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Malte Ubl
0e943fedb0
While loops discarded every loop-carried fact, so the escape-time counter
in `while (x * x + y * y <= 4 && it < MAX) { ...; it++ }` stayed a double:
its increment, its bound compare and the `it === MAX` test after the loop
all ran in floating point.
guardedLoopCounterFacts bounds a counter that the loop changes only by
increments of positive integer literals outside nested loops, switch and
exception regions, when a conjunct of the condition compares it below a
literal or a binding the loop never writes, and the condition itself never
writes it. The body runs only after that conjunct held, so every pass
starts at most at the bound and climbs by at most the sum of the body's
increments; the counter starts at its entry fact and only grows. The range
holds at every read inside and after the loop, so it also feeds the
loop-carried closure as an invariant.
The mandelbrot counter becomes an i32 slot. Corpus 5333 pins escape-time,
reversed, inclusive, multi-increment, early-exit and module-level counters,
and every case that must stay double (counters written by their condition,
decrements, fractional and unknown steps, nested increments, written
bounds, disjunctions, fractional, -0, NaN and infinite starts, limits past
2^31, 2^32 and 2^53) against Node.