Stdlib: is_array, is_string, is_null, is_int type guards (JIT)

[PurHur]

Problem

Validation before superglobal access often uses:

if (is_string($_GET['id'] ?? '')) { /* ... */ }

docs/capabilities.md lists is_array, is_string, is_null, is_int as yes in VM, but JIT may not lower them to fast type-byte checks — hot paths in routers regress to generic calls.

Goal

Ensure is_* type guards are fast in JIT (return i1, branch-friendly) and remain correct in VM/AOT for web validation patterns.

Implementation hints

Audit first

grep -R "function is_string" ext/ lib/
script/capability-matrix.php --check

Confirm whether gap is JIT-only or VM stub.

VM

• Reuse Variable::type / existing ext/types/ implementations.
• is_string must accept internal string representation used by superglobal values.

JIT (lib/JIT.php + ext/types/)

• Lower to TYPE_* byte compare → i1 (same pattern as other type builtins in matrix).
• Do not box superglobals unnecessarily before is_*.

Tests

Case	Purpose
is_string($_GET['x'] ?? '')	Web guard with #99 when landed
is_array($rows)	Router table check
JIT PHPT group	--group llvm compliance if exists

Acceptance criteria

docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  php bin/jit.php -r 'var_dump(is_string("a"));'

Prints bool(true) without falling back to VM interpreter for the check itself (verify via JIT compliance or dedicated unit test).

Verification (local / Docker only)

./script/ci-local.sh --filter 'is_string|is_array'

Requires LLVM (#98); use make test-docker on harness hosts.

Dependencies

• Language: Null coalescing operator (??) in compiler pipeline #99 ?? for idiomatic superglobal guards
• Runtime: Undefined array/superglobal key — Zend notice parity #273 undefined key policy (inputs to is_*)
• JIT: Dynamic hashtable read/write for $_GET[$key] and $_POST[$key] #86 / Web: Runtime-populated superglobals for JIT and AOT (per-request $_GET/$_POST) #49 JIT superglobal slices

Links

• docs/capabilities.md (types module rows)
• 🗺️ ROADMAP: Compile a small PHP web application (living document) #78 ROADMAP Phase 4

[PurHur]

AOT runtime status (2026-05-21)

Partial compile/lowering fixes are in PR #464. Docker aot-link suite: 118 tests, 1 failure.

Still failing

test/fixtures/aot/cases/coalesce_get_present.phpt — binary runs but stdout is empty (expected Ada\n).

# After script/install-llvm9.sh and vendor deps in php-compiler:22.04-dev
printf '%s\n' '<?php' '$name = $_GET["name"] ?? "Guest";' 'echo $name, "\n";' > /tmp/coalesce.php
php bin/compile.php -q name=Ada -o /tmp/coalesce /tmp/coalesce.php
QUERY_STRING=name=Ada /tmp/coalesce | od -An -c   # shows only "\n"

PHPUnit:

Failed asserting that two strings are equal.
--- Expected: 'Ada'
+++ Actual: ''

Likely cause

Same gap noted in e02df36: LLVM merge of ?? branch assignments into the coalesce result (distinct from the VM skip-eager-fetch / left-branch ARRAY_DIM_FETCH fixes). An if (1) { $n = $_GET['name']; } else { $n = 'Guest'; } AOT pattern prints Ada correctly; ?? through TYPE_COALESCE + merge block does not.