Delete CPS IR

pkg/compiler/lib/src/cps_ir/redundant_refinement.dart

-// Copyright (c) 2015, 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.
-
-library dart2js.cps_ir.redundant_refinement;
-
-import 'cps_ir_nodes.dart';
-import 'optimizers.dart' show Pass;
-import 'type_mask_system.dart';
-
-/// Removes [Refinement] nodes where the input value is already known to
-/// satisfy the refinement type.
-///
-/// Note: This pass improves loop-invariant code motion in the GVN pass because
-/// GVN will currently not hoist a primitive across a refinement guard.
-/// But some opportunities for hoisting are still missed.  A field access can
-/// safely be hoisted across a non-redundant refinement as long as the less
-/// refined value is still known to have the field.  For example:
-///
-///     class A { var field; }
-///     class B extends A {}
-///
-///     var x = getA();       // Return type is subclass of A.
-///     while (x is B) {      // Refinement to B is not redundant.
-///         x.field.baz++;    // x.field is safe for hoisting,
-///     }                     // but blocked by the refinement node.
-///
-/// Ideally, this pass should go away and GVN should handle refinements
-/// directly.
-class RedundantRefinementEliminator extends TrampolineRecursiveVisitor
-    implements Pass {
-  String get passName => 'Redundant refinement elimination';
-
-  TypeMaskSystem typeSystem;
-
-  RedundantRefinementEliminator(this.typeSystem);
-
-  void rewrite(FunctionDefinition node) {
-    visit(node);
-  }
-
-  Expression traverseLetPrim(LetPrim node) {
-    Expression next = node.body;
-    if (node.primitive is Refinement) {
-      Refinement refinement = node.primitive;
-      Primitive value = refinement.value.definition;
-      if (typeSystem.isMorePreciseOrEqual(value.type, refinement.refineType)) {
-        refinement
-          ..replaceUsesWith(value)
-          ..destroy();
-        node.remove();
-        return next;
-      }
-    }
-    return next;
-  }
-}