Building `PNode` trees out of a module's `.bif` is the bulk of the `lower` and
`cg` stages: their cost tracks the size of the dependency CLOSURE a stage loads,
not the module it compiles (a 370-byte module costs 0.20s/0.16s in lower/cg, the
main module 3.40s/3.16s). Since the link stage stopped loading the graph those
two are ~85% of the serial backend critical path. The goal is to let the backend
read the `.bif` directly through a `Cursor`, constructing no `PNode` at all.
`BNode` is the seam: a `Cursor` with `-d:newIcBackend`, a `PNode` without, which
is what every build does today. Codegen migrates one area at a time and the
compiler keeps building throughout.
The seam is thin on purpose. `ast`/`astdef` already give `PNode` the whole
vocabulary — `kind`, `len`, `safeLen`, `sym`, `typ`, `info`, `firstSon`,
`secondSon`, `lastSon` and `sons`/`isons`/`sonsFrom` — so bnode deliberately does
NOT redefine them for `PNode`: an identical second overload makes every call site
ambiguous (tried it; `lastSon` breaks first). It adds only `son` and `hasSons`,
and supplies the full vocabulary on the `Cursor` side as `{.error.}` stubs, so
flipping the define names the exact missing accessor AT ITS CALL SITE instead of
collapsing into a cascade of type errors.
Two notes for whoever continues this:
* The migration front is SIGNATURES, not call sites. Converting `n[i]` to the
iterator vocabulary changes nothing while the value is still `PNode`-typed —
flipping the define then reports a plain type mismatch. Changing one proc's
parameter from `PNode` to `BNode` is what moves it, and is a no-op with the
define off. `containsResult` and `allPathsAsgnResult` are converted as the
worked example.
* `BNode`'s cost model differs and the vocabulary is shaped around it: reading
child `i` of a `Cursor` is O(size of children 0..<i), so prefer `sons`/
`sonsFrom`/`isons` over indexing, and avoid `len` in a loop condition.
Note `type BNode = when defined(x): Cursor else: PNode` does not parse — `when`
is not an expression in type position; it needs a `when` block over two `type`
sections.
Inert: all 219 generated `.c` files and the linked binary are byte-identical to
the parent commit.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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