push.cpp

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/*
 * Copyright 2017 Nico Reißmann <nico.reissmann@gmail.com>
 * See COPYING for terms of redistribution.
 */
 
#include <jlm/llvm/ir/operators/delta.hpp>
#include <jlm/llvm/ir/RvsdgModule.hpp>
#include <jlm/llvm/opt/push.hpp>
#include <jlm/rvsdg/control.hpp>
#include <jlm/rvsdg/gamma.hpp>
#include <jlm/rvsdg/MatchType.hpp>
#include <jlm/rvsdg/Phi.hpp>
#include <jlm/rvsdg/theta.hpp>
#include <jlm/rvsdg/traverser.hpp>
#include <jlm/util/Statistics.hpp>
#include <jlm/util/time.hpp>
 
#include <algorithm>
#include <deque>
 
namespace jlm::llvm
{
 
class NodeHoisting::Statistics final : public util::Statistics
{
public:
  ~Statistics() override = default;
 
  explicit Statistics(const util::FilePath & sourceFile)
      : util::Statistics(Statistics::Id::PushNodes, sourceFile)
  {}
 
  void
  start(const rvsdg::Graph & graph) noexcept
  {
    AddMeasurement(Label::NumRvsdgInputsBefore, jlm::rvsdg::ninputs(&graph.GetRootRegion()));
    AddTimer(Label::Timer).start();
  }
 
  void
  end(const rvsdg::Graph & graph) noexcept
  {
    AddMeasurement(Label::NumRvsdgInputsAfter, jlm::rvsdg::ninputs(&graph.GetRootRegion()));
    GetTimer(Label::Timer).stop();
  }
 
  static std::unique_ptr<Statistics>
  Create(const util::FilePath & sourceFile)
  {
    return std::make_unique<Statistics>(sourceFile);
  }
};
 
class NodeHoisting::Context final
{
public:
  explicit Context(rvsdg::LambdaNode & lambdaNode)
      : LambdaSubregion_(lambdaNode.subregion())
  {}
 
  rvsdg::Region &
  getLambdaSubregion() const noexcept
  {
    return *LambdaSubregion_;
  }
 
  void
  addTargetRegion(const rvsdg::Node & node, rvsdg::Region & region) noexcept
  {
    JLM_ASSERT(TargetRegion_.find(&node) == TargetRegion_.end());
    TargetRegion_[&node] = &region;
  }
 
  rvsdg::Region &
  getTargetRegion(const rvsdg::Node & node) const noexcept
  {
    return *TargetRegion_.at(&node);
  }
 
  static std::unique_ptr<Context>
  create(rvsdg::LambdaNode & lambdaNode)
  {
    return std::make_unique<Context>(lambdaNode);
  }
 
private:
  rvsdg::Region * LambdaSubregion_;
  std::unordered_map<const rvsdg::Node *, rvsdg::Region *> TargetRegion_{};
};
 
NodeHoisting::~NodeHoisting() noexcept = default;
 
NodeHoisting::NodeHoisting()
    : Transformation("NodeHoisting")
{}
 
bool
NodeHoisting::isInvariantMemoryStateLoopVar(const rvsdg::ThetaNode::LoopVar & loopVar)
{
  if (!is<MemoryStateType>(loopVar.output->Type()))
    return false;
 
  if (loopVar.pre->nusers() != 1)
    return false;
 
  const auto userNode = rvsdg::TryGetOwnerNode<rvsdg::SimpleNode>(*loopVar.pre->Users().begin());
  const auto originNode = rvsdg::TryGetOwnerNode<rvsdg::SimpleNode>(*loopVar.post->origin());
 
  if (userNode != originNode)
    return false;
 
  return true;
}
 
rvsdg::Region &
NodeHoisting::computeTargetRegion(const rvsdg::Output & output) const
{
  // Handle lambda region arguments
  if (rvsdg::TryGetRegionParentNode<rvsdg::LambdaNode>(output))
  {
    return *output.region();
  }
 
