lib/IR/AffineMap.cpp

//===- AffineMap.cpp - MLIR Affine Map Classes ----------------------------===//
//
// 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/IR/AffineMap.h"
#include "mlir/IR/AffineExpr.h"
#include "mlir/IR/Attributes.h"
#include "mlir/Support/MathExtras.h"
#include "llvm/ADT/StringRef.h"

using namespace mlir;

namespace {

// AffineExprConstantFolder evaluates an affine expression using constant
// operands passed in 'operandConsts'. Returns a pointer to an IntegerAttr
// attribute representing the constant value of the affine expression
// evaluated on constant 'operandConsts'.
class AffineExprConstantFolder {
public:
  AffineExprConstantFolder(unsigned numDims,
                           ArrayRef<Attribute *> operandConsts)
      : numDims(numDims), operandConsts(operandConsts) {}

  /// Attempt to constant fold the specified affine expr, or return null on
  /// failure.
  IntegerAttr *constantFold(AffineExpr expr) {
    switch (expr->getKind()) {
    case AffineExprKind::Add:
      return constantFoldBinExpr(
          expr, [](int64_t lhs, int64_t rhs) { return lhs + rhs; });
    case AffineExprKind::Mul:
      return constantFoldBinExpr(
          expr, [](int64_t lhs, int64_t rhs) { return lhs * rhs; });
    case AffineExprKind::Mod:
      return constantFoldBinExpr(
          expr, [](int64_t lhs, uint64_t rhs) { return mod(lhs, rhs); });
    case AffineExprKind::FloorDiv:
      return constantFoldBinExpr(
          expr, [](int64_t lhs, uint64_t rhs) { return floorDiv(lhs, rhs); });
    case AffineExprKind::CeilDiv:
      return constantFoldBinExpr(
          expr, [](int64_t lhs, uint64_t rhs) { return ceilDiv(lhs, rhs); });
    case AffineExprKind::Constant:
      return IntegerAttr::get(expr.cast<AffineConstantExpr>()->getValue(),
                              expr->getContext());
    case AffineExprKind::DimId:
      return dyn_cast_or_null<IntegerAttr>(
          operandConsts[expr.cast<AffineDimExpr>()->getPosition()]);
    case AffineExprKind::SymbolId:
      return dyn_cast_or_null<IntegerAttr>(
          operandConsts[numDims +
                        expr.cast<AffineSymbolExpr>()->getPosition()]);
    }
  }

private:
  IntegerAttr *
  constantFoldBinExpr(AffineExpr expr,
                      std::function<uint64_t(int64_t, uint64_t)> op) {
    auto binOpExpr = expr.cast<AffineBinaryOpExpr>();
    auto *lhs = constantFold(binOpExpr->getLHS());
    auto *rhs = constantFold(binOpExpr->getRHS());
    if (!lhs || !rhs)
      return nullptr;
    return IntegerAttr::get(op(lhs->getValue(), rhs->getValue()),
                            expr->getContext());
  }

  // The number of dimension operands in AffineMap containing this expression.
  unsigned numDims;
  // The constant valued operands used to evaluate this AffineExpr.
  ArrayRef<Attribute *> operandConsts;
};

} // end anonymous namespace

AffineMap::AffineMap(unsigned numDims, unsigned numSymbols, unsigned numResults,
                     ArrayRef<AffineExpr> results,
                     ArrayRef<AffineExpr> rangeSizes)
    : numDims(numDims), numSymbols(numSymbols), numResults(numResults),
      results(results), rangeSizes(rangeSizes) {}

/// Returns a single constant result affine map.
AffineMap *AffineMap::getConstantMap(int64_t val, MLIRContext *context) {
  return get(/*dimCount=*/0, /*symbolCount=*/0,
             {getAffineConstantExpr(val, context)}, {});
}

bool AffineMap::isIdentity() {
  if (getNumDims() != getNumResults())
    return false;
  ArrayRef<AffineExpr> results = getResults();
  for (unsigned i = 0, numDims = getNumDims(); i < numDims; ++i) {
    auto expr = results[i].dyn_cast<AffineDimExpr>();
    if (!expr || expr->getPosition() != i)
      return false;
  }
  return true;
}

bool AffineMap::isSingleConstant() {
  return getNumResults() == 1 && getResult(0).isa<AffineConstantExpr>();
}

int64_t AffineMap::getSingleConstantResult() {
  assert(isSingleConstant() && "map must have a single constant result");
  return getResult(0).cast<AffineConstantExpr>()->getValue();
}

AffineExpr AffineMap::getResult(unsigned idx) { return results[idx]; }

/// Folds the results of the application of an affine map on the provided
/// operands to a constant if possible. Returns false if the folding happens,
/// true otherwise.
bool AffineMap::constantFold(ArrayRef<Attribute *> operandConstants,
                             SmallVectorImpl<Attribute *> &results) {
  assert(getNumInputs() == operandConstants.size());

  // Fold each of the result expressions.
  AffineExprConstantFolder exprFolder(getNumDims(), operandConstants);
  // Constant fold each AffineExprClass in AffineMap and add to 'results'.
  for (auto expr : getResults()) {
    auto *folded = exprFolder.constantFold(expr);
    // If we didn't fold to a constant, then folding fails.
    if (!folded)
      return true;

    results.push_back(folded);
  }
  assert(results.size() == getNumResults() &&
         "constant folding produced the wrong number of results");
  return false;
}