[cfe-dev] Clang and llvm IR - Generate FMA

[Anitha Boyapati]

<ping>

On 7 November 2012 21:54, David Blaikie <dblaikie at gmail.com> wrote:

> Adding Lang Hames who implemented fpcontract in LLVM and Clang & might
> know what's going on here.
>
> On Wed, Nov 7, 2012 at 12:08 AM, Anitha Boyapati
> <anitha.boyapati at gmail.com> wrote:
> > Hi,
> >
> > I am trying to generate FMA for X86 target ("bdver2") through
> > -ffp-contract=fast. [Sanity checks: bdver2 supports fma]
> >
> > While I am able to generate FMA for  "C" input, I could not when LLVM IR
> is
> > input. Example illustrated below:
> >
> > #input - C file
> > float test(float a, float b, float c) {
> >         return a*b+c;
> > }
> > The below arguments work fine -
> >
> > $clang -march=bdver2 -mfma -ffp-contract=fast -S test.c
> >
> > However, when I input the below llvm assembly(pasted at the end), clang
> (not
> > llc) fails to generate FMA. Any idea why and how I will be able to do
> that
> > through clang?
> >
> > $ clang -march=bdver2 -ffp-contract=fast -mfma -S test.ll -O3
> > $ more test.s
> >
> > test:                                   # @test
> >         .cfi_startproc
> > # BB#0:                                 # %entry
> >         vmulss  %xmm1, %xmm0, %xmm0
> >         vaddss  %xmm2, %xmm0, %xmm0
> >         ret
> > .Ltmp0:
> >         .size   test, .Ltmp0-test
> >         .cfi_endproc
> >
> >
> >
> > ; ModuleID = 'test.c'
> > target datalayout =
> >
> "e-p:64:64:64-S128-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f16:16:16-f32:32:32-f64:64:64-f128:128:128-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
> > target triple = "x86_64-unknown-linux-gnu"
> > module asm "\09.ident\09\22GCC: (GNU) 4.7.2 LLVM: 3.2svn\22"
> > define float @test(float %a, float %b, float %c) nounwind uwtable
> readnone {
> > entry:
> >   %0 = fmul float %a, %b
> >   %1 = fadd float %0, %c
> >   ret float %1
> > }
> >
> > --
> >  Anitha
> >
> >
> > _______________________________________________
> > cfe-dev mailing list
> > cfe-dev at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
> >
>



-- 
* Anitha*
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