INLINE_ALWAYS_MISMATCHING_TARGET_FEATURES in rustc_lint_defs::builtin - Rust
Description: The `inline_always_mismatching_target_features` lint will trigger when a function with the `#[inline(always)]` and `#[target_feature(enable = "...")]` attributes is called and cannot be inlined due to missing target features in the caller.

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## INLINE_ALWAYS_MISMATCHING_TARGET_FEATURES

# Static INLINE_ALWAYS_MISMATCHING_TARGET_FEATURES

Source

    pub static INLINE_ALWAYS_MISMATCHING_TARGET_FEATURES: &Lint

Expand description

The `inline_always_mismatching_target_features` lint will trigger when a function with the `#[inline(always)]` and `#[target_feature(enable = "...")]` attributes is called and cannot be inlined due to missing target features in the caller.

#### §Example

ⓘ

    #[inline(always)]
    #[target_feature(enable = "fp16")]
    unsafe fn callee() {
        // operations using fp16 types
    }

    // Caller does not enable the required target feature
    fn caller() {
        unsafe { callee(); }
    }

    fn main() {
        caller();
    }

This will produce:

    warning: call to `#[inline(always)]`-annotated `callee` requires the same target features. Function will not have `alwaysinline` attribute applied
      --> $DIR/builtin.rs:5192:14
       |
    10 |     unsafe { callee(); }
       |              ^^^^^^^^
       |
    note: `fp16` target feature enabled in `callee` here but missing from `caller`
      --> $DIR/builtin.rs:5185:1
       |
    3  | #[target_feature(enable = "fp16")]
       | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    4  | unsafe fn callee() {
       | ------------------
       = note: `#[warn(inline_always_mismatching_target_features)]` on by default
    warning: 1 warning emitted

#### §Explanation

Inlining a function with a target feature attribute into a caller that lacks the corresponding target feature can lead to unsound behavior. LLVM may select the wrong instructions or registers, or reorder operations, potentially resulting in runtime errors.