[LLVMdev] RFC: GEP as canonical form for pointer addressing

Ivan Godard
Thu, 20 Feb 2014 06:11:04 -0000

Philip Reames <listmail <at> philipreames.com> writes:

>
> RFC: GEP as canonical form for pointer addressing


<snip>

> In addition to my own use case, here's a few others which might come
up:
> - Backends for targets which support different operations on pointers vs
> integers.  Examples would be some of the older mainframe architectures.
> (There'd be a lot more work needed to support this.)

>
> Philip
>


It's not just old mainframes, it's some of the newest architecture as
well.
The Mill general-purpose architecture (http://ootbcomp.com) has non-integer
pointers and distinct pointer operations too. That LLVM loses pointerhood is
the biggest problem that we have identified while looking into using LLVM as
our supported compiler. It may be a killer, and we may have to fall back to
gcc. That would be a shame, but it does appear that the ir makes rash
assumptions about machine architecture.

"There'd be a lot more work needed to support this" is not
encouraging to
see, especially for a startup company with limited resources and little
prior exposure to LLVM internals.

Ivan