[mlir][memref] memref.subview: Verify result strides

[matthias-springer]

The memref.subview verifier currently checks result shape, element type, memory space and offset of the result type. However, the strides of the result type are currently not verified. This commit adds verification of result strides for non-rank reducing ops and fixes invalid IR in test cases.

Verification of result strides for ops with rank reductions is more complex (and there could be multiple possible result types). That is left for a separate commit.

Also refactor the implementation a bit:

• If computeMemRefRankReductionMask could not compute the dropped dimensions, there must be something wrong with the op. Return FailureOr instead of std::optional.
• isRankReducedMemRefType did much more than just checking whether the op has rank reductions or not. Inline the implementation into the verifier and add better comments.
• produceSubViewErrorMsg does not have to be templatized.

[llvmbot]

@llvm/pr-subscribers-mlir-gpu
@llvm/pr-subscribers-mlir-sparse
@llvm/pr-subscribers-mlir-memref

@llvm/pr-subscribers-mlir

Author: Matthias Springer (matthias-springer)

Changes

The memref.subview verifier currently checks result shape, element type, memory space and offset of the result type. However, the strides of the result type are currently not verified. This commit adds verification of result strides for non-rank reducing ops and fixes invalid IR in test cases.

Verification of result strides for ops with rank reductions is more complex (and there could be multiple possible result types). That is left for a separate commit.

Also refactor the implementation a bit:

• If computeMemRefRankReductionMask could not compute the dropped dimensions, there must be something wrong with the op. Return FailureOr instead of std::optional.
• isRankReducedMemRefType did much more than just checking whether the op has rank reductions or not. Inline the implementation into the verifier and add better comments.

---

Full diff: https://github.com/llvm/llvm-project/pull/79865.diff

5 Files Affected:

• (modified) mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp (+68-52)
• (modified) mlir/test/Dialect/GPU/decompose-memrefs.mlir (+3-3)
• (modified) mlir/test/Dialect/MemRef/fold-memref-alias-ops.mlir (+6-6)
• (modified) mlir/test/Dialect/MemRef/invalid.mlir (+9)
• (modified) mlir/test/Integration/Dialect/SparseTensor/CPU/sparse_rewrite_sort_coo.mlir (+4-4)

diff --git a/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp b/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp
index b79ab8f3d671e..922520e17a0d0 100644
--- a/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp
+++ b/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp
@@ -917,7 +917,7 @@ static std::map<int64_t, unsigned> getNumOccurences(ArrayRef<int64_t> vals) {
 /// This accounts for cases where there are multiple unit-dims, but only a
 /// subset of those are dropped. For MemRefTypes these can be disambiguated
 /// using the strides. If a dimension is dropped the stride must be dropped too.
-static std::optional<llvm::SmallBitVector>
+static FailureOr<llvm::SmallBitVector>
 computeMemRefRankReductionMask(MemRefType originalType, MemRefType reducedType,
                                ArrayRef<OpFoldResult> sizes) {
   llvm::SmallBitVector unusedDims(originalType.getRank());
@@ -941,7 +941,7 @@ computeMemRefRankReductionMask(MemRefType originalType, MemRefType reducedType,
           getStridesAndOffset(originalType, originalStrides, originalOffset)) ||
       failed(
           getStridesAndOffset(reducedType, candidateStrides, candidateOffset)))
-    return std::nullopt;
+    return failure();
 
   // For memrefs, a dimension is truly dropped if its corresponding stride is
   // also dropped. This is particularly important when more than one of the dims
@@ -976,22 +976,22 @@ computeMemRefRankReductionMask(MemRefType originalType, MemRefType reducedType,
         candidateStridesNumOccurences[originalStride]) {
       // This should never happen. Cant have a stride in the reduced rank type
       // that wasnt in the original one.
-      return std::nullopt;
+      return failure();
     }
   }
 
   if ((int64_t)unusedDims.count() + reducedType.getRank() !=
       originalType.getRank())
-    return std::nullopt;
+    return failure();
   return unusedDims;
 }
 
 llvm::SmallBitVector SubViewOp::getDroppedDims() {
   MemRefType sourceType = getSourceType();
   MemRefType resultType = getType();
-  std::optional<llvm::SmallBitVector> unusedDims =
+  FailureOr<llvm::SmallBitVector> unusedDims =
       computeMemRefRankReductionMask(sourceType, resultType, getMixedSizes());
-  assert(unusedDims && "unable to find unused dims of subview");
+  assert(succeeded(unusedDims) && "unable to find unused dims of subview");
   return *unusedDims;
 }
 
