_mm_pause does not require SSE2

Closes #705 .

Author: gnzlbg

crates/core_arch/src/x86/sse2.rs

@@ -17,10 +17,14 @@ use crate::{
 ///
 /// [Intel's documentation](https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_mm_pause)
 #[inline]
-#[target_feature(enable = "sse2")]
-#[cfg_attr(test, assert_instr(pause))]
+#[cfg_attr(
+    all(test, target_feature = "sse2"),
+    assert_instr(pause)
+)]
 #[stable(feature = "simd_x86", since = "1.27.0")]
 pub unsafe fn _mm_pause() {
+    // note: `pause` is guaranteed to be interpreted as a `nop` by CPUs without
+    // the SSE2 target-feature - therefore it does not require any target features
     pause()
 }
 
@@ -3191,9 +3195,9 @@ mod tests {
     use stdsimd_test::simd_test;
     use test::black_box; // Used to inhibit constant-folding.
 
-    #[simd_test(enable = "sse2")]
-    unsafe fn test_mm_pause() {
-        _mm_pause();
+    #[test]
+    fn test_mm_pause() {
+        unsafe { _mm_pause() }
     }
 
     #[simd_test(enable = "sse2")]

crates/stdsimd-verify/src/lib.rs

@@ -23,7 +23,7 @@ pub fn arm_functions(input: TokenStream) -> TokenStream {
 
 fn functions(input: TokenStream, dirs: &[&str]) -> TokenStream {
     let dir = Path::new(env!("CARGO_MANIFEST_DIR"));
-    let root = dir.parent().unwrap();
+    let root = dir.parent().expect("root-dir not found");
 
     let mut files = Vec::new();
     for dir in dirs {
@@ -199,11 +199,11 @@ fn extract_path_ident(path: &syn::Path) -> syn::Ident {
     if path.segments.len() != 1 {
         panic!("unsupported path that needs name resolution")
     }
-    match path.segments.first().unwrap().value().arguments {
+    match path.segments.first().expect("segment not found").value().arguments {
         syn::PathArguments::None => {}
         _ => panic!("unsupported path that has path arguments"),
     }
-    path.segments.first().unwrap().value().ident.clone()
+    path.segments.first().expect("segment not found").value().ident.clone()
 }
 
 fn walk(root: &Path, files: &mut Vec<(syn::File, String)>) {
@@ -224,9 +224,9 @@ fn walk(root: &Path, files: &mut Vec<(syn::File, String)>) {
 
         let mut contents = String::new();
         File::open(&path)
-            .unwrap()
+            .expect(&format!("can't open file at path: {}", path.display()))
             .read_to_string(&mut contents)
-            .unwrap();
+            .expect("failed to read file to string");
 
         files.push((
             syn::parse_str::<syn::File>(&contents).expect("failed to parse"),

crates/stdsimd-verify/tests/x86-intel.rs

@@ -254,6 +254,12 @@ fn matches(rust: &Function, intel: &Intrinsic) -> Result<(), String> {
     }
 
     for cpuid in &intel.cpuid {
+        // The pause intrinsic is in the SSE2 module, but it is backwards
+        // compatible with CPUs without SSE2, and it therefore does not need the
+        // target-feature attribute.
+        if rust.name == "_mm_pause" {
+            continue;
+        }
         // this is needed by _xsave and probably some related intrinsics,
         // but let's just skip it for now.
         if *cpuid == "XSS" {