[vector][mlir] Add required comments and test in vectorUnroll.cpp and invalid.mlir respectively

Author: Prakhar-Dixit

mlir/lib/Dialect/Vector/Transforms/VectorUnroll.cpp

@@ -437,6 +437,9 @@ struct UnrollElementwisePattern : public RewritePattern {
     auto dstVecType = cast<VectorType>(op->getResult(0).getType());
     SmallVector<int64_t> originalSize =
         *cast<VectorUnrollOpInterface>(op).getShapeForUnroll();
+    // Bail-out if rank(source) != rank(target). The main limitation here is the
+    // fact that `ExtractStridedSlice` requires the rank for the input and
+    // output to match. If needed, we can relax this later.
     if (originalSize.size() != targetShape->size())
       return failure();
     Location loc = op->getLoc();

mlir/test/Dialect/Vector/invalid.mlir

@@ -766,6 +766,16 @@ func.func @extract_strided_slice(%arg0: vector<4x8x16xf32>) {
   %1 = vector.extract_strided_slice %arg0 {offsets = [2], sizes = [2], strides = [1]} : vector<4x8x16xf32> to vector<3x1xf32>
 }
 
+// -----
+
+ func.func @extract_strided_slice() -> () {
+  // expected-error@+1 {{expected input vector rank to match target shape rank}}
+  %0 = arith.constant dense<1.000000e+00> : vector<24x2x2xf32>
+  %1 = vector.extract_strided_slice %0 {offsets = [0, 0], sizes = [2, 2], strides = [1, 1]}:
+         vector<24x2x2xf32> to vector<2x2xf32>
+  return
+}
+
 // -----
 
 #contraction_accesses = [