Regression: AOT mb_substr() not lowered — compile fails; VM/JIT match Zend (ext/mbstring/mbstring.c)

[PurHur]

Category

bug · php-src-strict · AOT · pillar 4

Problem

mb_substr(\"abcdef\", 2, 2) is cd on Zend/VM/JIT, but AOT compile aborts with mb_substr() is not lowered for JIT/AOT in this compiler build (ext/mbstring/mb_substr.php call()).

Repro	Zend / VM / JIT (2026-08-02, 8f314121e)	AOT
echo mb_substr(\"abcdef\", 2, 2), PHP_EOL;	cd	compile fails (LogicException)

Note: JIT succeeds (likely VM-execute fallback); only standalone AOT requires the missing call() lowering.

php-src reference

• php/php-src ext/mbstring/mbstring.c — PHP_FUNCTION(mb_substr)
• php/php-src ext/mbstring/mbstring.stub.php — arity 4

PHP implementation target

• ext/mbstring/mb_substr.php + new/extend ext/mbstring/JitMb* / lib/JIT/Builtin/ — PHP-in-PHP lowering; do not grow runtime/*.c

Repro

./script/docker-exec.sh -- bash -lc '
cat > /tmp/aot_mb_substr.php <<'"'"'PHP'"'"'
<?php
echo mb_substr(\"abcdef\", 2, 2), PHP_EOL;
PHP
echo -n \"zend=\"; php /tmp/aot_mb_substr.php
echo -n \"vm=\"; php bin/vm.php /tmp/aot_mb_substr.php 2>/dev/null
echo -n \"jit=\"; php bin/jit.php /tmp/aot_mb_substr.php 2>/dev/null
php bin/compile.php -o /tmp/aot_mb_substr /tmp/aot_mb_substr.php && /tmp/aot_mb_substr
'

Done when

• AOT binary prints cd
• Prefer --repeat 10 on the built binary
• Compliance or test/repro/ / AOT fixture guard
• php-src-strict; no php-compiler-strict shortcut

[PurHur]

Maintainer gate snapshot (filed with this batch)

Recorded here because #10533 comments are disabled (>2500).

Gate	Status	Note
bootstrap-inventory --check	green	OK 6817/6817
release-readiness --json	red	user_release_ready: no
north-star5-verify --fast	red	step 4f-m — gen-0 manifest/driver mismatch (#8713)
VM driver execute probe	green
gen-0 functional smoke	green
gen-0 provenance	stale	2 lowering commits since driver build

Sibling issues this run: #27029 localeconv · #27030 serialize · #27031 http_build_query

[PurHur]

claim: PHP Compiler Ext — I/O & Crypto — starting this run

Gate snapshot (this workspace, 2026-08-02):

• bootstrap-inventory --check: green (OK 6819/6819)
• release-readiness --json: still running; prior maintainer note: user_release_ready: no / north-star5-fast 4f-m gen-0 mismatch (Self-host M5: bootstrap-inventory argv driver size floor — grow beyond 451KB stub #8713)
• Targeting AOT mb_substr() lowering (php-src-strict)

[PurHur]

Merged in #27042

Verification: AOT mb_substr("abcdef", 2, 2) → cd; full UTF-8/null/negative fixture matched Zend 10/10; AotTest mb_substr + peer mb_strcut green; inventory 6819/6819.