From 54b6f6923e281ba68d13269b43faa927c6df83d5 Mon Sep 17 00:00:00 2001
From: Thom Chiovoloni <thom@shift.click>
Date: Mon, 28 Nov 2022 06:03:32 -0800
Subject: [PATCH] Avoid a scalar loop in `Simd::from_slice`

---
 crates/core_simd/src/lib.rs    |  1 +
 crates/core_simd/src/vector.rs | 11 ++++-------
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/crates/core_simd/src/lib.rs b/crates/core_simd/src/lib.rs
index 82873162969..34b79e630a4 100644
--- a/crates/core_simd/src/lib.rs
+++ b/crates/core_simd/src/lib.rs
@@ -1,5 +1,6 @@
 #![no_std]
 #![feature(
+    const_ptr_read,
     convert_float_to_int,
     decl_macro,
     intra_doc_pointers,
diff --git a/crates/core_simd/src/vector.rs b/crates/core_simd/src/vector.rs
index d109087eaa6..51b0d999a81 100644
--- a/crates/core_simd/src/vector.rs
+++ b/crates/core_simd/src/vector.rs
@@ -174,13 +174,10 @@ pub const fn from_slice(slice: &[T]) -> Self {
             slice.len() >= LANES,
             "slice length must be at least the number of lanes"
         );
-        let mut array = [slice[0]; LANES];
-        let mut i = 0;
-        while i < LANES {
-            array[i] = slice[i];
-            i += 1;
-        }
-        Self(array)
+        // Safety:
+        // - We've checked the length is sufficient.
+        // - `T` and `Simd<T, N>` are Copy types.
+        unsafe { slice.as_ptr().cast::<Self>().read_unaligned() }
     }
 
     /// Performs lanewise conversion of a SIMD vector's elements to another SIMD-valid type.