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https://issues.apache.org/jira/browse/GROOVY-12065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18086620#comment-18086620
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ASF GitHub Bot commented on GROOVY-12065:
-----------------------------------------
sonarqubecloud[bot] commented on PR #2591:
URL: https://github.com/apache/groovy/pull/2591#issuecomment-4639867095
## [](https://sonarcloud.io/dashboard?id=apache_groovy&pullRequest=2591)
**Quality Gate passed**
Issues
 [4 New
issues](https://sonarcloud.io/project/issues?id=apache_groovy&pullRequest=2591&issueStatuses=OPEN,CONFIRMED&sinceLeakPeriod=true)
 [0 Accepted
issues](https://sonarcloud.io/project/issues?id=apache_groovy&pullRequest=2591&issueStatuses=ACCEPTED)
Measures
 [0 Security
Hotspots](https://sonarcloud.io/project/security_hotspots?id=apache_groovy&pullRequest=2591&issueStatuses=OPEN,CONFIRMED&sinceLeakPeriod=true)
 [89.2% Coverage on New
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 [0.0% Duplication on New
Code](https://sonarcloud.io/component_measures?id=apache_groovy&pullRequest=2591&metric=new_duplicated_lines_density&view=list)
<!
> Implement peephole optimization for bytecode generation
> -------------------------------------------------------
>
> Key: GROOVY-12065
> URL: https://issues.apache.org/jira/browse/GROOVY-12065
> Project: Groovy
> Issue Type: Improvement
> Reporter: Daniel Sun
> Priority: Major
>
> h2. Overview
> This improvement introduces a dedicated, single-pass bytecode compaction
> layer via {{PeepholeOptimizingMethodVisitor}}. This adapter wraps the
> underlying ASM {{MethodVisitor}} during class generation
> ({{AsmClassGenerator}}), intercepting instruction streams within local basic
> blocks to eliminate redundant operations, rewrite conditional branches, and
> narrow constant instructions to their most optimal forms.
> Crucially, by decoupling peephole optimization from structural code
> generation, this approach significantly simplifies the constant emission
> logic inside {{OperandStack}}. Instead of maintaining verbose, duplicate
> routing logic for specialized primitive opcodes (such as {{ICONST_x}},
> {{BIPUSH}}, or {{FCONST_x}}), {{OperandStack}} now delegates constant pushing
> uniformly via {{visitLdcInsn}}. The stateful peephole layer then
> transparently condenses these instructions into their tightest bytecode
> representations under the hood.
> h2. Key Optimizations Implemented
> h3. 1. Redundant Instruction & Dead Code Elimination
> * *Discarded Assignment Values:* Eliminates wasteful {{DUP}} -> {{[X]STORE}}
> -> {{POP}} patterns typically produced during assignments where the
> expression result on the operand stack is unused. The optimizer flattens
> these directly into a single {{[X]STORE}}.
> * *Redundant Loads:* Detects situations where a local variable or constant is
> loaded ({{[X]LOAD}} / {{LDC}}) but immediately discarded via
> {{POP}}/{{POP2}}, or followed immediately by a void {{RETURN}}. The optimizer
> safely drops both operations while preserving interleaved local increments
> ({{IINC}}).
> h3. 2. Conditional Jump & Zero-Comparison Rewriting
> * Optimizes integer comparisons against zero by transforming expensive binary
> comparison sequences (e.g., {{ILOAD}} -> {{ICONST_0}} -> {{IF_ICMPxx}}) into
> compact unary zero-comparison instructions ({{IFxx}}). For instance, an
> {{IF_ICMPEQ}} branch against a buffered {{0}} constant is cleanly rewritten
> directly to {{IFEQ}}.
> h3. 3. Instruction Narrowing & Constant Compaction
> * Intercepts standard literal definitions and transparently narrows them down
> to the smallest possible specialized opcodes ({{ICONST_M1}} through
> {{ICONST_5}}, {{BIPUSH}}, {{SIPUSH}}, {{LCONST_0/1}}, {{FCONST_0/1/2}}, and
> {{DCONST_0/1}}).
> * Explicitly safeguards signed floating-point zeros ({{-0.0f}} and {{-0.0d}})
> from accidental flattening to guarantee strict IEEE 754 runtime compliance.
> h3. 4. Big Number Literal Lowering
> * Centralizes string-constructed object instantiations for {{BigDecimal}} and
> {{BigInteger}} literals by rewriting buffered constants into inline {{NEW}}
> -> {{DUP}} -> {{LDC [string]}} -> {{INVOKESPECIAL <init>}} pipelines
> seamlessly before stack emission.
> h2. Implementation Strategy & Safety Guardrails
> The {{PeepholeOptimizingMethodVisitor}} operates on a lightweight,
> stack-local sliding window. To fully preserve runtime semantics, debugging
> capabilities, and catch-block structures, the lookahead window is
> automatically flushed to the delegate visitor when encountering non-local
> boundaries or frame-altering instructions, including:
> * Control flow jumps and basic block {{Label}} targets.
> * Stack map frames ({{visitFrame}}).
> * Line numbers and local variable debug maps.
> * Method invocations and {{InvokeDynamic}} instructions.
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