fix comparing of function pointers

src/interpreter/mod.rs

@@ -1404,6 +1404,10 @@ pub fn read_primval(&mut self, ptr: Pointer, ty: Ty<'tcx>) -> EvalResult<'tcx, P
             (8, &ty::TyUint(UintTy::Us)) |
             (_, &ty::TyUint(UintTy::U64)) => PrimVal::U64(self.memory.read_uint(ptr, 8)? as u64),
 
+            (_, &ty::TyFnDef(def_id, substs, fn_ty)) => {
+                PrimVal::FnPtr(self.memory.create_fn_ptr(def_id, substs, fn_ty))
+            },
+            (_, &ty::TyFnPtr(_)) => self.memory.read_ptr(ptr).map(PrimVal::FnPtr)?,
             (_, &ty::TyRef(_, ty::TypeAndMut { ty, .. })) |
             (_, &ty::TyRawPtr(ty::TypeAndMut { ty, .. })) => {
                 if self.type_is_sized(ty) {

src/memory.rs

@@ -42,7 +42,7 @@ pub fn offset(self, i: isize) -> Self {
     }
 }
 
-#[derive(Debug, Copy, Clone)]
+#[derive(Debug, Copy, Clone, Hash, Eq, PartialEq)]
 pub struct FunctionDefinition<'tcx> {
     pub def_id: DefId,
     pub substs: &'tcx Substs<'tcx>,
@@ -59,6 +59,8 @@ pub struct Memory<'tcx> {
     /// Function "allocations". They exist solely so pointers have something to point to, and
     /// we can figure out what they point to.
     functions: HashMap<AllocId, FunctionDefinition<'tcx>>,
+    /// Inverse map of `functions` so we don't allocate a new pointer every time we need one
+    function_definitions: HashMap<FunctionDefinition<'tcx>, AllocId>,
     next_id: AllocId,
     pub pointer_size: usize,
 }
@@ -69,22 +71,29 @@ pub fn new(pointer_size: usize) -> Self {
         Memory {
             alloc_map: HashMap::new(),
             functions: HashMap::new(),
+            function_definitions: HashMap::new(),
             next_id: AllocId(0),
             pointer_size: pointer_size,
         }
     }
 
-    // FIXME: never create two pointers to the same def_id + substs combination
-    // maybe re-use the statics cache of the EvalContext?
     pub fn create_fn_ptr(&mut self, def_id: DefId, substs: &'tcx Substs<'tcx>, fn_ty: &'tcx BareFnTy<'tcx>) -> Pointer {
-        let id = self.next_id;
-        debug!("creating fn ptr: {}", id);
-        self.next_id.0 += 1;
-        self.functions.insert(id, FunctionDefinition {
+        let def = FunctionDefinition {
             def_id: def_id,
             substs: substs,
             fn_ty: fn_ty,
-        });
+        };
+        if let Some(&alloc_id) = self.function_definitions.get(&def) {
+            return Pointer {
+                alloc_id: alloc_id,
+                offset: 0,
+            };
+        }
+        let id = self.next_id;
+        debug!("creating fn ptr: {}", id);
+        self.next_id.0 += 1;
+        self.functions.insert(id, def);
+        self.function_definitions.insert(def, id);
         Pointer {
             alloc_id: id,
             offset: 0,
@@ -361,6 +370,7 @@ pub fn write_primval(&mut self, ptr: Pointer, val: PrimVal) -> EvalResult<'tcx,
             PrimVal::U32(n)  => self.write_uint(ptr, n as u64, 4),
             PrimVal::U64(n)  => self.write_uint(ptr, n as u64, 8),
             PrimVal::IntegerPtr(n) => self.write_uint(ptr, n as u64, pointer_size),
+            PrimVal::FnPtr(_p) |
             PrimVal::AbstractPtr(_p) => unimplemented!(),
         }
     }

src/primval.rs

@@ -10,6 +10,7 @@ pub enum PrimVal {
     U8(u8), U16(u16), U32(u32), U64(u64),
 
     AbstractPtr(Pointer),
+    FnPtr(Pointer),
     IntegerPtr(u64),
 }
 
@@ -130,9 +131,20 @@ fn unrelated_ptr_ops<'tcx>(bin_op: mir::BinOp) -> EvalResult<'tcx, PrimVal> {
 
         (IntegerPtr(l), IntegerPtr(r)) => int_binops!(IntegerPtr, l, r),
 
-        (AbstractPtr(_), IntegerPtr(_)) | (IntegerPtr(_), AbstractPtr(_)) =>
+        (AbstractPtr(_), IntegerPtr(_)) |
+        (IntegerPtr(_), AbstractPtr(_)) |
+        (FnPtr(_), AbstractPtr(_)) |
+        (AbstractPtr(_), FnPtr(_)) |
+        (FnPtr(_), IntegerPtr(_)) |
+        (IntegerPtr(_), FnPtr(_)) =>
             return unrelated_ptr_ops(bin_op),
 
+        (FnPtr(l_ptr), FnPtr(r_ptr)) => match bin_op {
+            Eq => Bool(l_ptr == r_ptr),
+            Ne => Bool(l_ptr != r_ptr),
+            _ => return Err(EvalError::Unimplemented(format!("unimplemented fn ptr comparison: {:?}", bin_op))),
+        },
+
         (AbstractPtr(l_ptr), AbstractPtr(r_ptr)) => {
             if l_ptr.alloc_id != r_ptr.alloc_id {
                 return unrelated_ptr_ops(bin_op);

tests/run-pass/function_pointers.rs

@@ -12,4 +12,6 @@ fn call_fn_ptr() -> i32 {
 
 fn main() {
     assert_eq!(call_fn_ptr(), 42);
+    assert!(return_fn_ptr() == f);
+    assert!(return_fn_ptr() as unsafe fn() -> i32 == f as fn() -> i32 as unsafe fn() -> i32);
 }