[llvm-dev] Opaque Pointers Help Wanted

Kaylor, Andrew via llvm-dev llvm-dev at lists.llvm.org
Mon Jun 21 14:27:48 PDT 2021

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?


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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