@@ -2745,7 +2745,7 @@ void SubViewOp::build(OpBuilder &b, OperationState &result, Value source,
 /// For ViewLikeOpInterface.
 Value SubViewOp::getViewSource() { return getSource(); }
 
-/// Return true if t1 and t2 have equal offsets (both dynamic or of same
+/// Return true if `t1` and `t2` have equal offsets (both dynamic or of same
 /// static value).
 static bool haveCompatibleOffsets(MemRefType t1, MemRefType t2) {
   int64_t t1Offset, t2Offset;
@@ -2755,56 +2755,41 @@ static bool haveCompatibleOffsets(MemRefType t1, MemRefType t2) {
   return succeeded(res1) && succeeded(res2) && t1Offset == t2Offset;
 }
 
-/// Checks if `original` Type type can be rank reduced to `reduced` type.
-/// This function is slight variant of `is subsequence` algorithm where
-/// not matching dimension must be 1.
-static SliceVerificationResult
-isRankReducedMemRefType(MemRefType originalType,
-                        MemRefType candidateRankReducedType,
-                        ArrayRef<OpFoldResult> sizes) {
-  auto partialRes = isRankReducedType(originalType, candidateRankReducedType);
-  if (partialRes != SliceVerificationResult::Success)
-    return partialRes;
-
-  auto optionalUnusedDimsMask = computeMemRefRankReductionMask(
-      originalType, candidateRankReducedType, sizes);
-
-  // Sizes cannot be matched in case empty vector is returned.
-  if (!optionalUnusedDimsMask)
-    return SliceVerificationResult::LayoutMismatch;
-
-  if (originalType.getMemorySpace() !=
-      candidateRankReducedType.getMemorySpace())
-    return SliceVerificationResult::MemSpaceMismatch;
-
-  // No amount of stride dropping can reconcile incompatible offsets.
-  if (!haveCompatibleOffsets(originalType, candidateRankReducedType))
-    return SliceVerificationResult::LayoutMismatch;
-
-  return SliceVerificationResult::Success;
+/// Return true if `t1` and `t2` have equal strides (both dynamic or of same
+/// static value).
+static bool haveCompatibleStrides(MemRefType t1, MemRefType t2) {
+  int64_t t1Offset, t2Offset;
+  SmallVector<int64_t> t1Strides, t2Strides;
+  auto res1 = getStridesAndOffset(t1, t1Strides, t1Offset);
+  auto res2 = getStridesAndOffset(t2, t2Strides, t2Offset);
+  if (failed(res1) || failed(res2))
+    return false;
+  for (auto [s1, s2] : llvm::zip_equal(t1Strides, t2Strides))
+    if (s1 != s2)
+      return false;
+  return true;
 }
 
-template <typename OpTy>
 static LogicalResult produceSubViewErrorMsg(SliceVerificationResult result,
-                                            OpTy op, Type expectedType) {
+                                            Operation *op, Type expectedType) {
   auto memrefType = llvm::cast<ShapedType>(expectedType);
   switch (result) {
   case SliceVerificationResult::Success:
     return success();
   case SliceVerificationResult::RankTooLarge:
-    return op.emitError("expected result rank to be smaller or equal to ")
+    return op->emitError("expected result rank to be smaller or equal to ")
            << "the source rank. ";
   case SliceVerificationResult::SizeMismatch:
-    return op.emitError("expected result type to be ")
+    return op->emitError("expected result type to be ")
            << expectedType
            << " or a rank-reduced version. (mismatch of result sizes) ";
   case SliceVerificationResult::ElemTypeMismatch:
-    return op.emitError("expected result element type to be ")
+    return op->emitError("expected result element type to be ")
            << memrefType.getElementType();
   case SliceVerificationResult::MemSpaceMismatch:
-    return op.emitError("expected result and source memory spaces to match.");
+    return op->emitError("expected result and source memory spaces to match.");
   case SliceVerificationResult::LayoutMismatch:
-    return op.emitError("expected result type to be ")
+    return op->emitError("expected result type to be ")
            << expectedType
            << " or a rank-reduced version. (mismatch of result layout) ";
   }
@@ -2826,13 +2811,46 @@ LogicalResult SubViewOp::verify() {
   if (!isStrided(baseType))
     return emitError("base type ") << baseType << " is not strided";
 
