diff --git a/mlir/lib/Analysis/AffineStructures.cpp b/mlir/lib/Analysis/AffineStructures.cpp
--- a/mlir/lib/Analysis/AffineStructures.cpp
+++ b/mlir/lib/Analysis/AffineStructures.cpp
@@ -527,15 +527,6 @@
   return success();
 }
 
-// Turn a dimension into a symbol.
-static void turnDimIntoSymbol(FlatAffineConstraints *cst, Value id) {
-  unsigned pos;
-  if (cst->findId(id, &pos) && pos < cst->getNumDimIds()) {
-    cst->swapId(pos, cst->getNumDimIds() - 1);
-    cst->setDimSymbolSeparation(cst->getNumSymbolIds() + 1);
-  }
-}
-
 // Turn a symbol into a dimension.
 static void turnSymbolIntoDim(FlatAffineConstraints *cst, Value id) {
   unsigned pos;
@@ -2014,13 +2005,6 @@
 FlatAffineConstraints::addLowerOrUpperBound(unsigned pos, AffineMap boundMap,
                                             ValueRange boundOperands, bool eq,
                                             bool lower) {
-  assert(pos < getNumDimAndSymbolIds() && "invalid position");
-  // Equality follows the logic of lower bound except that we add an equality
-  // instead of an inequality.
-  assert((!eq || boundMap.getNumResults() == 1) && "single result expected");
-  if (eq)
-    lower = true;
-
   // Fully compose map and operands; canonicalize and simplify so that we
   // transitively get to terminal symbols or loop IVs.
   auto map = boundMap;
@@ -2031,70 +2015,29 @@
   for (auto operand : operands)
     addInductionVarOrTerminalSymbol(operand);
 
-  FlatAffineConstraints localVarCst;
-  std::vector<SmallVector<int64_t, 8>> flatExprs;
-  if (failed(getFlattenedAffineExprs(map, &flatExprs, &localVarCst))) {
-    LLVM_DEBUG(llvm::dbgs() << "semi-affine expressions not yet supported\n");
-    return failure();
-  }
-
-  // Merge and align with localVarCst.
-  if (localVarCst.getNumLocalIds() > 0) {
-    // Set values for localVarCst.
-    localVarCst.setIdValues(0, localVarCst.getNumDimAndSymbolIds(), operands);
-    for (auto operand : operands) {
-      unsigned pos;
-      if (findId(operand, &pos)) {
-        if (pos >= getNumDimIds() && pos < getNumDimAndSymbolIds()) {
-          // If the local var cst has this as a dim, turn it into its symbol.
-          turnDimIntoSymbol(&localVarCst, operand);
-        } else if (pos < getNumDimIds()) {
-          // Or vice versa.
-          turnSymbolIntoDim(&localVarCst, operand);
-        }
-      }
-    }
-    mergeAndAlignIds(/*offset=*/0, this, &localVarCst);
-    append(localVarCst);
-  }
-
-  // Record positions of the operands in the constraint system. Need to do
-  // this here since the constraint system changes after a bound is added.
-  SmallVector<unsigned, 8> positions;
-  unsigned numOperands = operands.size();
-  for (auto operand : operands) {
-    unsigned pos;
-    if (!findId(operand, &pos))
-      assert(0 && "expected to be found");
-    positions.push_back(pos);
-  }
-
-  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.
-    for (unsigned j = 0, e = map.getNumInputs(); j < e; j++) {
-      ineq[positions[j]] = lower ? -flatExpr[j] : flatExpr[j];
-    }
-    // Copy over the local id coefficients.
-    unsigned numLocalIds = flatExpr.size() - 1 - numOperands;
-    for (unsigned jj = 0, j = getNumIds() - numLocalIds; jj < numLocalIds;
-         jj++, j++) {
-      ineq[j] =
-          lower ? -flatExpr[numOperands + jj] : flatExpr[numOperands + jj];
-    }
-    // Constant term.
-    ineq[getNumCols() - 1] =
-        lower ? -flatExpr[flatExpr.size() - 1]
-              // Upper bound in flattenedExpr is an exclusive one.
-              : flatExpr[flatExpr.size() - 1] - 1;
-    eq ? addEquality(ineq) : addInequality(ineq);
-  }
-  return success();
+  SmallVector<Value> dims, syms;
+#ifndef NDEBUG
+  SmallVector<Value> newSyms;
+  SmallVector<Value> *newSymsPtr = &newSyms;
+#else
+  SmallVector<Value> *newSymsPtr = nullptr;
+#endif // NDEBUG
+
+  dims.reserve(numDims);
+  syms.reserve(numSymbols);
+  for (unsigned i = 0; i < numDims; ++i)
+    dims.push_back(ids[i] ? *ids[i] : Value());
+  for (unsigned i = numDims, e = numDims + numSymbols; i < e; ++i)
+    syms.push_back(ids[i] ? *ids[i] : Value());
+
+  AffineMap alignedMap =
+      alignAffineMapWithValues(map, operands, dims, syms, newSymsPtr);
+  // All symbols are already part of this FlatAffineConstraints.
+  assert(syms.size() == newSymsPtr->size() && "unexpected new/missing symbols");
+  assert(std::equal(syms.begin(), syms.end(), newSymsPtr->begin()) &&
+         "unexpected new/missing symbols");
+
+  return addLowerOrUpperBound(pos, alignedMap, eq, lower);
 }
 
 // Adds slice lower bounds represented by lower bounds in 'lbMaps' and upper