Sema: convert slice sentinel to single pointer correctly

Author: Rexicon226

src/Sema.zig

@@ -26336,18 +26336,24 @@ fn zirMemcpy(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void
         const array_ty = try pt.arrayType(.{
             .child = dest_elem_ty.toIntern(),
             .len = len_u64,
+            .sentinel = sentinel: {
+                const info = dest_ty.ptrInfo(zcu);
+                break :sentinel info.sentinel;
+            },
         });
 
         const dest_array_ptr_ty = try pt.ptrType(info: {
             var info = dest_ty.ptrInfo(zcu);
             info.flags.size = .one;
             info.child = array_ty.toIntern();
+            info.sentinel = .none;
             break :info info;
         });
         const src_array_ptr_ty = try pt.ptrType(info: {
             var info = src_ty.ptrInfo(zcu);
             info.flags.size = .one;
             info.child = array_ty.toIntern();
+            info.sentinel = .none;
             break :info info;
         });
 

test/behavior/memcpy.zig

@@ -133,3 +133,16 @@ test "@memcpy zero-bit type with aliasing" {
     S.doTheTest();
     comptime S.doTheTest();
 }
+
+test "@memcpy with sentinel" {
+    const S = struct {
+        fn doTheTest() void {
+            const field = @typeInfo(struct { a: u32 }).@"struct".fields[0];
+            var buffer: [field.name.len]u8 = undefined;
+            @memcpy(&buffer, field.name);
+        }
+    };
+
+    S.doTheTest();
+    comptime S.doTheTest();
+}