Crystal recursive function resulting in a signal 11 (invalid memory access)? - tail-recursion

Question

I wanted to test recursive functions in Crystal, so I wrote something like...
def repeat(n)
return if n < 0
# Useless line just to do something
n + 1
repeat(n - 1)
end
repeat(100_000_000)
I didn't expect this to work with either crystal recurse.cr or crystal build recurse.cr, because neither one of those can optimize for tail call recursion - as expected, both resulted in stack overflows.
When I used the --release flag, it was totally fine - and incredibly fast.
If I did the following...
NUM = 100_000
def p(n)
puts n if n % (NUM / 4) == 0
end
def recursive_repeat(n)
return if n < 0
p(n)
recursive_repeat(n-1)
end
recursive_repeat(NUM)
... everything is fine - I don't even need to build it.
If I change to a much larger number and a non-recursive function, again it's fine...
NUM = 100_000_000
def p(n)
puts n if n % (NUM / 4) == 0
end
def repeat(num)
(0..num).each { |n| p(n) }
end
repeat(NUM)
If I instead use recursion, however...
NUM = 100_000
def p(n)
puts n if n % (NUM / 4) == 0
end
def recursive_repeat(n)
return if n < 0
p(n)
recursive_repeat(n-1)
end
recursive_repeat(NUM)
...I get the following output:
100000000
Invalid memory access (signal 11) at address 0x7fff500edff8
[4549929098] *CallStack::print_backtrace:Int32 +42
[4549928595] __crystal_sigfault_handler +35
[140735641769258] _sigtramp +26
[4549929024] *recursive_repeat<Int32>:Nil +416
[4549929028] *recursive_repeat<Int32>:Nil [phone] times)
[4549926888] main +2808
How does using puts like that trigger a stack overflow - especially given that it would only write 5 lines total?
Shouldn't this still be TCO?
Edit
Okay, to add to the weirdness, this works...
NUM = 100_000_000
def p(n)
puts n if n % (NUM / 4) == 0
end
def repeat(num)
(0..num).each { |n| p(n) }
end
repeat(NUM)
def recursive_repeat(n)
return if n < 0
p(n)
recursive_repeat(n-1)
end
recursive_repeat(NUM)
... but removing the call to repeat(NUM), literally keeping every other line the same, will again result in the error.