  // Handle gamma region arguments
  if (const auto gammaNode = rvsdg::TryGetRegionParentNode<rvsdg::GammaNode>(output))
  {
    if (output.Type()->Kind() == rvsdg::TypeKind::State)
    {
      // FIXME: This is a bit too conservative. For example, it avoids that load and store nodes are
      // hoisted out of a gamma node, but we would only like to avoid store nodes being hoisted out.
      // For load nodes, it is legal to hoist them out if they are not preceded by an IOBarrier.
      return *output.region();
    }
 
    const auto roleVar = gammaNode->MapBranchArgument(output);
    if (const auto entryVar = std::get_if<rvsdg::GammaNode::EntryVar>(&roleVar))
    {
      return computeTargetRegion(*entryVar->input->origin());
    }
 
    return *output.region();
  }
 
  // Handle theta region arguments
  if (const auto thetaNode = rvsdg::TryGetRegionParentNode<rvsdg::ThetaNode>(output))
  {
    const auto loopVar = thetaNode->MapPreLoopVar(output);
    if (rvsdg::ThetaLoopVarIsInvariant(loopVar))
    {
      return computeTargetRegion(*loopVar.input->origin());
    }
 
    if (isInvariantMemoryStateLoopVar(loopVar))
    {
      return computeTargetRegion(*loopVar.input->origin());
    }
 
    return *output.region();
  }
 
  // Handle gamma outputs
  if (const auto gammaNode = rvsdg::TryGetOwnerNode<rvsdg::GammaNode>(output))
  {
    return context_->getTargetRegion(*gammaNode);
  }
 
  // Handle theta outputs
  if (const auto thetaNode = rvsdg::TryGetOwnerNode<rvsdg::ThetaNode>(output))
  {
    return context_->getTargetRegion(*thetaNode);
  }
 
  // Handle simple node outputs
  if (const auto node = rvsdg::TryGetOwnerNode<rvsdg::SimpleNode>(output))
  {
    return context_->getTargetRegion(*node);
  }
 
  throw std::logic_error("Unhandled output type!");
}
 
rvsdg::Region &
NodeHoisting::computeTargetRegion(const rvsdg::Node & node) const
{
  if (node.ninputs() == 0)
  {
    // All nullary operations to date have exactly one output
    JLM_ASSERT(node.noutputs() == 1);
 
    // Control constants are used to instruct the control flow graph creation,
    // and will be removed in the back-end, so there is no need to hoist them.
    const auto outputType = node.output(0)->Type();
    if (is<rvsdg::ControlType>(outputType))
      return *node.region();
 
    // Other constants should be moved to the top-level of the function
    return context_->getLambdaSubregion();
  }
 
  // Compute target regions for all the inputs of the node
  rvsdg::Region * greatestCommonTargetRegion = nullptr;
 
  for (auto & input : node.Inputs())
  {
    auto & targetRegion = computeTargetRegion(*input.origin());
    if (&targetRegion == node.region())
    {
      // One of the node's predecessors cannot be hoisted, which means we can also not hoist this
      // node
      return *node.region();
    }
 
    // If we already have a common target region that is lower, keep it
    if (greatestCommonTargetRegion
        && greatestCommonTargetRegion->getDepth() >= targetRegion.getDepth())
      continue;
    greatestCommonTargetRegion = &targetRegion;
  }
 
  // Return the lowestmost common target region in the region tree among all inputs
  JLM_ASSERT(greatestCommonTargetRegion);
  return *greatestCommonTargetRegion;
}
 
void
NodeHoisting::markNodes(const rvsdg::Region & region)
{
  for (const auto node : rvsdg::TopDownConstTraverser(&region))
  {
    rvsdg::MatchTypeWithDefault(
        *node,
        [&](const rvsdg::StructuralNode & structuralNode)
        {
          // FIXME: We currently do not allow structural nodes (gamma and theta nodes) to be hoisted
          context_->addTargetRegion(structuralNode, *structuralNode.region());
 
          // Handle innermost regions
          for (auto & subregion : structuralNode.Subregions())
          {
            markNodes(subregion);
          }
        },
        [&](const rvsdg::SimpleNode & simpleNode)
        {
          rvsdg::Region & targetRegion = computeTargetRegion(simpleNode);
          context_->addTargetRegion(*node, targetRegion);
        },
        []()
        {
          throw std::logic_error("Unhandled node type!");
        });
  }
}
 
rvsdg::Output &
NodeHoisting::getOperandFromTargetRegion(rvsdg::Output & output, rvsdg::Region & targetRegion)
{
  if (output.region() == &targetRegion)
    return output;
 
  // Handle gamma subregion arguments
  if (const auto gammaNode = rvsdg::TryGetRegionParentNode<rvsdg::GammaNode>(output))
  {
    const auto roleVar = gammaNode->MapBranchArgument(output);
    if (const auto entryVar = std::get_if<rvsdg::GammaNode::EntryVar>(&roleVar))
    {
      return getOperandFromTargetRegion(*entryVar->input->origin(), targetRegion);
    }
  }
 
