csa-load-elimination.cc

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// Copyright 2019 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/csa-load-elimination.h"
 
#include "src/compiler/common-operator.h"
#include "src/compiler/node-matchers.h"
#include "src/compiler/node-properties.h"
#include "src/compiler/simplified-operator.h"
 
namespace v8 {
namespace internal {
namespace compiler {
 
Reduction CsaLoadElimination::Reduce(Node* node) {
  if (v8_flags.trace_turbo_load_elimination) {
    if (node->op()->EffectInputCount() > 0) {
      PrintF(" visit #%d:%s", node->id(), node->op()->mnemonic());
      if (node->op()->ValueInputCount() > 0) {
        PrintF("(");
        for (int i = 0; i < node->op()->ValueInputCount(); ++i) {
          if (i > 0) PrintF(", ");
          Node* const value = NodeProperties::GetValueInput(node, i);
          PrintF("#%d:%s", value->id(), value->op()->mnemonic());
        }
        PrintF(")");
      }
      PrintF("\n");
      for (int i = 0; i < node->op()->EffectInputCount(); ++i) {
        Node* const effect = NodeProperties::GetEffectInput(node, i);
        if (AbstractState const* const state = node_states_.Get(effect)) {
          PrintF("  state[%i]: #%d:%s\n", i, effect->id(),
                 effect->op()->mnemonic());
          state->mutable_state.Print();
          state->immutable_state.Print();
        } else {
          PrintF("  no state[%i]: #%d:%s\n", i, effect->id(),
                 effect->op()->mnemonic());
        }
      }
    }
  }
  switch (node->opcode()) {
    case IrOpcode::kLoadFromObject:
    case IrOpcode::kLoadImmutableFromObject:
      return ReduceLoadFromObject(node, ObjectAccessOf(node->op()));
    case IrOpcode::kStoreToObject:
    case IrOpcode::kInitializeImmutableInObject:
      return ReduceStoreToObject(node, ObjectAccessOf(node->op()));
    case IrOpcode::kDebugBreak:
    case IrOpcode::kAbortCSADcheck:
      // Avoid changing optimizations in the presence of debug instructions.
      return PropagateInputState(node);
    case IrOpcode::kCall:
      return ReduceCall(node);
    case IrOpcode::kEffectPhi:
      return ReduceEffectPhi(node);
    case IrOpcode::kDead:
      return NoChange();
    case IrOpcode::kStart:
      return ReduceStart(node);
    default:
      return ReduceOtherNode(node);
  }
  UNREACHABLE();
}
 
namespace CsaLoadEliminationHelpers {
 
bool Subsumes(MachineRepresentation from, MachineRepresentation to) {
  if (from == to) return true;
  if (IsAnyTagged(from)) return IsAnyTagged(to);
  if (IsIntegral(from)) {
    return IsIntegral(to) && ElementSizeInBytes(from) >= ElementSizeInBytes(to);
  }
  return false;
}
 
bool IsConstantObject(Node* object) {
  return object->opcode() == IrOpcode::kParameter ||
         object->opcode() == IrOpcode::kLoadImmutable ||
         NodeProperties::IsConstant(object);
}
 
bool IsFreshObject(Node* object) {
  return object->opcode() == IrOpcode::kAllocate ||
         object->opcode() == IrOpcode::kAllocateRaw;
}
 
}  // namespace CsaLoadEliminationHelpers
 
namespace Helpers = CsaLoadEliminationHelpers;
 
