[BUG] 0! == 0

[helehex]

Bug description

I've noticed a few weird bugs and discrepancies with for loops.
In this case, I'm using a factorial loop fac(), evaluated at 0, which should give 1, but instead gives 0.
Toggling any one of the comments in the example will fix it.

Steps to reproduce

fn main():
    # @parameter # uncomment this and it works
    for n in range(1):
        # print(n) # uncomment this and it works
        print(fac(n))
        # prints: 0


# @no_inline # uncomment this and it works
fn fac(n: Int) -> Int:
    var r = 1
    var i = n
    while i > 1:
        # This isnt reached, but:
        r *= i # comment this and it works
        i -= 1 # comment this and it works
    return r

System information

Host Information
  ================

  Target Triple: x86_64-unknown-linux
  CPU: skylake
  CPU Features: adx, aes, avx, avx2, bmi, bmi2, clflushopt, cmov, crc32, cx16, cx8, f16c, fma, fsgsbase, fxsr, invpcid, lzcnt, mmx, movbe, pclmul, popcnt, prfchw, rdrnd, rdseed, sahf, sgx, sse, sse2, sse3, sse4.1, sse4.2, ssse3, x87, xsave, xsavec, xsaveopt, xsaves

mojo 2024.8.405 (27e8e5b4)

modular 0.8.0 (39a426b5)

[soraros]

There are two other curious repros.

fn main():
    var r = 0

    @parameter
    for _ in range(10):
        r = 0

    print(r)  # prints 140726121024432

But the following, which should be semantically equivalent, works just fine.

fn main():
    var r = 0

    @parameter
    for i in range(10):
        @parameter
        if i == i:
            r = 0

    print(r)  # prints 0

[jjvraw]

Is the issue exclusive to main? An empty body also compiles and runs:

fn main():
    for i in range(10):

Can you reproduce those examples in other contexts outside of main?

[soraros]

@jjvraw I think that's a separate issue #3280.

[jjvraw]

Ah, I agree that the empty body of the for is then more likely related to that issue.

[jjvraw]

while i > 1: -> while i >= 1: also returns correctly

[helehex]

Original reproduction still gives 0.
Sora's addendum seems to be fixed though.