-  // Verify result type against inferred type.
-  auto expectedType = SubViewOp::inferResultType(
-      baseType, getStaticOffsets(), getStaticSizes(), getStaticStrides());
+  // Compute the expected result type, assuming that there are no rank
+  // reductions.
+  auto expectedType = cast<MemRefType>(SubViewOp::inferResultType(
+      baseType, getStaticOffsets(), getStaticSizes(), getStaticStrides()));
+
+  // Verify all properties of a shaped type: rank, element type and dimension
+  // sizes. This takes into account potential rank reductions.
+  auto shapedTypeVerification = isRankReducedType(
+      /*originalType=*/expectedType, /*candidateReducedType=*/subViewType);
+  if (shapedTypeVerification != SliceVerificationResult::Success)
+    return produceSubViewErrorMsg(shapedTypeVerification, *this, expectedType);
+
+  // Make sure that the memory space did not change.
+  if (expectedType.getMemorySpace() != subViewType.getMemorySpace())
+    return produceSubViewErrorMsg(SliceVerificationResult::MemSpaceMismatch,
+                                  *this, expectedType);
+
+  // Verify the offset of the layout map.
+  if (!haveCompatibleOffsets(expectedType, subViewType))
+    return produceSubViewErrorMsg(SliceVerificationResult::LayoutMismatch,
+                                  *this, expectedType);
+
+  // The only thing that's left to verify now are the strides. First, compute
+  // the unused dimensions due to rank reductions. We have to look at sizes and
+  // strides to decide which dimensions were dropped. This function also
+  // verifies strides in case of rank reductions.
+  auto unusedDims = computeMemRefRankReductionMask(expectedType, subViewType,
+                                                   getMixedSizes());
+  if (failed(unusedDims))
+    return produceSubViewErrorMsg(SliceVerificationResult::LayoutMismatch,
+                                  *this, expectedType);
+
+  // Strides must match if there are no rank reductions.
+  // TODO: Verify strides when there are rank reductions. Strides are partially
+  // checked in `computeMemRefRankReductionMask`.
+  if (unusedDims->none() && !haveCompatibleStrides(expectedType, subViewType))
+    return produceSubViewErrorMsg(SliceVerificationResult::LayoutMismatch,
+                                  *this, expectedType);
 
-  auto result = isRankReducedMemRefType(llvm::cast<MemRefType>(expectedType),
-                                        subViewType, getMixedSizes());
-  return produceSubViewErrorMsg(result, *this, expectedType);
+  return success();
 }
 
 raw_ostream &mlir::operator<<(raw_ostream &os, const Range &range) {
@@ -2882,11 +2900,9 @@ static MemRefType getCanonicalSubViewResultType(
     ArrayRef<OpFoldResult> mixedSizes, ArrayRef<OpFoldResult> mixedStrides) {
   auto nonRankReducedType = llvm::cast<MemRefType>(SubViewOp::inferResultType(
       sourceType, mixedOffsets, mixedSizes, mixedStrides));
-  std::optional<llvm::SmallBitVector> unusedDims =
-      computeMemRefRankReductionMask(currentSourceType, currentResultType,
-                                     mixedSizes);
-  // Return nullptr as failure mode.
-  if (!unusedDims)
+  FailureOr<llvm::SmallBitVector> unusedDims = computeMemRefRankReductionMask(
+      currentSourceType, currentResultType, mixedSizes);
+  if (failed(unusedDims))
     return nullptr;
 
