Quirks of #repr(align()) errors

[glandium]

2GiB alignments fail:

error[E0589]: invalid `repr(align)` attribute: larger than 2147483647
  --> src/main.rs:11:8
   |
11 | #[repr(align(2147483648))]
   |        ^^^^^^^^^^^^^^^^^

which could be considered fine, although I don't see why, besides the Layout::from_size_align limitation which I think is wrong (#32838 (comment)). But that's besides the point. The error message is kind of pointless talking about 2GiB - 1:

error[E0589]: invalid `repr(align)` attribute: not a power of two
  --> src/main.rs:11:8
   |
11 | #[repr(align(2147483647))]
   |        ^^^^^^^^^^^^^^^^^

Because any value larger than 1GiB will actually fail too because they're not powers of two.

Also, The error is unknown on error-index.html: https://doc.rust-lang.org/error-index.html#E0589

[glandium]

I could file a separate issue, but this seems to fall under the same:

#[repr(align(1073741824))]
struct Foo;

fn main() {
    Box::new(Foo);
}

yields

huge alignment values are unsupported
  %1 = alloca %Foo, align 1073741824
LLVM ERROR: Broken function found, compilation aborted!

512M works.