Static AARCH64_SOFTFLOAT_NEON

pub static AARCH64_SOFTFLOAT_NEON: &'static Lint

The aarch64_softfloat_neon lint detects usage of #[target_feature(enable = "neon")] on softfloat aarch64 targets. Enabling this target feature causes LLVM to alter the ABI of function calls, making this attribute unsound to use.

Example

#[target_feature(enable = "neon")]
fn with_neon() {}

This will produce:

error: enabling the `neon` target feature on the current target is unsound due to ABI issues
  --> $DIR/abi-incompatible-target-feature-attribute-fcw.rs:11:18
   |
   | #[target_feature(enable = "neon")]
   |                  ^^^^^^^^^^^^^^^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #134375 <https://github.com/rust-lang/rust/issues/134375>

Explanation

If a function like with_neon above ends up containing calls to LLVM builtins, those will not use the correct ABI. This is caused by a lack of support in LLVM for mixing code with and without the neon target feature. The target feature should never have been stabilized on this target due to this issue, but the problem was not known at the time of stabilization.