[PATCH] Fw: [LLVMdev] More FMA folding opportunities

[Olivier H Sallenave]

Hal,

You're right, I moved those heuristics in the target-independent combiner.

Thanks,
Olivier

(See attached file: patch-v3.diff)



From:	Hal Finkel <hfinkel at anl.gov>
To:	Olivier H Sallenave/Watson/IBM at IBMUS
Cc:	<llvm-commits at cs.uiuc.edu>
Date:	01/06/2015 06:52 PM
Subject:	Re: [PATCH] Fw: [LLVMdev] More FMA folding opportunities



----- Original Message -----
> From: "Olivier H Sallenave" <ohsallen at us.ibm.com>
> To: llvm-commits at cs.uiuc.edu
> Cc: "Hal Finkel" <hfinkel at anl.gov>
> Sent: Monday, January 5, 2015 9:51:22 AM
> Subject: Fw: [PATCH] Fw: [LLVMdev] More FMA folding opportunities
>
>
>
> Hi,
>
> Here's a more comprehensive patch also handling the fact that
> FP_EXTEND will later be removed for PPC. Accordingly, new patterns
> are implemented in the PPC-specific combiner:

Given that these are predicated on (TM.Options.UnsafeFPMath ||
TM.Options.AllowFPOpFusion == FPOpFusion::Fast), what makes them PPC
specific? Either of those two options allow us to compute the relevant
operations with extra precision, right?

 -Hal

>
> > Finally, specifically for the PPC target, we could ignore FP_EXTEND
> > in the patterns above as it will be removed by the Machine Common
> > Subexpression Elimination pass. For instance:
> >
> > fold (fadd (fpext (fmul x, y)), z) -> (fma x, y, z)
> > fold (fadd (fpext (fma x, y, (fmul u, v))), z) -> (fma x, y (fma u,
> > v, z))
>
> I also moved the tests in new files (fma-ext.ll, fma-assoc.ll) for
> more clarity.
>
> Thanks,
> Olivier
>
> (See attached file: patch-v2.diff)
>
>
>
> ----- Forwarded by Olivier H Sallenave/Watson/IBM on 01/05/2015 10:44
> AM -----
>
> From: Olivier H Sallenave/Watson/IBM
> To: llvm-commits at cs.uiuc.edu
> Cc: "Hal Finkel" <hfinkel at anl.gov>
> Date: 12/29/2014 05:09 PM
> Subject: [PATCH] Fw: [LLVMdev] More FMA folding opportunities
>
>
>
> Hi,
>
> Attached is a patch to support more FMA folding opportunities
> (especially for PPC) as discussed below.
>
> Thanks,
> Olivier
>
> (See attached file: patch.diff)
>
>
>
> ----- Forwarded by Olivier H Sallenave/Watson/IBM on 12/29/2014 04:56
> PM -----
>
> From: Hal Finkel <hfinkel at anl.gov>
> To: Olivier H Sallenave/Watson/IBM at IBMUS
> Cc: <llvmdev at cs.uiuc.edu>
> Date: 09/30/2014 08:08 PM
> Subject: Re: [LLVMdev] More FMA folding opportunities
>
>
>
>
> ----- Original Message -----
> > From: "Olivier H Sallenave" <ohsallen at us.ibm.com>
> > To: llvmdev at cs.uiuc.edu
> > Sent: Monday, September 29, 2014 3:34:51 PM
> > Subject: [LLVMdev] More FMA folding opportunities
> >
> > Hi,
> >
> > I think more opportunities might be added for FMA in the DAG
> > combiner, please tell me what you think. Right now, those cases are
> > implemented:
> >
> > fold (fadd (fmul x, y), z) -> (fma x, y, z)
> > fold (fadd x, (fmul y, z)) -> (fma y, z, x)
> >
> > When the TLI callback "enableAggressiveFMAFusion" returns true, we
> > might also support:
> >
> > fold (fadd (fma x, y, (fmul u, v)), z) -> (fma x, y (fma u, v, z))
> > fold (fadd x, (fma y, z, (fmul u, v)) -> (fma y, z (fma u, v, x))
> >
> > This kind of reassociation generates two FMA for (x^2 + y^2 + z).
>
> Yes, this all sounds reasonable.
>
> Thanks again,
> Hal

--
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory
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