diff --git a/src/eval.rs b/src/eval.rs
index fd5404a981d2..616e11a51561 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -1,3 +1,5 @@
+//! Main evaluator loop and setting up the initial stack frame.
+
 use rand::rngs::StdRng;
 use rand::SeedableRng;
 
diff --git a/src/machine.rs b/src/machine.rs
index 8ef5410f395f..9785d6a45560 100644
--- a/src/machine.rs
+++ b/src/machine.rs
@@ -1,3 +1,6 @@
+//! Global machine state as well as implementation of the interpreter engine
+//! `Machine` trait.
+
 use std::rc::Rc;
 use std::borrow::Cow;
 use std::collections::HashMap;
diff --git a/src/range_map.rs b/src/range_map.rs
index 16e7e2724179..f2cbd89f64da 100644
--- a/src/range_map.rs
+++ b/src/range_map.rs
@@ -1,5 +1,3 @@
-#![allow(unused)]
-
 //! Implements a map from integer indices to data.
 //! Rather than storing data for every index, internally, this maps entire ranges to the data.
 //! To this end, the APIs all work on ranges, not on individual integers. Ranges are split as
@@ -8,7 +6,6 @@
 //! via the iteration APIs.
 
 use std::ops;
-use std::num::NonZeroU64;
 
 use rustc::ty::layout::Size;
 
@@ -158,7 +155,7 @@ impl<T> RangeMap<T> {
                 let mut end_idx = first_idx; // when the loop is done, this is the first excluded element.
                 loop {
                     // Compute if `end` is the last element we need to look at.
-                    let done = (self.v[end_idx].range.end >= offset+len);
+                    let done = self.v[end_idx].range.end >= offset+len;
                     // We definitely need to include `end`, so move the index.
                     end_idx += 1;
                     debug_assert!(done || end_idx < self.v.len(), "iter_mut: end-offset {} is out-of-bounds", offset+len);
diff --git a/src/stacked_borrows.rs b/src/stacked_borrows.rs
index 524ad2b47af0..6e5bbf50941b 100644
--- a/src/stacked_borrows.rs
+++ b/src/stacked_borrows.rs
@@ -1,3 +1,6 @@
+//! Implements "Stacked Borrows".  See <https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md>
+//! for further information.
+
 use std::cell::RefCell;
 use std::collections::{HashMap, HashSet};
 use std::rc::Rc;
diff --git a/src/tls.rs b/src/tls.rs
index ddc301447c7e..73c778f66d25 100644
--- a/src/tls.rs
+++ b/src/tls.rs
@@ -1,3 +1,5 @@
+//! Implement thread-local storage.
+
 use std::collections::BTreeMap;
 
 use rustc_target::abi::LayoutOf;