[Openmp-dev] Malloc in target region

[Johannes Doerfert via Openmp-dev]

 >>>> On 6/24/20 6:40 AM, Jon Chesterfield via Openmp-dev wrote:
 >>>>> I can think of a few interpretations:
 >>>>> - One heap per process. Malloc on target or host, free from 
either. Writable from either, or some other device. Might mean 
intercepting host libc. Convenient, slow.
 >>>>> - One heap per device + one for host. Each independent, pointers 
only valid on the thing that called malloc.
 >>>>> - One heap per target offload region, inaccessible from host.
 >>>>> - Some other granularity.

I think the only thing we can reasonably support and that makes sense in
the general picture is:
   One heap per device + one for host

On 6/24/20 8:41 PM, Jeff Hammond via Openmp-dev wrote:
 >>> On 6/24/20 7:26 PM, Jeff Hammond wrote:
 >>> Does OpenMP 5 allow calling symbols that are not omp-declare-target?
 >>
 >> I'm not sure this is relevant because the implementation gets to 
provide such symbols (and we depend on it doing so in other cases, such 
as for math.h functions).
 >>
 > Is LLVM OpenMP going to assume one and only C RTL? Which one?

Yeah, that is a good question, ...

I think your last thought was the right starting point, you need to
declare target the symbol to access it on a device. That said, some
symbols the compiler will automagically provides as declare target
because people expect it. `math.h` is the poster child.

My first thought is that malloc on the device is provided and defined as
either
   `omp_alloc(size, omp_default_mem_alloc)`, or
   `omp_alloc(size, omp_cgroup_mem_allo)`.
free then with the respective `omp_free` call.

realloc and friends are available as soon as we have the counterparts in
OpenMP.


Cheers,
   Johannes

P.S. Thursday & Friday we have our workshop :)