llvm-project/mlir/lib/Analysis/Presburger/PresburgerRelation.cpp

//===- PresburgerRelation.cpp - MLIR PresburgerRelation Class -------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#include "mlir/Analysis/Presburger/PresburgerRelation.h"
#include "mlir/Analysis/Presburger/Simplex.h"
#include "mlir/Analysis/Presburger/Utils.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/SmallBitVector.h"

using namespace mlir;
using namespace presburger;

PresburgerRelation::PresburgerRelation(const IntegerRelation &disjunct)
    : PresburgerSpace(disjunct.getSpaceWithoutLocals()) {
  unionInPlace(disjunct);
}

unsigned PresburgerRelation::getNumDisjuncts() const {
  return disjuncts.size();
}

ArrayRef<IntegerRelation> PresburgerRelation::getAllDisjuncts() const {
  return disjuncts;
}

const IntegerRelation &PresburgerRelation::getDisjunct(unsigned index) const {
  assert(index < disjuncts.size() && "index out of bounds!");
  return disjuncts[index];
}

/// Mutate this set, turning it into the union of this set and the given
/// IntegerRelation.
void PresburgerRelation::unionInPlace(const IntegerRelation &disjunct) {
  assert(isSpaceCompatible(disjunct) && "Spaces should match");
  disjuncts.push_back(disjunct);
}

/// Mutate this set, turning it into the union of this set and the given set.
///
/// This is accomplished by simply adding all the disjuncts of the given set
/// to this set.
void PresburgerRelation::unionInPlace(const PresburgerRelation &set) {
  assert(isSpaceCompatible(set) && "Spaces should match");
  for (const IntegerRelation &disjunct : set.disjuncts)
    unionInPlace(disjunct);
}

/// Return the union of this set and the given set.
PresburgerRelation
PresburgerRelation::unionSet(const PresburgerRelation &set) const {
  assert(isSpaceCompatible(set) && "Spaces should match");
  PresburgerRelation result = *this;
  result.unionInPlace(set);
  return result;
}

/// A point is contained in the union iff any of the parts contain the point.
bool PresburgerRelation::containsPoint(ArrayRef<int64_t> point) const {
  return llvm::any_of(disjuncts, [&](const IntegerRelation &disjunct) {
    return (disjunct.containsPoint(point));
  });
}

PresburgerRelation
PresburgerRelation::getUniverse(const PresburgerSpace &space) {
  PresburgerRelation result(space);
  result.unionInPlace(IntegerRelation::getUniverse(space));
  return result;
}

PresburgerRelation PresburgerRelation::getEmpty(const PresburgerSpace &space) {
  return PresburgerRelation(space);
}

// Return the intersection of this set with the given set.
//
// We directly compute (S_1 or S_2 ...) and (T_1 or T_2 ...)
// as (S_1 and T_1) or (S_1 and T_2) or ...
//
// If S_i or T_j have local variables, then S_i and T_j contains the local
// variables of both.
PresburgerRelation
PresburgerRelation::intersect(const PresburgerRelation &set) const {
  assert(isSpaceCompatible(set) && "Spaces should match");

  PresburgerRelation result(getSpace());
  for (const IntegerRelation &csA : disjuncts) {
    for (const IntegerRelation &csB : set.disjuncts) {
      IntegerRelation intersection = csA.intersect(csB);
      if (!intersection.isEmpty())
        result.unionInPlace(intersection);
    }
  }
  return result;
}

