[turbofan] Try harder to avoid write barriers when writing Smis.

src/compiler/simplified-lowering.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/simplified-lowering.h"
 
 #include <limits>
 
 #include "src/address-map.h"
 #include "src/base/bits.h"
@@ skipping 2454 matching lines @@
         if (truncation.IsUnused()) return VisitUnused(node);
         FieldAccess access = FieldAccessOf(node->op());
         MachineRepresentation const representation =
             access.machine_type.representation();
         VisitUnop(node, UseInfoForBasePointer(access), representation);
         return;
       }
       case IrOpcode::kStoreField: {
         FieldAccess access = FieldAccessOf(node->op());
         NodeInfo* input_info = GetInfo(node->InputAt(1));
+        MachineRepresentation field_representation =
+            access.machine_type.representation();
+
+        // Make sure we convert to Smi if possible. This should help write
+        // barrier elimination.
+        if (field_representation == MachineRepresentation::kTagged &&
+            TypeOf(node->InputAt(1))->Is(Type::SignedSmall())) {
+          field_representation = MachineRepresentation::kTaggedSigned;
+        }
         WriteBarrierKind write_barrier_kind = WriteBarrierKindFor(
-            access.base_is_tagged, access.machine_type.representation(),
-            access.offset, access.type, input_info->representation(),
-            node->InputAt(1));
+            access.base_is_tagged, field_representation, access.offset,
+            access.type, input_info->representation(), node->InputAt(1));

[Benedikt Meurer, 2017/06/06 10:32:47]

Please give the node->InputAt(1) a name. (Same below)

+
         ProcessInput(node, 0, UseInfoForBasePointer(access));
-        ProcessInput(node, 1, TruncatingUseInfoFromRepresentation(
-                                  access.machine_type.representation()));
+        ProcessInput(node, 1,
+                     TruncatingUseInfoFromRepresentation(field_representation));
         ProcessRemainingInputs(node, 2);
         SetOutput(node, MachineRepresentation::kNone);
         if (lower()) {
           if (write_barrier_kind < access.write_barrier_kind) {
             access.write_barrier_kind = write_barrier_kind;
             NodeProperties::ChangeOp(
                 node, jsgraph_->simplified()->StoreField(access));
           }
         }
         return;
@@ skipping 49 matching lines @@
         if (truncation.IsUnused()) return VisitUnused(node);
         ElementAccess access = ElementAccessOf(node->op());
         VisitBinop(node, UseInfoForBasePointer(access),
                    UseInfo::TruncatingWord32(),
                    access.machine_type.representation());
         return;
       }
       case IrOpcode::kStoreElement: {
         ElementAccess access = ElementAccessOf(node->op());
         NodeInfo* input_info = GetInfo(node->InputAt(2));
+        MachineRepresentation element_representation =
+            access.machine_type.representation();
+
+        // Make sure we convert to Smi if possible. This should help write
+        // barrier elimination.
+        if (element_representation == MachineRepresentation::kTagged &&
+            TypeOf(node->InputAt(2))->Is(Type::SignedSmall())) {
+          element_representation = MachineRepresentation::kTaggedSigned;
+        }
         WriteBarrierKind write_barrier_kind = WriteBarrierKindFor(
-            access.base_is_tagged, access.machine_type.representation(),
-            access.type, input_info->representation(), node->InputAt(2));
+            access.base_is_tagged, element_representation, access.type,
+            input_info->representation(), node->InputAt(2));
         ProcessInput(node, 0, UseInfoForBasePointer(access));  // base
         ProcessInput(node, 1, UseInfo::TruncatingWord32());    // index
         ProcessInput(node, 2,
                      TruncatingUseInfoFromRepresentation(
-                         access.machine_type.representation()));  // value
+                         element_representation));  // value
         ProcessRemainingInputs(node, 3);
         SetOutput(node, MachineRepresentation::kNone);
         if (lower()) {
           if (write_barrier_kind < access.write_barrier_kind) {
             access.write_barrier_kind = write_barrier_kind;
             NodeProperties::ChangeOp(
                 node, jsgraph_->simplified()->StoreElement(access));
           }
         }
         return;
@@ skipping 1147 matching lines @@
         isolate(), graph()->zone(), callable.descriptor(), 0, flags,
         Operator::kNoProperties);
     to_number_operator_.set(common()->Call(desc));
   }
   return to_number_operator_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8