src/compiler/simd-scalar-lowering.cc

// Copyright 2016 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/simd-scalar-lowering.h"
#include "src/compiler/diamond.h"
#include "src/compiler/linkage.h"
#include "src/compiler/node-matchers.h"
#include "src/compiler/node-properties.h"

#include "src/compiler/node.h"
#include "src/wasm/wasm-module.h"

namespace v8 {
namespace internal {
namespace compiler {

SimdScalarLowering::SimdScalarLowering(
    Graph* graph, MachineOperatorBuilder* machine,
    CommonOperatorBuilder* common, Zone* zone,
    Signature<MachineRepresentation>* signature)
    : zone_(zone),
      graph_(graph),
      machine_(machine),
      common_(common),
      state_(graph, 3),
      stack_(zone),
      replacements_(nullptr),
      signature_(signature),
      placeholder_(
          graph->NewNode(common->Parameter(-2, "placeholder"), graph->start())),
      parameter_count_after_lowering_(-1) {
  DCHECK_NOT_NULL(graph);
  DCHECK_NOT_NULL(graph->end());
  replacements_ = zone->NewArray<Replacement>(graph->NodeCount());
  memset(replacements_, 0, sizeof(Replacement) * graph->NodeCount());
}

void SimdScalarLowering::LowerGraph() {
  stack_.push_back({graph()->end(), 0});
  state_.Set(graph()->end(), State::kOnStack);
  replacements_[graph()->end()->id()].type = SimdType::kInt32;

  while (!stack_.empty()) {
    NodeState& top = stack_.back();
    if (top.input_index == top.node->InputCount()) {
      // All inputs of top have already been lowered, now lower top.
      stack_.pop_back();
      state_.Set(top.node, State::kVisited);
      LowerNode(top.node);
    } else {
      // Push the next input onto the stack.
      Node* input = top.node->InputAt(top.input_index++);
      if (state_.Get(input) == State::kUnvisited) {
        SetLoweredType(input, top.node);
        if (input->opcode() == IrOpcode::kPhi) {
          // To break cycles with phi nodes we push phis on a separate stack so
          // that they are processed after all other nodes.
          PreparePhiReplacement(input);
          stack_.push_front({input, 0});
        } else {
          stack_.push_back({input, 0});
        }
        state_.Set(input, State::kOnStack);
      }
    }
  }
}

#define FOREACH_INT32X4_OPCODE(V) \
  V(Int32x4Add)                   \
  V(Int32x4ExtractLane)           \
  V(CreateInt32x4)

#define FOREACH_FLOAT32X4_OPCODE(V) \
  V(Float32x4Add)                   \
  V(Float32x4ExtractLane)           \
  V(CreateFloat32x4)

void SimdScalarLowering::SetLoweredType(Node* node, Node* output) {
  switch (node->opcode()) {
#define CASE_STMT(name) case IrOpcode::k##name:
    FOREACH_INT32X4_OPCODE(CASE_STMT)
    case IrOpcode::kReturn:
    case IrOpcode::kParameter:
    case IrOpcode::kCall: {
      replacements_[node->id()].type = SimdType::kInt32;
      break;
    }
      FOREACH_FLOAT32X4_OPCODE(CASE_STMT) {
        replacements_[node->id()].type = SimdType::kFloat32;
        break;
      }
#undef CASE_STMT
    default:
      replacements_[node->id()].type = replacements_[output->id()].type;
  }
}

static int GetParameterIndexAfterLowering(
    Signature<MachineRepresentation>* signature, int old_index) {
  // In function calls, the simd128 types are passed as 4 Int32 types. The
  // parameters are typecast to the types as needed for various operations.
  int result = old_index;
  for (int i = 0; i < old_index; i++) {
    if (signature->GetParam(i) == MachineRepresentation::kSimd128) {
      result += 3;
    }
  }
  return result;
}

