Rollup merge of #80232 - bugadani:roundtrip, r=estebank

Remove redundant def_id lookups

Simplify `DefId -> LocalDefId -> HirId -> LocalDefId -> DefId` chains.

Author: Dylan-DPC

compiler/rustc_middle/src/ty/consts.rs

@@ -92,8 +92,7 @@ impl<'tcx> Const<'tcx> {
                 let item_id = tcx.hir().get_parent_node(hir_id);
                 let item_def_id = tcx.hir().local_def_id(item_id);
                 let generics = tcx.generics_of(item_def_id.to_def_id());
-                let index =
-                    generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id).to_def_id()];
+                let index = generics.param_def_id_to_index[&def_id];
                 let name = tcx.hir().name(hir_id);
                 ty::ConstKind::Param(ty::ParamConst::new(index, name))
             }

compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -813,8 +813,7 @@ fn convert_path_expr<'a, 'tcx>(
             let item_id = cx.tcx.hir().get_parent_node(hir_id);
             let item_def_id = cx.tcx.hir().local_def_id(item_id);
             let generics = cx.tcx.generics_of(item_def_id);
-            let local_def_id = cx.tcx.hir().local_def_id(hir_id);
-            let index = generics.param_def_id_to_index[&local_def_id.to_def_id()];
+            let index = generics.param_def_id_to_index[&def_id];
             let name = cx.tcx.hir().name(hir_id);
             let val = ty::ConstKind::Param(ty::ParamConst::new(index, name));
             ExprKind::Literal {