lyng/docs/pi_spigot_perf_baseline.md

Pi Spigot JVM Baseline

Saved on April 4, 2026 before the List<Int> indexed-access follow-up fix.

Benchmark target:

• examples/pi-bench.py
• examples/pi-bench.lyng

Execution path:

• Python: python3 examples/pi-bench.py
• Lyng JVM: ./gradlew :lyng:runJvm --args='/home/sergeych/dev/lyng/examples/pi-bench.lyng'
• Constraint: do not use Kotlin/Native lyng CLI for perf comparisons

Baseline measurements:

• Python full script: 167 ms
• Lyng JVM full script: 1.287097604 s
• Python warm function average over 5 runs: 126.126 ms
• Lyng JVM warm function average over 5 runs: about 1071.6 ms

Baseline ratio:

• Full script: about 7.7x slower on Lyng JVM
• Warm function only: about 8.5x slower on Lyng JVM

Primary finding at baseline:

• The hot reminders[j] accesses in piSpigot were still lowered through boxed object index ops and boxed arithmetic.
• Newly added GET_INDEX_INT and SET_INDEX_INT only reached pi, not reminders.
• Root cause: initializer element inference handled list literals, but not List.fill(boxes) { 2 }, so reminders did not become known List<Int> at compile time.

After Optimizations 1-4

Follow-up change:

• propagate inferred lambda return class into bytecode compilation
• infer List.fill(...) element type from the fill lambda
• lower reminders[j] reads and writes to GET_INDEX_INT and SET_INDEX_INT
• add primitive-backed ObjList storage for all-int lists
• lower List.fill(Int) { Int } to LIST_FILL_INT
• stop boxing the integer index inside GET_INDEX_INT / SET_INDEX_INT

Verification:

• piSpigot disassembly now contains typed ops for reminders, for example:
  • GET_INDEX_INT s5(reminders), s10(j), ...
  • SET_INDEX_INT s5(reminders), s10(j), ...

Post-change measurements using jlyng:

• Full script: 655.819559 ms
• Warm 5-run total: 1.430945810 s
• Warm average per run: about 286.2 ms

Observed improvement vs baseline:

• Full script: about 1.96x faster (1.287 s -> 0.656 s)
• Warm function: about 3.74x faster (1071.6 ms -> 286.2 ms)

Residual gap vs Python baseline:

• Full script: Lyng JVM is still about 3.9x slower than Python (655.8 ms vs 167 ms)
• Warm function: Lyng JVM is still about 2.3x slower than Python (286.2 ms vs 126.126 ms)

Current benchmark-test snapshot (n=200, JVM test harness):

• optimized-int-division-rval-off: 135 ms
• optimized-int-division-rval-on: 125 ms
• piSpigot bytecode now contains:
  • LIST_FILL_INT for both pi and reminders
  • GET_INDEX_INT / SET_INDEX_INT for the hot indexed loop