diff --git a/rustfmt.toml b/rustfmt.toml
index df230cde9b713..bb656891446a2 100644
--- a/rustfmt.toml
+++ b/rustfmt.toml
@@ -4,3 +4,85 @@
 # be picked up automatically).
 version = "Two"
 use_small_heuristics = "Max"
+
+# by default we ignore everything in the repository
+# tidy only checks files which are not ignored, each entry follows gitignore style
+ignore = [
+    # remove directories below, or opt out their subdirectories, as they are formatted
+    "src/bootstrap/",
+    "src/build_helper/",
+    "src/liballoc/",
+    "src/libarena/",
+    "src/libcore/",
+    "src/libfmt_macros/",
+    "src/libgraphviz/",
+    "src/libpanic_abort/",
+    "src/libpanic_unwind/",
+    "src/libproc_macro/",
+    "src/libprofiler_builtins/",
+    "src/librustc/",
+    "src/librustc_apfloat/",
+    "src/librustc_asan/",
+    "src/librustc_codegen_llvm/",
+    "src/librustc_codegen_ssa/",
+    "src/librustc_codegen_utils/",
+    "src/librustc_data_structures/",
+    "src/librustc_driver/",
+    "src/librustc_errors/",
+    "src/librustc_feature/",
+    "src/librustc_incremental/",
+    "src/librustc_index/",
+    "src/librustc_interface/",
+    "src/librustc_lexer/",
+    "src/librustc_lint/",
+    "src/librustc_llvm/",
+    "src/librustc_lsan/",
+    "src/librustc_macros/",
+    "src/librustc_metadata/",
+    "src/librustc_mir/",
+    "src/librustc_msan/",
+    "src/librustc_parse/",
+    "src/librustc_passes/",
+    "src/librustc_plugin/",
+    "src/librustc_plugin_impl/",
+    "src/librustc_privacy/",
+    "src/librustc_resolve/",
+    "src/librustc_save_analysis/",
+    "src/librustc_session/",
+    "src/librustc_target/",
+    "src/librustc_traits/",
+    "src/librustc_tsan/",
+    "src/librustc_typeck/",
+    "src/librustdoc/",
+    "src/libserialize/",
+    "src/libstd/",
+    "src/libsyntax/",
+    "src/libsyntax_expand/",
+    "src/libsyntax_ext/",
+    "src/libsyntax_pos/",
+    "src/libterm/",
+    "src/libtest/",
+    "src/libunwind/",
+    "src/rtstartup/",
+    "src/rustc/",
+    "src/rustllvm/",
+    "src/test/",
+    "src/tools/",
+
+    # do not format submodules
+    "src/doc/book",
+    "src/doc/edition-guide",
+    "src/doc/embedded-book",
+    "src/doc/nomicon",
+    "src/doc/reference",
+    "src/doc/rust-by-example",
+    "src/doc/rustc-guide",
+    "src/llvm-project",
+    "src/stdarch",
+    "src/tools/cargo",
+    "src/tools/clippy",
+    "src/tools/miri",
+    "src/tools/rls",
+    "src/tools/rust-installer",
+    "src/tools/rustfmt",
+]
diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index bb169414886de..6737086f6e5b0 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -322,6 +322,7 @@ def __init__(self):
         self.date = ''
         self._download_url = ''
         self.rustc_channel = ''
+        self.rustfmt_channel = ''
         self.build = ''
         self.build_dir = os.path.join(os.getcwd(), "build")
         self.clean = False
@@ -344,6 +345,7 @@ def download_stage0(self):
         """
         rustc_channel = self.rustc_channel
         cargo_channel = self.cargo_channel
+        rustfmt_channel = self.rustfmt_channel
 
         def support_xz():
             try:
@@ -393,13 +395,29 @@ def support_xz():
             with output(self.cargo_stamp()) as cargo_stamp:
                 cargo_stamp.write(self.date)
 
-    def _download_stage0_helper(self, filename, pattern, tarball_suffix):
+        if self.rustfmt() and self.rustfmt().startswith(self.bin_root()) and (
+            not os.path.exists(self.rustfmt())
+            or self.program_out_of_date(self.rustfmt_stamp())
+        ):
+            if rustfmt_channel:
+                tarball_suffix = '.tar.xz' if support_xz() else '.tar.gz'
+                [channel, date] = rustfmt_channel.split('-', 1)
+                filename = "rustfmt-{}-{}{}".format(channel, self.build, tarball_suffix)
+                self._download_stage0_helper(filename, "rustfmt-preview", tarball_suffix, date)
+                self.fix_executable("{}/bin/rustfmt".format(self.bin_root()))
+                self.fix_executable("{}/bin/cargo-fmt".format(self.bin_root()))
+                with output(self.rustfmt_stamp()) as rustfmt_stamp:
+                    rustfmt_stamp.write(self.date)
+
+    def _download_stage0_helper(self, filename, pattern, tarball_suffix, date=None):
+        if date is None:
+            date = self.date
         cache_dst = os.path.join(self.build_dir, "cache")
-        rustc_cache = os.path.join(cache_dst, self.date)
+        rustc_cache = os.path.join(cache_dst, date)
         if not os.path.exists(rustc_cache):
             os.makedirs(rustc_cache)
 
