Guard the debug check at the start of every JS function with...

src/ia32/virtual-frame-ia32.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 437 matching lines @@
     }
   }
 }
 
 
 void VirtualFrame::Enter() {
   // Registers live on entry: esp, ebp, esi, edi.
   Comment cmnt(masm(), "[ Enter JS frame");
 
 #ifdef DEBUG
-  // Verify that edi contains a JS function.  The following code
-  // relies on eax being available for use.
-  __ test(edi, Immediate(kSmiTagMask));
-  __ Check(not_zero,
-           "VirtualFrame::Enter - edi is not a function (smi check).");
-  __ CmpObjectType(edi, JS_FUNCTION_TYPE, eax);
-  __ Check(equal,
-           "VirtualFrame::Enter - edi is not a function (map check).");
+  if (FLAG_debug_code) {
+    // Verify that edi contains a JS function.  The following code
+    // relies on eax being available for use.
+    __ test(edi, Immediate(kSmiTagMask));
+    __ Check(not_zero,
+             "VirtualFrame::Enter - edi is not a function (smi check).");
+    __ CmpObjectType(edi, JS_FUNCTION_TYPE, eax);
+    __ Check(equal,
+             "VirtualFrame::Enter - edi is not a function (map check).");
+  }
 #endif
 
   EmitPush(ebp);
 
   __ mov(ebp, Operand(esp));
 
   // Store the context in the frame.  The context is kept in esi and a
   // copy is stored in the frame.  The external reference to esi
   // remains.
   EmitPush(esi);
@@ skipping 601 matching lines @@
   ASSERT(stack_pointer_ == element_count() - 1);
   elements_.Add(FrameElement::MemoryElement());
   stack_pointer_++;
   __ push(immediate);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal