[mlir][sparse] support affine expression on dense dimensions (except constant affine)

[Peiming]

add test cases.

[Peiming]

rebase

[Peiming]

mlir/lib/Dialect/SparseTensor/Transforms/Sparsification.cpp

246–254

It is actually prepared for filter loop idx (which is not yet introduced in this patch). But I keep it here to avoid merge conflict.

[Peiming]

rebase.

[Peiming]

rename variables.

[Peiming]

clang format.

[aartbik]

mlir/include/mlir/Dialect/SparseTensor/Utils/Merger.h

155

add comment on filter loops

mlir/lib/Dialect/SparseTensor/Transforms/Sparsification.cpp

99

move data to end (just the way google3 style works

make it private

1215

here and below, this is very subjective but I like

// Handle xxx
if (...)

return ....

or

if (...)

return ... // handle x

a bit better than

if (...)

// Handle x.
return

if there are no braces. But since there is no style for this, your choice in the end

[Peiming]

address comments.

[Peiming]

mlir/include/mlir/Dialect/SparseTensor/Utils/Merger.h

155

Filter loops are not yet introduced. Will add the comment in that patch to be more consistent.

[Peiming]

rebase.

[aartbik]

mlir/include/mlir/Dialect/SparseTensor/Utils/Merger.h

155

Yeah, not sure why i said that ;-)
Must have been staring at something else in the stack

mlir/lib/Dialect/SparseTensor/Transforms/Sparsification.cpp

98

please add a bit of doc to the class, especially since the method names are a bit obscure, e.g. setPickedIterType does not have direct meaning on who picks what ;-)

258

please doc what expansion means here

324

this is a huge block of code inside the iteration graph computation, can we move this into own function with intuitive name so that the original idea of

AffineExpr f = map.getResult(toOrigDim(enc, d - 1));
   AffineExpr t = map.getResult(toOrigDim(enc, d));
   addAffineOrderings(adjM, inDegree, f, t, 0);

is preserved? Otherwise it is very hard to separate intended logic from heuristic addition

587–590

this Note that comment is obsolete too now, right, or at least need some adjustmnet

[Peiming]

mlir/lib/Dialect/SparseTensor/Transforms/Sparsification.cpp

324

The reason why I started from 0 is actually due to filter loops... because the filter loop constraints are not imposed between (d - 1, d) but on (d) alone.

Maybe I should do the refactoring on the patch where filter loop is introduced?

[aartbik]

mlir/lib/Dialect/SparseTensor/Transforms/Sparsification.cpp

324

Ok, put a TODO here and then I accept the future promise ;-_

[Peiming]

address comments.

[aartbik]

Messages crossed, but except for the typo, LGTM stands

mlir/lib/Dialect/SparseTensor/Transforms/Sparsification.cpp

289

typo Constraints

[Peiming]

fix typo.

[Peiming]

mlir/lib/Dialect/SparseTensor/Transforms/Sparsification.cpp

587–590

nice catch!

mlir/include/mlir/Dialect/SparseTensor/Utils/Merger.h

 /// tensor expressions. This allows for fine-tuning performance characteristics
 /// independently from the basic algorithm if bottlenecks are identified.
 class Merger {
 public:
   /// Constructs a merger for the given number of tensors and loops. The
   /// user supplies the number of tensors involved in the kernel, with the
   /// last tensor in this set denoting the output tensor. The merger adds an
   /// additional synthetic tensor at the end of this set to represent all
   /// invariant expressions in the kernel.
   Merger(unsigned t, unsigned l)
       : outTensor(t - 1), syntheticTensor(t), numTensors(t + 1), numLoops(l),
         hasSparseOut(false),
-        dimTypes(t + 1, std::vector<DimLevelType>(l, DimLevelType::Undef)),
-        loopIdxToDim(t + 1, std::vector<Optional<unsigned>>(l, llvm::None)) {}
+        dimTypes(numTensors,
+                 std::vector<DimLevelType>(numLoops, DimLevelType::Undef)),
+        loopIdxToDim(numTensors,
+                     std::vector<Optional<unsigned>>(numLoops, llvm::None)),
+        dimToLoopIdx(numTensors,
+                     std::vector<Optional<unsigned>>(numLoops, llvm::None)) {}
 