-        url = "{}/dist/{}".format(self._download_url, self.date)
+        url = "{}/dist/{}".format(self._download_url, date)
         tarball = os.path.join(rustc_cache, filename)
         if not os.path.exists(tarball):
             get("{}/{}".format(url, filename), tarball, verbose=self.verbose)
@@ -493,6 +511,16 @@ def cargo_stamp(self):
         """
         return os.path.join(self.bin_root(), '.cargo-stamp')
 
+    def rustfmt_stamp(self):
+        """Return the path for .rustfmt-stamp
+
+        >>> rb = RustBuild()
+        >>> rb.build_dir = "build"
+        >>> rb.rustfmt_stamp() == os.path.join("build", "stage0", ".rustfmt-stamp")
+        True
+        """
+        return os.path.join(self.bin_root(), '.rustfmt-stamp')
+
     def program_out_of_date(self, stamp_path):
         """Check if the given program stamp is out of date"""
         if not os.path.exists(stamp_path) or self.clean:
@@ -565,6 +593,12 @@ def rustc(self):
         """Return config path for rustc"""
         return self.program_config('rustc')
 
+    def rustfmt(self):
+        """Return config path for rustfmt"""
+        if not self.rustfmt_channel:
+            return None
+        return self.program_config('rustfmt')
+
     def program_config(self, program):
         """Return config path for the given program
 
@@ -868,6 +902,9 @@ def bootstrap(help_triggered):
     build.rustc_channel = data['rustc']
     build.cargo_channel = data['cargo']
 
+    if "rustfmt" in data:
+        build.rustfmt_channel = data['rustfmt']
+
     if 'dev' in data:
         build.set_dev_environment()
     else:
@@ -895,6 +932,8 @@ def bootstrap(help_triggered):
     env["RUSTC_BOOTSTRAP"] = '1'
     env["CARGO"] = build.cargo()
     env["RUSTC"] = build.rustc()
+    if build.rustfmt():
+        env["RUSTFMT"] = build.rustfmt()
     run(args, env=env, verbose=build.verbose)
 
 
diff --git a/src/bootstrap/bootstrap_test.py b/src/bootstrap/bootstrap_test.py
index 689298f32d03c..0e941e1367668 100644
--- a/src/bootstrap/bootstrap_test.py
+++ b/src/bootstrap/bootstrap_test.py
@@ -20,14 +20,14 @@ def setUp(self):
         os.mkdir(os.path.join(self.rust_root, "src"))
         with open(os.path.join(self.rust_root, "src",
                                "stage0.txt"), "w") as stage0:
-            stage0.write("#ignore\n\ndate: 2017-06-15\nrustc: beta\ncargo: beta")
+            stage0.write("#ignore\n\ndate: 2017-06-15\nrustc: beta\ncargo: beta\nrustfmt: beta")
 
     def tearDown(self):
         rmtree(self.rust_root)
 
     def test_stage0_data(self):
         """Extract data from stage0.txt"""
-        expected = {"date": "2017-06-15", "rustc": "beta", "cargo": "beta"}
+        expected = {"date": "2017-06-15", "rustc": "beta", "cargo": "beta", "rustfmt": "beta"}
         data = bootstrap.stage0_data(self.rust_root)
         self.assertDictEqual(data, expected)
 
diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index 8b0ad169cfc25..598b8001372ff 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -321,6 +321,7 @@ pub enum Kind {
     Check,
     Clippy,
     Fix,
+    Format,
     Test,
     Bench,
     Dist,
@@ -360,7 +361,7 @@ impl<'a> Builder<'a> {
                 tool::Miri,
                 native::Lld
             ),
-            Kind::Check | Kind::Clippy | Kind::Fix => describe!(
+            Kind::Check | Kind::Clippy | Kind::Fix | Kind::Format => describe!(
                 check::Std,
                 check::Rustc,
                 check::Rustdoc
@@ -524,7 +525,7 @@ impl<'a> Builder<'a> {
             Subcommand::Bench { ref paths, .. } => (Kind::Bench, &paths[..]),
             Subcommand::Dist { ref paths } => (Kind::Dist, &paths[..]),
             Subcommand::Install { ref paths } => (Kind::Install, &paths[..]),
-            Subcommand::Clean { .. } => panic!(),
+            Subcommand::Format { .. } | Subcommand::Clean { .. } => panic!(),
         };
 
         let builder = Builder {
diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index 5f2ef01bd5c45..3e67734e69078 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -5,6 +5,7 @@
 
 use std::collections::{HashMap, HashSet};
 use std::env;
+use std::ffi::OsString;
 use std::fs;
 use std::path::{Path, PathBuf};
 use std::process;
@@ -149,6 +150,7 @@ pub struct Config {
     // These are either the stage0 downloaded binaries or the locally installed ones.
     pub initial_cargo: PathBuf,
     pub initial_rustc: PathBuf,
+    pub initial_rustfmt: Option<PathBuf>,
     pub out: PathBuf,
 }
 
@@ -348,12 +350,16 @@ struct TomlTarget {
 impl Config {
     fn path_from_python(var_key: &str) -> PathBuf {
         match env::var_os(var_key) {
-            // Do not trust paths from Python and normalize them slightly (#49785).
-            Some(var_val) => Path::new(&var_val).components().collect(),
+            Some(var_val) => Self::normalize_python_path(var_val),
             _ => panic!("expected '{}' to be set", var_key),
         }
     }
 
