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

runtime/vm/intermediate_language.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 117 matching lines @@
 
 
 bool StrictCompareInstr::AttributesEqual(Instruction* other) const {
   StrictCompareInstr* other_op = other->AsStrictCompare();
   ASSERT(other_op != NULL);
   return kind() == other_op->kind();
 }
 
 
 bool BinarySmiOpInstr::AttributesEqual(Instruction* other) const {
   BinarySmiOpInstr* other_op = other->AsBinarySmiOp();

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

I think this should check for equality of the truncation flag.

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

Done.

   ASSERT(other_op != NULL);
   return (op_kind() == other_op->op_kind()) &&
       (overflow_ == other_op->overflow_);
 }
 
 
 bool LoadFieldInstr::AttributesEqual(Instruction* other) const {
   LoadFieldInstr* other_load = other->AsLoadField();
   ASSERT(other_load != NULL);
   ASSERT((offset_in_bytes() != other_load->offset_in_bytes()) ||
@@ skipping 694 matching lines @@
     case Token::kBIT_AND:
     case Token::kBIT_OR:
     case Token::kBIT_XOR:
       return false;
     case Token::kSHR: {
       // Can't deopt if shift-count is known positive.
       Range* right_range = this->right()->definition()->range();
       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_;
   }
 }
 
 
 bool BinarySmiOpInstr::RightIsPowerOfTwoConstant() const {
   if (!right()->definition()->IsConstant()) return false;
   const Object& constant = right()->definition()->AsConstant()->value();
   if (!constant.IsSmi()) return false;
@@ skipping 1338 matching lines @@
     default:
       UNREACHABLE();
   }
   return kPowRuntimeEntry;
 }
 
 
 #undef __
 
 }  // namespace dart