Switch to changing cp_non_overlap in tform

It was suggested to lower this in MIR instead of ssa, so do that instead.

compiler/rustc_mir/src/transform/check_unsafety.rs

@@ -115,7 +115,6 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
             | StatementKind::Retag { .. }
             | StatementKind::AscribeUserType(..)
             | StatementKind::Coverage(..)
-            | StatementKind::CopyNonOverlapping(..)
             | StatementKind::Nop => {
                 // safe (at least as emitted during MIR construction)
             }
@@ -124,6 +123,7 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
                 UnsafetyViolationKind::General,
                 UnsafetyViolationDetails::UseOfInlineAssembly,
             ),
+            StatementKind::CopyNonOverlapping(..) => unreachable!(),
         }
         self.super_statement(statement, location);
     }

compiler/rustc_mir/src/transform/lower_intrinsics.rs

@@ -40,6 +40,27 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
                             terminator.kind = TerminatorKind::Goto { target };
                         }
                     }
+                    sym::copy_nonoverlapping => {
+                        let target = destination.unwrap().1;
+                        let mut args = args.drain(..);
+                        block.statements.push(Statement {
+                            source_info: terminator.source_info,
+                            kind: StatementKind::CopyNonOverlapping(
+                                box rustc_middle::mir::CopyNonOverlapping {
+                                    src: args.next().unwrap(),
+                                    dst: args.next().unwrap(),
+                                    count: args.next().unwrap(),
+                                },
+                            ),
+                        });
+                        assert_eq!(
+                            args.next(),
+                            None,
+                            "Extra argument for copy_non_overlapping intrinsic"
+                        );
+                        drop(args);
+                        terminator.kind = TerminatorKind::Goto { target };
+                    }
                     sym::wrapping_add | sym::wrapping_sub | sym::wrapping_mul => {
                         if let Some((destination, target)) = *destination {
                             let lhs;

compiler/rustc_mir/src/transform/remove_noop_landing_pads.rs

@@ -39,7 +39,6 @@ impl RemoveNoopLandingPads {
                 | StatementKind::StorageDead(_)
                 | StatementKind::AscribeUserType(..)
                 | StatementKind::Coverage(..)
-                | StatementKind::CopyNonOverlapping(..)
                 | StatementKind::Nop => {
                     // These are all nops in a landing pad
                 }
@@ -56,6 +55,7 @@ impl RemoveNoopLandingPads {
                 StatementKind::Assign { .. }
                 | StatementKind::SetDiscriminant { .. }
                 | StatementKind::LlvmInlineAsm { .. }
+                | StatementKind::CopyNonOverlapping(..)
                 | StatementKind::Retag { .. } => {
                     return false;
                 }