+    /// Normalizes paths from Python slightly. We don't trust paths from Python (#49785).
+    fn normalize_python_path(path: OsString) -> PathBuf {
+        Path::new(&path).components().collect()
+    }
+
     pub fn default_opts() -> Config {
         let mut config = Config::default();
         config.llvm_optimize = true;
@@ -380,6 +386,7 @@ impl Config {
 
         config.initial_rustc = Config::path_from_python("RUSTC");
         config.initial_cargo = Config::path_from_python("CARGO");
+        config.initial_rustfmt = env::var_os("RUSTFMT").map(Config::normalize_python_path);
 
         config
     }
diff --git a/src/bootstrap/configure.py b/src/bootstrap/configure.py
index bb6041d7f3196..7cfc5385e2104 100755
--- a/src/bootstrap/configure.py
+++ b/src/bootstrap/configure.py
@@ -59,13 +59,13 @@ def v(*args):
 o("lld", "rust.lld", "build lld")
 o("lldb", "rust.lldb", "build lldb")
 o("missing-tools", "dist.missing-tools", "allow failures when building tools")
-o("use-libcxx", "llvm.use_libcxx", "build LLVM with libc++")
+o("use-libcxx", "llvm.use-libcxx", "build LLVM with libc++")
 
 o("cflags", "llvm.cflags", "build LLVM with these extra compiler flags")
 o("cxxflags", "llvm.cxxflags", "build LLVM with these extra compiler flags")
 o("ldflags", "llvm.ldflags", "build LLVM with these extra linker flags")
 
-o("llvm-libunwind", "rust.llvm_libunwind", "use LLVM libunwind")
+o("llvm-libunwind", "rust.llvm-libunwind", "use LLVM libunwind")
 
 # Optimization and debugging options. These may be overridden by the release
 # channel, etc.
diff --git a/src/bootstrap/flags.rs b/src/bootstrap/flags.rs
index 7b49cc0a9298c..b98e2c1bf2466 100644
--- a/src/bootstrap/flags.rs
+++ b/src/bootstrap/flags.rs
@@ -53,6 +53,9 @@ pub enum Subcommand {
     Fix {
         paths: Vec<PathBuf>,
     },
+    Format {
+        check: bool,
+    },
     Doc {
         paths: Vec<PathBuf>,
     },
@@ -102,6 +105,7 @@ Subcommands:
     check       Compile either the compiler or libraries, using cargo check
     clippy      Run clippy
     fix         Run cargo fix
+    fmt         Run rustfmt
     test        Build and run some test suites
     bench       Build and run some benchmarks
     doc         Build documentation
@@ -160,6 +164,7 @@ To learn more about a subcommand, run `./x.py <subcommand> -h`"
                 || (s == "check")
                 || (s == "clippy")
                 || (s == "fix")
+                || (s == "fmt")
                 || (s == "test")
                 || (s == "bench")
                 || (s == "doc")
@@ -222,6 +227,9 @@ To learn more about a subcommand, run `./x.py <subcommand> -h`"
             "clean" => {
                 opts.optflag("", "all", "clean all build artifacts");
             }
+            "fmt" => {
+                opts.optflag("", "check", "check formatting instead of applying.");
+            }
             _ => {}
         };
 
@@ -323,6 +331,17 @@ Arguments:
         ./x.py fix src/libcore src/libproc_macro",
                 );
             }
+            "fmt" => {
+                subcommand_help.push_str(
+                    "\n
+Arguments:
+    This subcommand optionally accepts a `--check` flag which succeeds if formatting is correct and
+    fails if it is not. For example:
+
+        ./x.py fmt
+        ./x.py fmt --check",
+                );
+            }
             "test" => {
                 subcommand_help.push_str(
                     "\n
@@ -388,7 +407,7 @@ Arguments:
 
             let maybe_rules_help = Builder::get_help(&build, subcommand.as_str());
             extra_help.push_str(maybe_rules_help.unwrap_or_default().as_str());
-        } else if subcommand.as_str() != "clean" {
+        } else if !(subcommand.as_str() == "clean" || subcommand.as_str() == "fmt") {
             extra_help.push_str(
                 format!(
                     "Run `./x.py {} -h -v` to see a list of available paths.",
@@ -439,6 +458,11 @@ Arguments:
                     all: matches.opt_present("all"),
                 }
             }
+            "fmt" => {
+                Subcommand::Format {
+                    check: matches.opt_present("check"),
+                }
+            }
             "dist" => Subcommand::Dist { paths },
             "install" => Subcommand::Install { paths },
             _ => {
diff --git a/src/bootstrap/format.rs b/src/bootstrap/format.rs
new file mode 100644
index 0000000000000..0c542594effeb
--- /dev/null
+++ b/src/bootstrap/format.rs
@@ -0,0 +1,28 @@
+//! Runs rustfmt on the repository.
+
+use crate::{util, Build};
+use std::process::Command;
+
+pub fn format(build: &Build, check: bool) {
+    let target = &build.build;
+    let rustfmt_path = build.config.initial_rustfmt.as_ref().unwrap_or_else(|| {
+        eprintln!("./x.py fmt is not supported on this channel");
+        std::process::exit(1);
+    }).clone();
+    let cargo_fmt_path = rustfmt_path.with_file_name(util::exe("cargo-fmt", &target));
+    assert!(cargo_fmt_path.is_file(), "{} not a file", cargo_fmt_path.display());
+
+    let mut cmd = Command::new(&cargo_fmt_path);
+    // cargo-fmt calls rustfmt as a bare command, so we need it to only find the correct one
+    cmd.env("PATH", cargo_fmt_path.parent().unwrap());
+    cmd.current_dir(&build.src);
+    cmd.arg("fmt");
+
+    if check {
+        cmd.arg("--");
+        cmd.arg("--check");
+    }
+
+    let status = cmd.status().expect("executing cargo-fmt");
+    assert!(status.success(), "cargo-fmt errored with status {:?}", status);
+}
diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index 080bef6853a20..ff9a55afa2957 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -147,6 +147,7 @@ mod builder;
 mod cache;
 mod tool;
 mod toolstate;
+mod format;
 
