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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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6
host/chez/compile-eval.ss
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@ -104,6 +104,12 @@
;; is only for the bare -e subset with no prelude. Turn prelude mode on once, here,
;; so every analyze->emit on this spine sees the full core.
((var-deref "jolt.backend-scheme" "set-prelude-mode!") #t)
;; Cache resolved var cells per reference site in runtime-compiled code (the big
;; win for libraries / REPL code). emit-image.ss turns this back off so the seed
;; mint and AOT build stay byte-deterministic. Guarded: the flag is absent in an
;; older seed during the first re-mint pass.
(let ((scv (var-deref "jolt.backend-scheme" "set-var-cache!")))
(when (procedure? scv) (scv #t)))
;; (quote X) -> X, else x — unwraps a quoted require spec.
(define (ce-unquote x)