The Pass Catalog

All counts, names, and symbols on this page apply to neuronx_cc 2.24.5133.0+58f8de22 (cp310 wheel; cp311/cp312 carry the same registries — only Cython hash suffixes and binary VAs drift). The four stages live in four binaries: neuronxcc/starfish/bin/hlo-opt (BuildID 93dd8bd9bd4c697b, not stripped), the MLIR pipeline inside that same hlo-opt, the Cython pass modules under neuronxcc/starfish/penguin/, and neuronxcc/starfish/lib/libwalrus.so (BuildID 92b4d331…). Treat every count as version-pinned — the re-derivation recipes in §5 re-run against any wheel.

Abstract

This appendix is the single consolidated index of every compiler pass in neuronx-cc, across all four optimization stages that a graph traverses on its way from XLA HLO to a packaged NEFF. There is no one place in the binaries where all four registries meet — each stage owns its own name→pass mechanism, in its own binary, with its own selection rule — so this page is the meeting point. It exists to answer one question for a reimplementer or a debugger: given a pass name, which stage owns it, what class does it construct, where in the pipeline does it run, and which wiki page documents it.

The four stages and their headline counts, each re-derived from the binary in §5:

1. hlo-opt B-strand — the --passes registry of HLO-level rewrites, 112 registered names → 112 classes, keyed by pass->name(). The source of truth is 4.1.
2. hlo2penguin C-strand (MLIR) — the imperatively-built mhlo/stablehlo pass pipeline that lowers optimized HLO to penguin.py text. 32 MHLO steps; the StableHLO fork is the same spine with 5 insertions = 37 steps. The source of truth is 4.32.
3. Penguin middle-end — a catalog of Cython pass modules (no flat registry), sequenced at run time by SharedCodeGenFlow generators. 248 total pass modules across four directories (71 + 131 + 6 + 40), of which ~8–10 in the two transforms/ dirs are helper libraries, not Pass classes. The source of truth is 5.7.
4. walrus backend — the GeneratorRegistration name→factory registry, 150 registered names collapsing to 121 distinct C++ classes (10 classes multi-registered), scheduled into ~180 pipeline steps. The source of truth is 8.1.

Each stage uses a structurally different name→pass mechanism, and that difference is itself the most useful thing this catalog records — a reimplementer who assumes one registry for the whole compiler will get all four wrong. §0 lays the four mechanisms side by side. §1–§4 index each stage's passes by family, with the documenting page per family. The full row-level tables are not reproduced here — they live in the four normative pages — because pasting 112 + 37 + ~240 + 150 rows would be a dump, not an index; this page is the map to those tables, with the cross-stage counts reconciled in one place.

This is a reference catalog, not an algorithm walkthrough; its value is completeness and correct cross-stage ordering. Confidence is per-row in §5: the four name counts (112 / 32+5 / 248 / 150) are CONFIRMED on the binary; the 121-class walrus total is STRONG (derived); the Penguin run order is STRONG (from the version-counter source-order trace).

0. The Four Registry Shapes

The single most important cross-stage fact is that each stage binds a pass name to a pass object by a different mechanism. They are not four instances of one design; they are four designs. A reimplementer must reproduce each one separately.

Two stages have a real string-keyed registry (1, 4); two build the pipeline imperatively with no name table at all (2, 3). The two registries even differ in where the key comes from: hlo-opt reads the key back off name() at registration (so the registrar source never shows it), while walrus passes the literal name straight into registerGenerator. That asymmetry is why recovering the 112 hlo-opt keys required walking each factory to its vtable, whereas the 150 walrus names grep straight out of the symbol table.

GOTCHA — "pass count" means four different things. Stage 1's 112 is registered names = classes (1:1). Stage 4's 150 is registered names, which is not the class count (121) — 10 classes answer to several names. Stage 3's 248 is modules, which is not the pass-class count (~8–10 are helper libs) and not the run-list length (a flow runs a subset, some passes twice). Stage 2's 32/37 is pipeline steps, every one gated, so the executed count depends on the CompileConfig. A single "total passes" number for the compiler is meaningless; always say which of name/class/module/step you mean.

1. Stage 1 — hlo-opt B-strand (112 passes)

xla::hilo::RegisterHiloHloPasses registers 112 passes into an llvm::StringMap keyed by each pass's name(). CONFIRMED — an objdump of the registrar body (0x1e72270–0x1e744af) shows exactly 112 call instructions targeting RegisterHloPass (0x1ebc3f0). Of the 112, 87 override their own Run (vtable+0x18) and 25 are OpExpander passes sharing xla::OpExpanderPass::Run @ 0x29f0bb0 and overriding InstructionMatchesPattern (vtable+0x28). Of provenance, 3 are stock XLA classes reused unchanged (tuple-simplifier, call-inliner, dce); the rest are Neuron-authored.

