Deduplicate some code between miri and const prop

src/librustc/mir/interpret/error.rs

@@ -389,6 +389,10 @@ pub enum UnsupportedOpInfo<'tcx> {
     /// Free-form case. Only for errors that are never caught!
     Unsupported(String),
 
+    /// FIXME(#64506) Error used to work around accessing projections of
+    /// uninhabited types.
+    UninhabitedValue,
+
     // -- Everything below is not categorized yet --
     FunctionAbiMismatch(Abi, Abi),
     FunctionArgMismatch(Ty<'tcx>, Ty<'tcx>),
@@ -552,6 +556,8 @@ impl fmt::Debug for UnsupportedOpInfo<'tcx> {
                     not a power of two"),
             Unsupported(ref msg) =>
                 write!(f, "{}", msg),
+            UninhabitedValue =>
+                write!(f, "tried to use an uninhabited value"),
         }
     }
 }

src/librustc_mir/const_eval.rs

@@ -21,7 +21,7 @@ use syntax::source_map::{Span, DUMMY_SP};
 
 use crate::interpret::{self,
     PlaceTy, MPlaceTy, OpTy, ImmTy, Immediate, Scalar, Pointer,
-    RawConst, ConstValue,
+    RawConst, ConstValue, Machine,
     InterpResult, InterpErrorInfo, GlobalId, InterpCx, StackPopCleanup,
     Allocation, AllocId, MemoryKind, Memory,
     snapshot, RefTracking, intern_const_alloc_recursive,
@@ -41,7 +41,7 @@ const DETECTOR_SNAPSHOT_PERIOD: isize = 256;
 /// that inform us about the generic bounds of the constant. E.g., using an associated constant
 /// of a function's generic parameter will require knowledge about the bounds on the generic
 /// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
-pub(crate) fn mk_eval_cx<'mir, 'tcx>(
+fn mk_eval_cx<'mir, 'tcx>(
     tcx: TyCtxt<'tcx>,
     span: Span,
     param_env: ty::ParamEnv<'tcx>,
@@ -169,7 +169,7 @@ fn eval_body_using_ecx<'mir, 'tcx>(
 }
 
 #[derive(Clone, Debug)]
-enum ConstEvalError {
+pub enum ConstEvalError {
     NeedsRfc(String),
 }
 
@@ -521,8 +521,8 @@ pub fn const_variant_index<'tcx>(
 /// Turn an interpreter error into something to report to the user.
 /// As a side-effect, if RUSTC_CTFE_BACKTRACE is set, this prints the backtrace.
 /// Should be called only if the error is actually going to to be reported!
-pub fn error_to_const_error<'mir, 'tcx>(
-    ecx: &InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
+pub fn error_to_const_error<'mir, 'tcx, M: Machine<'mir, 'tcx>>(
+    ecx: &InterpCx<'mir, 'tcx, M>,
     mut error: InterpErrorInfo<'tcx>,
 ) -> ConstEvalErr<'tcx> {
     error.print_backtrace();

src/librustc_mir/interpret/machine.rs

@@ -12,6 +12,7 @@ use rustc::ty::{self, Ty, TyCtxt};
 use super::{
     Allocation, AllocId, InterpResult, Scalar, AllocationExtra,
     InterpCx, PlaceTy, OpTy, ImmTy, MemoryKind, Pointer, Memory,
+    Frame, Operand,
 };
 
 /// Whether this kind of memory is allowed to leak
@@ -184,6 +185,22 @@ pub trait Machine<'mir, 'tcx>: Sized {
         dest: PlaceTy<'tcx, Self::PointerTag>,
     ) -> InterpResult<'tcx>;
 
+    /// Called to read the specified `local` from the `frame`.
+    fn access_local(
+        _ecx: &InterpCx<'mir, 'tcx, Self>,
+        frame: &Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>,
+        local: mir::Local,
+    ) -> InterpResult<'tcx, Operand<Self::PointerTag>> {
+        frame.locals[local].access()
+    }
+
+    /// Called before a `StaticKind::Static` value is accessed.
+    fn before_access_static(
+        _allocation: &Allocation,
+    ) -> InterpResult<'tcx> {
+        Ok(())
+    }
+
     /// Called to initialize the "extra" state of an allocation and make the pointers
     /// it contains (in relocations) tagged.  The way we construct allocations is
     /// to always first construct it without extra and then add the extra.

src/librustc_mir/interpret/memory.rs

@@ -462,6 +462,8 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
                     // Make sure we use the ID of the resolved memory, not the lazy one!
                     let id = raw_const.alloc_id;
                     let allocation = tcx.alloc_map.lock().unwrap_memory(id);
+
+                    M::before_access_static(allocation)?;
                     Cow::Borrowed(allocation)
                 }
             }

src/librustc_mir/interpret/operand.rs

@@ -458,7 +458,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             // Do not read from ZST, they might not be initialized
             Operand::Immediate(Scalar::zst().into())
         } else {
-            frame.locals[local].access()?
+            M::access_local(&self, frame, local)?
         };
         Ok(OpTy { op, layout })
     }
@@ -481,7 +481,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
     // Evaluate a place with the goal of reading from it.  This lets us sometimes
     // avoid allocations.
-    pub(super) fn eval_place_to_op(
+    pub fn eval_place_to_op(
         &self,
         place: &mir::Place<'tcx>,
         layout: Option<TyLayout<'tcx>>,

src/librustc_mir/interpret/place.rs

@@ -9,7 +9,7 @@ use rustc::mir;
 use rustc::mir::interpret::truncate;
 use rustc::ty::{self, Ty};
 use rustc::ty::layout::{
-    self, Size, Align, LayoutOf, TyLayout, HasDataLayout, VariantIdx, PrimitiveExt
+    self, Size, Abi, Align, LayoutOf, TyLayout, HasDataLayout, VariantIdx, PrimitiveExt
 };
 use rustc::ty::TypeFoldable;
 
@@ -385,6 +385,10 @@ where
                 stride * field
             }
             layout::FieldPlacement::Union(count) => {
+                // FIXME(#64506) `UninhabitedValue` can be removed when this issue is resolved
+                if base.layout.abi == Abi::Uninhabited {
+                    throw_unsup!(UninhabitedValue);
+                }
                 assert!(field < count as u64,
                         "Tried to access field {} of union with {} fields", field, count);
                 // Offset is always 0

src/librustc_mir/interpret/step.rs

@@ -132,7 +132,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     ///
     /// There is no separate `eval_rvalue` function. Instead, the code for handling each rvalue
     /// type writes its results directly into the memory specified by the place.
-    fn eval_rvalue_into_place(
+    pub fn eval_rvalue_into_place(
         &mut self,
         rvalue: &mir::Rvalue<'tcx>,
         place: &mir::Place<'tcx>,