Wires src/jolt/cgen.janet into the backend's :def emit. With JOLT_CGEN=1 (off by
default, needs direct-linking), a plain defn of a numeric-leaf fn is compiled to
C at def time and the cfunction installed as the var root, so direct-linked
callers embed native code. The fn is not inline-stashed when cgen fires —
callers must call the C fn, not inline the bytecode body. ^:redef/^:dynamic stay
bytecode.
The leaf-first rule falls out: run calls count-point (a user var), so run isn't a
numeric leaf and stays bytecode, calling the native count-point over the cheap
forward crossing. mandelbrot 200: 224ms -> 12.4ms (~18x), result unchanged.
Adds JOLT_CGEN to ctx-shaping-env-vars (rides the disk-cache key) and :cgen? to
resolve-run-mode. Default path (cgen off) is a no-op: cgen-root returns nil and
the normal bytecode emit runs. Gate green (117 files). Test:
test/integration/cgen-pipeline-test.janet.
Co-authored-by: Yogthos <yogthos@gmail.com>
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