Rollup merge of #87583 - tmiasko:compression-cache, r=wesleywiser

Refactor compression cache in v0 symbol mangler

* Remove redundant option around compression caches (they are always present).
* Flatten compression caches into symbol mangler to avoid dynamic memory allocation.
* Implement printer for `&mut SymbolMangler` instead of `SymbolMangler` to avoid passing now slightly larger symbol mangler by value.

Author: JohnTitor

compiler/rustc_symbol_mangling/src/v0.rs

@@ -23,15 +23,12 @@ pub(super) fn mangle(
     let substs = tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), instance.substs);
 
     let prefix = "_R";
-    let mut cx = SymbolMangler {
+    let mut cx = &mut SymbolMangler {
         tcx,
-        compress: Some(Box::new(CompressionCaches {
-            start_offset: prefix.len(),
-
-            paths: FxHashMap::default(),
-            types: FxHashMap::default(),
-            consts: FxHashMap::default(),
-        })),
+        start_offset: prefix.len(),
+        paths: FxHashMap::default(),
+        types: FxHashMap::default(),
+        consts: FxHashMap::default(),
         binders: vec![],
         out: String::from(prefix),
     };
@@ -52,17 +49,7 @@ pub(super) fn mangle(
     if let Some(instantiating_crate) = instantiating_crate {
         cx = cx.print_def_path(instantiating_crate.as_def_id(), &[]).unwrap();
     }
-    cx.out
-}
-
-struct CompressionCaches<'tcx> {
-    // The length of the prefix in `out` (e.g. 2 for `_R`).
-    start_offset: usize,
-
-    // The values are start positions in `out`, in bytes.
-    paths: FxHashMap<(DefId, &'tcx [GenericArg<'tcx>]), usize>,
-    types: FxHashMap<Ty<'tcx>, usize>,
-    consts: FxHashMap<&'tcx ty::Const<'tcx>, usize>,
+    std::mem::take(&mut cx.out)
 }
 
 struct BinderLevel {
@@ -81,9 +68,15 @@ struct BinderLevel {
 
 struct SymbolMangler<'tcx> {
     tcx: TyCtxt<'tcx>,
-    compress: Option<Box<CompressionCaches<'tcx>>>,
     binders: Vec<BinderLevel>,
     out: String,
+
+    /// The length of the prefix in `out` (e.g. 2 for `_R`).
+    start_offset: usize,
+    /// The values are start positions in `out`, in bytes.
+    paths: FxHashMap<(DefId, &'tcx [GenericArg<'tcx>]), usize>,
+    types: FxHashMap<Ty<'tcx>, usize>,
+    consts: FxHashMap<&'tcx ty::Const<'tcx>, usize>,
 }
 
 impl SymbolMangler<'tcx> {
@@ -160,13 +153,13 @@ impl SymbolMangler<'tcx> {
         self.push(ident);
     }
 
-    fn path_append_ns(
-        mut self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, !>,
+    fn path_append_ns<'a>(
+        mut self: &'a mut Self,
+        print_prefix: impl FnOnce(&'a mut Self) -> Result<&'a mut Self, !>,
         ns: char,
         disambiguator: u64,
         name: &str,
-    ) -> Result<Self, !> {
+    ) -> Result<&'a mut Self, !> {
         self.push("N");
         self.out.push(ns);
         self = print_prefix(self)?;
@@ -175,17 +168,17 @@ impl SymbolMangler<'tcx> {
         Ok(self)
     }
 
-    fn print_backref(mut self, i: usize) -> Result<Self, !> {
+    fn print_backref(&mut self, i: usize) -> Result<&mut Self, !> {
         self.push("B");
-        self.push_integer_62((i - self.compress.as_ref().unwrap().start_offset) as u64);
+        self.push_integer_62((i - self.start_offset) as u64);
         Ok(self)
     }
 
-    fn in_binder<T>(
-        mut self,
+    fn in_binder<'a, T>(
+        mut self: &'a mut Self,
         value: &ty::Binder<'tcx, T>,
-        print_value: impl FnOnce(Self, &T) -> Result<Self, !>,
-    ) -> Result<Self, !>
+        print_value: impl FnOnce(&'a mut Self, &T) -> Result<&'a mut Self, !>,
+    ) -> Result<&'a mut Self, !>
     where
         T: TypeFoldable<'tcx>,
     {
@@ -218,7 +211,7 @@ impl SymbolMangler<'tcx> {
     }
 }
 
-impl Printer<'tcx> for SymbolMangler<'tcx> {
+impl Printer<'tcx> for &mut SymbolMangler<'tcx> {
     type Error = !;
 
     type Path = Self;
@@ -236,7 +229,7 @@ impl Printer<'tcx> for SymbolMangler<'tcx> {
         def_id: DefId,
         substs: &'tcx [GenericArg<'tcx>],
     ) -> Result<Self::Path, Self::Error> {
-        if let Some(&i) = self.compress.as_ref().and_then(|c| c.paths.get(&(def_id, substs))) {
+        if let Some(&i) = self.paths.get(&(def_id, substs)) {
             return self.print_backref(i);
         }
         let start = self.out.len();
@@ -246,9 +239,7 @@ impl Printer<'tcx> for SymbolMangler<'tcx> {
         // Only cache paths that do not refer to an enclosing
         // binder (which would change depending on context).
         if !substs.iter().any(|k| k.has_escaping_bound_vars()) {
-            if let Some(c) = &mut self.compress {
-                c.paths.insert((def_id, substs), start);
-            }
+            self.paths.insert((def_id, substs), start);
         }
         Ok(self)
     }
@@ -312,7 +303,7 @@ impl Printer<'tcx> for SymbolMangler<'tcx> {
         Ok(self)
     }
 
-    fn print_region(mut self, region: ty::Region<'_>) -> Result<Self::Region, Self::Error> {
+    fn print_region(self, region: ty::Region<'_>) -> Result<Self::Region, Self::Error> {
         let i = match *region {
             // Erased lifetimes use the index 0, for a
             // shorter mangling of `L_`.
@@ -367,7 +358,7 @@ impl Printer<'tcx> for SymbolMangler<'tcx> {
             return Ok(self);
         }
 
-        if let Some(&i) = self.compress.as_ref().and_then(|c| c.types.get(&ty)) {
+        if let Some(&i) = self.types.get(&ty) {
             return self.print_backref(i);
         }
         let start = self.out.len();
@@ -476,9 +467,7 @@ impl Printer<'tcx> for SymbolMangler<'tcx> {
         // Only cache types that do not refer to an enclosing
         // binder (which would change depending on context).
         if !ty.has_escaping_bound_vars() {
-            if let Some(c) = &mut self.compress {
-                c.types.insert(ty, start);
-            }
+            self.types.insert(ty, start);
         }
         Ok(self)
     }
@@ -545,7 +534,7 @@ impl Printer<'tcx> for SymbolMangler<'tcx> {
     }
 
     fn print_const(mut self, ct: &'tcx ty::Const<'tcx>) -> Result<Self::Const, Self::Error> {
-        if let Some(&i) = self.compress.as_ref().and_then(|c| c.consts.get(&ct)) {
+        if let Some(&i) = self.consts.get(&ct) {
             return self.print_backref(i);
         }
         let start = self.out.len();
@@ -583,14 +572,12 @@ impl Printer<'tcx> for SymbolMangler<'tcx> {
         // Only cache consts that do not refer to an enclosing
         // binder (which would change depending on context).
         if !ct.has_escaping_bound_vars() {
-            if let Some(c) = &mut self.compress {
-                c.consts.insert(ct, start);
-            }
+            self.consts.insert(ct, start);
         }
         Ok(self)
     }
 
-    fn path_crate(mut self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
+    fn path_crate(self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
         self.push("C");
         let stable_crate_id = self.tcx.def_path_hash(cnum.as_def_id()).stable_crate_id();
         self.push_disambiguator(stable_crate_id.to_u64());