polly parallel giving inconsistent results

[Rohan Rayan]

Hello All

I am running a simple matrix multiply program (see attached file).

I am getting inconsistent results when running it with clang and polly with and without parallelization.

With single core:

Command: ./llvm-project/build/bin/clang -O3 -mllvm -polly  matmul.c

Result: sum = 433588338688.000000

With parallelization:

Command: ../llvm-project/build/bin/clang -O3 -mllvm -polly -mllvm -polly-parallel -lgomp -mllvm -polly-num-threads=4 matmul.c

Result: sum = 315474345984.000000

[Siddharth Bhat]

Hello,

Thank you for the report. I've pushed a commit here  (https://reviews.llvm.org/D125202), which will take a couple of days to be reviewed. In the meantime,

I suggest running:

Command: ../llvm-project/build/bin/clang -O3 -mllvm --polly-pattern-matching-based-opts=false -mllvm -polly -mllvm -polly-parallel -lgomp -mllvm -polly-num-threads=4 matmul.c

Result: sum = 433588338688.000000

Best,

~Siddharth

[Rohan Rayan]

Thanks.

With the command you provided, the results match. Although the runtime performance for this particular application seems to degrade on parallelization.

~Rohan Rayan