implement kernel -> ssa for function that returns a constant

pkg/compiler/lib/src/ssa/graph_builder.dart

 // Copyright (c) 2016, 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 '../elements/elements.dart';
 import '../types/types.dart';
 import 'nodes.dart';
 
 /// Base class for objects that build up an SSA graph.
 ///
 /// This contains helpers for building the graph and tracking information about
 /// the current state of the graph being built.
 abstract class GraphBuilder {
   /// Holds the resulting SSA graph.
   final HGraph graph = new HGraph();
 
+  /// A stack of instructions.
+  ///
+  /// We build the SSA graph by simulating a stack machine.
+  List<HInstruction> stack = <HInstruction>[];
+
+
+  void push(HInstruction instruction) {
+    add(instruction);
+    stack.add(instruction);
+  }
+
+  HInstruction pop() {
+    return stack.removeLast();
+  }
+
+  void dup() {
+    stack.add(stack.last);
+  }
+
   HBasicBlock _current;
 
   /// The current block to add instructions to. Might be null, if we are
   /// visiting dead code, but see [isReachable].
   HBasicBlock get current => _current;
 
   void set current(c) {
     isReachable = c != null;
     _current = c;
   }
@@ skipping 69 matching lines @@
     HParameterValue result = new HParameterValue(parameter, type);
     if (lastAddedParameter == null) {
       graph.entry.addBefore(graph.entry.first, result);
     } else {
       graph.entry.addAfter(lastAddedParameter, result);
     }
     lastAddedParameter = result;
     return result;
   }
 }