llvm-project/mlir/lib/Transforms/Utils/Utils.cpp

//===- Utils.cpp ---- Misc utilities for code and data transformation -----===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements miscellaneous transformation routines for non-loop IR
// structures.
//
//===----------------------------------------------------------------------===//

#include "mlir/Transforms/Utils.h"

#include "mlir/Analysis/AffineAnalysis.h"
#include "mlir/Analysis/AffineStructures.h"
#include "mlir/Analysis/Utils.h"
#include "mlir/Dialect/Affine/IR/AffineOps.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/Dominance.h"
#include "mlir/IR/Function.h"
#include "mlir/IR/Module.h"
#include "mlir/Support/MathExtras.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/TypeSwitch.h"
using namespace mlir;

/// Return true if this operation dereferences one or more memref's.
// Temporary utility: will be replaced when this is modeled through
// side-effects/op traits. TODO
static bool isMemRefDereferencingOp(Operation &op) {
  return isa<AffineReadOpInterface, AffineWriteOpInterface, AffineDmaStartOp,
             AffineDmaWaitOp>(op);
}

/// Return the AffineMapAttr associated with memory 'op' on 'memref'.
static NamedAttribute getAffineMapAttrForMemRef(Operation *op, Value memref) {
  return TypeSwitch<Operation *, NamedAttribute>(op)
      .Case<AffineDmaStartOp, AffineReadOpInterface, AffinePrefetchOp,
            AffineWriteOpInterface, AffineDmaWaitOp>(
          [=](auto op) { return op.getAffineMapAttrForMemRef(memref); });
}

// Perform the replacement in `op`.
LogicalResult mlir::replaceAllMemRefUsesWith(Value oldMemRef, Value newMemRef,
                                             Operation *op,
                                             ArrayRef<Value> extraIndices,
                                             AffineMap indexRemap,
                                             ArrayRef<Value> extraOperands,
                                             ArrayRef<Value> symbolOperands,
                                             bool allowNonDereferencingOps) {
  unsigned newMemRefRank = newMemRef.getType().cast<MemRefType>().getRank();
  (void)newMemRefRank; // unused in opt mode
  unsigned oldMemRefRank = oldMemRef.getType().cast<MemRefType>().getRank();
  (void)oldMemRefRank; // unused in opt mode
  if (indexRemap) {
    assert(indexRemap.getNumSymbols() == symbolOperands.size() &&
           "symbolic operand count mismatch");
    assert(indexRemap.getNumInputs() ==
           extraOperands.size() + oldMemRefRank + symbolOperands.size());
    assert(indexRemap.getNumResults() + extraIndices.size() == newMemRefRank);
  } else {
    assert(oldMemRefRank + extraIndices.size() == newMemRefRank);
  }

  // Assert same elemental type.
  assert(oldMemRef.getType().cast<MemRefType>().getElementType() ==
         newMemRef.getType().cast<MemRefType>().getElementType());

  SmallVector<unsigned, 2> usePositions;
  for (const auto &opEntry : llvm::enumerate(op->getOperands())) {
    if (opEntry.value() == oldMemRef)
      usePositions.push_back(opEntry.index());
  }

  // If memref doesn't appear, nothing to do.
  if (usePositions.empty())
    return success();

  if (usePositions.size() > 1) {
    // TODO: extend it for this case when needed (rare).
    assert(false && "multiple dereferencing uses in a single op not supported");
    return failure();
  }

  unsigned memRefOperandPos = usePositions.front();

  OpBuilder builder(op);
  // The following checks if op is dereferencing memref and performs the access
  // index rewrites.
  if (!isMemRefDereferencingOp(*op)) {
    if (!allowNonDereferencingOps)
      // Failure: memref used in a non-dereferencing context (potentially
      // escapes); no replacement in these cases unless allowNonDereferencingOps
      // is set.
      return failure();
    op->setOperand(memRefOperandPos, newMemRef);
    return success();
  }
  // Perform index rewrites for the dereferencing op and then replace the op
  NamedAttribute oldMapAttrPair = getAffineMapAttrForMemRef(op, oldMemRef);
  AffineMap oldMap = oldMapAttrPair.second.cast<AffineMapAttr>().getValue();
  unsigned oldMapNumInputs = oldMap.getNumInputs();
  SmallVector<Value, 4> oldMapOperands(
      op->operand_begin() + memRefOperandPos + 1,
      op->operand_begin() + memRefOperandPos + 1 + oldMapNumInputs);

  // Apply 'oldMemRefOperands = oldMap(oldMapOperands)'.
  SmallVector<Value, 4> oldMemRefOperands;
  SmallVector<Value, 4> affineApplyOps;
  oldMemRefOperands.reserve(oldMemRefRank);
  if (oldMap != builder.getMultiDimIdentityMap(oldMap.getNumDims())) {
    for (auto resultExpr : oldMap.getResults()) {
      auto singleResMap = AffineMap::get(oldMap.getNumDims(),
                                         oldMap.getNumSymbols(), resultExpr);
      auto afOp = builder.create<AffineApplyOp>(op->getLoc(), singleResMap,
                                                oldMapOperands);
      oldMemRefOperands.push_back(afOp);
      affineApplyOps.push_back(afOp);
    }
  } else {
    oldMemRefOperands.assign(oldMapOperands.begin(), oldMapOperands.end());
  }

  // Construct new indices as a remap of the old ones if a remapping has been
  // provided. The indices of a memref come right after it, i.e.,
  // at position memRefOperandPos + 1.
  SmallVector<Value, 4> remapOperands;
  remapOperands.reserve(extraOperands.size() + oldMemRefRank +
                        symbolOperands.size());
  remapOperands.append(extraOperands.begin(), extraOperands.end());
  remapOperands.append(oldMemRefOperands.begin(), oldMemRefOperands.end());
  remapOperands.append(symbolOperands.begin(), symbolOperands.end());

  SmallVector<Value, 4> remapOutputs;
  remapOutputs.reserve(oldMemRefRank);

  if (indexRemap &&
      indexRemap != builder.getMultiDimIdentityMap(indexRemap.getNumDims())) {
    // Remapped indices.
    for (auto resultExpr : indexRemap.getResults()) {
      auto singleResMap = AffineMap::get(
          indexRemap.getNumDims(), indexRemap.getNumSymbols(), resultExpr);
      auto afOp = builder.create<AffineApplyOp>(op->getLoc(), singleResMap,
                                                remapOperands);
      remapOutputs.push_back(afOp);
      affineApplyOps.push_back(afOp);
    }
  } else {
    // No remapping specified.
    remapOutputs.assign(remapOperands.begin(), remapOperands.end());
  }

  SmallVector<Value, 4> newMapOperands;
  newMapOperands.reserve(newMemRefRank);

  // Prepend 'extraIndices' in 'newMapOperands'.
  for (Value extraIndex : extraIndices) {
    assert(extraIndex.getDefiningOp()->getNumResults() == 1 &&
           "single result op's expected to generate these indices");
    assert((isValidDim(extraIndex) || isValidSymbol(extraIndex)) &&
           "invalid memory op index");
    newMapOperands.push_back(extraIndex);
  }

  // Append 'remapOutputs' to 'newMapOperands'.
  newMapOperands.append(remapOutputs.begin(), remapOutputs.end());

  // Create new fully composed AffineMap for new op to be created.
  assert(newMapOperands.size() == newMemRefRank);
  auto newMap = builder.getMultiDimIdentityMap(newMemRefRank);
  // TODO: Avoid creating/deleting temporary AffineApplyOps here.
  fullyComposeAffineMapAndOperands(&newMap, &newMapOperands);
  newMap = simplifyAffineMap(newMap);
  canonicalizeMapAndOperands(&newMap, &newMapOperands);
  // Remove any affine.apply's that became dead as a result of composition.
  for (Value value : affineApplyOps)
    if (value.use_empty())
      value.getDefiningOp()->erase();

  OperationState state(op->getLoc(), op->getName());
  // Construct the new operation using this memref.
  state.operands.reserve(op->getNumOperands() + extraIndices.size());
  // Insert the non-memref operands.
  state.operands.append(op->operand_begin(),
                        op->operand_begin() + memRefOperandPos);
  // Insert the new memref value.
  state.operands.push_back(newMemRef);

  // Insert the new memref map operands.
  state.operands.append(newMapOperands.begin(), newMapOperands.end());