// static
template <typename OuterKey>
void CsaLoadElimination::HalfState::IntersectWith(
    OuterMap<OuterKey>& to, const OuterMap<OuterKey>& from) {
  FieldInfo empty_info;
  for (const std::pair<OuterKey, InnerMap>& to_map : to) {
    InnerMap to_map_copy(to_map.second);
    OuterKey key = to_map.first;
    InnerMap current_map = from.Get(key);
    for (std::pair<Node*, FieldInfo> info : to_map.second) {
      if (current_map.Get(info.first) != info.second) {
        to_map_copy.Set(info.first, empty_info);
      }
    }
    to.Set(key, to_map_copy);
  }
}
 
void CsaLoadElimination::HalfState::IntersectWith(HalfState const* that) {
  IntersectWith(fresh_entries_, that->fresh_entries_);
  IntersectWith(constant_entries_, that->constant_entries_);
  IntersectWith(arbitrary_entries_, that->arbitrary_entries_);
  IntersectWith(fresh_unknown_entries_, that->fresh_unknown_entries_);
  IntersectWith(constant_unknown_entries_, that->constant_unknown_entries_);
  IntersectWith(arbitrary_unknown_entries_, that->arbitrary_unknown_entries_);
}
 
CsaLoadElimination::HalfState const* CsaLoadElimination::HalfState::KillField(
    Node* object, Node* offset, MachineRepresentation repr) const {
  HalfState* result = zone_->New<HalfState>(*this);
  UnknownOffsetInfos empty_unknown(zone_, InnerMap(zone_));
  IntPtrMatcher m(offset);
  if (m.HasResolvedValue()) {
    uint32_t num_offset = static_cast<uint32_t>(m.ResolvedValue());
    if (Helpers::IsFreshObject(object)) {
      // May alias with:
      // - The same object/offset
      // - Arbitrary objects with the same offset
      // - The same object, unkwown offset
      // - Arbitrary objects with unkwown offset
      result->KillOffsetInFresh(object, num_offset, repr);
      KillOffset(result->arbitrary_entries_, num_offset, repr, zone_);
      result->fresh_unknown_entries_.Set(object, InnerMap(zone_));
      result->arbitrary_unknown_entries_ = empty_unknown;
    } else if (Helpers::IsConstantObject(object)) {
      // May alias with:
      // - Constant/arbitrary objects with the same offset
      // - Constant/arbitrary objects with unkwown offset
      KillOffset(result->constant_entries_, num_offset, repr, zone_);
      KillOffset(result->arbitrary_entries_, num_offset, repr, zone_);
      result->constant_unknown_entries_ = empty_unknown;
      result->arbitrary_unknown_entries_ = empty_unknown;
    } else {
      // May alias with:
      // - Any object with the same or unknown offset
      KillOffset(result->fresh_entries_, num_offset, repr, zone_);
      KillOffset(result->constant_entries_, num_offset, repr, zone_);
      KillOffset(result->arbitrary_entries_, num_offset, repr, zone_);
      result->fresh_unknown_entries_ = empty_unknown;
      result->constant_unknown_entries_ = empty_unknown;
      result->arbitrary_unknown_entries_ = empty_unknown;
    }
  } else {
    ConstantOffsetInfos empty_constant(zone_, InnerMap(zone_));
    if (Helpers::IsFreshObject(object)) {
      // May alias with:
      // - The same object with any known/unknown offset
      // - Arbitrary objects with any known/unknown offset
      for (auto map : result->fresh_entries_) {
        // TODO(manoskouk): Consider adding a map from fresh objects to offsets
        // to implement this efficiently.
        InnerMap map_copy(map.second);
        map_copy.Set(object, FieldInfo());
        result->fresh_entries_.Set(map.first, map_copy);
      }
      result->fresh_unknown_entries_.Set(object, InnerMap(zone_));
      result->arbitrary_entries_ = empty_constant;
      result->arbitrary_unknown_entries_ = empty_unknown;
    } else if (Helpers::IsConstantObject(object)) {
      // May alias with:
      // - Constant/arbitrary objects with the any known/unknown offset
      result->constant_entries_ = empty_constant;
      result->constant_unknown_entries_ = empty_unknown;
      result->arbitrary_entries_ = empty_constant;
      result->arbitrary_unknown_entries_ = empty_unknown;
    } else {
      // May alias with anything. Clear the state.
      return zone_->New<HalfState>(zone_);
    }
  }
 