   auto layout = llvm::cast<StridedLayoutAttr>(nonRankReducedType.getLayout());
diff --git a/mlir/test/Dialect/GPU/decompose-memrefs.mlir b/mlir/test/Dialect/GPU/decompose-memrefs.mlir
index d714010d0f254..56fc9a66b7ace 100644
--- a/mlir/test/Dialect/GPU/decompose-memrefs.mlir
+++ b/mlir/test/Dialect/GPU/decompose-memrefs.mlir
@@ -119,7 +119,7 @@ func.func @decompose_subview(%arg0 : memref<?x?x?xf32>) {
 //       CHECK:  %[[IDX1:.*]] = affine.apply #[[MAP1]]()[%[[STRIDES]]#1]
 //       CHECK:  %[[IDX2:.*]] = affine.apply #[[MAP2]]()[%[[TX]], %[[STRIDES]]#0, %[[TY]], %[[STRIDES]]#1, %[[TZ]]]
 //       CHECK:  %[[PTR:.*]] = memref.reinterpret_cast %[[BASE]] to offset: [%[[IDX2]]], sizes: [%{{.*}}, %{{.*}}, %{{.*}}], strides: [%[[IDX]], %[[IDX1]], 4]
-//       CHECK:  "test.test"(%[[PTR]]) : (memref<?x?x?xf32, strided<[?, ?, ?], offset: ?>>) -> ()
+//       CHECK:  "test.test"(%[[PTR]]) : (memref<?x?x?xf32, strided<[?, ?, 4], offset: ?>>) -> ()
 func.func @decompose_subview_strided(%arg0 : memref<?x?x?xf32>) {
   %c0 = arith.constant 0 : index
   %c1 = arith.constant 1 : index
@@ -129,8 +129,8 @@ func.func @decompose_subview_strided(%arg0 : memref<?x?x?xf32>) {
   %block_dim2 = memref.dim %arg0, %c2 : memref<?x?x?xf32>
   gpu.launch blocks(%bx, %by, %bz) in (%grid_x = %c1, %grid_y = %c1, %grid_z = %c1)
              threads(%tx, %ty, %tz) in (%block_x = %block_dim0, %block_y = %block_dim1, %block_z = %block_dim2) {
-    %res = memref.subview %arg0[%tx, %ty, %tz] [%c2, %c2, %c2] [2, 3, 4] : memref<?x?x?xf32> to memref<?x?x?xf32, strided<[?, ?, ?], offset: ?>>
-    "test.test"(%res) : (memref<?x?x?xf32, strided<[?, ?, ?], offset: ?>>) -> ()
+    %res = memref.subview %arg0[%tx, %ty, %tz] [%c2, %c2, %c2] [2, 3, 4] : memref<?x?x?xf32> to memref<?x?x?xf32, strided<[?, ?, 4], offset: ?>>
+    "test.test"(%res) : (memref<?x?x?xf32, strided<[?, ?, 4], offset: ?>>) -> ()
     gpu.terminator
   }
   return
diff --git a/mlir/test/Dialect/MemRef/fold-memref-alias-ops.mlir b/mlir/test/Dialect/MemRef/fold-memref-alias-ops.mlir
index 96b72e042b9e0..3407bdbc7c8f9 100644
--- a/mlir/test/Dialect/MemRef/fold-memref-alias-ops.mlir
+++ b/mlir/test/Dialect/MemRef/fold-memref-alias-ops.mlir
@@ -595,9 +595,9 @@ func.func @subview_of_subview(%m: memref<1x1024xf32, 3>, %pos: index)
 {
   %0 = memref.subview %m[3, %pos] [1, 2] [1, 1]
       : memref<1x1024xf32, 3>
-        to memref<1x2xf32, strided<[1024, 2], offset: ?>, 3>
+        to memref<1x2xf32, strided<[1024, 1], offset: ?>, 3>
   %1 = memref.subview %0[1, 2] [1, 1] [1, 1]
-      : memref<1x2xf32, strided<[1024, 2], offset: ?>, 3>
+      : memref<1x2xf32, strided<[1024, 1], offset: ?>, 3>
         to memref<f32, strided<[], offset: ?>, 3>
   return %1 : memref<f32, strided<[], offset: ?>, 3>
 }
@@ -675,9 +675,9 @@ func.func @fold_gpu_subgroup_mma_store_matrix_1d(%dst: memref<?xvector<4xf32>>,
 // CHECK-LABEL: func.func @fold_gpu_subgroup_mma_load_matrix_2d
 //  CHECK-SAME: %[[SRC:.+]]: memref<128x128xf32>
 func.func @fold_gpu_subgroup_mma_load_matrix_2d(%arg0 : memref<128x128xf32>, %arg1 : index, %arg2 : index, %arg3 : index, %arg4 : index) -> !gpu.mma_matrix<16x16xf16, "COp"> {
-  %subview = memref.subview %arg0[%arg1, %arg2][64, 32][2, 1] : memref<128x128xf32> to memref<64x32xf32, strided<[64, 1], offset: ?>>
+  %subview = memref.subview %arg0[%arg1, %arg2][64, 32][2, 1] : memref<128x128xf32> to memref<64x32xf32, strided<[256, 1], offset: ?>>
   // CHECK: gpu.subgroup_mma_load_matrix %[[SRC]][{{.+}}] {leadDimension = 32 : index} : memref<128x128xf32> -> !gpu.mma_matrix<16x16xf16, "COp">
-  %matrix = gpu.subgroup_mma_load_matrix %subview[%arg3, %arg4] {leadDimension = 32 : index} : memref<64x32xf32, strided<[64, 1], offset: ?>> -> !gpu.mma_matrix<16x16xf16, "COp">
+  %matrix = gpu.subgroup_mma_load_matrix %subview[%arg3, %arg4] {leadDimension = 32 : index} : memref<64x32xf32, strided<[256, 1], offset: ?>> -> !gpu.mma_matrix<16x16xf16, "COp">
   return %matrix : !gpu.mma_matrix<16x16xf16, "COp">
 }
 
