Use load-store instead of memcpy for short integer arrays

compiler/rustc_codegen_ssa/src/base.rs

@@ -380,7 +380,19 @@ pub fn memcpy_ty<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         return;
     }
 
-    bx.memcpy(dst, dst_align, src, src_align, bx.cx().const_usize(size), flags);
+    if flags == MemFlags::empty()
+        && let Some(bty) = bx.cx().scalar_copy_backend_type(layout)
+    {
+        // I look forward to only supporting opaque pointers
+        let pty = bx.type_ptr_to(bty);
+        let src = bx.pointercast(src, pty);
+        let dst = bx.pointercast(dst, pty);
+
+        let temp = bx.load(bty, src, src_align);
+        bx.store(temp, dst, dst_align);
+    } else {
+        bx.memcpy(dst, dst_align, src, src_align, bx.cx().const_usize(size), flags);
+    }
 }
 
 pub fn codegen_instance<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>>(