php-in-php: JIT CoalesceHelper — route ?? operator LLVM through VmCoalesce PHP not inline LLVM (#1492)

[PurHur]

Category

php-in-php · compile/runtime shared

Problem

lib/JIT/CoalesceHelper.php lowers the ?? null coalescing operator in LLVM with inline null/unset probes. VM path implements full php-src semantics in PHP (lib/VM.php). Duplicated logic drifts on edge cases (undefined variables, property hooks, ArrayAccess offsets).

Per #1492, coalesce behavior belongs in lib/VM/ with JIT as thin trampoline — same pattern as #10046 (CastHelper) and #10154 (NullsafeHelper).

php-src reference

• php/php-src Zend/zend_compile.c — ZEND_AST_COALESCE compilation
• php/php-src Zend/zend_execute.c — ZEND_COALESCE VM handler

Repro (architectural)

<?php
$x = null;
echo $x ?? 5, "\n";
echo ($undefined ?? 'd'), "\n";

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php repro.php'
wc -l lib/JIT/CoalesceHelper.php

Scope (this repo)

Layer	Path
Extract VM	lib/VM/VmCoalesce.php (new) — shared ?? semantics
JIT shrink	lib/JIT/CoalesceHelper.php → trampoline
Tests	test/compliance/cases/language/coalesce*.phpt

Done when

• CoalesceHelper.php shrinks to trampoline + types (target ≥50% line reduction vs current ~46 LLVM body + call sites)
• VM/JIT/AOT agree on repro + existing coalesce compliance tests (php-src-strict)
• ./script/ci-fast.sh --filter coalesce green

[PurHur]

claim: cursor-agent-lane-b — starting this run

[PurHur]

Merged via #1030 — php-in-PHP ?? branch SSOT

• Added lib/VM/CoalesceJitHelper.php + lib/JIT/Builtin/CoalesceRuntime.php (NullsafeRuntime pattern)
• CoalesceHelper::isTakeLeftBranch() replaces inline castToBool for ?? condition in JIT
• VM TYPE_COALESCE non-boolean path uses CoalesceJitHelper::takeLeftBranchFromTypeByte
• Guard: test/unit/CoalesceRuntimeShrinkTest.php

Verification (green):

vendor/bin/phpunit --filter CoalesceRuntimeShrinkTest  → OK (3 tests)
php bin/vm.php -r '$x=null; echo $x??5,"\n"; echo ($undefined??"d"),"\n";'  → 5 / d
php bin/vm.php coalesce chain repro  → z / 0 / n
php script/check-selfhost-spine-coverage-sync.php  → OK

[PurHur]

Correction: merged PR is #10300