[MLIR][Prebsurger] Add IntegerRelation::intersect supporting locals properly

[Groverkss]

LGTM.

mlir/include/mlir/Analysis/Presburger/IntegerRelation.h

public:
 
   // Clones this object.
   std::unique_ptr<IntegerRelation> clone() const;
 
   /// Appends constraints from `other` into `this`. This is equivalent to an
   /// intersection with no simplification of any sort attempted.
   void append(const IntegerRelation &other);
 
+  /// Return the intersection of the two sets.
+  /// If there are locals, they will be merged.
+  IntegerRelation intersect(IntegerRelation other) const;
+
   /// Return whether `this` and `other` are equal. This is integer-exact
   /// and somewhat expensive, since it uses the integer emptiness check
   /// (see IntegerRelation::findIntegerSample()).
   bool isEqual(const IntegerRelation &other) const;
 
   /// Return whether this is a subset of the given IntegerRelation. This is
   /// integer-exact and somewhat expensive, since it uses the integer emptiness
   /// check (see IntegerRelation::findIntegerSample()).

mlir/lib/Analysis/Presburger/IntegerRelation.cpp

void IntegerRelation::append(const IntegerRelation &other) {
   for (unsigned r = 0, e = other.getNumInequalities(); r < e; r++) {
     addInequality(other.getInequality(r));
   }
   for (unsigned r = 0, e = other.getNumEqualities(); r < e; r++) {
     addEquality(other.getEquality(r));
   }
 }
 
+IntegerRelation IntegerRelation::intersect(IntegerRelation other) const {
+  IntegerRelation result = *this;
+  result.mergeLocalIds(other);
+  result.append(other);
+  return result;
+}
+
 bool IntegerRelation::isEqual(const IntegerRelation &other) const {
   assert(PresburgerLocalSpace::isEqual(other) && "Spaces must be equal.");
   return PresburgerRelation(*this).isEqual(PresburgerRelation(other));
 }
 
 bool IntegerRelation::isSubsetOf(const IntegerRelation &other) const {
   assert(PresburgerLocalSpace::isEqual(other) && "Spaces must be equal.");
   return PresburgerRelation(*this).isSubsetOf(PresburgerRelation(other));

mlir/lib/Analysis/Presburger/PresburgerRelation.cpp

 PresburgerRelation
 PresburgerRelation::intersect(const PresburgerRelation &set) const {
   assert(PresburgerSpace::isEqual(set) && "Spaces should match");
 
   PresburgerRelation result(getNumDomainIds(), getNumRangeIds(),
                             getNumSymbolIds());
   for (const IntegerRelation &csA : integerRelations) {
     for (const IntegerRelation &csB : set.integerRelations) {
-      IntegerRelation csACopy = csA, csBCopy = csB;
-      csACopy.mergeLocalIds(csBCopy);
-      csACopy.append(csBCopy);
-      if (!csACopy.isEmpty())
-        result.unionInPlace(csACopy);
+      IntegerRelation intersection = csA.intersect(csB);
+      if (!intersection.isEmpty())
+        result.unionInPlace(intersection);
     }
   }
   return result;
 }
 
 /// Return `coeffs` with all the elements negated.
 static SmallVector<int64_t, 8> getNegatedCoeffs(ArrayRef<int64_t> coeffs) {
   SmallVector<int64_t, 8> negatedCoeffs;