try fixing the assembly forma of barrier

Author: mofeing

mlir/include/mlir/Dialect/MPI/IR/MPIOps.td

@@ -328,7 +328,18 @@ def MPI_Barrier : MPI_Op<"barrier", []> {
 
   let results = (outs Optional<MPI_Retval>:$retval);
 
-  let assemblyFormat = "(`(` $comm ^ `)`)? attr-dict (`:` type($retval) ^)?";
+  // TODO fix assembly format
+  // let assemblyFormat = "("
+  //                      "(attr-dict) ^"
+  //                      "(attr-dict `:` type($retval)) ^"
+  //                      "(`(` $comm `)` attr-dict `:` type($comm)) ^"
+  //                      "(`(` $comm `)` attr-dict `:` type($comm) `->` type($retval))"
+  //                      ")?";
+  let assemblyFormat = [{
+    (`(` $comm ^ `)`)? attr-dict
+    (`:` type($comm) ^ `->`):(`:`)?
+    type(results)
+  }];
 }
 
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