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Eliminates per-call heap allocations for three hot list-building patterns
identified by pprof in v0.6.5:
- parseStringAtom: single plain string literals now take an early return
that skips the plainParts []string accumulator entirely; multi-part strings
write into p.ar.plainPartsBuf (pre-grown, reused per parse).
- parseSimpleStmtList: var stmts []Stmt replaced by the arena scratch buffer
p.ar.simpleStmtBuf; callers consume via append(outer, ss...) before the
next call, satisfying the safety contract. The inline-block path copies out.
- parseExprBasedStmt: targets := []Expr{lhs} replaced by contiguous segments
of p.ar.exprLists, a new slab field reset per parse alongside the node slabs.
Serial: +2% (116.8 → 119.0 MB/s). Parallel: +5% (400.6 → 419.4 MB/s).
Allocs/op: −29% (2.0M → 1.43M). B/op: −14% (64 MB → 55 MB).
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Summary
parseStringAtomfast path: single plain string literals return directly fromarenaAlloc— noplainParts []stringallocation; multi-part strings reusep.ar.plainPartsBufparseSimpleStmtListscratch buffer:var stmts []Stmtreplaced by arena'ssimpleStmtBuf; callers consume viaappend(outer, ss...)before the next call; inline-block path copies out to protect AST correctnessexprLists):targets := []Expr{lhs}replaced by contiguous segments in a newp.ar.exprListsarena slab, reset per parseBenchmark (Apple M4, 10 cores)
Test plan
go test ./...passes