Merge (x & y) == 0 pattern to emit a single test instruction.

runtime/vm/assembler_x64.cc

Index: runtime/vm/assembler_x64.cc
===================================================================
--- runtime/vm/assembler_x64.cc	(revision 29964)
+++ runtime/vm/assembler_x64.cc	(working copy)
@@ -1458,6 +1458,17 @@
 }
 
 
+void Assembler::TestImmediate(Register dst, const Immediate& imm, Register pp) {
+  if (CanLoadImmediateFromPool(imm, pp)) {
+    ASSERT(dst != TMP);
+    LoadImmediate(TMP, imm, pp);
+    testq(dst, TMP);
+  } else {
+    testq(dst, imm);
+  }
+}
+
+
 void Assembler::andl(Register dst, Register src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   Operand operand(src);