/// Return the set difference b \ s and accumulate the result into `result`.
/// `simplex` must correspond to b.
///
/// In the following, U denotes union, ^ denotes intersection, \ denotes set
/// difference and ~ denotes complement.
/// Let b be the IntegerRelation and s = (U_i s_i) be the set. We want
/// b \ (U_i s_i).
///
/// Let s_i = ^_j s_ij, where each s_ij is a single inequality. To compute
/// b \ s_i = b ^ ~s_i, we partition s_i based on the first violated inequality:
/// ~s_i = (~s_i1) U (s_i1 ^ ~s_i2) U (s_i1 ^ s_i2 ^ ~s_i3) U ...
/// And the required result is (b ^ ~s_i1) U (b ^ s_i1 ^ ~s_i2) U ...
/// We recurse by subtracting U_{j > i} S_j from each of these parts and
/// returning the union of the results. Each equality is handled as a
/// conjunction of two inequalities.
///
/// Note that the same approach works even if an inequality involves a floor
/// division. For example, the complement of x <= 7*floor(x/7) is still
/// x > 7*floor(x/7). Since b \ s_i contains the inequalities of both b and s_i
/// (or the complements of those inequalities), b \ s_i may contain the
/// divisions present in both b and s_i. Therefore, we need to add the local
/// division variables of both b and s_i to each part in the result. This means
/// adding the local variables of both b and s_i, as well as the corresponding
/// division inequalities to each part. Since the division inequalities are
/// added to each part, we can skip the parts where the complement of any
/// division inequality is added, as these parts will become empty anyway.
///
/// As a heuristic, we try adding all the constraints and check if simplex
/// says that the intersection is empty. If it is, then subtracting this
/// disjuncts is a no-op and we just skip it. Also, in the process we find out
/// that some constraints are redundant. These redundant constraints are
/// ignored.
///
/// b and simplex are callee saved, i.e., their values on return are
/// semantically equivalent to their values when the function is called.
///
/// b should not have duplicate divs because this might lead to existing
/// divs disappearing in the call to mergeLocalIds below, which cannot be
/// handled.
static void subtractRecursively(IntegerRelation &b, Simplex &simplex,
                                const PresburgerRelation &s, unsigned i,
                                PresburgerRelation &result) {
  if (i == s.getNumDisjuncts()) {
    result.unionInPlace(b);
    return;
  }

  IntegerRelation sI = s.getDisjunct(i);
  // Remove the duplicate divs up front to avoid them possibly disappearing
  // in the call to mergeLocalIds below.
  sI.removeDuplicateDivs();

  // Below, we append some additional constraints and ids to b. We want to
  // rollback b to its initial state before returning, which we will do by
  // removing all constraints beyond the original number of inequalities
  // and equalities, so we store these counts first.
  const IntegerRelation::CountsSnapshot bCounts = b.getCounts();
  // Similarly, we also want to rollback simplex to its original state.
  const unsigned initialSnapshot = simplex.getSnapshot();

  auto restoreState = [&]() {
    b.truncate(bCounts);
    simplex.rollback(initialSnapshot);
  };

  // Automatically restore the original state when we return.
  auto stateRestorer = llvm::make_scope_exit(restoreState);

  // Find out which inequalities of sI correspond to division inequalities for
  // the local variables of sI.
  std::vector<MaybeLocalRepr> repr(sI.getNumLocalIds());
  sI.getLocalReprs(repr);

  // Add sI's locals to b, after b's locals. Also add b's locals to sI, before
  // sI's locals.
  b.mergeLocalIds(sI);

  // Mark which inequalities of sI are division inequalities and add all such
  // inequalities to b.
  llvm::SmallBitVector isDivInequality(sI.getNumInequalities());
  for (MaybeLocalRepr &maybeInequality : repr) {
    assert(maybeInequality.kind == ReprKind::Inequality &&
           "Subtraction is not supported when a representation of the local "
           "variables of the subtrahend cannot be found!");
    auto lb = maybeInequality.repr.inequalityPair.lowerBoundIdx;
    auto ub = maybeInequality.repr.inequalityPair.upperBoundIdx;

    b.addInequality(sI.getInequality(lb));
    b.addInequality(sI.getInequality(ub));

    assert(lb != ub &&
           "Upper and lower bounds must be different inequalities!");
    isDivInequality[lb] = true;
    isDivInequality[ub] = true;
  }

  unsigned offset = simplex.getNumConstraints();
  unsigned numLocalsAdded =
      b.getNumLocalIds() - bCounts.getSpace().getNumLocalIds();
  simplex.appendVariable(numLocalsAdded);

  unsigned snapshotBeforeIntersect = simplex.getSnapshot();
  simplex.intersectIntegerRelation(sI);

  if (simplex.isEmpty()) {
    // b ^ s_i is empty, so b \ s_i = b. We move directly to i + 1.
    // We are ignoring level i completely, so we restore the state
    // *before* going to level i + 1.
    restoreState();
    subtractRecursively(b, simplex, s, i + 1, result);

