[MLIR] Simplex::getRationalSample: return an optional, empty if Simplex is empty

Author: Superty

mlir/include/mlir/Analysis/Presburger/Simplex.h

@@ -182,9 +182,9 @@ class SimplexBase {
   /// Add all the constraints from the given IntegerPolyhedron.
   void intersectIntegerPolyhedron(const IntegerPolyhedron &poly);
 
-  /// Returns a rational sample point. This should not be called when Simplex is
+  /// Returns a rational sample point. Returns an empty optional if Simplex is
   /// empty.
-  SmallVector<Fraction, 8> getRationalSample() const;
+  Optional<SmallVector<Fraction, 8>> getRationalSample() const;
 
   /// Returns the current sample point if it is integral. Otherwise, returns
   /// None.

mlir/lib/Analysis/Presburger/IntegerPolyhedron.cpp

@@ -759,8 +759,10 @@ Optional<SmallVector<int64_t, 8>> IntegerPolyhedron::findIntegerSample() const {
   // full-dimensional cone and is hence non-empty.
   Simplex shrunkenConeSimplex(cone);
   assert(!shrunkenConeSimplex.isEmpty() && "Shrunken cone cannot be empty!");
+
+  // The sample will always exist since the shrunken cone is non-empty.
   SmallVector<Fraction, 8> shrunkenConeSample =
-      shrunkenConeSimplex.getRationalSample();
+      *shrunkenConeSimplex.getRationalSample();
 
   SmallVector<int64_t, 8> coneSample(llvm::map_range(shrunkenConeSample, ceil));
 

mlir/lib/Analysis/Presburger/Simplex.cpp

@@ -745,8 +745,9 @@ Simplex Simplex::makeProduct(const Simplex &a, const Simplex &b) {
   return result;
 }
 
-SmallVector<Fraction, 8> SimplexBase::getRationalSample() const {
-  assert(!empty && "This should not be called when Simplex is empty.");
+Optional<SmallVector<Fraction, 8>> SimplexBase::getRationalSample() const {
+  if (empty)
+    return {};
 
   SmallVector<Fraction, 8> sample;
   sample.reserve(var.size());
@@ -770,7 +771,9 @@ SimplexBase::getSamplePointIfIntegral() const {
   // If the tableau is empty, no sample point exists.
   if (empty)
     return {};
-  SmallVector<Fraction, 8> rationalSample = getRationalSample();
+
+  // The value will always exist since the Simplex is non-empty.
+  SmallVector<Fraction, 8> rationalSample = *getRationalSample();
   SmallVector<int64_t, 8> integerSample;
   integerSample.reserve(var.size());
   for (const Fraction &coord : rationalSample) {