dart2dart: Implementation of simple try/catch.

pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart

Index: pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
diff --git a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
index 3181b59be3448c22e0a9d4ccfecf4ca6c5606f53..5d3cb519d2b99e2a7fa4b14d1eb1a670c5344ce5 100644
--- a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
+++ b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
@@ -57,6 +57,15 @@ class Builder extends cps_ir.Visitor<Node> {
   // is the mapping from continuations to labels.
   final Map<cps_ir.Continuation, Label> labels = <cps_ir.Continuation, Label>{};
 
+  /// A stack of singly-used labels that can be safely inlined at their use
+  /// site.
+  ///
+  /// Code for continuations with exactly one use is inlined at the use site.
+  /// This is not safe if the code is moved inside the scope of an exception
+  /// handler (i.e., into a try block).  We keep a stack of singly-referenced
+  /// continuations that are in scope without crossing a binding for a handler.
+  List<cps_ir.Continuation> safeForInlining = <cps_ir.Continuation>[];
+
   ExecutableElement currentElement;
   cps_ir.Continuation returnContinuation;
 
@@ -372,12 +381,16 @@ class Builder extends cps_ir.Visitor<Node> {
 
   Statement visitLetCont(cps_ir.LetCont node) {
     // Introduce labels for continuations that need them.
+    int safeForInliningLengthOnEntry = safeForInlining.length;
     for (cps_ir.Continuation continuation in node.continuations) {
       if (continuation.hasMultipleUses) {
         labels[continuation] = new Label();
+      } else {
+        safeForInlining.add(continuation);
       }
     }
     Statement body = visit(node.body);
+    safeForInlining.length = safeForInliningLengthOnEntry;
     // Continuations are bound at the same level, but they have to be
     // translated as if nested.  This is because the body can invoke any
     // of them from anywhere, so it must be nested inside all of them.
@@ -401,6 +414,17 @@ class Builder extends cps_ir.Visitor<Node> {
     return current;
   }
 
+  Statement visitLetHandler(cps_ir.LetHandler node) {
+    List<cps_ir.Continuation> saved = safeForInlining;
+    safeForInlining = <cps_ir.Continuation>[];
+    Statement tryBody = visit(node.body);
+    safeForInlining = saved;
+    List<Variable> catchParameters =
+        node.handler.parameters.map(getVariable).toList();
+    Statement catchBody = visit(node.handler.body);
+    return new Try(tryBody, catchParameters, catchBody);
+  }
+
   Statement visitInvokeStatic(cps_ir.InvokeStatic node) {
     // Calls are translated to direct style.
     List<Expression> arguments = translateArguments(node.arguments);
@@ -509,9 +533,13 @@ class Builder extends cps_ir.Visitor<Node> {
                   ? new Continue(labels[cont])
                   : new WhileTrue(labels[cont], visit(cont.body));
             } else {
-              return cont.hasExactlyOneUse
-                  ? visit(cont.body)
-                  : new Break(labels[cont]);
+              if (cont.hasExactlyOneUse) {
+                if (safeForInlining.contains(cont)) {
+                  return visit(cont.body);
+                }
+                labels[cont] = new Label();
+              }
+              return new Break(labels[cont]);
             }
           });
     }