crucible-mir: Properly parse ArrayToPointer casts

Although `crucible-mir` had support for translating these sorts of casts, it
did not parse them properly. This patch adds a dedicated `ArrayToPointer`
`CastKind` and ensures that it is handled properly in the `crucible-mir` JSON
parser and translator.

Fixes #1224.

crucible-mir/CHANGELOG.md

@@ -1,3 +1,8 @@
+# next -- TBA
+
+* Fix a bug in which `crucible-mir` would fail to parse MIR JSON code involving
+  casts from array references to pointers.
+
 # 0.2 -- 2024-02-05
 
 * `crucible-mir` now supports the `nightly-2023-01-23` Rust toolchain. Some of

crucible-mir/src/Mir/JSON.hs

@@ -401,6 +401,7 @@ instance FromJSON CastKind where
                                                Just (String "Pointer(UnsafeFnPointer)") -> pure UnsafeFnPointer
                                                Just (String "Pointer(Unsize)") -> pure Unsize
                                                Just (String "Pointer(MutToConstPointer)") -> pure MutToConstPointer
+                                               Just (String "Pointer(ArrayToPointer)") -> pure ArrayToPointer
                                                Just (String "UnsizeVtable") -> UnsizeVtable <$> v .: "vtable"
                                                -- TODO: actually plumb this information through if it is relevant
                                                -- instead of using Misc. See

crucible-mir/src/Mir/Mir.hs

@@ -468,6 +468,7 @@ data CastKind =
   | Unsize
   | UnsizeVtable VtableName
   | MutToConstPointer
+  | ArrayToPointer
   deriving (Show,Eq, Ord, Generic)
 
 data Constant = Constant Ty ConstVal

crucible-mir/src/Mir/Trans.hs

@@ -868,7 +868,7 @@ evalCast' ck ty1 e ty2  = do
         -> return $ MirExp (MirReferenceRepr tpr) (getSlicePtr e')
 
       --  *const [T; N] -> *const T (get first element)
-      (M.Misc, M.TyRawPtr (M.TyArray t1 _) m1, M.TyRawPtr t2 m2)
+      (M.ArrayToPointer, M.TyRawPtr (M.TyArray t1 _) m1, M.TyRawPtr t2 m2)
         | t1 == t2, m1 == m2, MirExp (MirReferenceRepr (MirVectorRepr tpr)) e' <- e
         -> MirExp (MirReferenceRepr tpr) <$> subindexRef tpr e' (R.App $ usizeLit 0)
 

crux-mir/test/conc_eval/ptr/coerce_array_to_pointer.rs

@@ -0,0 +1,20 @@
+type T = u64;
+const COUNT: usize = 16;
+
+pub fn output_array(src: &[T; COUNT], dst: *mut T) {
+    unsafe {
+        std::ptr::copy(src as *const T, dst, COUNT);
+    }
+}
+
+#[cfg_attr(crux, crux::test)]
+pub fn crux_test() -> T {
+    let src: &[T; COUNT] = &[42; COUNT];
+    let dst: &mut [T; COUNT] = &mut [0; COUNT];
+    output_array(src, dst as *mut T);
+    dst[0]
+}
+
+pub fn main() {
+    println!("{:?}", crux_test());
+}