Auto merge of #74214 - nnethercote:change-SymbolName-name, r=eddyb

Change `SymbolName::name` to a `&str`.

This eliminates a bunch of `Symbol::intern()` and `Symbol::as_str()`
calls, which is good, because they require locking the interner.

Note that the unsafety in `from_cycle_error()` is identical to the
unsafety on other adjacent impls.

r? @eddyb

src/librustc_codegen_llvm/callee.rs

@@ -35,7 +35,7 @@ pub fn get_fn(cx: &CodegenCx<'ll, 'tcx>, instance: Instance<'tcx>) -> &'ll Value
         return llfn;
     }
 
-    let sym = tcx.symbol_name(instance).name.as_str();
+    let sym = tcx.symbol_name(instance).name;
     debug!("get_fn({:?}: {:?}) => {}", instance, instance.monomorphic_ty(cx.tcx()), sym);
 
     let fn_abi = FnAbi::of_instance(cx, instance, &[]);

src/librustc_codegen_llvm/consts.rs

@@ -18,7 +18,7 @@ use rustc_middle::mir::interpret::{
 use rustc_middle::mir::mono::MonoItem;
 use rustc_middle::ty::{self, Instance, Ty};
 use rustc_middle::{bug, span_bug};
-use rustc_span::symbol::{sym, Symbol};
+use rustc_span::symbol::sym;
 use rustc_span::Span;
 use rustc_target::abi::{Align, HasDataLayout, LayoutOf, Primitive, Scalar, Size};
 
@@ -107,11 +107,10 @@ fn check_and_apply_linkage(
     cx: &CodegenCx<'ll, 'tcx>,
     attrs: &CodegenFnAttrs,
     ty: Ty<'tcx>,
-    sym: Symbol,
+    sym: &str,
     span: Span,
 ) -> &'ll Value {
     let llty = cx.layout_of(ty).llvm_type(cx);
-    let sym = sym.as_str();
     if let Some(linkage) = attrs.linkage {
         debug!("get_static: sym={} linkage={:?}", sym, linkage);
 
@@ -215,14 +214,13 @@ impl CodegenCx<'ll, 'tcx> {
             // FIXME: refactor this to work without accessing the HIR
             let (g, attrs) = match self.tcx.hir().get(id) {
                 Node::Item(&hir::Item { attrs, span, kind: hir::ItemKind::Static(..), .. }) => {
-                    let sym_str = sym.as_str();
-                    if let Some(g) = self.get_declared_value(&sym_str) {
+                    if let Some(g) = self.get_declared_value(sym) {
                         if self.val_ty(g) != self.type_ptr_to(llty) {
                             span_bug!(span, "Conflicting types for static");
                         }
                     }
 
-                    let g = self.declare_global(&sym_str, llty);
+                    let g = self.declare_global(sym, llty);
 
                     if !self.tcx.is_reachable_non_generic(def_id) {
                         unsafe {

src/librustc_codegen_llvm/debuginfo/metadata.rs

@@ -2468,8 +2468,7 @@ pub fn create_global_var_metadata(cx: &CodegenCx<'ll, '_>, def_id: DefId, global
     let variable_type = Instance::mono(cx.tcx, def_id).monomorphic_ty(cx.tcx);
     let type_metadata = type_metadata(cx, variable_type, span);
     let var_name = tcx.item_name(def_id).as_str();
-    let linkage_name: &str =
-        &mangled_name_of_instance(cx, Instance::mono(tcx, def_id)).name.as_str();
+    let linkage_name = mangled_name_of_instance(cx, Instance::mono(tcx, def_id)).name;
     // When empty, linkage_name field is omitted,
     // which is what we want for no_mangle statics
     let linkage_name = if var_name == linkage_name { "" } else { linkage_name };

src/librustc_codegen_llvm/debuginfo/mod.rs

@@ -267,7 +267,7 @@ impl DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         let substs = instance.substs.truncate_to(self.tcx(), generics);
         let template_parameters = get_template_parameters(self, &generics, substs, &mut name);
 