    // We already restored the state above and the recursive call should have
    // restored to the same state before returning, so we don't need to restore
    // the state again.
    stateRestorer.release();
    return;
  }

  simplex.detectRedundant();

  // Equalities are added to simplex as a pair of inequalities.
  unsigned totalNewSimplexInequalities =
      2 * sI.getNumEqualities() + sI.getNumInequalities();
  llvm::SmallBitVector isMarkedRedundant(totalNewSimplexInequalities);
  for (unsigned j = 0; j < totalNewSimplexInequalities; j++)
    isMarkedRedundant[j] = simplex.isMarkedRedundant(offset + j);

  simplex.rollback(snapshotBeforeIntersect);

  // Recurse with the part b ^ ~ineq. Note that b is modified throughout
  // subtractRecursively. At the time this function is called, the current b is
  // actually equal to b ^ s_i1 ^ s_i2 ^ ... ^ s_ij, and ineq is the next
  // inequality, s_{i,j+1}. This function recurses into the next level i + 1
  // with the part b ^ s_i1 ^ s_i2 ^ ... ^ s_ij ^ ~s_{i,j+1}.
  auto recurseWithInequality = [&, i](ArrayRef<int64_t> ineq) {
    SimplexRollbackScopeExit scopeExit(simplex);
    b.addInequality(ineq);
    simplex.addInequality(ineq);
    subtractRecursively(b, simplex, s, i + 1, result);
    b.removeInequality(b.getNumInequalities() - 1);
  };

  // For each inequality ineq, we first recurse with the part where ineq
  // is not satisfied, and then add the ineq to b and simplex because
  // ineq must be satisfied by all later parts.
  auto processInequality = [&](ArrayRef<int64_t> ineq) {
    recurseWithInequality(getComplementIneq(ineq));
    b.addInequality(ineq);
    simplex.addInequality(ineq);
  };

  // Process all the inequalities, ignoring redundant inequalities and division
  // inequalities. The result is correct whether or not we ignore these, but
  // ignoring them makes the result simpler.
  for (unsigned j = 0, e = sI.getNumInequalities(); j < e; j++) {
    if (isMarkedRedundant[j])
      continue;
    if (isDivInequality[j])
      continue;
    processInequality(sI.getInequality(j));
  }

  offset = sI.getNumInequalities();
  for (unsigned j = 0, e = sI.getNumEqualities(); j < e; ++j) {
    ArrayRef<int64_t> coeffs = sI.getEquality(j);
    // For each equality, process the positive and negative inequalities that
    // make up this equality. If Simplex found an inequality to be redundant, we
    // skip it as above to make the result simpler. Divisions are always
    // represented in terms of inequalities and not equalities, so we do not
    // check for division inequalities here.
    if (!isMarkedRedundant[offset + 2 * j])
      processInequality(coeffs);
    if (!isMarkedRedundant[offset + 2 * j + 1])
      processInequality(getNegatedCoeffs(coeffs));
  }
}

/// Return the set difference disjunct \ set.
///
/// The disjunct here is modified in subtractRecursively, so it cannot be a
/// const reference even though it is restored to its original state before
/// returning from that function.
static PresburgerRelation getSetDifference(IntegerRelation disjunct,
                                           const PresburgerRelation &set) {
  assert(disjunct.isSpaceCompatible(set) && "Spaces should match");
  if (disjunct.isEmptyByGCDTest())
    return PresburgerRelation::getEmpty(disjunct.getSpaceWithoutLocals());

  // Remove duplicate divs up front here as subtractRecursively does not support
  // this set having duplicate divs.
  disjunct.removeDuplicateDivs();

  PresburgerRelation result =
      PresburgerRelation::getEmpty(disjunct.getSpaceWithoutLocals());
  Simplex simplex(disjunct);
  subtractRecursively(disjunct, simplex, set, 0, result);
  return result;
}

/// Return the complement of this set.
PresburgerRelation PresburgerRelation::complement() const {
  return getSetDifference(IntegerRelation::getUniverse(getSpace()), *this);
}

/// Return the result of subtract the given set from this set, i.e.,
/// return `this \ set`.
PresburgerRelation
PresburgerRelation::subtract(const PresburgerRelation &set) const {
  assert(isSpaceCompatible(set) && "Spaces should match");
  PresburgerRelation result(getSpace());
  // We compute (U_i t_i) \ (U_i set_i) as U_i (t_i \ V_i set_i).
  for (const IntegerRelation &disjunct : disjuncts)
    result.unionInPlace(getSetDifference(disjunct, set));
  return result;
}

