[PATCH] [LLVMdev] More FMA folding opportunities

[Hal Finkel]

----- Original Message -----
> From: "Olivier H Sallenave" <ohsallen at us.ibm.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: llvm-commits at cs.uiuc.edu
> Sent: Friday, January 9, 2015 11:59:07 AM
> Subject: Re: [PATCH] [LLVMdev] More FMA folding opportunities
>  
> Hi Hal,
> 
> I am wondering if we should move the FP_EXTEND cases to the
> PPC-specific combiner:
> 
> (fadd (fpext (fmul x, y)), z) -> (fma (fpext x), (fpext y), z)
> 
> We know that for PPC the FPEXT nodes will be removed, but it'll
> likely not be the case for other architectures. For those, you end
> up with one FMADD rather than one FMUL and one FADD, but also have
> two FPEXT nodes rather than one. I would not expect this to take
> more cycles to run, but there's no way to systematically check that
> since the cost models are not necessarily accurate.
> 
> In the end, the "aggressive" flag only ensures that you can combine
> one FMUL node with many FADD nodes.
> 
> What do you think?

I think we already have too much code in the PPCISelLowering that could be in the target-independent combiner, appropriately guarded. We already have TLI hooks for isTruncateFree, isZExtFree, isFNegFree, isFAbsFree, and we could certainly add an isFPExtFree hook at well.

 -Hal

> 
> Olivier
> 
> Inactive hide details for Hal Finkel ---01/08/2015 08:36:56
> PM-------- Original Message ----- > From: "Hal Finkel"
> <hfinkel at anlHal Finkel ---01/08/2015 08:36:56 PM-------- Original
> Message ----- > From: "Hal Finkel" <hfinkel at anl.gov>
> 
> From: Hal Finkel <hfinkel at anl.gov>
> To: Owen Anderson <resistor at mac.com>
> Cc: Olivier H Sallenave/Watson/IBM at IBMUS, <llvm-commits at cs.uiuc.edu>
> Date: 01/08/2015 08:36 PM
> Subject: Re: [PATCH] [LLVMdev] More FMA folding opportunities
> 
> 
> 
> 
> ----- Original Message -----
> > From: "Hal Finkel" <hfinkel at anl.gov>
> > To: "Owen Anderson" <resistor at mac.com>
> > Cc: "Olivier H Sallenave" <ohsallen at us.ibm.com>,
> > llvm-commits at cs.uiuc.edu
> > Sent: Thursday, January 8, 2015 6:48:34 PM
> > Subject: Re: [PATCH] [LLVMdev] More FMA folding opportunities
> > 
> > ----- Original Message -----
> > > From: "Hal Finkel" <hfinkel at anl.gov>
> > > To: "Owen Anderson" <resistor at mac.com>
> > > Cc: "Olivier H Sallenave" <ohsallen at us.ibm.com>,
> > > llvm-commits at cs.uiuc.edu
> > > Sent: Thursday, January 8, 2015 6:19:14 PM
> > > Subject: Re: [PATCH] [LLVMdev] More FMA folding opportunities
> > > 
> > > ----- Original Message -----
> > > > From: "Owen Anderson" <resistor at mac.com>
> > > > To: "Hal Finkel" <hfinkel at anl.gov>
> > > > Cc: "Olivier H Sallenave" <ohsallen at us.ibm.com>,
> > > > llvm-commits at cs.uiuc.edu
> > > > Sent: Thursday, January 8, 2015 6:16:57 PM
> > > > Subject: Re: [PATCH] [LLVMdev] More FMA folding opportunities
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > On Jan 8, 2015, at 6:06 PM, Hal Finkel < hfinkel at anl.gov >
> > > > wrote:
> > > > 
> > > > Olivier, Aditya is right. You need to add the FP_EXTEND to the
> > > > operands of the resulting FMA as appropriate. Can you please
> > > > fix
> > > > that? We can also move those under the "aggressive" flag for
> > > > now.
> > > > 
> > > > 
> > > > Can you fix or revert this ASAP, please? The missing extends
> > > > are
> > > > breaking our branches pretty badly.
> > > 
> > > Yep, will do in a few minutes.
> > 
> > I moved the transformations behind the aggressive flag in r225485
> > --
> > that should unbreak your builds while I fix the extends.
> 
> FP_EXTEND nodes added as of r225492. Thanks for pointing this out!
> 
> -Hal
> 
> > 
> > -Hal
> > 
> > > 
> > > -Hal
> > > 
> > > > 
> > > > 
> > > > —Owen
> > > 
> > > --
> > > Hal Finkel
> > > Assistant Computational Scientist
> > > Leadership Computing Facility
> > > Argonne National Laboratory
> > > 
> > > _______________________________________________
> > > llvm-commits mailing list
> > > llvm-commits at cs.uiuc.edu
> > > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> > > 
> > 
> > --
> > Hal Finkel
> > Assistant Computational Scientist
> > Leadership Computing Facility
> > Argonne National Laboratory
> > 
> > _______________________________________________
> > llvm-commits mailing list
> > llvm-commits at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> > 
> 
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
> 
> 
> 

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