int SimdScalarLowering::GetParameterCountAfterLowering() {
  if (parameter_count_after_lowering_ == -1) {
    // GetParameterIndexAfterLowering(parameter_count) returns the parameter
    // count after lowering.
    parameter_count_after_lowering_ = GetParameterIndexAfterLowering(
        signature(), static_cast<int>(signature()->parameter_count()));
  }
  return parameter_count_after_lowering_;
}

static int GetReturnCountAfterLowering(
    Signature<MachineRepresentation>* signature) {
  int result = static_cast<int>(signature->return_count());
  for (int i = 0; i < static_cast<int>(signature->return_count()); i++) {
    if (signature->GetReturn(i) == MachineRepresentation::kSimd128) {
      result += 3;
    }
  }
  return result;
}

void SimdScalarLowering::LowerNode(Node* node) {
  SimdType rep_type = ReplacementType(node);
  switch (node->opcode()) {
    case IrOpcode::kStart: {
      int parameter_count = GetParameterCountAfterLowering();
      // Only exchange the node if the parameter count actually changed.
      if (parameter_count != static_cast<int>(signature()->parameter_count())) {
        int delta =
            parameter_count - static_cast<int>(signature()->parameter_count());
        int new_output_count = node->op()->ValueOutputCount() + delta;
        NodeProperties::ChangeOp(node, common()->Start(new_output_count));
      }
      break;
    }
    case IrOpcode::kParameter: {
      DCHECK(node->InputCount() == 1);
      // Only exchange the node if the parameter count actually changed. We do
      // not even have to do the default lowering because the the start node,
      // the only input of a parameter node, only changes if the parameter count
      // changes.
      if (GetParameterCountAfterLowering() !=
          static_cast<int>(signature()->parameter_count())) {
        int old_index = ParameterIndexOf(node->op());
        int new_index = GetParameterIndexAfterLowering(signature(), old_index);
        if (old_index == new_index) {
          NodeProperties::ChangeOp(node, common()->Parameter(new_index));

          Node* new_node[kMaxLanes];
          for (int i = 0; i < kMaxLanes; i++) {
            new_node[i] = nullptr;
          }
          new_node[0] = node;
          if (signature()->GetParam(old_index) ==
              MachineRepresentation::kSimd128) {
            for (int i = 1; i < kMaxLanes; i++) {
              new_node[i] = graph()->NewNode(common()->Parameter(new_index + i),
                                             graph()->start());
            }
          }
          ReplaceNode(node, new_node);
        }
      }
      break;
    }
    case IrOpcode::kReturn: {
      DefaultLowering(node);
      int new_return_count = GetReturnCountAfterLowering(signature());
      if (static_cast<int>(signature()->return_count()) != new_return_count) {
        NodeProperties::ChangeOp(node, common()->Return(new_return_count));
      }
      break;
    }
    case IrOpcode::kCall: {
      // TODO(turbofan): Make WASM code const-correct wrt. CallDescriptor.
      CallDescriptor* descriptor =
          const_cast<CallDescriptor*>(CallDescriptorOf(node->op()));
      if (DefaultLowering(node) ||
          (descriptor->ReturnCount() == 1 &&
           descriptor->GetReturnType(0) == MachineType::Simd128())) {
        // We have to adjust the call descriptor.
        const Operator* op =
            common()->Call(wasm::ModuleEnv::GetI32WasmCallDescriptorForSimd(
                zone(), descriptor));
        NodeProperties::ChangeOp(node, op);
      }
      if (descriptor->ReturnCount() == 1 &&
          descriptor->GetReturnType(0) == MachineType::Simd128()) {
        // We access the additional return values through projections.
        Node* rep_node[kMaxLanes];
        for (int i = 0; i < kMaxLanes; i++) {
          rep_node[i] =
              graph()->NewNode(common()->Projection(i), node, graph()->start());
        }
        ReplaceNode(node, rep_node);
      }
      break;
    }
    case IrOpcode::kPhi: {
      MachineRepresentation rep = PhiRepresentationOf(node->op());
      if (rep == MachineRepresentation::kSimd128) {
        // The replacement nodes have already been created, we only have to
        // replace placeholder nodes.
        Node** rep_node = GetReplacements(node);
        for (int i = 0; i < node->op()->ValueInputCount(); i++) {
          Node** rep_input =
              GetReplacementsWithType(node->InputAt(i), rep_type);
          for (int j = 0; j < kMaxLanes; j++) {
            rep_node[j]->ReplaceInput(i, rep_input[j]);
          }
        }
      } else {
        DefaultLowering(node);
      }
      break;
    }

