[LLVMdev] Testing the new CFL alias analysis

[Jiangning Liu]

Hi Hal,

I run on SPEC2000 on cortex-a57(AArch64), and got the following results,

(It is to measure run-time reduction, and negative is better performance)

spec.cpu2000.ref.183_equake 33.77%
spec.cpu2000.ref.179_art 13.44%
spec.cpu2000.ref.256_bzip2 7.80%
spec.cpu2000.ref.186_crafty 3.69%
spec.cpu2000.ref.175_vpr 2.96%
spec.cpu2000.ref.176_gcc 1.77%
spec.cpu2000.ref.252_eon 1.77%
spec.cpu2000.ref.254_gap 1.19%
spec.cpu2000.ref.197_parser 1.15%
spec.cpu2000.ref.253_perlbmk 1.11%
spec.cpu2000.ref.300_twolf -1.04%

So we can see almost all got worse performance.

The command line option I'm using is "-O3 -std=gnu89 -ffast-math
-fslp-vectorize -fvectorize -mcpu=cortex-a57 -mllvm -use-cfl-aa -mllvm
-use-cfl-aa-in-codegen"

I didn't try compile-time, and I think your test on POWER7 native build
should already meant something for other hosts. Also I don't have a good
benchmark suit for compile time testing. My past experiences showed both
llvm-test-suite (single/multiple) and spec benchmark are not good
benchmarks for compile time testing.

Thanks,
-Jiangning

2014-09-04 1:11 GMT+08:00 Hal Finkel <hfinkel at anl.gov>:

> Hello everyone,
>
> One of Google's summer interns, George Burgess IV, created an
> implementation of the CFL pointer-aliasing analysis algorithm, and this has
> now been added to LLVM trunk. Now we should determine whether it is
> worthwhile adding this to the default optimization pipeline. For ease of
> testing, I've added the command line option -use-cfl-aa which will cause
> the CFL analysis to be added to the optimization pipeline. This can be used
> with the opt program, and also via Clang by passing: -mllvm -use-cfl-aa.
>
> For the purpose of testing with those targets that make use of aliasing
> analysis during code generation, there is also a corresponding
> -use-cfl-aa-in-codegen option.
>
> Running the test suite on one of our IBM POWER7 systems (comparing -O3
> -mcpu=native to -O3 -mcpu=native -mllvm -use-cfl-aa -mllvm
> -use-cfl-aa-in-codegen [testing without use in code generation were
> essentially the same]), I see no significant compile-time changes, and the
> following performance results:
>   speedup:
>     MultiSource/Benchmarks/mafft/pairlocalalign: -11.5862% +/- 5.9257%
>
>   slowdown:
>     MultiSource/Benchmarks/FreeBench/neural/neural: 158.679% +/- 22.3212%
>     MultiSource/Benchmarks/MiBench/consumer-typeset/consumer-typeset:
> 0.627176% +/- 0.290698%
>     MultiSource/Benchmarks/Ptrdist/ks/ks: 57.5457% +/- 21.8869%
>
> I ran the test suite 20 times in each configuration, using make -j48 each
> time, so I'll only pick up large changes. I've not yet investigated the
> cause of the slowdowns (or the speedup), and I really need people to try
> this on x86, ARM, etc. I appears, however, the better aliasing analysis
> results might have some negative unintended consequences, and we'll need to
> look at those closely.
>
> Please let me know how this fares on your systems!
>
> Thanks again,
> Hal
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
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