[mlir] Added documentation for bufferization to memref conversion pass.

[dfki-jugr]

Summary

Added documentation to clearify the purpose of the bufferization to memref pass
and added some remarks.

[herhut]

mlir/include/mlir/Conversion/Passes.td

144

nit: eliminates

mlir/include/mlir/Conversion/Passes.td

 
 //===----------------------------------------------------------------------===//
 // BufferizationToMemRef
 //===----------------------------------------------------------------------===//
 
 def ConvertBufferizationToMemRef : Pass<"convert-bufferization-to-memref"> {
   let summary = "Convert operations from the Bufferization dialect to the "
                 "MemRef dialect";
+  let description = [{
+
+    This pass converts bufferization operations into memref operations.
+
+    In the current state, this pass only transforms a `bufferization.clone`
+    operation into `memref.alloc` and `memref.copy` operations. This conversion
+    is needed, since some clone operations could remain after applying several
+    transformation processes. Currently, only `canonicalize` transforms clone
+    operations or even eliminate them. This can lead to errors if any clone op
+    survived after all conversion passes (starting from the bufferization
+    dialect) are performed.
+
+    See:
+    https://llvm.discourse.group/t/bufferization-error-related-to-memref-clone/4665
+
+    To avoid these errors, this pass can be performed as a last clean-up pass to
+    transform remaining operations and to proceed in other dialects (memref
+    e.g.).
+
+    Note that this pass only transforms the operation without any further
+    analyses. This pass does not consider any memory analysis or optimization
+    and hence does not resolve any memory leaks.
+
+  }];
   let constructor = "mlir::createBufferizationToMemRefPass()";
   let dependentDialects = ["arith::ArithmeticDialect", "memref::MemRefDialect"];
 }
 
 //===----------------------------------------------------------------------===//
 // ComplexToLLVM
 //===----------------------------------------------------------------------===//