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

4 files changed, 15 insertions, 10 deletions

diff --git a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
index 9c30c81123b..ca7862c9dc4 100644
--- a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
+++ b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
@@ -511,7 +511,9 @@ impl<'cx, 'tcx> TypeFolder<'tcx> for Canonicalizer<'cx, 'tcx> {
             }
             ty::ConstKind::Placeholder(placeholder) => {
                 return self.canonicalize_const_var(
-                    CanonicalVarInfo { kind: CanonicalVarKind::PlaceholderConst(placeholder) },
+                    CanonicalVarInfo {
+                        kind: CanonicalVarKind::PlaceholderConst(placeholder, ct.ty()),
+                    },
                     ct,
                 );
             }
@@ -695,11 +697,14 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
                             ..placeholder
                         })
                     }
-                    CanonicalVarKind::PlaceholderConst(placeholder) => {
-                        CanonicalVarKind::PlaceholderConst(ty::Placeholder {
-                            universe: reverse_universe_map[&placeholder.universe],
-                            ..placeholder
-                        })
+                    CanonicalVarKind::PlaceholderConst(placeholder, t) => {
+                        CanonicalVarKind::PlaceholderConst(
+                            ty::Placeholder {
+                                universe: reverse_universe_map[&placeholder.universe],
+                                ..placeholder
+                            },
+                            t,
+                        )
                     }
                 },
             })
diff --git a/compiler/rustc_infer/src/infer/canonical/mod.rs b/compiler/rustc_infer/src/infer/canonical/mod.rs
index f251d561c60..a9294a85e51 100644
--- a/compiler/rustc_infer/src/infer/canonical/mod.rs
+++ b/compiler/rustc_infer/src/infer/canonical/mod.rs
@@ -144,13 +144,13 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
                 )
                 .into(),
 
-            CanonicalVarKind::PlaceholderConst(ty::PlaceholderConst { universe, name }) => {
+            CanonicalVarKind::PlaceholderConst(ty::PlaceholderConst { universe, name }, ty) => {
                 let universe_mapped = universe_map(universe);
                 let placeholder_mapped = ty::PlaceholderConst { universe: universe_mapped, name };
                 self.tcx
                     .mk_const(ty::ConstS {
                         kind: ty::ConstKind::Placeholder(placeholder_mapped),
-                        ty: name.ty,
+                        ty,
                     })
                     .into()
             }
diff --git a/compiler/rustc_infer/src/infer/higher_ranked/mod.rs b/compiler/rustc_infer/src/infer/higher_ranked/mod.rs
index ed257c144e0..9bdd437333b 100644
--- a/compiler/rustc_infer/src/infer/higher_ranked/mod.rs
+++ b/compiler/rustc_infer/src/infer/higher_ranked/mod.rs
@@ -97,7 +97,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 self.tcx.mk_const(ty::ConstS {
                     kind: ty::ConstKind::Placeholder(ty::PlaceholderConst {
                         universe: next_universe,
-                        name: ty::BoundConst { var: bound_var, ty },
+                        name: bound_var,
                     }),
                     ty,
                 })
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 0424b5a7c44..1546c9ccff2 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -2067,7 +2067,7 @@ fn replace_param_and_infer_substs_with_placeholder<'tcx>(
                     ty,
                     kind: ty::ConstKind::Placeholder(ty::PlaceholderConst {
                         universe: ty::UniverseIndex::ROOT,
-                        name: ty::BoundConst { ty, var: ty::BoundVar::from_usize(idx) },
+                        name: ty::BoundVar::from_usize(idx),
                     }),
                 })
                 .into()