php-in-php: drop always-on LibcExtern printf after NestedJIT module-local (#31606/#31682 shape)

[PurHur]

Category

php-in-php · runtime-shrink (#1492, peer #31606 / #31682 / #31655)

Problem

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

1. User-script printf() already routes through PHP (JitPrintf / __compiler_printf / printf_ — Stdlib: printf() — formatted output to stdout (ext/standard/formatted_print.c parity) #3681).
2. The only NestedJIT lookupFunction('printf') consumers are four internal emitters that can declare printf module-locally.

Symbol	NestedJIT lookupFunction consumers	Target
printf	JitHeader, JitSetcookie, JitSessionStorageKernel (Set-Cookie), ScriptExit::echoString	module-local ensureLibcPrintf

Path	Today	Target
User-script printf()	JitPrintf / __compiler_printf	unchanged
LibcExtern	always-on printf	drop row
NestedJIT header/cookie/echo	rely on always-on	ensureLibcPrintf then lookup

php-src reference

• php/php-src ext/standard/formatted_print.c — PHP_FUNCTION(printf) (user-script semantics stay in PHP)
• NestedJIT uses libc printf only as a thin stdout format trampoline (not user printf())

PHP implementation target

• ext/standard/JitHeader.php, JitSetcookie.php, JitSessionStorageKernel.php — module-local ensure
• lib/JIT/Builtin/ScriptExit.php — module-local ensure
• lib/JIT/LibcExtern.php — drop always-on 'printf' row
• test/unit/LibcExternDeadDeclsRuntimeShrinkTest.php (+ targeted shrink guards)

Repro / verify

./script/phpunit.sh --filter 'LibcExternDeadDeclsRuntimeShrinkTest|LibcNameCollisionRuntimeShrinkTest'
./script/docker-exec.sh -- bash -lc 'php bin/vm.php -r "printf(\"%s\\n\", \"ok\");"'
./script/docker-exec.sh -- bash -lc 'php bin/jit.php -r "printf(\"%s\\n\", \"ok\");"'

Done when

• LibcExtern has no 'printf' => row
• NestedJIT consumers declare printf module-locally before lookup
• User-script printf() still matches Zend via VM/JIT
• No new lib/AOT/runtime/*.c
• php-src-strict; no php-compiler-strict shortcut

Note

#10533 comments are locked (2500+); candidate recorded here instead of a tracker comment.

[PurHur]

claim: PHP Runtime → PHP — starting this run

Dropping always-on LibcExtern printf → NestedJIT module-local decls (user-script printf stays on JitPrintf / __compiler_printf). Branch: agent/runtime-php-printf-31706.

[PurHur]

Merged in #31708

Verification

• ./script/phpunit.sh --filter 'LibcExternDeadDeclsRuntimeShrinkTest|LibcNameCollisionRuntimeShrinkTest|PrintfBuiltinTest::testVm' → OK (20 tests, 191 assertions)
• VM / JIT printf("%s\n", "ok") → ok
• AOT native printf still RUN:139 on master (pre-existing; not introduced by this drop)

Shrink

• Dropped always-on printf from LibcExtern
• Module-local: LibcExtern::ensurePrintf() used by JitHeader, JitSetcookie, JitSessionStorageKernel, ScriptExit