-        let linkage_name: &str = &mangled_name_of_instance(self, instance).name.as_str();
+        let linkage_name = &mangled_name_of_instance(self, instance).name;
         // Omit the linkage_name if it is the same as subprogram name.
         let linkage_name = if &name == linkage_name { "" } else { linkage_name };
 

src/librustc_codegen_llvm/debuginfo/namespace.rs

@@ -12,7 +12,7 @@ use rustc_hir::definitions::DefPathData;
 pub fn mangled_name_of_instance<'a, 'tcx>(
     cx: &CodegenCx<'a, 'tcx>,
     instance: Instance<'tcx>,
-) -> ty::SymbolName {
+) -> ty::SymbolName<'tcx> {
     let tcx = cx.tcx;
     tcx.symbol_name(instance)
 }

src/librustc_codegen_llvm/intrinsic.rs

@@ -196,7 +196,7 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
                 // and/or monomorphization invalidates these assumptions.
                 let coverageinfo = tcx.coverageinfo(caller_instance.def_id());
                 let mangled_fn = tcx.symbol_name(caller_instance);
-                let (mangled_fn_name, _len_val) = self.const_str(mangled_fn.name);
+                let (mangled_fn_name, _len_val) = self.const_str(Symbol::intern(mangled_fn.name));
                 let hash = self.const_u64(coverageinfo.hash);
                 let num_counters = self.const_u32(coverageinfo.num_counters);
                 use coverage::count_code_region_args::*;

src/librustc_codegen_ssa/back/symbol_export.rs

@@ -16,7 +16,6 @@ use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
 use rustc_middle::ty::Instance;
 use rustc_middle::ty::{SymbolName, TyCtxt};
 use rustc_session::config::{CrateType, SanitizerSet};
-use rustc_span::symbol::sym;
 
 pub fn threshold(tcx: TyCtxt<'_>) -> SymbolExportLevel {
     crates_export_threshold(&tcx.sess.crate_types())
@@ -117,9 +116,9 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, cnum: CrateNum) -> DefIdMap<
                 // In general though we won't link right if these
                 // symbols are stripped, and LTO currently strips them.
                 match name {
-                    sym::rust_eh_personality
-                    | sym::rust_eh_register_frames
-                    | sym::rust_eh_unregister_frames =>
+                    "rust_eh_personality"
+                    | "rust_eh_register_frames"
+                    | "rust_eh_unregister_frames" =>
                         SymbolExportLevel::C,
                     _ => SymbolExportLevel::Rust,
                 }
@@ -177,15 +176,15 @@ fn exported_symbols_provider_local(
         .collect();
 
     if tcx.entry_fn(LOCAL_CRATE).is_some() {
-        let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new("main"));
+        let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, "main"));
 
         symbols.push((exported_symbol, SymbolExportLevel::C));
     }
 
     if tcx.allocator_kind().is_some() {
         for method in ALLOCATOR_METHODS {
             let symbol_name = format!("__rust_{}", method.name);
-            let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(&symbol_name));
+            let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
 
             symbols.push((exported_symbol, SymbolExportLevel::Rust));
         }
@@ -199,7 +198,7 @@ fn exported_symbols_provider_local(
             ["__llvm_profile_raw_version", "__llvm_profile_filename"];
 
         symbols.extend(PROFILER_WEAK_SYMBOLS.iter().map(|sym| {
-            let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(sym));
+            let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, sym));
             (exported_symbol, SymbolExportLevel::C)
         }));
     }
@@ -209,14 +208,14 @@ fn exported_symbols_provider_local(
         const MSAN_WEAK_SYMBOLS: [&str; 2] = ["__msan_track_origins", "__msan_keep_going"];
 
