Fix a pair of bugs in the translation of 'if' nodes.

runtime/vm/flow_graph_builder.cc

 // 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.
 
 #include "vm/flow_graph_builder.h"
 
 #include "vm/flags.h"
 #include "vm/intermediate_language.h"
 #include "vm/os.h"
 #include "vm/parser.h"
@@ skipping 35 matching lines @@
   // and a pair of effect graph fragments with zero or one available exits.
   // We want to append the branch and (if necessary) a join node to this
   // graph fragment.
   ASSERT(is_open());
 
   // 1. Connect the test to this graph.
   Append(test_fragment);
 
   // 2. Connect the true and false bodies to the test if they are reachable,
   // and if so record their exits (if any).
+  Instruction* true_exit = NULL;
+  Instruction* false_exit = NULL;
   if (test_fragment.can_be_true()) {
-    Instruction* true_exit = NULL;
-    Instruction* false_exit = NULL;
     TargetEntryInstr* true_entry = new TargetEntryInstr();
     *test_fragment.true_successor_address() = true_entry;
     true_entry->SetSuccessor(true_fragment.entry());
     true_exit = true_fragment.is_empty() ? true_entry : true_fragment.exit();
 
     TargetEntryInstr* false_entry = new TargetEntryInstr();
     *test_fragment.false_successor_address() = false_entry;
     false_entry->SetSuccessor(false_fragment.entry());
     false_exit =
         false_fragment.is_empty() ? false_entry : false_fragment.exit();

[srdjan, 2012/02/23 16:27:22]

When can false_exit and true_exit be NULL, i.e., when can
false/true_fragment.exit() be NULL?

+  }
 
+  // 3. Add a join or select one (or neither) of the arms as exit.
+  if (true_exit == NULL) {
+    exit_ = false_exit;  // May be NULL.
+  } else if (false_exit == NULL) {
+    exit_ = true_exit;
+  } else {
     exit_ = new JoinEntryInstr();
     true_exit->SetSuccessor(exit_);
     false_exit->SetSuccessor(exit_);
   }
 }
 
 
 void EffectGraphVisitor::TieLoop(const TestGraphVisitor& test_fragment,
                                  const EffectGraphVisitor& body_fragment) {
   // We have: a test graph fragment with zero, one, or two available exits;
@@ skipping 318 matching lines @@
   Bailout("TestGraphVisitor::VisitConditionalExprNode");
 }
 
 
 // <Statement> ::= If { condition: <Expression>
 //                      true_branch: <Sequence>
 //                      false_branch: <Sequence> }
 void EffectGraphVisitor::VisitIfNode(IfNode* node) {
   TestGraphVisitor for_test(owner(), temp_index());
   node->condition()->Visit(&for_test);
-  Append(for_test);
 
   EffectGraphVisitor for_true(owner(), temp_index());
   EffectGraphVisitor for_false(owner(), temp_index());
 
   if (for_test.can_be_true()) {
     node->true_branch()->Visit(&for_true);
     // The for_false graph fragment will be empty (default graph fragment)
     // if we do not call Visit.
     if (node->false_branch() != NULL) node->false_branch()->Visit(&for_false);
   }
@@ skipping 479 matching lines @@
     // Number the blocks in reverse postorder starting with 0.
     intptr_t last_index = postorder_block_entries_.length() - 1;
     for (intptr_t i = last_index; i >= 0; --i) {
       postorder_block_entries_[i]->SetBlockNumber(last_index - i);
     }
   }
   PrintGraph();
 }
 
 }  // namespace dart