implement kernel -> ssa for function that returns a constant

pkg/compiler/lib/src/ssa/builder.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.
 
 import 'dart:collection';
 
 import 'package:js_runtime/shared/embedded_names.dart';
 
 import '../closure.dart';
 import '../common.dart';
@@ skipping 399 matching lines @@
    * or inlined by this builder.
    */
   final List<Element> sourceElementStack = <Element>[];
 
   LocalsHandler localsHandler;
 
   HInstruction rethrowableException;
 
   Map<JumpTarget, JumpHandler> jumpTargets = <JumpTarget, JumpHandler>{};
 
-  // We build the Ssa graph by simulating a stack machine.
-  List<HInstruction> stack = <HInstruction>[];
-
   /// Returns `true` if the current element is an `async` function.
   bool get isBuildingAsyncFunction {
     Element element = sourceElement;
     return (element is FunctionElement &&
         element.asyncMarker == AsyncMarker.ASYNC);
   }
 
   // TODO(sigmund): make most args optional
   SsaBuilder(
       this.target,
@@ skipping 1466 matching lines @@
     add(assertIsSubtype);
   }
 
   HGraph closeFunction() {
     // TODO(kasperl): Make this goto an implicit return.
     if (!isAborted()) closeAndGotoExit(new HGoto());
     graph.finalize();
     return graph;
   }
 
-  void push(HInstruction instruction) {
-    add(instruction);
-    stack.add(instruction);
-  }
-
   void pushWithPosition(HInstruction instruction, ast.Node node) {
     push(attachPosition(instruction, node));
   }
 
-  HInstruction pop() {
-    return stack.removeLast();
-  }
-
-  void dup() {
-    stack.add(stack.last);
-  }
-
   HInstruction popBoolified() {
     HInstruction value = pop();
     if (_checkOrTrustTypes) {
       return potentiallyCheckOrTrustType(value, compiler.coreTypes.boolType,
           kind: HTypeConversion.BOOLEAN_CONVERSION_CHECK);
     }
     HInstruction result = new HBoolify(value, backend.boolType);
     add(result);
     return result;
   }
@@ skipping 5902 matching lines @@
   const _LoopTypeVisitor();
   int visitNode(ast.Node node) => HLoopBlockInformation.NOT_A_LOOP;
   int visitWhile(ast.While node) => HLoopBlockInformation.WHILE_LOOP;
   int visitFor(ast.For node) => HLoopBlockInformation.FOR_LOOP;
   int visitDoWhile(ast.DoWhile node) => HLoopBlockInformation.DO_WHILE_LOOP;
   int visitAsyncForIn(ast.AsyncForIn node) => HLoopBlockInformation.FOR_IN_LOOP;
   int visitSyncForIn(ast.SyncForIn node) => HLoopBlockInformation.FOR_IN_LOOP;
   int visitSwitchStatement(ast.SwitchStatement node) =>
       HLoopBlockInformation.SWITCH_CONTINUE_LOOP;
 }