    case IrOpcode::kInt32x4Add: {
      DCHECK(node->InputCount() == 2);
      Node** rep_left = GetReplacementsWithType(node->InputAt(0), rep_type);
      Node** rep_right = GetReplacementsWithType(node->InputAt(1), rep_type);
      Node* rep_node[kMaxLanes];
      for (int i = 0; i < kMaxLanes; i++) {
        rep_node[i] =
            graph()->NewNode(machine()->Int32Add(), rep_left[i], rep_right[i]);
      }
      ReplaceNode(node, rep_node);
      break;
    }

    case IrOpcode::kCreateInt32x4: {
      Node* rep_node[kMaxLanes];
      for (int i = 0; i < kMaxLanes; i++) {
        DCHECK(!HasReplacement(1, node->InputAt(i)));
        rep_node[i] = node->InputAt(i);
      }
      ReplaceNode(node, rep_node);
      break;
    }

    case IrOpcode::kInt32x4ExtractLane: {
      Node* laneNode = node->InputAt(1);
      DCHECK_EQ(laneNode->opcode(), IrOpcode::kInt32Constant);
      int32_t lane = OpParameter<int32_t>(laneNode);
      Node* rep_node[kMaxLanes] = {
          GetReplacementsWithType(node->InputAt(0), rep_type)[lane], nullptr,
          nullptr, nullptr};
      ReplaceNode(node, rep_node);
      break;
    }

    case IrOpcode::kFloat32x4Add: {
      DCHECK(node->InputCount() == 2);
      Node** rep_left = GetReplacementsWithType(node->InputAt(0), rep_type);
      Node** rep_right = GetReplacementsWithType(node->InputAt(1), rep_type);
      Node* rep_node[kMaxLanes];
      for (int i = 0; i < kMaxLanes; i++) {
        rep_node[i] = graph()->NewNode(machine()->Float32Add(), rep_left[i],
                                       rep_right[i]);
      }
      ReplaceNode(node, rep_node);
      break;
    }

    case IrOpcode::kCreateFloat32x4: {
      Node* rep_node[kMaxLanes];
      for (int i = 0; i < kMaxLanes; i++) {
        DCHECK(!HasReplacement(1, node->InputAt(i)));
        rep_node[i] = node->InputAt(i);
      }
      ReplaceNode(node, rep_node);
      break;
    }

    case IrOpcode::kFloat32x4ExtractLane: {
      Node* laneNode = node->InputAt(1);
      DCHECK_EQ(laneNode->opcode(), IrOpcode::kInt32Constant);
      int32_t lane = OpParameter<int32_t>(laneNode);
      Node* rep_node[kMaxLanes] = {
          GetReplacementsWithType(node->InputAt(0), rep_type)[lane], nullptr,
          nullptr, nullptr};
      ReplaceNode(node, rep_node);
      break;
    }

    default: { DefaultLowering(node); }
  }
}

bool SimdScalarLowering::DefaultLowering(Node* node) {
  bool something_changed = false;
  for (int i = NodeProperties::PastValueIndex(node) - 1; i >= 0; i--) {
    Node* input = node->InputAt(i);
    if (HasReplacement(0, input)) {
      something_changed = true;
      node->ReplaceInput(i, GetReplacements(input)[0]);
    }
    if (HasReplacement(1, input)) {
      something_changed = true;
      for (int j = 1; j < kMaxLanes; j++) {
        node->InsertInput(zone(), i + j, GetReplacements(input)[j]);
      }
    }
  }
  return something_changed;
}

