Remove a sorting operation from used_crates

1 files changed, 18 insertions, 2 deletions

diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index 0036935be67..15c4ce8a4d0 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/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(),