formatted docs | monomorphize-abi-alignment.rs

Author: Kivooeo

tests/ui/codegen/mono-respects-abi-alignment.rs

@@ -1,19 +1,20 @@
-//@ run-pass
+//! Test that monomorphization correctly distinguishes types with different ABI alignment.
+//!
+//! On x86_64-linux-gnu and similar platforms, structs get 8-byte "preferred"
+//! alignment, but their "ABI" alignment (what actually matters for data layout)
+//! is the largest alignment of any field. If monomorphization incorrectly uses
+//! "preferred" alignment instead of "ABI" alignment, it might unify types `A`
+//! and `B` even though `S<A>` and `S<B>` have field `t` at different offsets,
+//! leading to incorrect method dispatch for `unwrap()`.
 
-#![allow(non_upper_case_globals)]
-#![allow(dead_code)]
-/*!
- * On x86_64-linux-gnu and possibly other platforms, structs get 8-byte "preferred" alignment,
- * but their "ABI" alignment (i.e., what actually matters for data layout) is the largest alignment
- * of any field. (Also, `u64` has 8-byte ABI alignment; this is not always true).
- *
- * On such platforms, if monomorphize uses the "preferred" alignment, then it will unify
- * `A` and `B`, even though `S<A>` and `S<B>` have the field `t` at different offsets,
- * and apply the wrong instance of the method `unwrap`.
- */
+//@ run-pass
 
 #[derive(Copy, Clone)]
-struct S<T> { i:u8, t:T }
+struct S<T> {
+    #[allow(dead_code)]
+    i: u8,
+    t: T,
+}
 
 impl<T> S<T> {
     fn unwrap(self) -> T {
@@ -22,14 +23,15 @@ impl<T> S<T> {
 }
 
 #[derive(Copy, Clone, PartialEq, Debug)]
-struct A((u32, u32));
+struct A((u32, u32)); // Different ABI alignment than B
 
 #[derive(Copy, Clone, PartialEq, Debug)]
-struct B(u64);
+struct B(u64); // Different ABI alignment than A
 
 pub fn main() {
-    static Ca: S<A> = S { i: 0, t: A((13, 104)) };
-    static Cb: S<B> = S { i: 0, t: B(31337) };
-    assert_eq!(Ca.unwrap(), A((13, 104)));
-    assert_eq!(Cb.unwrap(), B(31337));
+    static CA: S<A> = S { i: 0, t: A((13, 104)) };
+    static CB: S<B> = S { i: 0, t: B(31337) };
+
+    assert_eq!(CA.unwrap(), A((13, 104)));
+    assert_eq!(CB.unwrap(), B(31337));
 }