Make codegen_fn_attrs query cheap to clone

This is an attempt to recover a perf loss observed in rust-lang#52993 by making the
result of the `codegen_fn_attrs` query cheap to clone as more and more parts of
the compiler start to use this query.

src/librustc/middle/reachable.rs

@@ -51,7 +51,7 @@ fn generics_require_inlining(generics: &ty::Generics) -> bool {
 // true for functions.
 fn item_might_be_inlined(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                          item: &hir::Item,
-                         attrs: CodegenFnAttrs) -> bool {
+                         attrs: &CodegenFnAttrs) -> bool {
     if attrs.requests_inline() {
         return true
     }
@@ -77,7 +77,7 @@ fn method_might_be_inlined<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     if let Some(impl_node_id) = tcx.hir.as_local_node_id(impl_src) {
         match tcx.hir.find(impl_node_id) {
             Some(hir_map::NodeItem(item)) =>
-                item_might_be_inlined(tcx, &item, codegen_fn_attrs),
+                item_might_be_inlined(tcx, &item, &codegen_fn_attrs),
             Some(..) | None =>
                 span_bug!(impl_item.span, "impl did is not an item")
         }
@@ -171,7 +171,7 @@ impl<'a, 'tcx> ReachableContext<'a, 'tcx> {
             Some(hir_map::NodeItem(item)) => {
                 match item.node {
                     hir::ItemKind::Fn(..) =>
-                        item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id)),
+                        item_might_be_inlined(self.tcx, &item, &self.tcx.codegen_fn_attrs(def_id)),
                     _ => false,
                 }
             }
@@ -264,7 +264,7 @@ impl<'a, 'tcx> ReachableContext<'a, 'tcx> {
                         let def_id = self.tcx.hir.local_def_id(item.id);
                         if item_might_be_inlined(self.tcx,
                                                  &item,
-                                                 self.tcx.codegen_fn_attrs(def_id)) {
+                                                 &self.tcx.codegen_fn_attrs(def_id)) {
                             self.visit_nested_body(body);
                         }
                     }

src/librustc/ty/query/mod.rs

@@ -321,7 +321,7 @@ define_queries! { <'tcx>
     },
 
     Codegen {
-        [] fn codegen_fn_attrs: codegen_fn_attrs(DefId) -> CodegenFnAttrs,
+        [] fn codegen_fn_attrs: codegen_fn_attrs(DefId) -> Lrc<CodegenFnAttrs>,
     },
 
     Other {

src/librustc_codegen_llvm/attributes.rs

@@ -139,8 +139,12 @@ pub fn from_fn_attrs(
     llfn: &'ll Value,
     id: Option<DefId>,
 ) {
-    let codegen_fn_attrs = id.map(|id| cx.tcx.codegen_fn_attrs(id))
-        .unwrap_or(CodegenFnAttrs::new());
+    let codegen_fn_attrs = id.map(|id| cx.tcx.codegen_fn_attrs(id));
+    let default = CodegenFnAttrs::new();
+    let codegen_fn_attrs = codegen_fn_attrs
+        .as_ref()
+        .map(|s| &**s)
+        .unwrap_or(&default);
 
     inline(llfn, codegen_fn_attrs.inline);
 

src/librustc_typeck/collect.rs

@@ -39,6 +39,7 @@ use rustc::ty::util::Discr;
 use rustc::util::captures::Captures;
 use rustc::util::nodemap::FxHashMap;
 use rustc_target::spec::abi;
+use rustc_data_structures::sync::Lrc;
 
 use syntax::ast;
 use syntax::ast::MetaItemKind;
@@ -1979,7 +1980,7 @@ fn linkage_by_name<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId, name: &
     }
 }
 
-fn codegen_fn_attrs<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, id: DefId) -> CodegenFnAttrs {
+fn codegen_fn_attrs<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, id: DefId) -> Lrc<CodegenFnAttrs> {
     let attrs = tcx.get_attrs(id);
 
     let mut codegen_fn_attrs = CodegenFnAttrs::new();
@@ -2096,5 +2097,5 @@ fn codegen_fn_attrs<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, id: DefId) -> Codegen
         }
     }
 
-    codegen_fn_attrs
+    Lrc::new(codegen_fn_attrs)
 }