  return result;
}
 
CsaLoadElimination::HalfState const* CsaLoadElimination::HalfState::AddField(
    Node* object, Node* offset, Node* value, MachineRepresentation repr) const {
  HalfState* new_state = zone_->New<HalfState>(*this);
  IntPtrMatcher m(offset);
  if (m.HasResolvedValue()) {
    uint32_t offset_num = static_cast<uint32_t>(m.ResolvedValue());
    ConstantOffsetInfos& infos = Helpers::IsFreshObject(object)
                                     ? new_state->fresh_entries_
                                     : Helpers::IsConstantObject(object)
                                           ? new_state->constant_entries_
                                           : new_state->arbitrary_entries_;
    Update(infos, offset_num, object, FieldInfo(value, repr));
  } else {
    UnknownOffsetInfos& infos =
        Helpers::IsFreshObject(object)
            ? new_state->fresh_unknown_entries_
            : Helpers::IsConstantObject(object)
                  ? new_state->constant_unknown_entries_
                  : new_state->arbitrary_unknown_entries_;
    Update(infos, object, offset, FieldInfo(value, repr));
  }
  return new_state;
}
 
CsaLoadElimination::FieldInfo CsaLoadElimination::HalfState::Lookup(
    Node* object, Node* offset) const {
  IntPtrMatcher m(offset);
  if (m.HasResolvedValue()) {
    uint32_t num_offset = static_cast<uint32_t>(m.ResolvedValue());
    const ConstantOffsetInfos& infos = Helpers::IsFreshObject(object)
                                           ? fresh_entries_
                                           : Helpers::IsConstantObject(object)
                                                 ? constant_entries_
                                                 : arbitrary_entries_;
    return infos.Get(num_offset).Get(object);
  } else {
    const UnknownOffsetInfos& infos = Helpers::IsFreshObject(object)
                                          ? fresh_unknown_entries_
                                          : Helpers::IsConstantObject(object)
                                                ? constant_unknown_entries_
                                                : arbitrary_unknown_entries_;
    return infos.Get(object).Get(offset);
  }
}
 
// static
// Kill all elements in {infos} that overlap with an element with {offset} and
// size {ElementSizeInBytes(repr)}.
void CsaLoadElimination::HalfState::KillOffset(ConstantOffsetInfos& infos,
                                               uint32_t offset,
                                               MachineRepresentation repr,
                                               Zone* zone) {
  // All elements in the range [{offset}, {offset + ElementSizeInBytes(repr)})
  // are in the killed range. We do not need to traverse the inner maps, we can
  // just clear them.
  for (int i = 0; i < ElementSizeInBytes(repr); i++) {
    infos.Set(offset + i, InnerMap(zone));
  }
 
  // Now we have to remove all elements in earlier offsets that overlap with an
  // element in {offset}.
  // The earliest offset that may overlap with {offset} is
  // {kMaximumReprSizeInBytes - 1} before.
  uint32_t initial_offset = offset >= kMaximumReprSizeInBytes - 1
                                ? offset - (kMaximumReprSizeInBytes - 1)
                                : 0;
  // For all offsets from {initial_offset} to {offset}, we traverse the
  // respective inner map, and reset all elements that are large enough to
  // overlap with {offset}.
  for (uint32_t i = initial_offset; i < offset; i++) {
    InnerMap map_copy(infos.Get(i));
    for (const std::pair<Node*, FieldInfo> info : infos.Get(i)) {
      if (info.second.representation != MachineRepresentation::kNone &&
          ElementSizeInBytes(info.second.representation) >
              static_cast<int>(offset - i)) {
        map_copy.Set(info.first, {});
      }
    }
    infos.Set(i, map_copy);
  }
}
 
