llvm/mlir/lib/Transforms/DialectConversion.cpp

//===- DialectConversion.cpp - MLIR dialect conversion generic pass -------===//
//
// Copyright 2019 The MLIR Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// =============================================================================

#include "mlir/Transforms/DialectConversion.h"
#include "mlir/IR/Block.h"
#include "mlir/IR/BlockAndValueMapping.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/Function.h"
#include "mlir/IR/Module.h"
#include "mlir/Transforms/Utils.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"

using namespace mlir;

#define DEBUG_TYPE "dialect-conversion"

//===----------------------------------------------------------------------===//
// ArgConverter
//===----------------------------------------------------------------------===//
namespace {
/// This class provides a simple interface for converting the types of block
/// arguments. This is done by inserting fake cast operations that map from the
/// illegal type to the original type to allow for undoing pending rewrites in
/// the case of failure.
struct ArgConverter {
  ArgConverter(TypeConverter *typeConverter, PatternRewriter &rewriter)
      : castOpName(kCastName, rewriter.getContext()),
        loc(rewriter.getUnknownLoc()), typeConverter(typeConverter),
        rewriter(rewriter) {}

  /// Erase any rewrites registered for arguments to blocks within the given
  /// region. This function is called when the given region is to be destroyed.
  void cancelPendingRewrites(Block *block);

  /// Cleanup and undo any generated conversions for the arguments of block.
  /// This method differs from 'cancelPendingRewrites' in that it returns the
  /// block signature to its original state.
  void discardPendingRewrites(Block *block);

  /// Replace usages of the cast operations with the argument directly.
  void applyRewrites();

  /// Return if the signature of the given block has already been converted.
  bool hasBeenConverted(Block *block) const { return argMapping.count(block); }

  /// Attempt to convert the signature of the given region.
  LogicalResult convertSignature(Region &region, BlockAndValueMapping &mapping);

  /// Attempt to convert the signature of the given block.
  LogicalResult convertSignature(Block *block, BlockAndValueMapping &mapping);

  /// Apply the given signature conversion on the given block.
  void applySignatureConversion(
      Block *block, TypeConverter::SignatureConversion &signatureConversion,
      BlockAndValueMapping &mapping);

  /// Convert the given block argument given the provided set of new argument
  /// values that are to replace it. This function returns the operation used
  /// to perform the conversion.
  Operation *convertArgument(BlockArgument *origArg,
                             ArrayRef<Value *> newValues,
                             BlockAndValueMapping &mapping);

  /// A utility function used to create a conversion cast operation with the
  /// given input and result types.
  Operation *createCast(ArrayRef<Value *> inputs, Type outputType);

  /// This is an operation name for a fake operation that is inserted during the
  /// conversion process. Operations of this type are guaranteed to never escape
  /// the converter.
  static constexpr StringLiteral kCastName = "__mlir_conversion.cast";
  OperationName castOpName;

  /// This is a collection of cast operations that were generated during the
  /// conversion process when converting the types of block arguments.
  llvm::MapVector<Block *, SmallVector<Operation *, 4>> argMapping;

  /// An instance of the unknown location that is used when generating
  /// producers.
  Location loc;

  /// The type converter to use when changing types.
  TypeConverter *typeConverter;

  /// The pattern rewriter to use when materializing conversions.
  PatternRewriter &rewriter;
};

constexpr StringLiteral ArgConverter::kCastName;

/// Erase any rewrites registered for arguments to the given block.
void ArgConverter::cancelPendingRewrites(Block *block) {
  auto it = argMapping.find(block);
  if (it == argMapping.end())
    return;
  for (auto *op : it->second) {
    op->dropAllDefinedValueUses();
    op->erase();
  }
  argMapping.erase(it);
}

/// Cleanup and undo any generated conversions for the arguments of block.
/// This method differs from 'cancelPendingRewrites' in that it returns the
/// block signature to its original state.
void ArgConverter::discardPendingRewrites(Block *block) {
  auto it = argMapping.find(block);
  if (it == argMapping.end())
    return;

  // Erase all of the new arguments.
  for (int i = block->getNumArguments() - 1; i >= 0; --i) {
    block->getArgument(i)->dropAllUses();
    block->eraseArgument(i, /*updatePredTerms=*/false);
  }

  // Re-instate the old arguments.
  auto &mapping = it->second;
  for (unsigned i = 0, e = mapping.size(); i != e; ++i) {
    auto *op = mapping[i];
    auto *arg = block->addArgument(op->getResult(0)->getType());
    op->getResult(0)->replaceAllUsesWith(arg);

    // If this operation is within a block, it will be cleaned up automatically.
    if (!op->getBlock())
      op->erase();
  }
  argMapping.erase(it);
}

/// Replace usages of the cast operations with the argument directly.
void ArgConverter::applyRewrites() {
  Block *block;
  ArrayRef<Operation *> argOps;
  for (auto &mapping : argMapping) {
    std::tie(block, argOps) = mapping;

    // Process the remapping for each of the original arguments.
    for (unsigned i = 0, e = argOps.size(); i != e; ++i) {
      auto *op = argOps[i];

      // Handle the case of a 1->N value mapping.
      if (op->getNumOperands() > 1) {
        // If all of the uses were removed, we can drop this op. Otherwise,
        // keep the operation alive and let the user handle any remaining
        // usages.
        if (op->use_empty())
          op->erase();
        continue;
      }

      // If mapping is 1-1, replace the remaining uses and drop the cast
      // operation.
      // FIXME(riverriddle) This should check that the result type and operand
      // type are the same, otherwise it should force a conversion to be
      // materialized. This works around a current limitation with regards to
      // region entry argument type conversion.
      if (op->getNumOperands() == 1) {
        op->getResult(0)->replaceAllUsesWith(op->getOperand(0));
        op->destroy();
        continue;
      }

