Add test and improve comment

kani-compiler/src/kani_middle/transform/rustc_intrinsics.rs

@@ -78,9 +78,16 @@ impl<'a> ReplaceIntrinsicVisitor<'a> {
 }
 
 impl MutMirVisitor for ReplaceIntrinsicVisitor<'_> {
-    /// Replace the terminator for some intrinsics.
+    /// Replace the terminator for some rustc's intrinsics.
     ///
-    /// Note that intrinsics must always be called directly.
+    /// In some cases, we replace a function call to a rustc intrinsic by a call to the
+    /// corresponding Kani intrinsic.
+    ///
+    /// Our models are usually augmented by some trait bounds, or they leverage Kani intrinsics to
+    /// implement the given semantics.
+    ///
+    /// Note that we only need to replace function calls since intrinsics must always be called
+    /// directly. I.e., no need to handle function pointers.
     fn visit_terminator(&mut self, term: &mut Terminator) {
         if let TerminatorKind::Call { func, .. } = &mut term.kind {
             if let TyKind::RigidTy(RigidTy::FnDef(def, args)) =

tests/expected/intrinsics/align_of_dst.expected

@@ -0,0 +1,6 @@
+Checking harness check_zst1024...
+Checking harness check_large...
+Checking harness check_1char_tup...
+Checking harness check_1zst_usize...
+
+Complete - 4 successfully verified harnesses, 0 failures, 4 total

tests/expected/intrinsics/align_of_dst.rs

@@ -0,0 +1,75 @@
+// Copyright Kani Contributors
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! This test case checks the behavior of `align_of_val_raw` for dynamically sized types.
+
+#![feature(layout_for_ptr)]
+#![feature(ptr_metadata)]
+
+use std::any::Any;
+use std::mem::align_of;
+
+#[allow(unused)]
+#[derive(Clone, Copy, kani::Arbitrary)]
+struct Wrapper<T, U: ?Sized> {
+    head: T,
+    dst: U,
+}
+
+/// Create a ZST with an alignment of 1024.
+#[allow(unused)]
+#[repr(align(1024))]
+#[derive(kani::Arbitrary)]
+struct Zst1024;
+
+/// Create a structure with large alignment (2^29).
+///
+/// This seems to be the maximum supported today:
+/// <https://github.com/rust-lang/rust/blob/7db7489f9bc2/tests/ui/repr/repr-align.rs#L11>
+#[repr(align(536870912))]
+#[derive(kani::Arbitrary)]
+struct LargeAlign {
+    data: [usize; 100],
+}
+
+/// Generates a harness with different type combinations and check the alignment is correct.
+/// We use a constant for the original type, so it is pre-populated by the compiler.
+///
+/// ## Parameters
+/// - `name`: Name of the harness.
+/// - `t1` / `t2`: Types used for different tail and head combinations.
+/// - `expected`: The expected alignment.
+macro_rules! check_alignment {
+    ($name:ident, $t1:ty, $t2:ty, $expected:expr) => {
+        #[kani::proof]
+        fn $name() {
+            const EXPECTED: usize = align_of::<Wrapper<$t1, $t2>>();
+            assert_eq!(EXPECTED, $expected);
+
+            let var: Wrapper<$t1, $t2> = kani::any();
+            let wide_ptr: &Wrapper<$t1, dyn Any> = &var as &_;
+            let dyn_t2_align = align_of_val(wide_ptr);
+            assert_eq!(dyn_t2_align, EXPECTED, "Expected same alignment as before coercion");
+
+            let var: Wrapper<$t2, $t1> = kani::any();
+            let wide_ptr: &Wrapper<$t2, dyn Any> = &var as &_;
+            let dyn_t1_align = align_of_val(wide_ptr);
+            assert_eq!(dyn_t1_align, EXPECTED, "Expected same alignment as before coercion");
+
+            let var: Wrapper<$t1, [$t2; 0]> = kani::any();
+            let wide_ptr: &Wrapper<$t1, [$t2]> = &var as &_;
+            let slice_t2_align = align_of_val(wide_ptr);
+            assert_eq!(slice_t2_align, EXPECTED, "Expected same alignment as before coercion");
+
+            let var: Wrapper<$t2, [$t1; 0]> = kani::any();
+            let wide_ptr: &Wrapper<$t2, [$t1]> = &var as &_;
+            let slice_t1_align = align_of_val(wide_ptr);
+            assert_eq!(slice_t1_align, EXPECTED, "Expected same alignment as before coercion");
+        }
+    };
+}
+
+check_alignment!(check_1zst_usize, usize, (), align_of::<usize>());
+check_alignment!(check_1char_tup, (char, usize, u128), char, align_of::<u128>());
+check_alignment!(check_zst1024, (char, usize, u128), Zst1024, align_of::<Zst1024>());
+check_alignment!(check_large, u128, LargeAlign, align_of::<LargeAlign>());