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
Finkel, Hal J. via llvm-dev
2019-Mar-13 15:27 UTC
[llvm-dev] Scalable Vector Types in IR - Next Steps?
On 3/13/19 9:29 AM, Renato Golin wrote:> 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.Renato, I understand your frustration, but I don't want an unproductive conclusion to be drawn. We should encourage our community members to talk to each other both on the mailing list and off the mailing list. We have in-person discussions at the developers' meetings, and my experience is that sitting in a room with someone, or sometimes talking with someone over the phone, can really help reach a mutual understanding more effectively than mailing-list communication. However, the critical step is that the outcome of that conversation should be summarized, in a timely manner, for the mailing list (or put in the relevant code review, bug report, etc.) so that the rest of us can provide input.> Agreeing to implementations > in private is asking to get bad reviews in public+1 -Hal> , 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-- Hal Finkel Lead, Compiler Technology and Programming Languages Leadership Computing Facility Argonne National Laboratory
Renato Golin via llvm-dev
2019-Mar-13 15:55 UTC
[llvm-dev] Scalable Vector Types in IR - Next Steps?
On Wed, 13 Mar 2019 at 15:27, Finkel, Hal J. <hfinkel at anl.gov> wrote:> However, > the critical step is that the outcome of that conversation should be > summarized, in a timely manner, for the mailing list (or put in the > relevant code review, bug report, etc.) so that the rest of us can > provide input.That was my point. Discussing personally on the dev meetings is essential, but without follow through, the people on the meeting will be following a different path than the rest of the community. Right now, whatever conclusions were drawn at that meeting are still "behind closed doors", which pushed me and David to continue reviewing patches that were essentially dead and have parallel discussions that were not only moot, but counter-productive. --renato
Graham Hunter via llvm-dev
2019-Mar-13 16:04 UTC
[llvm-dev] Scalable Vector Types in IR - Next Steps?
Hi Renato,> It goes without saying that those discussions should have been had in > the mailing list, not behind closed doors.I have encouraged people to respond on the list or the RFC many times, but I've not had much luck in getting people to post even if they approve of the idea.> Agreeing to implementations > in private is asking to get bad reviews in public, as the SVE process > has shown *over and over again*.There isn't an agreement on the implementation yet; I have posted two possibilities and am trying to get consensus on an approach from the community.>> 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.There's no consensus on supporting the opaque types either yet. Even if we do end up going down that route, it could be modified -- as I mentioned in my notes, I could introduce a single toplevel type to the IR if I stored additional data in it (making it effectively the same as the current VectorType, just opaque to existing optimization passes), and then would be able to lower directly to the existing scalable MVTs we have.> 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.The new patches are just meant to demonstrate the basics of the opaque type to see if there's greater consensus in exploring this approach instead of the VLA approach.> Without context, it's hard to know what's going on.The current state is just what you stated in your initial email in this chain; we have a solution that seems to work (in principal) for SVE, RVV, and SX-Aurora, but not enough people that care about VLA vectorization beyond those groups. Given the time constraints, Arm is being pushed to consider a plan B to get something working in time for early 2020. -Graham
Amara Emerson via llvm-dev
2019-Mar-13 18:45 UTC
[llvm-dev] Scalable Vector Types in IR - Next Steps?
Disclaimer: I’m only speaking for myself, not Apple. This is really disappointing. Resorting to multi-versioned fixed length vectorization isn’t a solution that’s competitive with the native VLA support, so it doesn’t look like a credible alternative suggestion (at least not without elaborating it on the mailing list). Without a practical alternative, it’s essentially saying “no” to a whole class of vector architectures of which SVE is only one. Amara> On Mar 13, 2019, at 9:04 AM, Graham Hunter via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > Hi Renato, > >> It goes without saying that those discussions should have been had in >> the mailing list, not behind closed doors. > > I have encouraged people to respond on the list or the RFC many times, > but I've not had much luck in getting people to post even if they > approve of the idea. > >> Agreeing to implementations >> in private is asking to get bad reviews in public, as the SVE process >> has shown *over and over again*. > > There isn't an agreement on the implementation yet; I have posted two > possibilities and am trying to get consensus on an approach from the > community. > >>> 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. > > There's no consensus on supporting the opaque types either yet. Even > if we do end up going down that route, it could be modified -- as I > mentioned in my notes, I could introduce a single toplevel type to > the IR if I stored additional data in it (making it effectively the > same as the current VectorType, just opaque to existing optimization > passes), and then would be able to lower directly to the existing > scalable MVTs we have. > > >> 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. > > The new patches are just meant to demonstrate the basics of the opaque > type to see if there's greater consensus in exploring this approach > instead of the VLA approach. > >> Without context, it's hard to know what's going on. > > The current state is just what you stated in your initial email in this > chain; we have a solution that seems to work (in principal) for SVE, RVV, > and SX-Aurora, but not enough people that care about VLA vectorization > beyond those groups. > > Given the time constraints, Arm is being pushed to consider a plan B to > get something working in time for early 2020. > > -Graham > > > > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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