      // Otherwise, if there are any dangling uses then replace the fake
      // conversion operation with one generated by the type converter. This
      // is necessary as the cast must persist in the IR after conversion.
      auto *opResult = op->getResult(0);
      if (!opResult->use_empty()) {
        rewriter.setInsertionPointToStart(block);
        SmallVector<Value *, 1> operands(op->getOperands());
        auto *newOp = typeConverter->materializeConversion(
            rewriter, opResult->getType(), operands, op->getLoc());
        opResult->replaceAllUsesWith(newOp->getResult(0));
      }
      op->destroy();
    }
  }
}

/// Converts the signature of the given region.
LogicalResult ArgConverter::convertSignature(Region &region,
                                             BlockAndValueMapping &mapping) {
  if (auto conversion = typeConverter->convertRegionSignature(
          region.getContainingOp(), region.getRegionNumber())) {
    if (!region.empty())
      applySignatureConversion(&region.front(), *conversion, mapping);
    return success();
  }
  return failure();
}

/// Converts the signature of the given entry block.
LogicalResult ArgConverter::convertSignature(Block *block,
                                             BlockAndValueMapping &mapping) {
  auto conversion = typeConverter->convertBlockSignature(block);
  if (conversion)
    return applySignatureConversion(block, *conversion, mapping), success();
  return failure();
}

/// Apply the given signature conversion on the given block.
void ArgConverter::applySignatureConversion(
    Block *block, TypeConverter::SignatureConversion &signatureConversion,
    BlockAndValueMapping &mapping) {
  unsigned origArgCount = block->getNumArguments();
  auto convertedTypes = signatureConversion.getConvertedArgTypes();
  if (origArgCount == 0 && convertedTypes.empty())
    return;

  SmallVector<Value *, 4> newArgRange(block->addArguments(convertedTypes));
  ArrayRef<Value *> newArgRef(newArgRange);

  // Remap each of the original arguments as determined by the signature
  // conversion.
  auto &newArgMapping = argMapping[block];
  rewriter.setInsertionPointToStart(block);
  for (unsigned i = 0; i != origArgCount; ++i) {
    ArrayRef<Value *> remappedValues;
    if (auto inputMap = signatureConversion.getInputMapping(i))
      remappedValues = newArgRef.slice(inputMap->inputNo, inputMap->size);

    BlockArgument *arg = block->getArgument(i);
    newArgMapping.push_back(convertArgument(arg, remappedValues, mapping));
  }

  // Erase all of the original arguments.
  for (unsigned i = 0; i != origArgCount; ++i)
    block->eraseArgument(0, /*updatePredTerms=*/false);
}

/// Convert the given block argument given the provided set of new argument
/// values that are to replace it. This function returns the operation used
/// to perform the conversion.
Operation *ArgConverter::convertArgument(BlockArgument *origArg,
                                         ArrayRef<Value *> newValues,
                                         BlockAndValueMapping &mapping) {
  // Handle the cases of 1->0 or 1->1 mappings.
  if (newValues.size() < 2) {
    // Create a temporary producer for the argument during the conversion
    // process.
    auto *cast = createCast(newValues, origArg->getType());
    origArg->replaceAllUsesWith(cast->getResult(0));

    // Insert a mapping between this argument and the one that is replacing
    // it.
    if (!newValues.empty())
      mapping.map(cast->getResult(0), newValues[0]);
    return cast;
  }

  // Otherwise, this is a 1->N mapping. Call into the provided type converter
  // to pack the new values.
  auto *cast = typeConverter->materializeConversion(
      rewriter, origArg->getType(), newValues, loc);
  assert(cast->getNumResults() == 1 &&
         cast->getNumOperands() == newValues.size());
  origArg->replaceAllUsesWith(cast->getResult(0));
  return cast;
}

/// A utility function used to create a conversion cast operation with the
/// given input and result types.
Operation *ArgConverter::createCast(ArrayRef<Value *> inputs, Type outputType) {
  return Operation::create(loc, castOpName, inputs, outputType, llvm::None,
                           llvm::None, 0, false, outputType.getContext());
}

//===----------------------------------------------------------------------===//
// DialectConversionRewriter
//===----------------------------------------------------------------------===//

/// This class contains a snapshot of the current conversion rewriter state.
/// This is useful when saving and undoing a set of rewrites.
struct RewriterState {
  RewriterState(unsigned numCreatedOperations, unsigned numReplacements,
                unsigned numBlockActions, unsigned numTypeConversions)
      : numCreatedOperations(numCreatedOperations),
        numReplacements(numReplacements), numBlockActions(numBlockActions),
        numTypeConversions(numTypeConversions) {}

  /// The current number of created operations.
  unsigned numCreatedOperations;

  /// The current number of replacements queued.
  unsigned numReplacements;

  /// The current number of block actions performed.
  unsigned numBlockActions;

  /// The current number of type conversion actions performed.
  unsigned numTypeConversions;
};

/// This class implements a pattern rewriter for ConversionPattern
/// patterns. It automatically performs remapping of replaced operation values.
struct DialectConversionRewriter final : public PatternRewriter {
  /// This class represents one requested operation replacement via 'replaceOp'.
  struct OpReplacement {
    OpReplacement() = default;
    OpReplacement(Operation *op, ArrayRef<Value *> newValues)
        : op(op), newValues(newValues.begin(), newValues.end()) {}

    Operation *op;
    SmallVector<Value *, 2> newValues;
  };

  /// The kind of the block action performed during the rewrite.  Actions can be
  /// undone if the conversion fails.
  enum class BlockActionKind { Split, Move };