/// T is a subset of S iff T \ S is empty, since if T \ S contains a
/// point then this is a point that is contained in T but not S, and
/// if T contains a point that is not in S, this also lies in T \ S.
bool PresburgerRelation::isSubsetOf(const PresburgerRelation &set) const {
  return this->subtract(set).isIntegerEmpty();
}

/// Two sets are equal iff they are subsets of each other.
bool PresburgerRelation::isEqual(const PresburgerRelation &set) const {
  assert(isSpaceCompatible(set) && "Spaces should match");
  return this->isSubsetOf(set) && set.isSubsetOf(*this);
}

/// Return true if all the sets in the union are known to be integer empty,
/// false otherwise.
bool PresburgerRelation::isIntegerEmpty() const {
  // The set is empty iff all of the disjuncts are empty.
  return llvm::all_of(disjuncts, std::mem_fn(&IntegerRelation::isIntegerEmpty));
}

bool PresburgerRelation::findIntegerSample(SmallVectorImpl<int64_t> &sample) {
  // A sample exists iff any of the disjuncts contains a sample.
  for (const IntegerRelation &disjunct : disjuncts) {
    if (Optional<SmallVector<int64_t, 8>> opt = disjunct.findIntegerSample()) {
      sample = std::move(*opt);
      return true;
    }
  }
  return false;
}

Optional<uint64_t> PresburgerRelation::computeVolume() const {
  assert(getNumSymbolIds() == 0 && "Symbols are not yet supported!");
  // The sum of the volumes of the disjuncts is a valid overapproximation of the
  // volume of their union, even if they overlap.
  uint64_t result = 0;
  for (const IntegerRelation &disjunct : disjuncts) {
    Optional<uint64_t> volume = disjunct.computeVolume();
    if (!volume)
      return {};
    result += *volume;
  }
  return result;
}

/// The SetCoalescer class contains all functionality concerning the coalesce
/// heuristic. It is built from a `PresburgerRelation` and has the `coalesce()`
/// function as its main API. The coalesce heuristic simplifies the
/// representation of a PresburgerRelation. In particular, it removes all
/// disjuncts which are subsets of other disjuncts in the union and it combines
/// sets that overlap and can be combined in a convex way.
class presburger::SetCoalescer {

public:
  /// Simplifies the representation of a PresburgerSet.
  PresburgerRelation coalesce();

  /// Construct a SetCoalescer from a PresburgerSet.
  SetCoalescer(const PresburgerRelation &s);

private:
  /// The space of the set the SetCoalescer is coalescing.
  PresburgerSpace space;

  /// The current list of `IntegerRelation`s that the currently coalesced set is
  /// the union of.
  SmallVector<IntegerRelation, 2> disjuncts;
  /// The list of `Simplex`s constructed from the elements of `disjuncts`.
  SmallVector<Simplex, 2> simplices;

  /// The list of all inversed equalities during typing. This ensures that
  /// the constraints exist even after the typing function has concluded.
  SmallVector<SmallVector<int64_t, 2>, 2> negEqs;

  /// `redundantIneqsA` is the inequalities of `a` that are redundant for `b`
  /// (similarly for `cuttingIneqsA`, `redundantIneqsB`, and `cuttingIneqsB`).
  SmallVector<ArrayRef<int64_t>, 2> redundantIneqsA;
  SmallVector<ArrayRef<int64_t>, 2> cuttingIneqsA;

  SmallVector<ArrayRef<int64_t>, 2> redundantIneqsB;
  SmallVector<ArrayRef<int64_t>, 2> cuttingIneqsB;

  /// Given a Simplex `simp` and one of its inequalities `ineq`, check
  /// that the facet of `simp` where `ineq` holds as an equality is contained
  /// within `a`.
  bool isFacetContained(ArrayRef<int64_t> ineq, Simplex &simp);

  /// Removes redundant constraints from `disjunct`, adds it to `disjuncts` and
  /// removes the disjuncts at position `i` and `j`. Updates `simplices` to
  /// reflect the changes. `i` and `j` cannot be equal.
  void addCoalescedDisjunct(unsigned i, unsigned j,
                            const IntegerRelation &disjunct);

