use associated const for machine controlling mutable statics

So get rid of the IsStatic trait again

Author: RalfJung

src/librustc_mir/const_eval.rs

@@ -26,11 +26,11 @@ use syntax::source_map::Span;
 
 use rustc::mir::interpret::{
     EvalResult, EvalError, EvalErrorKind, GlobalId,
-    Scalar, AllocId, Allocation, ConstValue, AllocType,
+    Scalar, Allocation, ConstValue,
 };
 use interpret::{self,
     Place, PlaceTy, MemPlace, OpTy, Operand, Value,
-    EvalContext, StackPopCleanup, MemoryKind, Memory,
+    EvalContext, StackPopCleanup, MemoryKind,
 };
 
 pub fn mk_borrowck_eval_cx<'a, 'mir, 'tcx>(
@@ -232,17 +232,12 @@ impl Error for ConstEvalError {
     }
 }
 
-impl interpret::IsStatic for ! {
-    fn is_static(self) -> bool {
-        // unreachable
-        self
-    }
-}
-
 impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeEvaluator {
     type MemoryData = ();
     type MemoryKinds = !;
 
+    const MUT_STATIC_KIND: Option<!> = None; // no mutating of statics allowed
+
     fn find_fn<'a>(
         ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
         instance: ty::Instance<'tcx>,
@@ -308,19 +303,6 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeEvaluator {
         }
     }
 
-    fn access_static_mut<'a, 'm>(
-        mem: &'m mut Memory<'a, 'mir, 'tcx, Self>,
-        id: AllocId,
-    ) -> EvalResult<'tcx, &'m mut Allocation> {
-        // This is always an error, we do not allow mutating statics
-        match mem.tcx.alloc_map.lock().get(id) {
-            Some(AllocType::Memory(..)) |
-            Some(AllocType::Static(..)) => err!(ModifiedConstantMemory),
-            Some(AllocType::Function(..)) => err!(DerefFunctionPointer),
-            None => err!(DanglingPointerDeref),
-        }
-    }
-
     fn find_foreign_static<'a>(
         _tcx: TyCtxtAt<'a, 'tcx, 'tcx>,
         _def_id: DefId,

src/librustc_mir/interpret/machine.rs

@@ -15,16 +15,11 @@
 use std::hash::Hash;
 
 use rustc::hir::def_id::DefId;
-use rustc::mir::interpret::{AllocId, Allocation, EvalResult, Scalar};
+use rustc::mir::interpret::{Allocation, EvalResult, Scalar};
 use rustc::mir;
 use rustc::ty::{self, layout::TyLayout, query::TyCtxtAt};
 
-use super::{EvalContext, PlaceTy, OpTy, Memory};
-
-/// Used by the machine to tell if a certain allocation is for static memory
-pub trait IsStatic {
-    fn is_static(self) -> bool;
-}
+use super::{EvalContext, PlaceTy, OpTy};
 
 /// Methods of this trait signifies a point where CTFE evaluation would fail
 /// and some use case dependent behaviour can instead be applied
@@ -33,7 +28,10 @@ pub trait Machine<'mir, 'tcx>: Clone + Eq + Hash {
     type MemoryData: Clone + Eq + Hash;
 
     /// Additional memory kinds a machine wishes to distinguish from the builtin ones
-    type MemoryKinds: ::std::fmt::Debug + Copy + Clone + Eq + Hash + IsStatic;
+    type MemoryKinds: ::std::fmt::Debug + Copy + Clone + Eq + Hash;
+
+    /// The memory kind to use for mutated statics -- or None if those are not supported.
+    const MUT_STATIC_KIND: Option<Self::MemoryKinds>;
 
     /// Entry point to all function calls.
     ///
@@ -63,6 +61,9 @@ pub trait Machine<'mir, 'tcx>: Clone + Eq + Hash {
     ) -> EvalResult<'tcx>;
 
     /// Called for read access to a foreign static item.
+    /// This can be called multiple times for the same static item and should return consistent
+    /// results.  Once the item is *written* the first time, as usual for statics a copy is
+    /// made and this function is not called again.
     fn find_foreign_static<'a>(
         tcx: TyCtxtAt<'a, 'tcx, 'tcx>,
         def_id: DefId,
@@ -83,12 +84,6 @@ pub trait Machine<'mir, 'tcx>: Clone + Eq + Hash {
         right_layout: TyLayout<'tcx>,
     ) -> EvalResult<'tcx, Option<(Scalar, bool)>>;
 
-    /// Called when requiring mutable access to data in a static.
-    fn access_static_mut<'a, 'm>(
-        mem: &'m mut Memory<'a, 'mir, 'tcx, Self>,
-        id: AllocId,
-    ) -> EvalResult<'tcx, &'m mut Allocation>;
-
     /// Heap allocations via the `box` keyword
     ///
     /// Returns a pointer to the allocated memory

src/librustc_mir/interpret/memory.rs

@@ -29,7 +29,7 @@ use rustc_data_structures::fx::{FxHashSet, FxHashMap, FxHasher};
 
 use syntax::ast::Mutability;
 
-use super::{Machine, IsStatic};
+use super::Machine;
 
 #[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)]
 pub enum MemoryKind<T> {
@@ -39,23 +39,16 @@ pub enum MemoryKind<T> {
     Machine(T),
 }
 