         symbols.extend(MSAN_WEAK_SYMBOLS.iter().map(|sym| {
-            let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(sym));
+            let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, sym));
             (exported_symbol, SymbolExportLevel::C)
         }));
     }
 
     if tcx.sess.crate_types().contains(&CrateType::Dylib) {
         let symbol_name = metadata_symbol_name(tcx);
-        let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(&symbol_name));
+        let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
 
         symbols.push((exported_symbol, SymbolExportLevel::Rust));
     }

src/librustc_codegen_ssa/mono_item.rs

@@ -64,7 +64,7 @@ impl<'a, 'tcx: 'a> MonoItemExt<'a, 'tcx> for MonoItem<'tcx> {
             cx.codegen_unit().name()
         );
 
-        let symbol_name = self.symbol_name(cx.tcx()).name.as_str();
+        let symbol_name = self.symbol_name(cx.tcx()).name;
 
         debug!("symbol {}", &symbol_name);
 

src/librustc_metadata/rmeta/encoder.rs

@@ -558,7 +558,7 @@ impl<'tcx> EncodeContext<'tcx> {
         // Encode exported symbols info. This is prefetched in `encode_metadata` so we encode
         // this late to give the prefetching as much time as possible to complete.
         i = self.position();
-        let exported_symbols = self.tcx.exported_symbols(LOCAL_CRATE);
+        let exported_symbols = tcx.exported_symbols(LOCAL_CRATE);
         let exported_symbols = self.encode_exported_symbols(&exported_symbols);
         let exported_symbols_bytes = self.position() - i;
 
@@ -622,7 +622,7 @@ impl<'tcx> EncodeContext<'tcx> {
 
         let total_bytes = self.position();
 
-        if self.tcx.sess.meta_stats() {
+        if tcx.sess.meta_stats() {
             let mut zero_bytes = 0;
             for e in self.opaque.data.iter() {
                 if *e == 0 {
@@ -1541,7 +1541,7 @@ impl EncodeContext<'tcx> {
     ) -> Lazy<[(ExportedSymbol<'tcx>, SymbolExportLevel)]> {
         // The metadata symbol name is special. It should not show up in
         // downstream crates.
-        let metadata_symbol_name = SymbolName::new(&metadata_symbol_name(self.tcx));
+        let metadata_symbol_name = SymbolName::new(self.tcx, &metadata_symbol_name(self.tcx));
 
         self.lazy(
             exported_symbols

src/librustc_middle/middle/exported_symbols.rs

@@ -26,13 +26,13 @@ pub enum ExportedSymbol<'tcx> {
     NonGeneric(DefId),
     Generic(DefId, SubstsRef<'tcx>),
     DropGlue(Ty<'tcx>),
-    NoDefId(ty::SymbolName),
+    NoDefId(ty::SymbolName<'tcx>),
 }
 
 impl<'tcx> ExportedSymbol<'tcx> {
     /// This is the symbol name of an instance if it is instantiated in the
     /// local crate.
-    pub fn symbol_name_for_local_instance(&self, tcx: TyCtxt<'tcx>) -> ty::SymbolName {
+    pub fn symbol_name_for_local_instance(&self, tcx: TyCtxt<'tcx>) -> ty::SymbolName<'tcx> {
         match *self {
             ExportedSymbol::NonGeneric(def_id) => tcx.symbol_name(ty::Instance::mono(tcx, def_id)),
             ExportedSymbol::Generic(def_id, substs) => {

