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[MLIR] Fix negative gcd in normalizeDivisionByGCD function.

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When the coefficients of dividend are negative, the gcd may be negative
which will change the sign of dividend and overflow denominator.

Reviewed By: Groverkss

Differential Revision: https://reviews.llvm.org/D117911
This commit is contained in:
Prashant Kumar 2022-01-21 23:53:22 +05:30
parent 55d887b833
commit b6098c07cb
2 changed files with 29 additions and 2 deletions
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7
mlir/lib/Analysis/Presburger/Utils.cpp
View File

@ -25,7 +25,10 @@ static void normalizeDivisionByGCD(SmallVectorImpl<int64_t> &dividend,
unsigned &divisor) {
if (divisor == 0 || dividend.empty())
return;
int64_t gcd = llvm::greatestCommonDivisor(dividend.front(), int64_t(divisor));
// We take the absolute value of dividend's coefficients to make sure that
// `gcd` is positive.
int64_t gcd =
llvm::greatestCommonDivisor(std::abs(dividend.front()), int64_t(divisor));
// The reason for ignoring the constant term is as follows.
// For a division:
@ -35,7 +38,7 @@ static void normalizeDivisionByGCD(SmallVectorImpl<int64_t> &dividend,
// Since `{a/m}/d` in the dividend satisfies 0 <= {a/m}/d < 1/d, it will not
// influence the result of the floor division and thus, can be ignored.
for (size_t i = 1, m = dividend.size() - 1; i < m; i++) {
gcd = llvm::greatestCommonDivisor(dividend[i], gcd);
gcd = llvm::greatestCommonDivisor(std::abs(dividend[i]), gcd);
if (gcd == 1)
return;
}

24
mlir/unittests/Analysis/Presburger/IntegerPolyhedronTest.cpp
View File

@ -969,4 +969,28 @@ TEST(IntegerPolyhedronTest, mergeDivisionsConstants) {
}
}
TEST(IntegerPolyhedronTest, negativeDividends) {
// (x) : (exists y = [-x + 1 / 2], z = [-x - 2 / 3]: y + z >= x).
IntegerPolyhedron poly1(1);
poly1.addLocalFloorDiv({-1, 1}, 2); // y = [x + 1 / 2].
// Normalization test with negative dividends
poly1.addLocalFloorDiv({-3, 0, -6}, 9); // z = [3x + 6 / 9] -> [x + 2 / 3].
poly1.addInequality({-1, 1, 1, 0}); // y + z >= x.
// (x) : (exists y = [x + 1 / 3], z = [x + 2 / 3]: y + z <= x).
IntegerPolyhedron poly2(1);
// Normalization test.
poly2.addLocalFloorDiv({-2, 2}, 4); // y = [-2x + 2 / 4] -> [-x + 1 / 2].
poly2.addLocalFloorDiv({-1, 0, -2}, 3); // z = [-x - 2 / 3].
poly2.addInequality({1, -1, -1, 0}); // y + z <= x.
poly1.mergeLocalIds(poly2);
// Merging triggers normalization.
std::vector<SmallVector<int64_t, 8>> divisions = {{-1, 0, 0, 1},
{-1, 0, 0, -2}};
SmallVector<unsigned, 8> denoms = {2, 3};
checkDivisionRepresentation(poly1, divisions, denoms);
}
} // namespace mlir