[llvm-dev] Scalable Vector Types in IR - Next Steps?

[Renato Golin via llvm-dev]

Hi folks,

We seem to be converging on how the representation of scalable vectors
will be implemented in IR, and we also have support for such vectors
in the AArch64 back-end. We're also fresh out of the release process
and have a good number of months to hash out potential problems until
next release. What are the next steps to get this merged into trunk?

Given this is a major change to IR, we need more core developers
reviews before approving. The current quasi-consensus means now it's
the time for you to look closer. :)

This change per se shouldn't change how any of the passes or lowering
behave, but it will introduce the ability to break things in the
future. Unlike the "new pass manager", we can't create a "new IR", so
it needs to be a change that everyone is conscious and willing to take
on the project to stabilize it until the next release.

Here are some of the reviews on the matter, mostly agreed upon by the
current reviewers:
https://reviews.llvm.org/D32530
https://reviews.llvm.org/D53137
https://reviews.llvm.org/D47770

And the corresponding RFC threads:
http://lists.llvm.org/pipermail/llvm-dev/2016-November/106819.html
http://lists.llvm.org/pipermail/llvm-dev/2017-March/110772.html
http://lists.llvm.org/pipermail/llvm-dev/2017-June/113587.html
http://lists.llvm.org/pipermail/llvm-dev/2018-April/122517.html
http://lists.llvm.org/pipermail/llvm-dev/2018-June/123780.html

There is also an ongoing discussion about vector predication, which is
related but not depending on the scalable representation in IR:
https://reviews.llvm.org/D57504

And the corresponding RFC thread:
http://lists.llvm.org/pipermail/llvm-dev/2019-January/129791.html

cheers,
--renato