From 6d95c56a40724a5c4c62a8f3d2afa1f7725da067 Mon Sep 17 00:00:00 2001
From: Taiki Endo <te316e89@gmail.com>
Date: Tue, 24 Jan 2023 23:28:44 +0900
Subject: [PATCH] aarch64: Support detecting FEAT_LSE on Windows

---
 src/imp/atomic128/aarch64.rs                |   3 +-
 src/imp/atomic128/detect/aarch64_windows.rs | 113 ++++++++++++++++++++
 2 files changed, 115 insertions(+), 1 deletion(-)
 create mode 100644 src/imp/atomic128/detect/aarch64_windows.rs

diff --git a/src/imp/atomic128/aarch64.rs b/src/imp/atomic128/aarch64.rs
index f3da91ab6..3e27dd49a 100644
--- a/src/imp/atomic128/aarch64.rs
+++ b/src/imp/atomic128/aarch64.rs
@@ -45,7 +45,8 @@
 
 include!("macros.rs");
 
-#[path = "detect/aarch64_std.rs"]
+#[cfg_attr(target_os = "windows", path = "detect/aarch64_windows.rs")]
+#[cfg_attr(not(target_os = "windows"), path = "detect/aarch64_std.rs")]
 mod detect;
 
 #[cfg(not(portable_atomic_no_asm))]
diff --git a/src/imp/atomic128/detect/aarch64_windows.rs b/src/imp/atomic128/detect/aarch64_windows.rs
new file mode 100644
index 000000000..1d212d966
--- /dev/null
+++ b/src/imp/atomic128/detect/aarch64_windows.rs
@@ -0,0 +1,113 @@
+// As of nightly-2023-01-23, is_aarch64_feature_detected doesn't support detecting FEAT_LSE on Windows.
+// https://github.com/rust-lang/stdarch/blob/a0c30f3e3c75adcd6ee7efc94014ebcead61c507/crates/std_detect/src/detect/os/windows/aarch64.rs
+// https://github.com/rust-lang/stdarch/pull/1373
+//
+// Refs: https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-isprocessorfeaturepresent
+
+#![cfg_attr(
+    any(
+        portable_atomic_no_aarch64_target_feature,
+        portable_atomic_no_outline_atomics,
+        any(target_feature = "lse", portable_atomic_target_feature = "lse")
+    ),
+    allow(dead_code)
+)]
+
+include!("common.rs");
+
+use core::sync::atomic::{AtomicU32, Ordering};
+
+impl CpuInfo {
+    const INIT: u32 = 0;
+    const HAS_LSE: u32 = 1;
+}
+
+#[inline]
+pub(crate) fn has_lse() -> bool {
+    #[cfg(any(target_feature = "lse", portable_atomic_target_feature = "lse"))]
+    {
+        // FEAT_LSE is statically available.
+        true
+    }
+    #[cfg(not(any(target_feature = "lse", portable_atomic_target_feature = "lse")))]
+    {
+        detect().test(CpuInfo::HAS_LSE)
+    }
+}
+
+#[allow(clippy::upper_case_acronyms)]
+#[inline]
+fn _detect(info: &mut CpuInfo) {
+    type DWORD = u32;
+    type BOOL = i32;
+
+    const FALSE: BOOL = 0;
+    // Defined in winnt.h of Windows SDK.
+    const PF_ARM_V81_ATOMIC_INSTRUCTIONS_AVAILABLE: DWORD = 34;
+
+    extern "system" {
+        fn IsProcessorFeaturePresent(ProcessorFeature: DWORD) -> BOOL;
+    }
+
+    info.set(CpuInfo::INIT);
+    // SAFETY: calling IsProcessorFeaturePresent is safe, and FALSE is also
+    // returned if the HAL does not support detection of the specified feature.
+    if unsafe { IsProcessorFeaturePresent(PF_ARM_V81_ATOMIC_INSTRUCTIONS_AVAILABLE) != FALSE } {
+        info.set(CpuInfo::HAS_LSE);
+    }
+}
+
+#[inline]
+fn detect() -> CpuInfo {
+    static CACHE: AtomicU32 = AtomicU32::new(0);
+    let mut info = CpuInfo(CACHE.load(Ordering::Relaxed));
+    if info.0 != 0 {
+        return info;
+    }
+    _detect(&mut info);
+    CACHE.store(info.0, Ordering::Relaxed);
+    info
+}
+
+#[allow(clippy::undocumented_unsafe_blocks)]
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_bit_flags() {
+        let mut x = CpuInfo(0);
+        assert!(!x.test(CpuInfo::INIT));
+        assert!(!x.test(CpuInfo::HAS_LSE));
+        x.set(CpuInfo::INIT);
+        assert!(x.test(CpuInfo::INIT));
+        assert!(!x.test(CpuInfo::HAS_LSE));
+        x.set(CpuInfo::HAS_LSE);
+        assert!(x.test(CpuInfo::INIT));
+        assert!(x.test(CpuInfo::HAS_LSE));
+    }
+
+    #[test]
+    fn test_detect() {
+        if has_lse() {
+            assert!(detect().test(CpuInfo::HAS_LSE));
+            #[cfg(any(
+                target_feature = "lse",
+                portable_atomic_target_feature = "lse",
+                not(portable_atomic_no_aarch64_target_feature),
+            ))]
+            unsafe {
+                use core::cell::UnsafeCell;
+                let v = UnsafeCell::new(0);
+                assert_eq!(
+                    super::super::_compare_exchange_casp(v.get(), 0, 1, Ordering::SeqCst),
+                    0
+                );
+                assert_eq!(*v.get(), 1);
+            }
+        } else {
+            assert!(!detect().test(CpuInfo::HAS_LSE));
+            assert!(!std::arch::is_aarch64_feature_detected!("lse"));
+        }
+    }
+}