  /// Checks whether `a` and `b` can be combined in a convex sense, if there
  /// exist cutting inequalities.
  ///
  /// An example of this case:
  ///    ___________        ___________
  ///   /   /  |   /       /          /
  ///   \   \  |  /   ==>  \         /
  ///    \   \ | /          \       /
  ///     \___\|/            \_____/
  ///
  ///
  LogicalResult coalescePairCutCase(unsigned i, unsigned j);

  /// Types the inequality `ineq` according to its `IneqType` for `simp` into
  /// `redundantIneqsB` and `cuttingIneqsB`. Returns success, if no separate
  /// inequalities were encountered. Otherwise, returns failure.
  LogicalResult typeInequality(ArrayRef<int64_t> ineq, Simplex &simp);

  /// Types the equality `eq`, i.e. for `eq` == 0, types both `eq` >= 0 and
  /// -`eq` >= 0 according to their `IneqType` for `simp` into
  /// `redundantIneqsB` and `cuttingIneqsB`. Returns success, if no separate
  /// inequalities were encountered. Otherwise, returns failure.
  LogicalResult typeEquality(ArrayRef<int64_t> eq, Simplex &simp);

  /// Replaces the element at position `i` with the last element and erases
  /// the last element for both `disjuncts` and `simplices`.
  void eraseDisjunct(unsigned i);

  /// Attempts to coalesce the two IntegerRelations at position `i` and `j`
  /// in `disjuncts` in-place. Returns whether the disjuncts were
  /// successfully coalesced. The simplices in `simplices` need to be the ones
  /// constructed from `disjuncts`. At this point, there are no empty
  /// disjuncts in `disjuncts` left.
  LogicalResult coalescePair(unsigned i, unsigned j);
};

/// Constructs a `SetCoalescer` from a `PresburgerRelation`. Only adds non-empty
/// `IntegerRelation`s to the `disjuncts` vector.
SetCoalescer::SetCoalescer(const PresburgerRelation &s) : space(s.getSpace()) {

  disjuncts = s.disjuncts;

  simplices.reserve(s.getNumDisjuncts());
  // Note that disjuncts.size() changes during the loop.
  for (unsigned i = 0; i < disjuncts.size();) {
    disjuncts[i].removeRedundantConstraints();
    Simplex simp(disjuncts[i]);
    if (simp.isEmpty()) {
      disjuncts[i] = disjuncts[disjuncts.size() - 1];
      disjuncts.pop_back();
      continue;
    }
    ++i;
    simplices.push_back(simp);
  }
}

/// Simplifies the representation of a PresburgerSet.
PresburgerRelation SetCoalescer::coalesce() {
  // For all tuples of IntegerRelations, check whether they can be
  // coalesced. When coalescing is successful, the contained IntegerRelation
  // is swapped with the last element of `disjuncts` and subsequently erased
  // and similarly for simplices.
  for (unsigned i = 0; i < disjuncts.size();) {

    // TODO: This does some comparisons two times (index 0 with 1 and index 1
    // with 0).
    bool broken = false;
    for (unsigned j = 0, e = disjuncts.size(); j < e; ++j) {
      negEqs.clear();
      redundantIneqsA.clear();
      redundantIneqsB.clear();
      cuttingIneqsA.clear();
      cuttingIneqsB.clear();
      if (i == j)
        continue;
      if (coalescePair(i, j).succeeded()) {
        broken = true;
        break;
      }
    }

    // Only if the inner loop was not broken, i is incremented. This is
    // required as otherwise, if a coalescing occurs, the IntegerRelation
    // now at position i is not compared.
    if (!broken)
      ++i;
  }

