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

Review URL: http://codereview.chromium.org/1118008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4235 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/ia32/codegen-ia32.cc

@@ -7380,6 +7380,15 @@ void CodeGenerator::Int32BinaryOperation(BinaryOperation* node) {
       __ 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);

test/mjsunit/div-mod.js

@@ -169,3 +169,24 @@ function compute_mod(dividend, divisor) {
   assertEquals(somenum, somenum % -0x40000000, "%minsmi-32");
   assertEquals(somenum, somenum % -0x80000000, "%minsmi-64");
 })();
+
+
+// Side-effect-free expressions containing bit operations use
+// an optimized compiler with int32 values.   Ensure that modulus
+// produces negative zeros correctly.
+function negative_zero_modulus_test() {
+  var x = 4;
+  var y = -4;
+  x = x + x - x;
+  y = y + y - y;
+  var z = (y | y | y | y) % x;
+  assertEquals(-1 / 0, 1 / z);
+  z = (x | x | x | x) % x;
+  assertEquals(1 / 0, 1 / z);
+  z = (y | y | y | y) % y;
+  assertEquals(-1 / 0, 1 / z);
+  z = (x | x | x | x) % y;
+  assertEquals(1 / 0, 1 / z);
+}
+
+negative_zero_modulus_test();