[MLIR][Presburger] normalizeDivisionByGCD: fix bug when constant term is negative

[Groverkss]

LGTM. Please fix the clang-format error before landing.

[arjunp]

clang-format

mlir/lib/Analysis/Presburger/Utils.cpp

static void normalizeDivisionByGCD(SmallVectorImpl<int64_t> &dividend,
   for (size_t i = 1, m = dividend.size() - 1; i < m; i++) {
     gcd = llvm::greatestCommonDivisor(std::abs(dividend[i]), gcd);
     if (gcd == 1)
       return;
   }
 
   // Normalize the dividend and the denominator.
   std::transform(dividend.begin(), dividend.end(), dividend.begin(),
-                 [gcd](int64_t &n) { return floor((double)(n / gcd)); });
+                 [gcd](int64_t &n) { return floorDiv(n, gcd); });
   divisor /= gcd;
 }
 
 /// Check if the pos^th identifier can be represented as a division using upper
 /// bound inequality at position `ubIneq` and lower bound inequality at position
 /// `lbIneq`.
 ///
 /// Let `id` be the pos^th identifier, then `id` is equivalent to

mlir/unittests/Analysis/Presburger/IntegerPolyhedronTest.cpp

TEST(IntegerPolyhedronTest, computeLocalReprNoRepr) {
 
   std::vector<SmallVector<int64_t, 8>> divisions = {{0, 0, 0}};
   SmallVector<unsigned, 8> denoms = {0};
 
   // Check that no division is computed.
   checkDivisionRepresentation(poly, divisions, denoms);
 }
 
+TEST(IntegerPolyhedronTest, computeLocalReprNegConstNormalize) {
+  MLIRContext context;
+  IntegerPolyhedron poly =
+      parsePoly("(x, q) : (-1 - 3*x - 6 * q >= 0, 6 + 3*x + 6*q >= 0)", &context);
+  // Convert q to a local variable.
+  poly.convertDimToLocal(1, 2);
+
+  // q = floor((-1/3 - x)/2)
+  //   = floor((1/3) + (-1 - x)/2)
+  //   = floor((-1 - x)/2).
+  std::vector<SmallVector<int64_t, 8>> divisions = {{-1, 0, -1}};
+  SmallVector<unsigned, 8> denoms = {2};
+  checkDivisionRepresentation(poly, divisions, denoms);
+}
+
 TEST(IntegerPolyhedronTest, simplifyLocalsTest) {
   // (x) : (exists y: 2x + y = 1 and y = 2).
   IntegerPolyhedron poly(1, 0, 1);
   poly.addEquality({2, 1, -1});
   poly.addEquality({0, 1, -2});
 
   EXPECT_TRUE(poly.isEmpty());