php-in-php: JIT StringJsonDecodeJit — route json_decode()/json_validate() through VmJson PHP not ~2.1k-line LLVM (#1492)

[PurHur]

Category

php-in-php — shrink json_decode LLVM duplicate (#9267 covers json_encode only)

Problem

json_encode() migration is tracked in #9267, but json_decode() / json_validate() still use StringJsonDecodeJit.php (~2,128 lines of hand-written LLVM implementing __compiler_json_decode / validation paths, mirroring phpc_json_decode.c).

VM paths already use PHP scanners in ext/json/ — JIT/AOT should call the same PHP helpers, not maintain a second parser in LLVM.

php-src reference

• php/php-src ext/json/php_json.c — php_json_decode(), php_json_decode_ex()
• php/php-src ext/json/php_json_parser.c

Repro

# VM (PHP scanner) works for basic decode:
./script/docker-exec.sh -- php bin/vm.php -r '
var_export(json_decode("{\"a\":1}", true));
'
# array ('a' => 1,)

# LLVM duplicate footprint:
wc -l lib/JIT/Builtin/StringJsonDecodeJit.php

# JIT must match VM after migration:
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/jit.php -r "
var_export(json_decode(\"{\\\"a\\\":1}\", true));
"'

# json_validate flags path (coordinate #8748 enum TypeError separately):
./script/docker-exec.sh -- php bin/vm.php -r '
var_export(json_validate("{}"));
var_export(json_validate("{"));
'

Scope (this repo)

Path	Work
ext/json/VmJson*.php	SSOT decode/validate
lib/JIT/Builtin/StringJsonDecodeJit.php	Replace with PHP bridge
lib/JIT/Builtin/StringJsonDecode.php	Wire bridge
ext/standard/json_validate.php	Share scanner with decode
Tests	Extend existing json compliance PHPTs for JIT path

Done when

• StringJsonDecodeJit.php shrinks to thin ABI (>80% line reduction target)
• VM + JIT/AOT agree on decode/validate repro matrix (objects, arrays, depth, invalid JSON → null/false)
• JSON_THROW_ON_ERROR behavior follows Stdlib: json_decode()/json_encode() with JSON_THROW_ON_ERROR must throw JsonException (ext/json/php_json.c) #9032 once landed (do not regress)
• ./script/ci-local.sh --filter JsonDecode green

Related

• php-in-php: JIT StringJsonEncode — route json_encode() through VmJson PHP not __compiler_json_encode_* LLVM (#1492) #9267 json_encode PHP-in-PHP migration
• Stdlib: json_decode()/json_encode() with JSON_THROW_ON_ERROR must throw JsonException (ext/json/php_json.c) #9032 JSON_THROW_ON_ERROR
• Stdlib: json_decode() — enum case json operand must TypeError (ext/json/php_json.c, php-src-strict) #8844 / Stdlib: json_validate() — enum case operand must TypeError (ext/json/php_json.c, php-src-strict) #8748 enum operand TypeErrors
• North star Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

claim: PHP Runtime → PHP — batch (#9359) — route json_decode/json_validate JIT through JsonDecodeJitHelper PHP (StringJsonDecode bridge, shrink StringJsonDecode.php LLVM delegation).

[PurHur]

Merged via #11918.

Verification:

• JsonDecodeRuntimeShrinkTest + StringJsonDecodeRuntimeStandaloneTest green
• Compliance: 17 tests (json_decode + json_last_error JIT/VM paths)
• VM/JIT repro: json_decode('{"a":1}', true) → array('a'=>1)
• make bootstrap-selfhost-vm-driver-execute-probe OK

JIT/normal modules now bridge __compiler_json_decode/validate/last_error* to JsonDecodeJitHelper PHP (VmJson SSOT). StringJsonDecodeJit LLVM (~2128 LOC) retained for standalone AOT only.