diff --git a/src/liballoc/collections/vec_deque/tests.rs b/src/liballoc/collections/vec_deque/tests.rs
index fc2ec7908e823..960af4bfda053 100644
--- a/src/liballoc/collections/vec_deque/tests.rs
+++ b/src/liballoc/collections/vec_deque/tests.rs
@@ -1,7 +1,5 @@
 use super::*;
 
-use test;
-
 #[bench]
 #[cfg_attr(miri, ignore)] // isolated Miri does not support benchmarks
 fn bench_push_back_100(b: &mut test::Bencher) {
diff --git a/src/librustc_ast_pretty/pprust/tests.rs b/src/librustc_ast_pretty/pprust/tests.rs
index f51439f89ffbe..f92e40ed6ffab 100644
--- a/src/librustc_ast_pretty/pprust/tests.rs
+++ b/src/librustc_ast_pretty/pprust/tests.rs
@@ -2,7 +2,6 @@ use super::*;
 
 use rustc_ast::ast;
 use rustc_ast::with_default_globals;
-use rustc_span;
 use rustc_span::source_map::respan;
 use rustc_span::symbol::Ident;
 
diff --git a/src/librustc_data_structures/sync.rs b/src/librustc_data_structures/sync.rs
index 39afb3d82ff5a..53d831749ceb7 100644
--- a/src/librustc_data_structures/sync.rs
+++ b/src/librustc_data_structures/sync.rs
@@ -358,7 +358,6 @@ cfg_if! {
         use parking_lot::Mutex as InnerLock;
         use parking_lot::RwLock as InnerRwLock;
 
-        use std;
         use std::thread;
         pub use rayon::{join, scope};
 
diff --git a/src/libstd/os/illumos/fs.rs b/src/libstd/os/illumos/fs.rs
index 2abbf1fa9fa16..b668aa2595d67 100644
--- a/src/libstd/os/illumos/fs.rs
+++ b/src/libstd/os/illumos/fs.rs
@@ -1,7 +1,5 @@
 #![stable(feature = "metadata_ext", since = "1.1.0")]
 
-use libc;
-
 use crate::fs::Metadata;
 use crate::sys_common::AsInner;
 
diff --git a/src/libstd/sys/unix/ext/net.rs b/src/libstd/sys/unix/ext/net.rs
index cd24605ec7ab7..ada8eaa1c9745 100644
--- a/src/libstd/sys/unix/ext/net.rs
+++ b/src/libstd/sys/unix/ext/net.rs
@@ -2,9 +2,6 @@
 
 //! Unix-specific networking functionality
 
-#[cfg(unix)]
-use libc;
-
 // FIXME(#43348): Make libc adapt #[doc(cfg(...))] so we don't need these fake definitions here?
 #[cfg(not(unix))]
 #[allow(non_camel_case_types)]
diff --git a/src/libstd/sys/vxworks/args.rs b/src/libstd/sys/vxworks/args.rs
index efd615f404db6..adff6c489bbc9 100644
--- a/src/libstd/sys/vxworks/args.rs
+++ b/src/libstd/sys/vxworks/args.rs
@@ -56,7 +56,6 @@ mod imp {
     use crate::ffi::{CStr, OsString};
     use crate::marker::PhantomData;
     use crate::ptr;
-    use libc;
 
     use crate::sys_common::mutex::Mutex;
 
diff --git a/src/libstd/sys/vxworks/ext/fs.rs b/src/libstd/sys/vxworks/ext/fs.rs
index 9864a855df738..7cc64658ee1a9 100644
--- a/src/libstd/sys/vxworks/ext/fs.rs
+++ b/src/libstd/sys/vxworks/ext/fs.rs
@@ -6,7 +6,6 @@ use crate::path::Path;
 use crate::sys;
 use crate::sys::platform::fs::MetadataExt as UnixMetadataExt;
 use crate::sys_common::{AsInner, AsInnerMut, FromInner};
-use libc;
 