  // Insert the remaining operands unmodified.
  state.operands.append(op->operand_begin() + memRefOperandPos + 1 +
                            oldMapNumInputs,
                        op->operand_end());

  // Result types don't change. Both memref's are of the same elemental type.
  state.types.reserve(op->getNumResults());
  for (auto result : op->getResults())
    state.types.push_back(result.getType());

  // Add attribute for 'newMap', other Attributes do not change.
  auto newMapAttr = AffineMapAttr::get(newMap);
  for (auto namedAttr : op->getAttrs()) {
    if (namedAttr.first == oldMapAttrPair.first)
      state.attributes.push_back({namedAttr.first, newMapAttr});
    else
      state.attributes.push_back(namedAttr);
  }

  // Create the new operation.
  auto *repOp = builder.createOperation(state);
  op->replaceAllUsesWith(repOp);
  op->erase();

  return success();
}

LogicalResult mlir::replaceAllMemRefUsesWith(
    Value oldMemRef, Value newMemRef, ArrayRef<Value> extraIndices,
    AffineMap indexRemap, ArrayRef<Value> extraOperands,
    ArrayRef<Value> symbolOperands, Operation *domInstFilter,
    Operation *postDomInstFilter, bool allowNonDereferencingOps,
    bool replaceInDeallocOp) {
  unsigned newMemRefRank = newMemRef.getType().cast<MemRefType>().getRank();
  (void)newMemRefRank; // unused in opt mode
  unsigned oldMemRefRank = oldMemRef.getType().cast<MemRefType>().getRank();
  (void)oldMemRefRank;
  if (indexRemap) {
    assert(indexRemap.getNumSymbols() == symbolOperands.size() &&
           "symbol operand count mismatch");
    assert(indexRemap.getNumInputs() ==
           extraOperands.size() + oldMemRefRank + symbolOperands.size());
    assert(indexRemap.getNumResults() + extraIndices.size() == newMemRefRank);
  } else {
    assert(oldMemRefRank + extraIndices.size() == newMemRefRank);
  }

  // Assert same elemental type.
  assert(oldMemRef.getType().cast<MemRefType>().getElementType() ==
         newMemRef.getType().cast<MemRefType>().getElementType());

  std::unique_ptr<DominanceInfo> domInfo;
  std::unique_ptr<PostDominanceInfo> postDomInfo;
  if (domInstFilter)
    domInfo = std::make_unique<DominanceInfo>(
        domInstFilter->getParentOfType<FuncOp>());

  if (postDomInstFilter)
    postDomInfo = std::make_unique<PostDominanceInfo>(
        postDomInstFilter->getParentOfType<FuncOp>());

  // Walk all uses of old memref; collect ops to perform replacement. We use a
  // DenseSet since an operation could potentially have multiple uses of a
  // memref (although rare), and the replacement later is going to erase ops.
  DenseSet<Operation *> opsToReplace;
  for (auto *op : oldMemRef.getUsers()) {
    // Skip this use if it's not dominated by domInstFilter.
    if (domInstFilter && !domInfo->dominates(domInstFilter, op))
      continue;

    // Skip this use if it's not post-dominated by postDomInstFilter.
    if (postDomInstFilter && !postDomInfo->postDominates(postDomInstFilter, op))
      continue;

    // Skip dealloc's - no replacement is necessary, and a memref replacement
    // at other uses doesn't hurt these dealloc's.
    if (isa<DeallocOp>(op) && !replaceInDeallocOp)
      continue;

    // Check if the memref was used in a non-dereferencing context. It is fine
    // for the memref to be used in a non-dereferencing way outside of the
    // region where this replacement is happening.
    if (!isMemRefDereferencingOp(*op)) {
      if (!allowNonDereferencingOps)
        return failure();
      // Currently we support the following non-dereferencing ops to be a
      // candidate for replacement: Dealloc, CallOp and ReturnOp.
      // TODO: Add support for other kinds of ops.
      if (!op->hasTrait<OpTrait::MemRefsNormalizable>())
        return failure();
    }

