Anastasia added inline comments.
================
Comment at: lib/CodeGen/CGCall.cpp:80
+ // used with the same version of generated operators.
+ RecTy = Context.getAddrSpaceQualType(RecTy, LangAS::opencl_generic);
+
----------------
rjmccall wrote:
> Anastasia wrote:
> > rjmccall wrote:
> > > I would suggest taking this opportunity to set up the AST to support
> > > declaring methods in an arbitrary address space, so that you can just ask
> > > a `CXXMethodDecl` what address space it's in. You don't have to actually
> > > add language support for that — OpenCL C++ would simply change the it to
> > > the generic address space instead of the default — but I think that's the
> > > right technical approach for implementing this, as opposed to adding a
> > > bunch of OpenCL C++ -specific logic all over the compiler that just
> > > hardcodes a different address space.
> > I quite like this idea. Apart from providing more clean implementation, it
> > opens opportunities for solving several problems that I am trying to
> > understand how to address. Specifically I am trying to find a way to
> > 'overload' methods based on the address space of the object.
> >
> > For example, if an object is created in the address space 1 then
> > programmers should be able to provide a method to be used for objects in
> > such address space for efficiency or even correctness issue.
> >
> > The reasons I am looking at it is that currently C++ doesn't make much
> > sense for address spaces, because we are removing them to generate just one
> > implementation with generic/default address space. However,
> > - Not all address spaces can be converted to generic/default address space.
> > Example in OpenCL is constant AS that can't be converted to any other.
> > - Higher performance can be achieved on some HW when using specific address
> > spaces instead of default.
> >
> > I was wondering if a method qualifier is a good language solution for this?
> > For example in OpenCL we could write something like:
> >
> > class foo
> > {
> > public:
> > void bar() __private; // implies bar(__private foo*)
> > void bar() __constant; // implies bar(__constant foo*)
> > };
> >
> > I guess in C++ it can be done similarly:
> >
> > class foo
> > {
> > public:
> > void bar() __attribute__((address_space(1)));
> > void bar() __attribute__((address_space(2)));
> > };
> >
> > I would quite like to solve this generically, not just for OpenCL. I think
> > a lot of implementation can be unified/reused then.
> >
> > Without this address spaces seem pretty useless with C++ because they are
> > just cast away to generic/default and no specific address space ends up at
> > the AST level at all. This means implementation will have to rely on the
> > optimizers to recover/deduce address spaces. But I would quite like to
> > provide a way for the developers to manually tune the code for address
> > spaces, just as it was done for OpenCL C.
> >
> > Let me know if you have any thought/suggestions.
> > I was wondering if a method qualifier is a good language solution for this?
> > For example in OpenCL we could write something like:
>
> Yes, I think that's a very natural extension of C++'s method-qualification
> rules for `const` and `volatile`. Overloads would then be resolved based on
> which address space was the best match.
>
> Now, to briefly take a holistic perspective on the language design, this
> feature would *strongly* benefit from a way to make a method templated over
> the address space of `this`. Unfortunately, I don't think that's reasonable
> to solve in a language extension; it's really something that needs core
> language work. That would be a pretty big leap in scope; that said, if
> you're interested in pursuing it, I'd be happy to share some thoughts on how
> it'd look, and I think there are several people in the Clang community who
> could help you with putting a proposal before the committee.
Thanks! Yes, I believe some template-based approach could make this a lot more
usable. I would be really interested to learn more about your ideas. I would
also quite like to see this properly in the spec. I will follow up with you in
a separate thread.
Repository:
rC Clang
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D54862/new/
https://reviews.llvm.org/D54862
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