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A tail alternatives whose branches are all stateless can never be
resumed: each branch either matches the whole remainder or fails
deterministically. Fold such alts into tailAltMatcher -- the branches
are tried in order with no checkpoints and no matchState, so e.g.
{abc*def,abc?def,abc[zte]def} now matches without touching the state
pool at all.
Alternative-heavy benchmarks improve 65-75% (24ns -> 8ns on the shaped
ones, 61ns -> 21ns on the four-branch row); patterns with stateful
branches ({a*b*c,d}) or non-tail alts ({a,b}c) are unchanged.
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A tail alternatives whose branches are all stateless can never be resumed: each branch either matches the whole remainder or fails deterministically. Fold such alts into tailAltMatcher -- the branches are tried in order with no checkpoints and no matchState, so e.g. {abc*def,abc?def,abc[zte]def} now matches without touching the state pool at all.
Alternative-heavy benchmarks improve 65-75% (24ns -> 8ns on the shaped ones, 61ns -> 21ns on the four-branch row); patterns with stateful branches ({abc,d}) or non-tail alts ({a,b}c) are unchanged.