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

[Hal Finkel]

----- 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