1 files changed, 104 insertions, 0 deletions
diff --git a/library/stdarch/crates/std_detect/src/detect/mod.rs b/library/stdarch/crates/std_detect/src/detect/mod.rs
new file mode 100644
index 000000000..2bca84ca1
--- /dev/null
+++ b/library/stdarch/crates/std_detect/src/detect/mod.rs
@@ -0,0 +1,104 @@
+//! This module implements run-time feature detection.
+//!
+//! The `is_{arch}_feature_detected!("feature-name")` macros take the name of a
+//! feature as a string-literal, and return a boolean indicating whether the
+//! feature is enabled at run-time or not.
+//!
+//! These macros do two things:
+//! * map the string-literal into an integer stored as a `Feature` enum,
+//! * call a `os::check_for(x: Feature)` function that returns `true` if the
+//! feature is enabled.
+//!
+//! The `Feature` enums are also implemented in the `arch/{target_arch}.rs`
+//! modules.
+//!
+//! The `check_for` functions are, in general, Operating System dependent. Most
+//! architectures do not allow user-space programs to query the feature bits
+//! due to security concerns (x86 is the big exception). These functions are
+//! implemented in the `os/{target_os}.rs` modules.
+
+use cfg_if::cfg_if;
+
+#[macro_use]
+mod macros;
+
+mod arch;
+
+// This module needs to be public because the `is_{arch}_feature_detected!`
+// macros expand calls to items within it in user crates.
+#[doc(hidden)]
+pub use self::arch::__is_feature_detected;
+
+pub(crate) use self::arch::Feature;
+
+mod bit;
+mod cache;
+
+cfg_if! {
+    if #[cfg(miri)] {
+        // When running under miri all target-features that are not enabled at
+        // compile-time are reported as disabled at run-time.
+        //
+        // For features for which `cfg(target_feature)` returns true,
+        // this run-time detection logic is never called.
+        #[path = "os/other.rs"]
+        mod os;
+    } else if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
+        // On x86/x86_64 no OS specific functionality is required.
+        #[path = "os/x86.rs"]
+        mod os;
+    } else if #[cfg(all(target_os = "linux", feature = "libc"))] {
+        #[path = "os/linux/mod.rs"]
+        mod os;
+    } else if #[cfg(all(target_os = "freebsd", feature = "libc"))] {
+        #[cfg(target_arch = "aarch64")]
+        #[path = "os/aarch64.rs"]
+        mod aarch64;
+        #[path = "os/freebsd/mod.rs"]
+        mod os;
+    } else if #[cfg(all(target_os = "windows", target_arch = "aarch64"))] {
+        #[path = "os/windows/aarch64.rs"]
+        mod os;
+    } else {
+        #[path = "os/other.rs"]
+        mod os;
+    }
+}
+
+/// Performs run-time feature detection.
+#[inline]
+#[allow(dead_code)]
+fn check_for(x: Feature) -> bool {
+    cache::test(x as u32)
+}
+
+/// Returns an `Iterator<Item=(&'static str, bool)>` where
+/// `Item.0` is the feature name, and `Item.1` is a `bool` which
+/// is `true` if the feature is supported by the host and `false` otherwise.
+#[unstable(feature = "stdsimd", issue = "27731")]
+pub fn features() -> impl Iterator<Item = (&'static str, bool)> {
+    cfg_if! {
+        if #[cfg(any(
+            target_arch = "x86",
+            target_arch = "x86_64",
+            target_arch = "arm",
+            target_arch = "aarch64",
+            target_arch = "riscv32",
+            target_arch = "riscv64",
+            target_arch = "powerpc",
+            target_arch = "powerpc64",
+            target_arch = "mips",
+            target_arch = "mips64",
+        ))] {
+            (0_u8..Feature::_last as u8).map(|discriminant: u8| {
+                #[allow(bindings_with_variant_name)] // RISC-V has Feature::f
+                let f: Feature = unsafe { core::mem::transmute(discriminant) };
+                let name: &'static str = f.to_str();
+                let enabled: bool = check_for(f);
+                (name, enabled)
+            })
+        } else {
+            None.into_iter()
+        }
+    }
+}