Immediately create an Option instead of reallocating for it later

Author: oli-obk

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -68,7 +68,8 @@ pub(super) const UNKNOWN_COLUMN_NUMBER: c_uint = 0;
 
 const NO_SCOPE_METADATA: Option<&DIScope> = None;
 /// A function that returns an empty list of generic parameter debuginfo nodes.
-const NO_GENERICS: for<'ll> fn(&CodegenCx<'ll, '_>) -> SmallVec<&'ll DIType> = |_| SmallVec::new();
+const NO_GENERICS: for<'ll> fn(&CodegenCx<'ll, '_>) -> SmallVec<Option<&'ll DIType>> =
+    |_| SmallVec::new();
 
 // SmallVec is used quite a bit in this module, so create a shorthand.
 // The actual number of elements is not so important.
@@ -1287,7 +1288,7 @@ fn build_union_type_di_node<'ll, 'tcx>(
 fn build_generic_type_param_di_nodes<'ll, 'tcx>(
     cx: &CodegenCx<'ll, 'tcx>,
     ty: Ty<'tcx>,
-) -> SmallVec<&'ll DIType> {
+) -> SmallVec<Option<&'ll DIType>> {
     if let ty::Adt(def, args) = *ty.kind() {
         if args.types().next().is_some() {
             let generics = cx.tcx.generics_of(def.did());
@@ -1297,7 +1298,7 @@ fn build_generic_type_param_di_nodes<'ll, 'tcx>(
                     kind.as_type().map(|ty| {
                         let actual_type = cx.tcx.normalize_erasing_regions(cx.typing_env(), ty);
                         let actual_type_di_node = type_di_node(cx, actual_type);
-                        cx.create_template_type_parameter(name.as_str(), actual_type_di_node)
+                        Some(cx.create_template_type_parameter(name.as_str(), actual_type_di_node))
                     })
                 })
                 .collect();

compiler/rustc_codegen_llvm/src/debuginfo/metadata/type_map.rs

@@ -257,16 +257,15 @@ pub(super) fn build_type_with_children<'ll, 'tcx>(
     cx: &CodegenCx<'ll, 'tcx>,
     stub_info: StubInfo<'ll, 'tcx>,
     members: impl FnOnce(&CodegenCx<'ll, 'tcx>, &'ll DIType) -> SmallVec<&'ll DIType>,
-    generics: impl FnOnce(&CodegenCx<'ll, 'tcx>) -> SmallVec<&'ll DIType>,
+    generics: impl FnOnce(&CodegenCx<'ll, 'tcx>) -> SmallVec<Option<&'ll DIType>>,
 ) -> DINodeCreationResult<'ll> {
     assert_eq!(debug_context(cx).type_map.di_node_for_unique_id(stub_info.unique_type_id), None);
 
     debug_context(cx).type_map.insert(stub_info.unique_type_id, stub_info.metadata);
 
     let members: SmallVec<_> =
         members(cx, stub_info.metadata).into_iter().map(|node| Some(node)).collect();
-    let generics: SmallVec<Option<&'ll DIType>> =
-        generics(cx).into_iter().map(|node| Some(node)).collect();
+    let generics = generics(cx);
 
     if !(members.is_empty() && generics.is_empty()) {
         unsafe {