Fix breakage and comment tests as requested

Author: 1c3t3a

compiler/rustc_mir_transform/src/check_pointers.rs

@@ -178,7 +178,7 @@ impl<'a, 'tcx> PointerFinder<'a, 'tcx> {
 
 impl<'a, 'tcx> Visitor<'tcx> for PointerFinder<'a, 'tcx> {
     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
-        if !self.should_visit_place(context) && !place.is_indirect() {
+        if !self.should_visit_place(context) || !place.is_indirect() {
             return;
         }
 

tests/ui/mir/null/addrof_null.rs

@@ -1,3 +1,4 @@
+// Make sure that we don't actually insert a check for `addr_of!`.
 //@ run-pass
 //@ compile-flags: -C debug-assertions
 

tests/ui/mir/null/place_without_read.rs

@@ -1,3 +1,4 @@
+// Make sure that we don't actually insert a check for places that do not read.
 //@ run-pass
 //@ compile-flags: -C debug-assertions
 

tests/ui/mir/null/zero_sized_access.rs

@@ -1,3 +1,5 @@
+// Make sure that we don't actually insert a check for zero-sized reads or writes
+// to null, because they are actually allowed.
 //@ run-pass
 //@ compile-flags: -C debug-assertions
 
@@ -6,4 +8,8 @@ fn main() {
     unsafe {
         *(ptr) = ();
     }
+    let ptr1: *const () = std::ptr::null_mut();
+    unsafe {
+        let _ptr = *ptr1;
+    }
 }