Comment by palmtree3000

Yep. Here's an example I found once: https://godbolt.org/z/XQBcR9

  pub fn mul1(mut a: i32, b:i32) -> i32 {
      let mut out = 0;
      while a != 0 {
          out += b;
          a-=1;
      }
      out
  }

  pub fn mul2(a: i32, b: i32) -> i32 {
      if a == 0 {
          0
      } else {
          b + mul2(a-1, b)
      }
  }

Both are optimized to imul. But that's not actually correct: neither of these should terminate for negative a!

Incidentally, this is actually a rust bug, caused by LLVM performing this optimization despite it being illegal in rust.