dart2dart: Implementation of simple try/catch.

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

 // Copyright (c) 2014, 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.
 
 library tree_ir_builder;
 
 import '../dart2jslib.dart' as dart2js;
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../cps_ir/cps_ir_nodes.dart' as cps_ir;
@@ skipping 39 matching lines @@
   final Map<Local, List<Variable>> local2variables = <Local, List<Variable>>{};
 
   /// Like [local2variables], except for mutable variables.
   final Map<cps_ir.MutableVariable, Variable> local2mutable =
       <cps_ir.MutableVariable, Variable>{};
 
   // Continuations with more than one use are replaced with Tree labels.  This
   // 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;
 
   Builder parent;
 
   Builder(this.internalError, [this.parent]);
 
   Builder createInnerBuilder() {
     return new Builder(internalError, this);
   }
@@ skipping 295 matching lines @@
       return new Assign(variable, definition, visit(node.body));
     }
   }
 
   Statement visitRunnableBody(cps_ir.RunnableBody node) {
     return visit(node.body);
   }
 
   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.
     //
     // The continuation bodies are not always translated directly here because
     // they may have been already translated:
     //   * For singly-used continuations, the continuation's body is
     //     translated at the site of the continuation invocation.
     //   * For recursive continuations, there is a single non-recursive
     //     invocation.  The continuation's body is translated at the site
     //     of the non-recursive continuation invocation.
     // See visitInvokeContinuation for the implementation.
     Statement current = body;
     for (cps_ir.Continuation continuation in node.continuations.reversed) {
       Label label = labels[continuation];
       if (label != null && !continuation.isRecursive) {
         current =
             new LabeledStatement(label, current, visit(continuation.body));
       }
     }
     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);
     Expression invoke = new InvokeStatic(node.target, node.selector, arguments);
     return continueWithExpression(node.continuation, invoke);
   }
 
   Statement visitInvokeMethod(cps_ir.InvokeMethod node) {
     Expression invoke = new InvokeMethod(getVariableReference(node.receiver),
                                          node.selector,
@@ skipping 88 matching lines @@
             //   * Recursive continuations
             //     - There is a single non-recursive invocation.  Translate
             //       the continuation body inline as a labeled loop at the
             //       invocation site.
             //     - Translate the recursive invocations to Continue.
             if (cont.isRecursive) {
               return node.isRecursive
                   ? 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]);
             }
           });
     }
   }
 
   Statement visitBranch(cps_ir.Branch node) {
     Expression condition = visit(node.condition);
     Statement thenStatement, elseStatement;
     cps_ir.Continuation cont = node.trueContinuation.definition;
     assert(cont.parameters.isEmpty);
@@ skipping 64 matching lines @@
     // visited.
     internalError(CURRENT_ELEMENT_SPANNABLE, 'Unexpected IR node: $node.');
     return null;
   }
 
   Expression visitIsTrue(cps_ir.IsTrue node) {
     return getVariableReference(node.value);
   }
 }