[llvm-dev] Opaque Pointers Help Wanted

[David Blaikie via llvm-dev]

It looks like Craig's pointed out some cases that come up in LLVM. Perhaps
you could try fixing one of the in-tree examples to help explore/set the
direction for your out of tree work?

Metadata arguments sound like a direction worth exploring. (& would be
consistent with the way parameter attributes have been approached - still
using a type argument even though the length is all that matters in those
cases)

On Mon, Jun 21, 2021 at 2:28 PM Kaylor, Andrew via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> This has probably been discussed somewhere, but I missed it. Can you
> elaborate a bit on this?
>
>
>
>    - Allow bitcode auto-upgrade of legacy pointer type to the new opaque
>    pointer type (not to be turned on until ready)
>       - To support legacy bitcode, such as legacy stores/loads, we need
>       to track pointee types for all values since legacy instructions may infer
>       the types from a pointer operand's pointee type
>
> I‘m specifically trying to understand what will happen when typed pointer
> support is removed. How will IR with typed pointers be auto-upgraded to
> pure opaque pointer IR? Will the bitcode reader keep some level of typed
> pointer support indefinitely?
>
>
>
>
>
> Also, do you have a plan for replacing intrinsics that currently rely on
> pointee types? For example, the load instruction was updated to take an
> explicit type operand but I don’t think we can do the same thing for an
> intrinsic like llvm.masked.load since there is Value for Type. This is an
> easy problem to work around for something like masked.load, but more
> complicated if anyone has a downstream GEP-like intrinsic that needs more
> than the size of an element (spoiler alert: I do have such an intrinsic).
> Would you use a metadata argument?
>
>
>
> Thanks,
>
> Andy
>
>
>
>
>
> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of *Arthur
> Eubanks via llvm-dev
> *Sent:* Monday, June 21, 2021 12:03 PM
> *To:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* [llvm-dev] Opaque Pointers Help Wanted
>
>
>
> For the opaque pointers project,
> https://llvm.org/docs/OpaquePointers.html#transition-plan contains high
> level steps for what to do before we can enable opaque pointers. (Looks
> like the page hasn't been rebuilt in a while,
> https://github.com/llvm/llvm-project/blob/main/llvm/docs/OpaquePointers.rst#transition-plan
> contains some more concrete steps)
>
>
>
> Essentially almost all of the work boils down to figuring out how to
> remove calls to `PointerType::getElementType()` and
> `Type::getPointerElementType()`. Everything else derives from that.
>
>
>
> Any help with this is welcome and appreciated!
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