[jira] [Assigned] (GROOVY-12065) Implement peephole optimization for bytecode generation

["Eric Milles (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/GROOVY-12065?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Eric Milles reassigned GROOVY-12065:
------------------------------------

    Assignee: Daniel Sun

> 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
>            Assignee: 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 to Implement
> 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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