Hello Zoltan Borok-Nagy, Joe McDonnell, Csaba Ringhofer, Impala Public Jenkins,
I'd like you to reexamine a change. Please visit
http://gerrit.cloudera.org:8080/24997
to look at the new patch set (#11).
Change subject: IMPALA-11917: Codegen branch-free reads of nullable scalar slots
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IMPALA-11917: Codegen branch-free reads of nullable scalar slots
After the LLVM 22 upgrade, TPC-DS Q99's streaming aggregation was ~20%
slower than with LLVM 5. Its UpdateTuple compiled to 269 instructions
with 22 branches (LLVM 5: 84 instructions, 5 branches).
GetSlotRef wraps each slot read in a null-check diamond. Once several
reads of the same slots are inlined into a single function, LLVM 22
no longer merges these diamonds. Each read keeps its own branch and
conditional load, and the packed *Val is rebuilt via shifts and cmovs.
Replacing the phi with a select after the branch doesn't help, because
InstCombine converts a select back into a phi when a dominating branch
tests the same condition.
When the tuple is not nullable and the slot is a nullable simple scalar
(i.e. not string, timestamp, collection, struct or variant), GetSlotRef
now loads the slot unconditionally and selects on the null bit. This
is safe because the slot is always within the tuple's memory. With no
branch on the null bit, LLVM combines the null checks and CSEs the
loads across expressions, so UpdateTuple compiles to 88 instructions
with 6 branches. 09:AGGREGATE STREAMING in Q99 drops from 39-41ms to
32-33ms, matching LLVM 5.
Codegen for other types didn't change as they showed no improvement.
Testing:
- Q99 results on tpcds20_parquet match with codegen enabled and
disabled.
- Ran tests/query_test/test_tpcds_queries.py.
Change-Id: I6edaf90100cc3360a7c93d3218eb6956fcec24f0
Assisted-by: Claude Opus 5.5 (GitHub Copilot)
---
M be/src/codegen/codegen-anyval.cc
M be/src/codegen/codegen-anyval.h
M be/src/exprs/slot-ref.cc
M be/src/exprs/slot-ref.h
4 files changed, 90 insertions(+), 1 deletion(-)
git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/97/24997/11
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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I6edaf90100cc3360a7c93d3218eb6956fcec24f0
Gerrit-Change-Number: 24997
Gerrit-PatchSet: 11
Gerrit-Owner: Michael Smith <[email protected]>
Gerrit-Reviewer: Csaba Ringhofer <[email protected]>
Gerrit-Reviewer: Impala Public Jenkins <[email protected]>
Gerrit-Reviewer: Joe McDonnell <[email protected]>
Gerrit-Reviewer: Michael Smith <[email protected]>
Gerrit-Reviewer: Zoltan Borok-Nagy <[email protected]>
