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IC: correct instance-name format in design doc

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The content key is hashed into <disamb> (setInstanceDisamb), not a separate
.key. token; document that the cross-TU merge and DCE already key on the
module-suffix-stripped name.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Araq
2026-06-13 20:28:43 +02:00
parent 934bf39029
commit d269ccff26
1 changed files with 17 additions and 9 deletions
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doc/ic.md
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@@ -57,17 +57,25 @@ NIF symbols and ownership
=========================
(See ``../nifspec/doc/nif-spec.md``.) A global symbol is
``<ident>.<disamb>.<moduleSuffix>`` or, for a generic instantiation,
``<ident>.<disamb>.<key>.<moduleSuffix>`` where ``key`` is the instantiation
encoded by the *NIF-trees-as-identifiers* scheme. Two consequences drive the
``<ident>.<disamb>.<moduleSuffix>``. For a **generic instantiation** the
`<disamb>` is not a counter but a *content hash* — `setInstanceDisamb`
(``modulegraphs.nim``) MD5s the generic's identity plus the `typeKey` of every
concrete type argument, masks it to 30 bits and tags it with `InstanceDisambBit`.
So the only part of the name that varies between two modules making the **same**
instantiation (`seq[Foo]`) is the `<moduleSuffix>`. Two consequences drive the
backend:
- **Instance names are content-addressed**: the same instantiation (`seq[Foo]`)
produced in different modules yields the *same* `key`, so a deterministic
dedup is possible *by name*.
- **The suffix names an owner module.** Today an instance's owner is the module
whose process minted it (`itemId.module`), which is process-local mint order —
the root of the *single-writer* hazard below.
- **Instance names are content-addressed**: the same instantiation produced in
different modules yields the *same* `<ident>.<disamb>`, so a deterministic dedup
is possible by the *module-suffix-stripped* name. The cross-TU merge
(`ccgtypes.sharedInstanceCName`, keyed via `graph.icSharedSigs`) and the DCE
analysis (`dce.computeLiveSymbols`, its `uniq` set) both already key on this
stripped form.
- **The suffix names a mint-site owner.** Today the `<moduleSuffix>` is the
module *that minted the instance* (the instantiation site), so the same
instance has a different full name in each module that makes it; *which* TU
emits the single definition is then decided at codegen by the
reuse/redirect machinery — the root of the *single-writer* hazard below.
The driver: graph construction (`commandIc`)
============================================