Rollup merge of #47656 - ishitatsuyuki:patch-1, r=nikomatsakis

[perf] Use std based dedup in projection

Unstable sort was added recently, and the code that is being modified is 3 years old. As quicksort doesn't allocate it will likely perform as well as, or better than linear search.

I didn't benchmark. Have a perf run.

src/librustc/traits/project.rs

@@ -101,7 +101,7 @@ pub struct MismatchedProjectionTypes<'tcx> {
     pub err: ty::error::TypeError<'tcx>
 }
 
-#[derive(PartialEq, Eq, Debug)]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Debug)]
 enum ProjectionTyCandidate<'tcx> {
     // from a where-clause in the env or object type
     ParamEnv(ty::PolyProjectionPredicate<'tcx>),
@@ -838,21 +838,12 @@ fn project_type<'cx, 'gcx, 'tcx>(
     // Drop duplicates.
     //
     // Note: `candidates.vec` seems to be on the critical path of the
-    // compiler. Replacing it with an hash set was also tried, which would
-    // render the following dedup unnecessary. It led to cleaner code but
-    // prolonged compiling time of `librustc` from 5m30s to 6m in one test, or
-    // ~9% performance lost.
-    if candidates.vec.len() > 1 {
-        let mut i = 0;
-        while i < candidates.vec.len() {
-            let has_dup = (0..i).any(|j| candidates.vec[i] == candidates.vec[j]);
-            if has_dup {
-                candidates.vec.swap_remove(i);
-            } else {
-                i += 1;
-            }
-        }
-    }
+    // compiler. Replacing it with an HashSet was also tried, which would
+    // render the following dedup unnecessary. The original comment indicated
+    // that it was 9% slower, but that data is now obsolete and a new
+    // benchmark should be performed.
+    candidates.vec.sort_unstable();
+    candidates.vec.dedup();
 
     // Prefer where-clauses. As in select, if there are multiple
     // candidates, we prefer where-clause candidates over impls.  This

src/librustc/ty/mod.rs

@@ -41,6 +41,7 @@ use serialize::{self, Encodable, Encoder};
 use std::cell::RefCell;
 use std::collections::BTreeMap;
 use std::cmp;
+use std::cmp::Ordering;
 use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::iter::FromIterator;
@@ -499,6 +500,20 @@ impl<'tcx> Hash for TyS<'tcx> {
     }
 }
 
+impl<'tcx> Ord for TyS<'tcx> {
+    #[inline]
+    fn cmp(&self, other: &TyS<'tcx>) -> Ordering {
+        // (self as *const _).cmp(other as *const _)
+        (self as *const TyS<'tcx>).cmp(&(other as *const TyS<'tcx>))
+    }
+}
+impl<'tcx> PartialOrd for TyS<'tcx> {
+    #[inline]
+    fn partial_cmp(&self, other: &TyS<'tcx>) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
 impl<'tcx> TyS<'tcx> {
     pub fn is_primitive_ty(&self) -> bool {
         match self.sty {
@@ -568,6 +583,19 @@ impl<T> PartialEq for Slice<T> {
 }
 impl<T> Eq for Slice<T> {}
 
+impl<T> Ord for Slice<T> {
+    #[inline]
+    fn cmp(&self, other: &Slice<T>) -> Ordering {
+        (&self.0 as *const [T]).cmp(&(&other.0 as *const [T]))
+    }
+}
+impl<T> PartialOrd for Slice<T> {
+    #[inline]
+    fn partial_cmp(&self, other: &Slice<T>) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
 impl<T> Hash for Slice<T> {
     fn hash<H: Hasher>(&self, s: &mut H) {
         (self.as_ptr(), self.len()).hash(s)
@@ -1103,7 +1131,7 @@ pub type PolySubtypePredicate<'tcx> = ty::Binder<SubtypePredicate<'tcx>>;
 /// equality between arbitrary types. Processing an instance of
 /// Form #2 eventually yields one of these `ProjectionPredicate`
 /// instances to normalize the LHS.
-#[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, RustcEncodable, RustcDecodable)]
 pub struct ProjectionPredicate<'tcx> {
     pub projection_ty: ProjectionTy<'tcx>,
     pub ty: Ty<'tcx>,

src/librustc/ty/sty.rs

@@ -638,7 +638,7 @@ impl<'tcx> PolyExistentialTraitRef<'tcx> {
 /// erase, or otherwise "discharge" these bound regions, we change the
 /// type from `Binder<T>` to just `T` (see
 /// e.g. `liberate_late_bound_regions`).
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
 pub struct Binder<T>(pub T);
 
 impl<T> Binder<T> {
@@ -738,7 +738,7 @@ impl<T> Binder<T> {
 
 /// Represents the projection of an associated type. In explicit UFCS
 /// form this would be written `<T as Trait<..>>::N`.
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
 pub struct ProjectionTy<'tcx> {
     /// The parameters of the associated item.
     pub substs: &'tcx Substs<'tcx>,

src/librustc/ty/subst.rs

@@ -29,7 +29,7 @@ use std::mem;
 /// To reduce memory usage, a `Kind` is a interned pointer,
 /// with the lowest 2 bits being reserved for a tag to
 /// indicate the type (`Ty` or `Region`) it points to.
-#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct Kind<'tcx> {
     ptr: NonZero<usize>,
     marker: PhantomData<(Ty<'tcx>, ty::Region<'tcx>)>