Redundant length check needed to optimize out panicking bounds check in loop

While working on https://github.com/rust-lang/rust/pull/147436, I noticed the following code has a panicking bounds check in the loop body that is removed when both slice lengths received from as_chunks are checked.

The slices are checked to be equal length at the start of the function, so the number of chunks and loop iterations is known to be equal.

I tried this code, which manually zips two instances of as_chunks array slices together with a while-loop:

#[inline(never)]
pub const fn all_less_than(s: &[u8], other: &[u8]) -> bool {
    if s.len() != other.len() {
        return false;
    }

    const N: usize = 16;
    let (a, _) = s.as_chunks::<N>();
    let (b, _) = other.as_chunks::<N>();

    let mut i = 0;
    while i < a.len() {
        let mut less_than = true;
        let mut j = 0;
        while j < N {
            less_than &= a[i][j] < b[i][j];
            j += 1;
        }

        if !less_than {
            return false;
        }

        i += 1;
    }

    true
}

I expected to not need to check the length for b since it's known to be equal.

When I change the loop condition from while i < a.len() to while i < a.len() && i < b.len(), the panic branch is removed.
https://rust.godbolt.org/z/azrbYq4Gv

.LBB0_4:
        sub     r8, 1
        jb      .LBB0_8
        movdqu  xmm0, xmmword ptr [rdi + rcx]
        movdqu  xmm1, xmmword ptr [rdx + rcx]
        pmaxub  xmm1, xmm0
        pcmpeqb xmm1, xmm0
        pmovmskb        eax, xmm1
        test    eax, eax
        sete    al
        jne     .LBB0_7
        add     rcx, 16
        cmp     r9, 1
        mov     r9, r8
        jne     .LBB0_4

.LBB0_4:
        movdqu  xmm0, xmmword ptr [rdi + rcx]
        movdqu  xmm1, xmmword ptr [rdx + rcx]
        pmaxub  xmm1, xmm0
        pcmpeqb xmm1, xmm0
        pmovmskb        eax, xmm1
        add     rsi, -1
        setb    r8b
        test    eax, eax
        sete    al
        jne     .LBB0_6
        add     rcx, 16
        test    r8b, r8b
        jne     .LBB0_4

Meta

Playground nightly

Nightly channel
Build using the Nightly version: 1.92.0-nightly
(2025-10-20 4068bafedd8ba724e332)

Start with the all_less_than reproducer on the linked Rust Playground using the reported nightly version, then compare the two generated assembly outputs. Investigate why the loop retains a panicking bounds check unless both as_chunks slice lengths are tested; done when the redundant length condition is no longer needed for the check to be optimized out.