 #[cfg(windows)]
 mod job;
@@ -421,6 +422,10 @@ impl Build {
             job::setup(self);
         }
 
+        if let Subcommand::Format { check } = self.config.cmd {
+            return format::format(self, check);
+        }
+
         if let Subcommand::Clean { all } = self.config.cmd {
             return clean::clean(self, all);
         }
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index c086bf2cf402a..17aea17e69e0b 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -4,10 +4,10 @@
 //! our CI.
 
 use std::env;
-//use std::ffi::OsString;
+use std::ffi::OsString;
 use std::fmt;
 use std::fs;
-//use std::iter;
+use std::iter;
 use std::path::{Path, PathBuf};
 use std::process::Command;
 
@@ -204,8 +204,8 @@ impl Step for Cargo {
     }
 
     /// Runs `cargo test` for `cargo` packaged with Rust.
-    fn run(self, _builder: &Builder<'_>) {
-        /*let compiler = builder.compiler(self.stage, self.host);
+    fn run(self, builder: &Builder<'_>) {
+        let compiler = builder.compiler(self.stage, self.host);
 
         builder.ensure(tool::Cargo {
             compiler,
@@ -235,7 +235,7 @@ impl Step for Cargo {
 
         cargo.env("PATH", &path_for_cargo(builder, compiler));
 
-        try_run(builder, &mut cargo.into());*/
+        try_run(builder, &mut cargo.into());
     }
 }
 
@@ -590,14 +590,14 @@ impl Step for Clippy {
     }
 }
 
-//fn path_for_cargo(builder: &Builder<'_>, compiler: Compiler) -> OsString {
-//    // Configure PATH to find the right rustc. NB. we have to use PATH
-//    // and not RUSTC because the Cargo test suite has tests that will
-//    // fail if rustc is not spelled `rustc`.
-//    let path = builder.sysroot(compiler).join("bin");
-//    let old_path = env::var_os("PATH").unwrap_or_default();
-//    env::join_paths(iter::once(path).chain(env::split_paths(&old_path))).expect("")
-//}
+fn path_for_cargo(builder: &Builder<'_>, compiler: Compiler) -> OsString {
+    // Configure PATH to find the right rustc. NB. we have to use PATH
+    // and not RUSTC because the Cargo test suite has tests that will
+    // fail if rustc is not spelled `rustc`.
+    let path = builder.sysroot(compiler).join("bin");
+    let old_path = env::var_os("PATH").unwrap_or_default();
+    env::join_paths(iter::once(path).chain(env::split_paths(&old_path))).expect("")
+}
 
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
 pub struct RustdocTheme {
@@ -779,6 +779,9 @@ impl Step for Tidy {
     /// This tool in `src/tools` checks up on various bits and pieces of style and
     /// otherwise just implements a few lint-like checks that are specific to the
     /// compiler itself.
+    ///
+    /// Once tidy passes, this step also runs `fmt --check` if tests are being run
+    /// for the `dev` or `nightly` channels.
     fn run(self, builder: &Builder<'_>) {
         let mut cmd = builder.tool_cmd(Tool::Tidy);
         cmd.arg(builder.src.join("src"));
@@ -792,6 +795,11 @@ impl Step for Tidy {
 
         builder.info("tidy check");
         try_run(builder, &mut cmd);
+
+        if builder.config.channel == "dev" || builder.config.channel == "nightly" {
+            builder.info("fmt check");
+            crate::format::format(&builder.build, true);
+        }
     }
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
diff --git a/src/ci/run.sh b/src/ci/run.sh
index 4afd61bf8a7ba..73c3a964f5396 100755
--- a/src/ci/run.sh
+++ b/src/ci/run.sh
@@ -37,8 +37,6 @@ if [ "$DIST_SRC" = "" ]; then
   RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --disable-dist-src"
 fi
 
-RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.parallel-compiler"
-
 # If we're deploying artifacts then we set the release channel, otherwise if
 # we're not deploying then we want to be sure to enable all assertions because
 # we'll be running tests
@@ -46,8 +44,13 @@ RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.parallel-compiler"
 # FIXME: need a scheme for changing this `nightly` value to `beta` and `stable`
 #        either automatically or manually.
 export RUST_RELEASE_CHANNEL=nightly
+
+# Always set the release channel for bootstrap; this is normally not important (i.e., only dist
+# builds would seem to matter) but in practice bootstrap wants to know whether we're targeting
+# master, beta, or stable with a build to determine whether to run some checks (notably toolstate).
+RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --release-channel=$RUST_RELEASE_CHANNEL"
+
 if [ "$DEPLOY$DEPLOY_ALT" = "1" ]; then
-  RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --release-channel=$RUST_RELEASE_CHANNEL"
   RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --enable-llvm-static-stdcpp"
   RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.remap-debuginfo"
   RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --debuginfo-level-std=1"
@@ -55,6 +58,9 @@ if [ "$DEPLOY$DEPLOY_ALT" = "1" ]; then
   if [ "$NO_LLVM_ASSERTIONS" = "1" ]; then
     RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --disable-llvm-assertions"
   elif [ "$DEPLOY_ALT" != "" ]; then
+    if [ "$NO_PARALLEL_COMPILER" = "" ]; then
+      RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.parallel-compiler"
+    fi
     RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --enable-llvm-assertions"
     RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.verify-llvm-ir"
   fi
diff --git a/src/librustc/dep_graph/graph.rs b/src/librustc/dep_graph/graph.rs
index aa7f4f2155dd1..d952bf7ab9e25 100644
--- a/src/librustc/dep_graph/graph.rs
+++ b/src/librustc/dep_graph/graph.rs
@@ -3,7 +3,7 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_index::vec::{Idx, IndexVec};
 use smallvec::SmallVec;
-use rustc_data_structures::sync::{Lrc, Lock, AtomicU32, AtomicUsize, Ordering};
+use rustc_data_structures::sync::{Lrc, Lock, AtomicU32, AtomicU64, Ordering};
 use rustc_data_structures::sharded::{self, Sharded};
 use std::sync::atomic::Ordering::SeqCst;
 use std::env;
@@ -485,8 +485,8 @@ impl DepGraph {
         if cfg!(debug_assertions) {
             let current_dep_graph = &self.data.as_ref().unwrap().current;
 
-            Some((current_dep_graph.total_read_count.load(SeqCst) as u64,
-                  current_dep_graph.total_duplicate_read_count.load(SeqCst) as u64))
+            Some((current_dep_graph.total_read_count.load(SeqCst),
+                  current_dep_graph.total_duplicate_read_count.load(SeqCst)))
         } else {
             None
         }
@@ -970,8 +970,8 @@ pub(super) struct CurrentDepGraph {
 
     /// These are simple counters that are for profiling and
     /// debugging and only active with `debug_assertions`.
-    total_read_count: AtomicUsize,
-    total_duplicate_read_count: AtomicUsize,
+    total_read_count: AtomicU64,
+    total_duplicate_read_count: AtomicU64,
 }
 
 impl CurrentDepGraph {
@@ -1012,8 +1012,8 @@ impl CurrentDepGraph {
             )),
             anon_id_seed: stable_hasher.finish(),
             forbidden_edge,
-            total_read_count: AtomicUsize::new(0),
-            total_duplicate_read_count: AtomicUsize::new(0),
+            total_read_count: AtomicU64::new(0),
+            total_duplicate_read_count: AtomicU64::new(0),
         }
     }
 
diff --git a/src/librustc_codegen_ssa/mir/rvalue.rs b/src/librustc_codegen_ssa/mir/rvalue.rs
index 488ae8dbf9036..55d63f18cd906 100644
--- a/src/librustc_codegen_ssa/mir/rvalue.rs
+++ b/src/librustc_codegen_ssa/mir/rvalue.rs
@@ -341,6 +341,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                                     llval
                                 }
                             }
+                            (CastTy::Int(_), CastTy::Float) => {
+                                if signed {
+                                    bx.sitofp(llval, ll_t_out)
+                                } else {
+                                    bx.uitofp(llval, ll_t_out)
+                                }
+                            }
                             (CastTy::Ptr(_), CastTy::Ptr(_)) |
                             (CastTy::FnPtr, CastTy::Ptr(_)) |
                             (CastTy::RPtr(_), CastTy::Ptr(_)) =>
@@ -352,8 +359,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                                 let usize_llval = bx.intcast(llval, bx.cx().type_isize(), signed);
                                 bx.inttoptr(usize_llval, ll_t_out)
                             }
-                            (CastTy::Int(_), CastTy::Float) =>
-                                cast_int_to_float(&mut bx, signed, llval, ll_t_in, ll_t_out),
                             (CastTy::Float, CastTy::Int(IntTy::I)) =>
                                 cast_float_to_int(&mut bx, true, llval, ll_t_in, ll_t_out),
                             (CastTy::Float, CastTy::Int(_)) =>
@@ -720,40 +725,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     }
 }
 
