core: Add ARM64 FJCVTZS instruction optimization for f64 to i32

Author: CrazyboyQCD

core/src/ecma_conversions.rs

@@ -40,9 +40,53 @@ pub fn f64_to_wrapping_u32(n: f64) -> u32 {
 /// Converts an `f64` to an `i32` with ECMAScript `ToInt32` wrapping behavior.
 /// The value will be wrapped in the range [-2^31, 2^31).
 pub fn f64_to_wrapping_i32(n: f64) -> i32 {
+    #[cfg(target_arch = "aarch64")]
+    #[cfg(target_feature = "jsconv")]
+    {
+        // macOS aarch64 always has jsconv feature
+        // SAFETY: macOS aarch64 always supports jsconv
+        unsafe { f64_to_wrapping_int32_arm64(n) }
+    }
+    #[cfg(target_arch = "aarch64")]
+    #[cfg(not(target_feature = "jsconv"))]
+    {
+        if std::arch::is_aarch64_feature_detected!("jsconv") {
+            // SAFETY: Feature detection confirmed jsconv is available
+            unsafe { f64_to_wrapping_int32_arm64(n) }
+        } else {
+            f64_to_wrapping_i32_generic(n)
+        }
+    }
+    #[cfg(not(target_arch = "aarch64"))]
+    {
+        f64_to_wrapping_i32_generic(n)
+    }
+}
+
+#[allow(unused)]
+fn f64_to_wrapping_i32_generic(n: f64) -> i32 {
     f64_to_wrapping_u32(n) as i32
 }
 
+#[allow(unused)]
+#[cfg(target_arch = "aarch64")]
+#[target_feature(enable = "jsconv")]
+/// Converts an `f64` to an `i32` with ECMAScript `ToInt32` wrapping behavior.
+/// The value will be wrapped in the range [-2^31, 2^31).
+/// Optimized for macOS aarch64 with the fjcvtzs instruction.
+unsafe fn f64_to_wrapping_int32_arm64(number: f64) -> i32 {
+    let ret: i32;
+    // SAFETY: fjcvtzs instruction is available on macOS aarch64.
+    unsafe {
+        std::arch::asm!(
+            "fjcvtzs {dst:w}, {src:d}",
+            src = in(vreg) number,
+            dst = out(reg) ret,
+        );
+    }
+    ret
+}
+
 /// Implements the IEEE-754 "Round to nearest, ties to even" rounding rule.
 /// (e.g., both 1.5 and 2.5 will round to 2).
 /// This also clamps out-of-range values and NaN to `i32::MIN`.