JIT Stdlib: implode, explode, and str_replace for templates and routing

[PurHur]

Problem

Several high-frequency string/array builtins throw at JIT compile time:

• ext/standard/implode.php — implode() is not implemented for JIT
• ext/standard/explode.php — explode() is not implemented for JIT
• ext/standard/str_replace.php — str_replace() is not implemented for JIT

VM mode already runs these (compliance/real tests exist for many stdlib functions). AOT/JIT web apps that build HTML from arrays or split paths cannot compile until these are lowered.

Goal

Implement LLVM lowering (or VM fallback shim) for implode, explode, and str_replace with parity to VM semantics for the common web subset.

Tasks

• Audit VM implementations in ext/standard/ for each function
• Add JitImplode, JitExplode, JitStrReplace helpers mirroring existing patterns (JitStrpos, JitStrPad)
• Support glue/separator as string; reject unsupported types with clear errors
• explode: limit argument, empty-string edge cases per PHP
• Compliance PHPT cases under test/compliance/cases/stdlib/ marked for JIT
• AOT fixture: simple template loop building HTML via implode

Acceptance criteria

$parts = ['<li>', 'a', '</li>'];
echo implode('', $parts);
$segments = explode('/', trim($_SERVER['REQUEST_URI'], '/'));

…compiles and runs identically in VM, JIT, and AOT.

Key files

• ext/standard/implode.php, explode.php, str_replace.php
• lib/JIT/Call/Native.php, lib/JIT/Builtin/

Blocks

• Reference app: examples/003-MiniWebApp (router, templates, forms) #67 Reference app (template rendering)
• Language: Implement foreach (CFG → VM → JIT) #53 foreach (often paired with implode for list HTML)

Related

• Arrays: Full associative array support (string keys, holes, rehash) #66 Associative arrays (array keys for implode keys mode later)

[PurHur]

Partial fix merged in #240: str_replace() now has LLVM JIT/AOT lowering (JitStrReplace). implode / explode were already covered; this issue remains open for any remaining parity gaps on those two.