php-in-php: drop always-on LibcExtern snprintf after NestedJIT module-local (#32068 shape)

[PurHur]

Category

php-in-php · runtime-shrink (#1492, peer #32068 strlen / #31706 printf / #31997 strtod)

Problem

Always-on LibcExtern still registers libc snprintf(3) even though:

1. User-script sprintf() / printf() already live in PHP (JitPrintf / SprintfSnprintfRuntime / ext/standard formatted_print) — not an always-on libc row.
2. NestedJIT leaves (~38 files) call lookupFunction('snprintf') for compile-time C-string formatting (warnings, number_format, decbin/decoct/dechex, session, OB, Reflection) — they rely on the always-on row.
3. ensurePrintf() already exists after the printf drop (php-in-php: drop always-on LibcExtern printf after NestedJIT module-local (#31606/#31682 shape) #31706); snprintf is the sibling still in the always-on table. JitNlLanginfo already has a module-local ensureSnprintf that should fold into LibcExtern.

Path	Today	Target
User-script sprintf()/printf()	PHP helpers (JitPrintf / SprintfSnprintfRuntime)	unchanged
LibcExtern	always-on snprintf row	drop row
NestedJIT consumers	rely on always-on	LibcExtern::ensureSnprintf() before lookup
EMBED MCJIT	__phpc_host_snprintf always-on alias	unchanged (#98 / #21109 / #21124)

php-src reference

• Userland: php/php-src ext/standard/formatted_print.c — PHP_FUNCTION(sprintf) / printf
• php/php-src ext/standard/math.c — number_format / decoct / dechex / decbin string conversion

PHP implementation target

• lib/JIT/LibcExtern.php — drop 'snprintf' always-on row; add ensureSnprintf() (peer ensurePrintf php-in-php: drop always-on LibcExtern printf after NestedJIT module-local (#31606/#31682 shape) #31706)
• NestedJIT consumers call LibcExtern::ensureSnprintf() before lookupFunction('snprintf')
• ext/standard/JitNlLanginfo.php — fold local ensureSnprintf into LibcExtern::ensureSnprintf
• test/unit/LibcExternDeadDeclsRuntimeShrinkTest.php + shrink guard — assert row gone + consumer wiring

Repro

./script/phpunit.sh --filter LibcExternDeadDeclsRuntimeShrinkTest
./script/phpunit.sh --filter SnprintfRuntimeShrinkTest

Done when

• LibcExtern has no always-on 'snprintf' => row
• All NestedJIT lookupFunction('snprintf') sites call ensureSnprintf() first (or declare module-locally)
• LibcExternDeadDeclsRuntimeShrinkTest + shrink guard green
• php-src-strict; user-script sprintf()/printf() behavior unchanged
• __phpc_host_snprintf always-on alias remains for EMBED MCJIT

[PurHur]

claim: PHP Runtime → PHP — starting this run

Drop always-on LibcExtern snprintf after NestedJIT module-local ensureSnprintf (peer #32068 strlen / #31706 printf).

[PurHur]

Merged #32093

Verification

• ./script/phpunit.sh --filter 'LibcExternDeadDeclsRuntimeShrinkTest|SnprintfRuntimeShrinkTest|LibcExternMathRuntimeShrinkTest' → OK 34 tests, 624 assertions
• VM smoke: decoct(10) / dechex(255) / sprintf("%d", 42) → 12 / ff / 42

C surface: dropped always-on LibcExtern snprintf row; deleted local JitNlLanginfo::ensureSnprintf / JitDate::ensureSnprintf. NestedJIT leaves call LibcExtern::ensureSnprintf(). User-script sprintf/printf unchanged (JitPrintf / SprintfSnprintfRuntime). EMBED MCJIT keeps __phpc_host_snprintf.