diff --git a/tests/fail/dangling_pointers/dangling_pointer_project_underscore.rs b/tests/fail/dangling_pointers/dangling_pointer_project_underscore_let.rs
similarity index 100%
rename from tests/fail/dangling_pointers/dangling_pointer_project_underscore.rs
rename to tests/fail/dangling_pointers/dangling_pointer_project_underscore_let.rs
diff --git a/tests/fail/dangling_pointers/dangling_pointer_project_underscore.stderr b/tests/fail/dangling_pointers/dangling_pointer_project_underscore_let.stderr
similarity index 82%
rename from tests/fail/dangling_pointers/dangling_pointer_project_underscore.stderr
rename to tests/fail/dangling_pointers/dangling_pointer_project_underscore_let.stderr
index 20f3a25a0b..16841626dc 100644
--- a/tests/fail/dangling_pointers/dangling_pointer_project_underscore.stderr
+++ b/tests/fail/dangling_pointers/dangling_pointer_project_underscore_let.stderr
@@ -1,5 +1,5 @@
 error: Undefined Behavior: out-of-bounds pointer arithmetic: ALLOC has been freed, so this pointer is dangling
-  --> $DIR/dangling_pointer_project_underscore.rs:LL:CC
+  --> $DIR/dangling_pointer_project_underscore_let.rs:LL:CC
    |
 LL |         let _ = (*p).1;
    |                 ^^^^^^ out-of-bounds pointer arithmetic: ALLOC has been freed, so this pointer is dangling
@@ -7,17 +7,17 @@ LL |         let _ = (*p).1;
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
 help: ALLOC was allocated here:
-  --> $DIR/dangling_pointer_project_underscore.rs:LL:CC
+  --> $DIR/dangling_pointer_project_underscore_let.rs:LL:CC
    |
 LL |         let b = Box::new(42);
    |                 ^^^^^^^^^^^^
 help: ALLOC was deallocated here:
-  --> $DIR/dangling_pointer_project_underscore.rs:LL:CC
+  --> $DIR/dangling_pointer_project_underscore_let.rs:LL:CC
    |
 LL |     };
    |     ^
    = note: BACKTRACE (of the first span):
-   = note: inside `main` at $DIR/dangling_pointer_project_underscore.rs:LL:CC
+   = note: inside `main` at $DIR/dangling_pointer_project_underscore_let.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
 
diff --git a/tests/fail/dangling_pointers/dangling_pointer_project_underscore_let_type_annotation.rs b/tests/fail/dangling_pointers/dangling_pointer_project_underscore_let_type_annotation.rs
new file mode 100644
index 0000000000..fc10a826c1
--- /dev/null
+++ b/tests/fail/dangling_pointers/dangling_pointer_project_underscore_let_type_annotation.rs
@@ -0,0 +1,12 @@
+// Make sure we find these even with many checks disabled.
+//@compile-flags: -Zmiri-disable-alignment-check -Zmiri-disable-stacked-borrows -Zmiri-disable-validation
+
+fn main() {
+    let p = {
+        let b = Box::new(42);
+        &*b as *const i32 as *const (u8, u8, u8, u8)
+    };
+    unsafe {
+        let _: u8 = (*p).1; //~ ERROR: out-of-bounds pointer arithmetic
+    }
+}
diff --git a/tests/fail/dangling_pointers/dangling_pointer_project_underscore_let_type_annotation.stderr b/tests/fail/dangling_pointers/dangling_pointer_project_underscore_let_type_annotation.stderr
new file mode 100644
index 0000000000..0cdb6639a2
--- /dev/null
+++ b/tests/fail/dangling_pointers/dangling_pointer_project_underscore_let_type_annotation.stderr
@@ -0,0 +1,25 @@
+error: Undefined Behavior: out-of-bounds pointer arithmetic: ALLOC has been freed, so this pointer is dangling
+  --> $DIR/dangling_pointer_project_underscore_let_type_annotation.rs:LL:CC
+   |
+LL |         let _: u8 = (*p).1;
+   |                     ^^^^^^ out-of-bounds pointer arithmetic: ALLOC has been freed, so this pointer is dangling
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+help: ALLOC was allocated here:
+  --> $DIR/dangling_pointer_project_underscore_let_type_annotation.rs:LL:CC
+   |
+LL |         let b = Box::new(42);
+   |                 ^^^^^^^^^^^^
+help: ALLOC was deallocated here:
+  --> $DIR/dangling_pointer_project_underscore_let_type_annotation.rs:LL:CC
+   |
+LL |     };
+   |     ^
+   = note: BACKTRACE (of the first span):
+   = note: inside `main` at $DIR/dangling_pointer_project_underscore_let_type_annotation.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to previous error
+
diff --git a/tests/fail/dangling_pointers/dangling_pointer_project_underscore_match.rs b/tests/fail/dangling_pointers/dangling_pointer_project_underscore_match.rs
new file mode 100644
index 0000000000..8541da8485
--- /dev/null
+++ b/tests/fail/dangling_pointers/dangling_pointer_project_underscore_match.rs
@@ -0,0 +1,15 @@
+// Make sure we find these even with many checks disabled.
+//@compile-flags: -Zmiri-disable-alignment-check -Zmiri-disable-stacked-borrows -Zmiri-disable-validation
+
+fn main() {
+    let p = {
+        let b = Box::new(42);
+        &*b as *const i32 as *const (u8, u8, u8, u8)
+    };
+    unsafe {
+        match (*p).1 {
+            //~^ ERROR: out-of-bounds pointer arithmetic
+            _ => {}
+        }
+    }
+}
diff --git a/tests/fail/dangling_pointers/dangling_pointer_project_underscore_match.stderr b/tests/fail/dangling_pointers/dangling_pointer_project_underscore_match.stderr
new file mode 100644
index 0000000000..625a7b5f60
--- /dev/null
+++ b/tests/fail/dangling_pointers/dangling_pointer_project_underscore_match.stderr
@@ -0,0 +1,25 @@
+error: Undefined Behavior: out-of-bounds pointer arithmetic: ALLOC has been freed, so this pointer is dangling
+  --> $DIR/dangling_pointer_project_underscore_match.rs:LL:CC
+   |
+LL |         match (*p).1 {
+   |               ^^^^^^ out-of-bounds pointer arithmetic: ALLOC has been freed, so this pointer is dangling
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+help: ALLOC was allocated here:
+  --> $DIR/dangling_pointer_project_underscore_match.rs:LL:CC
+   |
+LL |         let b = Box::new(42);
+   |                 ^^^^^^^^^^^^
+help: ALLOC was deallocated here:
+  --> $DIR/dangling_pointer_project_underscore_match.rs:LL:CC
+   |
+LL |     };
+   |     ^
+   = note: BACKTRACE (of the first span):
+   = note: inside `main` at $DIR/dangling_pointer_project_underscore_match.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to previous error
+
diff --git a/tests/pass/underscore_pattern.rs b/tests/pass/underscore_pattern.rs
index f9b42c5bc8..b0e85bc1bb 100644
--- a/tests/pass/underscore_pattern.rs
+++ b/tests/pass/underscore_pattern.rs
@@ -3,15 +3,15 @@
 use std::ptr;
 
 fn main() {
-    dangling_deref_match();
-    union_uninhabited_match();
+    dangling_match();
+    invalid_match();
     dangling_let();
     invalid_let();
     dangling_let_type_annotation();
     invalid_let_type_annotation();
 }
 
-fn dangling_deref_match() {
+fn dangling_match() {
     let p = {
         let b = Box::new(42);
         &*b as *const i32
@@ -23,20 +23,15 @@ fn dangling_deref_match() {
     }
 }
 
-fn union_uninhabited_match() {
-    #[derive(Copy, Clone)]
-    enum Void {}
+fn invalid_match() {
     union Uninit<T: Copy> {
         value: T,
         uninit: (),
     }
     unsafe {
-        let x: Uninit<Void> = Uninit { uninit: () };
+        let x: Uninit<bool> = Uninit { uninit: () };
         match x.value {
-            // rustc warns about un unreachable pattern,
-            // but is wrong in unsafe code.
-            #[allow(unreachable_patterns)]
-            _ => println!("hi from the void!"),
+            _ => {}
         }
     }
 }
diff --git a/tests/pass/underscore_pattern.stdout b/tests/pass/underscore_pattern.stdout
deleted file mode 100644
index ff731696f0..0000000000
--- a/tests/pass/underscore_pattern.stdout
+++ /dev/null
@@ -1 +0,0 @@
-hi from the void!