change stdlib circular dependencies handling

2 files changed, 8 insertions, 102 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index e9171823c24..d37a2cc8c8e 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -1,6 +1,6 @@
 use rustc_arena::TypedArena;
 use rustc_ast::CRATE_NODE_ID;
-use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
+use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::memmap::Mmap;
 use rustc_data_structures::temp_dir::MaybeTempDir;
 use rustc_errors::{ErrorGuaranteed, Handler};
@@ -1714,6 +1714,13 @@ fn add_post_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor
 /// that are necessary for the linking. They are only present in symbol table but not actually
 /// used in any sections, so the linker will therefore pick relevant rlibs for linking, but
 /// unused `#[no_mangle]` or `#[used]` can still be discard by GC sections.
+///
+/// There's a few internal crates in the standard library (aka libcore and
+/// libstd) which actually have a circular dependence upon one another. This
+/// currently arises through "weak lang items" where libcore requires things
+/// like `rust_begin_unwind` but libstd ends up defining it. To get this
+/// circular dependence to work correctly we declare some of these things
+/// in this synthetic object.
 fn add_linked_symbol_object(
     cmd: &mut dyn Linker,
     sess: &Session,
@@ -2333,65 +2340,10 @@ fn add_upstream_rust_crates<'a>(
     // crates.
     let deps = &codegen_results.crate_info.used_crates;
 
-    // There's a few internal crates in the standard library (aka libcore and
-    // libstd) which actually have a circular dependence upon one another. This
-    // currently arises through "weak lang items" where libcore requires things
-    // like `rust_begin_unwind` but libstd ends up defining it. To get this
-    // circular dependence to work correctly in all situations we'll need to be
-    // sure to correctly apply the `--start-group` and `--end-group` options to
-    // GNU linkers, otherwise if we don't use any other symbol from the standard
-    // library it'll get discarded and the whole application won't link.
-    //
-    // In this loop we're calculating the `group_end`, after which crate to
-    // pass `--end-group` and `group_start`, before which crate to pass
-    // `--start-group`. We currently do this by passing `--end-group` after
-    // the first crate (when iterating backwards) that requires a lang item
-    // defined somewhere else. Once that's set then when we've defined all the
-    // necessary lang items we'll pass `--start-group`.
-    //
-    // Note that this isn't amazing logic for now but it should do the trick
-    // for the current implementation of the standard library.
-    let mut group_end = None;
-    let mut group_start = None;
-    // Crates available for linking thus far.
-    let mut available = FxHashSet::default();
-    // Crates required to satisfy dependencies discovered so far.
-    let mut required = FxHashSet::default();
-
-    let info = &codegen_results.crate_info;
-    for &cnum in deps.iter().rev() {
-        if let Some(missing) = info.missing_lang_items.get(&cnum) {
-            let missing_crates = missing.iter().map(|i| info.lang_item_to_crate.get(i).copied());
-            required.extend(missing_crates);
-        }
-
-        required.insert(Some(cnum));
-        available.insert(Some(cnum));
-
-        if required.len() > available.len() && group_end.is_none() {
-            group_end = Some(cnum);
-        }
-        if required.len() == available.len() && group_end.is_some() {
-            group_start = Some(cnum);
-            break;
-        }
-    }
-
-    // If we didn't end up filling in all lang items from upstream crates then
-    // we'll be filling it in with our crate. This probably means we're the
-    // standard library itself, so skip this for now.
-    if group_end.is_some() && group_start.is_none() {
-        group_end = None;
-    }
-
     let mut compiler_builtins = None;
     let search_path = OnceCell::new();
 
     for &cnum in deps.iter() {
-        if group_start == Some(cnum) {
-            cmd.group_start();
-        }
-
         // We may not pass all crates through to the linker. Some crates may
         // appear statically in an existing dylib, meaning we'll pick up all the
         // symbols from the dylib.
@@ -2470,10 +2422,6 @@ fn add_upstream_rust_crates<'a>(
             }
             Linkage::Dynamic => add_dynamic_crate(cmd, sess, &src.dylib.as_ref().unwrap().0),
         }
-
-        if group_end == Some(cnum) {
-            cmd.group_end();
-        }
     }
 
     // compiler-builtins are always placed last to ensure that they're
diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index 8c6f526b054..949a356fce1 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -183,8 +183,6 @@ pub trait Linker {
     fn no_default_libraries(&mut self);
     fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType, symbols: &[String]);
     fn subsystem(&mut self, subsystem: &str);
-    fn group_start(&mut self);
-    fn group_end(&mut self);
     fn linker_plugin_lto(&mut self);
     fn add_eh_frame_header(&mut self) {}
     fn add_no_exec(&mut self) {}
@@ -730,18 +728,6 @@ impl<'a> Linker for GccLinker<'a> {
         self.hint_dynamic(); // Reset to default before returning the composed command line.
     }
 
-    fn group_start(&mut self) {
-        if self.takes_hints() {
-            self.linker_arg("--start-group");
-        }
-    }
-
-    fn group_end(&mut self) {
-        if self.takes_hints() {
-            self.linker_arg("--end-group");
-        }
-    }
-
     fn linker_plugin_lto(&mut self) {
         match self.sess.opts.cg.linker_plugin_lto {
             LinkerPluginLto::Disabled => {
@@ -1019,10 +1005,6 @@ impl<'a> Linker for MsvcLinker<'a> {
         }
     }
 
-    // MSVC doesn't need group indicators
-    fn group_start(&mut self) {}
-    fn group_end(&mut self) {}
-
     fn linker_plugin_lto(&mut self) {
         // Do nothing
     }
@@ -1165,10 +1147,6 @@ impl<'a> Linker for EmLinker<'a> {
         // noop
     }
 
-    // Appears not necessary on Emscripten
-    fn group_start(&mut self) {}
-    fn group_end(&mut self) {}
-
     fn linker_plugin_lto(&mut self) {
         // Do nothing
     }
@@ -1344,10 +1322,6 @@ impl<'a> Linker for WasmLd<'a> {
 
     fn subsystem(&mut self, _subsystem: &str) {}
 
-    // Not needed for now with LLD
-    fn group_start(&mut self) {}
-    fn group_end(&mut self) {}
-
     fn linker_plugin_lto(&mut self) {
         // Do nothing for now
     }
@@ -1476,14 +1450,6 @@ impl<'a> Linker for L4Bender<'a> {
         self.hint_static(); // Reset to default before returning the composed command line.
     }
 
-    fn group_start(&mut self) {
-        self.cmd.arg("--start-group");
-    }
-
-    fn group_end(&mut self) {
-        self.cmd.arg("--end-group");
-    }
-
     fn linker_plugin_lto(&mut self) {}
 
     fn control_flow_guard(&mut self) {}
@@ -1664,10 +1630,6 @@ impl<'a> Linker for PtxLinker<'a> {
 
     fn subsystem(&mut self, _subsystem: &str) {}
 
-    fn group_start(&mut self) {}
-
-    fn group_end(&mut self) {}
-
     fn linker_plugin_lto(&mut self) {}
 }
 
@@ -1777,9 +1739,5 @@ impl<'a> Linker for BpfLinker<'a> {
 
     fn subsystem(&mut self, _subsystem: &str) {}
 
-    fn group_start(&mut self) {}
-
-    fn group_end(&mut self) {}
-
     fn linker_plugin_lto(&mut self) {}
 }