[MLIR][Presburger] removeTrivialRedundancy: skip unnecessary check for duplicate constraints (#138969)

`removeTrivialRedundancy` first marks duplicate rows redundant, then
when multiple rows differ only by a constant term, it removes all but
one of them. Since the latter removes all but one duplicate row as well,
it is unnecessary (redundant!) to mark duplicate rows redundant. So we
remove this step.

Author: leontyumen

mlir/lib/Analysis/Presburger/IntegerRelation.cpp

@@ -21,7 +21,6 @@
 #include "mlir/Analysis/Presburger/Simplex.h"
 #include "mlir/Analysis/Presburger/Utils.h"
 #include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/Sequence.h"
 #include "llvm/ADT/SmallBitVector.h"
@@ -45,7 +44,6 @@ using namespace mlir;
 using namespace presburger;
 
 using llvm::SmallDenseMap;
-using llvm::SmallDenseSet;
 
 std::unique_ptr<IntegerRelation> IntegerRelation::clone() const {
   return std::make_unique<IntegerRelation>(*this);
@@ -1824,8 +1822,6 @@ void IntegerRelation::removeTrivialRedundancy() {
   // for a given row.
   SmallDenseMap<ArrayRef<DynamicAPInt>, std::pair<unsigned, DynamicAPInt>>
       rowsWithoutConstTerm;
-  // To unique rows.
-  SmallDenseSet<ArrayRef<DynamicAPInt>, 8> rowSet;
 
   // Check if constraint is of the form <non-negative-constant> >= 0.
   auto isTriviallyValid = [&](unsigned r) -> bool {
@@ -1840,8 +1836,7 @@ void IntegerRelation::removeTrivialRedundancy() {
   SmallVector<bool, 256> redunIneq(getNumInequalities(), false);
   for (unsigned r = 0, e = getNumInequalities(); r < e; r++) {
     DynamicAPInt *rowStart = &inequalities(r, 0);
-    auto row = ArrayRef<DynamicAPInt>(rowStart, getNumCols());
-    if (isTriviallyValid(r) || !rowSet.insert(row).second) {
+    if (isTriviallyValid(r)) {
       redunIneq[r] = true;
       continue;
     }