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

runtime/vm/compiler.cc

 // Copyright (c) 2012, 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/compiler.h"
 
 #include "vm/assembler.h"
 
 #include "vm/ast_printer.h"
 #include "vm/code_generator.h"
@@ skipping 202 matching lines @@
 
       // Do optimizations that depend on the propagated type information.
       optimizer.Canonicalize();
 
       if (FLAG_constant_propagation) {
         ConstantPropagator::Optimize(flow_graph);
         // A canonicalization pass to remove e.g. smi checks on smi constants.
         optimizer.Canonicalize();
       }
 
+      // Optimize (a << b) & c patterns. Must occur before
+      // 'Selectrepresentations' which inserts conversion nodes.
+      optimizer.TryOptimizeLeftShiftWithBitAndPattern();
+
       // Unbox doubles. Performed after constant propagation to minimize
       // interference from phis merging double values and tagged
       // values comming from dead paths.
       optimizer.SelectRepresentations();
 
       if (FLAG_common_subexpression_elimination) {
         if (DominatorBasedCSE::Optimize(flow_graph)) {
           // Do another round of CSE to take secondary effects into account:
           // e.g. when eliminating dependent loads (a.x[0] + a.x[0])
           // TODO(fschneider): Change to a one-pass optimization pass.
@@ skipping 412 matching lines @@
       Object::Handle(isolate->object_store()->sticky_error());
     isolate->object_store()->clear_sticky_error();
     isolate->set_long_jump_base(base);
     return result.raw();
   }
   UNREACHABLE();
   return Object::null();
 }
 
 }  // namespace dart