Fix GVN for polymorphic loads....

src/hydrogen.cc

 // Copyright 2010 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
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@@ skipping 1437 matching lines @@
 
 // Only move instructions that postdominate the loop header (i.e. are
 // always executed inside the loop). This is to avoid unnecessary
 // deoptimizations assuming the loop is executed at least once.
 // TODO(fschneider): Better type feedback should give us information
 // about code that was never executed.
 bool HGlobalValueNumberer::ShouldMove(HInstruction* instr,
                                       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) {
     for (int i = 1; i < loop_header->predecessors()->length(); ++i) {
       bool found = false;
       HBasicBlock* pred = loop_header->predecessors()->at(i);
       while (pred != loop_header) {
         if (pred == block) found = true;
         pred = pred->dominator();
       }
@@ skipping 2057 matching lines @@
   // different maps are identical. In that case we can avoid
   // repeatedly generating the same prototype map checks.
   for (int i = 0; i < number_of_types; ++i) {
     Handle<Map> map = types->at(i);
     LookupResult lookup;
     map->LookupInDescriptors(NULL, *name, &lookup);
     if (lookup.IsProperty() && lookup.type() == FIELD) {
       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 {
       needs_generic = true;
     }
   }
 
   // If none of the properties were named fields we generate a
   // generic load.
   if (maps.length() == 0) {
@@ skipping 18 matching lines @@
 
     HBasicBlock* new_exit_block =
         BuildTypeSwitch(&maps, &subgraphs, object, expr->id());
     subgraph()->set_exit_block(new_exit_block);
   }
 
   if (subgraph()->HasExit()) ast_context()->ReturnValue(Pop());
 }
 
 
-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));
   }
 
   int index = lookup->GetLocalFieldIndexFromMap(*type);
   if (index < 0) {
     // Negative property indices are in-object properties, indexed
     // from the end of the fixed part of the object.
     int offset = (index * kPointerSize) + type->instance_size();
@@ skipping 2083 matching lines @@
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify();
   if (chunk_ != NULL) chunk_->Verify();
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal