JIT: spl_autoload_register compile-time lowering (#1369 phase 2)

[PurHur]

Problem

#1369 closed with VM spl_autoload_register() on master. Capability matrix and docs/stdlib-jit-audit.md still mark JIT as no — project builds that rely on PSR-4 at runtime cannot use phpc serve --jit or JIT compliance for autoloaded classes.

#1762 (dynamic require / manifest PSR-4 at AOT build time) is orthogonal: this issue is JIT lowering when autoload callbacks run during JIT execution.

Goal

spl_autoload_register callbacks compile under LLVM 9 the same way other ext/standard/ builtins do, for the MiniWebApp / self-host subset:

1. Register callback list in VM hashtable (already works)
2. JIT TYPE_CALL into autoload callbacks for known class names (static string FQCN v1)
3. Document dynamic class names as VM-only in docs/capabilities.md

Implementation hints

Layer	Files	Notes
Builtin	ext/standard/spl_autoload_register.php	VM entry exists
JIT stub	lib/JIT/Builtin/	Add or extend autoload invoke path
Class load	lib/VM.php, lib/Runtime.php	Mirror VM autoload trigger before JIT
Lint	lib/Lint/UnsupportedRegistry.php	Remove JIT deferral when green
Tests	test/unit/SplAutoloadRegisterBuiltinTest.php	Extend with @group llvm execute

Unblock order

#1369 VM ✅ → this issue (JIT) → #1770 project includes → #207 serve --jit

Acceptance criteria

./script/ci-local.sh --filter SplAutoloadRegister
# JIT path (when LLVM ready):
docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  vendor/bin/phpunit --group llvm --filter SplAutoloadRegister

• docs/capabilities.md row: spl_autoload_register JIT = yes (or documented subset)
• No regression in VM compliance tests from Stdlib: spl_autoload_register() VM (closes #1369) #1405

Verification (local / Docker only)

No GitHub Actions (#394 ✅). Use ./script/docker-ci-local.sh on harness hosts.

Dependencies

• Stdlib: spl_autoload_register() — VM + LLVM JIT/AOT #1369 ✅ VM
• AOT: Dynamic require/include discovery for project build (phase 2 of #154) #1762 — AOT manifest autoload (parallel)
• JIT: Project include lowering for 003-MiniWebApp (phpc serve --jit blocked on #475) #1770, Language: JIT include/require compile-time lowering (#54 follow-up) #475 — project JIT graph
• Roadmap wave 3: full PHP language + stdlib gaps tracker (#1354–#1379) #1380 / Wave 3 close-out: land remaining language + debug_backtrace (#1380 finish line) #1751 — wave 3 stdlib audit sync

Links

• ROADMAP 🗺️ ROADMAP: Compile a small PHP web application (living document) #78 Phase 2 Stdlib
• docs/stdlib-jit-audit.md
• Self-host Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492, M2 spine growth: batch tracker (compiler_lib_spine_smoke → full inventory) #1419 (spine may include spl_autoload_register.php)

[PurHur]

File map (batch 107 expansion)

Existing JIT scaffolding — extend rather than rewrite:

File	Action
lib/JIT/SplAutoloadCallbackPolicy.php	Document supported callback forms; align with VM #1369 ✅
lib/JIT/Builtin/SplAutoloadOutput.php	Wire __phpc_spl_autoload_dispatch into call lowering
lib/JIT.php	On class-not-found before fatal, invoke autoload dispatch (mirror VM path)
ext/standard/spl_autoload_register.php	VM reference — no behavior change
test/unit/SplAutoloadRegisterBuiltinTest.php	Add @group llvm execute when class name is static string

Unblock chain: this issue → #1770 project includes → #587 JIT project test → #1869/#730 gate defaults.

Audit sync: after green, run php script/capability-matrix.php and php script/stdlib-jit-audit.php (or doc-only row in docs/capabilities.md).

./script/ci-local.sh --filter SplAutoloadRegister