   /// Adds a tensor expression. Returns its index.
   unsigned addExp(Kind k, unsigned e0, unsigned e1 = -1u, Value v = Value(),
                   Operation *op = nullptr);
   unsigned addExp(Kind k, unsigned e, Value v, Operation *op = nullptr) {
     return addExp(k, e, -1u, v, op);
   }
   unsigned addExp(Kind k, Value v, Operation *op = nullptr) {
DimLevelType getDimLevelType(unsigned t, unsigned i) const {
     return dimTypes[t][i];
   }
 
   /// Gets the dimension level type of `b`.
   DimLevelType getDimLevelType(unsigned b) const {
     return getDimLevelType(tensor(b), index(b));
   }
 
+  Optional<unsigned> getLoopIdx(unsigned t, unsigned dim) const {
+    assert(t < numTensors && dim < numLoops);
+    return dimToLoopIdx[t][dim];
+  }
+
   /// Gets the dimension number of the the `t`th tensor on `i`th loop.
   Optional<unsigned> getDimNum(unsigned t, unsigned i) const {
     assert(t < numTensors && i < numLoops);
     return loopIdxToDim[t][i];
   }
 
   /// Gets the dimension number of `b`.
   Optional<unsigned> getDimNum(unsigned b) const {
     return getDimNum(tensor(b), index(b));
   }
 
   /// Sets the dimension and dimension level type of the `t`th tensor on `i`th
   /// loop.
   void setDimAndDimLevelType(unsigned t, unsigned i, unsigned dim,
                              DimLevelType dlt) {
     assert(isValidDLT(dlt));
     dimTypes[t][i] = dlt;
     loopIdxToDim[t][i] = dim;
+    assert(dim < numLoops);
+    dimToLoopIdx[t][dim] = i;
   }
 
   // Iterates the bits of a lattice, for each set bit, converts it into the
   // corresponding tensor dimension and invokes the callback.
   void foreachTidDimPairInBits(
       const BitVector &bits,
       function_ref<void(unsigned b, unsigned tid, Optional<unsigned> dim,
                         DimLevelType dlt)>
private:
   const unsigned numTensors;
   const unsigned numLoops;
   bool hasSparseOut;
   // Map that converts pair<tensor id, loop id> to the corresponding dimension
   // level type.
   std::vector<std::vector<DimLevelType>> dimTypes;
   // Map that converts pair<tensor id, loop id> to the corresponding dimension.
   std::vector<std::vector<Optional<unsigned>>> loopIdxToDim;
+  // Map that converts pair<tensor id, dim> to the corresponding loop id.
+  std::vector<std::vector<Optional<unsigned>>> dimToLoopIdx;
   llvm::SmallVector<TensorExp> tensorExps;
   llvm::SmallVector<LatPoint> latPoints;
   llvm::SmallVector<SmallVector<unsigned>> latSets;
 };
 
 } // namespace sparse_tensor
 } // namespace mlir
 
 #endif // MLIR_DIALECT_SPARSETENSOR_UTILS_MERGER_H_

mlir/lib/Dialect/SparseTensor/Transforms/CodegenUtils.h

 // loopEmiter.enterLoopOverTensorAtDim(T1, 1);
 // loopEmiter.exitCurrentLoop();
 // loopEmiter.enterLoopOverTensorAtDim(T2, 1);
 // loopEmiter.exitCurrentLoop(); // exit k
 // loopEmiter.exitCurrentLoop(); // exit j
 // loopEmiter.exitCurrentLoop(); // exit i
 //===----------------------------------------------------------------------===//
 
-// TODO: Sparsification should also rely on this class to generate loops.
 class SparseTensorLoopEmitter {
 public:
   /// Optional callback function to setup dense output tensors when
   /// initializing the loop emitter (e.g., to fill a dense output with zeros).
   using OutputUpdater = function_ref<Value(OpBuilder &builder, Location loc,
                                            Value memref, Value tensor)>;
 
   /// Constructor: take an array of tensors inputs, on which the generated loops
public:
   /// return the reduction variable used inside the generated loop.
   Operation *enterLoopOverTensorAtDim(OpBuilder &builder, Location loc,
                                       size_t tid, size_t dim,
                                       MutableArrayRef<Value> reduc = {},
                                       bool isParallel = false,
                                       ArrayRef<size_t> extraTids = {},
                                       ArrayRef<size_t> extraDims = {});
 
+
+  void genDenseAffineAddressAtCurLevel(OpBuilder &builder, Location loc,
+                                       size_t tid, size_t dim,
+                                       AffineExpr affine);
+
   /// Emits a co-iteration loop over a set of tensors.
   Operation *enterCoIterationOverTensorsAtDims(
       OpBuilder &builder, Location loc, ArrayRef<size_t> tids,
       ArrayRef<size_t> dims, bool needsUniv, MutableArrayRef<Value> reduc = {},
       ArrayRef<size_t> extraTids = {}, ArrayRef<size_t> extraDims = {});
 
   void exitCurrentLoop(RewriterBase &rewriter, Location loc,
                        MutableArrayRef<Value> reduc = {});

mlir/lib/Dialect/SparseTensor/Transforms/CodegenUtils.cpp

Operation *SparseTensorLoopEmitter::enterLoopOverTensorAtDim(
   loopStack.emplace_back(ArrayRef<size_t>(tid), ArrayRef<size_t>(dim), loop,
                          coord[tid][dim]);
   // Emit extra locals.
   emitExtraLocalsForTensorsAtDenseDims(builder, loc, extraTids, extraDims);
 
   return loop;
 }
 
+
+void SparseTensorLoopEmitter::genDenseAffineAddressAtCurLevel(
+    OpBuilder &builder, Location loc, size_t tid, size_t dim,
+    AffineExpr affine) {
+  Value affineV = genAffine(builder, affine, loc);
+  pidxs[tid][dim] = genAddress(builder, loc, tid, dim, affineV);
+}
+
 Operation *SparseTensorLoopEmitter::enterCoIterationOverTensorsAtDims(
     OpBuilder &builder, Location loc, ArrayRef<size_t> tids,
     ArrayRef<size_t> dims, bool needsUniv, MutableArrayRef<Value> reduc,
     ArrayRef<size_t> extraTids, ArrayRef<size_t> extraDims) {
   assert(tids.size() == dims.size());
   SmallVector<Type> types;
   SmallVector<Value> operands;
   // Construct the while-loop with a parameter for each index.

mlir/lib/Dialect/SparseTensor/Transforms/Sparsification.cpp

 #include "mlir/Dialect/Linalg/Utils/Utils.h"
 #include "mlir/Dialect/MemRef/IR/MemRef.h"
 #include "mlir/Dialect/SCF/IR/SCF.h"
 #include "mlir/Dialect/SCF/Transforms/Transforms.h"
 #include "mlir/Dialect/SparseTensor/IR/SparseTensor.h"
 #include "mlir/Dialect/SparseTensor/Transforms/Passes.h"
 #include "mlir/Dialect/SparseTensor/Utils/Merger.h"
 #include "mlir/Dialect/Tensor/IR/Tensor.h"
+#include "mlir/IR/AffineExprVisitor.h"
 #include "mlir/IR/Matchers.h"
 #include "mlir/IR/TensorEncoding.h"
 #include "llvm/ADT/SmallBitVector.h"
 
 using namespace mlir;
 using namespace mlir::sparse_tensor;
 
 //===----------------------------------------------------------------------===//
Value getLoopIdxValue(size_t loopIdx) const {
     for (unsigned lv = 0; lv < topSort.size(); lv++)
       if (topSort[lv] == loopIdx)
         return loopEmitter.getLoopIV(lv);
 
     llvm_unreachable("invalid loop index");
   }
 };
 
+class ParallelAffineDimFinder
+    : public AffineExprVisitor<ParallelAffineDimFinder> {
+  AffineExpr paraDim;
+  utils::IteratorType pickIterType;
+  SmallVector<utils::IteratorType> iterTypes;
+
+public:
+  explicit ParallelAffineDimFinder(linalg::GenericOp op)
+      : iterTypes(op.getIteratorTypesArray()) {}
+  void visitDimExpr(AffineDimExpr expr) {
+    if (paraDim == nullptr || pickIterType == iterTypes[expr.getPosition()]) {
+      paraDim = expr;
+    }
+  }
+
+  void setPickedIterType(utils::IteratorType iterType) {
+    pickIterType = iterType;
+  }
+
+  AffineDimExpr getDimExpr() const { return paraDim.cast<AffineDimExpr>(); }
+};
 } // namespace
 
 //===----------------------------------------------------------------------===//
 // Sparse compiler analysis methods.
 //===----------------------------------------------------------------------===//
 
 /// Helper method to construct a permuted dimension ordering
 /// that adheres to the given topological sort.
for (unsigned dst = 0; dst < n; dst++)
       }
   }
   return topSort.size() == n;
 }
 
 /// Helper method to add all constraints from the indices in one affine
 /// expression before all indices in the other affine expression. For
 /// example i0+i1 < i2+i3+1 yields i0<i2, i0<i3, i1<i2, and i1<i3.
+/// The affine expression `a` is empty iff `fidx` have a value, leading to
+/// b = (i0 + i1) < fidx => i0 < fidx, i1 < fidx.
+/// The affine expression `b` is empty iff `tidx` have a value, leading to
+/// tidx < a = (i0 + i1) => tidx < i0, tidx < i1.
 static void addAffineOrderings(std::vector<std::vector<bool>> &adjM,
                                std::vector<unsigned> &inDegree, AffineExpr a,
-                               AffineExpr b, unsigned fidx) {
-  switch (a.getKind()) {
-  case AffineExprKind::DimId: {
-    unsigned idx = a.cast<AffineDimExpr>().getPosition();
-    if (b)
-      addAffineOrderings(adjM, inDegree, b, AffineExpr(), idx);
-    else if (!adjM[fidx][idx]) {
-      adjM[fidx][idx] = true;
-      inDegree[idx]++;
-    }
+                               AffineExpr b, Optional<unsigned> fidx,
+                               Optional<unsigned> tidx) {
+  if (!a && !b) {
+    // Recursion leaf.
+    assert(fidx && tidx);
+    unsigned f = *fidx, t = *tidx;
+    if (!adjM[f][t]) {
+      adjM[f][t] = true;
+      inDegree[t]++;
+    }
+    return;
+  auto toExpand = a ? a : b;
+  switch (toExpand.getKind()) {
+  case AffineExprKind::DimId: {
+    auto idx = toExpand.cast<AffineDimExpr>().getPosition();
+    if (toExpand == a)
+      addAffineOrderings(adjM, inDegree, AffineExpr(), b, idx, tidx);
+    else // toExpand == b
+      addAffineOrderings(adjM, inDegree, a, AffineExpr(), fidx, idx);
     break;
   }
   case AffineExprKind::Add:
   case AffineExprKind::Mul: {
-    auto binOp = a.cast<AffineBinaryOpExpr>();
-    addAffineOrderings(adjM, inDegree, binOp.getLHS(), b, fidx);
-    addAffineOrderings(adjM, inDegree, binOp.getRHS(), b, fidx);
+    auto binOp = toExpand.cast<AffineBinaryOpExpr>();
+    if (toExpand == a) {
+      addAffineOrderings(adjM, inDegree, binOp.getLHS(), b, fidx, tidx);
+      addAffineOrderings(adjM, inDegree, binOp.getRHS(), b, fidx, tidx);
+    } else {
+      addAffineOrderings(adjM, inDegree, a, binOp.getLHS(), fidx, tidx);
+      addAffineOrderings(adjM, inDegree, a, binOp.getRHS(), fidx, tidx);
+    }
     break;
   }
   default:
     break;
   }
 }
 
 /// Computes a topologically sorted iteration graph for the linalg operation.
 /// Ensures all tensors are visited in natural index order. This is essential
 /// for sparse storage formats since these only support access along fixed
 /// dimensions. Even for dense storage formats, however, the natural index
 /// order yields innermost unit-stride access with better spatial locality.
 static bool computeIterationGraph(Merger &merger, linalg::GenericOp op,
                                   std::vector<unsigned> &topSort, unsigned mask,
                                   OpOperand *skip = nullptr) {
   // Set up an n x n from/to adjacency matrix of the iteration graph
   // for the implicit loop indices i_0 .. i_n-1.
   unsigned n = op.getNumLoops();
   std::vector<std::vector<bool>> adjM(n, std::vector<bool>(n, false));
   std::vector<unsigned> inDegree(n, 0); // in-degree of each node.
for (OpOperand &t : op->getOpOperands()) {
     assert(map.getNumDims() == n);
     // Skip dense tensor constraints when not requested.
     if (!(mask & SortMask::kIncludeDense) && !enc)
       continue;
     // Each tensor expression and optional dimension ordering (row-major
     // by default) puts an ordering constraint on the loop indices. For
     // example, the tensor expresion A_ijk forces the ordering i < j < k
     // on the loop indices if no explicit dimension ordering is given.
-    for (unsigned d = 1, rank = map.getNumResults(); d < rank; d++) {
-      AffineExpr f = map.getResult(toOrigDim(enc, d - 1));
-      AffineExpr t = map.getResult(toOrigDim(enc, d));
-      addAffineOrderings(adjM, inDegree, f, t, 0);
+    for (unsigned d = 0, rank = map.getNumResults(); d < rank; d++) {
+      AffineExpr ta = map.getResult(toOrigDim(enc, d));
+      Optional<unsigned> tldx = merger.getLoopIdx(t.getOperandNumber(), d);
+
+      if (d > 0) {
+        AffineExpr fa = map.getResult(toOrigDim(enc, d - 1));
+        Optional<unsigned> fldx =
+            merger.getLoopIdx(t.getOperandNumber(), d - 1);
+
+        if (!(mask & SortMask::kIncludeDense) && !tldx) {
+          ParallelAffineDimFinder finder(op);
+          // e.g, for [dense, dense] -> (d0 + d1, d2 + d3)
+          // It is totally fine to have loop sequence d0->d2->d1->d3 instead of
+          // requiring d0 < d2, d1 < d2, d0 < d3, d1 < d3.
+          // We use a heuristic here to only pick one dim expression from each
+          // compound affine expression to establish the order between two dense
+          // dimensions.
+          // NOTE: The ordering can only be loosen when the destination level is
+          // dense, for [dense, sparse] -> (d0 + d1, d2), we still require both
+          // d0 < d2 and d1 < d2 to ensure correct ordering (i.e., no ordering
+          // like d0->d2->d1).
+          // TODO: this is obviously a sub optimal solution.
+          if (!fldx && fa.isa<AffineConstantExpr>()) {
+            assert(isDenseDLT(getDimLevelType(enc, d - 1)) &&
+                   !fa.isa<AffineDimExpr>());
+            // Heuristic: we prefer parallel loop for lhs to reduce the chance
+            // we add reduce < parallel ordering.
+            finder.setPickedIterType(utils::IteratorType::parallel);
+            finder.walkPostOrder(fa);
+            fa = finder.getDimExpr();
+            fldx = finder.getDimExpr().getPosition();
+          }
+          if (!ta.isa<AffineConstantExpr>()) {
+            // Dense compound affine
+            assert(isDenseDLT(getDimLevelType(enc, d)) &&
+                   !ta.isa<AffineDimExpr>());
+            // Heuristic: we prefer reduction loop for rhs to reduce the chance
+            // addint reduce < parallel ordering.
+            finder.setPickedIterType(utils::IteratorType::reduction);
+            finder.walkPostOrder(ta);
+            ta = finder.getDimExpr();
+            tldx = finder.getDimExpr().getPosition();
+          }
+        }
+
+        addAffineOrderings(adjM, inDegree, fa, ta, fldx, tldx);
+      }
     }
     // Push unrelated loops into sparse iteration space, so these
     // will be skipped more often.
     if (mask & SortMask::kIncludeUndef) {
       unsigned tensor = t.getOperandNumber();
       for (unsigned i = 0; i < n; i++)
         if (isCompressedDLT(merger.getDimLevelType(tensor, i)) ||
             isSingletonDLT(merger.getDimLevelType(tensor, i))) {

 static Value genSubscript(CodeGen &codegen, OpBuilder &builder,
                           linalg::GenericOp op, OpOperand *t,
                           SmallVectorImpl<Value> &args) {
   unsigned tensor = t->getOperandNumber();
   auto map = op.getMatchingIndexingMap(t);
   auto enc = getSparseTensorEncoding(t->get().getType());
   unsigned rank = map.getNumResults();
   if (enc) {
     // Note that currently, all sparse subscripts are simple.
     // TODO: accept affine too?
     assert(map.getResult(toOrigDim(enc, rank - 1)).getKind() ==
            AffineExprKind::DimId);
     Value pidx = codegen.loopEmitter.getPidxs()[tensor].back();
     assert(pidx);
     args.push_back(pidx); // position index
   } else {
     for (unsigned d = 0; d < rank; d++) {
       AffineExpr a = map.getResult(d);
       args.push_back(codegen.loopEmitter.genAffine(builder, a, op.getLoc()));
     }
if (t == codegen.sparseOut) {
     if (!rhs) {
       // Only unary and binary are allowed to return uninitialized rhs
       // to indicate missing output.
       assert(merger.exp(exp).kind == kUnary || merger.exp(exp).kind == kBinary);
     } else if (merger.exp(exp).kind == kSelect) {
       // Select operation insertion.
       Value insChain = codegen.insChain;
       assert(insChain);
-      scf::IfOp ifOp = builder.create<scf::IfOp>(
-          loc, insChain.getType(), rhs, /*else=*/true);
+      scf::IfOp ifOp = builder.create<scf::IfOp>(loc, insChain.getType(), rhs,
+                                                 /*else=*/true);
       builder.setInsertionPointToStart(&ifOp.getThenRegion().front());
       // Existing value was preserved to be used here.
       assert(merger.exp(exp).val);
       Value v0 = merger.exp(exp).val;
       genInsertionStore(codegen, builder, op, t, v0);
       merger.exp(exp).val = Value();
       // Yield modified insertion chain along true branch.
       builder.create<scf::YieldOp>(op.getLoc(), codegen.insChain);
for (unsigned i = 1; i < lsize; i++) {
       unsigned li = merger.set(lts)[i];
       if (!merger.hasAnySparse(merger.lat(li).simple))
         return true;
     }
   }
   return false;
 }
 
-static void translateBitsToTidDimPairs(Merger &merger, CodeGen &codegen,
-                                       unsigned li, unsigned idx,
-                                       SmallVectorImpl<size_t> &condTids,
-                                       SmallVectorImpl<size_t> &condDims,
-                                       SmallVectorImpl<size_t> &extraTids,
-                                       SmallVectorImpl<size_t> &extraDims) {
+static void translateBitsToTidDimPairs(
+    Merger &merger, CodeGen &codegen, linalg::GenericOp op, unsigned li,
+    unsigned idx, SmallVectorImpl<size_t> &condTids,
+    SmallVectorImpl<size_t> &condDims, SmallVectorImpl<size_t> &extraTids,
+    SmallVectorImpl<size_t> &extraDims, SmallVectorImpl<size_t> &affineTids,
+    SmallVectorImpl<size_t> &affineDims, SmallVectorImpl<AffineExpr> &exps) {
+
   const BitVector &all = merger.lat(li).bits;
   const BitVector &simple = merger.lat(li).simple;
 
   // Converts bits to array + dim pair
   merger.foreachTidDimPairInBits(all, [&, idx](unsigned b, unsigned tid,
                                                Optional<unsigned> dim,
                                                DimLevelType dlt) {
     if (simple.test(b)) {
if (simple.test(b)) {
           return;
       }
       condTids.push_back(tid);
       condDims.push_back(dim.value());
     } else if (isDenseDLT(dlt)) {
       // TODO: get rid of extraTids and extraDims.
       extraTids.push_back(tid);
       extraDims.push_back(dim.value());
+    } else {
+      assert(isUndefDLT(dlt));
+      if (tid >= op.getNumDpsInputs())
+        // We only handle affine expression on input tensors (for now).
+        return;
+      OpOperand *operand = &op->getOpOperand(tid);
+      auto enc = getSparseTensorEncoding(operand->get().getType());
+      if (!enc)
+        // Non-annotated dense tensors requires no special handling.
+        return;
+
+      ArrayRef<AffineExpr> affines =
+          op.getMatchingIndexingMap(operand).getResults();
+      assert(affines.size() == enc.getDimLevelType().size());
+      for (unsigned i = 0, e = affines.size(); i < e; i++) {
+        AffineExpr exp = affines[toOrigDim(enc, i)];
+        if (exp.isa<AffineDimExpr>() || !isDenseDLT(getDimLevelType(enc, i)))
+          // Skip simple affine expression and non dense dimensions (which has
+          // it own filter loop).
+          continue;
+
+        // Constant affine expressions on dense level required to be generated
+        // when
+        // 1. The previous level is an (at-level) invariant compound dense
+        // affine (with no corresponding loop idx); or
+        // 2. The previous level is being generated right now.
+        if (exp.isa<AffineConstantExpr>()) {
+          // TODO:  Should we come up with a more adhersive way to handle
+          // constant expression? We now requires two (somehow ad-hoc) code for
+          // it.
+          assert(false && "do not support constant affine");
+        }
+
+        bool atLevel = false;
+        if (isInvariantAffine(codegen, exp, idx, atLevel) && atLevel) {
+          // If the compound affine is invariant and we are right at the
+          // level. We need to generate the address according to the affine
+          // expression. This is also the best place we can do it to avoid
+          // putting it inside inner loops.
+          // NOTE: It assumes that the levels of the input tensor are
+          // initialized in order, another more admissible approach might be
+          // accepting out-of-order access between consecutive dense levels.
+          affineTids.push_back(tid);
+          affineDims.push_back(i);
+          exps.push_back(exp);
+        }
+      }
     }
   });
 
   if (isDenseDLT(merger.getDimLevelType(merger.getOutTensorID(), idx))) {
     // Note that we generate dense indices of the output tensor
     // unconditionally, since they may not appear in the lattice, but may be
     // needed for linearized codegen.
     // Only dense dimensions should be optimized from conditions.
     auto dim = merger.getDimNum(merger.getOutTensorID(), idx).value();
     extraTids.push_back(merger.getOutTensorID());
     extraDims.push_back(dim);
   }
 }
 
 /// Starts a single loop in current sequence.
 static Operation *startLoop(Merger &merger, CodeGen &codegen,
                             OpBuilder &builder, linalg::GenericOp op,
                             unsigned at, unsigned li, bool needsUniv) {
   // The set of tensors + dims to generate loops on
   SmallVector<size_t> condTids, condDims;
   // The set of (dense) tensors that is optimized from condition, yet still
   // need extra locals to iterate on them.
   SmallVector<size_t> extraTids, extraDims;
-
-  translateBitsToTidDimPairs(merger, codegen, li, codegen.topSort[at], condTids,
-                             condDims, extraTids, extraDims);
+  // The set of dense tensors with non-trivial affine expression that just
+  // becomes invariant and the address shall now be generated at the current
+  // level.
+  SmallVector<size_t> affineTids, affineDims;
+  SmallVector<AffineExpr> affines;
+
+  translateBitsToTidDimPairs(merger, codegen, op, li, codegen.topSort[at],
+                             condTids, condDims, extraTids, extraDims,
+                             affineTids, affineDims, affines);
   // Emit the for/while-loop control.
   Operation *loop = genLoop(merger, codegen, builder, op, at, needsUniv,
                             condTids, condDims, extraTids, extraDims);
+
+  for (auto [tid, dim, exp] : llvm::zip(affineTids, affineDims, affines)) {
+    codegen.loopEmitter.genDenseAffineAddressAtCurLevel(builder, op.getLoc(),
+                                                        tid, dim, exp);
+  }
   return loop;
 }
 
 /// Ends a single loop in current sequence. Returns new values for needsUniv.
 static bool endLoop(Merger &merger, CodeGen &codegen, RewriterBase &rewriter,
                     linalg::GenericOp op, Operation *loop, unsigned idx,
                     unsigned li, bool needsUniv) {
   // End a while-loop.