fix: don't lint null as UB for volatile

Also remove a now-unneeded `allow` line.

Author: LuigiPiucco

compiler/rustc_lint/src/ptr_nulls.rs

@@ -160,12 +160,10 @@ impl<'tcx> LateLintPass<'tcx> for PtrNullChecks {
                 let (arg_indices, are_zsts_allowed): (&[_], _) = match diag_name {
                     sym::ptr_read
                     | sym::ptr_read_unaligned
-                    | sym::ptr_read_volatile
                     | sym::ptr_replace
                     | sym::ptr_write
                     | sym::ptr_write_bytes
-                    | sym::ptr_write_unaligned
-                    | sym::ptr_write_volatile => (&[0], true),
+                    | sym::ptr_write_unaligned => (&[0], true),
                     sym::slice_from_raw_parts | sym::slice_from_raw_parts_mut => (&[0], false),
                     sym::ptr_copy
                     | sym::ptr_copy_nonoverlapping

tests/ui/precondition-checks/read_volatile.rs

@@ -3,8 +3,6 @@
 //@ error-pattern: unsafe precondition(s) violated: ptr::read_volatile requires
 //@ revisions: misaligned
 
-#![allow(invalid_null_arguments)]
-
 use std::ptr;
 
 fn main() {