[cfe-dev] About OpenCL 2.x Dynamic Parallelism

[Bekket McClane via cfe-dev]

> 
> In [Objective-]C, If the block is expected to persist beyond the lifetime of the caller, then the callee is expected to call _Block_copy to promote it to the heap.  The compiler emits copy helpers (and descriptors for captured variables that have trivial copy semantics) that allow this to work with a little bit of support from the blocks runtime library.
> 
> For OpenCL, you may want to generalise this slightly to provide different target address spaces for the copy,

I like this idea, but it might not so easy to allocate spaces in global or local address space and tell sub-kernel to access them without draining the storage space. Maybe a memory manager is required. 

> but note that for __block to work correctly the target address space must be readable (and writeable) in the context of the caller.  If you do not support __block variables then this is not an issue.

Fortunately, OpenCL-C 2.x doesn’t allow __block attribute : )

> 
> It sounds as if OpenCL’s requirements are much simpler than [Objective-]C’s.  I looked at implementing flattening for blocks a few years ago, but it becomes quite complex when a single variable is bound to multiple blocks and the potential performance improvements did not justify the increased complexity.  This is not an issue for you though.
> 
> It sounds as if OpenCL’s blocks are actually far closer to C++ lambdas with a default copy capture than they are to [Objective-]C blocks.  It might be cleaner and simpler to treat them as special syntax for lambdas than as special semantics for blocks
> 
> David

Cheers,

McClane

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