While working on #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

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