@@ -686,9 +686,9 @@ func.func @fold_gpu_subgroup_mma_load_matrix_2d(%arg0 : memref<128x128xf32>, %ar
 // CHECK-LABEL: func.func @fold_gpu_subgroup_mma_load_matrix_2d
 //  CHECK-SAME: %[[DST:.+]]: memref<128x128xf32>
 func.func @fold_gpu_subgroup_mma_load_matrix_2d(%arg0 : memref<128x128xf32>, %arg1 : index, %arg2 : index, %arg3 : index, %arg4 : index, %matrix: !gpu.mma_matrix<16x16xf16, "COp">) {
-  %subview = memref.subview %arg0[%arg1, %arg2][64, 32][2, 1] : memref<128x128xf32> to memref<64x32xf32, strided<[64, 1], offset: ?>>
+  %subview = memref.subview %arg0[%arg1, %arg2][64, 32][2, 1] : memref<128x128xf32> to memref<64x32xf32, strided<[256, 1], offset: ?>>
   // CHECK: gpu.subgroup_mma_store_matrix %{{.+}}, %[[DST]][{{.+}}] {leadDimension = 32 : index} : !gpu.mma_matrix<16x16xf16, "COp">, memref<128x128xf32>
-  gpu.subgroup_mma_store_matrix %matrix, %subview[%arg3, %arg4] {leadDimension = 32 : index} :  !gpu.mma_matrix<16x16xf16, "COp">, memref<64x32xf32, strided<[64, 1], offset: ?>>
+  gpu.subgroup_mma_store_matrix %matrix, %subview[%arg3, %arg4] {leadDimension = 32 : index} :  !gpu.mma_matrix<16x16xf16, "COp">, memref<64x32xf32, strided<[256, 1], offset: ?>>
   return
 }
 
diff --git a/mlir/test/Dialect/MemRef/invalid.mlir b/mlir/test/Dialect/MemRef/invalid.mlir
index 7bb7a2affcbd1..be60a3dcb1b20 100644
--- a/mlir/test/Dialect/MemRef/invalid.mlir
+++ b/mlir/test/Dialect/MemRef/invalid.mlir
@@ -1073,3 +1073,12 @@ func.func @dim_0_ranked(%arg : memref<f32>, %arg1 : index) {
   memref.dim %arg, %arg1 : memref<f32> // expected-error {{'memref.dim' op operand #0 must be unranked.memref of any type values or non-0-ranked.memref of any type values, but got 'memref<f32>'}}
   return
 }
+
+// -----
+
+func.func @subview_invalid_strides(%m: memref<7x22x333x4444xi32>) {
+  // expected-error @below{{expected result type to be 'memref<7x11x333x4444xi32, strided<[32556744, 2959704, 4444, 1]>>' or a rank-reduced version. (mismatch of result layout)}}
+  %subview = memref.subview %m[0, 0, 0, 0] [7, 11, 333, 4444] [1, 2, 1, 1]
+      : memref<7x22x333x4444xi32> to memref<7x11x333x4444xi32>
+  return
+}
diff --git a/mlir/test/Integration/Dialect/SparseTensor/CPU/sparse_rewrite_sort_coo.mlir b/mlir/test/Integration/Dialect/SparseTensor/CPU/sparse_rewrite_sort_coo.mlir
index 3773cca9c8d69..e7dd0ad32a243 100644
--- a/mlir/test/Integration/Dialect/SparseTensor/CPU/sparse_rewrite_sort_coo.mlir
+++ b/mlir/test/Integration/Dialect/SparseTensor/CPU/sparse_rewrite_sort_coo.mlir
@@ -88,10 +88,10 @@ module {
     // Prepare a buffer for x0, x1, x2, y0 and a buffer for y1.
     %xys = memref.alloc() : memref<20xi32>
     %xy = memref.cast %xys : memref<20xi32> to memref<?xi32>
-    %x0 = memref.subview %xy[%i0][%i5][%i4] : memref<?xi32> to memref<?xi32, strided<[4], offset: ?>>
-    %x1 = memref.subview %xy[%i1][%i5][%i4] : memref<?xi32> to memref<?xi32, strided<[4], offset: ?>>
-    %x2 = memref.subview %xy[%i2][%i5][%i4] : memref<?xi32> to memref<?xi32, strided<[4], offset: ?>>
-    %y0 = memref.subview %xy[%i3][%i5][%i4] : memref<?xi32> to memref<?xi32, strided<[4], offset: ?>>
+    %x0 = memref.subview %xy[%i0][%i5][4] : memref<?xi32> to memref<?xi32, strided<[4], offset: ?>>
+    %x1 = memref.subview %xy[%i1][%i5][4] : memref<?xi32> to memref<?xi32, strided<[4], offset: ?>>
+    %x2 = memref.subview %xy[%i2][%i5][4] : memref<?xi32> to memref<?xi32, strided<[4], offset: ?>>
+    %y0 = memref.subview %xy[%i3][%i5][4] : memref<?xi32> to memref<?xi32, strided<[4], offset: ?>>
     %y1s = memref.alloc() : memref<7xi32>
     %y1 = memref.cast %y1s : memref<7xi32> to memref<?xi32>
 

