Lazy implementation of final variables.

lib/compiler/implementation/ssa/nodes.dart

Index: lib/compiler/implementation/ssa/nodes.dart
diff --git a/lib/compiler/implementation/ssa/nodes.dart b/lib/compiler/implementation/ssa/nodes.dart
index 5fc48d3c314b70210c66cc48feb08934fd32a1bb..1e0474fc0db5ca195b20ed5728f6b44b9da2374b 100644
--- a/lib/compiler/implementation/ssa/nodes.dart
+++ b/lib/compiler/implementation/ssa/nodes.dart
@@ -37,6 +37,7 @@ interface HVisitor<R> {
   R visitInvokeStatic(HInvokeStatic node);
   R visitInvokeSuper(HInvokeSuper node);
   R visitIs(HIs node);
+  R visitLazyStatic(HLazyStatic node);
   R visitLess(HLess node);
   R visitLessEqual(HLessEqual node);
   R visitLiteralList(HLiteralList node);
@@ -296,6 +297,7 @@ class HBaseVisitor extends HGraphVisitor implements HVisitor {
   visitInvokeStatic(HInvokeStatic node) => visitInvoke(node);
   visitInvokeSuper(HInvokeSuper node) => visitInvoke(node);
   visitJump(HJump node) => visitControlFlow(node);
+  visitLazyStatic(HLazyStatic node) => visitStatic(node);
   visitLess(HLess node) => visitRelational(node);
   visitLessEqual(HLessEqual node) => visitRelational(node);
   visitLiteralList(HLiteralList node) => visitInstruction(node);
@@ -2252,6 +2254,24 @@ class HStatic extends HInstruction {
   bool isCodeMotionInvariant() => !element.isAssignable();
 }
 
+/** An [HLazyStatic] is a static that is initialized lazily at first read. */
+class HLazyStatic extends HStatic {
+  HLazyStatic(Element element) : super(element);
+
+  void prepareGvn(HTypeMap types) {
+    // TODO: The first access has side-effects, but we afterwards we should be
+    // able to GVN.
+    setAllSideEffects();

[kasperl, 2012/08/17 09:30:04]

Can't you just enable GVN for the lazy-static and keep it having all side
effects? It would be neat if we could read it into a local variable on first
access (and kill stuff in our GVN map) but then just use the local after that.

[floitsch, 2012/09/04 17:32:21]

I tried, but iirc there are some assumptions and asserts.

+  }
+
+  toString() => 'lazy static ${element.name}';
+  accept(HVisitor visitor) => visitor.visitLazyStatic(this);
+
+  int typeCode() => 30;
+  // TODO(floitsch): can we do better here?
+  bool isCodeMotionInvariant() => false;
+}
+
 class HStaticStore extends HInstruction {
   Element element;
   HStaticStore(this.element, HInstruction value) : super(<HInstruction>[value]);