[mlir][memref] Fix CollapseShapeOp verifier

[springerm]

Summary

Depends On D122641

[springerm]

update

[springerm]

typo

[mravishankar]

mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp

1836

Calling out the same assumption as the expand shape patch. The strides might not be in the same order as the dimensions. So if this is "unsupported" behavior needs to be verified or called out in the op semantics.

1910

Can we return an actual error message here?

[nicolasvasilache]

mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp

1853

Same comments as in https://reviews.llvm.org/D122641, with likely a slightly different implementation solving the problem with much lower code complexity.

1929

same here re https://reviews.llvm.org/D122641, use of (generalized) saturated_arith will reduce all this complexity and will turn into a simple reduce 1-liner idiom (or map idiom with capture if we don't have a reduce idiom).

[springerm]

address comments

[springerm]

simplify code

[springerm]

update

[springerm]

simplify code

[mravishankar]

If I am reading this right, this works for the case where stride are not row-major ordered. If so please add a test for that. Removing my blocker

[springerm]

update

[nicolasvasilache]

I am unclear why this landed as there were outstanding unaddressed comments.
Sent a followup cleanup here: https://reviews.llvm.org/D122845

[springerm]

Oh I must have landed this by accident.

mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td

def MemRef_ExpandShapeOp : MemRef_ReassociativeReshapeOp<"expand_shape"> {
   let extraClassDeclaration = commonExtraClassDeclaration;
   let hasVerifier = 1;
 }
 
 def MemRef_CollapseShapeOp : MemRef_ReassociativeReshapeOp<"collapse_shape"> {
   let summary = "operation to produce a memref with a smaller rank.";
   let description = [{
     The `memref.collapse_shape` op produces a new view with a smaller rank
-    whose sizes are a reassociation of the original `view`. Depending on
-    whether or not the reassociated MemRefType is contiguous, the resulting
-    memref may require explicit alloc and copies.
+    whose sizes are a reassociation of the original `view`. The operation is
+    limited to such reassociations, where subsequent, contiguous dimensions are
+    collapsed into a single dimension. Such reassociations never require
+    additional allocs or copies.
+
+    Collapsing non-contiguous dimensions is undefined behavior. When a group of
+    dimensions can be statically proven to be non-contiguous, collapses of such
+    groups are rejected in the verifier on a best-effort basis. In the general
+    case, collapses of dynamically-sized dims with dynamic strides cannot be
+    proven to be contiguous or non-contiguous due to limitations in the memref
+    type.
 
     A reassociation is defined as a continuous grouping of dimensions and is
     represented with an array of I64ArrayAttr attribute.
 
-    For now, it is assumed that either:
-      1. a reassociation produces and consumes contiguous MemRefType or,
-      2. the reshape op will be folded into its consumers (by changing the shape
-         of the computations).
-    All other cases are undefined behavior and a reshape op may not lower to
-    LLVM if it cannot be proven statically that it does not require alloc+copy.
-
-    The result memref type of a reshape can be zero-ranked if the operand
-    memref type is statically shaped with all dimensions being unit extent. In
-    such case the reassociation map is empty.
-
-    The verification rule is that the reassociation maps are applied to the
-    operand memref with the larger rank to obtain the result memref with the
-    smaller rank.
+    Note: Only the dimensions within a reassociation group must be contiguous.
+    The remaining dimensions may be non-contiguous.
+
+    The result memref type can be zero-ranked if the source memref type is
+    statically shaped with all dimensions being unit extent. In such a case, the
+    reassociation indices must be empty.
 
     Examples:
 
     ```mlir
     // Dimension collapse (i, j) -> i' and k -> k'
     %1 = memref.collapse_shape %0 [[0, 1], [2]] :
         memref<?x?x?xf32, stride_spec> into memref<?x?xf32, stride_spec_2>
     ```
+
+    For simplicity, this op may not be used to cast dynamicity of dimension
+    sizes and/or strides. I.e., a result dimension must be dynamic if and only
+    if at least one dimension in the corresponding reassociation group is
+    dynamic. Similarly, the stride of a result dimension must be dynamic if and
+    only if the corresponding start dimension in the source type is dynamic.
+
+    Note: This op currently assumes that the inner strides are of the
+    source/result layout map are the faster-varying ones.
   }];
   let builders = [
     // Builders for a contracting reshape whose result type is computed from
     // `src` and `reassociation`.
     OpBuilder<(ins "Value":$src,
       "ArrayRef<ReassociationIndices>":$reassociation,
       CArg<"ArrayRef<NamedAttribute>", "{}">:$attrs)>,
     OpBuilder<(ins "Value":$src,

mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp

for (auto idx = dim, e = dim + extent; idx + 1 < e; ++idx) {
     // TODO: Refine this by passing the proper nDims and nSymbols so we can
     // simplify on the fly and catch more reshapable cases.
     if (strides[idx] != strides[idx + 1] * sizes[idx + 1])
       return false;
   }
   return true;
 }
 
-/// Compute the MemRefType obtained by applying the `reassociation` (which is
-/// expected to be valid) to `type`.
-/// If `type` is Contiguous MemRefType, this always produce a contiguous
-/// MemRefType.
-static MemRefType
-computeReshapeCollapsedType(MemRefType type,
-                            ArrayRef<AffineMap> reassociation) {
-  auto sizes = type.getShape();
-  AffineExpr offset;
-  SmallVector<AffineExpr, 4> strides;
-  auto status = getStridesAndOffset(type, strides, offset);
-  auto isIdentityLayout = type.getLayout().isIdentity();
-  (void)status;
-  assert(succeeded(status) && "expected strided memref");
-
-  SmallVector<int64_t, 4> newSizes;
-  newSizes.reserve(reassociation.size());
-  SmallVector<AffineExpr, 4> newStrides;
-  newStrides.reserve(reassociation.size());
-
-  // Use the fact that reassociation is valid to simplify the logic: only use
-  // each map's rank.
-  assert(isReassociationValid(reassociation) && "invalid reassociation");
-  unsigned currentDim = 0;
-  for (AffineMap m : reassociation) {
-    unsigned dim = m.getNumResults();
-    int64_t size = 1;
-    AffineExpr stride = strides[currentDim + dim - 1];
-    if (isIdentityLayout ||
-        isReshapableDimBand(currentDim, dim, sizes, strides)) {
-      for (unsigned d = 0; d < dim; ++d) {
-        int64_t currentSize = sizes[currentDim + d];
-        if (ShapedType::isDynamic(currentSize)) {
-          size = ShapedType::kDynamicSize;
-          break;
-        }
-        size *= currentSize;
-      }
-    } else {
-      size = ShapedType::kDynamicSize;
-      stride = AffineExpr();
-    }
-    newSizes.push_back(size);
-    newStrides.push_back(stride);
-    currentDim += dim;
-  }
-
-  // Early-exit: if `type` is contiguous, the result must be contiguous.
-  if (canonicalizeStridedLayout(type).getLayout().isIdentity())
-    return MemRefType::Builder(type).setShape(newSizes).setLayout({});
-
-  // Convert back to int64_t because we don't have enough information to create
-  // new strided layouts from AffineExpr only. This corresponds to a case where
-  // copies may be necessary.
-  int64_t intOffset = ShapedType::kDynamicStrideOrOffset;
-  if (auto o = offset.dyn_cast<AffineConstantExpr>())
-    intOffset = o.getValue();
-  SmallVector<int64_t, 4> intStrides;
-  intStrides.reserve(strides.size());
-  for (auto stride : newStrides) {
-    if (auto cst = stride.dyn_cast_or_null<AffineConstantExpr>())
-      intStrides.push_back(cst.getValue());
-    else
-      intStrides.push_back(ShapedType::kDynamicStrideOrOffset);
-  }
-  auto layout =
-      makeStridedLinearLayoutMap(intStrides, intOffset, type.getContext());
-  return canonicalizeStridedLayout(
-      MemRefType::Builder(type).setShape(newSizes).setLayout(
-          AffineMapAttr::get(layout)));
-}
-
-void CollapseShapeOp::build(OpBuilder &b, OperationState &result, Value src,
-                            ArrayRef<ReassociationIndices> reassociation,
-                            ArrayRef<NamedAttribute> attrs) {
-  auto memRefType = src.getType().cast<MemRefType>();
-  auto resultType = computeReshapeCollapsedType(
-      memRefType, getSymbolLessAffineMaps(convertReassociationIndicesToExprs(
-                      b.getContext(), reassociation)));
-  build(b, result, resultType, src, attrs);
-  result.addAttribute(getReassociationAttrName(),
-                      getReassociationIndicesAttribute(b, reassociation));
-}
-
-template <typename ReshapeOp,
-          bool isExpansion = std::is_same<ReshapeOp, ExpandShapeOp>::value>
-static LogicalResult verifyReshapeOp(ReshapeOp op, MemRefType expandedType,
-                                     MemRefType collapsedType) {
-  if (failed(
-          verifyReshapeLikeTypes(op, expandedType, collapsedType, isExpansion)))
-    return failure();
-  auto maps = op.getReassociationMaps();
-  MemRefType expectedType = computeReshapeCollapsedType(expandedType, maps);
-  if (collapsedType != expectedType)
-    return op.emitOpError("expected collapsed type to be ")
-           << expectedType << ", but got " << collapsedType;
-  return success();
-}
-
 /// Compute the layout map after expanding a given source MemRef type with the
 /// specified reassociation indices.
 static FailureOr<AffineMap>
 computeExpandedLayoutMap(MemRefType srcType, ArrayRef<int64_t> resultShape,
                          ArrayRef<ReassociationIndices> reassociation) {
   SmallVector<int64_t> srcStrides, resultStrides(resultShape.size(), 0);
   int64_t srcOffset;
   if (failed(getStridesAndOffset(srcType, srcStrides, srcOffset)))

