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

[Anitha B Gollamudi]

On 15 November 2012 13:25, Lang Hames <lhames at gmail.com> wrote:
> Hi Anitha,
>
> Sorry about the delayed response. This was caused by -ffp-contract being
> implemented as a language option, which aren't parsed when compiling
> bitcode. I have made -ffp-contract a codegen option in r168027, which should
> fix your issue.
>

Thanks Lang! Just back-ported the patch to older revision(162999). It worked.

-Anitha

>
>
> On Tue, Nov 13, 2012 at 9:04 PM, Anitha Boyapati <anitha.boyapati at gmail.com>
> wrote:
>>
>> <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
>>
>



-- 
 Anitha