add vector ABI check test for calling extern fn

Author: RalfJung

tests/ui/simd-abi-checks.rs

@@ -4,7 +4,7 @@
 
 #![feature(avx512_target_feature)]
 #![feature(portable_simd)]
-#![feature(target_feature_11)]
+#![feature(target_feature_11, simd_ffi)]
 #![allow(improper_ctypes_definitions)]
 
 use std::arch::x86_64::*;
@@ -91,4 +91,20 @@ fn main() {
     unsafe {
         in_closure()();
     }
+
+    unsafe {
+        #[expect(improper_ctypes)]
+        extern "C" {
+            fn some_extern() -> __m256;
+        }
+        some_extern();
+        //~^ WARNING this function call uses a SIMD vector type that (with the chosen ABI) requires the `avx` target feature, which is not enabled in the caller
+        //~| WARNING this was previously accepted by the compiler
+    }
+}
+
+#[no_mangle]
+#[target_feature(enable = "avx")]
+fn some_extern() -> __m256 {
+    todo!()
 }

tests/ui/simd-abi-checks.stderr

@@ -59,6 +59,16 @@ LL |         w(Wrapper(g()));
    = note: for more information, see issue #116558 <https://github.com/rust-lang/rust/issues/116558>
    = help: consider enabling it globally (`-C target-feature=+avx`) or locally (`#[target_feature(enable="avx")]`)
 
+warning: this function call uses a SIMD vector type that (with the chosen ABI) requires the `avx` target feature, which is not enabled in the caller
+  --> $DIR/simd-abi-checks.rs:100:9
+   |
+LL |         some_extern();
+   |         ^^^^^^^^^^^^^ function called here
+   |
+   = 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 #116558 <https://github.com/rust-lang/rust/issues/116558>
+   = help: consider enabling it globally (`-C target-feature=+avx`) or locally (`#[target_feature(enable="avx")]`)
+
 warning: this function definition uses a SIMD vector type that (with the chosen ABI) requires the `avx` target feature, which is not enabled
   --> $DIR/simd-abi-checks.rs:27:1
    |
@@ -99,5 +109,5 @@ LL |     || g()
    = note: for more information, see issue #116558 <https://github.com/rust-lang/rust/issues/116558>
    = help: consider enabling it globally (`-C target-feature=+avx`) or locally (`#[target_feature(enable="avx")]`)
 
-warning: 10 warnings emitted
+warning: 11 warnings emitted