 }
 
 void ExpandShapeOp::getCanonicalizationPatterns(RewritePatternSet &results,
                                                 MLIRContext *context) {
   results.add<CollapseReshapeOps<ExpandShapeOp>,
               CollapseMixedReshapeOps<ExpandShapeOp, CollapseShapeOp>>(context);
 }
 
+/// Compute the layout map after collapsing a given source MemRef type with the
+/// specified reassociation indices.
+///
+/// Note: All collapsed dims in a reassociation group must be contiguous. It is
+/// not possible to check this by inspecting a MemRefType in the general case.
+/// But it is assumed. If this is not the case, the behavior is undefined.
+static FailureOr<AffineMap>
+computeCollapsedLayoutMap(MemRefType srcType, ArrayRef<int64_t> resultShape,
+                          ArrayRef<ReassociationIndices> reassociation) {
+  SmallVector<int64_t> srcStrides, resultStrides;
+  int64_t srcOffset;
+  if (failed(getStridesAndOffset(srcType, srcStrides, srcOffset)))
+    return failure();
+  assert(resultShape.size() == reassociation.size() && "invalid reassociation");
+
+  // Iterate over all reassociation groups from the back. Example:
+  // source shape   = [20, ?,   5, 10, 2]
+  // source strides = [ ?, ?, 800, 80, 4]
+  // reassociation  = [[0, 1], [2, 3], [4]]
+  // result shape   = [     ?,     50,   2]
+  //
+  // Note: The result shape is not needed in this computation. It is just used
+  // check that the size of the reassociation is correct.
+  for (ReassociationIndices group : llvm::reverse(reassociation)) {
+    // A result dim has the same stride as the first dimension (least
+    // significant one) in the corresponding reassociation group. E.g.:
+    // reassociation  = [[0, 1], [2, 3], [4]]
+    //                       |       |    |
+    //                       v       v    v
+    //                       ?      80    4
+    int64_t resultStride = srcStrides[group.pop_back_val()];
+
+    // The following is just a best-effort check for non-contiguous source
+    // strides within a reassociation group. E.g.:
+    // reassociation  = [[0, 1], [2, 3], [4]]
+    //                           ^^^^^^
+    // Iteratively compute the next stride within the reassociation group
+    // one-by-one. Start with the stride computed above. E.g.:
+    // reassociation  = [[0, 1], [2, 3], [4]]
+    //                               |
+    //                               v
+    //                  nextStride = 80
+    int64_t nextStride = resultStride;
+    for (int64_t nextDim : llvm::reverse(group)) {
+      // Next expected stride is previous stride multiplied by dim size, e.g.:
+      // reassociation  = [[0, 1], [2, 3], [4]]
+      //                            |
+      //                            v
+      //    nextStride = 80 * 10 = 800
+      nextStride =
+          computeNextStride(nextStride, srcType.getDimSize(nextDim + 1));
+
+      // Ensure that the source actually has this stride value. E.g.:
+      // source strides = [ ?, ?, 800, 80, 4]
+      //                           |
+      //                           v
+      //                  same stride, OK
+      // If strides are dynamic, we cannot verify anything statically.
+      if (!ShapedType::isDynamicStrideOrOffset(srcStrides[nextDim]) &&
+          !ShapedType::isDynamicStrideOrOffset(nextStride) &&
+          srcStrides[nextDim] != nextStride) {
+        // Attempting to collapse non-contiguous dimensions. This is forbidden.
+        // Note: This check does not handle cases where strides and dimension
+        // sizes are dynamic. Such dims could still turn out to be non-
+        // contiguous at runtime. This check is only a best effort to catch
+        // illegal collapses at verification time.
+        return failure();
+      }
+    }
+
+    resultStrides.push_back(resultStride);
+  }
+
+  return makeStridedLinearLayoutMap(
+      llvm::to_vector<8>(llvm::reverse(resultStrides)), srcOffset,
+      srcType.getContext());
+}
+
+static MemRefType
+computeCollapsedType(MemRefType srcType,
+                     ArrayRef<ReassociationIndices> reassociation) {
+  SmallVector<int64_t> resultShape;
+  for (const ReassociationIndices &group : reassociation) {
+    int64_t groupSize = 1;
+    for (int64_t srcDim : group) {
+      if (srcType.isDynamicDim(srcDim)) {
+        // Source dim is dynamic, so the collapsed dim is also dynamic.
+        groupSize = ShapedType::kDynamicSize;
+        break;
+      }
+
+      groupSize *= srcType.getDimSize(srcDim);
+    }
+
+    resultShape.push_back(groupSize);
+  }
+
+  if (srcType.getLayout().isIdentity()) {
+    // If the source is contiguous (i.e., no layout map specified), so is the
+    // result.
+    MemRefLayoutAttrInterface layout;
+    return MemRefType::get(resultShape, srcType.getElementType(), layout,
+                           srcType.getMemorySpace());
+  }
+
+  // Source may not be fully contiguous. Compute the layout map.
+  // Note: Dimensions that are collapsed into a single dim are assumed to be
+  // contiguous.
+  FailureOr<AffineMap> computedLayout =
+      computeCollapsedLayoutMap(srcType, resultShape, reassociation);
+  assert(succeeded(computedLayout) &&
+         "invalid source layout map or collapsing non-contiguous dims");
+  auto computedType =
+      MemRefType::get(resultShape, srcType.getElementType(), *computedLayout,
+                      srcType.getMemorySpaceAsInt());
+  return canonicalizeStridedLayout(computedType);
+}
+
+void CollapseShapeOp::build(OpBuilder &b, OperationState &result, Value src,
+                            ArrayRef<ReassociationIndices> reassociation,
+                            ArrayRef<NamedAttribute> attrs) {
+  auto srcType = src.getType().cast<MemRefType>();
+  MemRefType resultType = computeCollapsedType(srcType, reassociation);
+  build(b, result, resultType, src, attrs);
+  result.addAttribute(getReassociationAttrName(),
+                      getReassociationIndicesAttribute(b, reassociation));
+}
+
 LogicalResult CollapseShapeOp::verify() {
-  return verifyReshapeOp(*this, getSrcType(), getResultType());
+  MemRefType srcType = getSrcType();
+  MemRefType resultType = getResultType();
+
+  // Verify result shape.
+  if (failed(verifyCollapsedShape(getOperation(), resultType.getShape(),
+                                  srcType.getShape(), getReassociationIndices(),
+                                  /*allowMultipleDynamicDimsPerGroup=*/true)))
+    return failure();
+
+  // Compute expected result type (including layout map).
+  MemRefType expectedResultType;
+  if (srcType.getLayout().isIdentity()) {
+    // If the source is contiguous (i.e., no layout map specified), so is the
+    // result.
+    MemRefLayoutAttrInterface layout;
+    expectedResultType =
+        MemRefType::get(resultType.getShape(), srcType.getElementType(), layout,
+                        srcType.getMemorySpace());
+  } else {
+    // Source may not be fully contiguous. Compute the layout map.
+    // Note: Dimensions that are collapsed into a single dim are assumed to be
+    // contiguous.
+    FailureOr<AffineMap> computedLayout = computeCollapsedLayoutMap(
+        srcType, resultType.getShape(), getReassociationIndices());
+    if (failed(computedLayout))
+      return emitOpError(
+          "invalid source layout map or collapsing non-contiguous dims");
+    auto computedType =
+        MemRefType::get(resultType.getShape(), srcType.getElementType(),
+                        *computedLayout, srcType.getMemorySpaceAsInt());
+    expectedResultType = canonicalizeStridedLayout(computedType);
+  }
+
+  auto canonicalizedResultType = canonicalizeStridedLayout(resultType);
+  if (expectedResultType != canonicalizedResultType)
+    return emitOpError("expected collapsed type to be ")
+           << expectedResultType << " but found " << canonicalizedResultType;
+
+  return success();
 }
 
 struct CollapseShapeOpMemRefCastFolder
     : public OpRewritePattern<CollapseShapeOp> {
 public:
   using OpRewritePattern<CollapseShapeOp>::OpRewritePattern;
 
   LogicalResult matchAndRewrite(CollapseShapeOp op,
                                 PatternRewriter &rewriter) const override {
     auto cast = op.getOperand().getDefiningOp<CastOp>();
     if (!cast)
       return failure();
 
     if (!CastOp::canFoldIntoConsumerOp(cast))
       return failure();
 
-    Type newResultType = computeReshapeCollapsedType(
-        cast.getOperand().getType().cast<MemRefType>(),
-        op.getReassociationMaps());
+    Type newResultType =
+        computeCollapsedType(cast.getOperand().getType().cast<MemRefType>(),
+                             op.getReassociationIndices());
 
     if (newResultType == op.getResultType()) {
       rewriter.updateRootInPlace(
           op, [&]() { op.srcMutable().assign(cast.source()); });
     } else {
       Value newOp = rewriter.create<CollapseShapeOp>(
           op->getLoc(), cast.source(), op.getReassociationIndices());
       rewriter.replaceOpWithNewOp<CastOp>(op, op.getType(), newOp);

mlir/test/Dialect/MemRef/invalid.mlir

func @expand_shape(%arg0: memref<f32>) {
   // expected-error @+1 {{rank 0 memrefs can only be extended/collapsed with/from ones}}
   %0 = memref.expand_shape %arg0 [] : memref<f32> into memref<1x2xf32>
   return
 }
 
 // -----
 
 func @collapse_shape_to_higher_rank(%arg0: memref<f32>) {
-  // expected-error @+1 {{expected the type 'memref<f32>' to have higher rank than the type = 'memref<1xf32>'}}
+  // expected-error @+1 {{op reassociation index 0 is out of bounds}}
   %0 = memref.collapse_shape %arg0 [[0]] : memref<f32> into memref<1xf32>
 }
 
 // -----
 
 func @expand_shape_to_smaller_rank(%arg0: memref<1xf32>) {
   // expected-error @+1 {{op reassociation index 0 is out of bounds}}
   %0 = memref.expand_shape %arg0 [[0]] : memref<1xf32> into memref<f32>
 }
 
 // -----
 
 func @expand_shape_invalid_result_layout(
     %arg0: memref<30x20xf32, offset : 100, strides : [4000, 2]>) {
   // expected-error @+1 {{expected expanded type to be 'memref<2x15x20xf32, affine_map<(d0, d1, d2) -> (d0 * 60000 + d1 * 4000 + d2 * 2 + 100)>>' but found 'memref<2x15x20xf32, affine_map<(d0, d1, d2) -> (d0 * 5000 + d1 * 4000 + d2 * 2 + 100)>>'}}
   %0 = memref.expand_shape %arg0 [[0, 1], [2]] :
       memref<30x20xf32, offset : 100, strides : [4000, 2]>
       into memref<2x15x20xf32, offset : 100, strides : [5000, 4000, 2]>
 }
 
 // -----
 
-func @collapse_shape(%arg0: memref<?xf32>) {
-  // expected-error @+1 {{expected to collapse or expand dims}}
-  %0 = memref.collapse_shape %arg0 [[0]] : memref<?xf32> into memref<?xf32>
-}
-
-// -----
-
 func @collapse_shape_mismatch_indices_num(%arg0: memref<?x?x?xf32>) {
-  // expected-error @+1 {{expected rank of the collapsed type(2) to be the number of reassociation maps(1)}}
+  // expected-error @+1 {{invalid number of reassociation groups: found 1, expected 2}}
   %0 = memref.collapse_shape %arg0 [[0, 1]] :
     memref<?x?x?xf32> into memref<?x?xf32, offset: 0, strides: [?, 1]>
 }
 
 // -----
 
 func @collapse_shape_invalid_reassociation(%arg0: memref<?x?x?xf32>) {
-  // expected-error @+1 {{expected reassociation map #1 to be valid and contiguous}}
+  // expected-error @+1 {{reassociation indices must be contiguous}}
   %0 = memref.collapse_shape %arg0 [[0, 1], [1, 2]] :
     memref<?x?x?xf32> into memref<?x?xf32, offset: 0, strides: [?, 1]>
 }
 
 // -----
 
+func @collapse_shape_reshaping_non_contiguous(
+    %arg0: memref<3x4x5xf32, offset: 0, strides: [270, 50, 10]>) {
+  // expected-error @+1 {{invalid source layout map or collapsing non-contiguous dims}}
+  %0 = memref.collapse_shape %arg0 [[0, 1], [2]] :
+      memref<3x4x5xf32, offset: 0, strides: [270, 50, 10]>
+      into memref<12x5xf32, offset: 0, strides: [50, 1]>
+  return
+}
+
+// -----
+
 func @collapse_shape_wrong_collapsed_type(%arg0: memref<?x?x?xf32>) {
-  // expected-error @+1 {{expected collapsed type to be 'memref<?x?xf32>', but got 'memref<?x?xf32, affine_map<(d0, d1)[s0] -> (d0 * s0 + d1)>>'}}
+  // expected-error @+1 {{expected collapsed type to be 'memref<?x?xf32>' but found 'memref<?x?xf32, affine_map<(d0, d1)[s0] -> (d0 * s0 + d1)>>'}}
   %0 = memref.collapse_shape %arg0 [[0, 1], [2]] :
     memref<?x?x?xf32> into memref<?x?xf32, affine_map<(d0, d1)[s0] -> (d0 * s0 + d1)>>
 }
 
 // -----
 
 func @expand_shape_illegal_dynamic_memref
   (%arg0: memref<?x?x?xf32>) -> memref<?x?x?x4x?xf32> {
%0 = memref.expand_shape %arg0 [[0], [1], [2, 3, 4]]
       : memref<2x3x20xf32> into memref<2x3x2x4x5xf32>
   return %0 : memref<2x3x2x4x5xf32>
 }
 
 // -----
 
 func @collapse_shape_illegal_static_memref
   (%arg0: memref<2x3x2x4x5xf32>) -> memref<2x3x20xf32> {
-  // expected-error @+1 {{expected dimension 2 of collapsed type to be static value of 40}}
+  // expected-error @+1 {{collapsed dim size (20) must equal reassociation group size (40)}}
   %0 = memref.collapse_shape %arg0 [[0], [1], [2, 3, 4]]
       : memref<2x3x2x4x5xf32> into memref<2x3x20xf32>
   return %0 : memref<2x3x20xf32>
 }
 
 // -----
 
 func @expand_shape_illegal_mixed_memref(%arg0 : memref<?x?xf32>)
%0 = memref.expand_shape %arg0 [[0], [1, 2]]
       : memref<?x21xf32> into memref<?x4x5xf32>
   return %0 : memref<?x4x5xf32>
 }
 
 // -----
 
 func @collapse_shape_illegal_mixed_memref(%arg0 : memref<?x4x5xf32>)
     -> memref<?x?xf32> {
-  // expected-error @+1 {{expected dimension 1 of collapsed type to be static value of 5}}
+  // expected-error @+1 {{collapsed dim (1) must be dynamic if and only if reassociation group is dynamic}}
   %0 = memref.collapse_shape %arg0 [[0, 1], [2]]
       : memref<?x4x5xf32> into memref<?x?xf32>
   return %0 : memref<?x?xf32>
 }
 
 // -----
 
 func @collapse_shape_illegal_mixed_memref_2(%arg0 : memref<?x4x5xf32>)
     -> memref<?x?xf32> {
-  // expected-error @+1 {{expected dimension 1 of collapsed type to be static value of 20}}
+  // expected-error @+1 {{collapsed dim (1) must be dynamic if and only if reassociation group is dynamic}}
   %0 = memref.collapse_shape %arg0 [[0], [1, 2]]
       : memref<?x4x5xf32> into memref<?x?xf32>
   return %0 : memref<?x?xf32>
 }
 
 // -----
 
 func @invalid_view(%arg0 : index, %arg1 : index, %arg2 : index) {

mlir/test/Dialect/MemRef/ops.mlir

 
 // CHECK-LABEL: func @expand_collapse_shape_static
 func @expand_collapse_shape_static(
     %arg0: memref<3x4x5xf32>,
     %arg1: tensor<3x4x5xf32>,
     %arg2: tensor<3x?x5xf32>,
     %arg3: memref<30x20xf32, offset : 100, strides : [4000, 2]>,
     %arg4: memref<1x5xf32, affine_map<(d0, d1)[s0] -> (d0 * 5 + s0 + d1)>>,
-    %arg5: memref<f32>) {
+    %arg5: memref<f32>,
+    %arg6: memref<3x4x5xf32, offset: 0, strides: [240, 60, 10]>,
+    %arg7: memref<1x2049xi64, affine_map<(d0, d1)[s0, s1, s2] -> (d0 * s1 + s0 + d1 * s2)>>) {
   // Reshapes that collapse and expand back a contiguous buffer.
 //       CHECK:   memref.collapse_shape {{.*}} {{\[}}[0, 1], [2]]
 //  CHECK-SAME:     memref<3x4x5xf32> into memref<12x5xf32>
   %0 = memref.collapse_shape %arg0 [[0, 1], [2]] :
     memref<3x4x5xf32> into memref<12x5xf32>
 
 //       CHECK:   memref.expand_shape {{.*}} {{\[}}[0, 1], [2]]
 //  CHECK-SAME:     memref<12x5xf32> into memref<3x4x5xf32>
%l1 = memref.expand_shape %arg3 [[0, 1], [2]] :
       memref<30x20xf32, offset : 100, strides : [4000, 2]>
       into memref<2x15x20xf32, offset : 100, strides : [60000, 4000, 2]>
 
 //       CHECK:   memref.expand_shape {{.*}} {{\[}}[0], [1, 2]]
   %r4 = memref.expand_shape %arg4 [[0], [1, 2]] :
       memref<1x5xf32, affine_map<(d0, d1)[s0] -> (d0 * 5 + s0 + d1)>> into
       memref<1x1x5xf32, affine_map<(d0, d1, d2)[s0] -> (d0 * 5 + s0 + d2 + d1 * 5)>>
 
+  // Note: Only the collapsed two shapes are contiguous in the follow test case.
+//       CHECK:   memref.collapse_shape {{.*}} {{\[}}[0, 1], [2]]
+  %r6 = memref.collapse_shape %arg6 [[0, 1], [2]] :
+      memref<3x4x5xf32, offset: 0, strides: [240, 60, 10]> into
+      memref<12x5xf32, offset: 0, strides: [60, 10]>
+
+//       CHECK:   memref.collapse_shape {{.*}} {{\[}}[0, 1]]
+  %r7 = memref.collapse_shape %arg7 [[0, 1]] :
+      memref<1x2049xi64, affine_map<(d0, d1)[s0, s1, s2] -> (d0 * s1 + s0 + d1 * s2)>> into
+      memref<2049xi64, affine_map<(d0)[s0, s1] -> (d0 * s1 + s0)>>
+
   // Reshapes that expand and collapse back a contiguous buffer with some 1's.
 //       CHECK:   memref.expand_shape {{.*}} {{\[}}[0, 1], [2], [3, 4]]
 //  CHECK-SAME:     memref<3x4x5xf32> into memref<1x3x4x1x5xf32>
   %3 = memref.expand_shape %arg0 [[0, 1], [2], [3, 4]] :
     memref<3x4x5xf32> into memref<1x3x4x1x5xf32>
 
 //       CHECK:   memref.collapse_shape {{.*}} {{\[}}[0, 1], [2], [3, 4]]
 //  CHECK-SAME:     memref<1x3x4x1x5xf32> into memref<3x4x5xf32>