core: Use __jcvt() intrinsic on AArch64 for f64→i32 conversion

.github/workflows/release_nightly.yml

@@ -142,9 +142,9 @@ jobs:
           ref: ${{ needs.create-nightly-release.outputs.tag_name }}
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
         with:
-          toolchain: stable
+          toolchain: nightly
           targets: ${{ matrix.target }}
 
       - name: Install Linux dependencies
@@ -339,9 +339,9 @@ jobs:
           ref: ${{ needs.create-nightly-release.outputs.tag_name }}
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
         with:
-          toolchain: stable
+          toolchain: nightly
 
       - name: Generate report
         run: ./stub-report/generate-report.sh
@@ -372,9 +372,9 @@ jobs:
           ref: ${{ needs.create-nightly-release.outputs.tag_name }}
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
         with:
-          toolchain: stable
+          toolchain: nightly
           targets: wasm32-unknown-unknown
           components: rust-src
 

.github/workflows/test_extension_dockerfile.yml

@@ -17,9 +17,9 @@ jobs:
       - uses: actions/checkout@v6
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
         with:
-          toolchain: stable
+          toolchain: nightly
           targets: wasm32-unknown-unknown
           components: rust-src
 

.github/workflows/test_rust.yml

@@ -63,19 +63,17 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust_version: [stable]
+        rust_version: [nightly]
         os: [ubuntu-24.04, ubuntu-24.04-arm, windows-2025, macos-15]
         include:
           - rust_version: nightly
             os: ubuntu-24.04
-          - rust_version: beta
-            os: ubuntu-24.04
 
     steps:
       - uses: actions/checkout@v6
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
         with:
           toolchain: ${{ matrix.rust_version }}
 
@@ -127,13 +125,13 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust_version: [stable, beta, nightly]
+        rust_version: [nightly]
 
     steps:
       - uses: actions/checkout@v6
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
         with:
           toolchain: ${{ matrix.rust_version }}
           components: rustfmt, clippy
@@ -286,7 +284,7 @@ jobs:
       - uses: actions/checkout@v6
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
 
       - name: Check licenses, duplicates, and advisories
         uses: EmbarkStudios/cargo-deny-action@v2
@@ -309,13 +307,11 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        rust_version: [stable]
+        rust_version: [nightly]
         os: [ubuntu-24.04, ubuntu-24.04-arm, windows-2025, macos-15]
         include:
           - rust_version: nightly
             os: ubuntu-24.04
-          - rust_version: beta
-            os: ubuntu-24.04
 
     steps:
       - name: No-op
@@ -328,7 +324,7 @@ jobs:
     runs-on: ubuntu-24.04
     strategy:
       matrix:
-        rust_version: [stable, beta, nightly]
+        rust_version: [nightly]
 
     steps:
       - name: No-op

.github/workflows/test_web.yml

@@ -49,7 +49,7 @@ jobs:
           cache-dependency-path: web/package-lock.json
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
         with:
           targets: wasm32-unknown-unknown
 
@@ -114,7 +114,7 @@ jobs:
           cache-dependency-path: web/package-lock.json
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
         with:
           targets: wasm32-unknown-unknown
 

core/src/ecma_conversions.rs

@@ -44,8 +44,10 @@ pub fn f64_to_wrapping_i32(n: f64) -> i32 {
     #[cfg(target_arch = "aarch64")]
     {
         if std::arch::is_aarch64_feature_detected!("jsconv") {
-            // SAFETY: `jsconv` feature is checked in both compile time and runtime to be existed, so it's safe to call.
-            unsafe { f64_to_wrapping_int32_aarch64(n) }
+            // 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 aarch64 cpu with the fjcvtzs instruction.
+            unsafe { std::arch::aarch64::__jcvt(n) }
         } else {
             f64_to_wrapping_i32_generic(n)
         }
@@ -59,32 +61,6 @@ fn f64_to_wrapping_i32_generic(n: f64) -> i32 {
     f64_to_wrapping_u32(n) as i32
 }
 
-/// 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 aarch64 cpu with the fjcvtzs instruction.
-///
-/// # Safety
-///
-/// The caller must ensure either:
-/// - The target platform is aarch64 with `jsconv` feature enabled, or
-/// - Runtime feature detection has been performed to verify `jsconv` support
-#[allow(unused)]
-#[cfg(target_arch = "aarch64")]
-#[target_feature(enable = "jsconv")]
-unsafe fn f64_to_wrapping_int32_aarch64(number: f64) -> i32 {
-    let ret: i32;
-    // SAFETY: fjcvtzs instruction is available under jsconv feature.
-    unsafe {
-        std::arch::asm!(
-            "fjcvtzs {dst:w}, {src:d}",
-            src = in(vreg) number,
-            dst = out(reg) ret,
-            options(nostack, nomem, pure)
-        );
-    }
-    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`.

core/src/lib.rs

@@ -4,6 +4,9 @@
 // This lint is good in theory, but in AVMs we often need to do `let x = args.get(0); let y = args.get(1);` etc.
 // It'd make those much less readable and consistent.
 #![allow(clippy::get_first)]
+// This enables the core::arch::aarch64::__jcvt() intrinsic, which is used to convert a f64 into an
+// i32 the JavaScript way on ARMv8.3+.
+#![feature(stdarch_aarch64_jscvt)]
 
 #[macro_use]
 mod display_object;