add rt-detection for 32-bit mips

Author: gnzlbg

ci/run.sh

@@ -13,9 +13,6 @@ case ${TARGET} in
     aarch*)
         export RUSTFLAGS="${RUSTFLAGS} -C target-feature=+neon"
         ;;
-    mips64*)
-        export RUSTFLAGS="${RUSTFLAGS} -C target-cpu=mips64r6"
-        ;;
     *)
         ;;
 esac

crates/simd-test-macro/src/lib.rs

@@ -72,14 +72,20 @@ pub fn simd_test(
         .expect(&format!("target triple contained no \"-\": {}", target)) {
         "i686" | "x86_64" | "i586" => "is_x86_feature_detected",
         "arm" => "is_arm_feature_detected",
-        "aarch64" => "is_aarch64_feature_detected", 
+        "aarch64" => "is_aarch64_feature_detected",
         "powerpc64" => "is_powerpc64_feature_detected",
-        "mips64" | "mips64el" => {
+        "mips" | "mipsel" => {
+            // FIXME:
             // On MIPS CI run-time feature detection always returns false due to
             // this qemu bug: https://bugs.launchpad.net/qemu/+bug/1754372
             //
             // This is a workaround to force the MIPS tests to always run on CI.
             force_test = true;
+            "is_mips_feature_detected"
+        },
+        "mips64" | "mips64el" => {
+            // FIXME: see above
+            force_test = true;
             "is_mips64_feature_detected"
         },
         t => panic!("unknown target: {}", t),

stdsimd/arch/detect/mips.rs

@@ -0,0 +1,56 @@
+//! Run-time feature detection on MIPS.
+
+use super::cache;
+
+#[cfg(target_os = "linux")]
+use super::{bit, linux};
+
+#[macro_export]
+#[unstable(feature = "stdsimd", issue = "0")]
+macro_rules! is_mips_feature_detected {
+    ("msa") => {
+        cfg!(target_feature = "msa") ||
+            $crate::arch::detect::check_for($crate::arch::detect::Feature::msa)
+    };
+    ($t:tt) => { compile_error!(concat!("unknown mips target feature: ", $t)) };
+}
+
+/// MIPS CPU Feature enum. Each variant denotes a position in a bitset for a
+/// particular feature.
+///
+/// PLEASE: do not use this, it is an implementation detail subject to change.
+#[doc(hidden)]
+#[allow(non_camel_case_types)]
+#[repr(u8)]
+pub enum Feature {
+    /// MIPS SIMD Architecture (MSA)
+    msa,
+}
+
+pub fn detect_features() -> cache::Initializer {
+    let mut value = cache::Initializer::default();
+    fill_features(&mut value);
+    value
+}
+
+#[cfg(not(target_os = "linux"))]
+fn fill_features(_value: &mut cache::Initializer) {}
+
+#[cfg(target_os = "linux")]
+fn fill_features(value: &mut cache::Initializer) {
+    let mut enable_feature = |f, enable| {
+        if enable {
+            value.set(f as u32);
+        }
+    };
+
+    // The values are part of the platform-specific [asm/cputable.h][cputable]
+    //
+    // [cputable]: https://github.com/torvalds/linux/blob/master/arch/mips/include/uapi/asm/hwcap.h
+    if let Ok(auxv) = linux::auxvec::auxv() {
+        enable_feature(Feature::msa, bit::test(auxv.hwcap, 1));
+        return
+    }
+
+    // TODO: fall back via cpuinfo
+}