implement kernel -> ssa for function that returns a constant

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

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index e44ebf3b6c1d1a683aa13237b7c036c16af89fbe..2dc48955cddbb2f54726f3cec0840c53e869747f 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -417,9 +417,6 @@ class SsaBuilder extends ast.Visitor
 
   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;
@@ -1906,23 +1903,10 @@ class SsaBuilder extends ast.Visitor
     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) {