Remove a sorting operation from used_crates

Author: bjorn3

compiler/rustc_codegen_ssa/src/base.rs

@@ -19,7 +19,7 @@ use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_hir::lang_items::LangItem;
 use rustc_index::vec::Idx;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
-use rustc_middle::middle::cstore::{self, EncodedMetadata};
+use rustc_middle::middle::cstore::EncodedMetadata;
 use rustc_middle::middle::lang_items;
 use rustc_middle::mir::mono::{CodegenUnit, CodegenUnitNameBuilder, MonoItem};
 use rustc_middle::ty::layout::{HasTyCtxt, TyAndLayout};
@@ -769,6 +769,22 @@ impl CrateInfo {
             subsystem.to_string()
         });
 
+        // This list is used when generating the command line to pass through to
+        // system linker. The linker expects undefined symbols on the left of the
+        // command line to be defined in libraries on the right, not the other way
+        // around. For more info, see some comments in the add_used_library function
+        // below.
+        //
+        // In order to get this left-to-right dependency ordering, we use the reverse
+        // postorder of all crates putting the leaves at the right-most positions.
+        let used_crates = tcx
+            .postorder_cnums(())
+            .iter()
+            .rev()
+            .copied()
+            .filter(|&cnum| !tcx.dep_kind(cnum).macros_only())
+            .collect();
+
         let mut info = CrateInfo {
             local_crate_name,
             panic_runtime: None,
@@ -778,7 +794,7 @@ impl CrateInfo {
             native_libraries: Default::default(),
             used_libraries: tcx.native_libraries(LOCAL_CRATE).iter().map(Into::into).collect(),
             crate_name: Default::default(),
-            used_crates: cstore::used_crates(tcx),
+            used_crates,
             used_crate_source: Default::default(),
             lang_item_to_crate: Default::default(),
             missing_lang_items: Default::default(),

compiler/rustc_middle/src/middle/cstore.rs

@@ -197,30 +197,3 @@ pub trait CrateStore {
 }
 
 pub type CrateStoreDyn = dyn CrateStore + sync::Sync;
-
-// This method is used when generating the command line to pass through to
-// system linker. The linker expects undefined symbols on the left of the
-// command line to be defined in libraries on the right, not the other way
-// around. For more info, see some comments in the add_used_library function
-// below.
-//
-// In order to get this left-to-right dependency ordering, we perform a
-// topological sort of all crates putting the leaves at the right-most
-// positions.
-pub fn used_crates(tcx: TyCtxt<'_>) -> Vec<CrateNum> {
-    let mut libs = tcx
-        .crates(())
-        .iter()
-        .cloned()
-        .filter_map(|cnum| {
-            if tcx.dep_kind(cnum).macros_only() {
-                return None;
-            }
-            Some(cnum)
-        })
-        .collect::<Vec<_>>();
-    let mut ordering = tcx.postorder_cnums(()).to_owned();
-    ordering.reverse();
-    libs.sort_by_cached_key(|&a| ordering.iter().position(|x| *x == a));
-    libs
-}