void CsaLoadElimination::HalfState::KillOffsetInFresh(
    Node* const object, uint32_t offset, MachineRepresentation repr) {
  for (int i = 0; i < ElementSizeInBytes(repr); i++) {
    Update(fresh_entries_, offset + i, object, {});
  }
  uint32_t initial_offset = offset >= kMaximumReprSizeInBytes - 1
                                ? offset - (kMaximumReprSizeInBytes - 1)
                                : 0;
  for (uint32_t i = initial_offset; i < offset; i++) {
    const FieldInfo& info = fresh_entries_.Get(i).Get(object);
    if (info.representation != MachineRepresentation::kNone &&
        ElementSizeInBytes(info.representation) >
            static_cast<int>(offset - i)) {
      Update(fresh_entries_, i, object, {});
    }
  }
}
 
// static
void CsaLoadElimination::HalfState::Print(
    const CsaLoadElimination::HalfState::ConstantOffsetInfos& infos) {
  for (const auto outer_entry : infos) {
    for (const auto inner_entry : outer_entry.second) {
      Node* object = inner_entry.first;
      uint32_t offset = outer_entry.first;
      FieldInfo info = inner_entry.second;
      PrintF("    #%d:%s+(%d) -> #%d:%s [repr=%s]\n", object->id(),
             object->op()->mnemonic(), offset, info.value->id(),
             info.value->op()->mnemonic(),
             MachineReprToString(info.representation));
    }
  }
}
 
// static
void CsaLoadElimination::HalfState::Print(
    const CsaLoadElimination::HalfState::UnknownOffsetInfos& infos) {
  for (const auto outer_entry : infos) {
    for (const auto inner_entry : outer_entry.second) {
      Node* object = outer_entry.first;
      Node* offset = inner_entry.first;
      FieldInfo info = inner_entry.second;
      PrintF("    #%d:%s+#%d:%s -> #%d:%s [repr=%s]\n", object->id(),
             object->op()->mnemonic(), offset->id(), offset->op()->mnemonic(),
             info.value->id(), info.value->op()->mnemonic(),
             MachineReprToString(info.representation));
    }
  }
}
 
void CsaLoadElimination::HalfState::Print() const {
  Print(fresh_entries_);
  Print(constant_entries_);
  Print(arbitrary_entries_);
  Print(fresh_unknown_entries_);
  Print(constant_unknown_entries_);
  Print(arbitrary_unknown_entries_);
}
 
// We may encounter a mutable/immutable inconsistency if the same field offset
// is loaded/stored from the same object both as mutable and immutable. This can
// only happen in code where the object has been cast to two different
// incompatible types, i.e. in unreachable code. For safety, we introduce an
// Unreachable node before the load/store.
Reduction CsaLoadElimination::AssertUnreachable(Node* node) {
  Node* effect = NodeProperties::GetEffectInput(node);
  Node* control = NodeProperties::GetControlInput(node);
  Node* unreachable =
      graph()->NewNode(jsgraph()->common()->Unreachable(), effect, control);
  return Replace(unreachable);
}
 
Reduction CsaLoadElimination::ReduceLoadFromObject(Node* node,
                                                   ObjectAccess const& access) {
  DCHECK(node->opcode() == IrOpcode::kLoadFromObject ||
         node->opcode() == IrOpcode::kLoadImmutableFromObject);
  Node* object = NodeProperties::GetValueInput(node, 0);
  Node* offset = NodeProperties::GetValueInput(node, 1);
  Node* effect = NodeProperties::GetEffectInput(node);
  AbstractState const* state = node_states_.Get(effect);
  if (state == nullptr) return NoChange();
  bool is_mutable = node->opcode() == IrOpcode::kLoadFromObject;
  // We can only find the field in the wrong half-state in unreachable code.
  if (!(is_mutable ? &state->immutable_state : &state->mutable_state)
           ->Lookup(object, offset)
           .IsEmpty()) {
    Node* control = NodeProperties::GetControlInput(node);
    Node* unreachable =
        graph()->NewNode(jsgraph()->common()->Unreachable(), effect, control);
    auto rep = ObjectAccessOf(node->op()).machine_type.representation();
    Node* dead_value =
        graph()->NewNode(jsgraph()->common()->DeadValue(rep), unreachable);
    ReplaceWithValue(node, dead_value, unreachable, control);
    node->Kill();
    return Replace(dead_value);
  }
  HalfState const* half_state =
      is_mutable ? &state->mutable_state : &state->immutable_state;
 