The 112-row name→class→vtable→entry table is not duplicated here — it is the canonical table in 4.1 §2. Below is the index of that table by family, pointing each family at the 4.x page that documents it.

NOTE — the registration order (1..112) in 4.1 §2 is the registrar's emission order and serves as the default-pipeline proxy — it is not the run order. The executed run-list is a driver-supplied ordered name subset assembled outside hlo-opt's registrar, then filtered by --passes (whitelist) / --skip-pass (blacklist). The family table above is sorted by topic, not by registration index; cross-reference 4.1 §2 for the exact #.

2. Stage 2 — hlo2penguin C-strand MLIR pipeline (32 + 5 = 37 steps)

After the 112 B-strand passes run, optimized HLO is imported into mhlo and a fixed, imperatively-built MLIR pipeline rewrites it down to penguin.py text. There is no registry: hilo::registerMHLOPasses @ 0x1ee12f0 is a flat pm.addPass(...) spine, and the linear source order is the pipeline order. The StableHLO fork (hilo::registerStableHLOPasses @ 0x1ee2120, selected by CompileConfig byte [+0x1CA]≠0) is the same spine with 5 extra insertions — 32 → 37 steps. Every step except the terminal emitter is gated on a CompileConfig byte (default-off unless a cl::opt flips it; the lone default-on is step 6 LowerComplex, set by a static initializer).

The full ordered MHLO spine is the canonical listing in 4.32. Index of the 32 steps by family:

The 5 StableHLO-only insertions (32 → 37)

The StableHLO spine twins every MHLO step and adds 5 of its own (4.32):

QUIRK — step 25 is prepended, not appended. SixtyFourHack's gate (jz→altblk @ 0x1ee19a0, on global qword_9C71338==0) inserts it before step 26 PenguinizeIO, so it runs ahead of IO packaging despite appearing 25th in the source. A reimplementer who addPass-es it in textual position sequences it wrong. (STRONG — disasm-only control flow.)

3. Stage 3 — Penguin middle-end (248 modules, run-list ~varies)

The Penguin middle-end is not a registry and not a flat pipeline — it is a catalog of Cython pass modules sequenced at run time by generator functions. Four directories partition the catalog; counts are ls-verified (excluding __init__):

The targets/transforms/autotune/ subpackage (6 modules: Autotuner _Compiler _PerformanceMetric _Search _TreeSearch _TreeSearchVisualizer) is counted separately, not in the 131.

GOTCHA — module count ≠ pass count. ~8–10 modules in the two transforms/ dirs export no Pass/DotTransform subclass — they are helper libraries (DataflowUtil InstTransformUtils IPUtils LoopTransformUtils TensorContractUtils TensorOpUtils InstBuilder IntrinsicBuilder DataflowUtils). The real pass-class set is the subset whose top-level class subclasses DotTransform or BaseAnalysis. The 248 is the verifiable module anchor; the pass-class subset is a few smaller. (STRONG — by-class filtering not exhaustively enumerated.)

Run order — the driver, not the directory

There is no static order in the directory listing. The order is set by the four SharedCodeGenFlow generators (peephole_optimizations, legalize_pe_insts, nki_codegen, codegen_optimization_post_tritium_fusion), each yielding PassType specs that a PassConstructorBuilder folds. The canonical post-fusion list (with its required/optional qualifiers and the spill-vectorize-respill double-FastSpillGeneration) is in 5.7. Index of the high-population families:

QUIRK — a pass can appear twice in the run-list. FastSpillGeneration runs before and after SFKVectorizer (vectorization creates new live ranges to spill); nki_codegen is chained into the post-fusion list. A set-based reimplementation that de-dups specs by class silently drops the second spill. The Penguin run-list length is therefore not a function of the module count — it is the generator's yield sequence, with repeats. (CONFIRMED membership; STRONG order — version-counter source-order trace.)

4. Stage 4 — walrus backend (150 names → 121 classes)

The walrus backend is a GeneratorRegistration registry: 150 register_generator_<name>__ static initializers each install a name → factory entry, but they construct only 121 distinct C++ pass classes — 10 classes are registered under multiple names, parameterized at construction by a memory space, optimization level, or scheduling phase. The pipeline schedules these into ~180 steps (some names at several positions, plus interposed !isRealPass check/dump/sim passes).

• 150 CONFIRMED on the binary: nm -DC libwalrus.so | rg -o 'register_generator_[a-z0-9_]+' | sort -u | wc -l = 150.
• 121 STRONG (derived): count of distinct _M_invoke ctor targets over the 150 bodies. The 10 multi-registered groups contribute 29 surplus names (9+7+3+2+2+2+1+1+1+1); 121 + 29 = 150.

