Auto merge of #48694 - kennytm:rollup, r=kennytm

Rollup of 8 pull requests

- Successful merges: #48283, #48466, #48569, #48629, #48637, #48680, #48513, #48664
- Failed merges:

.gitmodules

@@ -50,3 +50,6 @@
 [submodule "src/llvm-emscripten"]
 	path = src/llvm-emscripten
 	url = https://github.com/rust-lang/llvm
+[submodule "src/stdsimd"]
+	path = src/stdsimd
+	url = https://github.com/rust-lang-nursery/stdsimd

config.toml.example

@@ -321,6 +321,9 @@
 # bootstrap)
 #codegen-backends = ["llvm"]
 
+# This is the name of the directory in which codegen backends will get installed
+#codegen-backends-dir = "codegen-backends"
+
 # Flag indicating whether `libstd` calls an imported function to handle basic IO
 # when targeting WebAssembly. Enable this to debug tests for the `wasm32-unknown-unknown`
 # target, as without this option the test output will not be captured.

src/bootstrap/bootstrap.py

@@ -314,7 +314,6 @@ class RustBuild(object):
         self.build_dir = os.path.join(os.getcwd(), "build")
         self.clean = False
         self.config_toml = ''
-        self.printed = False
         self.rust_root = os.path.abspath(os.path.join(__file__, '../../..'))
         self.use_locked_deps = ''
         self.use_vendored_sources = ''
@@ -336,7 +335,6 @@ class RustBuild(object):
         if self.rustc().startswith(self.bin_root()) and \
                 (not os.path.exists(self.rustc()) or
                  self.program_out_of_date(self.rustc_stamp())):
-            self.print_what_bootstrap_means()
             if os.path.exists(self.bin_root()):
                 shutil.rmtree(self.bin_root())
             filename = "rust-std-{}-{}.tar.gz".format(
@@ -351,10 +349,17 @@ class RustBuild(object):
             with open(self.rustc_stamp(), 'w') as rust_stamp:
                 rust_stamp.write(self.date)
 
+            # This is required so that we don't mix incompatible MinGW
+            # libraries/binaries that are included in rust-std with
+            # the system MinGW ones.
+            if "pc-windows-gnu" in self.build:
+                filename = "rust-mingw-{}-{}.tar.gz".format(
+                    rustc_channel, self.build)
+                self._download_stage0_helper(filename, "rust-mingw")
+
         if self.cargo().startswith(self.bin_root()) and \
                 (not os.path.exists(self.cargo()) or
                  self.program_out_of_date(self.cargo_stamp())):
-            self.print_what_bootstrap_means()
             filename = "cargo-{}-{}.tar.gz".format(cargo_channel, self.build)
             self._download_stage0_helper(filename, "cargo")
             self.fix_executable("{}/bin/cargo".format(self.bin_root()))
@@ -555,23 +560,6 @@ class RustBuild(object):
             return '.exe'
         return ''
 
-    def print_what_bootstrap_means(self):
-        """Prints more information about the build system"""
-        if hasattr(self, 'printed'):
-            return
-        self.printed = True
-        if os.path.exists(self.bootstrap_binary()):
-            return
-        if '--help' not in sys.argv or len(sys.argv) == 1:
-            return
-
-        print('info: the build system for Rust is written in Rust, so this')
-        print('      script is now going to download a stage0 rust compiler')
-        print('      and then compile the build system itself')
-        print('')
-        print('info: in the meantime you can read more about rustbuild at')
-        print('      src/bootstrap/README.md before the download finishes')
-
     def bootstrap_binary(self):
         """Return the path of the boostrap binary
 
@@ -585,7 +573,6 @@ class RustBuild(object):
 
     def build_bootstrap(self):
         """Build bootstrap"""
-        self.print_what_bootstrap_means()
         build_dir = os.path.join(self.build_dir, "bootstrap")
         if self.clean and os.path.exists(build_dir):
             shutil.rmtree(build_dir)
@@ -670,8 +657,16 @@ class RustBuild(object):
         self._download_url = 'https://dev-static.rust-lang.org'
 
