[MLIR][Presburger] getDivRepr: fix bug where dividend was negated

[arjunp]

Summary

Also updated the tests, which were asserting the wrong behaviour.

[Groverkss]

LGTM.

mlir/lib/Analysis/Presburger/Utils.cpp

static LogicalResult getDivRepr(const IntegerRelation &cst, unsigned pos,
   int64_t signDiv = tempDiv < 0 ? -1 : 1;
 
   // The divisor is always a positive integer.
   divisor = tempDiv * signDiv;
 
   expr.resize(cst.getNumCols(), 0);
   for (unsigned i = 0, e = cst.getNumIds(); i < e; ++i)
     if (i != pos)
-      expr[i] = signDiv * cst.atEq(eqInd, i);
+      expr[i] = -signDiv * cst.atEq(eqInd, i);
 
-  expr.back() = signDiv * cst.atEq(eqInd, cst.getNumCols() - 1);
+  expr.back() = -signDiv * cst.atEq(eqInd, cst.getNumCols() - 1);
   normalizeDivisionByGCD(expr, divisor);
 
   return success();
 }
 
 // Returns `false` if the constraints depends on a variable for which an
 // explicit representation has not been found yet, otherwise returns `true`.
 static bool checkExplicitRepresentation(const IntegerRelation &cst,

mlir/unittests/Analysis/Presburger/IntegerPolyhedronTest.cpp

 }
 
 TEST(IntegerPolyhedronTest, computeLocalReprFromEquality) {
   {
     IntegerPolyhedron poly = parsePoly("(i, j, q) : (-4*q + i + j == 0)");
     // Convert `q` to a local variable.
     poly.convertToLocal(IdKind::SetDim, 2, 3);
 
-    std::vector<SmallVector<int64_t, 8>> divisions = {{-1, -1, 0, 0}};
+    std::vector<SmallVector<int64_t, 8>> divisions = {{1, 1, 0, 0}};
     SmallVector<unsigned, 8> denoms = {4};
 
     checkDivisionRepresentation(poly, divisions, denoms);
   }
   {
     IntegerPolyhedron poly = parsePoly("(i, j, q) : (4*q - i - j == 0)");
     // Convert `q` to a local variable.
     poly.convertToLocal(IdKind::SetDim, 2, 3);
 
-    std::vector<SmallVector<int64_t, 8>> divisions = {{-1, -1, 0, 0}};
+    std::vector<SmallVector<int64_t, 8>> divisions = {{1, 1, 0, 0}};
     SmallVector<unsigned, 8> denoms = {4};
 
     checkDivisionRepresentation(poly, divisions, denoms);
   }
   {
     IntegerPolyhedron poly = parsePoly("(i, j, q) : (3*q + i + j - 2 == 0)");
     // Convert `q` to a local variable.
     poly.convertToLocal(IdKind::SetDim, 2, 3);
 
-    std::vector<SmallVector<int64_t, 8>> divisions = {{1, 1, 0, -2}};
+    std::vector<SmallVector<int64_t, 8>> divisions = {{-1, -1, 0, 2}};
     SmallVector<unsigned, 8> denoms = {3};
 
     checkDivisionRepresentation(poly, divisions, denoms);
   }
 }
 
 TEST(IntegerPolyhedronTest, computeLocalReprFromEqualityAndInequality) {
   {
     IntegerPolyhedron poly =
         parsePoly("(i, j, q, k) : (-3*k + i + j == 0, 4*q - "
                   "i - j + 2 >= 0, -4*q + i + j >= 0)");
     // Convert `q` and `k` to local variables.
     poly.convertToLocal(IdKind::SetDim, 2, 4);
 
     std::vector<SmallVector<int64_t, 8>> divisions = {{1, 1, 0, 0, 1},
-                                                      {-1, -1, 0, 0, 0}};
+                                                      {1, 1, 0, 0, 0}};
     SmallVector<unsigned, 8> denoms = {4, 3};
 
     checkDivisionRepresentation(poly, divisions, denoms);
   }
 }
 
 TEST(IntegerPolyhedronTest, computeLocalReprNoRepr) {
   IntegerPolyhedron poly =