diff --git a/lib/codegen/src/bforest/map.rs b/lib/codegen/src/bforest/map.rs
index b6a62ef419..7cfa824a43 100644
--- a/lib/codegen/src/bforest/map.rs
+++ b/lib/codegen/src/bforest/map.rs
@@ -3,6 +3,10 @@
 use super::{Comparator, Forest, Node, NodeData, NodePool, Path, INNER_SIZE};
 use packed_option::PackedOption;
 use std::marker::PhantomData;
+#[cfg(test)]
+use std::fmt;
+#[cfg(test)]
+use std::string::String;
 
 /// Tag type defining forest types for a map.
 struct MapTypes<K, V, C>(PhantomData<(K, V, C)>);
@@ -207,14 +211,14 @@ where
 #[cfg(test)]
 impl<K, V, C> Map<K, V, C>
 where
-    K: Copy + ::std::fmt::Display,
+    K: Copy + fmt::Display,
     V: Copy,
     C: Comparator<K>,
 {
     /// Verify consistency.
     fn verify(&self, forest: &MapForest<K, V, C>, comp: &C)
     where
-        NodeData<MapTypes<K, V, C>>: ::std::fmt::Display,
+        NodeData<MapTypes<K, V, C>>: fmt::Display,
     {
         if let Some(root) = self.root.expand() {
             forest.nodes.verify_tree(root, comp);
@@ -222,7 +226,7 @@ where
     }
 
     /// Get a text version of the path to `key`.
-    fn tpath(&self, key: K, forest: &MapForest<K, V, C>, comp: &C) -> ::std::string::String {
+    fn tpath(&self, key: K, forest: &MapForest<K, V, C>, comp: &C) -> String {
         use std::string::ToString;
         match self.root.expand() {
             None => "map(empty)".to_string(),
@@ -406,8 +410,8 @@ where
 #[cfg(test)]
 impl<'a, K, V, C> MapCursor<'a, K, V, C>
 where
-    K: Copy + ::std::fmt::Display,
-    V: Copy + ::std::fmt::Display,
+    K: Copy + fmt::Display,
+    V: Copy + fmt::Display,
     C: Comparator<K>,
 {
     fn verify(&self) {
@@ -416,7 +420,7 @@ where
     }
 
     /// Get a text version of the path to the current position.
-    fn tpath(&self) -> ::std::string::String {
+    fn tpath(&self) -> String {
         use std::string::ToString;
         self.path.to_string()
     }
diff --git a/lib/codegen/src/bforest/pool.rs b/lib/codegen/src/bforest/pool.rs
index eed9402c84..d543991312 100644
--- a/lib/codegen/src/bforest/pool.rs
+++ b/lib/codegen/src/bforest/pool.rs
@@ -3,6 +3,8 @@
 use super::{Forest, Node, NodeData};
 use entity::PrimaryMap;
 use std::ops::{Index, IndexMut};
+#[cfg(test)]
+use std::fmt;
 
 /// A pool of nodes, including a free list.
 pub(super) struct NodePool<F: Forest> {
@@ -74,8 +76,8 @@ impl<F: Forest> NodePool<F> {
     /// Verify the consistency of the tree rooted at `node`.
     pub fn verify_tree(&self, node: Node, comp: &F::Comparator)
     where
-        NodeData<F>: ::std::fmt::Display,
-        F::Key: ::std::fmt::Display,
+        NodeData<F>: fmt::Display,
+        F::Key: fmt::Display,
     {
         use super::Comparator;
         use entity::SparseSet;
diff --git a/lib/codegen/src/bforest/set.rs b/lib/codegen/src/bforest/set.rs
index 3c479dd876..667cd133e2 100644
--- a/lib/codegen/src/bforest/set.rs
+++ b/lib/codegen/src/bforest/set.rs
@@ -3,6 +3,10 @@
 use super::{Comparator, Forest, Node, NodeData, NodePool, Path, SetValue, INNER_SIZE};
 use packed_option::PackedOption;
 use std::marker::PhantomData;
+#[cfg(test)]
+use std::fmt;
+#[cfg(test)]
+use std::string::String;
 
 /// Tag type defining forest types for a set.
 struct SetTypes<K, C>(PhantomData<(K, C)>);
@@ -305,7 +309,7 @@ where
 #[cfg(test)]
 impl<'a, K, C> SetCursor<'a, K, C>
 where
-    K: Copy + ::std::fmt::Display,
+    K: Copy + fmt::Display,
     C: Comparator<K>,
 {
     fn verify(&self) {
@@ -314,7 +318,7 @@ where
     }
 
     /// Get a text version of the path to the current position.
-    fn tpath(&self) -> ::std::string::String {
+    fn tpath(&self) -> String {
         use std::string::ToString;
         self.path.to_string()
     }
diff --git a/lib/codegen/src/dbg.rs b/lib/codegen/src/dbg.rs
index 6c51bd23e5..a514dd7a05 100644
--- a/lib/codegen/src/dbg.rs
+++ b/lib/codegen/src/dbg.rs
@@ -116,7 +116,6 @@ macro_rules! dbg {
         if $crate::dbg::enabled() {
             // Drop the error result so we don't get compiler errors for ignoring it.
             // What are you going to do, log the error?
-            #[cfg(feature = "std")]
             $crate::dbg::writeln_with_format_args(format_args!($($arg)+)).ok();
         }
     }
diff --git a/lib/codegen/src/ir/extname.rs b/lib/codegen/src/ir/extname.rs
index dcb3666703..ed723be6fe 100644
--- a/lib/codegen/src/ir/extname.rs
+++ b/lib/codegen/src/ir/extname.rs
@@ -121,6 +121,7 @@ mod tests {
     use super::ExternalName;
     use ir::LibCall;
     use std::string::ToString;
+    use std::u32;
 
     #[test]
     fn display_testcase() {
@@ -143,7 +144,7 @@ mod tests {
         assert_eq!(ExternalName::user(0, 0).to_string(), "u0:0");
         assert_eq!(ExternalName::user(1, 1).to_string(), "u1:1");
         assert_eq!(
-            ExternalName::user(::std::u32::MAX, ::std::u32::MAX).to_string(),
+            ExternalName::user(u32::MAX, u32::MAX).to_string(),
             "u4294967295:4294967295"
         );
     }
diff --git a/lib/codegen/src/legalizer/libcall.rs b/lib/codegen/src/legalizer/libcall.rs
index 8f69cba18d..17f9174706 100644
--- a/lib/codegen/src/legalizer/libcall.rs
+++ b/lib/codegen/src/legalizer/libcall.rs
@@ -2,6 +2,7 @@
 
 use ir;
 use ir::InstBuilder;
+use std::vec::Vec;
 
 /// Try to expand `inst` as a library call, returning true is successful.
 pub fn expand_as_libcall(inst: ir::Inst, func: &mut ir::Function) -> bool {
@@ -15,7 +16,7 @@ pub fn expand_as_libcall(inst: ir::Inst, func: &mut ir::Function) -> bool {
     let funcref = find_funcref(libcall, func).unwrap_or_else(|| make_funcref(libcall, inst, func));
 
     // Now we convert `inst` to a call. First save the arguments.
-    let mut args = vec![];
+    let mut args = Vec::new();
     args.extend_from_slice(func.dfg.inst_args(inst));
     // The replace builder will preserve the instruction result values.
     func.dfg.replace(inst).call(funcref, &args);