  MachineRepresentation representation = access.machine_type.representation();
  FieldInfo lookup_result = half_state->Lookup(object, offset);
  if (!lookup_result.IsEmpty()) {
    // Make sure we don't reuse values that were recorded with a different
    // representation or resurrect dead {replacement} nodes.
    MachineRepresentation from = lookup_result.representation;
    if (Helpers::Subsumes(from, representation) &&
        !lookup_result.value->IsDead()) {
      Node* replacement =
          TruncateAndExtend(lookup_result.value, from, access.machine_type);
      ReplaceWithValue(node, replacement, effect);
      // This might have opened an opportunity for escape analysis to eliminate
      // the object altogether.
      Revisit(object);
      return Replace(replacement);
    }
  }
  half_state = half_state->AddField(object, offset, node, representation);
 
  AbstractState const* new_state =
      is_mutable
          ? zone()->New<AbstractState>(*half_state, state->immutable_state)
          : zone()->New<AbstractState>(state->mutable_state, *half_state);
 
  return UpdateState(node, new_state);
}
 
Reduction CsaLoadElimination::ReduceStoreToObject(Node* node,
                                                  ObjectAccess const& access) {
  DCHECK(node->opcode() == IrOpcode::kStoreToObject ||
         node->opcode() == IrOpcode::kInitializeImmutableInObject);
  Node* object = NodeProperties::GetValueInput(node, 0);
  Node* offset = NodeProperties::GetValueInput(node, 1);
  Node* value = NodeProperties::GetValueInput(node, 2);
  Node* effect = NodeProperties::GetEffectInput(node);
  AbstractState const* state = node_states_.Get(effect);
  if (state == nullptr) return NoChange();
  MachineRepresentation repr = access.machine_type.representation();
  if (node->opcode() == IrOpcode::kStoreToObject) {
    // We can only find the field in the wrong half-state in unreachable code.
    if (!(state->immutable_state.Lookup(object, offset).IsEmpty())) {
      return AssertUnreachable(node);
    }
    HalfState const* mutable_state =
        state->mutable_state.KillField(object, offset, repr);
    mutable_state = mutable_state->AddField(object, offset, value, repr);
    AbstractState const* new_state =
        zone()->New<AbstractState>(*mutable_state, state->immutable_state);
    return UpdateState(node, new_state);
  } else {
    // We can only find the field in the wrong half-state in unreachable code.
    if (!(state->mutable_state.Lookup(object, offset).IsEmpty())) {
      return AssertUnreachable(node);
    }
    // We should not initialize the same immutable field twice.
    DCHECK(state->immutable_state.Lookup(object, offset).IsEmpty());
    HalfState const* immutable_state =
        state->immutable_state.AddField(object, offset, value, repr);
    AbstractState const* new_state =
        zone()->New<AbstractState>(state->mutable_state, *immutable_state);
    return UpdateState(node, new_state);
  }
}
 
Reduction CsaLoadElimination::ReduceEffectPhi(Node* node) {
  Node* const effect0 = NodeProperties::GetEffectInput(node, 0);
  Node* const control = NodeProperties::GetControlInput(node);
  AbstractState const* state0 = node_states_.Get(effect0);
  if (state0 == nullptr) return NoChange();
  if (control->opcode() == IrOpcode::kLoop) {
    // Here we rely on having only reducible loops:
    // The loop entry edge always dominates the header, so we can just take
    // the state from the first input, and compute the loop state based on it.
    AbstractState const* state = ComputeLoopState(node, state0);
    return UpdateState(node, state);
  }
  DCHECK_EQ(IrOpcode::kMerge, control->opcode());
 
