Let relational comparison operators quickly compare a string with itself.

src/ia32/codegen-ia32.cc

 // Copyright 2010 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 11671 matching lines @@
     // Test for NaN. Sadly, we can't just compare to Factory::nan_value(),
     // so we do the second best thing - test it ourselves.
     // Note: if cc_ != equal, never_nan_nan_ is not used.
     if (never_nan_nan_ && (cc_ == equal)) {
       __ Set(eax, Immediate(Smi::FromInt(EQUAL)));
       __ ret(0);
     } else {
       Label heap_number;
       __ cmp(FieldOperand(edx, HeapObject::kMapOffset),
              Immediate(Factory::heap_number_map()));
-      if (cc_ == equal) {
-        __ j(equal, &heap_number);
-        // Identical objects are equal for operators ==, !=, and ===.
-        __ Set(eax, Immediate(Smi::FromInt(EQUAL)));
-        __ ret(0);
-      } else {
-        // Identical objects must call ToPrimitive for <, <=, >, and >=.
-        __ j(not_equal, &not_identical);
+      __ j(equal, &heap_number);
+      if (cc_ != equal) {
+        // Call runtime on identical JSObjects.  Otherwise return equal.
+        __ CmpObjectType(eax, FIRST_JS_OBJECT_TYPE, ecx);
+        __ j(above_equal, &not_identical);
       }
+      __ Set(eax, Immediate(Smi::FromInt(EQUAL)));
+      __ ret(0);
+
       __ bind(&heap_number);
       // It is a heap number, so return non-equal if it's NaN and equal if
       // it's not NaN.
       // The representation of NaN values has all exponent bits (52..62) set,
       // and not all mantissa bits (0..51) clear.
       // We only accept QNaNs, which have bit 51 set.
       // Read top bits of double representation (second word of value).
 
       // Value is a QNaN if value & kQuietNaNMask == kQuietNaNMask, i.e.,
       // all bits in the mask are set. We only need to check the word
@@ skipping 2059 matching lines @@
   masm.GetCode(&desc);
   // Call the function from C++.
   return FUNCTION_CAST<MemCopyFunction>(buffer);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32