Store promoted_fragments on the MIR instead of in the pass

Author: ecstatic-morse

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -23,7 +23,6 @@ use rustc_span::Span;
 
 use rustc_index::vec::{Idx, IndexVec};
 
-use std::cell::Cell;
 use std::{cmp, iter, mem};
 
 use crate::transform::check_consts::{qualifs, ConstCx};
@@ -33,14 +32,12 @@ use crate::transform::check_consts::{qualifs, ConstCx};
 /// Promotion is the extraction of promotable temps into separate MIR bodies so they can have
 /// `'static` lifetime.
 ///
-/// After this pass is run, `promoted_fragments` will hold the MIR body corresponding to each
+/// After this pass is run, `body.promoted_fragments` will hold the MIR body corresponding to each
 /// newly created `Constant`.
 #[derive(Default)]
-pub struct PromoteTemps<'tcx> {
-    pub promoted_fragments: Cell<IndexVec<Promoted, Body<'tcx>>>,
-}
+pub struct PromoteTemps;
 
-impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> {
+impl<'tcx> MirPass<'tcx> for PromoteTemps {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         // There's not really any point in promoting errorful MIR.
         //
@@ -61,7 +58,7 @@ impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> {
         let promotable_candidates = validate_candidates(&ccx, &temps, &all_candidates);
 
         let promoted = promote_candidates(body, tcx, temps, promotable_candidates);
-        self.promoted_fragments.set(promoted);
+        body.promoted_fragments = promoted;
     }
 }
 

compiler/rustc_middle/src/mir/mod.rs

@@ -263,6 +263,12 @@ pub struct Body<'tcx> {
     /// potentially allow things like `[u8; std::mem::size_of::<T>() * 0]` due to this.
     pub is_polymorphic: bool,
 
+    /// A list of MIR fragments for promotable temps inside this body.
+    ///
+    /// This field is only populated during the `PromoteTemps` MIR pass and will be emptied
+    /// immediately after.
+    pub promoted_fragments: IndexVec<Promoted, Body<'tcx>>,
+
     predecessor_cache: PredecessorCache,
     is_cyclic: GraphIsCyclicCache,
 }
@@ -311,6 +317,7 @@ impl<'tcx> Body<'tcx> {
             is_polymorphic: false,
             predecessor_cache: PredecessorCache::new(),
             is_cyclic: GraphIsCyclicCache::new(),
+            promoted_fragments: Default::default(),
         };
         body.is_polymorphic = body.definitely_has_param_types_or_consts(tcx);
         body
@@ -338,6 +345,7 @@ impl<'tcx> Body<'tcx> {
             is_polymorphic: false,
             predecessor_cache: PredecessorCache::new(),
             is_cyclic: GraphIsCyclicCache::new(),
+            promoted_fragments: Default::default(),
         }
     }
 

compiler/rustc_mir_transform/src/lib.rs

@@ -328,7 +328,7 @@ fn mir_promoted(
 
     run_passes(tcx, &mut body, MirPhase::ConstPromotion, &[promote, opt_coverage]);
 
-    let promoted = promote_pass.promoted_fragments.into_inner();
+    let promoted = std::mem::take(&mut body.promoted_fragments);
     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 }