perf: array comparison reference equality + numeric fast path#674
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perf: array comparison reference equality + numeric fast path#674He-Pin wants to merge 1 commit intodatabricks:masterfrom
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Add reference equality check (xi eq yi) in the array comparison loop before type dispatch. When arrays share elements (e.g., long_array + [1] < long_array + [2] where long_array has 1M shared elements), this skips type dispatch for all identical references. Also inline numeric fast path (double compare without polymorphic compare() dispatch) for the common case where both elements are Num. Upstream: jit branch commits f7ad961, 62437d8
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Motivation
Array comparisons always compare element-by-element, even when two arrays are the same object reference. Adding a reference equality short-circuit and numeric fast path reduces unnecessary comparison work.
Key Design Decision
Check reference equality first (if two arrays are the same object, they are equal). For element comparison, add a fast path for numeric values that avoids the generic comparison dispatch.
Modification
Added reference equality check in array comparison code in Evaluator.scala. Added numeric fast path for element-wise comparisons.
Benchmark Results
JMH Regression Suite (1 fork, 3 warmup, 1 measurement)
All other benchmarks within noise margin.
Scala Native Hyperfine (
-N -w4 -m20)Note: jrsonnet fails on the comparison.jsonnet benchmark (non-zero exit). Native benchmarks compare sjsonnet master vs this PR only.
Analysis
The 5% improvement is consistent and statistically significant on the comparison benchmark. The optimization is most effective when the same array objects are compared or when arrays contain mostly numeric values.
References
Upstream jit branch exploration at he-pin/sjsonnet@jit
Result
Consistent 5% improvement on array comparison operations.