[turbofan] Teach ad-hoc load elimination about atomic regions.

src/compiler/load-elimination.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/load-elimination.h"
 
 #include "src/compiler/node-properties.h"
 #include "src/compiler/simplified-operator.h"
 
 namespace v8 {
@@ skipping 10 matching lines @@
     default:
       break;
   }
   return NoChange();
 }
 
 
 Reduction LoadElimination::ReduceLoadField(Node* node) {
   DCHECK_EQ(IrOpcode::kLoadField, node->opcode());
   FieldAccess const access = FieldAccessOf(node->op());
-  Node* const object = NodeProperties::GetValueInput(node, 0);
+  Node* object = NodeProperties::GetValueInput(node, 0);
   for (Node* effect = NodeProperties::GetEffectInput(node);;
        effect = NodeProperties::GetEffectInput(effect)) {
     switch (effect->opcode()) {
       case IrOpcode::kLoadField: {
         if (object == NodeProperties::GetValueInput(effect, 0) &&
             access == FieldAccessOf(effect->op())) {
           Node* const value = effect;
           ReplaceWithValue(node, value);
           return Replace(value);
         }
         break;
       }
       case IrOpcode::kStoreField: {
         if (access == FieldAccessOf(effect->op())) {
           if (object == NodeProperties::GetValueInput(effect, 0)) {
             Node* const value = NodeProperties::GetValueInput(effect, 1);
             ReplaceWithValue(node, value);
             return Replace(value);
           }
           // TODO(turbofan): Alias analysis to the rescue?
           return NoChange();
         }
         break;
       }
+      case IrOpcode::kBeginRegion:
       case IrOpcode::kStoreBuffer:
       case IrOpcode::kStoreElement: {
         // These can never interfere with field loads.
         break;
       }
+      case IrOpcode::kFinishRegion: {
+        // "Look through" FinishRegion nodes to make LoadElimination capable
+        // of looking into atomic regions.
+        if (object == effect) object = NodeProperties::GetValueInput(effect, 0);
+        break;
+      }
+      case IrOpcode::kAllocate: {
+        // Allocations don't interfere with field loads. In case we see the
+        // actual allocation for the {object} we can abort.
+        if (object == effect) return NoChange();
+        break;
+      }
       default: {
         if (!effect->op()->HasProperty(Operator::kNoWrite) ||
             effect->op()->EffectInputCount() != 1) {
           return NoChange();
         }
         break;
       }
     }
   }
   UNREACHABLE();
   return NoChange();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8