-fn cast_int_to_float<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
-    bx: &mut Bx,
-    signed: bool,
-    x: Bx::Value,
-    int_ty: Bx::Type,
-    float_ty: Bx::Type
-) -> Bx::Value {
-    // Most integer types, even i128, fit into [-f32::MAX, f32::MAX] after rounding.
-    // It's only u128 -> f32 that can cause overflows (i.e., should yield infinity).
-    // LLVM's uitofp produces undef in those cases, so we manually check for that case.
-    let is_u128_to_f32 = !signed &&
-        bx.cx().int_width(int_ty) == 128 &&
-        bx.cx().float_width(float_ty) == 32;
-    if is_u128_to_f32 {
-        // All inputs greater or equal to (f32::MAX + 0.5 ULP) are rounded to infinity,
-        // and for everything else LLVM's uitofp works just fine.
-        use rustc_apfloat::ieee::Single;
-        const MAX_F32_PLUS_HALF_ULP: u128 = ((1 << (Single::PRECISION + 1)) - 1)
-                                            << (Single::MAX_EXP - Single::PRECISION as i16);
-        let max = bx.cx().const_uint_big(int_ty, MAX_F32_PLUS_HALF_ULP);
-        let overflow = bx.icmp(IntPredicate::IntUGE, x, max);
-        let infinity_bits = bx.cx().const_u32(ieee::Single::INFINITY.to_bits() as u32);
-        let infinity = bx.bitcast(infinity_bits, float_ty);
-        let fp = bx.uitofp(x, float_ty);
-        bx.select(overflow, infinity, fp)
-    } else {
-        if signed {
-            bx.sitofp(x, float_ty)
-        } else {
-            bx.uitofp(x, float_ty)
-        }
-    }
-}
-
 fn cast_float_to_int<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     bx: &mut Bx,
     signed: bool,
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index 02611a36aaebc..fb541637e5f79 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/src/librustc_data_structures/lib.rs
@@ -24,7 +24,6 @@
 #![feature(integer_atomics)]
 #![feature(test)]
 #![feature(associated_type_bounds)]
-#![feature(cfg_target_has_atomic)]
 
 #![cfg_attr(unix, feature(libc))]
 
diff --git a/src/librustc_data_structures/sync.rs b/src/librustc_data_structures/sync.rs
index c4aed0628ba42..6a19f52897e5d 100644
--- a/src/librustc_data_structures/sync.rs
+++ b/src/librustc_data_structures/sync.rs
@@ -317,9 +317,7 @@ cfg_if! {
         pub use parking_lot::MutexGuard as LockGuard;
         pub use parking_lot::MappedMutexGuard as MappedLockGuard;
 
-        pub use std::sync::atomic::{AtomicBool, AtomicUsize, AtomicU32};
-        #[cfg(target_has_atomic = "64")]
-        pub use std::sync::atomic::{AtomicU64};
+        pub use std::sync::atomic::{AtomicBool, AtomicUsize, AtomicU32, AtomicU64};
 
         pub use crossbeam_utils::atomic::AtomicCell;
 
diff --git a/src/librustc_fs_util/lib.rs b/src/librustc_fs_util/lib.rs
index eaf08d76b9905..289b9f30c3bbb 100644
--- a/src/librustc_fs_util/lib.rs
+++ b/src/librustc_fs_util/lib.rs
@@ -1,7 +1,7 @@
-use std::path::{Path, PathBuf};
 use std::ffi::CString;
 use std::fs;
 use std::io;
+use std::path::{Path, PathBuf};
 
 // Unfortunately, on windows, it looks like msvcrt.dll is silently translating
 // verbatim paths under the hood to non-verbatim paths! This manifests itself as
@@ -21,8 +21,8 @@ use std::io;
 //   https://github.com/rust-lang/rust/issues/25505#issuecomment-102876737
 #[cfg(windows)]
 pub fn fix_windows_verbatim_for_gcc(p: &Path) -> PathBuf {
-    use std::path;
     use std::ffi::OsString;
+    use std::path;
     let mut components = p.components();
     let prefix = match components.next() {
         Some(path::Component::Prefix(p)) => p,
@@ -68,12 +68,10 @@ pub fn link_or_copy<P: AsRef<Path>, Q: AsRef<Path>>(p: P, q: Q) -> io::Result<Li
 
     match fs::hard_link(p, q) {
         Ok(()) => Ok(LinkOrCopy::Link),
-        Err(_) => {
-            match fs::copy(p, q) {
-                Ok(_) => Ok(LinkOrCopy::Copy),
-                Err(e) => Err(e),
-            }
-        }
+        Err(_) => match fs::copy(p, q) {
+            Ok(_) => Ok(LinkOrCopy::Copy),
+            Err(e) => Err(e),
+        },
     }
 }
 
@@ -86,29 +84,28 @@ pub enum RenameOrCopyRemove {
 /// Rename `p` into `q`, preferring to use `rename` if possible.
 /// If `rename` fails (rename may fail for reasons such as crossing
 /// filesystem), fallback to copy & remove
-pub fn rename_or_copy_remove<P: AsRef<Path>, Q: AsRef<Path>>(p: P,
-                                                             q: Q)
-                                                             -> io::Result<RenameOrCopyRemove> {
+pub fn rename_or_copy_remove<P: AsRef<Path>, Q: AsRef<Path>>(
+    p: P,
+    q: Q,
+) -> io::Result<RenameOrCopyRemove> {
     let p = p.as_ref();
     let q = q.as_ref();
     match fs::rename(p, q) {
         Ok(()) => Ok(RenameOrCopyRemove::Rename),
-        Err(_) => {
-            match fs::copy(p, q) {
-                Ok(_) => {
-                    fs::remove_file(p)?;
-                    Ok(RenameOrCopyRemove::CopyRemove)
-                }
-                Err(e) => Err(e),
+        Err(_) => match fs::copy(p, q) {
+            Ok(_) => {
+                fs::remove_file(p)?;
+                Ok(RenameOrCopyRemove::CopyRemove)
             }
-        }
+            Err(e) => Err(e),
+        },
     }
 }
 
