[llvm-dev] RFC: Removal of noduplicate attribute

[Nicolai Hähnle-Montoro via llvm-dev]

On Tue, Oct 29, 2019 at 11:57 AM Savonichev, Andrew via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> > These are good points. I think the first question should be: Do we know
> > of any active users of this attribute right now? If not, deprecation
> > seems like something we could do, e.g., through a warning in clang and
> > in the middle-end to ensure other front-ends are aware of it as well.
>
> Noduplicate attribute is still used by the Intel OpenCL Compiler for CPU.
> The main use case is to prevent loop unroll when an OpenCL barrier is called
> within a loop. Although such loop can be unrolled and keep its semantic intact, but
> this introduces a lot of distinct barrier calls, and each of them has to
> be handled separately.
>
> In other words, "noduplicate" serves as a hint to not unroll a loop if a
> certain function is called in a loop body.

I don't quite understand the reasoning behind this. Is it because your
backend turns each individual barrier call into a large chunk of code?

If so, would it be a long-term viable alternative to inform the
various code size heuristics about this instead of using
`noduplicate`?

Cheers,
Nicolai
-- 
Lerne, wie die Welt wirklich ist,
aber vergiss niemals, wie sie sein sollte.