On 18 December 2013 12:31, Tim Northover <t.p.northover at gmail.com> wrote:> That's what I thought! But we do seem to generate vfma on Cortex-A9. > Wonder if that's a bug, or Cortex-A9 is "VFPv3, but chuck in vfma > too"? >Hi Tim, I believe that's the NEON VMLA, not the VFP one. There was a discussion in the past about not using NEON and VFP interchangeably due to IEEE assurances (which NEON doesn't have), but the performance gains are too big. I think the conclusion is to only use NEON instead of VFP (when they're semantically similar) when -unsafe-math is on. cheers, --renato -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20131218/0ca54323/attachment.html>
> I believe that's the NEON VMLA, not the VFP one.Turns out I was misreading the assembly. I wish "vmla" and "vfma" weren't so similar-looking. For Suyog that means the option "-ffp-contract=fast" is needed to get vfma when needed. Sorry about the bad information earlier. Cheers. Tim.
> "-ffp-contract=fast" is neededCorrect - clang is different than gcc, icc, msvc, xlc, etc. on this. Still haven't seen any explanation for how this is better though... http://llvm.org/bugs/show_bug.cgi?id=17188 http://llvm.org/bugs/show_bug.cgi?id=17211 On Wed, Dec 18, 2013 at 6:02 AM, Tim Northover <t.p.northover at gmail.com>wrote:> > I believe that's the NEON VMLA, not the VFP one. > > Turns out I was misreading the assembly. I wish "vmla" and "vfma" > weren't so similar-looking. > > For Suyog that means the option "-ffp-contract=fast" is needed to get > vfma when needed. Sorry about the bad information earlier. > > Cheers. > > Tim. > _______________________________________________ > 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/20131218/b6625009/attachment.html>