Support for stack traces in catch blocks.

frog/leg/ssa/builder.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.
 
 class Interceptors {
   Compiler compiler;
   Interceptors(Compiler this.compiler);
 
   SourceString mapOperatorToMethodName(Operator op) {
     String name = op.source.stringValue;
@@ skipping 75 matching lines @@
     return compiler.findHelper(const SourceString('indexSet'));
   }
 
   Element getEqualsNullInterceptor() {
     return compiler.findHelper(const SourceString('eqNull'));
   }
 
   Element getExceptionUnwrapper() {
     return compiler.findHelper(const SourceString('unwrapException'));
   }
+
+  Element getTraceFromException() {
+    return compiler.findHelper(const SourceString('getTraceFromException'));
+  }
 }
 
 class SsaBuilderTask extends CompilerTask {
   SsaBuilderTask(Compiler compiler)
     : super(compiler), interceptors = new Interceptors(compiler);
   String get name() => 'SSA builder';
   Interceptors interceptors;
 
   HGraph build(WorkItem work) {
     return measure(() {
@@ skipping 2201 matching lines @@
       // Note that the name of this element is irrelevant.
       Element element = new Element(
           const SourceString('exception'), ElementKind.PARAMETER, work.element);
       HParameterValue exception = new HParameterValue(element);
       add(exception);
       HInstruction oldRethrowableException = rethrowableException;
       rethrowableException = exception;
       push(new HStatic(interceptors.getExceptionUnwrapper()));
       List<HInstruction> inputs = <HInstruction>[pop(), exception];
       HInvokeStatic unwrappedException =
-        new HInvokeStatic(Selector.INVOCATION_1, inputs);
+          new HInvokeStatic(Selector.INVOCATION_1, inputs);
       add(unwrappedException);
 
       tryInstruction.exception = exception;
+
+      bool requiresTrace = false;
+      for (CatchBlock block in node.catchBlocks) {
+        if (block.trace != null) {
+          requiresTrace = true;
+          break;
+        }
+      }
+
+      HInstruction traceInstruction = null;

[floitsch, 2012/03/06 10:22:32]

Did you consider to fetch the trace lazily (in the visitThen) instead of
eagerly?

[ngeoffray, 2012/03/06 12:12:50]

Yes. But the last implementation I ended up with did not do this. I have upaded
the code to do it lazily.

+      if (requiresTrace) {
+        push(new HStatic(interceptors.getTraceFromException()));
+        traceInstruction = new HInvokeStatic(Selector.INVOCATION_1,
+                                             <HInstruction>[pop(), exception]);
+        add(traceInstruction);
+      }
+
       Link<Node> link = node.catchBlocks.nodes;
 
       void pushCondition(CatchBlock catchBlock) {
         VariableDefinitions declaration = catchBlock.formals.nodes.head;
         HInstruction condition = null;
         if (declaration.type == null) {
           condition = graph.addNewLiteralTrue();
           stack.add(condition);
         } else {
           Element typeElement = elements[declaration.type];
           if (typeElement == null) {
             compiler.cancel('Catch with unresolved type', node: catchBlock);
           }
           condition = new HIs(typeElement, unwrappedException);
           push(condition);
         }
       }
 
       void visitThen() {
         CatchBlock catchBlock = link.head;
         link = link.tail;
-        VariableDefinitions declaration = catchBlock.formals.nodes.head;
-        localsHandler.updateLocal(elements[declaration.definitions.nodes.head],
+        localsHandler.updateLocal(elements[catchBlock.exception],
                                   unwrappedException);
+        Node trace = catchBlock.trace; 
+        if (trace != null) {
+          localsHandler.updateLocal(elements[trace], traceInstruction);
+        }
         visit(catchBlock);
       }
 
       void visitElse() {
         if (link.isEmpty()) {
           close(new HThrow(exception, isRethrow: true));
         } else {
           CatchBlock newBlock = link.head;
           pushCondition(newBlock);
           handleIf(visitThen, visitElse);
@@ skipping 44 matching lines @@
     // Normally, we would call [close] here. However, then we hit
     // another unimplemented feature: aborting loop body. Simply
     // calling [add] does not work as it asserts that the instruction
     // isn't a control flow instruction. So we inline parts of [add].
     current.addAfter(current.last, new HThrow(message));
     if (isExpression) {
       stack.add(graph.addNewLiteralNull());
     }
   }
 }