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

[Lang Hames]

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.

- Lang.


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*
>
>
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