Fix GVN for polymorphic loads....

src/hydrogen.cc

Index: src/hydrogen.cc
===================================================================
--- src/hydrogen.cc	(revision 6079)
+++ src/hydrogen.cc	(working copy)
@@ -1455,6 +1455,13 @@
                                       HBasicBlock* loop_header) {
   if (!instr->IsChange() &&
       FLAG_aggressive_loop_invariant_motion) return true;
+
+  // Don't hoist named loads that are part of polymorphic loads.
+  if (instr->IsLoadNamedField() &&

[Kevin Millikin (Chromium), 2010/12/20 12:34:34]

You could accomplish essentially the same thing by not setting kUseGVN for
polymorphic named loads.  That seems nicer than a special case in the
implementation.

We would use the ability to share them via GVN, but I don't think we can do that
in practice anyway.

+      HLoadNamedField::cast(instr)->is_polymorphic()) {
+    return false;
+  }
+
   HBasicBlock* block = instr->block();
   bool result = true;
   if (block != loop_header) {
@@ -3532,9 +3539,10 @@
       maps.Add(map);
       HSubgraph* subgraph = CreateBranchSubgraph(environment());
       SubgraphScope scope(this, subgraph);
-      HInstruction* instr =
+      HLoadNamedField* instr =
           BuildLoadNamedField(object, expr, map, &lookup, false);
       instr->set_position(expr->position());
+      instr->set_is_polymorphic(true);
       PushAndAdd(instr);
       subgraphs.Add(subgraph);
     } else {
@@ -3573,11 +3581,11 @@
 }
 
 
-HInstruction* HGraphBuilder::BuildLoadNamedField(HValue* object,
-                                                 Property* expr,
-                                                 Handle<Map> type,
-                                                 LookupResult* lookup,
-                                                 bool smi_and_map_check) {
+HLoadNamedField* HGraphBuilder::BuildLoadNamedField(HValue* object,
+                                                    Property* expr,
+                                                    Handle<Map> type,
+                                                    LookupResult* lookup,
+                                                    bool smi_and_map_check) {
   if (smi_and_map_check) {
     AddInstruction(new HCheckNonSmi(object));
     AddInstruction(new HCheckMap(object, type));