Optimize qualified- / simple- ident? / keyword? / symbol?


There are some optimizations that we can make for the simple-ident?, qualified-ident?, simple-symbol?, qualified-symbol?, simple-keyword?, and qualified-keyword? functions.

Two separate optimization can be done.

In places where boolean is used (the qualified- fns), we can instead use some? for a faster implementation:

1 (boolean (and (symbol? x) (namespace x) true))

can be converted to simply

1 (and (symbol? x) (some? (namespace x)))

Focusing on just V8 for now, for

1 (simple-benchmark [x 'a/b f #(qualified-symbol? x)] (f) 100000000)

and subtracting out the baseline cost for

1 (simple-benchmark [x 'a/b f (fn [] x)] (f) 100000000)

this yields a speedup of 1.74.

Since we know that we are dealing with keywords or symbols when applying namespace, we can furthermore use (.-ns x).

Alone this gives a speedup of 2.21 and when combined with the previous optimization as

1 (and (symbol? x) (some? (.-ns x)))

we see a combined speedup approaching infinity (the operation effectively becomes free, taking the same time as the baseline).

Note that we could perhaps use predicate-induced type inference along with a new macro for namespace that emits .-ns instead, but CLJS-2866 currently hinges on looking at the test in an if, while expressions like the above cause optimized js* output with short-circuiting &&.

These optimizations would be good because these functions are often used in spec-based generative code testing where performance can be an issue.

We have test coverage for these functions in cljs.predicates-test.

For reference here is the JavaScript currently emitted for qualified-symbol?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 function cljs$core$qualified_symbol_QMARK_(x) { return cljs.core.boolean$( (function() { var and__8540__auto__ = x instanceof cljs.core.Symbol; if (and__8540__auto__) { var and__8540__auto____$1 = cljs.core.namespace(x); if (cljs.core.truth_(and__8540__auto____$1)) { return true; } else { return and__8540__auto____$1; } } else { return and__8540__auto__; } })() ); }

and here is what we get with the revisions

1 2 3 function cljs$user$qualified_symbol_QMARK_(x) { return x instanceof cljs.core.Symbol && !(x.ns == null); }

(The compactness of this revised implementation means that it might be further inlinable via Closure for more speedups for whole-program optimization.)







Mike Fikes