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

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
===================================================================
--- runtime/vm/intermediate_language.cc	(revision 18705)
+++ runtime/vm/intermediate_language.cc	(working copy)
@@ -850,6 +850,14 @@
       return (right_range == NULL)
           || !right_range->IsWithin(0, RangeBoundary::kPlusInfinity);
     }
+    case Token::kSHL: {
+      Range* right_range = this->right()->definition()->range();
+      if ((right_range != NULL) && is_truncating()) {
+        // Can deoptimize if right can be negative.
+        return !right_range->IsWithin(0, RangeBoundary::kPlusInfinity);
+      }
+      return overflow_;

[Vyacheslav Egorov (Google), 2013/02/20 00:37:06]

I think this can be just return true;

[srdjan, 2013/02/21 00:47:17]

Done.

+    }
     default:
       return overflow_;
   }