add documentation

Author: AntonLydike

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

@@ -15,7 +15,11 @@ def MPI_Dialect : Dialect {
   let name = "mpi";
   let cppNamespace = "::mlir::mpi";
   let description = [{
-    TODO
+    This dialect models the Message Passing Interface (MPI), version 4.0. It is meant
+    to serve as a targetable dialect, that can be lowered to multiple MPI implementations
+    and hide differences in ABI between these. The dialect models the functions of the MPI
+    specification as close to 1:1 as possible while preserving SSA value semantics where it
+    makes sense, and uses `memref` types instead of bare pointers.
 
     This dialect is under active development, and while stability is an
     eventual goal, it is not guaranteed at this juncture. Given the early state,

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

@@ -23,7 +23,8 @@ def MPI_InitOp : MPI_Op<"init", [
   ]> {
   let summary = "Initialize the MPI library, equivalent to `MPI_Init(NULL, NULL)`";
   let description = [{
-    Passing &argc, &argv is not supported currently, also inspecting the return value is not supported.
+    Passing &argc, &argv is not supported currently.
+    Inspecting the return value (error code) is also not supported.
   }];
 
   let assemblyFormat = "attr-dict";
@@ -39,6 +40,7 @@ def MPI_CommRankOp : MPI_Op<"comm_rank", [
   let summary = "Get the current rank, equivalent to `MPI_Comm_rank(MPI_COMM_WORLD, &rank)`";
   let description = [{
     Communicators other than `MPI_COMM_WORLD` are not supprted for now.
+    Inspecting the return value (error code) is also not supported.
   }];
 
   let results = (outs
@@ -59,6 +61,7 @@ def MPI_SendOp : MPI_Op<"send", [
   let summary = "Equivalent to `MPI_Send(ptr, size, dtype, dest, tag, MPI_COMM_WORLD)`";
   let description = [{
     Communicators other than `MPI_COMM_WORLD` are not supprted for now.
+    Inspecting the return value (error code) is also not supported.
   }];
 
   let arguments = (ins
@@ -80,6 +83,8 @@ def MPI_RecvOp : MPI_Op<"recv", [
   let summary = "Equivalent to `MPI_Recv(ptr, size, dtype, dest, tag, MPI_COMM_WORLD, MPI_STATUS_IGNORE)`";
   let description = [{
     Communicators other than `MPI_COMM_WORLD` are not supprted for now.
+    The MPI_Status is set to `MPI_STATUS_IGNORE`, as the status object is not yet ported to MLIR.
+    Inspecting the return value (error code) is also not supported.
   }];
 
   let arguments = (ins
@@ -100,7 +105,7 @@ def MPI_FinalizeOp : MPI_Op<"finalize", [
   ]> {
   let summary = "Finalize the MPI library, equivalent to `MPI_Finalize()`";
   let description = [{
-    
+    Inspecting the return value (error code) is not supported.
   }];
 
   let assemblyFormat = "attr-dict";