  PresburgerRelation newSet = PresburgerRelation::getEmpty(space);
  for (unsigned i = 0, e = disjuncts.size(); i < e; ++i)
    newSet.unionInPlace(disjuncts[i]);

  return newSet;
}

/// Given a Simplex `simp` and one of its inequalities `ineq`, check
/// that all inequalities of `cuttingIneqsB` are redundant for the facet of
/// `simp` where `ineq` holds as an equality is contained within `a`.
bool SetCoalescer::isFacetContained(ArrayRef<int64_t> ineq, Simplex &simp) {
  SimplexRollbackScopeExit scopeExit(simp);
  simp.addEquality(ineq);
  return llvm::all_of(cuttingIneqsB, [&simp](ArrayRef<int64_t> curr) {
    return simp.isRedundantInequality(curr);
  });
}

void SetCoalescer::addCoalescedDisjunct(unsigned i, unsigned j,
                                        const IntegerRelation &disjunct) {
  assert(i != j && "The indices must refer to different disjuncts");
  unsigned n = disjuncts.size();
  if (j == n - 1) {
    // This case needs special handling since position `n` - 1 is removed
    // from the vector, hence the `IntegerRelation` at position `n` - 2 is
    // lost otherwise.
    disjuncts[i] = disjuncts[n - 2];
    disjuncts.pop_back();
    disjuncts[n - 2] = disjunct;
    disjuncts[n - 2].removeRedundantConstraints();

    simplices[i] = simplices[n - 2];
    simplices.pop_back();
    simplices[n - 2] = Simplex(disjuncts[n - 2]);

  } else {
    // Other possible edge cases are correct since for `j` or `i` == `n` -
    // 2, the `IntegerRelation` at position `n` - 2 should be lost. The
    // case `i` == `n` - 1 makes the first following statement a noop.
    // Hence, in this case the same thing is done as above, but with `j`
    // rather than `i`.
    disjuncts[i] = disjuncts[n - 1];
    disjuncts[j] = disjuncts[n - 2];
    disjuncts.pop_back();
    disjuncts[n - 2] = disjunct;
    disjuncts[n - 2].removeRedundantConstraints();

    simplices[i] = simplices[n - 1];
    simplices[j] = simplices[n - 2];
    simplices.pop_back();
    simplices[n - 2] = Simplex(disjuncts[n - 2]);
  }
}

/// Given two polyhedra `a` and `b` at positions `i` and `j` in
/// `disjuncts` and `redundantIneqsA` being the inequalities of `a` that
/// are redundant for `b` (similarly for `cuttingIneqsA`, `redundantIneqsB`,
/// and `cuttingIneqsB`), Checks whether the facets of all cutting
/// inequalites of `a` are contained in `b`. If so, a new polyhedron
/// consisting of all redundant inequalites of `a` and `b` and all
/// equalities of both is created.
///
/// An example of this case:
///    ___________        ___________
///   /   /  |   /       /          /
///   \   \  |  /   ==>  \         /
///    \   \ | /          \       /
///     \___\|/            \_____/
///
///
LogicalResult SetCoalescer::coalescePairCutCase(unsigned i, unsigned j) {
  /// All inequalities of `b` need to be redundant. We already know that the
  /// redundant ones are, so only the cutting ones remain to be checked.
  Simplex &simp = simplices[i];
  IntegerRelation &disjunct = disjuncts[i];
  if (llvm::any_of(cuttingIneqsA, [this, &simp](ArrayRef<int64_t> curr) {
        return !isFacetContained(curr, simp);
      }))
    return failure();
  IntegerRelation newSet(disjunct.getSpace());

  for (ArrayRef<int64_t> curr : redundantIneqsA)
    newSet.addInequality(curr);

  for (ArrayRef<int64_t> curr : redundantIneqsB)
    newSet.addInequality(curr);

  addCoalescedDisjunct(i, j, newSet);
  return success();
}

LogicalResult SetCoalescer::typeInequality(ArrayRef<int64_t> ineq,
                                           Simplex &simp) {
  Simplex::IneqType type = simp.findIneqType(ineq);
  if (type == Simplex::IneqType::Redundant)
    redundantIneqsB.push_back(ineq);
  else if (type == Simplex::IneqType::Cut)
    cuttingIneqsB.push_back(ineq);
  else
    return failure();
  return success();
}

LogicalResult SetCoalescer::typeEquality(ArrayRef<int64_t> eq, Simplex &simp) {
  if (typeInequality(eq, simp).failed())
    return failure();
  negEqs.push_back(getNegatedCoeffs(eq));
  ArrayRef<int64_t> inv(negEqs.back());
  if (typeInequality(inv, simp).failed())
    return failure();
  return success();
}

void SetCoalescer::eraseDisjunct(unsigned i) {
  assert(simplices.size() == disjuncts.size() &&
         "simplices and disjuncts must be equally as long");
  disjuncts[i] = disjuncts.back();
  disjuncts.pop_back();
  simplices[i] = simplices.back();
  simplices.pop_back();
}

