lyng/docs/perf_plan_jvm.md

JVM-only Performance Optimization Plan (Saved)

Date: 2025-11-10 22:14 (local)

This document captures the agreed next optimization steps so we can restore the plan later if needed.

Objectives

• Reduce overhead on the call/argument path.
• Extend and harden PIC performance (fields/methods/locals).
• Improve R-value fast paths and interpreter hot nodes (loops, ranges, lists).
• Make scope frame pooling thread-safe on JVM so it can be enabled by default later.
• Keep semantics correct and all JVM tests green.

Prioritized tasks (now)

1. Call/argument path: fewer allocs, tighter fast paths

• Extend small-arity zero-alloc path to 6–8 args; benchmark with CallMixedArityBenchmarkTest.
• Splat handling: fast-path single-list splats; benchmark with CallSplatBenchmarkTest.
• Arg builder micro-optimizations: capacity hints, avoid redundant copies, inline simple branches.
• Optional-chaining fast return (SKIP_ARGS_ON_NULL_RECEIVER) coverage audit, add A/B bench.

2. Scope frame pooling: per-thread safety on JVM

• Replace global deque with ThreadLocal pool on JVM (and Android) actuals.
• Keep frameId uniqueness and pool size cap.
• Verify with DeepPoolingStressJvmTest, CallPoolingBenchmarkTest, and spot benches.
• Do NOT flip default yet; keep SCOPE_POOL=false unless explicitly approved.

Next tasks (queued)

3. PICs: cheaper misses, broader hits

• Method PIC 2→3/4 entries (tiny LRU); validate with PicInvalidationJvmTest.
• Field PIC micro-fast path for read-then-write pairs.

4. Locals and slots

• Ensure EMIT_FAST_LOCAL_REFS coverage across compiler sites.
• Pre-size slots/nameToSlot when local counts are known; re-run LocalVarBenchmarkTest.

5. R-value fast path coverage

• Cover index reads on primitive lists, pure receivers, assignment RHS where safe.
• Add benches in ExpressionBenchmarkTest.

6. Collections & ranges

• Tight counted loop for (Int..Int) in for.
• Primitive-specialized ObjList ops (map, filter, sum, contains) under PRIMITIVE_FASTOPS.

7. Regex and string ops

• Cache compiled regex for string literals at compile time; tiny LRU for dynamic patterns under a new REGEX_CACHE flag.

8. JIT micro-tweaks

• Inline tiny helpers; prefer arrays for hot buffers; finalize hot classes where safe.

Validation matrix

• Always re-run: CallBenchmarkTest, CallMixedArityBenchmarkTest, PicBenchmarkTest, ExpressionBenchmarkTest, ArithmeticBenchmarkTest, CallPoolingBenchmarkTest, DeepPoolingStressJvmTest.
• Use 3× medians where comparing flags; keep :lynglib:jvmTest green.

Notes

• All risky changes remain flag-guarded and JVM-only where applicable.
• Documentation and perf tables updated after each cycle.