[MLIR] NFC. Improve API signature + clang-tidy warning in IntegerRelation

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

@@ -738,11 +738,11 @@ class IntegerRelation {
   /// Same as findSymbolicIntegerLexMin but produces lexmax instead of lexmin
   SymbolicLexOpt findSymbolicIntegerLexMax() const;
 
-  /// Searches for a constraint with a non-zero coefficient at `colIdx` in
-  /// equality (isEq=true) or inequality (isEq=false) constraints.
-  /// Returns true and sets row found in search in `rowIdx`, false otherwise.
-  bool findConstraintWithNonZeroAt(unsigned colIdx, bool isEq,
-                                   unsigned *rowIdx) const;
+  /// Finds a constraint with a non-zero coefficient at `colIdx` in equality
+  /// (isEq=true) or inequality (isEq=false) constraints. Returns the position
+  /// of the row if it was found or none otherwise.
+  std::optional<unsigned> findConstraintWithNonZeroAt(unsigned colIdx,
+                                                      bool isEq) const;
 
   /// Return the set difference of this set and the given set, i.e.,
   /// return `this \ set`.

mlir/lib/Analysis/FlatLinearValueConstraints.cpp

@@ -635,8 +635,8 @@ static void computeUnknownVars(const FlatLinearConstraints &cst,
       }
 
       // Detect a variable as an expression of other variables.
-      unsigned idx;
-      if (!cst.findConstraintWithNonZeroAt(pos, /*isEq=*/true, &idx)) {
+      std::optional<unsigned> idx;
+      if (!(idx = cst.findConstraintWithNonZeroAt(pos, /*isEq=*/true))) {
         continue;
       }
 
@@ -646,7 +646,7 @@ static void computeUnknownVars(const FlatLinearConstraints &cst,
       for (j = 0, e = cst.getNumVars(); j < e; ++j) {
         if (j == pos)
           continue;
-        int64_t c = cst.atEq64(idx, j);
+        int64_t c = cst.atEq64(*idx, j);
         if (c == 0)
           continue;
         // If any of the involved IDs hasn't been found yet, we can't proceed.
@@ -660,8 +660,8 @@ static void computeUnknownVars(const FlatLinearConstraints &cst,
         continue;
 
       // Add constant term to AffineExpr.
-      expr = expr + cst.atEq64(idx, cst.getNumVars());
-      int64_t vPos = cst.atEq64(idx, pos);
+      expr = expr + cst.atEq64(*idx, cst.getNumVars());
+      int64_t vPos = cst.atEq64(*idx, pos);
       assert(vPos != 0 && "expected non-zero here");
       if (vPos > 0)
         expr = (-expr).floorDiv(vPos);

mlir/lib/Analysis/Presburger/IntegerRelation.cpp

@@ -564,22 +564,18 @@ void IntegerRelation::clearAndCopyFrom(const IntegerRelation &other) {
   *this = other;
 }
 
-// Searches for a constraint with a non-zero coefficient at `colIdx` in
-// equality (isEq=true) or inequality (isEq=false) constraints.
-// Returns true and sets row found in search in `rowIdx`, false otherwise.
-bool IntegerRelation::findConstraintWithNonZeroAt(unsigned colIdx, bool isEq,
-                                                  unsigned *rowIdx) const {
+std::optional<unsigned>
+IntegerRelation::findConstraintWithNonZeroAt(unsigned colIdx, bool isEq) const {
   assert(colIdx < getNumCols() && "position out of bounds");
   auto at = [&](unsigned rowIdx) -> DynamicAPInt {
     return isEq ? atEq(rowIdx, colIdx) : atIneq(rowIdx, colIdx);
   };
   unsigned e = isEq ? getNumEqualities() : getNumInequalities();
-  for (*rowIdx = 0; *rowIdx < e; ++(*rowIdx)) {
-    if (at(*rowIdx) != 0) {
-      return true;
-    }
+  for (unsigned rowIdx = 0; rowIdx < e; ++rowIdx) {
+    if (at(rowIdx) != 0)
+      return rowIdx;
   }
-  return false;
+  return std::nullopt;
 }
 
 void IntegerRelation::normalizeConstraintsByGCD() {
@@ -1088,31 +1084,30 @@ unsigned IntegerRelation::gaussianEliminateVars(unsigned posStart,
   unsigned pivotCol = 0;
   for (pivotCol = posStart; pivotCol < posLimit; ++pivotCol) {
     // Find a row which has a non-zero coefficient in column 'j'.
-    unsigned pivotRow;
-    if (!findConstraintWithNonZeroAt(pivotCol, /*isEq=*/true, &pivotRow)) {
-      // No pivot row in equalities with non-zero at 'pivotCol'.
-      if (!findConstraintWithNonZeroAt(pivotCol, /*isEq=*/false, &pivotRow)) {
-        // If inequalities are also non-zero in 'pivotCol', it can be
-        // eliminated.
-        continue;
-      }
-      break;
+    std::optional<unsigned> pivotRow =
+        findConstraintWithNonZeroAt(pivotCol, /*isEq=*/true);
+    // No pivot row in equalities with non-zero at 'pivotCol'.
+    if (!pivotRow) {
+      // If inequalities are also non-zero in 'pivotCol', it can be eliminated.
+      if ((pivotRow = findConstraintWithNonZeroAt(pivotCol, /*isEq=*/false)))
+        break;
+      continue;
     }
 
     // Eliminate variable at 'pivotCol' from each equality row.
     for (unsigned i = 0, e = getNumEqualities(); i < e; ++i) {
-      eliminateFromConstraint(this, i, pivotRow, pivotCol, posStart,
+      eliminateFromConstraint(this, i, *pivotRow, pivotCol, posStart,
                               /*isEq=*/true);
       equalities.normalizeRow(i);
     }
 
     // Eliminate variable at 'pivotCol' from each inequality row.
     for (unsigned i = 0, e = getNumInequalities(); i < e; ++i) {
-      eliminateFromConstraint(this, i, pivotRow, pivotCol, posStart,
+      eliminateFromConstraint(this, i, *pivotRow, pivotCol, posStart,
                               /*isEq=*/false);
       inequalities.normalizeRow(i);
     }
-    removeEquality(pivotRow);
+    removeEquality(*pivotRow);
     gcdTightenInequalities();
   }
   // Update position limit based on number eliminated.
@@ -1125,31 +1120,31 @@ unsigned IntegerRelation::gaussianEliminateVars(unsigned posStart,
 bool IntegerRelation::gaussianEliminate() {
   gcdTightenInequalities();
   unsigned firstVar = 0, vars = getNumVars();
-  unsigned nowDone, eqs, pivotRow;
+  unsigned nowDone, eqs;
+  std::optional<unsigned> pivotRow;
   for (nowDone = 0, eqs = getNumEqualities(); nowDone < eqs; ++nowDone) {
     // Finds the first non-empty column.
     for (; firstVar < vars; ++firstVar) {
-      if (!findConstraintWithNonZeroAt(firstVar, true, &pivotRow))
-        continue;
-      break;
+      if ((pivotRow = findConstraintWithNonZeroAt(firstVar, /*isEq=*/true)))
+        break;
     }
     // The matrix has been normalized to row echelon form.
     if (firstVar >= vars)
       break;
 
     // The first pivot row found is below where it should currently be placed.
-    if (pivotRow > nowDone) {
-      equalities.swapRows(pivotRow, nowDone);
-      pivotRow = nowDone;
+    if (*pivotRow > nowDone) {
+      equalities.swapRows(*pivotRow, nowDone);
+      *pivotRow = nowDone;
     }
 
     // Normalize all lower equations and all inequalities.
     for (unsigned i = nowDone + 1; i < eqs; ++i) {
-      eliminateFromConstraint(this, i, pivotRow, firstVar, 0, true);
+      eliminateFromConstraint(this, i, *pivotRow, firstVar, 0, true);
       equalities.normalizeRow(i);
     }
     for (unsigned i = 0, ineqs = getNumInequalities(); i < ineqs; ++i) {
-      eliminateFromConstraint(this, i, pivotRow, firstVar, 0, false);
+      eliminateFromConstraint(this, i, *pivotRow, firstVar, 0, false);
       inequalities.normalizeRow(i);
     }
     gcdTightenInequalities();
@@ -2290,9 +2285,8 @@ IntegerRelation::unionBoundingBox(const IntegerRelation &otherCst) {
 }
 
 bool IntegerRelation::isColZero(unsigned pos) const {
-  unsigned rowPos;
-  return !findConstraintWithNonZeroAt(pos, /*isEq=*/false, &rowPos) &&
-         !findConstraintWithNonZeroAt(pos, /*isEq=*/true, &rowPos);
+  return !findConstraintWithNonZeroAt(pos, /*isEq=*/false) &&
+         !findConstraintWithNonZeroAt(pos, /*isEq=*/true);
 }
 
 /// Find positions of inequalities and equalities that do not have a coefficient
@@ -2600,16 +2594,16 @@ void IntegerRelation::print(raw_ostream &os) const {
     for (unsigned j = 0, f = getNumCols(); j < f; ++j)
       updatePrintMetrics<DynamicAPInt>(atIneq(i, j), ptm);
   // Print using PrintMetrics.
-  unsigned MIN_SPACING = 1;
+  constexpr unsigned kMinSpacing = 1;
   for (unsigned i = 0, e = getNumEqualities(); i < e; ++i) {
     for (unsigned j = 0, f = getNumCols(); j < f; ++j) {
-      printWithPrintMetrics<DynamicAPInt>(os, atEq(i, j), MIN_SPACING, ptm);
+      printWithPrintMetrics<DynamicAPInt>(os, atEq(i, j), kMinSpacing, ptm);
     }
     os << "  = 0\n";
   }
   for (unsigned i = 0, e = getNumInequalities(); i < e; ++i) {
     for (unsigned j = 0, f = getNumCols(); j < f; ++j) {
-      printWithPrintMetrics<DynamicAPInt>(os, atIneq(i, j), MIN_SPACING, ptm);
+      printWithPrintMetrics<DynamicAPInt>(os, atIneq(i, j), kMinSpacing, ptm);
     }
     os << " >= 0\n";
   }