Self-host M3: defer emit-bridge IR until after spine pre-lower in compileM3EmitTuMainNative

[PurHur]

Problem

compileM3EmitTuMainNative in lib/JIT.php builds the emit bridge LLVM IR before bundled Runtime::parse / Runtime::compile are guaranteed to be real-lowered. When LLVM binds the stub (null-returning) version first, the resulting native binary produces parse returned null at runtime and the probe falls back to emit_path=zend partial.

This is the root cause identified in #2506 and the current blocker for #2442 (emit-TU execute without startup crash).

Repro

./script/docker-exec.sh -- bash -lc '
  source script/php-env.sh
  BOOTSTRAP_M3_LINK_COMPILE_DRIVER=1 \
  BOOTSTRAP_M3_COMPILE_DRIVER_REAL_LOWERING=1 \
  BOOTSTRAP_M3_RUNTIME_COMPILE=1 \
  ./script/bootstrap-selfhost-helloworld-probe.sh
'
# Expected: emit_path=native
# Actual:   emit_path=zend partial  (parse returned null)

Root cause

In lib/JIT.php, compileM3EmitTuMainNative() emits the bridge call to Runtime::parse before runQueue() / spine pre-lower has committed real lowering for the bundled Runtime methods. LLVM 9 resolves the call to the stub entry from an earlier compile pass.

Fix

Defer the emit-bridge IR construction until after runQueue() completes the spine pre-lower, or restructure compileM3EmitTuMainNative to emit the bridge as a post-queue step (similar to how compileRuntimeLoadJitM3Native gates its helpers).

Relevant code paths:

File	Symbol	Notes
lib/JIT.php	compileM3EmitTuMainNative()	Bridge IR built too early
lib/JIT.php	runQueue() / spine pre-lower	Must complete before bridge references Runtime symbols
test/bootstrap-aot/runtime_m3_emit_native_entry.php	smallest emit TU	Use for bisect
test/bootstrap-aot/compile_smoke_m3_emit_native_entry.php	mid emit TU	Second bisect step
test/bootstrap-aot/helloworld_m3_emit_native_entry.php	full emit TU	Final gate

Done when

• ./script/bootstrap-selfhost-helloworld-probe.sh (with BOOTSTRAP_M3_LINK_COMPILE_DRIVER=1 BOOTSTRAP_M3_COMPILE_DRIVER_REAL_LOWERING=1) reports emit_path=native (not zend partial)
• build/selfhost-helloworld-emit exits 0 with helloworld_compile_smoke: compile OK
• docs/bootstrap-m5-fast-path.md Step 2 updated to remove "bridge ordering" note

Gate sequence

# Smallest TU first:
BOOTSTRAP_M3_RUNTIME_COMPILE=1 make bootstrap-selfhost-runtime-compile-smoke
# Then full helloworld:
BOOTSTRAP_M3_LINK_COMPILE_DRIVER=1 BOOTSTRAP_M3_COMPILE_DRIVER_REAL_LOWERING=1 \
  BOOTSTRAP_M3_RUNTIME_COMPILE=1 \
  ./script/bootstrap-selfhost-helloworld-probe.sh

Dependencies

• M3 emit TU: runtime spine skip-list + emit phase diagnostics (#2442) #2506 ✅ — emit-TU skip list + diagnostics (merged; identified this root cause)
• Self-host M3: native emit-TU binaries run without startup crash #2442 — parent emit-TU execute tracker
• Self-host M3: compile-driver real lowering symbol batch tracker #1768 — allowlist batches (parallel; unblocked after this fix)

Epic #1492 · ROADMAP #78 Phase 0

[PurHur]

Worker priority P0 (May 2026 harness): first compile-path fix on M3 critical path. Verified repro on master via bootstrap-selfhost-helloworld-probe.sh with native emit flags — emit helper segfault. Parent #2442 · sibling #2513 · #2540. Epic #1492.

[PurHur]

Worker priority (May 2026, #1492): P0 on M3→M4 critical path. Verified repro on harness Docker — strict HelloWorld fails parse returned null (parser spine) until emit-TU spine lands. See updated #1492 milestone table.