Stdlib: gc_collect_cycles() return count — counts non-cyclic dtor as collected (Zend/zend_gc.c)

[PurHur]

Category

stdlib · runtime · php-src-strict

Problem

gc_collect_cycles() must return the number of cyclic zvals collected in the GC run. Zend returns 0 when the only cleanup is a normal __destruct from refcount dropping to zero (no cycles). This compiler's CycleCollector::collect() returns 1 in that scenario.

php-src reference

• php/php-src Zend/zend_gc.c — gc_collect_cycles, gc_remove_from_buffer
• php/php-src ext/standard/info.c — PHP_FUNCTION(gc_collect_cycles)

Repro (verified 2026-06-19)

test/repro/maintainer_gap_architect_run/probe_gc_collect.php:

<?php
class C { public function __destruct() { echo "dtor\n"; } }
$a = new C();
unset($a);
echo gc_collect_cycles(), "\n";

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php test/repro/maintainer_gap_architect_run/probe_gc_collect.php
php bin/vm.php test/repro/maintainer_gap_architect_run/probe_gc_collect.php
'

Engine	Output
Zend PHP 8.x	dtor then 0
VM today	dtor then 1

Scope

• lib/VM/CycleCollector.php — return count semantics
• ext/standard/gc_collect_cycles.php — VM builtin return
• ext/standard/GcCollectCyclesJitHelper.php / JIT path — match VM count
• Compliance: test/compliance/cases/runtime/gc_collect_cycles_return.phpt

PHP-in-PHP: fix in CycleCollector PHP; shrink any duplicate counting in LLVM per #9269 / #10087.

Done when

• Repro prints 0 after dtor on VM (php-src-strict)
• True cyclic graph still returns positive count (see test/compliance/cases/runtime/gc_collect_cycles.phpt)
• ./script/ci-fast.sh --filter gc_collect_cycles green

Related

• Runtime: gc_collect_cycles() — run cyclic GC (Zend GC parity) #3113 GC baseline · php-in-php: JIT GcCollectCyclesRuntime — route gc_collect_cycles() through CycleCollector PHP not ~1.3k-line LLVM (#1492) #9269 / php-in-php: JIT GcCollectCyclesNative — shrink phpc_gc.c ABI after PHP CycleCollector owns GC (#1492) #10087 php-in-PHP GC shrink · Stdlib: gc_status() return shape — extra keys running/protected/full/buffer_size not in php-src (ext/standard/php_gc.c) #9970 gc_status shape · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

claim: PHP Runtime → PHP — batch (issues #10257, #10111)

[PurHur]

Merged via #10940.

Verification:

php bin/vm.php test/repro/maintainer_gap_architect_run/probe_gc_collect.php
# dtor then 0

php bin/vm.php test/compliance/cases/runtime/gc_collect_cycles_return.phpt
# dtor then 0

php bin/vm.php test/compliance/cases/runtime/gc_collect_cycles.phpt
# 2 (cyclic count unchanged)