void SimdScalarLowering::ReplaceNode(Node* old, Node** new_node) {
  // if new_low == nullptr, then also new_high == nullptr.
  DCHECK(new_node[0] != nullptr ||
         (new_node[1] == nullptr && new_node[2] == nullptr &&
          new_node[3] == nullptr));
  for (int i = 0; i < kMaxLanes; i++) {
    replacements_[old->id()].node[i] = new_node[i];
  }
}

bool SimdScalarLowering::HasReplacement(size_t index, Node* node) {
  return replacements_[node->id()].node[index] != nullptr;
}

SimdScalarLowering::SimdType SimdScalarLowering::ReplacementType(Node* node) {
  return replacements_[node->id()].type;
}

Node** SimdScalarLowering::GetReplacements(Node* node) {
  Node** result = replacements_[node->id()].node;
  DCHECK(result);
  return result;
}

Node** SimdScalarLowering::GetReplacementsWithType(Node* node, SimdType type) {
  Node** replacements = GetReplacements(node);
  if (ReplacementType(node) == type) {
    return GetReplacements(node);
  }
  Node** result = zone()->NewArray<Node*>(kMaxLanes);
  if (ReplacementType(node) == SimdType::kInt32 && type == SimdType::kFloat32) {
    for (int i = 0; i < kMaxLanes; i++) {
      if (replacements[i] != nullptr) {
        result[i] = graph()->NewNode(machine()->BitcastInt32ToFloat32(),
                                     replacements[i]);
      } else {
        result[i] = nullptr;
      }
    }
  } else {
    for (int i = 0; i < kMaxLanes; i++) {
      if (replacements[i] != nullptr) {
        result[i] = graph()->NewNode(machine()->BitcastFloat32ToInt32(),
                                     replacements[i]);
      } else {
        result[i] = nullptr;
      }
    }
  }
  return result;
}

void SimdScalarLowering::PreparePhiReplacement(Node* phi) {
  MachineRepresentation rep = PhiRepresentationOf(phi->op());
  if (rep == MachineRepresentation::kSimd128) {
    // We have to create the replacements for a phi node before we actually
    // lower the phi to break potential cycles in the graph. The replacements of
    // input nodes do not exist yet, so we use a placeholder node to pass the
    // graph verifier.
    int value_count = phi->op()->ValueInputCount();
    SimdType type = ReplacementType(phi);
    Node** inputs_rep[kMaxLanes];
    for (int i = 0; i < kMaxLanes; i++) {
      inputs_rep[i] = zone()->NewArray<Node*>(value_count + 1);
      inputs_rep[i][value_count] = NodeProperties::GetControlInput(phi, 0);
    }
    for (int i = 0; i < value_count; i++) {
      for (int j = 0; j < kMaxLanes; j++) {
        inputs_rep[j][i] = placeholder_;
      }
    }
    Node* rep_nodes[kMaxLanes];
    for (int i = 0; i < kMaxLanes; i++) {
      if (type == SimdType::kInt32) {
        rep_nodes[i] = graph()->NewNode(
            common()->Phi(MachineRepresentation::kWord32, value_count),
            value_count + 1, inputs_rep[i], false);
      } else if (type == SimdType::kFloat32) {
        rep_nodes[i] = graph()->NewNode(
            common()->Phi(MachineRepresentation::kFloat32, value_count),
            value_count + 1, inputs_rep[i], false);
      } else {
        UNREACHABLE();
      }
    }
    ReplaceNode(phi, rep_nodes);
  }
}
}  // namespace compiler
}  // namespace internal
}  // namespace v8