[DO NOT MERGE] Check performance hit of emitting full metadata in check mode

Author: bjorn3

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -1836,11 +1836,6 @@ fn exported_symbols_for_non_proc_macro(
 }
 
 fn exported_symbols_for_proc_macro_crate(tcx: TyCtxt<'_>) -> Vec<(String, SymbolExportKind)> {
-    // `exported_symbols` will be empty when !should_codegen.
-    if !tcx.sess.opts.output_types.should_codegen() {
-        return Vec::new();
-    }
-
     let stable_crate_id = tcx.stable_crate_id(LOCAL_CRATE);
     let proc_macro_decls_name = tcx.sess.generate_proc_macro_decls_symbol(stable_crate_id);
 

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -47,10 +47,6 @@ pub fn crates_export_threshold(crate_types: &[CrateType]) -> SymbolExportLevel {
 }
 
 fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<SymbolExportInfo> {
-    if !tcx.sess.opts.output_types.should_codegen() && !tcx.is_sdylib_interface_build() {
-        return Default::default();
-    }
-
     let is_compiler_builtins = tcx.is_compiler_builtins(LOCAL_CRATE);
 
     let mut reachable_non_generics: DefIdMap<_> = tcx
@@ -166,10 +162,6 @@ fn exported_non_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 &[];
-    }
-
     // FIXME: Sorting this is unnecessary since we are sorting later anyway.
     //        Can we skip the later sorting?
     let sorted = tcx.with_stable_hashing_context(|hcx| {
@@ -221,10 +213,6 @@ 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() {

compiler/rustc_interface/src/passes.rs

@@ -1114,9 +1114,7 @@ fn run_required_analyses(tcx: TyCtxt<'_>) {
             // If we need to codegen, ensure that we emit all errors from
             // `mir_drops_elaborated_and_const_checked` now, to avoid discovering
             // them later during codegen.
-            if tcx.sess.opts.output_types.should_codegen()
-                || tcx.hir_body_const_context(def_id).is_some()
-            {
+            if tcx.hir_body_const_context(def_id).is_some() {
                 tcx.ensure_ok().mir_drops_elaborated_and_const_checked(def_id);
             }
             if tcx.is_coroutine(def_id.to_def_id()) {

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1111,11 +1111,7 @@ fn should_encode_mir(
 ) -> (bool, bool) {
     match tcx.def_kind(def_id) {
         // Constructors
-        DefKind::Ctor(_, _) => {
-            let mir_opt_base = tcx.sess.opts.output_types.should_codegen()
-                || tcx.sess.opts.unstable_opts.always_encode_mir;
-            (true, mir_opt_base)
-        }
+        DefKind::Ctor(_, _) => (true, true),
         // Constants
         DefKind::AnonConst | DefKind::InlineConst | DefKind::AssocConst | DefKind::Const => {
             (true, false)
@@ -1127,8 +1123,7 @@ fn should_encode_mir(
         DefKind::AssocFn | DefKind::Fn | DefKind::Closure => {
             let generics = tcx.generics_of(def_id);
             let opt = tcx.sess.opts.unstable_opts.always_encode_mir
-                || (tcx.sess.opts.output_types.should_codegen()
-                    && reachable_set.contains(&def_id)
+                || (reachable_set.contains(&def_id)
                     && (generics.requires_monomorphization(tcx)
                         || tcx.cross_crate_inlinable(def_id)));
             // The function has a `const` modifier or is in a `const trait`.
@@ -1858,10 +1853,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         // Encode all the deduced parameter attributes for everything that has MIR, even for items
         // that can't be inlined. But don't if we aren't optimizing in non-incremental mode, to
         // save the query traffic.
-        if tcx.sess.opts.output_types.should_codegen()
-            && tcx.sess.opts.optimize != OptLevel::No
-            && tcx.sess.opts.incremental.is_none()
-        {
+        if tcx.sess.opts.optimize != OptLevel::No && tcx.sess.opts.incremental.is_none() {
             for &local_def_id in tcx.mir_keys(()) {
                 if let DefKind::AssocFn | DefKind::Fn = tcx.def_kind(local_def_id) {
                     record_array!(self.tables.deduced_param_attrs[local_def_id.to_def_id()] <-
@@ -2263,11 +2255,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 /// Used to prefetch queries which will be needed later by metadata encoding.
 /// Only a subset of the queries are actually prefetched to keep this code smaller.
 fn prefetch_mir(tcx: TyCtxt<'_>) {
-    if !tcx.sess.opts.output_types.should_codegen() {
-        // We won't emit MIR, so don't prefetch it.
-        return;
-    }
-
     let reachable_set = tcx.reachable_set(());
     par_for_each_in(tcx.mir_keys(()), |&&def_id| {
         if tcx.is_trivial_const(def_id) {