Lifetime Bug #44

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opened 2026-08-11 18:08:55 +00:00 by Furkan · 1 comment

Furkan commented

2026-08-11 18:08:55 +00:00

I couldn't simplify the code so I'm gonna provide the code as is

import io

const {
    TOTAL = 4096
    L = 1 << 31
}

global {
    freq []uint
    cum []uint
}

calc_freqs(freq []uint) {
    freq['a'] = 335
    freq['b'] = 61
    freq['c'] = 114
    freq['d'] = 174
    freq['e'] = 520
    freq['f'] = 91
    freq['g'] = 83
    freq['h'] = 250
    freq['i'] = 285
    freq['j'] = 6
    freq['k'] = 32
    freq['l'] = 165
    freq['m'] = 99
    freq['n'] = 276
    freq['o'] = 307
    freq['p'] = 79
    freq['q'] = 4
    freq['r'] = 245
    freq['s'] = 259
    freq['t'] = 371
    freq['u'] = 113
    freq['v'] = 40
    freq['w'] = 97
    freq['x'] = 6
    freq['y'] = 81
    freq['z'] = 3
}

calc_cums(cum []uint) {
    cum['a'] = 0
    cum['b'] = 335
    cum['c'] = 396
    cum['d'] = 510
    cum['e'] = 684
    cum['f'] = 1204
    cum['g'] = 1295
    cum['h'] = 1378
    cum['i'] = 1628
    cum['j'] = 1913
    cum['k'] = 1919
    cum['l'] = 1951
    cum['m'] = 2116
    cum['n'] = 2215
    cum['o'] = 2491
    cum['p'] = 2798
    cum['q'] = 2877
    cum['r'] = 2881
    cum['s'] = 3126
    cum['t'] = 3385
    cum['u'] = 3756
    cum['v'] = 3869
    cum['w'] = 3909
    cum['x'] = 4006
    cum['y'] = 4012
    cum['z'] = 4093
}

encode(state uint, output []byte, output_pos uint, value byte) -> (uint, uint) {
    f := freq[value]

    x_max := 134217728 as uint
    x_max *= f

    loop {
        if state < x_max {
            loop.stop()
        }

        output[output_pos] = (state & 255) as byte
        output_pos += 1
        state >>= 8
    }

    q := state / f
    r := state % f

    state = q * TOTAL + r + cum[value]

    return state, output_pos
}

decode(state uint, input []byte, input_pos uint) -> (uint, byte, uint) {
    slot := state % TOTAL

    symbol := 0

    loop i := 0..128 {
        if freq[i] != 0 {
            if slot >= cum[i] {
                if slot < cum[i] + freq[i] {
                    symbol = i
                    loop.stop()
                }
            }
        }
    }

    f := freq[symbol]

    q := state / TOTAL
    r := slot - cum[symbol]

    state = q * f + r

    loop {
        if state >= L {
            loop.stop()
        }

        input_pos -= 1

        x := input[input_pos] as uint

        state = (state << 8) + x
    }

    return state, symbol as byte, input_pos
}

main() {
    freq = new(uint, 128)
    cum = new(uint, 128)

    calc_freqs(freq)
    calc_cums(cum)

    data := "aaaaaaaaasdsad"
    state := L as uint

    output := new(byte, data.len * 2)
    output_pos := 0 as uint

    loop i := 0..data.len {
        c := data[data.len - i - 1]
        state, output_pos = encode(state, output, output_pos, c)
    }

    io.writeLine(output_pos)

    decoded := new(byte, data.len)

    d := 0 as byte

    loop i := 0..data.len {
        state, d, output_pos = decode(state, output, output_pos)
        decoded[i] = d
    }

    io.writeLine(decoded)
    io.writeLine(output_pos) // try commenting out this line
}

when I comment out io.writeLine(output_pos) program crashes

here is some variations of this program only print changes

I have no idea how printing some numbers effect the calculation of other numbers I'm really confused

