`cannot guarantee tail call due to mismatched parameter counts`

[matthiaskrgr]

I tried this code:

//@ check-pass
// so this should compile.
#![expect(incomplete_features)]
#![feature(explicit_tail_calls)]

fn a(x: u32) -> u32 {
    become b(x);
}

#[track_caller]
fn b(x: u32) -> u32 { x + 42 }

fn main() {
    assert_eq!(a(128), 54);
}

Meta

rustc --version --verbose:

adcb3d3b4cd3b7c4cde642f3ed537037f293738e

Backtrace

cannot guarantee tail call due to mismatched parameter counts
  %2 = musttail call i32 @_ZN64FF3C930F77C71A201CC3F60E04A19F24F40C416034B4A3B4054609ACB4023FA01b17h0731788d0a0410ebE(i32 %0, ptr align 8 @2)
rustc-LLVM ERROR: Broken module found, compilation aborted!