AOT: split user-script builds into cached runtime TU + script TU — ~50% of every phpc build re-lowers identical JitHelpers (lib/Runtime.php)

[PurHur]

Category

performance · AOT compile pipeline

Problem

Every phpc build recompiles the fixed runtime helper set from scratch. Phase profile of phpc build -o /tmp/hello examples/000-HelloWorld/example.php (php-compiler:22.04-dev, LLVM 9, breadcrumb polling via PHP_COMPILER_JIT_PROGRESS_FILE, 2026-07-04, wall 2.66 s):

Phase	Wall	Share
PHP boot + autoload + JIT context init	0.66 s	25%
user-script parse + lower	0.06 s	2%
runtime JitHelper lowering (WeakRefRegistry, ErrorSilence, DirHandle, ParseStrNative, Progress, … — repeated runtime_parseandcompile_begin cycles)	1.24 s	47%
LLVM emit object	0.61 s	23%
link	0.14 s	5%

The helper set is identical for every user script — none of it depends on user code. Larger web examples pay 5.3 s (006) for the same reason.

Proposal (split compilation into parts)

1. Cache the runtime TU: lower all JitHelpers once into a versioned build/user-runtime.o (key: compiler tree hash + LLVM version), reuse across builds — the bootstrap path already has the TU-sidecar mechanics (PHP_COMPILER_M3_* emit-helper TUs, prelinked/bootstrap-gen0 blobs); user builds should get the same treatment.
2. Script TU: lower only {main} + user functions per build; link script.o + user-runtime.o + runtime C objects.
3. Optional: parallel emit when >1 TU is dirty.

Expected: hello-world ≈ 2.7 s → ≈ 0.9 s (boot + tiny lower/emit + link); web examples similar absolute savings.

Done when

• Second consecutive phpc build of a different script skips helper lowering (cache hit logged)
• Cache invalidates on compiler-tree change (hash key), verified by test
• examples/README benchmark bin/compile.php column drops accordingly
• benchmarks/README.md phpc-build column regenerated

[PurHur]

Scaffold landed as draft PR #16022 (default-off, PHP_COMPILER_HELPER_RUNTIME_O=1). Design pivots discovered on the way:

1. One superset module is not viable: cross-unit lowering produces signature drift (call-before-define materializes different types) → per-unit isolated subprocess emission, 96/137 units cached, Regression: user-script AOT builds broken for core string builtins — preg_match capture assign, explode CRLF, str_contains, substr negative length (bin/compile.php) #15642 crashers auto-skipped with fallback.
2. available_externally demotion crashes LLVM 9 emitToFile; the workable shape is: unit .o emitted as-is + per-script extern declarations synthesized from unit bitcode types + ld -z muldefs with the script object first.
3. Remaining blocker — init chains: every unit .o has its own __init__ (interned-constant setup); muldefs discards all but the script's, so cached helpers read uninitialized state (silent exit — Regression: strlen() on non-constant operand silently terminates AOT binaries — exit 0, output truncated; VM/JIT fine (root cause of #15624) #15632 symptom class). Required: emit-time rename of each unit init to a unique symbol + llvm.global_ctors registration, and idempotent helper-state init. That is the next work item.

Measured while the linking variant was live: hello 3.0→1.9 s, 006 project 5.3→2.2 s — consistent with the 47% profile, so the payoff stands once (3) lands.

[PurHur]

claim: PHP Runtime → PHP — starting this run (runtime TU cache + script TU split)