perf: inline numeric fast path in array comparison#693
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He-Pin wants to merge 1 commit intodatabricks:masterfrom
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perf: inline numeric fast path in array comparison#693He-Pin wants to merge 1 commit intodatabricks:masterfrom
He-Pin wants to merge 1 commit intodatabricks:masterfrom
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Inline Val.Num type check in the array comparison while loop to avoid polymorphic recursive compare() dispatch per element. For numeric array comparisons (e.g. 1M elements), this eliminates 1M recursive method calls with 5-branch pattern matching overhead. Uses asDouble (not raw extraction) to preserve NaN error behavior — std.log(-1) etc. can produce NaN in Val.Num, and asDouble correctly throws 'not a number', matching the official C++ jsonnet behavior. Uses java.lang.Double.compare() instead of compareTo() to avoid autoboxing overhead. Upstream: jit branch commit 62437d8
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Motivation
Array comparison in Jsonnet compares elements pairwise. When both elements are
Val.Num, the current code path goes through the generic comparison dispatch, adding virtual call and type-check overhead for the most common case.Key Design Decision
Add an inline fast path that directly compares
Val.Numvalues when both operands have the numeric type tag, avoiding the generic dispatch entirely.Modification
Val.Numtype check before generic comparison dispatchBenchmark Results
JMH (JVM, 3 iterations warmup + 3 measurement)
Analysis
The comparison2 benefit (-18.8%) is expected since that benchmark performs many array comparisons with numeric elements. This is a minimal-risk optimization (16 lines, zero semantic change) that adds a type check fast path.
References
Result
All 49 tests pass. All benchmarks positive, no regressions.