[mpich-discuss] Extensible Clang type annotation

[Dmitri Gribenko]

On Wed, Jan 2, 2013 at 8:09 PM, Dmitri Gribenko <gribozavr at gmail.com> wrote:
> On Wed, Jan 2, 2013 at 8:02 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>> On Wed, Jan 2, 2013 at 11:51 AM, Dmitri Gribenko <gribozavr at gmail.com>
>> wrote:
>>>
>>> [resending to the list, sorry for duplicates]
>>>
>>> On Wed, Jan 2, 2013 at 7:38 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>>> > Also, could there be a way (maybe in a future clang release) for me to
>>> > get
>>> > static type checking for my own types, such as __float128 or pair types
>>> > like
>>> > {long,long} (which are not in the MPI standard)? It can't truly be a
>>> > static
>>> > value because I have to create the type at run-time, but perhaps there
>>> > could
>>> > be a way to tell clang "I promise to set this type up like so."
>>>
>>> Sorry, I did not understand your requirements completely, but you can
>>> annotate your own 'MPI_Datatype's (as I described in the previous
>>> email).  Is that sufficient for your task?
>>
>>
>> I can't annotate mine because they don't have a static value. (Unless there
>> is a way that's not in the documentation.)
>>
>> I'm actually just setting
>>
>> MPI_Datatype MY_MPI_ENUM = MPI_INT;
>>
>> in a different compilation unit.
>
> Sorry if what I wrote was unclear.  Here's a complete example:
>
> $ cat t.cc
> #include <mpi.h>
>
> enum MyEnum { Foo };
> MPI_Datatype MyEnumDatatype MPICH_ATTR_TYPE_TAG(MyEnum);
>
> void foo(MyEnum e, int i) {
>   MPI_Send(&e, 1, MyEnumDatatype, 0, 0, MPI_COMM_WORLD);
>   MPI_Send(&i, 1, MyEnumDatatype, 0, 0, MPI_COMM_WORLD);
>   MPI_Send(&e, 1, MPI_INT, 0, 0, MPI_COMM_WORLD);
> }
>
> $ clang -fsyntax-only -I mpich2-build/src/include/ t.cc
> t.cc:8:12: warning: argument type 'int *' doesn't match specified
> 'MPI' type tag that requires 'MyEnum *' [-Wtype-safety]
>   MPI_Send(&i, 1, MyEnumDatatype, 0, 0, MPI_COMM_WORLD);
>            ^~     ~~~~~~~~~~~~~~
> t.cc:9:12: warning: argument type 'MyEnum *' doesn't match specified
> 'MPI' type tag that requires 'int *' [-Wtype-safety]
>   MPI_Send(&e, 1, MPI_INT, 0, 0, MPI_COMM_WORLD);
>            ^~     ~~~~~~~
> 2 warnings generated.

Please note that sending values of enumerated types this way might not
be a good idea in general, since the underlying type is
implementation-defined (C11 6.7.2.2p, C++11 [dcl.enum]p6, except for
enumerations with fixed underlying type).  So one can not assume that
it is always 'int' (unless one uses enumerations with fixed underlying
type).  It should be OK if you put a static assertion, though.

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>*/