherwise nothing to do: The number of formal parameters has already been
+  // passed in register eax by calling function. Just return it.
+  __ cmovq(equal, rax,
+           Operand(rdx, ArgumentsAdaptorFrameConstants::kLengthOffset));
   __ ret(0);
 }