[mlir][memref] Mark memref.buffer_cast as NoSideEffect

[herhut]

Summary

This brings it in line with the bultin unrealized_conversion_cast, which memref.buffer_cast is a specialized version of.

[herhut]

fix tests

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

def MemRef_AllocaOp : AllocLikeOp<"alloca", AutomaticAllocationScopeResource> {
   }];
 }
 
 //===----------------------------------------------------------------------===//
 // BufferCastOp
 //===----------------------------------------------------------------------===//
 
 def MemRef_BufferCastOp : MemRef_Op<"buffer_cast",
-    [SameOperandsAndResultShape, SameOperandsAndResultElementType,
+    [SameOperandsAndResultShape, SameOperandsAndResultElementType, NoSideEffect,
      TypesMatchWith<"type of 'tensor' is the tensor equivalent of 'memref'",
                     "memref", "tensor",
                     "getTensorTypeFromMemRefType($_self)">]> {
   let summary = "tensor to memref cast operation";
   let description = [{
     Casts a tensor to a memref.
 
     ```mlir
     // Result type is tensor<4x?xf32>
     %12 = memref.buffer_cast %10 : memref<4x?xf32, #map0, 42>
     ```
 
     Note, that mutating the result of the buffer cast operation leads to
     undefined behavior.
+
+    This operation is a specialized variant of the built-in
+    unrealized_conversion_cast and is intended for use in the context of
+    gradual bufferization.
   }];
 
   let arguments = (ins AnyTensor:$tensor);
   let results = (outs AnyRankedOrUnrankedMemRef:$memref);
   // This op is fully verified by traits.
   let verifier = ?;
 
   let assemblyFormat = "$tensor attr-dict `:` type($memref)";