Daniel Becker created IMPALA-8726:
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Summary: Autovectorisation leads to worse performance in bit
unpacking
Key: IMPALA-8726
URL: https://issues.apache.org/jira/browse/IMPALA-8726
Project: IMPALA
Issue Type: Improvement
Reporter: Daniel Becker
Attachments: no_vector.png
The compiler (GCC 4.9.2) autovectorises bit unpacking for bit widths 1, 2, 4
and 8 (function BitPacking::UnpackValues), but this leads to actually worse
performance (see the attached graph). We should consider whether it is worth
disabling autovectorisation for bit unpacking, but future compiler versions may
do a better job.
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