Optimize empty provenance range checks.

Currently it gets the pointers in the range and checks if the result is
empty, but it can be done faster if you combine those two steps.

1 files changed, 33 insertions, 0 deletions

diff --git a/compiler/rustc_data_structures/src/sorted_map.rs b/compiler/rustc_data_structures/src/sorted_map.rs
index 066ea03b4ac..a01a420dfbd 100644
--- a/compiler/rustc_data_structures/src/sorted_map.rs
+++ b/compiler/rustc_data_structures/src/sorted_map.rs
@@ -1,4 +1,5 @@
 use std::borrow::Borrow;
+use std::cmp::Ordering;
 use std::fmt::Debug;
 use std::mem;
 use std::ops::{Bound, Index, IndexMut, RangeBounds};
@@ -156,6 +157,38 @@ impl<K: Ord, V> SortedMap<K, V> {
         &self.data[start..end]
     }
 
+    /// `sm.range_is_empty(r)` == `sm.range(r).is_empty()`, but is faster.
+    #[inline]
+    pub fn range_is_empty<R>(&self, range: R) -> bool
+    where
+        R: RangeBounds<K>,
+    {
+        // `range` must (via `range_slice_indices`) search for the start and
+        // end separately. But here we can do a single binary search for the
+        // entire range. If a single `x` matching `range` is found then the
+        // range is *not* empty.
+        self.data
+            .binary_search_by(|(x, _)| {
+                // Is `x` below `range`?
+                match range.start_bound() {
+                    Bound::Included(start) if x < start => return Ordering::Less,
+                    Bound::Excluded(start) if x <= start => return Ordering::Less,
+                    _ => {}
+                };
+
+                // Is `x` above `range`?
+                match range.end_bound() {
+                    Bound::Included(end) if x > end => return Ordering::Greater,
+                    Bound::Excluded(end) if x >= end => return Ordering::Greater,
+                    _ => {}
+                };
+
+                // `x` must be within `range`.
+                Ordering::Equal
+            })
+            .is_err()
+    }
+
     #[inline]
     pub fn remove_range<R>(&mut self, range: R)
     where