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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
test/chez/corpus.edn
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@ -1550,6 +1550,12 @@
{:suite "numbers / variadic bit ops" :label "bit-xor in value position" :expected "0" :actual "(reduce bit-xor 0 [1 2 3])"}
{:suite "numbers / variadic bit ops" :label "bit-or via apply" :expected "7" :actual "(apply bit-or [1 2 4])"}
{:suite "numbers / variadic bit ops" :label "unsigned-shift over a full 64-bit value" :expected "17179869183" :actual "(unsigned-bit-shift-right -1 30)"}
;; var-reference cell caching (runtime path): a ref inside a fn caches the
;; resolved cell, but stays correct under redefinition (cell root mutated in
;; place) and dynamic binding (read goes through the binding-aware path).
{:suite "vars / cached reference stays correct" :label "redefinition is seen through a cached ref" :expected "2" :actual "(do (def x 1) (defn f [] x) (def x 2) (f))"}
{:suite "vars / cached reference stays correct" :label "dynamic binding is seen through a cached ref" :expected "[1 9 1]" :actual "(do (def ^:dynamic *d* 1) (defn g [] *d*) [(g) (binding [*d* 9] (g)) (g)])"}
{:suite "vars / cached reference stays correct" :label "forward reference resolves once the var is defined" :expected "42" :actual "(do (defn a [] (b)) (defn b [] 42) (a))"}
{:suite "predicates / nil & boolean" :label "nil? true" :expected "true" :actual "(nil? nil)"}
{:suite "predicates / nil & boolean" :label "nil? false" :expected "false" :actual "(nil? 0)"}
{:suite "predicates / nil & boolean" :label "some? true" :expected "true" :actual "(some? 0)"}