Allow loading constant function from proto chain.

This enables Crankshaft to use HConstant for loading constant functions
on the prototype chain when building a monomorphic load. This pattern
appears in several JavaScript frameworks.

R=svenpanne@chromium.org
TEST=mjsunit/compiler/proto-chain-constant

Review URL: https://codereview.chromium.org/12052008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13463 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen.cc

@@ -6290,7 +6290,7 @@ HInstruction* HOptimizedGraphBuilder::BuildLoadNamedMonomorphic(
     return new(zone()) HConstant(function, Representation::Tagged());
   }
 
-  // Handle a load from a known field somewhere in the protoype chain.
+  // Handle a load from a known field somewhere in the prototype chain.
   LookupInPrototypes(map, name, &lookup);
   if (lookup.IsField()) {
     Handle<JSObject> prototype(JSObject::cast(map->prototype()));
@@ -6302,6 +6302,17 @@ HInstruction* HOptimizedGraphBuilder::BuildLoadNamedMonomorphic(
     return BuildLoadNamedField(holder_value, holder_map, &lookup);
   }
 
+  // Handle a load of a constant function somewhere in the prototype chain.
+  if (lookup.IsConstantFunction()) {
+    Handle<JSObject> prototype(JSObject::cast(map->prototype()));
+    Handle<JSObject> holder(lookup.holder());
+    Handle<Map> holder_map(holder->map());
+    AddCheckMapsWithTransitions(object, map);
+    AddInstruction(new(zone()) HCheckPrototypeMaps(prototype, holder, zone()));
+    Handle<JSFunction> function(lookup.GetConstantFunctionFromMap(*holder_map));
+    return new(zone()) HConstant(function, Representation::Tagged());
+  }
+
   // No luck, do a generic load.
   return BuildLoadNamedGeneric(object, name, expr);
 }

test/mjsunit/compiler/proto-chain-constant.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
+
+// Test loading a constant function on the prototype chain.
+
+var c = Object.create;
+var obj4 = c(null, { f4: { value: function() { return 4; }, writable: true }});
+var obj3 = c(obj4, { f3: { value: function() { return 3; }, writable: true }});
+var obj2 = c(obj3, { f2: { value: function() { return 2; }, writable: true }});
+var obj1 = c(obj2, { f1: { value: function() { return 1; }, writable: true }});
+var obj0 = c(obj1, { f0: { value: function() { return 0; }, writable: true }});
+
+function get4(obj) { return obj.f4; }
+
+assertEquals(4, get4(obj0)());
+assertEquals(4, get4(obj0)());
+%OptimizeFunctionOnNextCall(get4);
+assertEquals(4, get4(obj0)());
+obj4.f4 = function() { return 5; };
+assertEquals(5, get4(obj0)());
+
+function get3(obj) { return obj.f3; }
+
+assertEquals(3, get3(obj0)());
+assertEquals(3, get3(obj0)());
+%OptimizeFunctionOnNextCall(get3);
+assertEquals(3, get3(obj0)());
+obj2.f3 = function() { return 6; };
+assertEquals(6, get3(obj0)());