Don't allow statement-nodes in expression contexts.

lib/compiler/implementation/ssa/nodes.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.
 
 interface HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
   R visitBitXor(HBitXor node);
@@ skipping 984 matching lines @@
   bool isStatement() => true;
   void prepareGvn() {
     assert(!hasSideEffects());
     setUseGvn();
   }
 }
 
 class HTypeGuard extends HCheck {
   final int state;
   final HType guardedType;
   bool isOn = false;

[Lasse Reichstein Nielsen, 2012/06/27 10:08:38]

What does "isOn" mean? Could it get a better name?

[floitsch, 2012/06/27 12:23:02]

renamed to isEnabled.
done.

   int checkedInputIndex = 0;
 
   HTypeGuard(this.guardedType, this.state, List<HInstruction> env) : super(env);
 
   HInstruction get guarded() => inputs[checkedInputIndex];
   HInstruction get checkedInput() => guarded;
 
   HType computeTypeFromInputTypes() {
     return isOn ? guardedType : guarded.propagatedType;
   }
 
   HType get guaranteedType() => isOn ? guardedType : HType.UNKNOWN;
 
   bool isControlFlow() => true;
 
+  bool isStatement() => isOn;
+
   accept(HVisitor visitor) => visitor.visitTypeGuard(this);
   int typeCode() => 1;
   bool typeEquals(other) => other is HTypeGuard;
   bool dataEquals(HTypeGuard other) {
     return guarded == other.guarded && guardedType == other.guardedType;
   }
 }
 
 class HBoundsCheck extends HCheck {
   static final int ALWAYS_FALSE = 0;
@@ skipping 1597 matching lines @@
   HBasicBlock get start() => expression.start;
   HBasicBlock get end() {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty());
     return statements.last().end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }