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(Region &region);

  /// Cleanup and undo any generated conversion values.
  void discardRewrites();

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

  /// Converts the signature of the given entry block.
  void convertSignature(Block *block,
                        TypeConverter::SignatureConversion &signatureConversion,
                        BlockAndValueMapping &mapping);

  /// Converts the arguments of the given block.
  LogicalResult convertArguments(Block *block, 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 blocks within the given
/// region. This function is called when the given region is to be destroyed.
void ArgConverter::cancelPendingRewrites(Region &region) {
  for (auto &block : region) {
    auto it = argMapping.find(&block);
    if (it == argMapping.end())
      continue;
    for (auto *op : it->second) {
      // If the operation exists within the parent block, like with 1->N cast
      // operations, we don't need to drop them. They will be automatically
      // cleaned up with the region is destroyed.
      if (op->getBlock())
        continue;

      op->dropAllDefinedValueUses();
      op->destroy();
    }
    argMapping.erase(it);
  }
}

/// Cleanup and undo any generated conversion values.
void ArgConverter::discardRewrites() {
  // On failure reinstate all of the original block arguments.
  Block *block;
  ArrayRef<Operation *> argOps;
  for (auto &mapping : argMapping) {
    std::tie(block, argOps) = mapping;

    // 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.
    for (unsigned i = 0, e = argOps.size(); i != e; ++i) {
      auto *op = argOps[i];
      auto *arg = block->addArgument(op->getResult(0)->getType());
      op->getResult(0)->replaceAllUsesWith(arg);

      // If this was a 1->N value mapping it exists within the parent block so
      // erase it instead of destroying.
      if (op->getBlock())
        op->erase();
      else
        op->destroy();
    }
  }
  argMapping.clear();
}

/// 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 from type to itself, replace the remaining uses and drop
      // the cast operation.
      if (op->getNumOperands() == 1 &&
          op->getResult(0)->getType() == op->getOperand(0)->getType()) {
        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 entry block.
void ArgConverter::convertSignature(
    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);
}

/// Converts the arguments of the given block.
LogicalResult ArgConverter::convertArguments(Block *block,
                                             BlockAndValueMapping &mapping) {
  unsigned origArgCount = block->getNumArguments();
  if (origArgCount == 0)
    return success();

  // Convert the types of each of the block arguments.
  SmallVector<SmallVector<Type, 1>, 4> newArgTypes(origArgCount);
  for (unsigned i = 0; i != origArgCount; ++i) {
    auto *arg = block->getArgument(i);
    if (failed(typeConverter->convertType(arg->getType(), newArgTypes[i])))
      return emitError(block->getParent()->getLoc())
             << "could not convert block argument of type " << arg->getType();
  }

  // Remap all of the original argument values.
  auto &newArgMapping = argMapping[block];
  rewriter.setInsertionPointToStart(block);
  for (unsigned i = 0; i != origArgCount; ++i) {
    SmallVector<Value *, 1> newArgs(block->addArguments(newArgTypes[i]));
    newArgMapping.push_back(
        convertArgument(block->getArgument(i), newArgs, mapping));
  }

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

/// 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)
      : numCreatedOperations(numCreatedOperations),
        numReplacements(numReplacements), numBlockActions(numBlockActions) {}

  /// 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;
};

/// 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;
  };

  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());
  }

  /// Reset the state of the rewriter to a previously saved point.
  void resetState(RewriterState state) {
    // 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 any block operations.
    undoBlockActions(state.numBlockActions);
  }

  /// 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;
      }
      }
    }
  }

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

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

    undoBlockActions();
  }

  /// 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(repl.newValues[i]);

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

      repl.op->erase();
    }

    argConverter.applyRewrites();
  }

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

  /// 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

LogicalResult
OperationLegalizer::legalize(Operation *op,
                             DialectConversionRewriter &rewriter) {
  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 == ConversionTarget::LegalizationAction::Legal)
      return success();

    // Otherwise, handle dynamic legalization.
    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();
  }

  // TODO(riverriddle) This currently has no cost model and doesn't prioritize
  // specific patterns in any way.
  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) == ConversionTarget::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) {
          return !legalizerPatterns.count(op) && !target.getOpAction(op);
        }))
      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);
}

//===----------------------------------------------------------------------===//
// FunctionConverter
//===----------------------------------------------------------------------===//
namespace {
// This class converts a single function 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 FunctionConverter {
  explicit FunctionConverter(MLIRContext *ctx, ConversionTarget &target,
                             OwningRewritePatternList &patterns,
                             TypeConverter *conversion = nullptr)
      : typeConverter(conversion), opLegalizer(target, patterns) {}

  /// Converts the given function to the conversion target. Returns failure on
  /// error, success otherwise. If 'signatureConversion' is provided, the
  /// arguments of the entry block are updated accordingly.
  LogicalResult
  convertFunction(FuncOp f,
                  TypeConverter::SignatureConversion *signatureConversion);

  /// Converts the given region starting from the entry block and following the
  /// block successors. Returns failure on error, success otherwise. Prints
  /// error messages at `loc`.
  LogicalResult convertRegion(DialectConversionRewriter &rewriter,
                              Region &region, bool convertEntryTypes = true);

  /// Converts a block by traversing its operations sequentially, attempting to
  /// match a pattern. If there is no match, recurses the operations regions if
  /// it has any.
  //
  /// After converting operations, traverses the successor blocks unless they
  /// have been visited already as indicated in `visitedBlocks`.
  LogicalResult convertBlock(DialectConversionRewriter &rewriter, Block *block,
                             DenseSet<Block *> &visitedBlocks);

  /// Pointer to a specific dialect conversion info.
  TypeConverter *typeConverter;

  /// The legalizer to use when converting operations.
  OperationLegalizer opLegalizer;
};
} // end anonymous namespace

LogicalResult
FunctionConverter::convertBlock(DialectConversionRewriter &rewriter,
                                Block *block,
                                DenseSet<Block *> &visitedBlocks) {
  // First, add the current block to the list of visited blocks.
  visitedBlocks.insert(block);

  if (block->empty())
    return success();

  // Preserve the successors before rewriting the operations.
  SmallVector<Block *, 4> successors(block->getSuccessors());

  // Iterate over ops and convert them.  Since the conversion may split the
  // block, we eagerly take the pointer to the next operation in it.  Splitting
  // moves the operations from one block to another, so this will keep
  // considering the original list of operations independently of the block
  // within which they are currently located.  This relies on iplist node API
  // to get the next node in the list witout knowing which list it is, iterators
  // are unsuitable because block splitting invalidates all iterators following
  // the current one. Any operation inserted by the conversion, independently of
  // its parent block, will be recursively legalized independently of this
  // function.
  Operation *current = &block->front();
  Operation *next = nullptr;
  do {
    next = current->getNextNode();
    // Traverse any held regions.
    for (auto &region : current->getRegions())
      if (!region.empty() && failed(convertRegion(rewriter, region)))
        return failure();

    // Legalize the current operation.
    (void)opLegalizer.legalize(current, rewriter);
  } while ((current = next));

  // Recurse to children that haven't been visited.
  for (Block *succ : successors) {
    if (visitedBlocks.count(succ))
      continue;
    if (failed(convertBlock(rewriter, succ, visitedBlocks)))
      return failure();
  }
  return success();
}

LogicalResult
FunctionConverter::convertRegion(DialectConversionRewriter &rewriter,
                                 Region &region, bool convertEntryTypes) {
  assert(!region.empty() && "expected non-empty region");

  // Create the arguments of each of the blocks in the region. If a type
  // converter was not provided, then we don't need to change any of the block
  // types.
  if (typeConverter) {
    for (Block &block :
         llvm::drop_begin(region.getBlocks(), convertEntryTypes ? 0 : 1)) {
      if (failed(
              rewriter.argConverter.convertArguments(&block, rewriter.mapping)))
        return failure();
    }
  }

  // Store the number of blocks before conversion (new blocks may be added due
  // to splits or moves, but the operations in them will be processed
  // elsewhere).
  unsigned numBlocks = std::distance(region.begin(), region.end());

  // Start a DFS-order traversal of the CFG to make sure defs are converted
  // before uses in dominated blocks.
  llvm::DenseSet<Block *> visitedBlocks;
  if (failed(convertBlock(rewriter, &region.front(), visitedBlocks)))
    return failure();

  // If some blocks are not reachable through successor chains, they should have
  // been removed by the DCE before this.
  if (visitedBlocks.size() != numBlocks)
    return emitError(region.getLoc(), "unreachable blocks were not converted");
  return success();
}

LogicalResult FunctionConverter::convertFunction(
    FuncOp f, TypeConverter::SignatureConversion *signatureConversion) {
  // If this is an external function, there is nothing else to do.
  if (f.isExternal())
    return success();

