[mlir][vector] Fix rewrite pattern API violation in VectorToSCF

[matthias-springer]

A rewrite pattern is not allowed to change the IR if it returns "failure". This commit fixes test/Conversion/VectorToSCF/vector-to-scf.mlir when running with MLIR_ENABLE_EXPENSIVE_PATTERN_API_CHECKS.

Processing operation : 'vector.transfer_read'(0x55823a409a60) {
  %5 = "vector.transfer_read"(%arg0, %0, %0, %2, %4) <{in_bounds = [true, true], operandSegmentSizes = array<i32: 1, 2, 1, 1>, permutation_map = affine_map<(d0, d1) -> (d0, d1)>}> : (memref<?x4xf32>, index, index, f32, vector<[4]x4xi1>) -> vector<[4]x4xf32>

  * Pattern (anonymous namespace)::lowering_n_d_unrolled::UnrollTransferReadConversion : 'vector.transfer_read -> ()' {
Trying to match "(anonymous namespace)::lowering_n_d_unrolled::UnrollTransferReadConversion"
    ** Insert  : 'vector.splat'(0x55823a445640)
"(anonymous namespace)::lowering_n_d_unrolled::UnrollTransferReadConversion" result 0
  } -> failure : pattern failed to match

LLVM ERROR: pattern returned failure but IR did change

[llvmbot]

@llvm/pr-subscribers-mlir

Author: Matthias Springer (matthias-springer)

Changes

A rewrite pattern is not allowed to change the IR if it returns "failure". This commit fixes test/Conversion/VectorToSCF/vector-to-scf.mlir when running with MLIR_ENABLE_EXPENSIVE_PATTERN_API_CHECKS.

Processing operation : 'vector.transfer_read'(0x55823a409a60) {
  %5 = "vector.transfer_read"(%arg0, %0, %0, %2, %4) <{in_bounds = [true, true], operandSegmentSizes = array<i32: 1, 2, 1, 1>, permutation_map = affine_map<(d0, d1) -> (d0, d1)>}> : (memref<?x4xf32>, index, index, f32, vector<[4]x4xi1>) -> vector<[4]x4xf32>

  * Pattern (anonymous namespace)::lowering_n_d_unrolled::UnrollTransferReadConversion : 'vector.transfer_read -> ()' {
Trying to match "(anonymous namespace)::lowering_n_d_unrolled::UnrollTransferReadConversion"
    ** Insert  : 'vector.splat'(0x55823a445640)
"(anonymous namespace)::lowering_n_d_unrolled::UnrollTransferReadConversion" result 0
  } -> failure : pattern failed to match

LLVM ERROR: pattern returned failure but IR did change

---

Full diff: https://github.com/llvm/llvm-project/pull/77909.diff

1 Files Affected:

• (modified) mlir/lib/Conversion/VectorToSCF/VectorToSCF.cpp (+4-5)

diff --git a/mlir/lib/Conversion/VectorToSCF/VectorToSCF.cpp b/mlir/lib/Conversion/VectorToSCF/VectorToSCF.cpp
index a1aff1ab36a52b..4dfd78a9b91042 100644
--- a/mlir/lib/Conversion/VectorToSCF/VectorToSCF.cpp
+++ b/mlir/lib/Conversion/VectorToSCF/VectorToSCF.cpp
@@ -1105,17 +1105,16 @@ struct UnrollTransferReadConversion
     if (xferOp.getVectorType().getElementType() !=
         xferOp.getShapedType().getElementType())
       return failure();
-
-    auto insertOp = getInsertOp(xferOp);
-    auto vec = getResultVector(xferOp, rewriter);
-    auto vecType = dyn_cast<VectorType>(vec.getType());
     auto xferVecType = xferOp.getVectorType();
-
     if (xferVecType.getScalableDims()[0]) {
       // Cannot unroll a scalable dimension at compile time.
       return failure();
     }
 
+    auto insertOp = getInsertOp(xferOp);
+    auto vec = getResultVector(xferOp, rewriter);
+    auto vecType = dyn_cast<VectorType>(vec.getType());
+
     VectorType newXferVecType = VectorType::Builder(xferVecType).dropDim(0);
 
     int64_t dimSize = xferVecType.getShape()[0];

[nicolasvasilache]

while we're here, can we also add some return notifyMatchFailure to improve UX?