rustc 1.71.1 fails to build for big-endian aarch64

[he32]

rustc 1.71.1 fails to build for big-endian aarch64, such as e.g. aarch64_be-unknown-netbsd.
The reason may be universal reliance on the neon feature for aarch64, while I think that is
not available in big-endian mode.

I expected to see this happen: The (cross)build ought to succeed.

Instead, this happened: The build errors out with

error[E0432]: unresolved imports `core::arch::aarch64::vqtbl1q_u8`, `core::arch::aarch64::vtbl1_u8`
  --> library/core/src/../../portable-simd/crates/core_simd/src/swizzle_dyn.rs:20:46
   |
20 |         use core::arch::aarch64::{uint8x8_t, vqtbl1q_u8, vtbl1_u8};
   |                                              ^^^^^^^^^^  ^^^^^^^^ no `vtbl1_u8` in `core_arch::arch::aarch64`
   |                                              |
   |                                              no `vqtbl1q_u8` in `core_arch::arch::aarch64`
   |
help: a similar name exists in the module
   |
20 |         use core::arch::aarch64::{uint8x8_t, vst1q_u8, vtbl1_u8};
   |                                              ~~~~~~~~
help: a similar name exists in the module
   |
20 |         use core::arch::aarch64::{uint8x8_t, vqtbl1q_u8, vtrn1_u8};
   |                                                          ~~~~~~~~

For more information about this error, try `rustc --explain E0432`.

Did not run successfully: exit status: 1

Meta

The implementation in
library/stdarch/crates/core_arch/src/aarch64/neon/mod.rs appears to only define
these if the target endian-ness is little-endian, ref.

/// Table look-up
#[inline]
#[cfg(target_endian = "little")]
#[target_feature(enable = "neon")]
#[cfg_attr(test, assert_instr(tbl))]
#[stable(feature = "neon_intrinsics", since = "1.59.0")]
pub unsafe fn vqtbl1q_u8(t: uint8x16_t, idx: uint8x16_t) -> uint8x16_t {
    transmute(vqtbl1q(transmute(t), transmute(idx)))
}

This is seen when cross-building from NetBSD/amd64, using the following rustc version:

rustc --version --verbose:

: {21} work/rust-bootstrap/bin/rustc --version --verbose
rustc 1.70.0 (90c541806 2023-05-31)
binary: rustc
commit-hash: 90c541806f23a127002de5b4038be731ba1458ca
commit-date: 2023-05-31
host: x86_64-unknown-netbsd
release: 1.70.0
LLVM version: 16.0.2
: {22} 

The last successful cross-build for this target was with 1.70.0, so this is
a new problem which arrived together with 1.71.0.

I suspect this problem occurs for all big-endian aarch64 targets, the other ones being
aarch64_be-unknown-linux-gnu and aarch64_be-unknown-linux-gnu_ilp32.

[taiki-e]

This was fixed in the nightly release over a month ago (rust-lang/portable-simd#348). AFAIK, no backport to 1.71 has been done though, as only tier 3 targets are affected.

[he32]

Thanks for the pointer, it's much appreciated.
I only build releases, and sometimes wonder "was this something I did", so reporting is not exactly instant.
I've applied a local fix for now and will validate the status of the build.

[est31]

Yeah tier 3 targets have no guarantee to build, but of course fixes are always welcome. If you use a tier 3 target and want to use stable releases without manual patching, I'd recommend regularly checking latest nightly (every 2-3 weeks to have time for fixes to get in) and optimally also beta, every time a new beta is branched off. You can also use pinned nightlies, then fixes will be available immediately .

Given that 1.72 will be released in a week, I don't think a backport will be done for 1.71 (edit: also not sure if the backport policy includes tier 3 fixes for stable, for beta there have been backports in the past). It might make sense to verify that 1.72 compiles. For that, you can try the beta compiler.

[he32]

Thanks for the pointer, it's much appreciated.
I only build releases, and sometimes wonder "was this something I did", so reporting is not exactly instant.
I've applied a local fix for now and it now again builds.