rustc-1.39.0-src.patch

# Add mrustc slice length intrinsics
--- src/libcore/intrinsics.rs
+++ src/libcore/intrinsics.rs
@@ -685,4 +685,8 @@
     pub fn min_align_of_val<T: ?Sized>(_: &T) -> usize;
 
+    /// Obtain the length of a slice pointer
+    #[cfg(rust_compiler="mrustc")]
+    pub fn mrustc_slice_len<T>(pointer: *const [T]) -> usize;
+
     /// Gets a static string slice containing the name of a type.
     pub fn type_name<T: ?Sized>() -> &'static str;
--- src/libcore/slice/mod.rs
+++ src/libcore/slice/mod.rs
@@ -68,5 +68,7 @@
     pub const fn len(&self) -> usize {
-        unsafe {
-            crate::ptr::Repr { rust: self }.raw.len
-        }
+        #[cfg(not(rust_compiler="mrustc"))]
+        const fn len_inner<T>(s: &[T]) -> usize { unsafe { crate::ptr::Repr { rust: self }.raw.len } };
+        #[cfg(rust_compiler="mrustc")]
+        const fn len_inner<T>(s: &[T]) -> usize { unsafe { crate::intrinsics::mrustc_slice_len(s) } }
+        len_inner(self)
     }