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backend: cache resolved var cells per reference site (run-path ~5x)

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Profiling jolt-i5if showed <=60-bit arithmetic is already native-fast; the real
general overhead in the run/-e/-m path is var resolution. Every var reference
compiled to (var-deref ns name), which builds + hashes a fresh "ns/name" string
and does a hashtable lookup per access (~45ns). The var cell is interned and
def-var! mutates it in place, so caching the resolved cell is sound under
redefinition.

Generalize the devirt per-site cache-cell mechanism to var value references: a
ref inside a fn resolves its cell once into the def's closure, then reads it via
var-cell-deref (a field read after the first). var-cell-deref is the cell-based
var-deref — binding-aware (dynamic vars + *ns* still resolve) and lenient on an
unbound root (a forward-declared var doesn't throw, unlike jolt-var-get).

Gated by a runtime flag: ON for runtime-compiled code (compile-eval.ss), OFF for
the seed mint and AOT build (emit-image.ss) so the seed stays a byte-fixpoint --
prelude.ss is unchanged, only image.ss picks up the new backend. ~5x on a
var-ref-heavy loop (1058ms->205ms); ~1.2x on test.check (its generators are more
deftype/dispatch-bound than var-deref-bound). No C/FFI.

Corpus rows pin redefinition / dynamic binding / forward ref through a cached
ref. make test + shakesmoke green, selfhost holds, SCI 211/218, certify 0-new.
This commit is contained in:
Yogthos 2026-06-28 12:36:35 -04:00
parent f17b68ccfe
commit 04180c1e4e
6 changed files with 245 additions and 164 deletions
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10
host/chez/dyn-binding.ss
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@ -117,6 +117,16 @@
((eq? cell star-ns-cell) (intern-ns! (chez-current-ns)))
(else (var-cell-root cell)))))))
;; var-deref's read on an ALREADY-RESOLVED cell — what compiled code emits when it
;; caches the cell at a reference site. Binding stack first, then *ns* thread-local,
;; else the raw root. Lenient on an unbound root (returns the sentinel), matching
;; var-deref — NOT the strict jolt-var-get, which throws "Unbound var".
(define (var-cell-deref cell)
(let ((bv (dyn-binding-value cell)))
(cond ((not (eq? bv dyn-no-binding)) bv)
((eq? cell star-ns-cell) (intern-ns! (chez-current-ns)))
(else (var-cell-root cell)))))
;; jolt-var-get (vars.ss): the var-get fn + deref/@ on a cell. Stack first, then
;; the original (which errors on an unbound root, matching Clojure).
(define %dyn-var-get jolt-var-get)