[LLVMdev] fmac generation for cortex-a9

[JF Bastien]

cat /proc/cpuinfo ?

Are you sure it's generating VFMA and not VMLA?


On Fri, Nov 9, 2012 at 9:35 AM, Sebastien DELDON-GNB <
sebastien.deldon at st.com> wrote:

> Hi Renato,
>
> It's definitively not A15. Can this be the case that NEON units for
> cortex-A9 support it but isn't documented/recommended ?
> And as mentioned before code is working !
>
> Seb
>
>
> > -----Original Message-----
> > From: rengolin at gmail.com [mailto:rengolin at gmail.com] On Behalf Of
> > Renato Golin
> > Sent: Friday, November 09, 2012 6:27 PM
> > To: Sebastien DELDON-GNB
> > Cc: JF Bastien; llvmdev at cs.uiuc.edu
> > Subject: Re: [LLVMdev] fmac generation for cortex-a9
> >
> > Hi Sebastien,
> >
> > ARMv7-M has VFMA and LLVM's "triple" is far from perfect.
> >
> > Wikipedia tells me NovaThor can also be A15, or STE could have cramped a
> > VFPv4 in it? ;) Or possibly, your code never branches into the VFMA.
> > Many things could be happening, but usually, VFMA shouldn't be generated
> > for A9.
> >
> > A GCC bug, maybe?
> >
> >
> > On 9 November 2012 16:51, Sebastien DELDON-GNB
> > <sebastien.deldon at st.com> wrote:
> > > Hi Bastien,
> > >
> > >
> > >
> > > Weird gcc is generating fma for my platform STEricsson Novathor with
> > > Linaro, code works. It also works when I use LLVM to generate fma
> > > (using llc -mtriple=armv7-eabi). Maybe someone from ARM can answer
> > the question ?
> > >
> > >
> > >
> > > Seb
> > >
> > >
> > >
> > > From: JF Bastien [mailto:jfb at google.com]
> > > Sent: Friday, November 09, 2012 5:36 PM
> > > To: Sebastien DELDON-GNB
> > > Cc: Anitha Boyapati; llvmdev at cs.uiuc.edu
> > >
> > >
> > > Subject: Re: [LLVMdev] fmac generation for cortex-a9
> > >
> > >
> > >
> > > AFAIK A9 doesn't have VFPv4 or AdvSIMDv2, so it doesn't have VFMA. I
> > > don't know what LLVM does, but it shouldn't emit VFMA when you target
> > > A9. VMLA isn't a fused multiply-add, it's a multiply followed by an
> > > add and has different latency as well as precision.
> > >
> > >
> > >
> > > On Thu, Nov 8, 2012 at 4:57 AM, Sebastien DELDON-GNB
> > > <sebastien.deldon at st.com> wrote:
> > >
> > > Hi Anitha,
> > >
> > > Thanks for your answer but -mcpu=cortex-a9 -mattr=+vfp4 doesn' t
> > > enable fused mac generation for me.
> > > I would like just to understand why -mtriple=armv7-eabi enables it
> > > while
> > > -mcpu=cortex-a9 seems to disable it ?
> > >
> > > Seb
> > >
> > >
> > >> -----Original Message-----
> > >> From: Anitha Boyapati [mailto:anitha.boyapati at gmail.com]
> > >> Sent: Thursday, November 08, 2012 10:22 AM
> > >> To: Sebastien DELDON-GNB
> > >> Cc: llvmdev at cs.uiuc.edu
> > >> Subject: Re: [LLVMdev] fmac generation for cortex-a9
> > >>
> > >> On 8 November 2012 13:56, Sebastien DELDON-GNB
> > >> <sebastien.deldon at st.com> wrote:
> > >> > Hi all,
> > >> >
> > >> >
> > >> >
> > >> >
> > >> >
> > >> > I've a .ll code that use double precision fmul/fadd or fmul/fsub.
> > >> > When
> > >
> > >> > I compile it using llc -mcpu=cortex-a9 I couldn't get vmla/vmls
> > >> > generated even using -fp-contract=fast, but when I use option
> > >> > -mtriple=armv7-eabi instead of -mcpu=cortex-a9 fused mac are
> > >
> > >> generated. Can someone explain me why  ?
> > >> >
> > >>
> > >> Perhaps you need to use some attributes. -mattr=+vfp4 Check
> > >> fusedMAC.ll from ARM codegen tests.
> > >>
> > >>
> > >> --
> > >>  Anitha
> > >
> > > _______________________________________________
> > > LLVM Developers mailing list
> > > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> > >
> > >
> > >
> > >
> > > _______________________________________________
> > > LLVM Developers mailing list
> > > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> > >
> >
> >
> >
> > --
> > cheers,
> > --renato
> >
> > http://systemcall.org/
>
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