I couldn't simplify the code so I'm gonna provide the code as is ``` import io const { TOTAL = 4096 L = 1 << 31 } global { freq []uint cum []uint } calc_freqs(freq []uint) { freq['a'] = 335 freq['b'] = 61 freq['c'] = 114 freq['d'] = 174 freq['e'] = 520 freq['f'] = 91 freq['g'] = 83 freq['h'] = 250 freq['i'] = 285 freq['j'] = 6 freq['k'] = 32 freq['l'] = 165 freq['m'] = 99 freq['n'] = 276 freq['o'] = 307 freq['p'] = 79 freq['q'] = 4 freq['r'] = 245 freq['s'] = 259 freq['t'] = 371 freq['u'] = 113 freq['v'] = 40 freq['w'] = 97 freq['x'] = 6 freq['y'] = 81 freq['z'] = 3 } calc_cums(cum []uint) { cum['a'] = 0 cum['b'] = 335 cum['c'] = 396 cum['d'] = 510 cum['e'] = 684 cum['f'] = 1204 cum['g'] = 1295 cum['h'] = 1378 cum['i'] = 1628 cum['j'] = 1913 cum['k'] = 1919 cum['l'] = 1951 cum['m'] = 2116 cum['n'] = 2215 cum['o'] = 2491 cum['p'] = 2798 cum['q'] = 2877 cum['r'] = 2881 cum['s'] = 3126 cum['t'] = 3385 cum['u'] = 3756 cum['v'] = 3869 cum['w'] = 3909 cum['x'] = 4006 cum['y'] = 4012 cum['z'] = 4093 } encode(state uint, output []byte, output_pos uint, value byte) -> (uint, uint) { f := freq[value] x_max := 134217728 as uint x_max *= f loop { if state < x_max { loop.stop() } output[output_pos] = (state & 255) as byte output_pos += 1 state >>= 8 } q := state / f r := state % f state = q * TOTAL + r + cum[value] return state, output_pos } decode(state uint, input []byte, input_pos uint) -> (uint, byte, uint) { slot := state % TOTAL symbol := 0 loop i := 0..128 { if freq[i] != 0 { if slot >= cum[i] { if slot < cum[i] + freq[i] { symbol = i loop.stop() } } } } f := freq[symbol] q := state / TOTAL r := slot - cum[symbol] state = q * f + r loop { if state >= L { loop.stop() } input_pos -= 1 x := input[input_pos] as uint state = (state << 8) + x } return state, symbol as byte, input_pos } main() { freq = new(uint, 128) cum = new(uint, 128) calc_freqs(freq) calc_cums(cum) data := "aaaaaaaaasdsad" state := L as uint output := new(byte, data.len * 2) output_pos := 0 as uint loop i := 0..data.len { c := data[data.len - i - 1] state, output_pos = encode(state, output, output_pos, c) } io.writeLine(output_pos) decoded := new(byte, data.len) d := 0 as byte loop i := 0..data.len { state, d, output_pos = decode(state, output, output_pos) decoded[i] = d } io.writeLine(decoded) io.writeLine(output_pos) // try commenting out this line } ``` when I comment out `io.writeLine(output_pos)` program crashes here is some variations of this program only print changes ![Screenshot 2026-08-11 210436](/attachments/6b5c606d-5cce-4767-9f9b-5f76b6385972) ![Screenshot 2026-08-11 210450](/attachments/ceaf8bdf-6442-4a7b-8876-65574469c6ff) ![Screenshot 2026-08-11 210514](/attachments/fa6326e5-ae21-4a4e-8cf6-a5a37deb3942) ![Screenshot 2026-08-11 210523](/attachments/15a89afa-43c5-4d7a-8acd-8a7043adf919) I have no idea how printing some numbers effect the calculation of other numbers I'm really confused

Screenshot 2026-08-11 210436.png

47 KiB

Screenshot 2026-08-11 210450.png

43 KiB

Screenshot 2026-08-11 210514.png

59 KiB

Screenshot 2026-08-11 210523.png

61 KiB

ed commented

2026-08-13 07:02:20 +00:00

Owner

This seems to be the result of an optimization.
There is some code in the assembler that will recognize patterns like these:

mov a, b
mov b, a

think of it as

a = b
b = a

...and it will drop the 2nd instruction because it is effectively a no-op.
However, this pattern is actually searched in the cycle detection and it should have caused a compiler panic, saying "cycle detected" because the automatic addition of a temporary register is not implemented yet.

The optimization dropped the second instruction which prevented the detection of the cycle.

To fix this, 2 things need to be implemented:

Skip this optimization in the parts of the code that rely on cycle detection.
Find a temporary register to resolve the cycle.

This seems to be the result of an optimization. There is some code in the assembler that will recognize patterns like these: ``` mov a, b mov b, a ``` think of it as ``` a = b b = a ``` ...and it will drop the 2nd instruction because it is effectively a no-op. However, this pattern is actually searched in the cycle detection and it should have caused a compiler panic, saying "cycle detected" because the automatic addition of a temporary register is not implemented yet. The optimization dropped the second instruction which prevented the detection of the cycle. To fix this, 2 things need to be implemented: 1. Skip this optimization in the parts of the code that rely on cycle detection. 2. Find a temporary register to resolve the cycle.

ed added the

bug

label

2026-08-14 10:40:01 +00:00

ed self-assigned this

2026-08-14 10:40:06 +00:00