Add an experimental unsafe(force_target_feature) attribute.

This uses the feature gate for
https://github.com/rust-lang/rust/issues/143352, but is described in
https://github.com/rust-lang/rfcs/pull/3820 which is strongly tied to
the experiment.

1 files changed, 33 insertions, 0 deletions

diff --git a/tests/assembly-llvm/force-target-feature.rs b/tests/assembly-llvm/force-target-feature.rs
new file mode 100644
index 00000000000..c11060d8d6d
--- /dev/null
+++ b/tests/assembly-llvm/force-target-feature.rs
@@ -0,0 +1,33 @@
+//@ only-x86_64
+//@ assembly-output: emit-asm
+//@ compile-flags: -C opt-level=3 -C target-feature=-avx2
+//@ ignore-sgx Tests incompatible with LVI mitigations
+
+#![feature(effective_target_features)]
+
+use std::arch::x86_64::{__m256i, _mm256_add_epi32, _mm256_setzero_si256};
+use std::ops::Add;
+
+#[derive(Clone, Copy)]
+struct AvxU32(__m256i);
+
+impl Add<AvxU32> for AvxU32 {
+    type Output = Self;
+
+    #[no_mangle]
+    #[inline(never)]
+    #[unsafe(force_target_feature(enable = "avx2"))]
+    fn add(self, oth: AvxU32) -> AvxU32 {
+        // CHECK-LABEL: add:
+        // CHECK-NOT: callq
+        // CHECK: vpaddd
+        // CHECK: retq
+        Self(_mm256_add_epi32(self.0, oth.0))
+    }
+}
+
+fn main() {
+    assert!(is_x86_feature_detected!("avx2"));
+    let v = AvxU32(unsafe { _mm256_setzero_si256() });
+    v + v;
+}