The full 150-name → class → granularity → evidence table is the canonical listing in 8.1 §"The full 150-name table". The 150→121 collapse must be represented, not flattened — here are the 10 multi-registered classes that produce the gap:

The other 111 names are 1:1 with their class. Index of the 150 names by family, pointing each at the documenting 8.x page:

GOTCHA — serial* is not "always serial". In 8.1's full table the granularity column shows a Fork tag only where an explicit add*ParallelPass<Class> template instance exists; serial* means "added by name (default serial child)" — but the same class may be fork-wrapped at a different call-site, because granularity is a property of the call-site, not the class. Do not read serial* as a guarantee.

5. Adversarial Self-Verification

The cross-stage counts that this catalog turns on, each re-challenged directly against the cp310 binaries:

1. Stage 1 = 112. objdump -d --start-address=0x1e72270 --stop-address=0x1e744b0 hlo-opt | rg -c 'call.*1ebc3f0' → 112 (calls to RegisterHloPass). One name per call, key = pass->name(). CONFIRMED on the binary.
2. Stage 2 = 32 MHLO + 5 = 37 StableHLO. registerMHLOPasses @ 0x1ee12f0 (3096 B) is a flat 32-step addPass spine; registerStableHLOPasses @ 0x1ee2120 (3142 B) is the twin + 5 insertions. The 5 inserts (HloLegalizeToStablehlo, ConvertCustomCallToAllReduce, FusionToComposite, LegalizeSRA, LegalizeScatter) are CONFIRMED in 4.32. Step count CONFIRMED; the SixtyFourHack prepend (step 25) is STRONG (disasm-only).
3. Stage 3 = 248 modules (71/131/6/40). ls <dir>/*.so | grep -v __init__ | wc -l in each of the four directories → 71, 131, 6, 40 (sum 248). targets/transforms/autotune/ = 6 (separate). targets/cayman/passes/ and targets/core_v4/passes/ contain only __init__. CONFIRMED on the binary (module count; pass-class subset is a few smaller — helper libs, flagged in §3).
4. Stage 4 = 150 names → 121 classes. nm -DC libwalrus.so | rg -o 'register_generator_[a-z0-9_]+' | sort -u | wc -l → 150 (CONFIRMED on the binary). The 10 multi-registered groups (MemoryAnalysis=10, ColoringAllocator=8, AddressRotation=4, DMAOptimization/FullUnroll/SeparateLoadAndCompute=3 each, four ×2) sum to 29 surplus names; 121 + 29 = 150. 150 CONFIRMED; 121 STRONG (distinct-ctor-target count over the verified 8.1 table, not independently grep-able).
5. The four name→pass mechanisms are genuinely different. Stage 1 = llvm::StringMap keyed by name() read-back; Stage 2 = imperative addPass with no name table; Stage 3 = PassType specs folded by PassConstructorBuilder, no name table; Stage 4 = _Hashtable keyed by the literal registerGenerator string. Each is documented and symbol-anchored in its normative page (4.1, 4.32, 5.7, 8.1). CONFIRMED.

No pass name on this page is fabricated: every name is the verbatim string carried by its normative source page, which in turn read it from the binary (name() literal, create…Pass factory symbol, __pyx_n_s_ interned token, or register_generator_*__ symbol). Where this catalog points a family at a documenting wiki page, the slug was confirmed present on disk; families with no dedicated detail page point at their stage's normative registry page. The libBIR/libwalrus binaries and their IDA databases are present in-corpus — backend class addresses cited via 8.1 are CONFIRMED, not inferred.

NOTE — what this page is not. It is an index, not a replacement for the four normative tables. The per-row name→class→vtable→entry detail for Stage 1 lives in 4.1 §2; the per-step MLIR spine in 4.32; the Penguin driver order in 5.7; and the full 150-name → class → granularity table in 8.1. This catalog reconciles their counts and gives one map across all four.

Related Components

Cross-References

• The hlo-opt Pass Registry (the --passes Table) — Stage 1, the 112-row canonical table this catalog indexes
• hlo2penguin MLIR Pipeline Order & Entry Flow — Stage 2, the imperative addPass MLIR spine
• Penguin Pass Roster & Pipeline Driver — Stage 3, the Cython module catalog and OptLevel gate
• BackendPass Hierarchy & the 150-Name→121-Class Registry — Stage 4, the walrus GeneratorRegistration registry
• The walrus Pass Pipeline & Optlevel Planes — how the 150 walrus names are scheduled per -O level
• The Opt-Level Planes — -O0..-O3 — the --optlevel dial that gates Stage 3 and Stage 4 selection
• walrus_driver Backend CLI & Pass Vocabulary — the --pass surface that drives the Stage 4 registry
• Master Opcode Reference · Master Dtype / Enum Reference — the sibling Part-14 reference catalogs