Mryange opened a new pull request, #69296:
URL: https://github.com/apache/doris/pull/69296
### What problem does this PR solve?
Issue Number: N/A
Problem Summary:
Nereids translates simple CASE expressions into searched CASE, materializing
a separate equality result for each WHEN key. Preserve eligible expressions as
simple CASE behind `enable_experimental_simple_case` (disabled by default),
evaluate the common input once, and compare it directly with literal keys in BE.
Support integer, DecimalV3 and string inputs with up to 256 non-NULL literal
keys. Preserve first-match semantics and Doris's batch-level THEN skipping.
Short-circuit evaluation and unsupported expression shapes retain searched
CASE. Use a simple ColumnView matching loop that allows automatic vectorization
without new row selectors.
Enable the experimental setting only after all BEs have been upgraded: older
BEs do not support this expression layout.
### Release note
Add an opt-in simple CASE execution path through
`enable_experimental_simple_case`; it is disabled by default and applies only
when short-circuit evaluation is disabled.
### Check List (For Author)
- Test
- [x] Regression test
- [ ] Unit Test
- [x] Manual test (details below)
- [ ] No need to test or manual test.
BE and FE builds, output generation and a normal rerun of
`test_simple_case_decimal_input` passed before the final matching-loop
simplification. The generated output contains 272 blocks: 68 cases match across
four setting combinations; 132 EXPLAIN checks verify optimized and fallback
paths. Added FE/BE unit tests have not been executed, including the new 257-row
boundary case.
For the final loop, a diagnostic compilation of the actual source with
Clang 20, AVX2 and `-O3 -DNDEBUG` succeeded. Compiler reports confirm SIMD
matching loops for integers and Decimal32/64/128, but not Decimal256 or
strings. This is not a full BE rebuild or a runtime performance measurement;
the final loop has not been rerun through the regression suite. Formatting,
build hygiene and targeted clang-tidy checks passed.
- Behavior changed:
- [ ] No.
- [x] Yes. Eligible CASE expressions use the new BE path only when
explicitly enabled; default behavior is unchanged.
- Does this need documentation?
- [x] No. Experimental setting, disabled by default.
- [ ] Yes.
### Check List (For Reviewer who merge this PR)
- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
- [ ] Add branch pick label
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