Auto merge of #100032 - BoxyUwU:no_ty_in_placeholder_const, r=compiler-errors

make `PlaceholderConst` not store the type of the const

Currently the `Placeholder` variant on `ConstKind` is 28 bytes when with this PR its 8 bytes, i am not sure this is really useful at all rn since `Unevaluated` and `Value` variants are huge still but eventually it should be possible to get both down to 16 bytes :thinking:. Mostly opening this to see if this change has any perf impact when done before it can make `ConstKind`/`ConstS` smaller

1 files changed, 1 insertions, 4 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index d22465db85b..6a4f582ac50 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -744,10 +744,7 @@ impl<'tcx> TypeFolder<'tcx> for BoundVarReplacer<'_, 'tcx> {
             }
             ty::ConstKind::Bound(debruijn, bound_const) if debruijn >= self.current_index => {
                 let universe = self.universe_for(debruijn);
-                let p = ty::PlaceholderConst {
-                    universe,
-                    name: ty::BoundConst { var: bound_const, ty: ct.ty() },
-                };
+                let p = ty::PlaceholderConst { universe, name: bound_const };
                 self.mapped_consts.insert(p, bound_const);
                 self.infcx
                     .tcx