[Openmp-dev] What changes to IR does late outlining require?

[Jon Chesterfield via Openmp-dev]

I'm trying to determine why offload outlining is done in clang. As far back
as 2012 or so the docs suggest that in IR would be better but doesn't work.
A thesis by Novillo is cited in one that talks about making optimizations
better, but doesn't obviously say why IR doesn't work for it / what
modifications would be required.

There are challenges compiling gpu code under the ssa/simt model, but
they're common to opencl/hip. I think we basically opt out of a lot of
optimizations at present.

Moving memory ops across a target region won't work but that's manageable.
Live in/out are roughly what we copy into the object for early outlining.

I'll ask this at the round table later, but any information the community
can offer before that will be helpful.

Thanks!

Jon
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