[cfe-dev] "generic" address space

[Eli Friedman]

On Tue, Jul 15, 2008 at 10:28 PM, Mon P Wang <wangmp at apple.com> wrote:
> Hi Eli,
> Whatever we do, it should be clear when examining the AST that we are
> matching an address space overloaded intrinsic.  I'm not sure what new AST
> expression tree would make sense.  I view it that we have an call expression
> to an address space overloaded intrinsic function.  When we check the
> argument and parameter of the signature, the normal rules follow except for
> parameters that can accept different address space.

The issue is that the types of the function arguments won't match the
type of the call, which would be surprising for most AST consumers.

> It is a bit unclear to me what happens with intrinsics that can take any
> integer width.  Looking briefily, it looks like clang will generate an
> implicit cast for the argument to integer.  Do we always generate the 32 bit
> integer version of these intrinsics?

Mmmm, it looks like clang's versions of the __sync_* builtins are
broken in that respect.  I think some custom logic is needed for the
overloading.

> Various DSPs (e.g TI TMS320C30), embedded architectures and GPUs support
> different address spaces. The Cell processor has local
> memory accessible only by the SPUs. Nvidia and AMD GPUs  typically have
> different address spaces for things like local or textures.  It is difficult
> to get their ISAs though AMD has released their R600 ISA
> (http://www.x.org/docs/AMD/r600isa.pdf).  I'll have to look to see what is
> available publicly.

Hmm, okay... I'm trying to get a feel for what sorts of intrinsics for
alternate address spaces we'll want, and for which ones it's useful to
overload the address space of the pointer arguments.  For example, for
the R600 ISA (which I skimmed), I can't think of any intrinsics for
which overloading would be useful; it seems like the address spaces
are implied by the instruction.  Do you have any examples where it
would be useful to overload the address space of platform-specific
intrinsics?

-Eli