[PATCH] [LLVMdev] More FMA folding opportunities

[Owen Anderson]

> On Jan 9, 2015, at 11:19 PM, Hal Finkel <hfinkel at anl.gov> wrote:
> 
> ----- 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.

That would make a lot of sense to me.

—Owen

> -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
> 
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