  // Shortcut for the case when we do not know anything about some input.
  int const input_count = node->op()->EffectInputCount();
  for (int i = 1; i < input_count; ++i) {
    Node* const effect = NodeProperties::GetEffectInput(node, i);
    if (node_states_.Get(effect) == nullptr) return NoChange();
  }
 
  // Make a copy of the first input's state and intersect it with the state
  // from other inputs.
  // TODO(manoskouk): Consider computing phis for at least a subset of the
  // state.
  AbstractState* state = zone()->New<AbstractState>(*state0);
  for (int i = 1; i < input_count; ++i) {
    Node* const input = NodeProperties::GetEffectInput(node, i);
    state->IntersectWith(node_states_.Get(input));
  }
  return UpdateState(node, state);
}
 
Reduction CsaLoadElimination::ReduceStart(Node* node) {
  return UpdateState(node, empty_state());
}
 
Reduction CsaLoadElimination::ReduceCall(Node* node) {
  Node* value = NodeProperties::GetValueInput(node, 0);
  ExternalReferenceMatcher m(value);
  if (m.Is(ExternalReference::check_object_type())) {
    return PropagateInputState(node);
  }
  return ReduceOtherNode(node);
}
 
Reduction CsaLoadElimination::ReduceOtherNode(Node* node) {
  if (node->op()->EffectInputCount() == 1 &&
      node->op()->EffectOutputCount() == 1) {
    Node* const effect = NodeProperties::GetEffectInput(node);
    AbstractState const* state = node_states_.Get(effect);
    // If we do not know anything about the predecessor, do not propagate just
    // yet because we will have to recompute anyway once we compute the
    // predecessor.
    if (state == nullptr) return NoChange();
    // If this {node} has some uncontrolled side effects, set its state to
    // the immutable half-state of its input state, otherwise to its input
    // state.
    return UpdateState(
        node, node->op()->HasProperty(Operator::kNoWrite)
                  ? state
                  : zone()->New<AbstractState>(HalfState(zone()),
                                               state->immutable_state));
  }
  DCHECK_EQ(0, node->op()->EffectOutputCount());
  return NoChange();
}
 
Reduction CsaLoadElimination::UpdateState(Node* node,
                                          AbstractState const* state) {
  AbstractState const* original = node_states_.Get(node);
  // Only signal that the {node} has Changed, if the information about {state}
  // has changed wrt. the {original}.
  if (state != original) {
    if (original == nullptr || !state->Equals(original)) {
      node_states_.Set(node, state);
      return Changed(node);
    }
  }
  return NoChange();
}
 
Reduction CsaLoadElimination::PropagateInputState(Node* node) {
  Node* const effect = NodeProperties::GetEffectInput(node);
  AbstractState const* state = node_states_.Get(effect);
  if (state == nullptr) return NoChange();
  return UpdateState(node, state);
}
 
