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Chris Tate
2840a92124
A while loop that advances a counter through a string, such as
while (pos < text.length) {
const ch = text.charCodeAt(pos);
pos++;
if (ch === 13 && pos < text.length && text.charCodeAt(pos) === 10) pos++;
...
}
kept the counter as a double, so every read converted it and every
charCodeAt took the general index path. The guarded while-counter facts
accepted only a literal or a binding the loop never writes as the
bound. They now also accept the length of a string binding the loop
never writes, which is at most 2^31 - 1 units.
The counter's maximum is also tracked along each path of the body
instead of summing every increment: an increment inside an `if` whose
condition compares the counter below such a bound starts from that
bound, and exits end their path. The second increment above therefore
keeps the counter within int32, and the counter gets int32 storage and
integer charCodeAt reads.