 
-def bootstrap():
+def bootstrap(help_triggered):
     """Configure, fetch, build and run the initial bootstrap"""
+
+    # If the user is asking for help, let them know that the whole download-and-build
+    # process has to happen before anything is printed out.
+    if help_triggered:
+        print("info: Downloading and building bootstrap before processing --help")
+        print("      command. See src/bootstrap/README.md for help with common")
+        print("      commands.")
+
     parser = argparse.ArgumentParser(description='Build rust')
     parser.add_argument('--config')
     parser.add_argument('--build')
@@ -708,7 +703,7 @@ def bootstrap():
             print('      and so in order to preserve your $HOME this will now')
             print('      use vendored sources by default. Note that if this')
             print('      does not work you should run a normal build first')
-            print('      before running a command like `sudo make install`')
+            print('      before running a command like `sudo ./x.py install`')
 
     if build.use_vendored_sources:
         if not os.path.exists('.cargo'):
@@ -734,7 +729,10 @@ def bootstrap():
     if 'dev' in data:
         build.set_dev_environment()
 
-    build.update_submodules()
+    # No help text depends on submodules. This check saves ~1 minute of git commands, even if
+    # all the submodules are present and downloaded!
+    if not help_triggered:
+        build.update_submodules()
 
     # Fetch/build the bootstrap
     build.build = args.build or build.build_triple()
@@ -760,7 +758,7 @@ def main():
     help_triggered = (
         '-h' in sys.argv) or ('--help' in sys.argv) or (len(sys.argv) == 1)
     try:
-        bootstrap()
+        bootstrap(help_triggered)
         if not help_triggered:
             print("Build completed successfully in {}".format(
                 format_build_time(time() - start_time)))

src/bootstrap/builder.rs

@@ -464,7 +464,7 @@ impl<'a> Builder<'a> {
 
     pub fn sysroot_codegen_backends(&self, compiler: Compiler) -> PathBuf {
         self.sysroot_libdir(compiler, compiler.host)
-            .with_file_name("codegen-backends")
+            .with_file_name(self.build.config.rust_codegen_backends_dir.clone())
     }
 
     /// Returns the compiler's libdir where it stores the dynamic libraries that

src/bootstrap/compile.rs

@@ -514,7 +514,8 @@ fn rustc_cargo_env(build: &Build, cargo: &mut Command) {
     cargo.env("CFG_RELEASE", build.rust_release())
          .env("CFG_RELEASE_CHANNEL", &build.config.channel)
          .env("CFG_VERSION", build.rust_version())
-         .env("CFG_PREFIX", build.config.prefix.clone().unwrap_or_default());
+         .env("CFG_PREFIX", build.config.prefix.clone().unwrap_or_default())
+         .env("CFG_CODEGEN_BACKENDS_DIR", &build.config.rust_codegen_backends_dir);
 
     let libdir_relative = build.config.libdir_relative().unwrap_or(Path::new("lib"));
     cargo.env("CFG_LIBDIR_RELATIVE", libdir_relative);

src/bootstrap/config.rs

@@ -96,6 +96,7 @@ pub struct Config {
     pub rust_debuginfo_tests: bool,
     pub rust_dist_src: bool,
     pub rust_codegen_backends: Vec<Interned<String>>,
+    pub rust_codegen_backends_dir: String,
 
     pub build: Interned<String>,
     pub hosts: Vec<Interned<String>>,
@@ -289,6 +290,7 @@ struct Rust {
     test_miri: Option<bool>,
     save_toolstates: Option<String>,
     codegen_backends: Option<Vec<String>>,
+    codegen_backends_dir: Option<String>,
     wasm_syscall: Option<bool>,
 }
 
@@ -330,6 +332,7 @@ impl Config {
         config.rust_dist_src = true;
         config.test_miri = false;
         config.rust_codegen_backends = vec![INTERNER.intern_str("llvm")];
+        config.rust_codegen_backends_dir = "codegen-backends".to_owned();
 
         config.rustc_error_format = flags.rustc_error_format;
         config.on_fail = flags.on_fail;
@@ -488,6 +491,8 @@ impl Config {
                     .collect();
             }
 
+            set(&mut config.rust_codegen_backends_dir, rust.codegen_backends_dir.clone());
+
             match rust.codegen_units {
                 Some(0) => config.rust_codegen_units = Some(num_cpus::get() as u32),
                 Some(n) => config.rust_codegen_units = Some(n),

src/bootstrap/dist.rs

@@ -590,7 +590,8 @@ impl Step for Std {
         let mut src = builder.sysroot_libdir(compiler, target).to_path_buf();
         src.pop(); // Remove the trailing /lib folder from the sysroot_libdir
         cp_filtered(&src, &dst, &|path| {
-            path.file_name().and_then(|s| s.to_str()) != Some("codegen-backends")
+            path.file_name().and_then(|s| s.to_str()) !=
+                Some(build.config.rust_codegen_backends_dir.as_str())
         });
 
         let mut cmd = rust_installer(builder);

