Remove dead opcodes

[NullVoxPopuli]

Human notes

From bot exploration here:

• [CLEANUP] Remove dead opcodes #21510

It does, indeed, look like this stuff is unused. Is good to drop code we aren't using, as all code is liability.

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AI Generated PR Summary and History

Removes opcodes that are vestigial on both sides of the pipeline:

• VM_POP_ARGS_OP (84): never emitted by the opcode compiler and has no runtime handler registered — a program containing it would crash.

• VM_JUMP_IF_OP (65): a runtime handler was registered, but the compiler never emits it; all conditionals compile through JumpUnless/JumpEq. Removing it drops a live (non-tree-shakeable) handler from the append-opcodes table.

• Wire format StrictModifier (5), StrictBlock (7), DynamicArg (20), StaticArg (21): never produced by the wire format encoder and never consumed by the opcode compiler; modifiers and blocks encode as plain Modifier/Block in both modes, and component args are encoded inline as hashes. Their only references were the opcode table itself, the interface types, and the wire-format debug printer. The wire format is version-locked (templates must be compiled by the matching compiler), so removing never-emitted opcodes is safe.

Opcode numbers are not reused; the freed numbers just become gaps like the existing ones (93-94, 101-102, 104).

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Some archaeology on how these six opcodes became dead, from glimmer-vm history (where these packages lived before vendoring):

VM_JUMP_IF_OP (65)

Dates back to the original {{#if}} inlining (glimmerjs/glimmer-vm@5fcd6da23, Nov 2015). Its last real job was compiling {{#unless}}: evaluate the condition, ToBoolean, then jumpIf('ELSE') to skip the main block when truthy ({{#if}} always used the mirror op, JumpUnless). It stopped being emitted in glimmerjs/glimmer-vm@8f5c02152 (Feb 2018), which introduced the structured tryIf builder helper — emitting only JumpUnless — and reformulated unless as an if with swapped branches. The runtime handler has been registered-but-unreachable for eight years since.

VM_POP_ARGS_OP (84)

Lived four days. Added in glimmerjs/glimmer-vm@c1ff46597 (Sep 8, 2017) to pop + clear the Arguments object after static component invocations; removed — builder method, handler, and metadata — in glimmerjs/glimmer-vm@19340c9e8 (Sep 12, 2017) when frames took over argument cleanup. The enum entry was left behind, and the Dec 2018 opcode-TOML metadata generator (glimmerjs/glimmer-vm@b442d4e75) then faithfully cataloged [syscall.argspop] and began regenerating DEBUG metadata for an op with no emitter and no handler, which every later refactor carried along.

StaticArg (21) / DynamicArg (20)

Never actually wire format, even when alive: from 2016 on they were an intermediate representation inside the compiler. The JS compiler pushed ['static-arg', name, value] while walking a component's opening tag, and ComponentBlock partitioned them via isArgument and flattened them into the component's args: [keys, values] hash at serialization time — so they never appeared in final wire output, and no opcode-compiler or runtime consumer for the integer form ever existed in the repo's history. The producing code was deleted in the strict-mode precompiler rewrite (glimmerjs/glimmer-vm@8e11b9116, Sep 2020), which encodes component args directly as hashes; the types, isArgument, and debug-printer cases have lingered since.

StrictModifier (5) / StrictBlock (7)

Born dead. Reserved in glimmerjs/glimmer-vm@4c56c2164 (Jul 2019, "Lay groundwork for lexical scope") as anticipated strict-mode variants of Modifier/Block. git log -S 'SexpOpcodes.StrictModifier' returns zero commits — nothing ever emitted or consumed them. When strict mode shipped in the 2020 precompiler it reused plain Modifier/Block for both modes, and the reserved slots were forgotten.

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The common pattern: each op died during a compiler-architecture rewrite (2017 frames, 2018 builder helpers, 2020 strict-mode precompiler) that replaced the mechanism but left the opcode registry — enums, types, TOML metadata — intact, and later tooling preserved the corpses. This PR is the first pass auditing the registry against actual emit/handle sites.

🤖 Generated with Claude Code

[github-actions]

📊 Size report

Tarball size — 1.2 MB → 1.2 MB

dist/dev   -0.03%↓

File	Before (Size / Brotli)	After (Size / Brotli)
./packages/@glimmer/wire-format/index.js	1.5 kB / 519 B	-7.77%↓1.3 kB / -5.59%↓490 B
./packages/shared-chunks/arguments-{hash}.js	62.6 kB / 12.2 kB	-0.6%↓62.2 kB / -0.22%↓12.2 kB
Total (Includes all files)	2.1 MB / 498 kB	-0.03%↓2.1 MB / -0.01%↓498 kB

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dist/prod   -0.03%↓

File	Before (Size / Brotli)	After (Size / Brotli)
./packages/@glimmer/wire-format/index.js	1.5 kB / 519 B	-7.77%↓1.3 kB / -5.59%↓490 B
./packages/shared-chunks/arguments-{hash}.js	58.4 kB / 11.3 kB	-0.64%↓58 kB / 11.3 kB
Total (Includes all files)	1.9 MB / 455.4 kB	-0.03%↓1.9 MB / 0%↑455.4 kB

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smoke-tests/v2-app-template/dist   -0.04%↓

File	Before (Size / Brotli)	After (Size / Brotli)
./assets/api-{hash}.js	287.9 kB / 77.5 kB	-0.05%↓287.8 kB / 0.07%↑77.5 kB
Total (Includes all files)	351.2 kB / 97.8 kB	-0.04%↓351.1 kB / 0.07%↑97.9 kB

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smoke-tests/v2-app-hello-world-template/dist   -0.11%↓

File	Before (Size / Brotli)	After (Size / Brotli)
./assets/main-{hash}.js	132.2 kB / 36.9 kB	-0.11%↓132.1 kB / 0.2%↑37 kB
Total (Includes all files)	132.6 kB / 37 kB	-0.11%↓132.4 kB / 0.3%↑37.1 kB

_{🤖 This report was automatically generated by wyvox/pkg-size}

[NullVoxPopuli]

no difference in perf in running pnpm bench