index: introduce and use FiniteBitSet

This commit introduces a `FiniteBitSet` type which replaces the manual
bit manipulation which was being performed in polymorphization.

Signed-off-by: David Wood <david@davidtw.co>

src/librustc_data_structures/stable_hasher.rs

@@ -469,6 +469,15 @@ impl<R: vec::Idx, C: vec::Idx, CTX> HashStable<CTX> for bit_set::BitMatrix<R, C>
     }
 }
 
+impl<T, CTX> HashStable<CTX> for bit_set::FiniteBitSet<T>
+where
+    T: HashStable<CTX> + bit_set::FiniteBitSetTy,
+{
+    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
+        self.0.hash_stable(hcx, hasher);
+    }
+}
+
 impl_stable_hash_via_hash!(::std::path::Path);
 impl_stable_hash_via_hash!(::std::path::PathBuf);
 

src/librustc_index/bit_set.rs

@@ -4,6 +4,7 @@ use std::fmt;
 use std::iter;
 use std::marker::PhantomData;
 use std::mem;
+use std::ops::{BitAnd, BitAndAssign, BitOrAssign, Not, Range, Shl};
 use std::slice;
 
 #[cfg(test)]
@@ -1001,3 +1002,137 @@ fn word_index_and_mask<T: Idx>(elem: T) -> (usize, Word) {
     let mask = 1 << (elem % WORD_BITS);
     (word_index, mask)
 }
+
+/// Integral type used to represent the bit set.
+pub trait FiniteBitSetTy:
+    BitAnd<Output = Self>
+    + BitAndAssign
+    + BitOrAssign
+    + Clone
+    + Copy
+    + Shl
+    + Not<Output = Self>
+    + PartialEq
+    + Sized
+{
+    /// Size of the domain representable by this type, e.g. 64 for `u64`.
+    const DOMAIN_SIZE: u32;
+
+    /// Value which represents the `FiniteBitSet` having every bit set.
+    const FILLED: Self;
+    /// Value which represents the `FiniteBitSet` having no bits set.
+    const EMPTY: Self;
+
+    /// Value for one as the integral type.
+    const ONE: Self;
+    /// Value for zero as the integral type.
+    const ZERO: Self;
+
+    /// Perform a checked left shift on the integral type.
+    fn checked_shl(self, rhs: u32) -> Option<Self>;
+    /// Perform a checked right shift on the integral type.
+    fn checked_shr(self, rhs: u32) -> Option<Self>;
+}
+
+impl FiniteBitSetTy for u64 {
+    const DOMAIN_SIZE: u32 = 64;
+
+    const FILLED: Self = Self::MAX;
+    const EMPTY: Self = Self::MIN;
+
+    const ONE: Self = 1u64;
+    const ZERO: Self = 0u64;
+
+    fn checked_shl(self, rhs: u32) -> Option<Self> {
+        self.checked_shl(rhs)
+    }
+
+    fn checked_shr(self, rhs: u32) -> Option<Self> {
+        self.checked_shr(rhs)
+    }
+}
+
+impl std::fmt::Debug for FiniteBitSet<u64> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:064b}", self.0)
+    }
+}
+
+impl FiniteBitSetTy for u128 {
+    const DOMAIN_SIZE: u32 = 128;
+
+    const FILLED: Self = Self::MAX;
+    const EMPTY: Self = Self::MIN;
+
+    const ONE: Self = 1u128;
+    const ZERO: Self = 0u128;
+
+    fn checked_shl(self, rhs: u32) -> Option<Self> {
+        self.checked_shl(rhs)
+    }
+
+    fn checked_shr(self, rhs: u32) -> Option<Self> {
+        self.checked_shr(rhs)
+    }
+}
+
+impl std::fmt::Debug for FiniteBitSet<u128> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:0128b}", self.0)
+    }
+}
+
+/// A fixed-sized bitset type represented by an integer type. Indices outwith than the range
+/// representable by `T` are considered set.
+#[derive(Copy, Clone, Eq, PartialEq, RustcDecodable, RustcEncodable)]
+pub struct FiniteBitSet<T: FiniteBitSetTy>(pub T);
+
+impl<T: FiniteBitSetTy> FiniteBitSet<T> {
+    /// Creates a new, empty bitset.
+    pub fn new_empty() -> Self {
+        Self(T::EMPTY)
+    }
+
+    /// Sets the `index`th bit.
+    pub fn set(&mut self, index: u32) {
+        self.0 |= T::ONE.checked_shl(index).unwrap_or(T::ZERO);
+    }
+
+    /// Unsets the `index`th bit.
+    pub fn clear(&mut self, index: u32) {
+        self.0 &= !T::ONE.checked_shl(index).unwrap_or(T::ZERO);
+    }
+
+    /// Sets the `i`th to `j`th bits.
+    pub fn set_range(&mut self, range: Range<u32>) {
+        let bits = T::FILLED
+            .checked_shl(range.end - range.start)
+            .unwrap_or(T::ZERO)
+            .not()
+            .checked_shl(range.start)
+            .unwrap_or(T::ZERO);
+        self.0 |= bits;
+    }
+
+    /// Is the set empty?
+    pub fn is_empty(&self) -> bool {
+        self.0 == T::EMPTY
+    }
+
+    /// Returns the domain size of the bitset.
+    pub fn within_domain(&self, index: u32) -> bool {
+        index < T::DOMAIN_SIZE
+    }
+
+    /// Returns if the `index`th bit is set.
+    pub fn contains(&self, index: u32) -> Option<bool> {
+        self.within_domain(index)
+            .then(|| ((self.0.checked_shr(index).unwrap_or(T::ONE)) & T::ONE) == T::ONE)
+    }
+}
+
+impl<T: FiniteBitSetTy> Default for FiniteBitSet<T> {
+    fn default() -> Self {
+        Self::new_empty()
+    }
+}

src/librustc_index/lib.rs

@@ -1,4 +1,5 @@
 #![feature(allow_internal_unstable)]
+#![feature(bool_to_option)]
 #![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(extend_one)]

src/librustc_metadata/rmeta/decoder.rs

@@ -1132,7 +1132,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .decode((self, tcx))
     }
 
-    fn get_unused_generic_params(&self, id: DefIndex) -> u64 {
+    fn get_unused_generic_params(&self, id: DefIndex) -> FiniteBitSet<u64> {
         self.root
             .tables
             .unused_generic_params

src/librustc_metadata/rmeta/mod.rs

@@ -9,7 +9,7 @@ use rustc_hir as hir;
 use rustc_hir::def::CtorKind;
 use rustc_hir::def_id::{DefId, DefIndex};
 use rustc_hir::lang_items;
-use rustc_index::vec::IndexVec;
+use rustc_index::{bit_set::FiniteBitSet, vec::IndexVec};
 use rustc_middle::hir::exports::Export;
 use rustc_middle::middle::cstore::{DepKind, ForeignModule, LinkagePreference, NativeLib};
 use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportLevel};
@@ -277,7 +277,7 @@ define_tables! {
     super_predicates: Table<DefIndex, Lazy!(ty::GenericPredicates<'tcx>)>,
     mir: Table<DefIndex, Lazy!(mir::Body<'tcx>)>,
     promoted_mir: Table<DefIndex, Lazy!(IndexVec<mir::Promoted, mir::Body<'tcx>>)>,
-    unused_generic_params: Table<DefIndex, Lazy<u64>>,
+    unused_generic_params: Table<DefIndex, Lazy<FiniteBitSet<u64>>>,
 }
 
 #[derive(Copy, Clone, RustcEncodable, RustcDecodable)]

src/librustc_middle/query/mod.rs

@@ -1309,7 +1309,7 @@ rustc_queries! {
         query codegen_unit(_: Symbol) -> &'tcx CodegenUnit<'tcx> {
             desc { "codegen_unit" }
         }
-        query unused_generic_params(key: DefId) -> u64 {
+        query unused_generic_params(key: DefId) -> FiniteBitSet<u64> {
             cache_on_disk_if { key.is_local() }
             desc {
                 |tcx| "determining which generic parameters are unused by `{}`",

src/librustc_middle/ty/instance.rs

@@ -474,20 +474,20 @@ impl<'tcx> Instance<'tcx> {
         }
 
         if let InstanceDef::Item(def) = self.def {
-            let results = tcx.unused_generic_params(def.did);
+            let unused = tcx.unused_generic_params(def.did);
 
-            if results == 0 {
+            if unused.is_empty() {
                 // Exit early if every parameter was used.
                 return self;
             }
 
-            debug!("polymorphize: results={:064b}", results);
+            debug!("polymorphize: unused={:?}", unused);
             let polymorphized_substs =
                 InternalSubsts::for_item(tcx, def.did, |param, _| match param.kind {
                 // If parameter is a const or type parameter..
                 ty::GenericParamDefKind::Const | ty::GenericParamDefKind::Type { .. } if
                     // ..and is within range and unused..
-                    param.index < 64 && ((results >> param.index) & 1) == 1 =>
+                    unused.contains(param.index).unwrap_or(false) =>
                         // ..then use the identity for this parameter.
                         tcx.mk_param_from_def(param),
                 // Otherwise, use the parameter as before.

src/librustc_middle/ty/query/mod.rs

@@ -44,7 +44,7 @@ use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, DefIdSet, LocalDefId};
 use rustc_hir::lang_items::{LangItem, LanguageItems};
 use rustc_hir::{Crate, HirIdSet, ItemLocalId, TraitCandidate};
-use rustc_index::vec::IndexVec;
+use rustc_index::{bit_set::FiniteBitSet, vec::IndexVec};
 use rustc_session::config::{EntryFnType, OptLevel, OutputFilenames, SymbolManglingVersion};
 use rustc_session::utils::NativeLibKind;
 use rustc_session::CrateDisambiguator;