Only compute vtable information during codegen

compiler/rustc_trait_selection/src/solve/assembly/mod.rs

@@ -3,6 +3,7 @@
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::InferCtxt;
 use rustc_infer::traits::query::NoSolution;
+use rustc_infer::traits::util::supertraits;
 use rustc_middle::bug;
 use rustc_middle::traits::solve::inspect::ProbeKind;
 use rustc_middle::traits::solve::{
@@ -743,14 +744,14 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
         // a projection goal.
         if let Some(principal) = bounds.principal() {
             let principal_trait_ref = principal.with_self_ty(tcx, self_ty);
-            self.walk_vtable(principal_trait_ref, |ecx, assumption, vtable_base, _| {
+            for (idx, assumption) in supertraits(self.interner(), principal_trait_ref).enumerate() {
                 candidates.extend(G::probe_and_consider_object_bound_candidate(
-                    ecx,
-                    CandidateSource::BuiltinImpl(BuiltinImplSource::Object { vtable_base }),
+                    self,
+                    CandidateSource::BuiltinImpl(BuiltinImplSource::Object(idx)),
                     goal,
                     assumption.upcast(tcx),
                 ));
-            });
+            }
         }
     }
 

compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs

@@ -24,7 +24,6 @@ use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Gen
 use std::ops::ControlFlow;
 
 use crate::traits::coherence;
-use crate::traits::vtable::{count_own_vtable_entries, prepare_vtable_segments, VtblSegment};
 
 use super::inspect::ProofTreeBuilder;
 use super::{search_graph, GoalEvaluationKind, FIXPOINT_STEP_LIMIT};
@@ -1022,41 +1021,6 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
             }
         }
     }
-
-    /// Walk through the vtable of a principal trait ref, executing a `supertrait_visitor`
-    /// for every trait ref encountered (including the principal). Passes both the vtable
-    /// base and the (optional) vptr slot.
-    pub(super) fn walk_vtable(
-        &mut self,
-        principal: ty::PolyTraitRef<'tcx>,
-        mut supertrait_visitor: impl FnMut(&mut Self, ty::PolyTraitRef<'tcx>, usize, Option<usize>),
-    ) {
-        let tcx = self.interner();
-        let mut offset = 0;
-        prepare_vtable_segments::<()>(tcx, principal, |segment| {
-            match segment {
-                VtblSegment::MetadataDSA => {
-                    offset += TyCtxt::COMMON_VTABLE_ENTRIES.len();
-                }
-                VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
-                    let own_vtable_entries = count_own_vtable_entries(tcx, trait_ref);
-
-                    supertrait_visitor(
-                        self,
-                        trait_ref,
-                        offset,
-                        emit_vptr.then(|| offset + own_vtable_entries),
-                    );
-
-                    offset += own_vtable_entries;
-                    if emit_vptr {
-                        offset += 1;
-                    }
-                }
-            }
-            ControlFlow::Continue(())
-        });
-    }
 }
 
 /// Eagerly replace aliases with inference variables, emitting `AliasRelate`

compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs

@@ -114,8 +114,8 @@ fn candidate_should_be_dropped_in_favor_of<'tcx>(
         // In the old trait solver, we arbitrarily choose lower vtable candidates
         // over higher ones.
         (
-            CandidateSource::BuiltinImpl(BuiltinImplSource::Object { vtable_base: a }),
-            CandidateSource::BuiltinImpl(BuiltinImplSource::Object { vtable_base: b }),
+            CandidateSource::BuiltinImpl(BuiltinImplSource::Object(a)),
+            CandidateSource::BuiltinImpl(BuiltinImplSource::Object(b)),
         ) => a >= b,
         // Prefer dyn candidates over non-dyn candidates. This is necessary to
         // handle the unsoundness between `impl<T: ?Sized> Any for T` and `dyn Any: Any`.

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -9,6 +9,7 @@ use rustc_hir::{LangItem, Movability};
 use rustc_infer::infer::InferCtxt;
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::solve::MaybeCause;
+use rustc_infer::traits::util::supertraits;
 use rustc_middle::bug;
 use rustc_middle::traits::solve::inspect::ProbeKind;
 use rustc_middle::traits::solve::{CandidateSource, Certainty, Goal, QueryResult};
@@ -756,24 +757,19 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
                 a_data.principal(),
             ));
         } else if let Some(a_principal) = a_data.principal() {
-            self.walk_vtable(
-                a_principal.with_self_ty(tcx, a_ty),
-                |ecx, new_a_principal, _, vtable_vptr_slot| {
-                    responses.extend(ecx.consider_builtin_upcast_to_principal(
-                        goal,
-                        CandidateSource::BuiltinImpl(BuiltinImplSource::TraitUpcasting {
-                            vtable_vptr_slot,
-                        }),
-                        a_data,
-                        a_region,
-                        b_data,
-                        b_region,
-                        Some(new_a_principal.map_bound(|trait_ref| {
-                            ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
-                        })),
-                    ));
-                },
-            );
+            for new_a_principal in supertraits(tcx, a_principal.with_self_ty(tcx, a_ty)).skip(1) {
+                responses.extend(self.consider_builtin_upcast_to_principal(
+                    goal,
+                    CandidateSource::BuiltinImpl(BuiltinImplSource::TraitUpcasting),
+                    a_data,
+                    a_region,
+                    b_data,
+                    b_region,
+                    Some(new_a_principal.map_bound(|trait_ref| {
+                        ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
+                    })),
+                ));
+            }
         }
 
         responses