We're not really using the ConstPropMachine anymore

Author: oli-obk

compiler/rustc_mir_transform/src/const_prop.rs

@@ -5,7 +5,6 @@ use rustc_const_eval::interpret::{
     self, compile_time_machine, AllocId, ConstAllocation, FnArg, Frame, ImmTy, InterpCx,
     InterpResult, OpTy, PlaceTy, Pointer,
 };
-use rustc_data_structures::fx::FxHashSet;
 use rustc_index::bit_set::BitSet;
 use rustc_index::IndexVec;
 use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
@@ -49,16 +48,7 @@ pub(crate) macro throw_machine_stop_str($($tt:tt)*) {{
     throw_machine_stop!(Zst)
 }}
 
-pub(crate) struct ConstPropMachine {
-    pub written_only_inside_own_block_locals: FxHashSet<Local>,
-    pub can_const_prop: IndexVec<Local, ConstPropMode>,
-}
-
-impl ConstPropMachine {
-    pub fn new(can_const_prop: IndexVec<Local, ConstPropMode>) -> Self {
-        Self { written_only_inside_own_block_locals: Default::default(), can_const_prop }
-    }
-}
+pub(crate) struct ConstPropMachine;
 
 impl<'mir, 'tcx: 'mir> interpret::Machine<'mir, 'tcx> for ConstPropMachine {
     compile_time_machine!(<'mir, 'tcx>);
@@ -132,23 +122,11 @@ impl<'mir, 'tcx: 'mir> interpret::Machine<'mir, 'tcx> for ConstPropMachine {
     }
 
     fn before_access_local_mut<'a>(
-        ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
-        frame: usize,
-        local: Local,
+        _ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
+        _frame: usize,
+        _local: Local,
     ) -> InterpResult<'tcx> {
-        assert_eq!(frame, 0);
-        match ecx.machine.can_const_prop[local] {
-            ConstPropMode::NoPropagation => {
-                throw_machine_stop_str!(
-                    "tried to write to a local that is marked as not propagatable"
-                )
-            }
-            ConstPropMode::OnlyInsideOwnBlock => {
-                ecx.machine.written_only_inside_own_block_locals.insert(local);
-            }
-            ConstPropMode::FullConstProp => {}
-        }
-        Ok(())
+        unreachable!()
     }
 
     fn before_access_global(

compiler/rustc_mir_transform/src/const_prop_lint.rs

@@ -5,6 +5,7 @@ use std::fmt::Debug;
 
 use rustc_const_eval::interpret::{ImmTy, Projectable};
 use rustc_const_eval::interpret::{InterpCx, InterpResult, OpTy, Scalar};
+use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def::DefKind;
 use rustc_hir::HirId;
 use rustc_index::bit_set::BitSet;
@@ -76,6 +77,8 @@ struct ConstPropagator<'mir, 'tcx> {
     visited_blocks: BitSet<BasicBlock>,
     locals: IndexVec<Local, Value<'tcx>>,
     body: &'mir Body<'tcx>,
+    written_only_inside_own_block_locals: FxHashSet<Local>,
+    can_const_prop: IndexVec<Local, ConstPropMode>,
 }
 
 #[derive(Debug, Clone)]
@@ -181,12 +184,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         let param_env = tcx.param_env_reveal_all_normalized(def_id);
 
         let can_const_prop = CanConstProp::check(tcx, param_env, body);
-        let ecx = InterpCx::new(
-            tcx,
-            tcx.def_span(def_id),
-            param_env,
-            ConstPropMachine::new(can_const_prop),
-        );
+        let ecx = InterpCx::new(tcx, tcx.def_span(def_id), param_env, ConstPropMachine);
 
         ConstPropagator {
             ecx,
@@ -196,6 +194,8 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             visited_blocks: BitSet::new_empty(body.basic_blocks.len()),
             locals: IndexVec::from_elem_n(Value::Uninit, body.local_decls.len()),
             body,
+            can_const_prop,
+            written_only_inside_own_block_locals: Default::default(),
         }
     }
 
@@ -212,14 +212,14 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
     /// but not reading from them anymore.
     fn remove_const(&mut self, local: Local) {
         self.locals[local] = Value::Uninit;
-        self.ecx.machine.written_only_inside_own_block_locals.remove(&local);
+        self.written_only_inside_own_block_locals.remove(&local);
     }
 
     fn access_mut(&mut self, place: &Place<'_>) -> Option<&mut Value<'tcx>> {
-        match self.ecx.machine.can_const_prop[place.local] {
+        match self.can_const_prop[place.local] {
             ConstPropMode::NoPropagation => return None,
             ConstPropMode::OnlyInsideOwnBlock => {
-                self.ecx.machine.written_only_inside_own_block_locals.insert(place.local);
+                self.written_only_inside_own_block_locals.insert(place.local);
             }
             ConstPropMode::FullConstProp => {}
         }
@@ -776,7 +776,7 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
 
         let Some(()) = self.check_rvalue(rvalue, location) else { return };
 
-        match self.ecx.machine.can_const_prop[place.local] {
+        match self.can_const_prop[place.local] {
             // Do nothing if the place is indirect.
             _ if place.is_indirect() => {}
             ConstPropMode::NoPropagation => self.ensure_not_propagated(place.local),
@@ -812,7 +812,7 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
 
         match statement.kind {
             StatementKind::SetDiscriminant { ref place, variant_index } => {
-                match self.ecx.machine.can_const_prop[place.local] {
+                match self.can_const_prop[place.local] {
                     // Do nothing if the place is indirect.
                     _ if place.is_indirect() => {}
                     ConstPropMode::NoPropagation => self.ensure_not_propagated(place.local),
@@ -879,23 +879,19 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
         // which were modified in the current block.
         // Take it out of the ecx so we can get a mutable reference to the ecx for `remove_const`.
         let mut written_only_inside_own_block_locals =
-            std::mem::take(&mut self.ecx.machine.written_only_inside_own_block_locals);
+            std::mem::take(&mut self.written_only_inside_own_block_locals);
 
         // This loop can get very hot for some bodies: it check each local in each bb.
         // To avoid this quadratic behaviour, we only clear the locals that were modified inside
         // the current block.
         for local in written_only_inside_own_block_locals.drain() {
-            debug_assert_eq!(
-                self.ecx.machine.can_const_prop[local],
-                ConstPropMode::OnlyInsideOwnBlock
-            );
+            debug_assert_eq!(self.can_const_prop[local], ConstPropMode::OnlyInsideOwnBlock);
             self.remove_const(local);
         }
-        self.ecx.machine.written_only_inside_own_block_locals =
-            written_only_inside_own_block_locals;
+        self.written_only_inside_own_block_locals = written_only_inside_own_block_locals;
 
         if cfg!(debug_assertions) {
-            for (local, &mode) in self.ecx.machine.can_const_prop.iter_enumerated() {
+            for (local, &mode) in self.can_const_prop.iter_enumerated() {
                 match mode {
                     ConstPropMode::FullConstProp => {}
                     ConstPropMode::NoPropagation | ConstPropMode::OnlyInsideOwnBlock => {