diff --git a/tests/compile-fail/maybe_null_pointer_deref_zst.rs b/tests/compile-fail/maybe_null_pointer_deref_zst.rs
new file mode 100644
index 000000000000..d9f5ad4c696e
--- /dev/null
+++ b/tests/compile-fail/maybe_null_pointer_deref_zst.rs
@@ -0,0 +1,5 @@
+fn main() {
+    // This pointer *could* be NULL so we cannot load from it, not even at ZST
+    let ptr = (&0u8 as *const u8).wrapping_sub(0x800) as *const ();
+    let _x: () = unsafe { *ptr }; //~ ERROR outside bounds
+}
diff --git a/tests/compile-fail/maybe_null_pointer_write_zst.rs b/tests/compile-fail/maybe_null_pointer_write_zst.rs
new file mode 100644
index 000000000000..ef46a469c3ad
--- /dev/null
+++ b/tests/compile-fail/maybe_null_pointer_write_zst.rs
@@ -0,0 +1,8 @@
+fn main() {
+    // This pointer *could* be NULL so we cannot load from it, not even at ZST.
+    // Not using the () type here, as writes of that type do not even have MIR generated.
+    // Also not assigning directly as that's array initialization, not assignment.
+    let zst_val = [1u8; 0];
+    let ptr = (&0u8 as *const u8).wrapping_sub(0x800) as *mut [u8; 0];
+    unsafe { *ptr = zst_val; } //~ ERROR outside bounds
+}
diff --git a/tests/compile-fail/null_pointer_deref_zst.rs b/tests/compile-fail/null_pointer_deref_zst.rs
new file mode 100644
index 000000000000..a8b23368616e
--- /dev/null
+++ b/tests/compile-fail/null_pointer_deref_zst.rs
@@ -0,0 +1,4 @@
+fn main() {
+    let x: () = unsafe { *std::ptr::null() }; //~ ERROR constant evaluation error: invalid use of NULL pointer
+    panic!("this should never print: {:?}", x);
+}
diff --git a/tests/compile-fail/null_pointer_write.rs b/tests/compile-fail/null_pointer_write.rs
new file mode 100644
index 000000000000..affb040bdedf
--- /dev/null
+++ b/tests/compile-fail/null_pointer_write.rs
@@ -0,0 +1,3 @@
+fn main() {
+    unsafe { *std::ptr::null_mut() = 0i32 }; //~ ERROR constant evaluation error: invalid use of NULL pointer
+}
diff --git a/tests/compile-fail/null_pointer_write_zst.rs b/tests/compile-fail/null_pointer_write_zst.rs
new file mode 100644
index 000000000000..433c69dbb032
--- /dev/null
+++ b/tests/compile-fail/null_pointer_write_zst.rs
@@ -0,0 +1,6 @@
+fn main() {
+    // Not using the () type here, as writes of that type do not even have MIR generated.
+    // Also not assigning directly as that's array initialization, not assignment.
+    let zst_val = [1u8; 0];
+    unsafe { *std::ptr::null_mut() = zst_val }; //~ ERROR constant evaluation error: invalid use of NULL pointer
+}
diff --git a/tests/run-pass/cast-rfc0401-vtable-kinds.rs b/tests/run-pass/cast-rfc0401-vtable-kinds.rs
index afbd4760a3c9..ebae26996b7b 100644
--- a/tests/run-pass/cast-rfc0401-vtable-kinds.rs
+++ b/tests/run-pass/cast-rfc0401-vtable-kinds.rs
@@ -8,10 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-
-// FIXME: remove the next line when https://github.com/rust-lang/rust/issues/43358 is resolved
-// compile-flags: -Zmir-opt-level=0
-
 // Check that you can cast between different pointers to trait objects
 // whose vtable have the same kind (both lengths, or both trait pointers).
 
diff --git a/tests/run-pass/const-vec-of-fns.rs b/tests/run-pass/const-vec-of-fns.rs
index 0338a766e262..e100ad5f4692 100644
--- a/tests/run-pass/const-vec-of-fns.rs
+++ b/tests/run-pass/const-vec-of-fns.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// pretty-expanded FIXME #23616
-
 /*!
  * Try to double-check that static fns have the right size (with or
  * without dummy env ptr, as appropriate) by iterating a size-2 array.
diff --git a/tests/run-pass/issue-20575.rs b/tests/run-pass/issue-20575.rs
index 7db7e3b28e8e..137d84c256be 100644
--- a/tests/run-pass/issue-20575.rs
+++ b/tests/run-pass/issue-20575.rs
@@ -10,8 +10,6 @@
 
