Recognize pattern (a << b) & c with c being a positive Smi and allow left shift to truncate the res…

runtime/vm/il_printer.cc

Index: runtime/vm/il_printer.cc
===================================================================
--- runtime/vm/il_printer.cc	(revision 18843)
+++ runtime/vm/il_printer.cc	(working copy)
@@ -517,8 +517,10 @@
 void BinarySmiOpInstr::PrintTo(BufferFormatter* f) const {
   Definition::PrintTo(f);
   f->Print(" %co", overflow_ ? '+' : '-');
+  f->Print(" %ct", is_truncating() ? '+' : '-');
 }
 
+
 void BinarySmiOpInstr::PrintOperandsTo(BufferFormatter* f) const {
   f->Print("%s, ", Token::Str(op_kind()));
   left()->PrintTo(f);