Unexpected possible index out of bounds warning in direct vector iteration

[Darion Cassel]

Issue

The following test case produces several error messages that center around a possible index out of bounds and analysis fixed point loop iterations exceeding their limit.

Steps to Reproduce

Test case that produces the wrong output:

pub fn test() {
    let mut bar: Vec<Foo> = vec!();
    bar.push(Foo { content: 0 });
    for i in 0..bar.len() {
        assume!(i < bar.len()); //~assumption is provably true and can be deleted
        add_tag!(&bar[i], SecretTaint); //~possible index out of bounds
        println!("{}", bar[i].content); 
    }
    //~Fixed point loop iterations exceeded limit of 10
}

Expected Behavior

The loop body contains vector indexing using the loop induction variable, which is bounded by the length of the vector; it is in-bounds. There should be no error messages raised by MIRAI.

Actual Results

Several error messages are raised:

1. MIRAI claims that the vector indexing is a case of possible index out of bounds. Yet, if an assumption is added to show that the induction variable does indeed fall within the vector bounds MIRAI notes that this assumption is provably true and can be deleted.
2. MIRAI raises the error Fixed point loop iterations exceeded limit of 10.

Environment

rustc 1.55.0-nightly (7c3872e6b 2021-06-24)