[cfe-commits] [PATCH] Compile-time MPI_Datatype checking, type arguments in attributes

[Matthieu Monrocq]

Le 11 février 2012 21:09, Dmitri Gribenko <gribozavr at gmail.com> a écrit :

> Hello,
>
> === Objective ===
> Implement a set of annotations for MPI libraries and a diagnostic for
> clang that checks that specified buffer type matches the passed
> MPI_Datatype.
>
> === Background ===
> Many MPI functions take a void* `buffer' and an MPI_Datatype (like
> MPI_INT, MPI_LONG etc) that describes how to send/receive that buffer.
>  For example,
>
> int MPI_Send(void *buf, int count, MPI_Datatype datatype, int dest,
>    int tag, MPI_Comm comm);
>
> Users call it like this:
> int *int_buf = ...;
> MPI_Send(int_buf, 1, MPI_INT, ...);
>
> Thus, user is on its own to ensure that buffer type matches the
> MPI_Datatype.
>
> === Annotation design ===
> I decided to annotate MPI functions that have buffer arguments and
> declarations of built-in `MPI_Datatype's.  Functions are easy: we use
> mpi_typed_arg(buffer-arg-index, type-arg-index) attribute:
>
> int MPI_Send(void *buf, int count, MPI_Datatype datatype, ...etc...)
>    __attribute__(( mpi_typed_arg(1,3) ));
>
>
Just a small remark here: indexes in C and C++ are usually 0-based, while
counting is 1-based. To avoid the ambiguity altogether it would be even
simpler to use the *names* of the arguments rather than their position, it
seems to be it would also be slightly easier to read and maintain.


> `MPI_Datatype's are trickier.  From the grammar of GNU attributes in
> lib/Parse/ParseDecl.cpp we see that there is no easy way to pass a
> type argument to an attribute.  For example, this is not currently
> parseable by clang:
>
> #define MPI_INT ((MPI_Datatype) &ompi_mpi_int)
> extern struct ompi_predefined_datatype_t ompi_mpi_int
>        __attribute__(( mpi_datatype(int) ));
>
> Matching C datatype for MPI_DATATYPE_NULL is void.
>
> #define MPI_DATATYPE_NULL ((MPI_Datatype) &ompi_mpi_int)
> extern struct ompi_predefined_datatype_t ompi_mpi_void
>        __attribute__(( mpi_datatype(void) ));
>
> While checking a function call we recognize mpi_datatype attribute if
> datatype argument is either:
> * an OpenMPI-style expression `((MPI_Datatype) &ident)';
> * a user-specified type `ident';
> where ident has mpi_datatype attribute.
>
> We emit a diagnostic in 2 cases.
> Case 1.  (Any type except MPI_DATATYPE_NULL)  All of the following is true:
> * buffer is not of `void *' type;
> * buffer's element type doesn't match specified MPI_Datatype.
>
> Case 2.  (MPI_DATATYPE_NULL)  All of the following is true:
> * buffer is not of `void *' type;
> * buffer is not a null pointer constant;
> * mpi_datatype(void) was specified.
>
> === Clang modifications ===
> We need to allow arbitrary types as attribute arguments.  If I
> understand everything correctly, GNU attribute grammar becomes
> ambiguous in that case, so attribute argument parsing will be driven
> by attribute name.  Fortunately, that is compatible with C++11
> attributes where attribute argument list is just a sequence of tokens
> with balanced delimiters.
>
> I added AttributeList::TypeArg member, the required AttributeList
> constructor and factory method.  In Attr.td a new field,
> HasTypeArgument, was added and a tablegen pass was implemented.  The
> parser uses the generated table to decide if it should parse a list of
> expressions or a type name.
>
> The check itself is called from Sema::CheckFunctionCall, which seems
> to be designed for similar purposes.
>
> === Compatibility ===
> The annotation-based approach is compatible with OpenMPI and LAM MPI.
> I already have a prototype patch for OpenMPI.
>
> MPICH is not compatible without refactoring their mpi.h header (they
> have MPI_XXX macros defined to magic numbers).
>
> === Miscellaneous ===
> There is an `iboutletcollection' attribute that takes a type argument.
>  It would be good if this implementation of type arguments could be
> used for that, too.
>
> Please see attached patch.  Parsing diagnostics are not very good (see
> testcase), advice is welcome.
>
> Dmitri
>
> --
> main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
> (j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/
>
>
-- Matthieu
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