Bikramjeet Vig created IMPALA-5980:
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Summary: Upgrade to LLVM 4 and migrate to NewGVN for improved
optimization perf
Key: IMPALA-5980
URL: https://issues.apache.org/jira/browse/IMPALA-5980
Project: IMPALA
Issue Type: Improvement
Components: Backend
Reporter: Bikramjeet Vig
As a part of IMPALA-5907 it was identified that the GVN optimization pass is
slow for large cases, specifically when huge expression trees are passed to it.
This slow GVN pass problem is a known issue
(https://groups.google.com/forum/#!msg/llvm-dev/ozsAceDmOuA/2O_QC6EiDgAJ) that
has motivated the llvm devs to develop a new GVN pass which is claimed to be
faster and is available in LLVM 4.
Therefore after upgrading to LLVM 4 we should try moving to the NewGVN pass and
figure out if it is helpful by doing a perf analysis.
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