LogicalResult SetCoalescer::coalescePair(unsigned i, unsigned j) {

  IntegerRelation &a = disjuncts[i];
  IntegerRelation &b = disjuncts[j];
  /// Handling of local ids is not yet implemented, so these cases are
  /// skipped.
  /// TODO: implement local id support.
  if (a.getNumLocalIds() != 0 || b.getNumLocalIds() != 0)
    return failure();
  Simplex &simpA = simplices[i];
  Simplex &simpB = simplices[j];

  // Organize all inequalities and equalities of `a` according to their type
  // for `b` into `redundantIneqsA` and `cuttingIneqsA` (and vice versa for
  // all inequalities of `b` according to their type in `a`). If a separate
  // inequality is encountered during typing, the two IntegerRelations
  // cannot be coalesced.
  for (int k = 0, e = a.getNumInequalities(); k < e; ++k)
    if (typeInequality(a.getInequality(k), simpB).failed())
      return failure();

  for (int k = 0, e = a.getNumEqualities(); k < e; ++k)
    if (typeEquality(a.getEquality(k), simpB).failed())
      return failure();

  std::swap(redundantIneqsA, redundantIneqsB);
  std::swap(cuttingIneqsA, cuttingIneqsB);

  for (int k = 0, e = b.getNumInequalities(); k < e; ++k)
    if (typeInequality(b.getInequality(k), simpA).failed())
      return failure();

  for (int k = 0, e = b.getNumEqualities(); k < e; ++k)
    if (typeEquality(b.getEquality(k), simpA).failed())
      return failure();

  // If there are no cutting inequalities of `a`, `b` is contained
  // within `a`.
  if (cuttingIneqsA.empty()) {
    eraseDisjunct(j);
    return success();
  }

  // Try to apply the cut case
  if (coalescePairCutCase(i, j).succeeded())
    return success();

  // Swap the vectors to compare the pair (j,i) instead of (i,j).
  std::swap(redundantIneqsA, redundantIneqsB);
  std::swap(cuttingIneqsA, cuttingIneqsB);

  // If there are no cutting inequalities of `a`, `b` is contained
  // within `a`.
  if (cuttingIneqsA.empty()) {
    eraseDisjunct(i);
    return success();
  }

  // Try to apply the cut case
  if (coalescePairCutCase(j, i).succeeded())
    return success();

  return failure();
}

PresburgerRelation PresburgerRelation::coalesce() const {
  return SetCoalescer(*this).coalesce();
}

void PresburgerRelation::print(raw_ostream &os) const {
  os << "Number of Disjuncts: " << getNumDisjuncts() << "\n";
  for (const IntegerRelation &disjunct : disjuncts) {
    disjunct.print(os);
    os << '\n';
  }
}

void PresburgerRelation::dump() const { print(llvm::errs()); }

PresburgerSet PresburgerSet::getUniverse(const PresburgerSpace &space) {
  PresburgerSet result(space);
  result.unionInPlace(IntegerPolyhedron::getUniverse(space));
  return result;
}

PresburgerSet PresburgerSet::getEmpty(const PresburgerSpace &space) {
  return PresburgerSet(space);
}

PresburgerSet::PresburgerSet(const IntegerPolyhedron &disjunct)
    : PresburgerRelation(disjunct) {}

PresburgerSet::PresburgerSet(const PresburgerRelation &set)
    : PresburgerRelation(set) {}

PresburgerSet PresburgerSet::unionSet(const PresburgerRelation &set) const {
  return PresburgerSet(PresburgerRelation::unionSet(set));
}

PresburgerSet PresburgerSet::intersect(const PresburgerRelation &set) const {
  return PresburgerSet(PresburgerRelation::intersect(set));
}

PresburgerSet PresburgerSet::complement() const {
  return PresburgerSet(PresburgerRelation::complement());
}

PresburgerSet PresburgerSet::subtract(const PresburgerRelation &set) const {
  return PresburgerSet(PresburgerRelation::subtract(set));
}

PresburgerSet PresburgerSet::coalesce() const {
  return PresburgerSet(PresburgerRelation::coalesce());
}