Fix three bugs with handling negative zero in the optimizing compiler.

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
===================================================================
--- src/hydrogen-instructions.cc	(revision 8868)
+++ src/hydrogen-instructions.cc	(working copy)
@@ -862,19 +862,10 @@
 
 
 Range* HValue::InferRange() {
-  if (representation().IsTagged()) {
-    // Tagged values are always in int32 range when converted to integer,
-    // but they can contain -0.
-    Range* result = new Range();
-    result->set_can_be_minus_zero(true);
-    return result;
-  } else if (representation().IsNone()) {
-    return NULL;
-  } else {
-    // Untagged integer32 cannot be -0 and we don't compute ranges for
-    // untagged doubles.
-    return new Range();
-  }
+  // Untagged integer32 cannot be -0, all other representations can.
+  Range* result = new Range();
+  result->set_can_be_minus_zero(!representation().IsInteger32());
+  return result;
 }