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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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5
host/chez/emit-image.ss
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@ -41,6 +41,11 @@
;; top-level entry: in direct-link mode it binds jv$<fqn> for a top-level def; off
;; that mode (the minter, runtime eval) it is exactly emit, so output is unchanged.
(define jolt-ce-emit-top (var-deref "jolt.backend-scheme" "emit-top-form"))
;; Seed mint and AOT build must stay byte-deterministic, so emit the image with var
;; cell-caching OFF (compile-eval.ss turned it on for runtime eval; this file loads
;; after it). Guarded for the first re-mint pass off an older seed.
(let ((scv (var-deref "jolt.backend-scheme" "set-var-cache!")))
(when (procedure? scv) (scv #f)))
(define (ei-compile-form ctx f optimize?)
(let ((ir (jolt-ce-analyze ctx f)))
(jolt-ce-emit-top (if optimize? (jolt-ce-run-passes ir ctx) ir))))