 /// Unix-specific extensions to [`File`].
 ///
diff --git a/src/libstd/sys/vxworks/rand.rs b/src/libstd/sys/vxworks/rand.rs
index 87ebd2c9593fc..3a1ff5fd3b9c6 100644
--- a/src/libstd/sys/vxworks/rand.rs
+++ b/src/libstd/sys/vxworks/rand.rs
@@ -13,7 +13,6 @@ pub fn hashmap_random_keys() -> (u64, u64) {
 mod imp {
     use crate::io;
     use core::sync::atomic::{AtomicBool, Ordering::Relaxed};
-    use libc;
 
     pub fn fill_bytes(v: &mut [u8]) {
         static RNG_INIT: AtomicBool = AtomicBool::new(false);
diff --git a/src/libstd/sys/vxworks/rwlock.rs b/src/libstd/sys/vxworks/rwlock.rs
index fd2e1a6e7bcfb..c90304c2b4a6a 100644
--- a/src/libstd/sys/vxworks/rwlock.rs
+++ b/src/libstd/sys/vxworks/rwlock.rs
@@ -1,6 +1,5 @@
 use crate::cell::UnsafeCell;
 use crate::sync::atomic::{AtomicUsize, Ordering};
-use libc;
 
 pub struct RWLock {
     inner: UnsafeCell<libc::pthread_rwlock_t>,
diff --git a/src/libstd/sys/vxworks/time.rs b/src/libstd/sys/vxworks/time.rs
index 8ebbf89213f32..8365c9ee9c995 100644
--- a/src/libstd/sys/vxworks/time.rs
+++ b/src/libstd/sys/vxworks/time.rs
@@ -1,7 +1,6 @@
 use crate::cmp::Ordering;
 use crate::time::Duration;
 use ::core::hash::{Hash, Hasher};
-use libc;
 
 pub use self::inner::{Instant, SystemTime, UNIX_EPOCH};
 use crate::convert::TryInto;
@@ -104,7 +103,6 @@ mod inner {
     use crate::fmt;
     use crate::sys::cvt;
     use crate::time::Duration;
-    use libc;
 
     use super::Timespec;
 
diff --git a/src/libstd/sys/wasi/alloc.rs b/src/libstd/sys/wasi/alloc.rs
index bc61416278401..57187851a14e3 100644
--- a/src/libstd/sys/wasi/alloc.rs
+++ b/src/libstd/sys/wasi/alloc.rs
@@ -1,7 +1,6 @@
 use crate::alloc::{GlobalAlloc, Layout, System};
 use crate::ptr;
 use crate::sys_common::alloc::{realloc_fallback, MIN_ALIGN};
-use libc;
 
 #[stable(feature = "alloc_system_type", since = "1.28.0")]
 unsafe impl GlobalAlloc for System {
diff --git a/src/tools/build-manifest/src/main.rs b/src/tools/build-manifest/src/main.rs
index 39baa6b8540df..9eb43eb2df43f 100644
--- a/src/tools/build-manifest/src/main.rs
+++ b/src/tools/build-manifest/src/main.rs
@@ -7,7 +7,6 @@
 #![deny(warnings)]
 
 use serde::Serialize;
-use toml;
 
 use std::collections::BTreeMap;
 use std::collections::HashMap;
diff --git a/src/tools/compiletest/src/json.rs b/src/tools/compiletest/src/json.rs
index 52d0cbd4bfd7a..6ac7c3b9b474a 100644
--- a/src/tools/compiletest/src/json.rs
+++ b/src/tools/compiletest/src/json.rs
@@ -4,7 +4,6 @@
 use crate::errors::{Error, ErrorKind};
 use crate::runtest::ProcRes;
 use serde::Deserialize;
-use serde_json;
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
 
diff --git a/src/tools/compiletest/src/main.rs b/src/tools/compiletest/src/main.rs
index c00b0f02c3a90..134ac66b7d15b 100644
--- a/src/tools/compiletest/src/main.rs
+++ b/src/tools/compiletest/src/main.rs
@@ -9,8 +9,6 @@ extern crate test;
 use crate::common::{expected_output_path, output_base_dir, output_relative_path, UI_EXTENSIONS};
 use crate::common::{CompareMode, Config, Debugger, Mode, PassMode, Pretty, TestPaths};
 use crate::util::logv;
-use env_logger;
-use getopts;
 use getopts::Options;
 use log::*;
 use std::env;
diff --git a/src/tools/compiletest/src/read2.rs b/src/tools/compiletest/src/read2.rs
index da1d3db49d70e..30a922057eb20 100644
--- a/src/tools/compiletest/src/read2.rs
+++ b/src/tools/compiletest/src/read2.rs
@@ -25,7 +25,6 @@ mod imp {
 
 #[cfg(unix)]
 mod imp {
-    use libc;
     use std::io;
     use std::io::prelude::*;
     use std::mem;
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 95ea4fb078955..dd0c68ecd4965 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -13,7 +13,6 @@ use crate::header::TestProps;
 use crate::json;
 use crate::util::get_pointer_width;
 use crate::util::{logv, PathBufExt};
-use diff;
 use regex::{Captures, Regex};
 use rustfix::{apply_suggestions, get_suggestions_from_json, Filter};