Hi, Last week I wrote llvm-dev and presented data that shows how enabling the vectorizer on -Os can improve the performance of many workloads and that it has negligible effects on code size. I also added a command line switch to make it easier for people to benchmark the vectorizer using -Os directly from clang without changing LLVM. Has anyone done any benchmarks on -Os + vectorization ? Thanks, Nadav
On 14 June 2013 05:37, Nadav Rotem <nrotem at apple.com> wrote:> Last week I wrote llvm-dev and presented data that shows how enabling the > vectorizer on -Os can improve the performance of many workloads and that it > has negligible effects on code size. I also added a command line switch to > make it easier for people to benchmark the vectorizer using -Os directly > from clang without changing LLVM. Has anyone done any benchmarks on -Os + > vectorization ? >Hi Nadav, I haven't, sorry. I'll run some tests on my Chromebook and will let you know. cheers, --renato -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130614/8fc2ab6a/attachment.html>
Hi Nadav, No noticeable difference between "-Os" and "-Os -fvectorize" in code size or compilation times in my tests, and only minimal performance improvements (small enough to be ignored). cheers, --renato On 14 June 2013 09:29, Renato Golin <renato.golin at linaro.org> wrote:> On 14 June 2013 05:37, Nadav Rotem <nrotem at apple.com> wrote: > >> Last week I wrote llvm-dev and presented data that shows how enabling the >> vectorizer on -Os can improve the performance of many workloads and that it >> has negligible effects on code size. I also added a command line switch to >> make it easier for people to benchmark the vectorizer using -Os directly >> from clang without changing LLVM. Has anyone done any benchmarks on -Os + >> vectorization ? >> > > Hi Nadav, > > I haven't, sorry. I'll run some tests on my Chromebook and will let you > know. > > cheers, > --renato >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130614/73689b14/attachment.html>
Sorry for the delays here. I am running our benchmark suite and will have data in a day or so. On Jun 13, 2013 9:40 PM, "Nadav Rotem" <nrotem at apple.com> wrote:> Hi, > > Last week I wrote llvm-dev and presented data that shows how enabling the > vectorizer on -Os can improve the performance of many workloads and that it > has negligible effects on code size. I also added a command line switch to > make it easier for people to benchmark the vectorizer using -Os directly > from clang without changing LLVM. Has anyone done any benchmarks on -Os + > vectorization ? > > Thanks, > Nadav > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130614/8be8c8d5/attachment.html>
All I have to say is *wow*. The vectorizer performs *remarkably* better now than it did the last time I benchmarked it. I'm stunned. I measured -O2 and -Os, as well as -march=x86-64 and -march=corei7-avx. My hope with the latter two was to cover both worst-case and best-case in terms of the quality of the vector ISA available. First, binary size growth. This is measured on average across a reasonably wide selection of binaries including large servers, video codecs, image processing, etc. O2, x86-64: 1% larger w/ vectorizer O2, corei7-avx: 1.2% larger Os, x86-64: 0.1% larger Os, corei7-avx: < 0.1% larger This is incredibly impressive IMO. =] The performance numbers are also pretty good. There are a couple of minor regressions, only one significant one. That one happens to be open source: https://code.google.com/p/snappy/source/browse/trunk/snappy.cc this slows down -- the vectorizer vectorizes a cold loop, which then gets inlined and blocks subsequent inlining. (Many thanks to Ben Kramer for pointing out the cause so quickly for me.) But there are a lot of potential solutions to this problem: 1) vectorize after inlining -- this has some problems (code growth mostly) but we might be able to solve them. 2) mark the cold path as cold so the optimizer is aware of it (tested this, it seems to work, but i'm still experimenting) 3) rewrite this part of snappy to be fundamentally better (the code as it is doesn't make a lot of sense to me, but i'm not an expert on it and will need time to figure out the best way to solve the issue) I'm actually happy with any of the 3, although #2 isn't terribly satisfying. But even if that's the result, I can live with it. So essentially, I think you should turn the vectorizer on completely. What's left seem very much like small isolated issues. Thanks for driving this whole thing and giving me time to do some evaluation. I'm really thrilled by the result. -Chandler On Fri, Jun 14, 2013 at 11:53 AM, Chandler Carruth <chandlerc at google.com>wrote:> Sorry for the delays here. I am running our benchmark suite and will have > data in a day or so. > On Jun 13, 2013 9:40 PM, "Nadav Rotem" <nrotem at apple.com> wrote: > >> Hi, >> >> Last week I wrote llvm-dev and presented data that shows how enabling the >> vectorizer on -Os can improve the performance of many workloads and that it >> has negligible effects on code size. I also added a command line switch to >> make it easier for people to benchmark the vectorizer using -Os directly >> from clang without changing LLVM. Has anyone done any benchmarks on -Os + >> vectorization ? >> >> Thanks, >> Nadav >> _______________________________________________ >> LLVM Developers mailing list >> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu >> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >> >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130615/c736da73/attachment.html>
More data point for you: Intel's ICC turns on loop vectorizer at -O2 and -Os too. Cheers, David On Thu, Jun 13, 2013 at 9:37 PM, Nadav Rotem <nrotem at apple.com> wrote:> Hi, > > Last week I wrote llvm-dev and presented data that shows how enabling the vectorizer on -Os can improve the performance of many workloads and that it has negligible effects on code size. I also added a command line switch to make it easier for people to benchmark the vectorizer using -Os directly from clang without changing LLVM. Has anyone done any benchmarks on -Os + vectorization ? > > Thanks, > Nadav > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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