diff --git a/lib/cretonne/src/partition_slice.rs b/lib/cretonne/src/partition_slice.rs
new file mode 100644
index 0000000000..9626b5fd37
--- /dev/null
+++ b/lib/cretonne/src/partition_slice.rs
@@ -0,0 +1,75 @@
+//! Rearrange the elements in a slice according to a predicate.
+
+/// Rearrange the elements of the mutable slice `s` such that elements where `p(t)` is true precede
+/// the elements where `p(t)` is false.
+///
+/// The order of elements is not preserved, unless the slice is already partitioned.
+///
+/// Returns the number of elements where `p(t)` is true.
+pub fn partition_slice<'a, T: 'a, F>(s: &'a mut [T], mut p: F) -> usize
+    where F: FnMut(&T) -> bool
+{
+    // Count the length of the prefix where `p` returns true.
+    let mut count = match s.iter().position(|t| !p(t)) {
+        Some(t) => t,
+        None => return s.len(),
+    };
+
+    // Swap remaining `true` elements into place.
+    //
+    // This actually preserves the order of the `true` elements, but the `false` elements get
+    // shuffled.
+    for i in count + 1..s.len() {
+        if p(&s[i]) {
+            s.swap(count, i);
+            count += 1;
+        }
+    }
+
+    count
+}
+
+#[cfg(test)]
+mod tests {
+    use super::partition_slice;
+
+    fn check(x: &[u32], want: &[u32]) {
+        assert_eq!(x.len(), want.len());
+        let want_count = want.iter().cloned().filter(|&x| x % 10 == 0).count();
+        let mut v = Vec::new();
+        v.extend(x.iter().cloned());
+        let count = partition_slice(&mut v[..], |&x| x % 10 == 0);
+        assert_eq!(v, want);
+        assert_eq!(count, want_count);
+    }
+
+    #[test]
+    fn empty() {
+        check(&[], &[]);
+    }
+
+    #[test]
+    fn singles() {
+        check(&[0], &[0]);
+        check(&[1], &[1]);
+        check(&[10], &[10]);
+    }
+
+    #[test]
+    fn doubles() {
+        check(&[0, 0], &[0, 0]);
+        check(&[0, 5], &[0, 5]);
+        check(&[5, 0], &[0, 5]);
+        check(&[5, 4], &[5, 4]);
+    }
+
+    #[test]
+    fn longer() {
+        check(&[1, 2, 3], &[1, 2, 3]);
+        check(&[1, 2, 10], &[10, 2, 1]); // Note: 2, 1 order not required.
+        check(&[1, 10, 2], &[10, 1, 2]); // Note: 1, 2 order not required.
+        check(&[1, 20, 10], &[20, 10, 1]);
+        check(&[1, 20, 3, 10], &[20, 10, 3, 1]);
+        check(&[20, 3, 10, 1], &[20, 10, 3, 1]);
+    }
+}