CsaLoadElimination::AbstractState const* CsaLoadElimination::ComputeLoopState(
    Node* node, AbstractState const* state) const {
  DCHECK_EQ(node->opcode(), IrOpcode::kEffectPhi);
  std::queue<Node*> queue;
  std::unordered_set<Node*> visited;
  visited.insert(node);
  for (int i = 1; i < node->InputCount() - 1; ++i) {
    queue.push(node->InputAt(i));
  }
  while (!queue.empty()) {
    Node* const current = queue.front();
    queue.pop();
    if (visited.insert(current).second) {
      if (current->opcode() == IrOpcode::kStoreToObject) {
        Node* object = NodeProperties::GetValueInput(current, 0);
        Node* offset = NodeProperties::GetValueInput(current, 1);
        MachineRepresentation repr =
            ObjectAccessOf(current->op()).machine_type.representation();
        const HalfState* new_mutable_state =
            state->mutable_state.KillField(object, offset, repr);
        state = zone()->New<AbstractState>(*new_mutable_state,
                                           state->immutable_state);
      } else if (current->opcode() == IrOpcode::kInitializeImmutableInObject) {
#if DEBUG
        // We are not allowed to reset an immutable (object, offset) pair.
        Node* object = NodeProperties::GetValueInput(current, 0);
        Node* offset = NodeProperties::GetValueInput(current, 1);
        CHECK(state->immutable_state.Lookup(object, offset).IsEmpty());
#endif
      } else if (!current->op()->HasProperty(Operator::kNoWrite)) {
        return zone()->New<AbstractState>(HalfState(zone()),
                                          state->immutable_state);
      }
      for (int i = 0; i < current->op()->EffectInputCount(); ++i) {
        queue.push(NodeProperties::GetEffectInput(current, i));
      }
    }
  }
  return state;
}
 
Node* CsaLoadElimination::TruncateAndExtend(Node* node,
                                            MachineRepresentation from,
                                            MachineType to) {
  DCHECK(Helpers::Subsumes(from, to.representation()));
  DCHECK_GE(ElementSizeInBytes(from), ElementSizeInBytes(to.representation()));
 
  if (to == MachineType::Int8() || to == MachineType::Int16()) {
    // 1st case: We want to eliminate a signed 8/16-bit load using the value
    // from a previous subsuming load or store. Since that value might be
    // outside 8/16-bit range, we first truncate it accordingly. Then we
    // sign-extend the result to 32-bit.
    DCHECK_EQ(to.semantic(), MachineSemantic::kInt32);
    if (from == MachineRepresentation::kWord64) {
      node = graph()->NewNode(machine()->TruncateInt64ToInt32(), node);
    }
    int shift = 32 - 8 * ElementSizeInBytes(to.representation());
    return graph()->NewNode(machine()->Word32Sar(),
                            graph()->NewNode(machine()->Word32Shl(), node,
                                             jsgraph()->Int32Constant(shift)),
                            jsgraph()->Int32Constant(shift));
  } else if (to == MachineType::Uint8() || to == MachineType::Uint16()) {
    // 2nd case: We want to eliminate an unsigned 8/16-bit load using the value
    // from a previous subsuming load or store. Since that value might be
    // outside 8/16-bit range, we first truncate it accordingly.
    if (from == MachineRepresentation::kWord64) {
      node = graph()->NewNode(machine()->TruncateInt64ToInt32(), node);
    }
    int mask = (1 << 8 * ElementSizeInBytes(to.representation())) - 1;
    return graph()->NewNode(machine()->Word32And(), node,
                            jsgraph()->Int32Constant(mask));
  } else if (from == MachineRepresentation::kWord64 &&
             to.representation() == MachineRepresentation::kWord32) {
    // 3rd case: Truncate 64-bits into 32-bits.
    return graph()->NewNode(machine()->TruncateInt64ToInt32(), node);
  } else {
    // 4th case: No need for truncation.
    DCHECK((from == to.representation() &&
            (from == MachineRepresentation::kWord32 ||
             from == MachineRepresentation::kWord64 || !IsIntegral(from))) ||
           (IsAnyTagged(from) && IsAnyTagged(to.representation())));
    return node;
  }
}
 
CommonOperatorBuilder* CsaLoadElimination::common() const {
  return jsgraph()->common();
}
 
MachineOperatorBuilder* CsaLoadElimination::machine() const {
  return jsgraph()->machine();
}
 
TFGraph* CsaLoadElimination::graph() const { return jsgraph()->graph(); }
 
Isolate* CsaLoadElimination::isolate() const { return jsgraph()->isolate(); }
 
}  // namespace compiler
}  // namespace internal
}  // namespace v8