cps-ir: Merge variables based on set-based liveness and graph coloring.

pkg/compiler/lib/src/dart_backend/backend.dart

 // 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.
 
 part of dart_backend;
 
 // TODO(ahe): This class is simply wrong.  This backend should use
 // elements when it can, not AST nodes.  Perhaps a [Map<Element,
 // TreeElements>] is what is needed.
 class ElementAst {
@@ skipping 150 matching lines @@
     // types are correctly marked as instantiated (Issue 21880).
     TypePropagator typePropagator = new TypePropagator(
         context.dartTypes,
         context.constantSystem,
         new UnitTypeSystem(),
         context.internalError);
     applyCpsPass(typePropagator);
     applyCpsPass(new RedundantPhiEliminator());
     applyCpsPass(new ShrinkingReducer());
 
-    // Do not rewrite the IR after variable allocation.  Allocation
-    // makes decisions based on an approximation of IR variable live
-    // ranges that can be invalidated by transforming the IR.
-    new cps_ir.RegisterAllocator(context.internalError).visit(cpsDefinition);
-
     tree_builder.Builder builder =
         new tree_builder.Builder(context.internalError);
     tree_ir.ExecutableDefinition treeDefinition = builder.build(cpsDefinition);
     assert(treeDefinition != null);
     context.traceGraph('Tree builder', treeDefinition);
     assert(checkTreeIntegrity(treeDefinition));
 
     // Transformations on the Tree IR.
     void applyTreePass(tree_opt.Pass pass) {
       pass.rewrite(treeDefinition);
       context.traceGraph(pass.passName, treeDefinition);
       assert(checkTreeIntegrity(treeDefinition));
     }
 
     applyTreePass(new StatementRewriter());
-    applyTreePass(new CopyPropagator());
+    applyTreePass(new VariableMerger());
     applyTreePass(new LoopRewriter());
     applyTreePass(new LogicalRewriter());
 
     // Backend-specific transformations.
     new backend_ast_emitter.UnshadowParameters().unshadow(treeDefinition);
     context.traceGraph('Unshadow parameters', treeDefinition);
 
     TreeElementMapping treeElements = new TreeElementMapping(element);
     backend_ast.ExecutableDefinition backendAst =
         backend_ast_emitter.emit(treeDefinition);
@@ skipping 360 matching lines @@
   }
 
   void traceGraph(String title, var irObject) {
     compiler.tracer.traceGraph(title, irObject);
   }
 
   DartTypes get dartTypes => compiler.types;
 
   InternalErrorFunction get internalError => compiler.internalError;
 }