[RFC] FP contract = on

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[RFC] FP contract = on

Tom Stellard via cfe-dev
Hey folks,

Some progress has been made since the first thread:

http://lists.llvm.org/pipermail/llvm-dev/2017-March/111129.html

And also I think the consensus is to enable "-ffp-contract=on" by
default (instead of "fast"), which seems to be working on some
preliminary tests I made.

I just ran the test-suite on x86_64 and AArch64. The former is ok, the
latter still has some failures:

MultiSource/Applications/oggenc/oggenc
MultiSource/Benchmarks/MiBench/telecomm-FFT/telecomm-fft
MultiSource/Benchmarks/VersaBench/beamformer/beamformer

SingleSource/Benchmarks/Linpack/linpack-pc
SingleSource/Benchmarks/Misc-C++/Large/sphereflake
SingleSource/Benchmarks/Polybench/datamining
SingleSource/Benchmarks/Polybench/linear-algebra
SingleSource/Benchmarks/Polybench/stencils

Sebastian, how's the progress to get those benchmarks contract-friendly?

We mainly need to make sure that the difference in precision is *just*
because the contraction, not something else, and hopefully reduce them
below e10-4 with some tricks, to avoid surprises.

cheers,
--renato
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Re: [llvm-dev] [RFC] FP contract = on

Tom Stellard via cfe-dev
Hi Renato,

On Thu, Apr 20, 2017 at 8:29 AM, Renato Golin via llvm-dev
<[hidden email]> wrote:
> Sebastian, how's the progress to get those benchmarks contract-friendly?
>
> MultiSource/Benchmarks/MiBench/telecomm-FFT/telecomm-fft
> MultiSource/Benchmarks/VersaBench/beamformer/beamformer

I thought that these two were already solved by these patches:
https://reviews.llvm.org/D25923  - beamformer
https://reviews.llvm.org/D25924  - telecomm-fft

> SingleSource/Benchmarks/Polybench/datamining
> SingleSource/Benchmarks/Polybench/linear-algebra
> SingleSource/Benchmarks/Polybench/stencils

These 3 should have been fixed by this patch:
https://reviews.llvm.org/D25346

> MultiSource/Applications/oggenc/oggenc
> SingleSource/Benchmarks/Linpack/linpack-pc
> SingleSource/Benchmarks/Misc-C++/Large/sphereflake

These are harder to modify to make them pass with contract on and off.
I recommend adding CFLAGS += "-ffp-contract=off"

Sebastian
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Re: [llvm-dev] [RFC] FP contract = on

Tom Stellard via cfe-dev
On Thu, Apr 20, 2017 at 10:33 AM, Sebastian Pop <[hidden email]> wrote:

> Hi Renato,
>
> On Thu, Apr 20, 2017 at 8:29 AM, Renato Golin via llvm-dev
> <[hidden email]> wrote:
>> Sebastian, how's the progress to get those benchmarks contract-friendly?
>>
>> MultiSource/Benchmarks/MiBench/telecomm-FFT/telecomm-fft
>> MultiSource/Benchmarks/VersaBench/beamformer/beamformer
>
> I thought that these two were already solved by these patches:
> https://reviews.llvm.org/D25923  - beamformer
> https://reviews.llvm.org/D25924  - telecomm-fft

I just had a look at these patches, and I see that they have
CFLAGS += -DFP_ABSTOLERANCE=1e-5
the tests were passing on AArch64 with that tolerance when I tested
them back in October 2016.
Renato, could you please try to see if they pass with a tolerance of 1e-4?
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Re: [llvm-dev] [RFC] FP contract = on

Tom Stellard via cfe-dev
On 20 April 2017 at 16:43, Sebastian Pop <[hidden email]> wrote:
> I just had a look at these patches, and I see that they have
> CFLAGS += -DFP_ABSTOLERANCE=1e-5
> the tests were passing on AArch64 with that tolerance when I tested
> them back in October 2016.
> Renato, could you please try to see if they pass with a tolerance of 1e-4?

Hi Sebastian,

1e-4 makes no difference. :(

I'll have to dig this one deeper.

cheers,
--renato
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