src/bootstrap/doc.rs

@@ -312,6 +312,7 @@ fn invoke_rustdoc(builder: &Builder, compiler: Compiler, target: Interned<String
     cmd.arg("--html-after-content").arg(&footer)
         .arg("--html-before-content").arg(&version_info)
         .arg("--html-in-header").arg(&favicon)
+        .arg("--markdown-no-toc")
         .arg("--markdown-playground-url")
         .arg("https://play.rust-lang.org/")
         .arg("-o").arg(&out)

src/libcore/lib.rs

@@ -68,16 +68,21 @@
 #![feature(allow_internal_unstable)]
 #![feature(asm)]
 #![feature(associated_type_defaults)]
+#![feature(attr_literals)]
 #![feature(cfg_target_feature)]
 #![feature(cfg_target_has_atomic)]
 #![feature(concat_idents)]
 #![feature(const_fn)]
 #![feature(custom_attribute)]
+#![feature(doc_spotlight)]
 #![feature(fundamental)]
 #![feature(i128_type)]
 #![feature(inclusive_range_syntax)]
 #![feature(intrinsics)]
+#![feature(iterator_flatten)]
+#![feature(iterator_repeat_with)]
 #![feature(lang_items)]
+#![feature(link_llvm_intrinsics)]
 #![feature(never_type)]
 #![feature(no_core)]
 #![feature(on_unimplemented)]
@@ -85,15 +90,17 @@
 #![feature(prelude_import)]
 #![feature(repr_simd, platform_intrinsics)]
 #![feature(rustc_attrs)]
+#![feature(rustc_const_unstable)]
+#![feature(simd_ffi)]
 #![feature(specialization)]
 #![feature(staged_api)]
+#![feature(stmt_expr_attributes)]
+#![feature(target_feature)]
 #![feature(unboxed_closures)]
 #![feature(untagged_unions)]
 #![feature(unwind_attributes)]
-#![feature(doc_spotlight)]
-#![feature(rustc_const_unstable)]
-#![feature(iterator_repeat_with)]
-#![feature(iterator_flatten)]
+
+#![cfg_attr(stage0, allow(unused_attributes))]
 
 #[prelude_import]
 #[allow(unused)]
@@ -179,3 +186,21 @@ mod char_private;
 mod iter_private;
 mod tuple;
 mod unit;
+
+// Pull in the the `coresimd` crate directly into libcore. This is where all the
+// architecture-specific (and vendor-specific) intrinsics are defined. AKA
+// things like SIMD and such. Note that the actual source for all this lies in a
+// different repository, rust-lang-nursery/stdsimd. That's why the setup here is
+// a bit wonky.
+#[path = "../stdsimd/coresimd/mod.rs"]
+#[allow(missing_docs, missing_debug_implementations, dead_code)]
+#[unstable(feature = "stdsimd", issue = "48556")]
+#[cfg(not(stage0))] // allow changes to how stdsimd works in stage0
+mod coresimd;
+
+#[unstable(feature = "stdsimd", issue = "48556")]
+#[cfg(not(stage0))]
+pub use coresimd::simd;
+#[unstable(feature = "stdsimd", issue = "48556")]
+#[cfg(not(stage0))]
+pub use coresimd::arch;

src/librustc_back/target/armv7_unknown_linux_musleabihf.rs

@@ -12,13 +12,7 @@ use LinkerFlavor;
 use target::{Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
-    let mut base = super::linux_musl_base::opts();
-
-    // Most of these settings are copied from the armv7_unknown_linux_gnueabihf
-    // target.
-    base.features = "+v7,+vfp3,+neon".to_string();
-    base.cpu = "cortex-a8".to_string();
-    base.max_atomic_width = Some(64);
+    let base = super::linux_musl_base::opts();
     Ok(Target {
         // It's important we use "gnueabihf" and not "musleabihf" here. LLVM
         // uses it to determine the calling convention and float ABI, and LLVM
@@ -33,9 +27,15 @@ pub fn target() -> TargetResult {
         target_env: "musl".to_string(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
+
+        // Most of these settings are copied from the armv7_unknown_linux_gnueabihf
+        // target.
         options: TargetOptions {
+            features: "+v7,+vfp3,+d16,+thumb2,-neon".to_string(),
+            cpu: "generic".to_string(),
+            max_atomic_width: Some(64),
             abi_blacklist: super::arm_base::abi_blacklist(),
             .. base
-        },
+        }
     })
 }

