Build: no incremental compilation for user projects — every `phpc build` re-lowers all files as one bundled TU and `PHP_COMPILER_CACHE=0` is forced (bin/compile.php, lib/Web/SourceBundler.php, lib/JIT/CompileCache.php)

[PurHur]

Category

Foundation: · build speed · child of #36188

Problem

• SourceBundler::bundleForAot() (lib/Web/SourceBundler.php:25-75) string-concatenates the entry and every include into one source blob → one Script → one Block → one LLVM module. Changing one file of a 200-file app re-lowers 200 files.
• CompileCache (lib/JIT/CompileCache.php:57-70) — a bitcode cache keyed on (realpath, mtime, sha256(source), fingerprint) — is wired only into Runtime::jit() (lib/Runtime.php:905-940), never into Runtime::standalone() (:956), and bin/compile.php:534 forces PHP_COMPILER_CACHE=0 for user AOT builds (the comment there documents a stale-cache bug rather than fixing the key).
• Nothing in a user build runs in parallel; the only fan-out in the repo is the cold helper-corpus emitter (script/emit-helper-runtime-object.php:489-560).
• Warm hello-world build on master 4eed6a2785 is 17 s (README claims ~6 s); MiniWebApp measured separately in the tracker.

The per-unit model that would fix this already exists for helpers (HelperRuntimeCache: fingerprinted unit.o + declarations-only unit.bc + manifest, bound via declareExternFromBitcode). The self-host split-TU work (#36147/#36155) is building the same cross-TU binding for the spine. User builds should be the third consumer of that one mechanism, not a separate design.

PHP implementation target

1. Cheap first step (M): make standalone() consult CompileCache keyed on sha256(bundled source) + HelperRuntimeCache::coreFingerprint() + helper-index digest + ABI version; restore the module and skip lowering when hit. Delete the PHP_COMPILER_CACHE=0 override once the key includes the helper index.
2. Per-file TUs (L): lower each include to its own module/object under build/user-object-cache/<sha>/{unit.o,unit.bc,manifest.json}; bind cross-file calls/classes via the split-TU manifest (PHP_COMPILER_EXTERNAL_METHOD_MANIFEST path in lib/AOT/ExternalMethodBind.php); emit unchanged files' objects from cache; emit changed ones in parallel worker processes (reuse the EMIT_JOBS scheduler); one link.
3. Unbound cross-TU references must be a hard error in this mode (never __value__writeNull, Self-host P0: JIT external class method calls in bundled lib (PhpParser, etc.) #579).
4. Drop the second new Runtime(MODE_AOT) (bin/compile.php:372 vs :382 — both run loadCoreModules()), and replace path-substring mode detection (phpc_compile_is_user_script_aot, :108-140: selfhost/, compile_driver.php…) with an explicit --mode=user|selfhost|chunk flag so a user project under a selfhost/ directory is not silently compiled with self-host stubs.

Repro

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && time ./phpc build --project examples/003-MiniWebApp -o build/mw1 \
  && touch examples/003-MiniWebApp/src/Router.php && time ./phpc build --project examples/003-MiniWebApp -o build/mw2'

Today both builds take the same time.

Done when

• Unchanged-source rebuild of MiniWebApp ≥ 3x faster than a cold one with byte-identical binary (step 1)
• One-file edit rebuilds in < 25 % of full-build wall (step 2); examples-web-smoke.sh and deploy-smoke.sh green on the incremental binary
• A fixture at test/fixtures/aot/selfhost/app.php builds as a user script (mode flag) and matches Zend
• PHP_COMPILER_BUILD_TIMING=json phase report (boot/parse/lower/opt/codegen/link ms) committed for hello-world and MiniWebApp

[PurHur]

claim: implementer-worker-lane-b — starting this run (lane overflow: #36143–#36148 closed; north-star5-verify-fast green; AOT compile cache for standalone step 1)