Hi, Are there any plans to integrate an autovectorizer for SPMD programs into LLVM? For example, there were previous discussions about integrating the whole function vectorizer (WFV) from Ralf Karrenberg into LLVM. Thanks, Zack -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150706/7acac468/attachment.html>
----- Original Message -----> From: "Zack Waters" <zswaters at gmail.com> > To: "llvmdev" <llvmdev at cs.uiuc.edu> > Sent: Monday, July 6, 2015 1:03:47 PM > Subject: [LLVMdev] SPMD Autovectorizer > > > > Hi, > > Are there any plans to integrate an autovectorizer for SPMD programs > into LLVM? For example, there were previous discussions about > integrating the whole function vectorizer (WFV) from Ralf Karrenberg > into LLVM. >I don't know of any concrete plans, but this is something I'd still like to see happen. If no one gets to it first, I may even work on it at some point. -Hal> > Thanks, > Zack > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >-- Hal Finkel Assistant Computational Scientist Leadership Computing Facility Argonne National Laboratory
On 07/06/2015 09:40 PM, Hal Finkel wrote:> I don't know of any concrete plans, but this is something I'd still > like to see happen. If no one gets to it first, I may even work on it > at some point.The pocl's kernel compiler's parallel region analysis could also provide for a starting point. It generates parallel loops out from the regions between barriers via static analysis which the vectorizers then vectorize/parallelize as they see fit for the target at hand (with assistance from the parallel loop annotations). The loops could even be converted (selectively) to OpenMP parallel loops for flexible parallelization when there are not too many work items and an SMP target has multiple cores, etc. The point is that the way those loops are mapped to hardware is up to other (target dependent) passes(*). However, the current upstream version is somewhat rusty with some known issues, and I'd like to try to find time after the summer to clean up an experimental private version and push it to pocl master. Maybe that could serve as a basis for LLVM upstreaming? Previously I've assumed that this part of the pocl kernel compiler could not be easily upstreamed to LLVM as it's not needed for C/C++ (and someone said other languages such as OpenCL C are very low priority), but if there's interest, I'd be happy to get that part upstreamed as well. (*) http://link.springer.com/article/10.1007/s10766-014-0320-y BR, -- --Pekka
On 6 July 2015 at 19:03, Zack Waters <zswaters at gmail.com> wrote:> Are there any plans to integrate an autovectorizer for SPMD programs into > LLVM? For example, there were previous discussions about integrating the > whole function vectorizer (WFV) from Ralf Karrenberg into LLVM.Wouldn't OpenMP account for some of that? At least on a single machine, could you have both parallel and simd optimisations done on the same loop? For MPI solutions, I believe just vectorising the code per architecture would achieve a similar goal. What other points could be relevant, here? cheers, --renato
On 07/07/2015 01:32 PM, Renato Golin wrote:> Wouldn't OpenMP account for some of that? At least on a single > machine, could you have both parallel and simd optimisations done on > the same loop?The point in SPMD program description (e.g. CUDA or OpenCL C) autovectorization is to produce something like OpenMP parallel loops or SIMD pragmas automatically from the single thread/WI description, adhering to its barrier synchronization semantics etc. That is, the output of this pass could be also converted to OpenMP SIMD constructs, if wanted. In pocl's case the output is simply a new kernel function (we call "work group function") that executes all WIs using parallel loops (which can be autovectorized more easily, or even multithreaded if seeing fit, or both). -- --Pekka