dart2js cps: Streamline expressions and primitives.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
index 37e91fe15c09214d1a826163661a57e93dcd4d6c..02bbe20faf6e886b795b0740ebed2f43fe6717e9 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
@@ -579,10 +579,9 @@ class GetMutableVariable extends Primitive {
 /// values.  This can be seen as a dereferencing assignment:
 ///
 ///   { [variable] := [value]; [body] }
-class SetMutableVariable extends InteriorExpression {
+class SetMutableVariable extends Primitive {
   final Reference<MutableVariable> variable;
   final Reference<Primitive> value;
-  Expression body;
 
   SetMutableVariable(MutableVariable variable, Primitive value)
       : this.variable = new Reference<MutableVariable>(variable),
@@ -590,10 +589,8 @@ class SetMutableVariable extends InteriorExpression {
 
   accept(Visitor visitor) => visitor.visitSetMutableVariable(this);
 
-  Expression plug(Expression expr) {
-    assert(body == null);
-    return body = expr;
-  }
+  bool get isSafeForElimination => false;
+  bool get isSafeForReordering => false;
 }
 
 /// Invoke a continuation in tail position.
@@ -662,22 +659,19 @@ class Branch extends TailExpression {
 }
 
 /// Directly assigns to a field on a given object.
-class SetField extends InteriorExpression {
+class SetField extends Primitive {
   final Reference<Primitive> object;
   FieldElement field;
   final Reference<Primitive> value;
-  Expression body;
 
   SetField(Primitive object, this.field, Primitive value)
       : this.object = new Reference<Primitive>(object),
         this.value = new Reference<Primitive>(value);
 
-  Expression plug(Expression expr) {
-    assert(body == null);
-    return body = expr;
-  }
-
   accept(Visitor visitor) => visitor.visitSetField(this);
+  
+  bool get isSafeForElimination => false;
+  bool get isSafeForReordering => false;
 }
 
 /// Directly reads from a field on a given object.
@@ -778,21 +772,18 @@ class GetStatic extends Primitive {
 }
 
 /// Sets the value of a static field.
-class SetStatic extends InteriorExpression {
+class SetStatic extends Primitive {
   final FieldElement element;
   final Reference<Primitive> value;
-  Expression body;
   final SourceInformation sourceInformation;
 
   SetStatic(this.element, Primitive value, [this.sourceInformation])
       : this.value = new Reference<Primitive>(value);
 
-  Expression plug(Expression expr) {
-    assert(body == null);
-    return body = expr;
-  }
-
   accept(Visitor visitor) => visitor.visitSetStatic(this);
+
+  bool get isSafeForElimination => false;
+  bool get isSafeForReordering => false;
 }
 
 /// Reads the value of a lazily initialized static field.
@@ -1288,7 +1279,6 @@ class RecursiveVisitor implements Visitor {
     processSetMutableVariable(node);
     processReference(node.variable);
     processReference(node.value);
-    visit(node.body);
   }
 
   processGetLazyStatic(GetLazyStatic node) {}
@@ -1370,7 +1360,6 @@ class RecursiveVisitor implements Visitor {
     processSetField(node);
     processReference(node.object);
     processReference(node.value);
-    visit(node.body);
   }
 
   processGetField(GetField node) {}
@@ -1388,7 +1377,6 @@ class RecursiveVisitor implements Visitor {
   visitSetStatic(SetStatic node) {
     processSetStatic(node);
     processReference(node.value);
-    visit(node.body);
   }
 
   processCreateBox(CreateBox node) {}