-impl<T: IsStatic> IsStatic for MemoryKind<T> {
-    fn is_static(self) -> bool {
-        match self {
-            MemoryKind::Stack => false,
-            MemoryKind::Machine(kind) => kind.is_static(),
-        }
-    }
-}
-
 #[derive(Clone)]
 pub struct Memory<'a, 'mir, 'tcx: 'a + 'mir, M: Machine<'mir, 'tcx>> {
     /// Additional data required by the Machine
     pub data: M::MemoryData,
 
     /// Allocations local to this instance of the miri engine.  The kind
     /// helps ensure that the same mechanism is used for allocation and
-    /// deallocation.
+    /// deallocation.  When an allocation is not found here, it is a
+    /// static and looked up in the `tcx` for read access.  Writing to
+    /// a static creates a copy here, in the machine.
     alloc_map: FxHashMap<AllocId, (MemoryKind<M::MemoryKinds>, Allocation)>,
 
     pub tcx: TyCtxtAt<'a, 'tcx, 'tcx>,
@@ -223,10 +216,6 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'a, 'mir, 'tcx, M> {
         Ok(new_ptr)
     }
 
-    pub fn is_static(&self, alloc_id: AllocId) -> bool {
-        self.alloc_map.get(&alloc_id).map_or(true, |&(kind, _)| kind.is_static())
-    }
-
     /// Deallocate a local, or do nothing if that local has been made into a static
     pub fn deallocate_local(&mut self, ptr: Pointer) -> EvalResult<'tcx> {
         // The allocation might be already removed by static interning.
@@ -354,10 +343,10 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'a, 'mir, 'tcx, M> {
 /// Allocation accessors
 impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'a, 'mir, 'tcx, M> {
     pub fn get(&self, id: AllocId) -> EvalResult<'tcx, &Allocation> {
-        // normal alloc?
         match self.alloc_map.get(&id) {
+            // Normal alloc?
             Some(alloc) => Ok(&alloc.1),
-            // No need to make any copies, just provide read access to the global static
+            // Static. No need to make any copies, just provide read access to the global static
             // memory in tcx.
             None => const_eval_static::<M>(self.tcx, id),
         }
@@ -368,14 +357,18 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'a, 'mir, 'tcx, M> {
         id: AllocId,
     ) -> EvalResult<'tcx, &mut Allocation> {
         // Static?
-        let alloc = if self.alloc_map.contains_key(&id) {
-            &mut self.alloc_map.get_mut(&id).unwrap().1
-        } else {
-            // The machine controls to what extend we are allowed to mutate global
-            // statics.  (We do not want to allow that during CTFE, but miri needs it.)
-            M::access_static_mut(self, id)?
-        };
-        // See if we can use this
+        if !self.alloc_map.contains_key(&id) {
+            // Ask the machine for what to do
+            if let Some(kind) = M::MUT_STATIC_KIND {
+                // The machine supports mutating statics.  Make a copy, use that.
+                self.deep_copy_static(id, MemoryKind::Machine(kind))?;
+            } else {
+                return err!(ModifiedConstantMemory)
+            }
+        }
+        // If we come here, we know the allocation is in our map
+        let alloc = &mut self.alloc_map.get_mut(&id).unwrap().1;
+        // See if we are allowed to mutate this
         if alloc.mutability == Mutability::Immutable {
             err!(ModifiedConstantMemory)
         } else {
@@ -489,10 +482,12 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'a, 'mir, 'tcx, M> {
 
     pub fn leak_report(&self) -> usize {
         trace!("### LEAK REPORT ###");
+        let mut_static_kind = M::MUT_STATIC_KIND.map(|k| MemoryKind::Machine(k));
         let leaks: Vec<_> = self.alloc_map
             .iter()
-            .filter_map(|(&id, (kind, _))|
-                if kind.is_static() { None } else { Some(id) } )
+            .filter_map(|(&id, &(kind, _))|
+                // exclude mutable statics
+                if Some(kind) == mut_static_kind { None } else { Some(id) } )
             .collect();
         let n = leaks.len();
         self.dump_allocs(leaks);
@@ -609,7 +604,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'a, 'mir, 'tcx, M> {
 
     /// The alloc_id must refer to a (mutable) static; a deep copy of that
     /// static is made into this memory.
-    pub fn deep_copy_static(
+    fn deep_copy_static(
         &mut self,
         id: AllocId,
         kind: MemoryKind<M::MemoryKinds>,
@@ -619,7 +614,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'a, 'mir, 'tcx, M> {
             return err!(ModifiedConstantMemory);
         }
         let old = self.alloc_map.insert(id, (kind, alloc.clone()));
-        assert!(old.is_none(), "deep_copy_static: must not overwrite memory with");
+        assert!(old.is_none(), "deep_copy_static: must not overwrite existing memory");
         Ok(())
     }
 

src/librustc_mir/interpret/mod.rs

@@ -31,7 +31,7 @@ pub use self::place::{Place, PlaceTy, MemPlace, MPlaceTy};
 
 pub use self::memory::{Memory, MemoryKind};
 
-pub use self::machine::{Machine, IsStatic};
+pub use self::machine::Machine;
 
 pub use self::operand::{Value, ValTy, Operand, OpTy};
 

src/librustc_mir/interpret/terminator.rs

@@ -110,7 +110,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
                                 }
                                 (instance, sig)
                             }
-                            ref other => bug!("instance def ty: {:?}", other),
+                            _ => bug!("unexpected fn ptr to ty: {:?}", instance_ty),
                         }
                     }
                     ty::FnDef(def_id, substs) => {