David Greene via llvm-dev
2019-Mar-12 15:17 UTC
[llvm-dev] Scalable Vector Types in IR - Next Steps?
Graham Hunter <Graham.Hunter at arm.com> writes:> We (Arm) have had more off-line discussions with some members of the > community and they have expressed some reservations on adding scalable > vectors as a first class type. They have proposed an alternative to > enable support for C-level intrinsics and autovectorization for SVE.Can we get a summary of those discussions? What are the concerns? -David
Graham Hunter via llvm-dev
2019-Mar-13 13:57 UTC
[llvm-dev] Scalable Vector Types in IR - Next Steps?
Hi David,> On 12 Mar 2019, at 15:17, David Greene <dag at cray.com> wrote: > > Graham Hunter <Graham.Hunter at arm.com> writes: > >> We (Arm) have had more off-line discussions with some members of the >> community and they have expressed some reservations on adding scalable >> vectors as a first class type. They have proposed an alternative to >> enable support for C-level intrinsics and autovectorization for SVE. > > Can we get a summary of those discussions? What are the concerns? > > -DavidI did ask them to post their arguments on the list, but I guess they've been busy for the last month (or forgot about it). The basic argument was that they didn't believe the value gained from enabling VLA autovectorization was worth the added complexity in maintaining the codebase. They were open to changing their minds if we could demonstrate sufficient demand for the feature. -Graham
Renato Golin via llvm-dev
2019-Mar-13 14:29 UTC
[llvm-dev] Scalable Vector Types in IR - Next Steps?
On Wed, 13 Mar 2019 at 13:57, Graham Hunter <Graham.Hunter at arm.com> wrote:> I did ask them to post their arguments on the list, but I guess they've been busy for the last month (or forgot about it).Who is "them" and who will write up a proposal / RFC on the use of intrinsics for both lowering and vectorisation? It goes without saying that those discussions should have been had in the mailing list, not behind closed doors. Agreeing to implementations in private is asking to get bad reviews in public, as the SVE process has shown *over and over again*. I don't understand why, after so many problems for so many years, this is still the modus operandi...> The basic argument was that they didn't believe the value gained from enabling VLA autovectorization was worth the added complexity in maintaining the codebase. They were open to changing their minds if we could demonstrate sufficient demand for the feature.In that case, the current patches to change the IR should be abandoned, as well as reverting the previous change to the types, so that we don't carry any unnecessary code forward. The review you sent seems to be a mechanical change to include the intrinsics, but the target lowering change seems to be too small to actually be able to lower anything. Without context, it's hard to know what's going on. cheers, --renato