 // Test that overloaded calls work with zero arity closures
 
-// pretty-expanded FIXME #23616
-
 fn main() {
     let functions: [Box<Fn() -> Option<()>>; 1] = [Box::new(|| None)];
 
diff --git a/tests/run-pass/pointers.rs b/tests/run-pass/pointers.rs
index 936ec73bcb8c..d8f030de0723 100644
--- a/tests/run-pass/pointers.rs
+++ b/tests/run-pass/pointers.rs
@@ -55,7 +55,11 @@ fn main() {
     assert_eq!(basic_ref_mut_var(), 3);
     assert_eq!(tuple_ref_mut(), (10, 22));
     assert_eq!(match_ref_mut(), 42);
-    // FIXME: improve this test... how?
+
+    // Compare even dangling pointers with NULL, and with others in the same allocation.
     assert!(dangling_pointer() != std::ptr::null());
     assert!(match dangling_pointer() as usize { 0 => false, _ => true });
+    let dangling = dangling_pointer();
+    assert!(dangling == dangling);
+    assert!(dangling.wrapping_add(1) != dangling);
 }
diff --git a/tests/run-pass/regions-lifetime-nonfree-late-bound.rs b/tests/run-pass/regions-lifetime-nonfree-late-bound.rs
index 1aef95d8a3f3..96f1217a254e 100644
--- a/tests/run-pass/regions-lifetime-nonfree-late-bound.rs
+++ b/tests/run-pass/regions-lifetime-nonfree-late-bound.rs
@@ -22,8 +22,6 @@
 // doing region-folding, when really all clients of the region-folding
 // case only want to see FREE lifetime variables, not bound ones.
 
-// pretty-expanded FIXME #23616
-
 #![allow(unused_features)]
 #![feature(box_syntax)]
 
diff --git a/tests/run-pass/sendable-class.rs b/tests/run-pass/sendable-class.rs
index b3e07d00f010..66f0c84e23c1 100644
--- a/tests/run-pass/sendable-class.rs
+++ b/tests/run-pass/sendable-class.rs
@@ -10,8 +10,6 @@
 
 // Test that a class with only sendable fields can be sent
 
-// pretty-expanded FIXME #23616
-
 use std::sync::mpsc::channel;
 
 #[allow(dead_code)]
diff --git a/tests/run-pass/zst.rs b/tests/run-pass/zst.rs
index c1c88875c5c8..c3bae4062fc2 100644
--- a/tests/run-pass/zst.rs
+++ b/tests/run-pass/zst.rs
@@ -11,8 +11,23 @@ fn use_zst() -> A {
 }
 
 fn main() {
+    // Not using the () type here, as writes of that type do not even have MIR generated.
+    // Also not assigning directly as that's array initialization, not assignment.
+    let zst_val = [1u8; 0];
+
     assert_eq!(zst_ret(), A);
     assert_eq!(use_zst(), A);
-    let x = 42 as *mut ();
-    unsafe { *x = (); }
+    let x = 42 as *mut [u8; 0];
+    // reading and writing is okay
+    unsafe { *x = zst_val; }
+    unsafe { let _y = *x; }
+
+    // We should even be able to use "true" pointers for ZST when the allocation has been
+    // removed already.  The box is for a non-ZST to make sure there actually is an allocation.
+    let mut x_box = Box::new(((), 1u8));
+    let x = &mut x_box.0 as *mut _ as *mut [u8; 0];
+    drop(x_box);
+    // reading and writing is okay
+    unsafe { *x = zst_val; }
+    unsafe { let _y = *x; }
 }
diff --git a/tests/run-pass/zst2.rs b/tests/run-pass/zst2.rs
deleted file mode 100644
index c2d7b88ea075..000000000000
--- a/tests/run-pass/zst2.rs
+++ /dev/null
@@ -1,12 +0,0 @@
-#![allow(dead_code)]
-
-#[derive(Debug)]
-struct A;
-
-fn main() {
-    // can't use assert_eq, b/c that will try to print the pointer addresses with full MIR enabled
-
-    // FIXME: Test disabled for now, see <https://github.com/solson/miri/issues/131>.
-    //assert!(&A as *const A as *const () == &() as *const _);
-    //assert!(&A as *const A == &A as *const A);
-}