Fix an error in optimized modulus operator, add unit test.

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 7362 matching lines @@
       Register right_reg = right.reg();
       left.Unuse();
       right.Unuse();
       edx_reg.Unuse();
       __ cmp(right_reg, 0);
       // Ensure divisor is positive: no chance of non-int32 or -0 result.
       unsafe_bailout_->Branch(less_equal);
       __ cdq();  // Sign-extend eax into edx:eax
       __ idiv(right_reg);
       if (op == Token::MOD) {
+        // Negative zero can arise as a negative divident with a zero result.
+        if (!node->no_negative_zero()) {
+          Label not_negative_zero;
+          __ test(edx, Operand(edx));
+          __ j(not_zero, &not_negative_zero);
+          __ test(eax, Operand(eax));
+          unsafe_bailout_->Branch(negative);
+          __ bind(&not_negative_zero);
+        }
         Result edx_result(edx, NumberInfo::Integer32());
         edx_result.set_untagged_int32(true);
         frame_->Push(&edx_result);
       } else {
         ASSERT(op == Token::DIV);
         __ test(edx, Operand(edx));
         unsafe_bailout_->Branch(not_equal);
         Result eax_result(eax, NumberInfo::Integer32());
         eax_result.set_untagged_int32(true);
         frame_->Push(&eax_result);
@@ skipping 5138 matching lines @@
 
   // Call the runtime; it returns -1 (less), 0 (equal), or 1 (greater)
   // tagged as a small integer.
   __ bind(&runtime);
   __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
 }
 
 #undef __
 
 } }  // namespace v8::internal