[cfe-dev] Setting a FunctionDecl as 'uncallable':

[Keane, Erich via cfe-dev]

I’m using the ‘emit’ functionality from attribute-target to get the target-cpu emitted properly, however I hadn’t realized it allowed multiple function definitions.  I’ll look into that one as well.

Thanks Richard!
-Erich

From: metafoo at gmail.com [mailto:metafoo at gmail.com] On Behalf Of Richard Smith
Sent: Thursday, July 6, 2017 11:41 AM
To: Keane, Erich <erich.keane at intel.com>; Eric Christopher <echristo at google.com>
Cc: Clang Dev <cfe-dev at lists.llvm.org>; Reid Kleckner <rnk at google.com>
Subject: Re: [cfe-dev] Setting a FunctionDecl as 'uncallable':

+echristo This sounds similar to attribute target. Perhaps some of the work there could be reused?

On 6 Jul 2017 11:32 am, "Keane, Erich via cfe-dev" <cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>> wrote:
Thanks!  I’ll look into enable_if and others.

To spoil my RFC:
__attribute__((cpu_specific(atom)))
void foo(){} // atom specific impl
__attribute__((cpu_specific(p3)))
void foo(){} // p3 specific impl
__attribute__((cpu_dispatch(atom, p3)))
void foo(){}; // dispatch function.

Each ‘foo’ implementation is emitted with different name mangling.  They are generally ALL considered the same function, Function Pointers, references, etc will all be to the ‘dispatch’ version of the function.

The dispatch function will be implemented in terms of an iFunc.

-Erich


From: Reid Kleckner [mailto:rnk at google.com<mailto:rnk at google.com>]
Sent: Thursday, July 6, 2017 11:25 AM
To: Keane, Erich <erich.keane at intel.com<mailto:erich.keane at intel.com>>
Cc: cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>
Subject: Re: [cfe-dev] Setting a FunctionDecl as 'uncallable':

My first guess would be that you want to modify overload resolution. I think the CUDA host/device attributes are involved there. You can also look at the implementation of __attribute__((enable_if)) as well.

However, do we really need a FunctionDecl for every subtarget specialization? How does a user trigger specialization? Can they do something like take a specialization and instantiate a class template with it?

On Thu, Jul 6, 2017 at 9:31 AM, Keane, Erich via cfe-dev <cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>> wrote:
Hi all-
I'm working on an attribute implementation (RFC coming once I get a better idea about the implementation details, cpu_dispatch/cpu_specific from ICC) that permits multiple definitions of a function.  All definitions of the function ARE emitted, however with different name-mangling.  1 version of the function keeps the normal name-mangling/linking, so all call-expressions should call THAT one.

My question is: Is there a way to mark a FunctionDecl as 'don't find me in lookup' such that it never ends up being a "Callee"?  Or should I be figuring out how to change the lookup-results here?

Thanks,
Erich
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