[llvm-dev] Polly Vectorization very large speedup

[Michael Kruse via llvm-dev]

In addition to vectorization, Polly also applies memory optimizations
(such as tiling). Correlation is one of the benchmarks where this
works particularly well.

In doubt, compare the output of the benchmark with and without Polly
(-DPOLYBENCH_DUMP_ARRAYS). Note that there may be floating-point
rounding differences, you could try `fpcmp` from the llvm-test-suite.
-polly-vectorizer=polly is not particularly well-tested, so a
miscompilation could indeed be the reason.

Michael

Am Fr., 28. Mai 2021 um 06:14 Uhr schrieb hameeza ahmed <hahmed2305 at gmail.com>:
>
> Hello,
> I have run polybench correlation with following command on LLVM-12.0;
> /home/clang+llvm-12.0.0-x86_64-linux-gnu-ubuntu-16.04/bin/clang -O3 -mllvm -polly -mllvm -polly-vectorizer=polly -I ../../../../utilities -I ../../../../datamining/correlation ../../../../utilities/polybench.c ../../../../datamining/correlation/correlation.c -lm -DPOLYBENCH_TIME  -DEXTRALARGE_DATASET -o polly-O3-vector-extralarge
>
>
> I am getting execution time of 0.100884s with polly-vectorizer
> However with LLVM -O3 time is 85.083153s
> polly vectorizer gives a speedup of 843.37x which is unbelievable.
> Why is that so? Am I running wrong command?
>
> Please guide.
>
> Thank You
> Regards
>
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