    // We'll first collect and then replace --- since replacement erases the op
    // that has the use, and that op could be postDomFilter or domFilter itself!
    opsToReplace.insert(op);
  }

  for (auto *op : opsToReplace) {
    if (failed(replaceAllMemRefUsesWith(
            oldMemRef, newMemRef, op, extraIndices, indexRemap, extraOperands,
            symbolOperands, allowNonDereferencingOps)))
      llvm_unreachable("memref replacement guaranteed to succeed here");
  }

  return success();
}

/// Given an operation, inserts one or more single result affine
/// apply operations, results of which are exclusively used by this operation
/// operation. The operands of these newly created affine apply ops are
/// guaranteed to be loop iterators or terminal symbols of a function.
///
/// Before
///
/// affine.for %i = 0 to #map(%N)
///   %idx = affine.apply (d0) -> (d0 mod 2) (%i)
///   "send"(%idx, %A, ...)
///   "compute"(%idx)
///
/// After
///
/// affine.for %i = 0 to #map(%N)
///   %idx = affine.apply (d0) -> (d0 mod 2) (%i)
///   "send"(%idx, %A, ...)
///   %idx_ = affine.apply (d0) -> (d0 mod 2) (%i)
///   "compute"(%idx_)
///
/// This allows applying different transformations on send and compute (for eg.
/// different shifts/delays).
///
/// Returns nullptr either if none of opInst's operands were the result of an
/// affine.apply and thus there was no affine computation slice to create, or if
/// all the affine.apply op's supplying operands to this opInst did not have any
/// uses besides this opInst; otherwise returns the list of affine.apply
/// operations created in output argument `sliceOps`.
void mlir::createAffineComputationSlice(
    Operation *opInst, SmallVectorImpl<AffineApplyOp> *sliceOps) {
  // Collect all operands that are results of affine apply ops.
  SmallVector<Value, 4> subOperands;
  subOperands.reserve(opInst->getNumOperands());
  for (auto operand : opInst->getOperands())
    if (isa_and_nonnull<AffineApplyOp>(operand.getDefiningOp()))
      subOperands.push_back(operand);

  // Gather sequence of AffineApplyOps reachable from 'subOperands'.
  SmallVector<Operation *, 4> affineApplyOps;
  getReachableAffineApplyOps(subOperands, affineApplyOps);
  // Skip transforming if there are no affine maps to compose.
  if (affineApplyOps.empty())
    return;

  // Check if all uses of the affine apply op's lie only in this op op, in
  // which case there would be nothing to do.
  bool localized = true;
  for (auto *op : affineApplyOps) {
    for (auto result : op->getResults()) {
      for (auto *user : result.getUsers()) {
        if (user != opInst) {
          localized = false;
          break;
        }
      }
    }
  }
  if (localized)
    return;

  OpBuilder builder(opInst);
  SmallVector<Value, 4> composedOpOperands(subOperands);
  auto composedMap = builder.getMultiDimIdentityMap(composedOpOperands.size());
  fullyComposeAffineMapAndOperands(&composedMap, &composedOpOperands);

  // Create an affine.apply for each of the map results.
  sliceOps->reserve(composedMap.getNumResults());
  for (auto resultExpr : composedMap.getResults()) {
    auto singleResMap = AffineMap::get(composedMap.getNumDims(),
                                       composedMap.getNumSymbols(), resultExpr);
    sliceOps->push_back(builder.create<AffineApplyOp>(
        opInst->getLoc(), singleResMap, composedOpOperands));
  }

  // Construct the new operands that include the results from the composed
  // affine apply op above instead of existing ones (subOperands). So, they
  // differ from opInst's operands only for those operands in 'subOperands', for
  // which they will be replaced by the corresponding one from 'sliceOps'.
  SmallVector<Value, 4> newOperands(opInst->getOperands());
  for (unsigned i = 0, e = newOperands.size(); i < e; i++) {
    // Replace the subOperands from among the new operands.
    unsigned j, f;
    for (j = 0, f = subOperands.size(); j < f; j++) {
      if (newOperands[i] == subOperands[j])
        break;
    }
    if (j < subOperands.size()) {
      newOperands[i] = (*sliceOps)[j];
    }
  }
  for (unsigned idx = 0, e = newOperands.size(); idx < e; idx++) {
    opInst->setOperand(idx, newOperands[idx]);
  }
}

// TODO: Currently works for static memrefs with a single layout map.
LogicalResult mlir::normalizeMemRef(AllocOp allocOp) {
  MemRefType memrefType = allocOp.getType();
  OpBuilder b(allocOp);

