fn check_custom_mir(
cx: &mut AcceptContext<'_, '_>,
dialect: Option<(MirDialect, Span)>,
phase: Option<(MirPhase, Span)>,
failed: &mut bool,
)fn check_custom_mir(
cx: &mut AcceptContext<'_, '_>,
dialect: Option<(MirDialect, Span)>,
phase: Option<(MirPhase, Span)>,
failed: &mut bool,
)