[makslevental]

@matthias-springer thanks for jumping on this so quickly! Btw, I rebased to kick the windows runner again.

[hanhanW]

I think this is causing a weird issue in downstream projects (i.e., IREE), and I don't have a proper fix yet. We have --iree-iree-hoist-statically-bound-allocations pass [implementation], which hoists the allocation ops and replace the original one with memref.subview. Then it triggers a verification issue. Below is the input IR, and it passes IR verification.

#map = affine_map<(d0) -> (d0, 16)>
func.func @nested_op_alloca_subview_use(%arg0 : index, %o0 : index, %o1 : index) {
  %c0 = arith.constant 0 : index
  %c1 = arith.constant 1 : index
  %c42 = arith.constant 42 : i32
  scf.for %iv = %c0 to %arg0 step %c1 {
    %0 = affine.min #map(%iv)
    %1 = memref.alloca(%0, %0) : memref<?x?xi32>
    %2 = memref.subview %1[%o0, %o1][%c1, %0][1, 1] : memref<?x?xi32> to memref<?x?xi32, strided<[?, 1], offset: ?>>
    scf.yield
  }
  return
}

After running the pass, we generate a alloca op outside of scf.for, and replace the old one with memref.subview. So we get

func.func @nested_op_alloca_subview_use(%arg0 : index, %o0 : index, %o1 : index) {
  %c0 = arith.constant 0 : index
  %c1 = arith.constant 1 : index
  %c42 = arith.constant 42 : i32
  %alloca = memref.alloca() : memref<16x16xi32>
  scf.for %iv = %c0 to %arg0 step %c1 {
    %0 = affine.min #map(%iv)
    %1 = memref.subview %alloca[0, 0] [%0, %0] [1, 1] : memref<16x16xi32> to memref<?x?xi32, strided<[16, 1]>>
    %2 = memref.subview %1[%o0, %o1][%c1, %0][1, 1] : memref<?x?xi32, strided<[16, 1]>> to memref<?x?xi32, strided<[?, 1], offset: ?>>
    scf.yield
  }
  return
}

Then the verification issue happens. It infers a different type in the second subview, because the strides change. The old type is memref<?x?xi32, strided<[?, 1], offset: ?>> and the expected type is memref<?x?xi32, strided<[16, 1], offset: ?>>. I think this could happen in other passes. Do you have a suggestion about how we can fix it, or can we revert the commit?

[matthias-springer]

You can insert a memref.cast to turn the static stride into a dynamic one:

    %1 = memref.subview %alloca[0, 0] [%0, %0] [1, 1] : memref<16x16xi32> to memref<?x?xi32, strided<[16, 1]>>
    %cast = memref.cast %1 : memref<?x?xi32, strided<[16, 1]>> to memref<?x?xi32, strided<[?, 1]>>
    %2 = memref.subview %cast[%o0, %o1][%c1, %0][1, 1] : memref<?x?xi32, strided<[?, 1]>> to memref<?x?xi32, strided<[?, 1], offset: ?>>

[makslevental]

Dumb question: shouldn't haveCompatibleOffsets and haveCompatibleStrides tolerate refined (non-dynamic) attribute values? If a user (whoever/whatever emits) static values for offsets/strides inferred to be dynamic, shouldn't that pass "a fortiori"?

[matthias-springer]

I would say no, because we also don't allow this for dimension sizes. They must be casted explicitly if there's static/dynamic mismatch.