[LLVMdev] fmac generation for cortex-a9

[JF Bastien]

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
>
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