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https://issues.apache.org/jira/browse/GROOVY-12284?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18106840#comment-18106840
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ASF GitHub Bot commented on GROOVY-12284:
-----------------------------------------
daniellansun commented on PR #2822:
URL: https://github.com/apache/groovy/pull/2822#issuecomment-5377692106
> > Verdict: sound and low-risk; I'd merge.
> > ### Minor nits (none blocking)
> >
> > * The `n == 0` branch in `Selector.sameClassesGuard` is unreachable from
its only call site (`anyMatch` on an empty `pt` is false, and a receiver is
always present). Harmless defensive code, and likely part of codecov's 6
uncovered lines.
> > * Chained `.bindTo().bindTo()...` could be a single
`MethodHandles.insertArguments(h, 0, c0, …, cN)` — marginally more idiomatic
and one adapter instead of four at arity 4; the JIT result is presumably the
same given the measurements.
> > * The `SameClassesGuardMhBench` javadoc says it "compiles only on
GROOVY-12284+" — it actually compiles anywhere (the overloads are resolved via
runtime `findStatic`) and would fail at `@Setup` on a pre-12284 tree. Cosmetic
doc inaccuracy.
> > * The two JMH benches and README section ride along in the PR; that's
consistent with how the ScopedInvalidationBench work landed, and keeping
`dynamic_arity4`/`dynamic_arity5` under GC profiling in the regression rotation
(as the report suggests) is worth doing so a regression back to a universal
collector can't land silently.
Thanks, Paul. All four nits addressed:
- **`n == 0`:** dropped the constant-`true` branch.
Codecov’s missing line there should go with it.
- **`insertArguments`:** done; same helper as above.
- **MH bench javadoc:** it does compile against any tree that has the
public overloads; `@Setup` fails with `NoSuchMethodException` before
GROOVY-12284. The javadoc now says that.
- **Benches:** kept, including `dynamic_arity4` / `dynamic_arity5` for
GC profiling so a return to a universal collector cannot land quietly.
> Specialize indy sameClasses guards for arity 1-4
> ------------------------------------------------
>
> Key: GROOVY-12284
> URL: https://issues.apache.org/jira/browse/GROOVY-12284
> Project: Groovy
> Issue Type: Improvement
> Reporter: Daniel Sun
> Priority: Major
>
> h3. Problem
> When an invokedynamic site is linked with all arguments non-null and at least
> one parameter type that is non-final (or a primitive wrapper — GROOVY-11782),
> {{Selector}} installs a same-class guard:
> {code:java}
> SAME_CLASSES
> .bindTo(expectedClasses)
> .asCollector(Object[].class, n)
> .asType(MethodType.methodType(boolean.class, pt));
> {code}
> {{asCollector}} of an {{Object}} array of length {{n}} allocates a fresh
> array on *every later invocation* of that site; the array overload of
> {{sameClasses}} then walks it.
> That is the hot path for ordinary dynamic Groovy calls of the shapes
> {{recv.foo()}}, {{recv.foo(a)}}, {{recv.foo(a, b)}}, {{recv.foo(a, b, c)}} —
> arity 1-4 (receiver plus 0-3 arguments). Dynamic indy sites almost always
> have {{Object}} parameter types, so this guard is the common case, not a rare
> fallback.
> (If any argument is {{null}} at link time, {{Selector}} already installs
> per-slot {{SAME_CLASS}} / {{IS_NULL}} tests and does not use the collector.)
> The classic MOP already specializes this check:
> {{MetaClassHelper.sameClasses}} has overloads for 0-4 arguments so the
> call-site cache does not box arguments into an array. The indy guard did not.
> h3. Goal
> Keep the same guard semantics (return {{false}} if any argument is {{null}}
> or has a different runtime class) without allocating an {{Object}} array on
> the common 1-4 arity shapes.
> h3. Approach
> ||Arity (incl. receiver)||Guard||
> |0|constant {{true}}|
> |1|existing {{SAME_CLASS}}|
> |2|new {{SAME_CLASSES_2}}|
> |3|new {{SAME_CLASSES_3}}|
> |4|new {{SAME_CLASSES_4}}|
> |5 or more|existing {{SAME_CLASSES}} plus {{asCollector}} (unchanged)|
> Expected classes are bound with {{bindTo}}. One {{guardWithTest}} at the
> site, via a single {{Selector.sameClassesGuard(args, pt)}} helper.
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