[v8-dev] Fix an error in optimized modulus operator, add unit test. (issue1118008)

[whesse]

Reviewers: fschneider,

Description:
Fix an error in optimized modulus operator, add unit test.
Please review this at http://codereview.chromium.org/1118008

SVN Base: http://v8.googlecode.com/svn/branches/bleeding_edge/

Affected files:
  M     src/ia32/codegen-ia32.cc
  M     test/mjsunit/div-mod.js


Index: test/mjsunit/div-mod.js
===================================================================
--- test/mjsunit/div-mod.js     (revision 4229)
+++ test/mjsunit/div-mod.js     (working copy)
@@ -169,3 +169,24 @@
   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();
Index: src/ia32/codegen-ia32.cc
===================================================================
--- src/ia32/codegen-ia32.cc    (revision 4230)
+++ src/ia32/codegen-ia32.cc    (working copy)
@@ -7380,6 +7380,15 @@
       __ 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);


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