X64: Implementation of a bunch of stubs, and some new opcodes.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index e60286a3e991b06b07e939ab22bd010ff2c0a640..5de6372ae4a2bcd29630706586b729d37e9b18f9 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -59,6 +59,18 @@ void MacroAssembler::Check(Condition cc, const char* msg) {
 }
 
 
+void MacroAssembler::NegativeZeroTest(Register result,
+                                      Register op,
+                                      Label* then_label) {
+  Label ok;
+  testq(result, result);
+  j(not_zero, &ok);
+  testq(op, op);
+  j(sign, then_label);
+  bind(&ok);
+}
+
+
 void MacroAssembler::ConstructAndTestJSFunction() {
   const int initial_buffer_size = 4 * KB;
   char* buffer = new char[initial_buffer_size];