  // Handle theta subregion arguments
  if (const auto thetaNode = rvsdg::TryGetRegionParentNode<rvsdg::ThetaNode>(output))
  {
    const auto loopVar = thetaNode->MapPreLoopVar(output);
    JLM_ASSERT(rvsdg::ThetaLoopVarIsInvariant(loopVar) || isInvariantMemoryStateLoopVar(loopVar));
    return getOperandFromTargetRegion(*loopVar.input->origin(), targetRegion);
  }
 
  throw std::logic_error("Unhandled output type!");
}
 
std::vector<rvsdg::Output *>
NodeHoisting::getOperandsFromTargetRegion(rvsdg::Node & node, rvsdg::Region & targetRegion)
{
  std::vector<rvsdg::Output *> operands;
  for (auto & input : node.Inputs())
  {
    auto & operand = getOperandFromTargetRegion(*input.origin(), targetRegion);
    operands.push_back(&operand);
  }
 
  return operands;
}
 
void
NodeHoisting::copyNodeToTargetRegion(rvsdg::Node & node) const
{
  auto & targetRegion = context_->getTargetRegion(node);
  JLM_ASSERT(&targetRegion != node.region());
 
  const auto operands = getOperandsFromTargetRegion(node, targetRegion);
  const auto copiedNode = node.copy(&targetRegion, operands);
 
  // FIXME: I really would like to have a zip function here, but C++ does not really seem to have
  // anything better to offer
  auto itOrg = std::begin(node.Outputs());
  const auto endOrg = std::end(node.Outputs());
  auto itCpy = std::begin(copiedNode->Outputs());
  const auto endCpy = std::end(copiedNode->Outputs());
  JLM_ASSERT(std::distance(itOrg, endOrg) == std::distance(itCpy, endCpy));
 
  for (; itOrg != endOrg; ++itOrg, ++itCpy)
  {
    auto & outputOrg = *itOrg;
    auto & outputCpy = *itCpy;
    auto & newOutputOrg = rvsdg::RouteToRegion(outputCpy, *node.region());
    outputOrg.divert_users(&newOutputOrg);
  }
}
 
void
NodeHoisting::hoistNodes(rvsdg::Region & region)
{
  // FIXME: We a routing unnecessary values through gamma and theta nodes. We should cluster
  // subgraphs that need to be hoisted to avoid unnecessary routing.
  for (const auto node : rvsdg::TopDownTraverser(&region))
  {
    auto & targetRegion = context_->getTargetRegion(*node);
    if (&targetRegion != node->region())
    {
      copyNodeToTargetRegion(*node);
    }
 
    // Handle innermost regions
    if (const auto structuralNode = dynamic_cast<rvsdg::StructuralNode *>(node))
    {
      for (auto & subregion : structuralNode->Subregions())
      {
        hoistNodes(subregion);
      }
    }
  }
 
  region.prune(false);
}
 
void
NodeHoisting::hoistNodesInLambda(rvsdg::LambdaNode & lambdaNode)
{
  context_ = Context::create(lambdaNode);
 
  markNodes(*lambdaNode.subregion());
  hoistNodes(*lambdaNode.subregion());
 
  context_.reset();
}
 
void
NodeHoisting::hoistNodesInRootRegion(rvsdg::Region & region)
{
  for (auto & node : rvsdg::TopDownTraverser(&region))
  {
    rvsdg::MatchTypeWithDefault(
        *node,
        [&](rvsdg::LambdaNode & lambdaNode)
        {
          hoistNodesInLambda(lambdaNode);
        },
        [&](rvsdg::PhiNode & phiNode)
        {
          hoistNodesInRootRegion(*phiNode.subregion());
        },
        [](rvsdg::DeltaNode &)
        {
          // Nothing needs to be done
        },
        [](rvsdg::SimpleNode &)
        {
          // Nothing needs to be done
        },
        [&]()
        {
          throw std::logic_error(util::strfmt("Unhandled node type: ", node->DebugString()));
        });
  }
}
 
void
NodeHoisting::Run(rvsdg::RvsdgModule & rvsdgModule, util::StatisticsCollector & statisticsCollector)
{
  auto statistics = Statistics::Create(rvsdgModule.SourceFilePath().value());
 
  statistics->start(rvsdgModule.Rvsdg());
  hoistNodesInRootRegion(rvsdgModule.Rvsdg().GetRootRegion());
  statistics->end(rvsdgModule.Rvsdg());
 
  statisticsCollector.CollectDemandedStatistics(std::move(statistics));
}
}