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

pkg/compiler/lib/src/js_backend/codegen/task.dart

 // Copyright (c) 2014, 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.
 
 /// Generate code using the cps-based IR pipeline.
 library code_generator_task;
 
 import 'glue.dart';
 import 'codegen.dart';
 import 'unsugar.dart';
@@ skipping 161 matching lines @@
     TypePropagator typePropagator = new TypePropagator<TypeMask>(
         compiler.types,
         constantSystem,
         new TypeMaskSystem(compiler),
         compiler.internalError);
     applyCpsPass(typePropagator);
     dumpTypedIR(cpsNode, 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.RegisterAllocator(compiler.internalError).visit(cpsNode);
     return cpsNode;
   }
 
   tree_ir.FunctionDefinition compileToTreeIR(cps.FunctionDefinition cpsNode) {
     tree_builder.Builder builder = new JsTreeBuilder(
         compiler.internalError, compiler.identicalFunction, glue);
     tree_ir.FunctionDefinition treeNode = builder.buildFunction(cpsNode);
     assert(treeNode != null);
     traceGraph('Tree builder', treeNode);
     assert(checkTreeIntegrity(treeNode));
     return treeNode;
   }
 
   static bool checkTreeIntegrity(tree_ir.ExecutableDefinition node) {
     new CheckTreeIntegrity().check(node);
     return true; // So this can be used from assert().
   }
 
   tree_ir.FunctionDefinition optimizeTreeIR(tree_ir.FunctionDefinition node) {
     void applyTreePass(tree_opt.Pass pass) {
       pass.rewrite(node);
       traceGraph(pass.passName, node);
       assert(checkTreeIntegrity(node));
     }
 
     applyTreePass(new StatementRewriter());
-    applyTreePass(new CopyPropagator());
+    applyTreePass(new VariableMerger());
     applyTreePass(new LoopRewriter());
     applyTreePass(new LogicalRewriter());
 
     return node;
   }
 
   js.Fun compileToJavaScript(CodegenWorkItem work,
                              tree_ir.FunctionDefinition definition) {
     CodeGenerator codeGen = new CodeGenerator(glue, work.registry);
 
     return attachPosition(codeGen.buildFunction(definition), work.element);
   }
 
   Iterable<CompilerTask> get tasks {
     // TODO(sigurdm): Make a better list of tasks.
     return <CompilerTask>[irBuilderTask]..addAll(fallbackCompiler.tasks);
   }
 
   js.Node attachPosition(js.Node node, AstElement element) {
     return node.withSourceInformation(
         StartEndSourceInformation.computeSourceInformation(element));
   }
 }