src/librustc_middle/mir/mono.rs

@@ -68,13 +68,13 @@ impl<'tcx> MonoItem<'tcx> {
         }
     }
 
-    pub fn symbol_name(&self, tcx: TyCtxt<'tcx>) -> SymbolName {
+    pub fn symbol_name(&self, tcx: TyCtxt<'tcx>) -> SymbolName<'tcx> {
         match *self {
             MonoItem::Fn(instance) => tcx.symbol_name(instance),
             MonoItem::Static(def_id) => tcx.symbol_name(Instance::mono(tcx, def_id)),
             MonoItem::GlobalAsm(hir_id) => {
                 let def_id = tcx.hir().local_def_id(hir_id);
-                SymbolName { name: Symbol::intern(&format!("global_asm_{:?}", def_id)) }
+                SymbolName::new(tcx, &format!("global_asm_{:?}", def_id))
             }
         }
     }
@@ -335,9 +335,9 @@ impl<'tcx> CodegenUnit<'tcx> {
         // The codegen tests rely on items being process in the same order as
         // they appear in the file, so for local items, we sort by node_id first
         #[derive(PartialEq, Eq, PartialOrd, Ord)]
-        pub struct ItemSortKey(Option<HirId>, SymbolName);
+        pub struct ItemSortKey<'tcx>(Option<HirId>, SymbolName<'tcx>);
 
-        fn item_sort_key<'tcx>(tcx: TyCtxt<'tcx>, item: MonoItem<'tcx>) -> ItemSortKey {
+        fn item_sort_key<'tcx>(tcx: TyCtxt<'tcx>, item: MonoItem<'tcx>) -> ItemSortKey<'tcx> {
             ItemSortKey(
                 match item {
                     MonoItem::Fn(ref instance) => {

src/librustc_middle/query/mod.rs

@@ -691,7 +691,7 @@ rustc_queries! {
         /// The `symbol_name` query provides the symbol name for calling a
         /// given instance from the local crate. In particular, it will also
         /// look up the correct symbol name of instances from upstream crates.
-        query symbol_name(key: ty::Instance<'tcx>) -> ty::SymbolName {
+        query symbol_name(key: ty::Instance<'tcx>) -> ty::SymbolName<'tcx> {
             desc { "computing the symbol for `{}`", key }
             cache_on_disk_if { true }
         }

src/librustc_middle/ty/codec.rs

@@ -262,6 +262,14 @@ where
     Ok(decoder.tcx().adt_def(def_id))
 }
 
+#[inline]
+pub fn decode_symbol_name<D>(decoder: &mut D) -> Result<ty::SymbolName<'tcx>, D::Error>
+where
+    D: TyDecoder<'tcx>,
+{
+    Ok(ty::SymbolName::new(decoder.tcx(), &decoder.read_str()?))
+}
+
 #[inline]
 pub fn decode_existential_predicate_slice<D>(
     decoder: &mut D,
@@ -504,6 +512,13 @@ macro_rules! implement_ty_decoder {
                 }
             }
 
+            impl<'_x, $($typaram),*> SpecializedDecoder<ty::SymbolName<'_x>>
+            for $DecoderName<$($typaram),*> {
+                fn specialized_decode(&mut self) -> Result<ty::SymbolName<'_x>, Self::Error> {
+                    unsafe { transmute(decode_symbol_name(self)) }
+                }
+            }
+
             impl<'_x, '_y, $($typaram),*> SpecializedDecoder<&'_x ty::List<ty::ExistentialPredicate<'_y>>>
             for $DecoderName<$($typaram),*>
             where &'_x ty::List<ty::ExistentialPredicate<'_y>>: UseSpecializedDecodable {

src/librustc_middle/ty/mod.rs

@@ -50,6 +50,7 @@ use std::hash::{Hash, Hasher};
 use std::marker::PhantomData;
 use std::ops::Range;
 use std::ptr;
+use std::str;
 
 pub use self::sty::BoundRegion::*;
 pub use self::sty::InferTy::*;
@@ -2988,40 +2989,37 @@ pub struct CrateInherentImpls {
     pub inherent_impls: DefIdMap<Vec<DefId>>,
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
-pub struct SymbolName {
-    // FIXME: we don't rely on interning or equality here - better have
-    // this be a `&'tcx str`.
-    pub name: Symbol,
-}
-
-impl SymbolName {
-    pub fn new(name: &str) -> SymbolName {
-        SymbolName { name: Symbol::intern(name) }
-    }
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, HashStable)]
+pub struct SymbolName<'tcx> {
+    /// `&str` gives a consistent ordering, which ensures reproducible builds.
+    pub name: &'tcx str,
 }
 
-impl PartialOrd for SymbolName {
-    fn partial_cmp(&self, other: &SymbolName) -> Option<Ordering> {
-        self.name.as_str().partial_cmp(&other.name.as_str())
+impl<'tcx> SymbolName<'tcx> {
+    pub fn new(tcx: TyCtxt<'tcx>, name: &str) -> SymbolName<'tcx> {
+        SymbolName {
+            name: unsafe { str::from_utf8_unchecked(tcx.arena.alloc_slice(name.as_bytes())) },
+        }
     }
 }
 
-/// Ordering must use the chars to ensure reproducible builds.
-impl Ord for SymbolName {
-    fn cmp(&self, other: &SymbolName) -> Ordering {
-        self.name.as_str().cmp(&other.name.as_str())
+impl<'tcx> fmt::Display for SymbolName<'tcx> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.name, fmt)
     }
 }
 
-impl fmt::Display for SymbolName {
+impl<'tcx> fmt::Debug for SymbolName<'tcx> {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Display::fmt(&self.name, fmt)
     }
 }
 
-impl fmt::Debug for SymbolName {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Display::fmt(&self.name, fmt)
+impl<'tcx> rustc_serialize::UseSpecializedEncodable for SymbolName<'tcx> {
+    fn default_encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_str(self.name)
     }
 }
+
+// The decoding takes place in `decode_symbol_name()`.
+impl<'tcx> rustc_serialize::UseSpecializedDecodable for SymbolName<'tcx> {}

src/librustc_middle/ty/query/values.rs

@@ -1,7 +1,5 @@
 use crate::ty::{self, AdtSizedConstraint, Ty, TyCtxt, TyS};
 
-use rustc_span::symbol::Symbol;
-
 pub(super) trait Value<'tcx>: Sized {
     fn from_cycle_error(tcx: TyCtxt<'tcx>) -> Self;
 }
@@ -21,9 +19,15 @@ impl<'tcx> Value<'tcx> for &'_ TyS<'_> {
     }
 }
 
-impl<'tcx> Value<'tcx> for ty::SymbolName {
-    fn from_cycle_error(_: TyCtxt<'tcx>) -> Self {
-        ty::SymbolName { name: Symbol::intern("<error>") }
+impl<'tcx> Value<'tcx> for ty::SymbolName<'_> {
+    fn from_cycle_error(tcx: TyCtxt<'tcx>) -> Self {
+        // SAFETY: This is never called when `Self` is not `SymbolName<'tcx>`.
+        // FIXME: Represent the above fact in the trait system somehow.
+        unsafe {
+            std::mem::transmute::<ty::SymbolName<'tcx>, ty::SymbolName<'_>>(ty::SymbolName::new(
+                tcx, "<error>",
+            ))
+        }
     }
 }
 

src/librustc_mir/monomorphize/partitioning.rs

@@ -817,7 +817,7 @@ where
             debug!("CodegenUnit {} estimated size {} :", cgu.name(), cgu.size_estimate());
 
             for (mono_item, linkage) in cgu.items() {
-                let symbol_name = mono_item.symbol_name(tcx).name.as_str();
+                let symbol_name = mono_item.symbol_name(tcx).name;
                 let symbol_hash_start = symbol_name.rfind('h');
                 let symbol_hash =
                     symbol_hash_start.map(|i| &symbol_name[i..]).unwrap_or("<no hash>");

src/librustc_span/symbol.rs

@@ -856,8 +856,6 @@ symbols! {
         rustc_unsafe_specialization_marker,
         rustc_variance,
         rust_eh_personality,
-        rust_eh_register_frames,
-        rust_eh_unregister_frames,
         rustfmt,
         rust_oom,
         rvalue_static_promotion,