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Chris Tate
142e10a0c4
`for (let i = 0, p = 0; i < count; i++, p += 4)` kept both counters as doubles: the counted-loop match takes a single declaration and a single update. A counted loop now also accepts further counters declared in its head and stepped by a constant in its update, when the condition does not read them and the body does not write them. On body entry k such a counter holds `start + step * k`, so its range follows from the driver's: k is at most the driver's span over its step. When that range can pass 2^53, the versioned loop tests `|start| + |step| * span / |driver step| <= 2^52` at run time, and an unproven start is tested for an exact safe integer, as the driver's is. Nested update blocks (`i++, j += 2, k--`) are flattened. Byte windows and dense loops still take only single-counter loops.