 #[cfg(unix)]
 pub fn path_to_c_string(p: &Path) -> CString {
-    use std::os::unix::ffi::OsStrExt;
     use std::ffi::OsStr;
+    use std::os::unix::ffi::OsStrExt;
     let p: &OsStr = p.as_ref();
     CString::new(p.as_bytes()).unwrap()
 }
diff --git a/src/librustc_session/config.rs b/src/librustc_session/config.rs
index 359c8b3e73a90..7f3bab8f23299 100644
--- a/src/librustc_session/config.rs
+++ b/src/librustc_session/config.rs
@@ -1358,11 +1358,11 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "prints the LLVM optimization passes being run"),
     ast_json: bool = (false, parse_bool, [UNTRACKED],
         "print the AST as JSON and halt"),
-    // We default to min(4, vCPUs) here since we want to avoid spawning *too*
-    // many threads -- that causes scalability issues due to contention on
-    // the jobserver pipe (at least) -- but 4 is a reasonable amount on systems
-    // with lots of cores.
-    threads: usize = (std::cmp::min(::num_cpus::get(), 4), parse_threads, [UNTRACKED],
+    // We default to 1 here since we want to behave like
+    // a sequential compiler for now. This'll likely be adjusted
+    // in the future. Note that -Zthreads=0 is the way to get
+    // the num_cpus behavior.
+    threads: usize = (1, parse_threads, [UNTRACKED],
         "use a thread pool with N threads"),
     ast_json_noexpand: bool = (false, parse_bool, [UNTRACKED],
         "print the pre-expansion AST as JSON and halt"),
diff --git a/src/librustc_session/session.rs b/src/librustc_session/session.rs
index 4e72249aed129..150d207e5bfe9 100644
--- a/src/librustc_session/session.rs
+++ b/src/librustc_session/session.rs
@@ -14,7 +14,7 @@ use rustc_errors::ErrorReported;
 
 use rustc_data_structures::base_n;
 use rustc_data_structures::sync::{
-    self, Lrc, Lock, OneThread, Once, AtomicUsize, Ordering,
+    self, Lrc, Lock, OneThread, Once, AtomicU64, AtomicUsize, Ordering,
     Ordering::SeqCst,
 };
 use rustc_data_structures::impl_stable_hash_via_hash;
@@ -119,7 +119,7 @@ pub struct Session {
     /// If `-zprint-fuel=crate`, `Some(crate)`.
     pub print_fuel_crate: Option<String>,
     /// Always set to zero and incremented so that we can print fuel expended by a crate.
-    pub print_fuel: AtomicUsize,
+    pub print_fuel: AtomicU64,
 
     /// Loaded up early on in the initialization of this `Session` to avoid
     /// false positives about a job server in our environment.
@@ -1116,7 +1116,7 @@ fn build_session_(
         out_of_fuel: false,
     });
     let print_fuel_crate = sopts.debugging_opts.print_fuel.clone();
-    let print_fuel = AtomicUsize::new(0);
+    let print_fuel = AtomicU64::new(0);
 
     let working_dir = env::current_dir().unwrap_or_else(|e|
         parse_sess.span_diagnostic
diff --git a/src/libstd/net/addr.rs b/src/libstd/net/addr.rs
index d5f4ece726bea..a9d88370c612f 100644
--- a/src/libstd/net/addr.rs
+++ b/src/libstd/net/addr.rs
@@ -4,7 +4,7 @@ use crate::hash;
 use crate::io;
 use crate::iter;
 use crate::mem;
-use crate::net::{hton, ntoh, IpAddr, Ipv4Addr, Ipv6Addr};
+use crate::net::{htons, ntohs, IpAddr, Ipv4Addr, Ipv6Addr};
 use crate::option;
 use crate::slice;
 use crate::sys::net::netc as c;
@@ -276,7 +276,7 @@ impl SocketAddrV4 {
         SocketAddrV4 {
             inner: c::sockaddr_in {
                 sin_family: c::AF_INET as c::sa_family_t,
-                sin_port: hton(port),
+                sin_port: htons(port),
                 sin_addr: *ip.as_inner(),
                 ..unsafe { mem::zeroed() }
             },
@@ -326,7 +326,7 @@ impl SocketAddrV4 {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn port(&self) -> u16 {
-        ntoh(self.inner.sin_port)
+        ntohs(self.inner.sin_port)
     }
 
     /// Changes the port number associated with this socket address.
@@ -342,7 +342,7 @@ impl SocketAddrV4 {
     /// ```
     #[stable(feature = "sockaddr_setters", since = "1.9.0")]
     pub fn set_port(&mut self, new_port: u16) {
-        self.inner.sin_port = hton(new_port);
+        self.inner.sin_port = htons(new_port);
     }
 }
 