  // Fetch a new memref type after normalizing the old memref to have an
  // identity map layout.
  MemRefType newMemRefType =
      normalizeMemRefType(memrefType, b, allocOp.getNumSymbolicOperands());
  if (newMemRefType == memrefType)
    // Either memrefType already had an identity map or the map couldn't be
    // transformed to an identity map.
    return failure();

  Value oldMemRef = allocOp.getResult();

  SmallVector<Value, 4> symbolOperands(allocOp.getSymbolicOperands());
  AllocOp newAlloc = b.create<AllocOp>(allocOp.getLoc(), newMemRefType,
                                       llvm::None, allocOp.alignmentAttr());
  AffineMap layoutMap = memrefType.getAffineMaps().front();
  // Replace all uses of the old memref.
  if (failed(replaceAllMemRefUsesWith(oldMemRef, /*newMemRef=*/newAlloc,
                                      /*extraIndices=*/{},
                                      /*indexRemap=*/layoutMap,
                                      /*extraOperands=*/{},
                                      /*symbolOperands=*/symbolOperands,
                                      /*domInstFilter=*/nullptr,
                                      /*postDomInstFilter=*/nullptr,
                                      /*allowDereferencingOps=*/true))) {
    // If it failed (due to escapes for example), bail out.
    newAlloc.erase();
    return failure();
  }
  // Replace any uses of the original alloc op and erase it. All remaining uses
  // have to be dealloc's; RAMUW above would've failed otherwise.
  assert(llvm::all_of(oldMemRef.getUsers(),
                      [](Operation *op) { return isa<DeallocOp>(op); }));
  oldMemRef.replaceAllUsesWith(newAlloc);
  allocOp.erase();
  return success();
}

MemRefType mlir::normalizeMemRefType(MemRefType memrefType, OpBuilder b,
                                     unsigned numSymbolicOperands) {
  unsigned rank = memrefType.getRank();
  if (rank == 0)
    return memrefType;

  ArrayRef<AffineMap> layoutMaps = memrefType.getAffineMaps();
  if (layoutMaps.empty() ||
      layoutMaps.front() == b.getMultiDimIdentityMap(rank)) {
    // Either no maps is associated with this memref or this memref has
    // a trivial (identity) map.
    return memrefType;
  }

  // We don't do any checks for one-to-one'ness; we assume that it is
  // one-to-one.

  // TODO: Only for static memref's for now.
  if (memrefType.getNumDynamicDims() > 0)
    return memrefType;

  // We have a single map that is not an identity map. Create a new memref
  // with the right shape and an identity layout map.
  ArrayRef<int64_t> shape = memrefType.getShape();
  // FlatAffineConstraint may later on use symbolicOperands.
  FlatAffineConstraints fac(rank, numSymbolicOperands);
  for (unsigned d = 0; d < rank; ++d) {
    fac.addConstantLowerBound(d, 0);
    fac.addConstantUpperBound(d, shape[d] - 1);
  }
  // We compose this map with the original index (logical) space to derive
  // the upper bounds for the new index space.
  AffineMap layoutMap = layoutMaps.front();
  unsigned newRank = layoutMap.getNumResults();
  if (failed(fac.composeMatchingMap(layoutMap)))
    return memrefType;
  // TODO: Handle semi-affine maps.
  // Project out the old data dimensions.
  fac.projectOut(newRank, fac.getNumIds() - newRank - fac.getNumLocalIds());
  SmallVector<int64_t, 4> newShape(newRank);
  for (unsigned d = 0; d < newRank; ++d) {
    // The lower bound for the shape is always zero.
    auto ubConst = fac.getConstantUpperBound(d);
    // For a static memref and an affine map with no symbols, this is
    // always bounded.
    assert(ubConst.hasValue() && "should always have an upper bound");
    if (ubConst.getValue() < 0)
      // This is due to an invalid map that maps to a negative space.
      return memrefType;
    newShape[d] = ubConst.getValue() + 1;
  }

  // Create the new memref type after trivializing the old layout map.
  MemRefType newMemRefType =
      MemRefType::Builder(memrefType)
          .setShape(newShape)
          .setAffineMaps(b.getMultiDimIdentityMap(newRank));

  return newMemRefType;
}