select_nth_unstable (partition_at_index) has plenty of redundant bounds checks

I wouldn't expect any panics other than panic_on_ord_violation and input arguments check, which should get optimized out.

https://rust.godbolt.org/z/h5P6Er8zr

.LBB2_96:
        lea     rax, [rip + .Lanon.c0a2eb89440bc2e212dbf84361b066b5.10]
        mov     qword ptr [rsp + 24], rax
        mov     qword ptr [rsp + 32], 1
        mov     qword ptr [rsp + 40], 8
        xorps   xmm0, xmm0
        movups  xmmword ptr [rsp + 48], xmm0
        lea     rsi, [rip + .Lanon.c0a2eb89440bc2e212dbf84361b066b5.13]
        lea     rdi, [rsp + 24]
        call    qword ptr [rip + core::panicking::panic_fmt::h22107f1a113fdabe@GOTPCREL]
.LBB2_97:
        lea     rax, [rip + .Lanon.c0a2eb89440bc2e212dbf84361b066b5.10]
        mov     qword ptr [rsp + 24], rax
        mov     qword ptr [rsp + 32], 1
        mov     qword ptr [rsp + 40], 8
        xorps   xmm0, xmm0
        movups  xmmword ptr [rsp + 48], xmm0
        lea     rsi, [rip + .Lanon.c0a2eb89440bc2e212dbf84361b066b5.14]
        lea     rdi, [rsp + 24]
        call    qword ptr [rip + core::panicking::panic_fmt::h22107f1a113fdabe@GOTPCREL]
.LBB2_95:
        ud2
.LBB2_15:
        lea     rdx, [rip + .Lanon.c0a2eb89440bc2e212dbf84361b066b5.12]
        mov     rsi, r13
        call    qword ptr [rip + core::panicking::panic_bounds_check::hdaa6e5107cd75dd9@GOTPCREL]
.LBB2_24:
        lea     rdx, [rip + .Lanon.c0a2eb89440bc2e212dbf84361b066b5.11]
        mov     rsi, r13
        call    qword ptr [rip + core::panicking::panic_bounds_check::hdaa6e5107cd75dd9@GOTPCREL]

Start with the Rust Compiler Explorer link and the select_nth_unstable/partition_at_index implementation named in the issue. Inspect the generated assembly and trace the indexed accesses that produce the reported bounds-check panics. Done means only panic_on_ord_violation and input-argument checks remain, with redundant bounds checks optimized out.