Web: Dynamic isset/empty on $_GET and $_POST keys in JIT

[PurHur]

Problem

IssetHelper optimizes isset($_GET['key']) via SuperglobalInit::compileTimeOffsetIsSet when the key is a string literal. Non-literal keys and runtime-populated superglobals need LLVM hashtable offsetIsSet calls.

Errors today:

• isset() on superglobals only supports a string literal key in this compiler build

VM tests (web_isset_get.phpt) pass; JIT compliance may differ.

Goal

isset($_GET[$param]) and empty($_GET['missing']) work when superglobals are runtime-filled.

Tasks

• JIT: __hashtable__offsetIsSet for sg_GET / sg_POST globals
• empty() lowering consistent with isset
• Remove or gate compile-time-only fast path behind optimization flag
• PHPT under test/compliance for JIT mode

Depends on

• Web: Runtime-populated superglobals for JIT and AOT (per-request $_GET/$_POST) #49 Runtime superglobals

Files

• lib/JIT/IssetHelper.php
• lib/JIT/SuperglobalInit.php

Implementation hints (May 2026)

JIT slice is tracked in #1901 — implement dynamic-key isset there; keep #70 as the literal-key / VM compliance umbrella or close when #1901 lands.

Layer	Files	Notes
Literal fast path	lib/JIT/SuperglobalInit.php	compileTimeOffsetIsSet when key is string literal
Dynamic JIT	lib/JIT/Builtin/IssetHelper.php	Non-literal → __hashtable__offsetIsSet on sg_GET / sg_POST (#1901)
Empty	lib/JIT.php	empty() must match isset semantics for runtime-filled tables
VM	test/compliance/cases/web/web_isset_get.phpt	Already green
AOT	test/aot/JitSuperglobalRefreshTest.php	Extend for dynamic key after JIT fix

Suggested PHPT (JIT)

• test/compliance/cases/web/web_isset_dynamic_get_jit.phpt (owned by JIT: isset/empty on runtime-populated sg_GET keys (close #49 JIT slice) #1901)
• test/compliance/cases/web/web_empty_dynamic_get_jit.phpt

Verification (local / Docker only)

./script/ci-fast.sh --filter web_isset
./script/ci-local.sh --filter JitSuperglobal
docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  ./script/ci-local.sh --filter web_isset_dynamic

Dependencies

• Web: Runtime-populated superglobals for JIT and AOT (per-request $_GET/$_POST) #49 — runtime-populated superglobals (parent)
• JIT: isset/empty on runtime-populated sg_GET keys (close #49 JIT slice) #1901 — JIT dynamic isset (preferred implementation issue)
• JIT: Per-run superglobal refresh for bin/jit.php (-q/-p between invocations) #642 — per-request superglobal refresh in JIT/AOT

Links

• ROADMAP 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 Phase 1 web-runtime
• Do not duplicate JIT: isset/empty on runtime-populated sg_GET keys (close #49 JIT slice) #1901 work — link PRs there and close Web: Dynamic isset/empty on $_GET and $_POST keys in JIT #70 when dynamic isset JIT is green