debug compiled no-op `transmute_copy` not inlined and contains precondition checks

I tried this code:

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=0c942f34da6a1a7f062435ea8b8e0920

#[unsafe(no_mangle)]
fn foo(x: [u8; 4]) -> u32 { unsafe { core::mem::transmute_copy(&x) } }
#[unsafe(no_mangle)]
fn bar(x: u32) -> u32 { unsafe { core::mem::transmute_copy(&x) } }

I expected to see this happen: Because both types are trivially copyable (same size, same type for the latter) it should compile down to a register move or whatever.

Instead, this happened: It isn't inlined, and there's a precondition check for the size despite the size being statically known.

I will say it's significantly better than what is emitted on 1.97.1.

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rustc --version --verbose:

1.99.0-nightly

(2026-08-12 c98d0cb27cc63afdd626)