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[MLIR][Presburger] Simplex::computeIntegerBounds: support unbounded directions by returning Optionals

This commit is contained in:
Arjun P 2022-02-08 20:53:43 +05:30
parent f0ef708dc1
commit 738c738b44
3 changed files with 14 additions and 13 deletions
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7
mlir/include/mlir/Analysis/Presburger/Simplex.h
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@ -537,8 +537,11 @@ public:
void detectRedundant();
/// Returns a (min, max) pair denoting the minimum and maximum integer values
/// of the given expression.
std::pair<int64_t, int64_t> computeIntegerBounds(ArrayRef<int64_t> coeffs);
/// of the given expression. If either of the values is unbounded, an empty
/// optional is returned in its place. If the result has min > max then no
/// integer value exists.
std::pair<Optional<int64_t>, Optional<int64_t>>
computeIntegerBounds(ArrayRef<int64_t> coeffs);
/// Returns true if the polytope is unbounded, i.e., extends to infinity in
/// some direction. Otherwise, returns false.

18
mlir/lib/Analysis/Presburger/Simplex.cpp
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@ -1456,7 +1456,7 @@ Optional<SmallVector<int64_t, 8>> Simplex::findIntegerSample() {
llvm::to_vector<8>(basis.getRow(level));
basisCoeffs.push_back(0);
int64_t minRoundedUp, maxRoundedDown;
Optional<int64_t> minRoundedUp, maxRoundedDown;
std::tie(minRoundedUp, maxRoundedDown) =
computeIntegerBounds(basisCoeffs);
@ -1475,8 +1475,10 @@ Optional<SmallVector<int64_t, 8>> Simplex::findIntegerSample() {
snapshotStack.push_back(getSnapshot());
// The smallest value in the range is the next value to try.
nextValueStack.push_back(minRoundedUp);
upperBoundStack.push_back(maxRoundedDown);
// The values in the optionals are guaranteed to exist since we know the
// polytope is bounded.
nextValueStack.push_back(*minRoundedUp);
upperBoundStack.push_back(*maxRoundedDown);
}
assert((snapshotStack.size() - 1 == level &&
@ -1513,21 +1515,17 @@ Optional<SmallVector<int64_t, 8>> Simplex::findIntegerSample() {
/// Compute the minimum and maximum integer values the expression can take. We
/// compute each separately.
std::pair<int64_t, int64_t>
std::pair<Optional<int64_t>, Optional<int64_t>>
Simplex::computeIntegerBounds(ArrayRef<int64_t> coeffs) {
int64_t minRoundedUp;
Optional<int64_t> minRoundedUp;
if (Optional<Fraction> maybeMin =
computeOptimum(Simplex::Direction::Down, coeffs))
minRoundedUp = ceil(*maybeMin);
else
llvm_unreachable("Tableau should not be unbounded");
int64_t maxRoundedDown;
Optional<int64_t> maxRoundedDown;
if (Optional<Fraction> maybeMax =
computeOptimum(Simplex::Direction::Up, coeffs))
maxRoundedDown = floor(*maybeMax);
else
llvm_unreachable("Tableau should not be unbounded");
return {minRoundedUp, maxRoundedDown};
}

2
mlir/unittests/Analysis/Presburger/SimplexTest.cpp
View File

@ -441,7 +441,7 @@ TEST(SimplexTest, appendVariable) {
EXPECT_EQ(simplex.getNumVariables(), 2u);
EXPECT_EQ(simplex.getNumConstraints(), 2u);
EXPECT_EQ(simplex.computeIntegerBounds({0, 1, 0}),
std::make_pair(yMin, yMax));
std::make_pair(Optional<int64_t>(yMin), Optional<int64_t>(yMax)));
simplex.rollback(snapshot1);
EXPECT_EQ(simplex.getNumVariables(), 1u);