remove a machine hook that is no longer used

Author: RalfJung

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -221,9 +221,6 @@ impl<'tcx, Prov: Provenance> LocalState<'tcx, Prov> {
 
     /// Overwrite the local. If the local can be overwritten in place, return a reference
     /// to do so; otherwise return the `MemPlace` to consult instead.
-    ///
-    /// Note: Before calling this, call the `before_access_local_mut` machine hook! You may be
-    /// invalidating machine invariants otherwise!
     #[inline(always)]
     pub(super) fn access_mut(&mut self) -> InterpResult<'tcx, &mut Operand<Prov>> {
         match &mut self.value {

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -260,24 +260,6 @@ pub trait Machine<'mir, 'tcx: 'mir>: Sized {
         F2::NAN
     }
 
-    /// Called before writing the specified `local` of the `frame`.
-    /// Since writing a ZST is not actually accessing memory or locals, this is never invoked
-    /// for ZST reads.
-    ///
-    /// Due to borrow checker trouble, we indicate the `frame` as an index rather than an `&mut
-    /// Frame`.
-    #[inline(always)]
-    fn before_access_local_mut<'a>(
-        _ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
-        _frame: usize,
-        _local: mir::Local,
-    ) -> InterpResult<'tcx>
-    where
-        'tcx: 'mir,
-    {
-        Ok(())
-    }
-
     /// Called before a basic block terminator is executed.
     #[inline]
     fn before_terminator(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {

compiler/rustc_const_eval/src/interpret/place.rs

@@ -624,7 +624,6 @@ where
                     dest.force_mplace(self)?
                 } else {
                     debug_assert_eq!(locals_addr, self.frame().locals_addr());
-                    M::before_access_local_mut(self, self.frame_idx(), local)?;
                     match self.frame_mut().locals[local].access_mut()? {
                         Operand::Immediate(local_val) => {
                             // Local can be updated in-place.
@@ -740,7 +739,6 @@ where
                     dest.force_mplace(self)?
                 } else {
                     debug_assert_eq!(locals_addr, self.frame().locals_addr());
-                    M::before_access_local_mut(self, self.frame_idx(), local)?;
                     match self.frame_mut().locals[local].access_mut()? {
                         Operand::Immediate(local) => {
                             *local = Immediate::Uninit;
@@ -921,7 +919,6 @@ where
         let mplace = match place.place {
             Place::Local { local, offset, locals_addr } => {
                 debug_assert_eq!(locals_addr, self.frame().locals_addr());
-                M::before_access_local_mut(self, self.frame_idx(), local)?;
                 let whole_local = match self.frame_mut().locals[local].access_mut()? {
                     &mut Operand::Immediate(local_val) => {
                         // We need to make an allocation.