src/librustc_driver/lib.rs

@@ -303,7 +303,9 @@ fn get_trans_sysroot(backend_name: &str) -> fn() -> Box<TransCrate> {
     let sysroot = sysroot_candidates.iter()
         .map(|sysroot| {
             let libdir = filesearch::relative_target_lib_path(&sysroot, &target);
-            sysroot.join(libdir).with_file_name("codegen-backends")
+            sysroot.join(libdir)
+                .with_file_name(option_env!("CFG_CODEGEN_BACKENDS_DIR")
+                                .unwrap_or("codegen-backends"))
         })
         .filter(|f| {
             info!("codegen backend candidate: {}", f.display());

src/librustdoc/README.md

@@ -0,0 +1,172 @@
+# The walking tour of rustdoc
+
+Rustdoc is implemented entirely within the crate `librustdoc`. After partially compiling a crate to
+get its AST (technically the HIR map) from rustc, librustdoc performs two major steps past that to
+render a set of documentation:
+
+* "Clean" the AST into a form that's more suited to creating documentation (and slightly more
+  resistant to churn in the compiler).
+* Use this cleaned AST to render a crate's documentation, one page at a time.
+
+Naturally, there's more than just this, and those descriptions simplify out lots of details, but
+that's the high-level overview.
+
+(Side note: this is a library crate! The `rustdoc` binary is crated using the project in
+`src/tools/rustdoc`. Note that literally all that does is call the `main()` that's in this crate's
+`lib.rs`, though.)
+
+## Cheat sheet
+
+* Use `x.py build --stage 1 src/libstd src/tools/rustdoc` to make a useable rustdoc you can run on
+  other projects.
+  * Add `src/libtest` to be able to use `rustdoc --test`.
+  * If you've used `rustup toolchain link local /path/to/build/$TARGET/stage1` previously, then
+    after the previous build command, `cargo +local doc` will Just Work.
+* Use `x.py doc --stage 1 src/libstd` to use this rustdoc to generate the standard library docs.
+  * The completed docs will be available in `build/$TARGET/doc/std`, though the bundle is meant to
+    be used as though you would copy out the `doc` folder to a web server, since that's where the
+    CSS/JS and landing page are.
+* Most of the HTML printing code is in `html/format.rs` and `html/render.rs`. It's in a bunch of
+  `fmt::Display` implementations and supplementary functions.
+* The types that got `Display` impls above are defined in `clean/mod.rs`, right next to the custom
+  `Clean` trait used to process them out of the rustc HIR.
+* The bits specific to using rustdoc as a test harness are in `test.rs`.
+* The Markdown renderer is loaded up in `html/markdown.rs`, including functions for extracting
+  doctests from a given block of Markdown.
+* The tests on rustdoc *output* are located in `src/test/rustdoc`, where they're handled by the test
+  runner of rustbuild and the supplementary script `src/etc/htmldocck.py`.
+* Tests on search index generation are located in `src/test/rustdoc-js`, as a series of JavaScript
+  files that encode queries on the standard library search index and expected results.
+
+## From crate to clean
+
+In `core.rs` are two central items: the `DocContext` struct, and the `run_core` function. The latter
+is where rustdoc calls out to rustc to compile a crate to the point where rustdoc can take over. The
+former is a state container used when crawling through a crate to gather its documentation.
+
+The main process of crate crawling is done in `clean/mod.rs` through several implementations of the
+`Clean` trait defined within. This is a conversion trait, which defines one method:
+
+```rust
+pub trait Clean<T> {
+    fn clean(&self, cx: &DocContext) -> T;
+}
+```
+
+`clean/mod.rs` also defines the types for the "cleaned" AST used later on to render documentation
+pages. Each usually accompanies an implementation of `Clean` that takes some AST or HIR type from
+rustc and converts it into the appropriate "cleaned" type. "Big" items like modules or associated
+items may have some extra processing in its `Clean` implementation, but for the most part these
+impls are straightforward conversions. The "entry point" to this module is the `impl Clean<Crate>
+for visit_ast::RustdocVisitor`, which is called by `run_core` above.
+
+You see, I actually lied a little earlier: There's another AST transformation that happens before
+the events in `clean/mod.rs`.  In `visit_ast.rs` is the type `RustdocVisitor`, which *actually*
+crawls a `hir::Crate` to get the first intermediate representation, defined in `doctree.rs`. This
+pass is mainly to get a few intermediate wrappers around the HIR types and to process visibility
+and inlining. This is where `#[doc(inline)]`, `#[doc(no_inline)]`, and `#[doc(hidden)]` are
+processed, as well as the logic for whether a `pub use` should get the full page or a "Reexport"
+line in the module page.
+
+The other major thing that happens in `clean/mod.rs` is the collection of doc comments and
+`#[doc=""]` attributes into a separate field of the Attributes struct, present on anything that gets
+hand-written documentation. This makes it easier to collect this documentation later in the process.
+
