php-in-php: JIT StringJsonEncode — route json_encode() through VmJson PHP not __compiler_json_encode_* LLVM (#1492)

[PurHur]

Category

php-in-php

Problem

json_encode() VM path already uses ext/standard/VmJson.php + VmJsonFormat.php, but JIT/AOT still lowers through ~540 lines of hand-written LLVM in lib/JIT/Builtin/StringJsonEncode.php (__compiler_json_encode_value, __compiler_json_encode_array). This duplicates UTF-8/NaN/Inf handling, enum/object encoding, and json_last_error() state that already exist in PHP — and drifts from VM behavior (see #9205 invalid UTF-8).

php-src reference

• ext/json/php_json.c — php_json_encode() / encoder error paths
• ext/json/php_json_encoder.c — value walk + UTF-8 validation

Repro (VM vs JIT divergence today)

<?php
$s = "\xC3\x28"; // invalid UTF-8
var_dump(json_encode($s));
var_dump(json_last_error(), json_last_error_msg());

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php repro.php'
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/jit.php repro.php'

Zend: false, JSON_ERROR_UTF8, message about malformed UTF-8.
VM today: replacement char + json_last_error() === 0 (#9205).
JIT: uses LLVM encoder — same or worse drift from VmJson.

Scope (this repo)

Area	Path	Action
Stdlib SSOT	ext/standard/VmJson.php, VmJsonFormat.php	Keep encoder semantics here
JIT bridge	new ext/standard/JitJsonEncode.php or extend existing	Call VM helpers from JIT like other migrated builtins
Delete/shrink	lib/JIT/Builtin/StringJsonEncode.php	Remove LLVM value walk; thin ABI trampoline only if unavoidable
Registry	lib/JIT/Builtin/Type.php	Stop registering __compiler_json_encode_* bodies
Tests	test/compliance/cases/ext/json_*.phpt	VM + JIT/AOT must agree

PHP-in-PHP rule: do not grow runtime/*.c for JSON encoding; port any missing edge cases into ext/standard/.

Done when (php-src-strict)

• JIT/AOT json_encode() calls the same PHP encoder path as VM (shared VmJson / helper), not LLVM hashtable walk
• lib/JIT/Builtin/StringJsonEncode.php deleted or reduced to a thin bridge (<50 lines) — cite lines removed in PR
• Stdlib: json_encode() invalid UTF-8 must return false + JSON_ERROR_UTF8 (ext/json/php_json.c) #9205 repro green on both VM and JIT after encoder unification
• Targeted PHPUnit/compliance guard for JIT json_encode parity
• docs/capabilities.md matrix unchanged or notes JIT PHPT green

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter JsonEncode'
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/jit.php test/repro/json_encode_utf8_invalid.php'

Links

• North star Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492
• UTF-8 error parity: Stdlib: json_encode() invalid UTF-8 must return false + JSON_ERROR_UTF8 (ext/json/php_json.c) #9205
• json_decode LLVM migration: php-in-php: JIT StringUnserialize — route unserialize() through VmUnserializeFormat PHP not __compiler_unserialize LLVM (#1492) #9163 (pair PR should share bridge pattern)

[PurHur]

claim: PHP Runtime → PHP — batch (issue #9267: StringJsonEncode LLVM → JsonEncodeJitHelper / VmJson PHP)

[PurHur]

Merged via #11484.

Verification: JsonEncodeRuntimeShrinkTest + StringJsonEncodeRuntimeStandaloneTest + JsonEncode filter (7 OK); VM/JIT json_encode repro match; spine sync + VM driver probe OK.

LLVM shrink: JIT embed StringJsonEncode.php 1030→155 LOC; LLVM monolith quarantined in StringJsonEncodeJit.php for standalone AOT only.