PEGO
M110: Compact VM Backtracking State
VM choice and repetition entries are pushed frequently. Keeping rare label/recovery data off the common entry reduces copied stack state.
Mechanism and Invariants
The VM moves label, recovery and skip-only fields to a separate label stack, indexed by the main entry. Saved heights use compact integers. Entry rollback must restore both stacks together so expectations, recovered errors and skip behavior stay unchanged.
Scope and State
Default recursive and iterative VM entry representation. Closure and generated Go/TypeScript have separate state layouts.
Reference Control
No maintained same-source large-entry layout comparator exists.
Evidence and Implementation
Record 033 reports historical entry size from 112 to 56 bytes and sampled VM improvements of 1–5% for full parsing and 2–6% recognition. Later recovery/filter/work-control state changes mean those sizes are historical, not a current layout assertion.
Evidence records: 033.
Source owners: entry and label stack,
iterative VM entry execution.
The comparison policy distinguishes same-source controls, historical changes and full checkpoints.