[jira] [Created] (GROOVY-12161) Omit identity catch-all for try/catch without finally and slim exception bytecode

["Daniel Sun (Jira)" <ji...@apache.org>]

Daniel Sun created GROOVY-12161:
-----------------------------------

             Summary: Omit identity catch-all for try/catch without finally and slim exception bytecode
                 Key: GROOVY-12161
                 URL: https://issues.apache.org/jira/browse/GROOVY-12161
             Project: Groovy
          Issue Type: Improvement
            Reporter: Daniel Sun


h2. Summary

{{StatementWriter.writeTryCatchFinally}} currently emits a catch-all identity rethrow ({{astore}} / {{aload}} / {{athrow}}) and an empty shared-finally path for *every* try/catch, including plain try/catch with no finally. That diverges from javac, bloats the exception table, and adds avoidable control-flow noise that is less JIT-friendly.

h2. Problem

For a plain try/catch (empty finally), the generator still:

* registers a catch-all handler that only stores and rethrows the throwable
* routes normal fall-through through an empty "finally" block and a second {{GOTO}} past the catch-all
* always creates a catch-side {{BlockRecorder}} even when there are no catch clauses

On abrupt exits ({{return}} / {{break}} / {{continue}}), {{CompileStack.applyBlockRecorder}} also emits a trailing {{NOP}} after inlined finally/synchronized guards, which is unnecessary once the restarted range can bind to the next real instruction.

Non-empty finally must keep a real catch-all so uncaught exceptions still run finally then rethrow. Nested try/catch inside try/finally must keep {{BlockRecorder}} range splitting so an enclosing finally inlined on {{return}} is *not* covered by an inner typed handler (regression risk for GROOVY-8229). Stack-map casts for assignments inside try (GROOVY-9805) continue to depend on an active {{BlockRecorder}}.

h2. Proposed approach

* Keep a {{BlockRecorder}} on try/catch regions always (empty finally ⇒ no-op excluded statement) so range splits, nested finally semantics, and GROOVY-9805 casts stay correct.
* When finally is empty: omit the catch-all identity rethrow and the empty shared-finally block; fall-through jumps straight to a join label after the handlers.
* When finally is non-empty: keep typed handlers first, then catch-all + shared fall-through finally (existing semantics).
* Only push a catch-side {{BlockRecorder}} when there is at least one {{catch}}.
* In {{applyBlockRecorder}}, keep a leading {{NOP}} so abrupt-exit-only try ranges stay non-empty (illegal empty exception ranges), but drop the trailing {{NOP}}.

h2. Expected bytecode shape (illustrative)

Plain try/catch after change — typed handlers only, no catch-all:

{code:java}
int m(int x) {
    try {
        return x
    } catch (RuntimeException e) {
        return -1
    }
}
{code}

Exception table should list only {{RuntimeException}} (possibly multiple ranges after return-path range splits), not a {{null}}/any handler, and must not contain an adjacent {{ASTORE}}/{{ALOAD}}/{{ATHROW}} identity rethrow.

Try/finally must still have a catch-all any-handler so finally runs for uncaught exceptions.




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