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

src/ia32/codegen-ia32.cc

 // Copyright 2006-2009 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 7718 matching lines @@
       __ InvokeBuiltin(Builtins::BIT_NOT, JUMP_FUNCTION);
       break;
     default:
       UNREACHABLE();
   }
 }
 
 
 void ArgumentsAccessStub::GenerateReadLength(MacroAssembler* masm) {
   // Check if the calling frame is an arguments adaptor frame.
-  Label adaptor;
   __ mov(edx, Operand(ebp, StandardFrameConstants::kCallerFPOffset));
   __ mov(ecx, Operand(edx, StandardFrameConstants::kContextOffset));
   __ cmp(Operand(ecx), Immediate(Smi::FromInt(StackFrame::ARGUMENTS_ADAPTOR)));
-  __ j(equal, &adaptor);
-
-  // Nothing to do: The formal number of parameters has already been
-  // passed in register eax by calling function. Just return it.
-  __ ret(0);
 
   // Arguments adaptor case: Read the arguments length from the
   // adaptor frame and return it.
-  __ bind(&adaptor);
-  __ mov(eax, Operand(edx, ArgumentsAdaptorFrameConstants::kLengthOffset));
+  // Otherwise nothing to do: The number of formal parameters has already been
+  // passed in register eax by calling function. Just return it.
+  if (CpuFeatures::IsSupported(CMOV)) {
+    CpuFeatures::Scope use_cmov(CMOV);
+    __ cmov(equal, eax,
+            Operand(edx, ArgumentsAdaptorFrameConstants::kLengthOffset));
+  } else {
+    Label exit;
+    __ j(not_equal, &exit);
+    __ mov(eax, Operand(edx, ArgumentsAdaptorFrameConstants::kLengthOffset));
+    __ bind(&exit);
+  }
   __ ret(0);
 }
 
 
 void ArgumentsAccessStub::GenerateReadElement(MacroAssembler* masm) {
   // The key is in edx and the parameter count is in eax.
 
   // The displacement is used for skipping the frame pointer on the
   // stack. It is the offset of the last parameter (if any) relative
   // to the frame pointer.
@@ skipping 1137 matching lines @@
     __ add(Operand(dest), Immediate(2));
   }
   __ sub(Operand(count), Immediate(1));
   __ j(not_zero, &loop);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal