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https://issues.apache.org/jira/browse/GROOVY-12065?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Daniel Sun updated GROOVY-12065:
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Summary: Implement peephole optimization for bytecode generation (was:
Implement peephole optimization for constant loading in bytecode generation)
> 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
>
> h3. Background
> Groovy's bytecode generator relied on ad-hoc, per-type conditional branches
> scattered across {{OperandStack}} and {{BytecodeHelper}} to select compact
> constant-loading instructions ({{{}ICONST_x{}}}, {{{}LCONST_x{}}},
> {{{}FCONST_x{}}}, {{{}DCONST_x{}}}, {{{}BIPUSH{}}}, {{{}SIPUSH{}}}) over the
> generic {{LDC}} instruction. This logic was fragile, inconsistent, and
> incomplete — for instance, {{BytecodeHelper.pushConstant()}} was missing the
> {{ICONST_M1}} case for the integer constant {{{}-1{}}}.
> h3. Change
> A new {{PeepholeOptimizingMethodVisitor}} — a {{MethodVisitor}} decorator —
> is introduced and inserted into the per-method visitor chain in
> {{{}AsmClassGenerator{}}}. It intercepts every {{visitLdcInsn}} and
> {{visitIntInsn(BIPUSH/SIPUSH, ...)}} call and rewrites each to the shortest
> valid equivalent opcode:
> ||Value||Emitted instruction||
> |{{int}} −1|{{ICONST_M1}}|
> |{{int}} 0–5|{{ICONST_0}} – {{ICONST_5}}|
> |{{int}} in [−128, 127]|{{BIPUSH}}|
> |{{int}} in [−32768, 32767]|{{SIPUSH}}|
> |{{long}} 0 / 1|{{LCONST_0}} / {{LCONST_1}}|
> |{{float}} 0 / 1 / 2|{{FCONST_0}} / {{FCONST_1}} / {{FCONST_2}}|
> |{{double}} 0 / 1|{{DCONST_0}} / {{DCONST_1}}|
> Signed-zero {{float}} and {{double}} values are handled correctly by
> comparing raw bit patterns (via {{Float.floatToRawIntBits}} /
> {{{}Double.doubleToRawLongBits{}}}) rather than {{{}=={}}}, preserving the
> {{-0.0}} / {{+0.0}} distinction that a straight equality check would collapse.
> All per-type branches previously inlined in {{OperandStack}} are replaced
> with plain {{visitLdcInsn(value)}} calls; the peephole visitor centralizes
> the selection uniformly for every generated method.
> {{BytecodeHelper.pushConstant()}} also gains the previously missing
> {{ICONST_M1}} branch.
>
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