Do not fetch HIR to check target features.

Author: cjgillot

compiler/rustc_codegen_ssa/src/target_features.rs

@@ -3,12 +3,12 @@ use rustc_attr::InstructionSetAttr;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::Applicability;
-use rustc_hir as hir;
+use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::TyCtxt;
+use rustc_middle::ty::{DefIdTree, TyCtxt};
 use rustc_session::parse::feature_err;
 use rustc_session::Session;
 use rustc_span::symbol::sym;
@@ -440,12 +440,9 @@ fn asm_target_features(tcx: TyCtxt<'_>, did: DefId) -> &FxHashSet<Symbol> {
 /// Checks the function annotated with `#[target_feature]` is not a safe
 /// trait method implementation, reporting an error if it is.
 pub fn check_target_feature_trait_unsafe(tcx: TyCtxt<'_>, id: LocalDefId, attr_span: Span) {
-    let hir_id = tcx.hir().local_def_id_to_hir_id(id);
-    let node = tcx.hir().get(hir_id);
-    if let hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) = node {
-        let parent_id = tcx.hir().get_parent_item(hir_id);
-        let parent_item = tcx.hir().expect_item(parent_id.def_id);
-        if let hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = parent_item.kind {
+    if let DefKind::AssocFn = tcx.def_kind(id) {
+        let parent_id = tcx.local_parent(id);
+        if let DefKind::Impl { of_trait: true } = tcx.def_kind(parent_id) {
             tcx.sess
                 .struct_span_err(
                     attr_span,