From 753c73a34961ae3c431dbb76afbfe48b81d93c90 Mon Sep 17 00:00:00 2001
From: bjorn3 <17426603+bjorn3@users.noreply.github.com>
Date: Wed, 25 Jun 2025 14:19:57 +0000
Subject: Split exported_symbols for generic and non-generic symbols

This reduces metadata decoder overhead during the monomorphization collector.
---
 compiler/rustc_codegen_ssa/src/back/linker.rs      |  5 +++-
 .../rustc_codegen_ssa/src/back/symbol_export.rs    | 28 ++++++++++++++++------
 compiler/rustc_codegen_ssa/src/back/write.rs       |  3 ++-
 3 files changed, 27 insertions(+), 9 deletions(-)

(limited to 'compiler/rustc_codegen_ssa/src')

diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index cd08c0fc30f..e726c0f8b5b 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -1794,7 +1794,10 @@ fn for_each_exported_symbols_include_dep<'tcx>(
     for (cnum, dep_format) in deps.iter_enumerated() {
         // For each dependency that we are linking to statically ...
         if *dep_format == Linkage::Static {
-            for &(symbol, info) in tcx.exported_symbols(cnum).iter() {
+            for &(symbol, info) in tcx.exported_non_generic_symbols(cnum).iter() {
+                callback(symbol, info, cnum);
+            }
+            for &(symbol, info) in tcx.exported_generic_symbols(cnum).iter() {
                 callback(symbol, info, cnum);
             }
         }
diff --git a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
index 19c005d418e..85c4530fd65 100644
--- a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
+++ b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
@@ -164,7 +164,7 @@ fn is_reachable_non_generic_provider_extern(tcx: TyCtxt<'_>, def_id: DefId) -> b
     tcx.reachable_non_generics(def_id.krate).contains_key(&def_id)
 }
 
-fn exported_symbols_provider_local<'tcx>(
+fn exported_non_generic_symbols_provider_local<'tcx>(
     tcx: TyCtxt<'tcx>,
     _: LocalCrate,
 ) -> &'tcx [(ExportedSymbol<'tcx>, SymbolExportInfo)] {
@@ -296,6 +296,22 @@ fn exported_symbols_provider_local<'tcx>(
         ));
     }
 
+    // Sort so we get a stable incr. comp. hash.
+    symbols.sort_by_cached_key(|s| s.0.symbol_name_for_local_instance(tcx));
+
+    tcx.arena.alloc_from_iter(symbols)
+}
+
+fn exported_generic_symbols_provider_local<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    _: LocalCrate,
+) -> &'tcx [(ExportedSymbol<'tcx>, SymbolExportInfo)] {
+    if !tcx.sess.opts.output_types.should_codegen() && !tcx.is_sdylib_interface_build() {
+        return &[];
+    }
+
+    let mut symbols: Vec<_> = vec![];
+
     if tcx.local_crate_exports_generics() {
         use rustc_middle::mir::mono::{Linkage, MonoItem, Visibility};
         use rustc_middle::ty::InstanceKind;
@@ -458,7 +474,7 @@ fn upstream_monomorphizations_provider(
     let async_drop_in_place_fn_def_id = tcx.lang_items().async_drop_in_place_fn();
 
     for &cnum in cnums.iter() {
-        for (exported_symbol, _) in tcx.exported_symbols(cnum).iter() {
+        for (exported_symbol, _) in tcx.exported_generic_symbols(cnum).iter() {
             let (def_id, args) = match *exported_symbol {
                 ExportedSymbol::Generic(def_id, args) => (def_id, args),
                 ExportedSymbol::DropGlue(ty) => {
@@ -480,10 +496,7 @@ fn upstream_monomorphizations_provider(
                 ExportedSymbol::AsyncDropGlue(def_id, ty) => (def_id, tcx.mk_args(&[ty.into()])),
                 ExportedSymbol::NonGeneric(..)
                 | ExportedSymbol::ThreadLocalShim(..)
-                | ExportedSymbol::NoDefId(..) => {
-                    // These are no monomorphizations
-                    continue;
-                }
+                | ExportedSymbol::NoDefId(..) => unreachable!("{exported_symbol:?}"),
             };
 
             let args_map = instances.entry(def_id).or_default();
@@ -538,7 +551,8 @@ fn is_unreachable_local_definition_provider(tcx: TyCtxt<'_>, def_id: LocalDefId)
 pub(crate) fn provide(providers: &mut Providers) {
     providers.reachable_non_generics = reachable_non_generics_provider;
     providers.is_reachable_non_generic = is_reachable_non_generic_provider_local;
-    providers.exported_symbols = exported_symbols_provider_local;
+    providers.exported_non_generic_symbols = exported_non_generic_symbols_provider_local;
+    providers.exported_generic_symbols = exported_generic_symbols_provider_local;
     providers.upstream_monomorphizations = upstream_monomorphizations_provider;
     providers.is_unreachable_local_definition = is_unreachable_local_definition_provider;
     providers.upstream_drop_glue_for = upstream_drop_glue_for_provider;
diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index c3bfe4c13cd..8330e4f7af0 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -1124,8 +1124,9 @@ fn start_executing_work<B: ExtraBackendMethods>(
 
         let copy_symbols = |cnum| {
             let symbols = tcx
-                .exported_symbols(cnum)
+                .exported_non_generic_symbols(cnum)
                 .iter()
+                .chain(tcx.exported_generic_symbols(cnum))
                 .map(|&(s, lvl)| (symbol_name_for_instance_in_crate(tcx, s, cnum), lvl))
                 .collect();
             Arc::new(symbols)
-- 
cgit 1.4.1-3-g733a5