Fix a bug with uninitialized const variables in the optimizing compiler.

We have to check for uninitialized uses before phi-elimination. Otherwise we
may miss such a use and result in using the hole value instead. This
causes a NULL-dereference or assertion failure.

BUG=96989
TEST=mjsunit/compiler/regress-96989.js
Review URL: http://codereview.chromium.org/7974009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9337 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen.cc

@@ -852,7 +852,7 @@ void HGraph::EliminateUnreachablePhis() {
 }
 
 
-bool HGraph::CheckPhis() {
+bool HGraph::CheckArgumentsPhiUses() {
   int block_count = blocks_.length();
   for (int i = 0; i < block_count; ++i) {
     for (int j = 0; j < blocks_[i]->phis()->length(); ++j) {
@@ -865,13 +865,11 @@ bool HGraph::CheckPhis() {
 }
 
 
-bool HGraph::CollectPhis() {
+bool HGraph::CheckConstPhiUses() {
   int block_count = blocks_.length();
-  phi_list_ = new ZoneList<HPhi*>(block_count);
   for (int i = 0; i < block_count; ++i) {
     for (int j = 0; j < blocks_[i]->phis()->length(); ++j) {
       HPhi* phi = blocks_[i]->phis()->at(j);
-      phi_list_->Add(phi);
       // Check for the hole value (from an uninitialized const).
       for (int k = 0; k < phi->OperandCount(); k++) {
         if (phi->OperandAt(k) == GetConstantHole()) return false;
@@ -882,6 +880,18 @@ bool HGraph::CollectPhis() {
 }
 
 
+void HGraph::CollectPhis() {
+  int block_count = blocks_.length();
+  phi_list_ = new ZoneList<HPhi*>(block_count);
+  for (int i = 0; i < block_count; ++i) {
+    for (int j = 0; j < blocks_[i]->phis()->length(); ++j) {
+      HPhi* phi = blocks_[i]->phis()->at(j);
+      phi_list_->Add(phi);
+    }
+  }
+}
+
+
 void HGraph::InferTypes(ZoneList<HValue*>* worklist) {
   BitVector in_worklist(GetMaximumValueID());
   for (int i = 0; i < worklist->length(); ++i) {
@@ -2329,16 +2339,17 @@ HGraph* HGraphBuilder::CreateGraph() {
 #endif
 
   graph()->PropagateDeoptimizingMark();
-  graph()->EliminateRedundantPhis();
-  if (!graph()->CheckPhis()) {
-    Bailout("Unsupported phi use of arguments object");
+  if (!graph()->CheckConstPhiUses()) {
+    Bailout("Unsupported phi use of const variable");
     return NULL;
   }
-  if (FLAG_eliminate_dead_phis) graph()->EliminateUnreachablePhis();
-  if (!graph()->CollectPhis()) {
-    Bailout("Unsupported phi use of uninitialized constant");
+  graph()->EliminateRedundantPhis();
+  if (!graph()->CheckArgumentsPhiUses()) {
+    Bailout("Unsupported phi use of arguments");
     return NULL;
   }
+  if (FLAG_eliminate_dead_phis) graph()->EliminateUnreachablePhis();
+  graph()->CollectPhis();
 
   HInferRepresentation rep(graph());
   rep.Analyze();

src/hydrogen.h

@@ -243,11 +243,13 @@ class HGraph: public ZoneObject {
 
   // Returns false if there are phi-uses of the arguments-object
   // which are not supported by the optimizing compiler.
-  bool CheckPhis();
+  bool CheckArgumentsPhiUses();
 
-  // Returns false if there are phi-uses of hole values comming
-  // from uninitialized consts.
-  bool CollectPhis();
+  // Returns false if there are phi-uses of an uninitialized const
+  // which are not supported by the optimizing compiler.
+  bool CheckConstPhiUses();
+
+  void CollectPhis();
 
   Handle<Code> Compile(CompilationInfo* info);
 

test/mjsunit/compiler/regress-96989.js

+// Copyright 2011 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+// Flags: --allow-natives-syntax
+
+// Test correct handling of uninitialized const.
+
+function test() {
+  for (var i = 41; i < 42; i++) {
+    var c = t ^ i;
+  }
+  const t;
+  return c;
+}
+
+for (var i=0; i<10; i++) test();
+%OptimizeFunctionOnNextCall(test);
+assertEquals(41, test());