cache tag for vtable; fn_alloc's don't have a stack nor tag

Author: RalfJung

src/librustc_mir/interpret/cast.rs

@@ -86,7 +86,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M>
                             def_id,
                             substs,
                         ).ok_or_else(|| InterpError::TooGeneric.into());
-                        let fn_ptr = self.memory.create_fn_alloc(instance?).with_default_tag();
+                        let fn_ptr = self.memory.create_fn_alloc(instance?);
                         self.write_scalar(Scalar::Ptr(fn_ptr.into()), dest)?;
                     }
                     _ => bug!("reify fn pointer on {:?}", src.layout.ty),
@@ -115,7 +115,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M>
                             substs,
                             ty::ClosureKind::FnOnce,
                         );
-                        let fn_ptr = self.memory.create_fn_alloc(instance).with_default_tag();
+                        let fn_ptr = self.memory.create_fn_alloc(instance);
                         let val = Immediate::Scalar(Scalar::Ptr(fn_ptr.into()).into());
                         self.write_immediate(val, dest)?;
                     }

src/librustc_mir/interpret/eval_context.rs

@@ -15,7 +15,7 @@ use rustc::ty::query::TyCtxtAt;
 use rustc_data_structures::indexed_vec::IndexVec;
 use rustc::mir::interpret::{
     ErrorHandled,
-    GlobalId, Scalar, FrameInfo, AllocId,
+    GlobalId, Scalar, Pointer, FrameInfo, AllocId,
     EvalResult, InterpError,
     truncate, sign_extend,
 };
@@ -43,7 +43,10 @@ pub struct InterpretCx<'a, 'mir, 'tcx: 'a + 'mir, M: Machine<'a, 'mir, 'tcx>> {
     pub(crate) stack: Vec<Frame<'mir, 'tcx, M::PointerTag, M::FrameExtra>>,
 
     /// A cache for deduplicating vtables
-    pub(super) vtables: FxHashMap<(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>), AllocId>,
+    pub(super) vtables: FxHashMap<
+            (Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>),
+            Pointer<M::PointerTag>
+        >,
 }
 
 /// A stack frame.

src/librustc_mir/interpret/memory.rs

@@ -108,8 +108,9 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> Memory<'a, 'mir, 'tcx, M> {
         }
     }
 
-    pub fn create_fn_alloc(&mut self, instance: Instance<'tcx>) -> Pointer {
-        Pointer::from(self.tcx.alloc_map.lock().create_fn_alloc(instance))
+    pub fn create_fn_alloc(&mut self, instance: Instance<'tcx>) -> Pointer<M::PointerTag> {
+        // Default tag is okay because anyway you cannot access memory with this.
+        Pointer::from(self.tcx.alloc_map.lock().create_fn_alloc(instance)).with_default_tag()
     }
 
     pub fn allocate_static_bytes(&mut self, bytes: &[u8]) -> Pointer {

src/librustc_mir/interpret/traits.rs

@@ -25,7 +25,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M>
             // always use the same vtable for the same (Type, Trait) combination.
             // That's not what happens in rustc, but emulating per-crate deduplication
             // does not sound like it actually makes anything any better.
-            return Ok(Pointer::from(vtable).with_default_tag());
+            return Ok(vtable);
         }
 
         let methods = if let Some(poly_trait_ref) = poly_trait_ref {
@@ -56,7 +56,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M>
         let tcx = &*self.tcx;
 
         let drop = crate::monomorphize::resolve_drop_in_place(*tcx, ty);
-        let drop = self.memory.create_fn_alloc(drop).with_default_tag();
+        let drop = self.memory.create_fn_alloc(drop);
         // no need to do any alignment checks on the memory accesses below, because we know the
         // allocation is correctly aligned as we created it above. Also we're only offsetting by
         // multiples of `ptr_align`, which means that it will stay aligned to `ptr_align`.
@@ -83,7 +83,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M>
                     def_id,
                     substs,
                 ).ok_or_else(|| InterpError::TooGeneric)?;
-                let fn_ptr = self.memory.create_fn_alloc(instance).with_default_tag();
+                let fn_ptr = self.memory.create_fn_alloc(instance);
                 let method_ptr = vtable.offset(ptr_size * (3 + i as u64), self)?;
                 self.memory
                     .get_mut(method_ptr.alloc_id)?
@@ -92,7 +92,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M>
         }
 
         self.memory.mark_immutable(vtable.alloc_id)?;
-        assert!(self.vtables.insert((ty, poly_trait_ref), vtable.alloc_id).is_none());
+        assert!(self.vtables.insert((ty, poly_trait_ref), vtable).is_none());
 
         Ok(vtable)
     }