From fac8b4e21a5621bb333d98a9ba15adc44e0284fb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <tomasz.miasko@gmail.com>
Date: Sat, 21 Nov 2020 00:00:00 +0000
Subject: [PATCH] Support building clone shims for arrays with generic size

---
 compiler/rustc_mir/src/shim.rs                | 19 +++++++++++++------
 .../array-clone-with-generic-size.rs          | 13 +++++++++++++
 2 files changed, 26 insertions(+), 6 deletions(-)
 create mode 100644 src/test/ui/mir/mir-inlining/array-clone-with-generic-size.rs

diff --git a/compiler/rustc_mir/src/shim.rs b/compiler/rustc_mir/src/shim.rs
index 3a1fa0018c1..aa5835686a2 100644
--- a/compiler/rustc_mir/src/shim.rs
+++ b/compiler/rustc_mir/src/shim.rs
@@ -308,10 +308,7 @@ fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -
 
     match self_ty.kind() {
         _ if is_copy => builder.copy_shim(),
-        ty::Array(ty, len) => {
-            let len = len.eval_usize(tcx, param_env);
-            builder.array_shim(dest, src, ty, len)
-        }
+        ty::Array(ty, len) => builder.array_shim(dest, src, ty, len),
         ty::Closure(_, substs) => {
             builder.tuple_like_shim(dest, src, substs.as_closure().upvar_tys())
         }
@@ -485,7 +482,13 @@ fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
         }
     }
 
-    fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
+    fn array_shim(
+        &mut self,
+        dest: Place<'tcx>,
+        src: Place<'tcx>,
+        ty: Ty<'tcx>,
+        len: &'tcx ty::Const<'tcx>,
+    ) {
         let tcx = self.tcx;
         let span = self.span;
 
@@ -503,7 +506,11 @@ fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len:
             ))),
             self.make_statement(StatementKind::Assign(box (
                 end,
-                Rvalue::Use(Operand::Constant(self.make_usize(len))),
+                Rvalue::Use(Operand::Constant(box Constant {
+                    span: self.span,
+                    user_ty: None,
+                    literal: len,
+                })),
             ))),
         ];
         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
diff --git a/src/test/ui/mir/mir-inlining/array-clone-with-generic-size.rs b/src/test/ui/mir/mir-inlining/array-clone-with-generic-size.rs
new file mode 100644
index 00000000000..8a96303e6b9
--- /dev/null
+++ b/src/test/ui/mir/mir-inlining/array-clone-with-generic-size.rs
@@ -0,0 +1,13 @@
+// Checks that we can build a clone shim for array with generic size.
+// Regression test for issue #79269.
+//
+// build-pass
+// compile-flags: -Zmir-opt-level=2 -Zvalidate-mir
+#![feature(min_const_generics)]
+
+#[derive(Clone)]
+struct Array<T, const N: usize>([T; N]);
+
+fn main() {
+    let _ = Array([0u32, 1u32, 2u32]).clone();
+}