Throw and a small fix to If.

frog/leg/ssa/builder.dart

 // Copyright (c) 2011, 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 SsaBuilderTask extends CompilerTask {
   SsaBuilderTask(Compiler compiler) : super(compiler);
   String get name() => 'SSA builder';
 
   HGraph build(Node tree, Map<Node, Element> elements) {
     return measure(() {
@@ skipping 305 matching lines @@
     }
     visit(node.expression);
     var value = pop();
     add(new HReturn(value));
     block.addSuccessor(graph.exit);
     // A return aborts the building of the current block.
     block = null;
   }
 
   visitThrow(Throw node) {
-    compiler.unimplemented("SsaBuilder.visitThrow");
+    if (node.expression === null) {
+      compiler.unimplemented("SsaBuilder: throw without expression");
+    }
+    visit(node.expression);
+    add(new HThrow(pop()));
+    // A throw aborts the building of the current block.
+    block = null;
   }
 
   visitTypeAnnotation(TypeAnnotation node) {
     // We currently ignore type annotations for generating code.
   }
 
   HInstruction updateDefinition(SendSet node) {
     if (node.receiver != null) {
       compiler.unimplemented("SsaBuilder: property access");
     }
@@ skipping 12 matching lines @@
       if (definition is Identifier) {
         compiler.unimplemented(
             "SsaBuilder.visitVariableDefinitions without initial value");
       } else {
         assert(definition is SendSet);
         updateDefinition(definition);
       }
     }
   }
 }