Category

php-in-php | runtime

Problem

Cycle collection and shutdown __destruct ordering still live partly in lib/AOT/runtime/phpc_gc.c (~400+ lines). Zend implements this in Zend/zend_gc.c; this repo already has lib/VM/Gc.php and gc_collect_cycles() in ext/standard/, but AOT/JIT paths call C helpers for:

• deferred destructor invocation on cyclic graphs (Stdlib: gc_disable/gc_enable/gc_enabled/gc_collect_cycles — JIT/AOT (ext/standard + Zend/zend_gc.c) #4023, Language: User __destruct() — JIT/AOT invoke on object release (phase 2 of #3144) #4013)
• shutdown pass ordering vs refcount-zero immediate destruct

Self-host (#1492) requires compiled lib/ to run GC semantics without growing runtime/*.c.

php-src reference

• php/php-src Zend/zend_gc.c — gc_collect_cycles, gc_possible_root
• php/php-src Zend/zend_execute.c — shutdown destructor pass
• Existing compliance: test/compliance/cases/runtime/gc_collect_cycles.phpt

Repro (behavior gap today)

<?php
class Node {
    public ?Node $next = null;
    public function __destruct() { echo "dtor\n"; }
}
$a = new Node();
$b = new Node();
$a->next = $b;
$b->next = $a;
unset($a, $b);
gc_collect_cycles();
// Zend: prints dtor (possibly twice depending on cycle handling)

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php repro_gc_cycle_destruct.php
php bin/vm.php repro_gc_cycle_destruct.php
# Compare output; AOT-linked binary must match VM (no missing dtor)
'

Also audit symbols: nm lib/AOT/runtime/*.o | grep phpc_gc — any call from compiled PHP builtins should route through VM PHP helpers after migration.

Scope (PHP-in-PHP first)

Done when

• Repro destructor output matches Zend on VM and AOT-linked driver
• Measurable lines removed from lib/AOT/runtime/phpc_gc.c (target: delete file or <50 line ABI)
• ./script/ci-fast.sh --filter gc_collect_cycles green
• php script/bootstrap-inventory.php --check still green

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter gc_collect_cycles'
make bootstrap-selfhost-link

Related

• Stdlib: gc_disable/gc_enable/gc_enabled/gc_collect_cycles — JIT/AOT (ext/standard + Zend/zend_gc.c) #4023 GC JIT/AOT · php-in-php: WeakReference/WeakMap — delete phpc_weakref.c (~156 lines), GC weak refs in lib/VM #5303 WeakRef C deletion · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492 M5