[mlir][affine] addLowerOrUpperBound: Disallow pos among boundOperands

Bounds such as `dim_{pos} <= c_1 * dim_x + ...` where `x == pos` are invalid. `addLowerOrUpperBound` previously added an incorrect inequality to the set. Such cases are now explicitly rejected.

Differential Revision: https://reviews.llvm.org/D107220

mlir/lib/Analysis/AffineStructures.cpp

@@ -2004,6 +2004,10 @@ FlatAffineConstraints::addLowerOrUpperBound(unsigned pos, AffineMap boundMap,
   }
 
   for (const auto &flatExpr : flatExprs) {
+    // Invalid bound: pos appears among the operands.
+    if (llvm::find(positions, pos) != positions.end())
+      continue;
+
     SmallVector<int64_t, 4> ineq(getNumCols(), 0);
     ineq[pos] = lower ? 1 : -1;
     // Dims and symbols.