@@ -368,7 +368,7 @@ impl SocketAddrV6 {
         SocketAddrV6 {
             inner: c::sockaddr_in6 {
                 sin6_family: c::AF_INET6 as c::sa_family_t,
-                sin6_port: hton(port),
+                sin6_port: htons(port),
                 sin6_addr: *ip.as_inner(),
                 sin6_flowinfo: flowinfo,
                 sin6_scope_id: scope_id,
@@ -420,7 +420,7 @@ impl SocketAddrV6 {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn port(&self) -> u16 {
-        ntoh(self.inner.sin6_port)
+        ntohs(self.inner.sin6_port)
     }
 
     /// Changes the port number associated with this socket address.
@@ -436,7 +436,7 @@ impl SocketAddrV6 {
     /// ```
     #[stable(feature = "sockaddr_setters", since = "1.9.0")]
     pub fn set_port(&mut self, new_port: u16) {
-        self.inner.sin6_port = hton(new_port);
+        self.inner.sin6_port = htons(new_port);
     }
 
     /// Returns the flow information associated with this address.
diff --git a/src/libstd/net/mod.rs b/src/libstd/net/mod.rs
index b68146939fdcc..8652ed8b046bb 100644
--- a/src/libstd/net/mod.rs
+++ b/src/libstd/net/mod.rs
@@ -85,21 +85,10 @@ pub enum Shutdown {
     Both,
 }
 
-#[doc(hidden)]
-trait NetInt {
-    fn from_be(i: Self) -> Self;
-    fn to_be(&self) -> Self;
-}
-macro_rules! doit {
-    ($($t:ident)*) => ($(impl NetInt for $t {
-        fn from_be(i: Self) -> Self { <$t>::from_be(i) }
-        fn to_be(&self) -> Self { <$t>::to_be(*self) }
-    })*)
-}
-doit! { i8 i16 i32 i64 isize u8 u16 u32 u64 usize }
-
-fn hton<I: NetInt>(i: I) -> I { i.to_be() }
-fn ntoh<I: NetInt>(i: I) -> I { I::from_be(i) }
+#[inline]
+const fn htons(i: u16) -> u16 { i.to_be() }
+#[inline]
+const fn ntohs(i: u16) -> u16 { u16::from_be(i) }
 
 fn each_addr<A: ToSocketAddrs, F, T>(addr: A, mut f: F) -> io::Result<T>
     where F: FnMut(io::Result<&SocketAddr>) -> io::Result<T>
diff --git a/src/stage0.txt b/src/stage0.txt
index 3c84890158381..ce132d619718b 100644
--- a/src/stage0.txt
+++ b/src/stage0.txt
@@ -16,6 +16,11 @@ date: 2019-11-06
 rustc: beta
 cargo: beta
 
+# We use a nightly rustfmt to format the source because it solves some bootstrapping
+# issues with use of new syntax in this repo. If you're looking at the beta/stable branch, this key should be omitted,
+# as we don't want to depend on rustfmt from nightly there.
+rustfmt: nightly-2019-11-05
+
 # When making a stable release the process currently looks like:
 #
 #   1. Produce stable build, upload it to dev-static
diff --git a/src/test/ui/traits/cycle-cache-err-60010.rs b/src/test/ui/traits/cycle-cache-err-60010.rs
index ebed4a02d0f33..cbddef082be67 100644
--- a/src/test/ui/traits/cycle-cache-err-60010.rs
+++ b/src/test/ui/traits/cycle-cache-err-60010.rs
@@ -28,7 +28,7 @@ struct SalsaStorage {
 }
 
 impl Database for RootDatabase {
-    type Storage = SalsaStorage;
+    type Storage = SalsaStorage; //~ ERROR overflow
 }
 impl HasQueryGroup for RootDatabase {}
 impl<DB> Query<DB> for ParseQuery
diff --git a/src/test/ui/traits/cycle-cache-err-60010.stderr b/src/test/ui/traits/cycle-cache-err-60010.stderr
index 2fc26bb11e3e3..295845b1146ef 100644
--- a/src/test/ui/traits/cycle-cache-err-60010.stderr
+++ b/src/test/ui/traits/cycle-cache-err-60010.stderr
@@ -6,6 +6,22 @@ LL |     _parse: <ParseQuery as Query<RootDatabase>>::Data,
    |
    = note: required because of the requirements on the impl of `Query<RootDatabase>` for `ParseQuery`
 
-error: aborting due to previous error
+error[E0275]: overflow evaluating the requirement `Runtime<RootDatabase>: std::panic::RefUnwindSafe`
+  --> $DIR/cycle-cache-err-60010.rs:31:5
+   |
+LL |     type Storage;
+   |          ------- associated type defined here
+...
+LL | impl Database for RootDatabase {
+   | ------------------------------ in this `impl` item
+LL |     type Storage = SalsaStorage;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: required because it appears within the type `RootDatabase`
+   = note: required because of the requirements on the impl of `SourceDatabase` for `RootDatabase`
+   = note: required because of the requirements on the impl of `Query<RootDatabase>` for `ParseQuery`
+   = note: required because it appears within the type `SalsaStorage`
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0275`.