TranformerCPS mutable variable capture bug #1229
Description
Consider the following program
def motz(n: Int): Int = {
if (n <= 1) {
1
} else {
val limit = n - 2
def product(i: Int): Int = {
motz(i) * motz(limit - i)
}
motz(n - 1) + sum(0, limit) { product }
}
}which is translated to
function motz_0(n_23, ks_1706, k_937) {
motz_1: while (true) {
if ((n_23 <= (1))) {
return () => k_937(1, ks_1706);
} else {
function product_2(i_45, ks_1707, k_938) {
return motz_0(i_45, ks_1707, (v_r_846, ks_1708) =>
motz_0((((n_23 - (2))) - i_45), ks_1708, (v_r_847, ks_1709) =>
() => k_938((v_r_846 * v_r_847), ks_1709)));
}
/* prepare call */
const tmp_n_1 = n_23;
const tmp_k_6 = k_937;
k_937 = (v_r_848, ks_1710) =>
sum_4(0, (tmp_n_1 - (2)), product_2, ks_1710, (v_r_849, ks_1711) =>
() => tmp_k_6((v_r_848 + v_r_849), ks_1711));
n_23 = (tmp_n_1 - (1));
continue motz_1;
}
}
}if not using optimizations (no-optimize). When the continuation k_937 is overwritten, we call sum_4 and correctly rename n to tmp_n_1. However, in product_2 we still use n_23 which is mutated before the continuation is called, altering the semantics.
Doing this correctly might be difficult since by the time we apply the substitution, the binding product_2 has already been introduced and is not considered anymore.
(this issue has been split off from #1200)