Auto merge of #116875 - nnethercote:rustc_monomorphize, r=wesleywiser

`rustc_monomorphize` cleanups

Just some small improvements I found while looking over this code.

r? `@wesleywiser`

Author: bors

Diff for: Cargo.lock

@@ -4270,7 +4270,6 @@ dependencies = [
  "rustc_errors",
  "rustc_fluent_macro",
  "rustc_hir",
- "rustc_index",
  "rustc_macros",
  "rustc_middle",
  "rustc_session",

Diff for: compiler/rustc_monomorphize/Cargo.toml

@@ -13,7 +13,6 @@ rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }
-rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_session = { path = "../rustc_session" }

Diff for: compiler/rustc_monomorphize/messages.ftl

@@ -27,8 +27,6 @@ monomorphize_type_length_limit = reached the type-length limit while instantiati
 monomorphize_unknown_cgu_collection_mode =
     unknown codegen-item collection mode '{$mode}', falling back to 'lazy' mode
 
-monomorphize_unknown_partition_strategy = unknown partitioning strategy
-
 monomorphize_unused_generic_params = item has unused generic parameters
 
 monomorphize_written_to_path = the full type name has been written to '{$path}'

Diff for: compiler/rustc_monomorphize/src/collector.rs

@@ -173,7 +173,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_middle::mir::interpret::{AllocId, ErrorHandled, GlobalAlloc, Scalar};
 use rustc_middle::mir::mono::{InstantiationMode, MonoItem};
 use rustc_middle::mir::visit::Visitor as MirVisitor;
-use rustc_middle::mir::{self, Local, Location};
+use rustc_middle::mir::{self, Location};
 use rustc_middle::query::TyCtxtAt;
 use rustc_middle::ty::adjustment::{CustomCoerceUnsized, PointerCoercion};
 use rustc_middle::ty::print::with_no_trimmed_paths;
@@ -874,14 +874,6 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
         self.super_operand(operand, location);
         self.check_operand_move_size(operand, location);
     }
-
-    fn visit_local(
-        &mut self,
-        _place_local: Local,
-        _context: mir::visit::PlaceContext,
-        _location: Location,
-    ) {
-    }
 }
 
 fn visit_drop_use<'tcx>(
@@ -1220,7 +1212,7 @@ impl<'v> RootCollector<'_, 'v> {
     }
 
     fn is_root(&self, def_id: LocalDefId) -> bool {
-        !item_requires_monomorphization(self.tcx, def_id)
+        !self.tcx.generics_of(def_id).requires_monomorphization(self.tcx)
             && match self.mode {
                 MonoItemCollectionMode::Eager => true,
                 MonoItemCollectionMode::Lazy => {
@@ -1283,11 +1275,6 @@ impl<'v> RootCollector<'_, 'v> {
     }
 }
 
-fn item_requires_monomorphization(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
-    let generics = tcx.generics_of(def_id);
-    generics.requires_monomorphization(tcx)
-}
-
 #[instrument(level = "debug", skip(tcx, output))]
 fn create_mono_items_for_default_impls<'tcx>(
     tcx: TyCtxt<'tcx>,
@@ -1394,17 +1381,6 @@ fn collect_alloc<'tcx>(tcx: TyCtxt<'tcx>, alloc_id: AllocId, output: &mut MonoIt
     }
 }
 
-fn add_assoc_fn<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    def_id: Option<DefId>,
-    fn_ident: Ident,
-    skip_move_check_fns: &mut Vec<DefId>,
-) {
-    if let Some(def_id) = def_id.and_then(|def_id| assoc_fn_of_type(tcx, def_id, fn_ident)) {
-        skip_move_check_fns.push(def_id);
-    }
-}
-
 fn assoc_fn_of_type<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, fn_ident: Ident) -> Option<DefId> {
     for impl_def_id in tcx.inherent_impls(def_id) {
         if let Some(new) = tcx.associated_items(impl_def_id).find_by_name_and_kind(
@@ -1420,26 +1396,16 @@ fn assoc_fn_of_type<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, fn_ident: Ident) ->
 }
 
 fn build_skip_move_check_fns(tcx: TyCtxt<'_>) -> Vec<DefId> {
-    let mut skip_move_check_fns = vec![];
-    add_assoc_fn(
-        tcx,
-        tcx.lang_items().owned_box(),
-        Ident::from_str("new"),
-        &mut skip_move_check_fns,
-    );
-    add_assoc_fn(
-        tcx,
-        tcx.get_diagnostic_item(sym::Arc),
-        Ident::from_str("new"),
-        &mut skip_move_check_fns,
-    );
-    add_assoc_fn(
-        tcx,
-        tcx.get_diagnostic_item(sym::Rc),
-        Ident::from_str("new"),
-        &mut skip_move_check_fns,
-    );
-    skip_move_check_fns
+    let fns = [
+        (tcx.lang_items().owned_box(), "new"),
+        (tcx.get_diagnostic_item(sym::Rc), "new"),
+        (tcx.get_diagnostic_item(sym::Arc), "new"),
+    ];
+    fns.into_iter()
+        .filter_map(|(def_id, fn_name)| {
+            def_id.and_then(|def_id| assoc_fn_of_type(tcx, def_id, Ident::from_str(fn_name)))
+        })
+        .collect::<Vec<_>>()
 }
 
 /// Scans the MIR in order to find function calls, closures, and drop-glue.

Diff for: compiler/rustc_monomorphize/src/errors.rs

@@ -75,10 +75,6 @@ pub struct LargeAssignmentsLint {
     pub limit: u64,
 }
 
-#[derive(Diagnostic)]
-#[diag(monomorphize_unknown_partition_strategy)]
-pub struct UnknownPartitionStrategy;
-
 #[derive(Diagnostic)]
 #[diag(monomorphize_symbol_already_defined)]
 pub struct SymbolAlreadyDefined {