  /// Original position of the given block in its parent region.  We cannot use
  /// a region iterator because it could have been invalidated by other region
  /// operations since the position was stored.
  struct BlockPosition {
    Region *region;
    Region::iterator::difference_type position;
  };

  /// The storage class for an undoable block action (one of BlockActionKind),
  /// contains the information necessary to undo this action.
  struct BlockAction {
    // A pointer to the block that was created by the action.
    Block *block;

    union {
      // In use if kind == BlockActionKind::Move and contains a pointer to the
      // region that originally contained the block as well as the position of
      // the block in that region.
      BlockPosition originalPosition;
      // In use if kind == BlockActionKind::Split and contains a pointer to the
      // block that was split into two parts.
      Block *originalBlock;
    };

    BlockActionKind kind;
  };

  /// A storage class representing a type conversion of a block or a region.
  struct TypeConversion {
    /// The region, or block, that had its types converted.
    llvm::PointerUnion<Region *, Block *> object;

    /// If the object is a region, this corresponds to the original attributes
    /// of the parent operation.
    NamedAttributeList originalParentAttributes;
  };

  DialectConversionRewriter(MLIRContext *ctx, TypeConverter *converter)
      : PatternRewriter(ctx), argConverter(converter, *this) {}
  ~DialectConversionRewriter() = default;

  /// Return the current state of the rewriter.
  RewriterState getCurrentState() {
    return RewriterState(createdOps.size(), replacements.size(),
                         blockActions.size(), typeConversions.size());
  }

  /// Reset the state of the rewriter to a previously saved point.
  void resetState(RewriterState state) {
    // Undo any type conversions or block actions.
    undoTypeConversions(state.numTypeConversions);
    undoBlockActions(state.numBlockActions);

    // Reset any replaced operations and undo any saved mappings.
    for (auto &repl : llvm::drop_begin(replacements, state.numReplacements))
      for (auto *result : repl.op->getResults())
        mapping.erase(result);
    replacements.resize(state.numReplacements);

    // Pop all of the newly created operations.
    while (createdOps.size() != state.numCreatedOperations)
      createdOps.pop_back_val()->erase();
  }

  /// Undo the block actions (motions, splits) one by one in reverse order until
  /// "numActionsToKeep" actions remains.
  void undoBlockActions(unsigned numActionsToKeep = 0) {
    for (auto &action :
         llvm::reverse(llvm::drop_begin(blockActions, numActionsToKeep))) {
      switch (action.kind) {
      // Merge back the block that was split out.
      case BlockActionKind::Split: {
        action.originalBlock->getOperations().splice(
            action.originalBlock->end(), action.block->getOperations());
        action.block->erase();
        break;
      }
      // Move the block back to its original position.
      case BlockActionKind::Move: {
        Region *originalRegion = action.originalPosition.region;
        originalRegion->getBlocks().splice(
            std::next(originalRegion->begin(),
                      action.originalPosition.position),
            action.block->getParent()->getBlocks(), action.block);
        break;
      }
      }
    }
    blockActions.resize(numActionsToKeep);
  }

  /// Undo the type conversion actions one by one, until "numActionsToKeep"
  /// actions remain.
  void undoTypeConversions(unsigned numActionsToKeep = 0) {
    for (auto &conversion :
         llvm::drop_begin(typeConversions, numActionsToKeep)) {
      if (auto *region = conversion.object.dyn_cast<Region *>())
        region->getContainingOp()->setAttrs(
            conversion.originalParentAttributes);
      else
        argConverter.discardPendingRewrites(conversion.object.get<Block *>());
    }
    typeConversions.resize(numActionsToKeep);
  }

  /// Cleanup and destroy any generated rewrite operations. This method is
  /// invoked when the conversion process fails.
  void discardRewrites() {
    undoTypeConversions();
    undoBlockActions();

    // Remove any newly created ops.
    for (auto *op : createdOps) {
      op->dropAllDefinedValueUses();
      op->erase();
    }
  }

  /// Apply all requested operation rewrites. This method is invoked when the
  /// conversion process succeeds.
  void applyRewrites() {
    // Apply all of the rewrites replacements requested during conversion.
    for (auto &repl : replacements) {
      for (unsigned i = 0, e = repl.newValues.size(); i != e; ++i)
        repl.op->getResult(i)->replaceAllUsesWith(
            mapping.lookupOrDefault(repl.newValues[i]));

      // if this operation defines any regions, drop any pending argument
      // rewrites.
      if (argConverter.typeConverter && repl.op->getNumRegions()) {
        for (auto &region : repl.op->getRegions())
          for (auto &block : region)
            argConverter.cancelPendingRewrites(&block);
      }
    }

    // In a second pass, erase all of the replaced operations in reverse. This
    // allows processing nested operations before their parent region is
    // destroyed.
    for (auto &repl : llvm::reverse(replacements))
      repl.op->erase();

    argConverter.applyRewrites();
  }

  /// Return if the given block has already been converted.
  bool hasSignatureBeenConverted(Block *block) {
    return argConverter.hasBeenConverted(block);
  }

  /// Convert the signature of the given region.
  LogicalResult convertRegionSignature(Region &region) {
    auto parentAttrs = region.getContainingOp()->getAttrList();
    auto result = argConverter.convertSignature(region, mapping);
    if (succeeded(result)) {
      typeConversions.push_back(TypeConversion{&region, parentAttrs});
      if (!region.empty())
        typeConversions.push_back(
            TypeConversion{&region.front(), NamedAttributeList()});
    }
    return result;
  }

  /// Convert the signature of the given block.
  LogicalResult convertBlockSignature(Block *block) {
    auto result = argConverter.convertSignature(block, mapping);
    if (succeeded(result))
      typeConversions.push_back(TypeConversion{block, NamedAttributeList()});
    return result;
  }

  /// PatternRewriter hook for replacing the results of an operation.
  void replaceOp(Operation *op, ArrayRef<Value *> newValues,
                 ArrayRef<Value *> valuesToRemoveIfDead) override {
    assert(newValues.size() == op->getNumResults());

    // Create mappings for each of the new result values.
    for (unsigned i = 0, e = newValues.size(); i < e; ++i) {
      assert((newValues[i] || op->getResult(i)->use_empty()) &&
             "result value has remaining uses that must be replaced");
      if (newValues[i])
        mapping.map(op->getResult(i), newValues[i]);
    }

    // Record the requested operation replacement.
    replacements.emplace_back(op, newValues);
  }

  /// PatternRewriter hook for splitting a block into two parts.
  Block *splitBlock(Block *block, Block::iterator before) override {
    auto *continuation = PatternRewriter::splitBlock(block, before);
    BlockAction action;
    action.kind = BlockActionKind::Split;
    action.block = continuation;
    action.originalBlock = block;
    blockActions.push_back(action);
    return continuation;
  }

  /// PatternRewriter hook for moving blocks out of a region.
  void inlineRegionBefore(Region &region, Region &parent,
                          Region::iterator before) override {
    for (auto &pair : llvm::enumerate(region)) {
      Block &block = pair.value();
      unsigned position = pair.index();
      BlockAction action;
      action.kind = BlockActionKind::Move;
      action.block = &block;
      action.originalPosition = {&region, position};
      blockActions.push_back(action);
    }
    PatternRewriter::inlineRegionBefore(region, parent, before);
  }

  /// PatternRewriter hook for creating a new operation.
  Operation *createOperation(const OperationState &state) override {
    auto *result = OpBuilder::createOperation(state);
    createdOps.push_back(result);
    return result;
  }

  /// PatternRewriter hook for updating the root operation in-place.
  void notifyRootUpdated(Operation *op) override {
    // The rewriter caches changes to the IR to allow for operating in-place and
    // backtracking. The rewrite is currently not capable of backtracking
    // in-place modifications.
    llvm_unreachable("in-place operation updates are not supported");
  }

  /// Remap the given operands to those with potentially different types.
  void remapValues(Operation::operand_range operands,
                   SmallVectorImpl<Value *> &remapped) {
    remapped.reserve(llvm::size(operands));
    for (Value *operand : operands)
      remapped.push_back(mapping.lookupOrDefault(operand));
  }

  // Mapping between replaced values that differ in type. This happens when
  // replacing a value with one of a different type.
  BlockAndValueMapping mapping;

  /// Utility used to convert block arguments.
  ArgConverter argConverter;

  /// Ordered vector of all of the newly created operations during conversion.
  SmallVector<Operation *, 4> createdOps;

  /// Ordered vector of any requested operation replacements.
  SmallVector<OpReplacement, 4> replacements;

  /// Ordered list of block operations (creations, splits, motions).
  SmallVector<BlockAction, 4> blockActions;

  /// Ordered list of type conversion actions.
  SmallVector<TypeConversion, 4> typeConversions;
};
} // end anonymous namespace

//===----------------------------------------------------------------------===//
// Conversion Patterns
//===----------------------------------------------------------------------===//

/// Attempt to match and rewrite the IR root at the specified operation.
PatternMatchResult
ConversionPattern::matchAndRewrite(Operation *op,
                                   PatternRewriter &rewriter) const {
  SmallVector<Value *, 4> operands;
  auto &dialectRewriter = static_cast<DialectConversionRewriter &>(rewriter);
  dialectRewriter.remapValues(op->getOperands(), operands);

  // If this operation has no successors, invoke the rewrite directly.
  if (op->getNumSuccessors() == 0)
    return matchAndRewrite(op, operands, rewriter);

  // Otherwise, we need to remap the successors.
  SmallVector<Block *, 2> destinations;
  destinations.reserve(op->getNumSuccessors());

  SmallVector<ArrayRef<Value *>, 2> operandsPerDestination;
  unsigned firstSuccessorOperand = op->getSuccessorOperandIndex(0);
  for (unsigned i = 0, seen = 0, e = op->getNumSuccessors(); i < e; ++i) {
    destinations.push_back(op->getSuccessor(i));

    // Lookup the successors operands.
    unsigned n = op->getNumSuccessorOperands(i);
    operandsPerDestination.push_back(
        llvm::makeArrayRef(operands.data() + firstSuccessorOperand + seen, n));
    seen += n;
  }

  // Rewrite the operation.
  return matchAndRewrite(
      op,
      llvm::makeArrayRef(operands.data(),
                         operands.data() + firstSuccessorOperand),
      destinations, operandsPerDestination, rewriter);
}

//===----------------------------------------------------------------------===//
// OperationLegalizer
//===----------------------------------------------------------------------===//

namespace {
/// A set of rewrite patterns that can be used to legalize a given operation.
using LegalizationPatterns = SmallVector<RewritePattern *, 1>;

/// This class defines a recursive operation legalizer.
class OperationLegalizer {
public:
  using LegalizationAction = ConversionTarget::LegalizationAction;

  OperationLegalizer(ConversionTarget &targetInfo,
                     OwningRewritePatternList &patterns)
      : target(targetInfo) {
    buildLegalizationGraph(patterns);
    computeLegalizationGraphBenefit();
  }

  /// Returns if the given operation is known to be illegal on the target.
  bool isIllegal(Operation *op) const;

  /// Attempt to legalize the given operation. Returns success if the operation
  /// was legalized, failure otherwise.
  LogicalResult legalize(Operation *op, DialectConversionRewriter &rewriter);

private:
  /// Attempt to legalize the given operation by applying the provided pattern.
  /// Returns success if the operation was legalized, failure otherwise.
  LogicalResult legalizePattern(Operation *op, RewritePattern *pattern,
                                DialectConversionRewriter &rewriter);

  /// Build an optimistic legalization graph given the provided patterns. This
  /// function populates 'legalizerPatterns' with the operations that are not
  /// directly legal, but may be transitively legal for the current target given
  /// the provided patterns.
  void buildLegalizationGraph(OwningRewritePatternList &patterns);

  /// Compute the benefit of each node within the computed legalization graph.
  /// This orders the patterns within 'legalizerPatterns' based upon two
  /// criteria:
  ///  1) Prefer patterns that have the lowest legalization depth, i.e.
  ///     represent the more direct mapping to the target.
  ///  2) When comparing patterns with the same legalization depth, prefer the
  ///     pattern with the highest PatternBenefit. This allows for users to
  ///     prefer specific legalizations over others.
  void computeLegalizationGraphBenefit();

  /// The current set of patterns that have been applied.
  llvm::SmallPtrSet<RewritePattern *, 8> appliedPatterns;

  /// The set of legality information for operations transitively supported by
  /// the target.
  DenseMap<OperationName, LegalizationPatterns> legalizerPatterns;

  /// The legalization information provided by the target.
  ConversionTarget &target;
};
} // namespace

bool OperationLegalizer::isIllegal(Operation *op) const {
  // Check if the target explicitly marked this operation as illegal.
  if (auto action = target.getOpAction(op->getName()))
    return action == LegalizationAction::Illegal;
  return false;
}

LogicalResult
OperationLegalizer::legalize(Operation *op,
                             DialectConversionRewriter &rewriter) {
  // Make sure that the signature of the parent block of this operation has been
  // converted.
  if (rewriter.argConverter.typeConverter) {
    auto *block = op->getBlock();
    if (block && !rewriter.hasSignatureBeenConverted(block)) {
      if (failed(block->isEntryBlock()
                     ? rewriter.convertRegionSignature(*block->getParent())
                     : rewriter.convertBlockSignature(block)))
        return failure();
    }
  }

  LLVM_DEBUG(llvm::dbgs() << "Legalizing operation : " << op->getName()
                          << "\n");

  // Check if this was marked legal by the target.
  if (auto action = target.getOpAction(op->getName())) {
    // Check if this operation is always legal.
    if (*action == LegalizationAction::Legal)
      return success();

    // Otherwise, handle dynamic legalization.
    if (*action == LegalizationAction::Dynamic) {
      LLVM_DEBUG(llvm::dbgs() << "- Trying dynamic legalization.\n");
      if (target.isDynamicallyLegal(op))
        return success();
    }

    // Fallthough to see if a pattern can convert this into a legal operation.
  }

  // Otherwise, we need to apply a legalization pattern to this operation.
  auto it = legalizerPatterns.find(op->getName());
  if (it == legalizerPatterns.end()) {
    LLVM_DEBUG(llvm::dbgs() << "-- FAIL : no known legalization path.\n");
    return failure();
  }

  // The patterns are sorted by expected benefit, so try to apply each in-order.
  for (auto *pattern : it->second)
    if (succeeded(legalizePattern(op, pattern, rewriter)))
      return success();

  LLVM_DEBUG(llvm::dbgs() << "-- FAIL : no matched legalization pattern.\n");
  return failure();
}

LogicalResult
OperationLegalizer::legalizePattern(Operation *op, RewritePattern *pattern,
                                    DialectConversionRewriter &rewriter) {
  LLVM_DEBUG({
    llvm::dbgs() << "-* Applying rewrite pattern '" << op->getName() << " -> (";
    interleaveComma(pattern->getGeneratedOps(), llvm::dbgs());
    llvm::dbgs() << ")'.\n";
  });

  // Ensure that we don't cycle by not allowing the same pattern to be
  // applied twice in the same recursion stack.
  // TODO(riverriddle) We could eventually converge, but that requires more
  // complicated analysis.
  if (!appliedPatterns.insert(pattern).second) {
    LLVM_DEBUG(llvm::dbgs() << "-- FAIL: Pattern was already applied.\n");
    return failure();
  }

  RewriterState curState = rewriter.getCurrentState();
  auto cleanupFailure = [&] {
    // Reset the rewriter state and pop this pattern.
    rewriter.resetState(curState);
    appliedPatterns.erase(pattern);
    return failure();
  };

  // Try to rewrite with the given pattern.
  rewriter.setInsertionPoint(op);
  if (!pattern->matchAndRewrite(op, rewriter)) {
    LLVM_DEBUG(llvm::dbgs() << "-- FAIL: Pattern failed to match.\n");
    return cleanupFailure();
  }

  // Recursively legalize each of the new operations.
  for (unsigned i = curState.numCreatedOperations,
                e = rewriter.createdOps.size();
       i != e; ++i) {
    if (failed(legalize(rewriter.createdOps[i], rewriter))) {
      LLVM_DEBUG(llvm::dbgs() << "-- FAIL: Generated operation was illegal.\n");
      return cleanupFailure();
    }
  }

  appliedPatterns.erase(pattern);
  return success();
}

void OperationLegalizer::buildLegalizationGraph(
    OwningRewritePatternList &patterns) {
  // A mapping between an operation and a set of operations that can be used to
  // generate it.
  DenseMap<OperationName, SmallPtrSet<OperationName, 2>> parentOps;
  // A mapping between an operation and any currently invalid patterns it has.
  DenseMap<OperationName, SmallPtrSet<RewritePattern *, 2>> invalidPatterns;
  // A worklist of patterns to consider for legality.
  llvm::SetVector<RewritePattern *> patternWorklist;

  // Build the mapping from operations to the parent ops that may generate them.
  for (auto &pattern : patterns) {
    auto root = pattern->getRootKind();

    // Skip operations that are always known to be legal.
    if (target.getOpAction(root) == LegalizationAction::Legal)
      continue;

    // Add this pattern to the invalid set for the root op and record this root
    // as a parent for any generated operations.
    invalidPatterns[root].insert(pattern.get());
    for (auto op : pattern->getGeneratedOps())
      parentOps[op].insert(root);

    // Add this pattern to the worklist.
    patternWorklist.insert(pattern.get());
  }

  while (!patternWorklist.empty()) {
    auto *pattern = patternWorklist.pop_back_val();

    // Check to see if any of the generated operations are invalid.
    if (llvm::any_of(pattern->getGeneratedOps(), [&](OperationName op) {
          auto action = target.getOpAction(op);
          return !legalizerPatterns.count(op) &&
                 (!action || action == LegalizationAction::Illegal);
        }))
      continue;

    // Otherwise, if all of the generated operation are valid, this op is now
    // legal so add all of the child patterns to the worklist.
    legalizerPatterns[pattern->getRootKind()].push_back(pattern);
    invalidPatterns[pattern->getRootKind()].erase(pattern);

    // Add any invalid patterns of the parent operations to see if they have now
    // become legal.
    for (auto op : parentOps[pattern->getRootKind()])
      patternWorklist.set_union(invalidPatterns[op]);
  }
}

void OperationLegalizer::computeLegalizationGraphBenefit() {
  // The smallest pattern depth, when legalizing an operation.
  DenseMap<OperationName, unsigned> minPatternDepth;

  // Compute the minimum legalization depth for a given operation.
  std::function<unsigned(OperationName)> computeDepth = [&](OperationName op) {
    // Check for existing depth.
    auto depthIt = minPatternDepth.find(op);
    if (depthIt != minPatternDepth.end())
      return depthIt->second;

    // If a mapping for this operation does not exist, then this operation
    // is always legal. Return 0 as the depth for a directly legal operation.
    auto opPatternsIt = legalizerPatterns.find(op);
    if (opPatternsIt == legalizerPatterns.end())
      return 0u;

    auto &minDepth = minPatternDepth[op];
    if (opPatternsIt->second.empty())
      return minDepth;

    // Initialize the depth to the maximum value.
    minDepth = std::numeric_limits<unsigned>::max();

    // Compute the depth for each pattern used to legalize this operation.
    SmallVector<std::pair<RewritePattern *, unsigned>, 4> patternsByDepth;
    patternsByDepth.reserve(opPatternsIt->second.size());
    for (RewritePattern *pattern : opPatternsIt->second) {
      unsigned depth = 0;
      for (auto generatedOp : pattern->getGeneratedOps())
        depth = std::max(depth, computeDepth(generatedOp) + 1);
      patternsByDepth.emplace_back(pattern, depth);

      // Update the min depth for this operation.
      minDepth = std::min(minDepth, depth);
    }

    // If the operation only has one legalization pattern, there is no need to
    // sort them.
    if (patternsByDepth.size() == 1)
      return minDepth;

    // Sort the patterns by those likely to be the most beneficial.
    llvm::array_pod_sort(
        patternsByDepth.begin(), patternsByDepth.end(),
        [](const std::pair<RewritePattern *, unsigned> *lhs,
           const std::pair<RewritePattern *, unsigned> *rhs) {
          // First sort by the smaller pattern legalization depth.
          if (lhs->second != rhs->second)
            return llvm::array_pod_sort_comparator<unsigned>(&lhs->second,
                                                             &rhs->second);

          // Then sort by the larger pattern benefit.
          auto lhsBenefit = lhs->first->getBenefit();
          auto rhsBenefit = rhs->first->getBenefit();
          return llvm::array_pod_sort_comparator<PatternBenefit>(&rhsBenefit,
                                                                 &lhsBenefit);
        });

    // Update the legalization pattern to use the new sorted list.
    opPatternsIt->second.clear();
    for (auto &patternIt : patternsByDepth)
      opPatternsIt->second.push_back(patternIt.first);

    return minDepth;
  };

  // For each operation that is transitively legal, compute a cost for it.
  for (auto &opIt : legalizerPatterns)
    if (!minPatternDepth.count(opIt.first))
      computeDepth(opIt.first);
}

//===----------------------------------------------------------------------===//
// OperationConverter
//===----------------------------------------------------------------------===//
namespace {
enum OpConversionMode {
  // In this mode, the conversion will ignore failed conversions to allow
  // illegal operations to co-exist in the IR.
  Partial,

  // In this mode, all operations must be legal for the given target for the
  // conversion to succeeed.
  Full,
};

// This class converts operations using the given pattern matcher. If a
// TypeConverter object is provided, then the types of block arguments will be
// converted using the appropriate 'convertType' calls.
struct OperationConverter {
  explicit OperationConverter(ConversionTarget &target,
                              OwningRewritePatternList &patterns,
                              OpConversionMode mode)
      : opLegalizer(target, patterns), mode(mode) {}

  /// Converts the given operations to the conversion target.
  LogicalResult convertOperations(ArrayRef<Operation *> ops,
                                  TypeConverter *typeConverter);

private:
  /// Converts an operation with the given rewriter.
  LogicalResult convert(DialectConversionRewriter &rewriter, Operation *op);

  /// Recursively collect all of the operations, to convert from within
  /// 'region'.
  LogicalResult computeConversionSet(Region &region,
                                     std::vector<Operation *> &toConvert);

  /// The legalizer to use when converting operations.
  OperationLegalizer opLegalizer;

  /// The conversion mode to use when legalizing operations.
  OpConversionMode mode;
};
} // end anonymous namespace

/// Recursively collect all of the blocks to convert from within 'region'.
LogicalResult
OperationConverter::computeConversionSet(Region &region,
                                         std::vector<Operation *> &toConvert) {
  if (region.empty())
    return success();

  // Traverse starting from the entry block.
  SmallVector<Block *, 16> worklist(1, &region.front());
  DenseSet<Block *> visitedBlocks;
  visitedBlocks.insert(&region.front());
  while (!worklist.empty()) {
    auto *block = worklist.pop_back_val();

    // Compute the conversion set of each of the nested operations.
    for (auto &op : *block) {
      toConvert.emplace_back(&op);
      for (auto &region : op.getRegions())
        computeConversionSet(region, toConvert);
    }

    // Recurse to children that haven't been visited.
    for (Block *succ : block->getSuccessors())
      if (visitedBlocks.insert(succ).second)
        worklist.push_back(succ);
  }

  // Check that all blocks in the region were visited.
  if (llvm::any_of(llvm::drop_begin(region.getBlocks(), 1),
                   [&](Block &block) { return !visitedBlocks.count(&block); }))
    return emitError(region.getLoc(), "unreachable blocks were not converted");
  return success();
}

/// Converts an operation with the given rewriter.
LogicalResult OperationConverter::convert(DialectConversionRewriter &rewriter,
                                          Operation *op) {
  // Legalize the given operation.
  if (failed(opLegalizer.legalize(op, rewriter))) {
    // Handle the case of a failed conversion for each of the different modes.
    /// Full conversions expect all operations to be converted.
    if (mode == OpConversionMode::Full)
      return op->emitError()
             << "failed to legalize operation '" << op->getName() << "'";
    /// Partial conversions allow conversions to fail iff the operation was not
    /// explicitly marked as illegal.
    if (mode == OpConversionMode::Partial && opLegalizer.isIllegal(op))
      return op->emitError()
             << "failed to legalize operation '" << op->getName()
             << "' that was explicitly marked illegal";
  }

  // Convert the signature of any empty regions of this operation, non-empty
  // regions are converted on demand when converting any operations contained
  // within.
  // FIXME(riverriddle) This should be replaced by patterns when the pattern
  // rewriter exposes functionality to remap region signatures.
  if (rewriter.argConverter.typeConverter) {
    for (auto &region : op->getRegions())
      if (region.empty() && failed(rewriter.convertRegionSignature(region)))
        return failure();
  }

  return success();
}

/// Converts the given top-level operation to the conversion target.
LogicalResult
OperationConverter::convertOperations(ArrayRef<Operation *> ops,
                                      TypeConverter *typeConverter) {
  if (ops.empty())
    return success();

  /// Compute the set of operations and blocks to convert.
  std::vector<Operation *> toConvert;
  for (auto *op : ops) {
    toConvert.emplace_back(op);
    for (auto &region : op->getRegions())
      if (failed(computeConversionSet(region, toConvert)))
        return failure();
  }

  // Convert each operation and discard rewrites on failure.
  DialectConversionRewriter rewriter(ops.front()->getContext(), typeConverter);
  for (auto *op : toConvert) {
    if (failed(convert(rewriter, op))) {
      rewriter.discardRewrites();
      return failure();
    }
  }

  // Otherwise the body conversion succeeded, so apply all rewrites.
  rewriter.applyRewrites();
  return success();
}

//===----------------------------------------------------------------------===//
// Type Conversion
//===----------------------------------------------------------------------===//

/// Append new result types to the signature conversion.
void TypeConverter::SignatureConversion::addResults(ArrayRef<Type> results) {
  resultTypes.append(results.begin(), results.end());
}

/// Remap an input of the original signature with a new set of types. The
/// new types are appended to the new signature conversion.
void TypeConverter::SignatureConversion::addInputs(unsigned origInputNo,
                                                   ArrayRef<Type> types) {
  assert(!types.empty() && "expected valid types");
  remapInput(origInputNo, /*newInputNo=*/argTypes.size(), types.size());
  addInputs(types);
}

/// Append new input types to the signature conversion, this should only be
/// used if the new types are not intended to remap an existing input.
void TypeConverter::SignatureConversion::addInputs(ArrayRef<Type> types) {
  assert(!types.empty() &&
         "1->0 type remappings don't need to be added explicitly");
  argTypes.append(types.begin(), types.end());
}

/// Remap an input of the original signature with a range of types in the
/// new signature.
void TypeConverter::SignatureConversion::remapInput(unsigned origInputNo,
                                                    unsigned newInputNo,
                                                    unsigned newInputCount) {
  assert(!remappedInputs[origInputNo] && "input has already been remapped");
  assert(newInputCount != 0 && "expected valid input count");
  remappedInputs[origInputNo] = InputMapping{newInputNo, newInputCount};
}

/// This hooks allows for converting a type.
LogicalResult TypeConverter::convertType(Type t,
                                         SmallVectorImpl<Type> &results) {
  if (auto newT = convertType(t)) {
    results.push_back(newT);
    return success();
  }
  return failure();
}

/// Convert the given FunctionType signature.
auto TypeConverter::convertSignature(FunctionType type)
    -> llvm::Optional<SignatureConversion> {
  SignatureConversion result(type.getNumInputs());
  if (failed(convertSignature(type, result)))
    return llvm::None;
  return result;
}

/// This hook allows for changing a FunctionType signature.
LogicalResult TypeConverter::convertSignature(FunctionType type,
                                              SignatureConversion &result) {
  // Convert the original function arguments.
  for (unsigned i = 0, e = type.getNumInputs(); i != e; ++i)
    if (failed(convertSignatureArg(i, type.getInput(i), result)))
      return failure();

  // Convert the original function results.
  SmallVector<Type, 1> convertedTypes;
  for (auto t : type.getResults()) {
    convertedTypes.clear();
    if (failed(convertType(t, convertedTypes)))
      return failure();
    result.addResults(convertedTypes);
  }

  return success();
}

/// This hook allows for converting a specific argument of a signature.
LogicalResult TypeConverter::convertSignatureArg(unsigned inputNo, Type type,
                                                 SignatureConversion &result) {
  // Try to convert the given input type.
  SmallVector<Type, 1> convertedTypes;
  if (failed(convertType(type, convertedTypes)))
    return failure();

  // If this argument is being dropped, there is nothing left to do.
  if (convertedTypes.empty())
    return success();

  // Otherwise, add the new inputs.
  result.addInputs(inputNo, convertedTypes);
  return success();
}

/// This hook defines how the signature of a region 'regionIdx', i.e. the
/// signature of the entry to the region, on the given operation 'op' is
/// converted. This function should return a valid conversion for the signature
/// on success, None otherwise.
///
/// The default behavior of this function is to invoke 'convertBlockSignature'
/// on the entry block, if one is present. This function also provides special
/// handling for FuncOp to update the type signature.
///
/// TODO(riverriddle) This should be replaced in favor of using patterns, but
/// the pattern rewriter needs to know how to properly replace/remap
/// arguments.
auto TypeConverter::convertRegionSignature(Operation *op, unsigned regionIdx)
    -> llvm::Optional<SignatureConversion> {
  // Provide explicit handling for FuncOp.
  if (auto funcOp = dyn_cast<FuncOp>(op)) {
    auto conversion = convertSignature(funcOp.getType());
    if (conversion)
      funcOp.setType(conversion->getConvertedType(funcOp.getContext()));
    return conversion;
  }

  // Otherwise, default to handle the arguments of the entry block for the given
  // region.
  auto &region = op->getRegion(regionIdx);
  if (region.empty())
    return SignatureConversion(/*numOrigInputs=*/0);
  return convertBlockSignature(&region.front());
}

/// This function converts the type signature of the given block, by invoking
/// 'convertSignatureArg' for each argument. This function should return a valid
/// conversion for the signature on success, None otherwise.
auto TypeConverter::convertBlockSignature(Block *block)
    -> llvm::Optional<SignatureConversion> {
  SignatureConversion conversion(block->getNumArguments());
  for (unsigned i = 0, e = block->getNumArguments(); i != e; ++i)
    if (failed(convertSignatureArg(i, block->getArgument(i)->getType(),
                                   conversion)))
      return llvm::None;
  return conversion;
}

//===----------------------------------------------------------------------===//
// ConversionTarget
//===----------------------------------------------------------------------===//

/// Register a legality action for the given operation.
void ConversionTarget::setOpAction(OperationName op,
                                   LegalizationAction action) {
  legalOperations[op] = action;
}

/// Register a legality action for the given dialects.
void ConversionTarget::setDialectAction(ArrayRef<StringRef> dialectNames,
                                        LegalizationAction action) {
  for (StringRef dialect : dialectNames)
    legalDialects[dialect] = action;
}

/// Get the legality action for the given operation.
auto ConversionTarget::getOpAction(OperationName op) const
    -> llvm::Optional<LegalizationAction> {
  // Check for an action for this specific operation.
  auto it = legalOperations.find(op);
  if (it != legalOperations.end())
    return it->second;
  // Otherwise, default to checking for an action on the parent dialect.
  auto dialectIt = legalDialects.find(op.getDialect());
  if (dialectIt != legalDialects.end())
    return dialectIt->second;
  return llvm::None;
}

//===----------------------------------------------------------------------===//
// Op Conversion Entry Points
//===----------------------------------------------------------------------===//

/// Apply a partial conversion on the given operations, and all nested
/// operations. This method converts as many operations to the target as
/// possible, ignoring operations that failed to legalize.
LogicalResult mlir::applyPartialConversion(ArrayRef<Operation *> ops,
                                           ConversionTarget &target,
                                           OwningRewritePatternList &&patterns,
                                           TypeConverter *converter) {
  OperationConverter opConverter(target, patterns, OpConversionMode::Partial);
  return opConverter.convertOperations(ops, converter);
}
LogicalResult mlir::applyPartialConversion(Operation *op,
                                           ConversionTarget &target,
                                           OwningRewritePatternList &&patterns,
                                           TypeConverter *converter) {
  return applyPartialConversion(llvm::makeArrayRef(op), target,
                                std::move(patterns), converter);
}

/// Apply a complete conversion on the given operations, and all nested
/// operations. This method will return failure if the conversion of any
/// operation fails.
LogicalResult mlir::applyFullConversion(ArrayRef<Operation *> ops,
                                        ConversionTarget &target,
                                        OwningRewritePatternList &&patterns,
                                        TypeConverter *converter) {
  OperationConverter opConverter(target, patterns, OpConversionMode::Full);
  return opConverter.convertOperations(ops, converter);
}
LogicalResult mlir::applyFullConversion(Operation *op, ConversionTarget &target,
                                        OwningRewritePatternList &&patterns,
                                        TypeConverter *converter) {
  return applyFullConversion(llvm::makeArrayRef(op), target,
                             std::move(patterns), converter);
}