Fix "Hole" leak in TryBuildConsolidatedElementLoad

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/23361007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16262 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen.cc

@@ -5529,6 +5529,7 @@ HInstruction* HOptimizedGraphBuilder::TryBuildConsolidatedElementLoad(
   bool has_smi_or_object_maps = false;
   bool has_js_array_access = false;
   bool has_non_js_array_access = false;
+  bool has_seen_holey_elements = false;
   Handle<Map> most_general_consolidated_map;
   for (int i = 0; i < maps->length(); ++i) {
     Handle<Map> map = maps->at(i);
@@ -5551,6 +5552,10 @@ HInstruction* HOptimizedGraphBuilder::TryBuildConsolidatedElementLoad(
     } else {
       return NULL;
     }
+    // Remember if we've ever seen holey elements.
+    if (IsHoleyElementsKind(map->elements_kind())) {
+      has_seen_holey_elements = true;
+    }
     // Remember the most general elements kind, the code for its load will
     // properly handle all of the more specific cases.
     if ((i == 0) || IsMoreGeneralElementsKindTransition(
@@ -5562,10 +5567,15 @@ HInstruction* HOptimizedGraphBuilder::TryBuildConsolidatedElementLoad(
   if (!has_double_maps && !has_smi_or_object_maps) return NULL;
 
   HCheckMaps* check_maps = Add<HCheckMaps>(object, maps);
+  // FAST_ELEMENTS is considered more general than FAST_HOLEY_SMI_ELEMENTS.
+  // If we've seen both, the consolidated load must use FAST_HOLEY_ELEMENTS.
+  ElementsKind consolidated_elements_kind = has_seen_holey_elements
+      ? GetHoleyElementsKind(most_general_consolidated_map->elements_kind())
+      : most_general_consolidated_map->elements_kind();
   HInstruction* instr = BuildUncheckedMonomorphicElementAccess(
       object, key, val, check_maps,
       most_general_consolidated_map->instance_type() == JS_ARRAY_TYPE,
-      most_general_consolidated_map->elements_kind(),
+      consolidated_elements_kind,
       false, NEVER_RETURN_HOLE, STANDARD_STORE);
   return instr;
 }

test/mjsunit/regress/consolidated-holey-load.js

+// Copyright 2013 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
+
+function foo(array) {
+  return array[0];
+}
+
+var a = [1, 2, , 4];  // Holey Smi elements.
+var b = ["abcd", 0];  // Fast elements.
+foo(b);  // Observe fast elements first, or the IC will transition without
+foo(a);  // going polymorphic.
+%OptimizeFunctionOnNextCall(foo);
+var c = [, 0];
+assertEquals(undefined, foo(c));  // Elided hole check will leak the hole.