`isqrt` treated as a `black_box`

I tried this code:

#[inline(never)]
pub const fn f(n: u8) {
    assert!(n >= 4);
    assert!(2 <= n.isqrt());
}

[!note]
I've tried:

• removing const
• replacing u8 by usize
• replacing 4 by 9 and 2 by 3

Outcome was the same

I expected to see this happen: 2nd assertion non-existent in assembly.

Instead, this happened:

# ... (snip)
.LBB0_4:
	leaq	.L__unnamed_4(%rip), %rdi
	leaq	.L__unnamed_5(%rip), %rdx
	movl	$32, %esi
	callq	*core::panicking::panic@GOTPCREL(%rip)
# ...
.L__unnamed_4:
	.ascii	"assertion failed: 2 <= n.isqrt()"
# ...

Meta

Playground

rustc --version --verbose:

1.84.0-nightly (2024-11-06 8549802939cd01111c46)

No Backtrace

@rustbot label: +I-slow, -C-bug

Start by reproducing the example in the linked Rust Playground with the reported nightly compiler and inspect the release assembly. Compare the handling of the const isqrt call with the surrounding assertions and compiler evaluation or optimization behavior. Done means the second assertion is eliminated when its condition is provably true, with appropriate regression coverage.