Complete miri test.

Author: cjgillot

src/tools/miri/tests/pass/function_pointers.rs

@@ -23,6 +23,10 @@ fn h(i: i32, j: i32) -> i32 {
     j * i * 7
 }
 
+fn i() -> i32 {
+    73
+}
+
 fn return_fn_ptr(f: fn() -> i32) -> fn() -> i32 {
     f
 }
@@ -72,9 +76,18 @@ fn main() {
     assert_eq!(indirect3(h), 210);
     assert_eq!(indirect_mut3(h), 210);
     assert_eq!(indirect_once3(h), 210);
-    let g = f as fn() -> i32;
-    assert!(return_fn_ptr(g) == g);
-    assert!(return_fn_ptr(g) as unsafe fn() -> i32 == g as fn() -> i32 as unsafe fn() -> i32);
+    // Check that `i` always has the same address. This is not guaranteed
+    // but Miri currently uses a fixed address for monomorphic functions.
+    assert!(return_fn_ptr(i) == i);
+    assert!(return_fn_ptr(i) as unsafe fn() -> i32 == i as fn() -> i32 as unsafe fn() -> i32);
+    // We don't check anything for `f`. Miri gives it many different addresses
+    // but mir-opts can turn them into the same address.
+    let _val = return_fn_ptr(f) != f;
+    // However, if we only turn `f` into a function pointer and use that pointer,
+    // it is equal to itself.
+    let f2 = f as fn() -> i32;
+    assert!(return_fn_ptr(f2) == f2);
+    assert!(return_fn_ptr(f2) as unsafe fn() -> i32 == f2 as fn() -> i32 as unsafe fn() -> i32);
 
     // Any non-null value is okay for function pointers.
     unsafe {