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https://issues.apache.org/jira/browse/GROOVY-12162?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18095950#comment-18095950
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ASF GitHub Bot commented on GROOVY-12162:
-----------------------------------------
daniellansun opened a new pull request, #2707:
URL: https://github.com/apache/groovy/pull/2707
https://issues.apache.org/jira/browse/GROOVY-12162
> Harden and extend bytecode peephole optimization
> ------------------------------------------------
>
> Key: GROOVY-12162
> URL: https://issues.apache.org/jira/browse/GROOVY-12162
> Project: Groovy
> Issue Type: Improvement
> Reporter: Daniel Sun
> Priority: Major
>
> h2. Overview
> Follow-up to GROOVY-12065. The initial peephole layer
> ({{{}PeepholeOptimizingMethodVisitor{}}}) only wrapped selected
> {{visitMethod}} call sites. After {{OperandStack}} started
> emitting constants via {{visitLdcInsn}} and relying on the
> peephole visitor for compaction, any method that was *not* wrapped
> regressed to non-compact forms. Class-generation error diagnostics
> that depended on {{TraceMethodVisitor}} were also broken once
> the peephole wrapper sat in front of the trace visitor.
> This improvement applies peephole compaction uniformly, restores
> diagnostics, and adds several safe local-window rewrites that
> further shrink generated bytecode without changing runtime
> semantics.
> h2. Problems Addressed
> * *Inconsistent application:* MOP bridges, call-site helpers,
> {{{}class${}}}, and other synthetic methods often bypassed the
> peephole wrapper while user methods did not.
> * *Broken classgen diagnostics:*
> {{mv instanceof TraceMethodVisitor}} no longer matched after
> wrapping, so "Last known generated bytecode" was never printed
> when {{visitMaxs}} failed under classgen logging.
> * *Incomplete dead-code patterns:*
> {{{}ALOAD{}}}/reference {{{}LDC{}}}; {{{}CHECKCAST{}}}; {{POP}}
> only dropped the cast (the load remained); bare
> {{{}DUP{}}}/{{{}DUP2{}}}; matching {{{}POP{}}}/{{{}POP2{}}} was left
> untouched; {{{}ACONST_NULL{}}}; {{IF_ACMP*}} was not rewritten
> to {{{}IFNULL{}}}/{{{}IFNONNULL{}}}.
> * *Side-effect caution:* dropping a standalone {{CHECKCAST}}
> immediately before void {{RETURN}} could discard a type-check
> side effect for a value already committed to the stack.
> h2. Changes
> h3. Uniform application
> * Introduce {{{}PeepholeOptimizingClassVisitor{}}}, installed once
> from {{{}WriterController{}}}, so every method body (including
> synthetic helpers) is routed through
> {{{}PeepholeOptimizingMethodVisitor{}}}.
> * Remove ad-hoc {{new PeepholeOptimizingMethodVisitor(...)}}
> wraps from {{AsmClassGenerator}} and {{{}CallSiteWriter{}}}.
> h3. Diagnostics
> * Add {{PeepholeOptimizingMethodVisitor.printTraceBytecode}} to
> walk the visitor chain and print a nested
> {{TraceMethodVisitor}} when present.
> h3. Additional rewrites (still single-pass / stack-local)
> * Attach {{CHECKCAST}} to a pending {{ALOAD}} or reference
> constant so load + cast + {{POP}} collapses completely when
> the value is unused; keep the cast when the value is used.
> * Rewrite {{{}ACONST_NULL{}}}; {{{}IF_ACMPEQ{}}}/{{{}IF_ACMPNE{}}} to
> {{{}IFNULL{}}}/{{{}IFNONNULL{}}}.
> * Eliminate bare {{{}DUP{}}}/{{{}DUP2{}}} followed by a matching pop
> (with or without an intervening store → store-only form).
> * On void {{{}RETURN{}}}, drop only pending variable/constant loads
> (preserving {{{}IINC{}}}); flush a standalone {{CHECKCAST}}
> instead of discarding it.
> * Buffer replacement flushes prior pending state instead of
> silently clearing it; integer constant emission reuses
> {{BytecodeHelper.pushConstant}} on the delegate.
> h2. Safety
> The visitor remains a single candidate window: pending state is
> flushed at labels, frames, line numbers, invokes, and other
> non-local boundaries. Signed zero constants continue to use raw-bit
> comparisons (GROOVY-9797).
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