  DialectConversionRewriter rewriter(f.getContext(), typeConverter);

  // Update the signature of the entry block.
  if (signatureConversion) {
    rewriter.argConverter.convertSignature(
        &f.getBody().front(), *signatureConversion, rewriter.mapping);
  }

  // Rewrite the function body.
  if (failed(
          convertRegion(rewriter, f.getBody(), /*convertEntryTypes=*/false))) {
    // Reset any of the generated rewrites.
    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,
    ArrayRef<NamedAttributeList> attrs) {
  assert(!types.empty() && "expected valid types");
  remapInput(origInputNo, /*newInputNo=*/argTypes.size(), types.size());
  addInputs(types, attrs);
}

/// 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, ArrayRef<NamedAttributeList> attrs) {
  assert(!types.empty() &&
         "1->0 type remappings don't need to be added explicitly");
  assert(attrs.empty() || types.size() == attrs.size());

  argTypes.append(types.begin(), types.end());
  if (attrs.empty())
    argAttrs.resize(argTypes.size());
  else
    argAttrs.append(attrs.begin(), attrs.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,
                                     ArrayRef<NamedAttributeList> argAttrs)
    -> llvm::Optional<SignatureConversion> {
  SignatureConversion result(type.getNumInputs());
  if (failed(convertSignature(type, argAttrs, result)))
    return llvm::None;
  return result;
}

/// This hook allows for changing a FunctionType signature.
LogicalResult
TypeConverter::convertSignature(FunctionType type,
                                ArrayRef<NamedAttributeList> argAttrs,
                                SignatureConversion &result) {
  // Convert the original function arguments.
  for (unsigned i = 0, e = type.getNumInputs(); i != e; ++i)
    if (failed(convertSignatureArg(i, type.getInput(i), argAttrs[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,
                                                 NamedAttributeList attrs,
                                                 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.
  auto convertedAttrs =
      convertedTypes.size() == 1 ? llvm::makeArrayRef(attrs) : llvm::None;
  result.addInputs(inputNo, convertedTypes, convertedAttrs);
  return success();
}

//===----------------------------------------------------------------------===//
// 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;
}

//===----------------------------------------------------------------------===//
// Conversion Application
//===----------------------------------------------------------------------===//

/// Convert the given module with the provided conversion patterns and type
/// conversion object. If conversion fails for specific functions, those
/// functions remains unmodified.
LogicalResult
mlir::applyConversionPatterns(ModuleOp module, ConversionTarget &target,
                              TypeConverter &converter,
                              OwningRewritePatternList &&patterns) {
  SmallVector<FuncOp, 32> allFunctions(module.getOps<FuncOp>());
  return applyConversionPatterns(allFunctions, target, converter,
                                 std::move(patterns));
}

/// Convert the given functions with the provided conversion patterns.
LogicalResult mlir::applyConversionPatterns(
    MutableArrayRef<FuncOp> fns, ConversionTarget &target,
    TypeConverter &converter, OwningRewritePatternList &&patterns) {
  if (fns.empty())
    return success();

  // Build the function converter.
  auto *ctx = fns.front().getContext();
  FunctionConverter funcConverter(ctx, target, patterns, &converter);

  // Try to convert each of the functions within the module.
  SmallVector<NamedAttributeList, 4> argAttrs;
  for (auto func : fns) {
    argAttrs.clear();
    func.getAllArgAttrs(argAttrs);

    // Convert the function type using the type converter.
    auto conversion = converter.convertSignature(func.getType(), argAttrs);
    if (!conversion)
      return failure();

    // Update the function signature.
    func.setType(conversion->getConvertedType(ctx));
    func.setAllArgAttrs(conversion->getConvertedArgAttrs());

    // Convert the body of this function.
    if (failed(funcConverter.convertFunction(func, &*conversion)))
      return failure();
  }

  return success();
}

/// Convert the given function with the provided conversion patterns. This will
/// convert as many of the operations within 'fn' as possible given the set of
/// patterns.
LogicalResult
mlir::applyConversionPatterns(FuncOp fn, ConversionTarget &target,
                              OwningRewritePatternList &&patterns) {
  // Convert the body of this function.
  FunctionConverter converter(fn.getContext(), target, patterns);
  return converter.convertFunction(fn, /*signatureConversion=*/nullptr);
}