+The primary output of this process is a clean::Crate with a tree of Items which describe the
+publicly-documentable items in the target crate.
+
+### Hot potato
+
+Before moving on to the next major step, a few important "passes" occur over the documentation.
+These do things like combine the separate "attributes" into a single string and strip leading
+whitespace to make the document easier on the markdown parser, or drop items that are not public or
+deliberately hidden with `#[doc(hidden)]`. These are all implemented in the `passes/` directory, one
+file per pass. By default, all of these passes are run on a crate, but the ones regarding dropping
+private/hidden items can be bypassed by passing `--document-private-items` to rustdoc.
+
+(Strictly speaking, you can fine-tune the passes run and even add your own, but [we're trying to
+deprecate that][44136]. If you need finer-grain control over these passes, please let us know!)
+
+[44136]: https://github.com/rust-lang/rust/issues/44136
+
+## From clean to crate
+
+This is where the "second phase" in rustdoc begins. This phase primarily lives in the `html/`
+folder, and it all starts with `run()` in `html/render.rs`. This code is responsible for setting up
+the `Context`, `SharedContext`, and `Cache` which are used during rendering, copying out the static
+files which live in every rendered set of documentation (things like the fonts, CSS, and JavaScript
+that live in `html/static/`), creating the search index, and printing out the source code rendering,
+before beginning the process of rendering all the documentation for the crate.
+
+Several functions implemented directly on `Context` take the `clean::Crate` and set up some state
+between rendering items or recursing on a module's child items. From here the "page rendering"
+begins, via an enormous `write!()` call in `html/layout.rs`. The parts that actually generate HTML
+from the items and documentation occurs within a series of `std::fmt::Display` implementations and
+functions that pass around a `&mut std::fmt::Formatter`. The top-level implementation that writes
+out the page body is the `impl<'a> fmt::Display for Item<'a>` in `html/render.rs`, which switches
+out to one of several `item_*` functions based on the kind of `Item` being rendered.
+
+Depending on what kind of rendering code you're looking for, you'll probably find it either in
+`html/render.rs` for major items like "what sections should I print for a struct page" or
+`html/format.rs` for smaller component pieces like "how should I print a where clause as part of
+some other item".
+
+Whenever rustdoc comes across an item that should print hand-written documentation alongside, it
+calls out to `html/markdown.rs` which interfaces with the Markdown parser. This is exposed as a
+series of types that wrap a string of Markdown, and implement `fmt::Display` to emit HTML text. It
+takes special care to enable certain features like footnotes and tables and add syntax highlighting
+to Rust code blocks (via `html/highlight.rs`) before running the Markdown parser. There's also a
+function in here (`find_testable_code`) that specifically scans for Rust code blocks so the
+test-runner code can find all the doctests in the crate.
+
+### From soup to nuts
+
+(alternate title: ["An unbroken thread that stretches from those first `Cell`s to us"][video])
+
+[video]: https://www.youtube.com/watch?v=hOLAGYmUQV0
+
+It's important to note that the AST cleaning can ask the compiler for information (crucially,
+`DocContext` contains a `TyCtxt`), but page rendering cannot. The `clean::Crate` created within
+`run_core` is passed outside the compiler context before being handed to `html::render::run`. This
+means that a lot of the "supplementary data" that isn't immediately available inside an item's
+definition, like which trait is the `Deref` trait used by the language, needs to be collected during
+cleaning, stored in the `DocContext`, and passed along to the `SharedContext` during HTML rendering.
+This manifests as a bunch of shared state, context variables, and `RefCell`s.
+
+Also of note is that some items that come from "asking the compiler" don't go directly into the
+`DocContext` - for example, when loading items from a foreign crate, rustdoc will ask about trait
+implementations and generate new `Item`s for the impls based on that information. This goes directly
+into the returned `Crate` rather than roundabout through the `DocContext`. This way, these
+implementations can be collected alongside the others, right before rendering the HTML.
+
+## Other tricks up its sleeve
+
+All this describes the process for generating HTML documentation from a Rust crate, but there are
+couple other major modes that rustdoc runs in. It can also be run on a standalone Markdown file, or
+it can run doctests on Rust code or standalone Markdown files. For the former, it shortcuts straight
+to `html/markdown.rs`, optionally including a mode which inserts a Table of Contents to the output
+HTML.
+
+For the latter, rustdoc runs a similar partial-compilation to get relevant documentation in
+`test.rs`, but instead of going through the full clean and render process, it runs a much simpler
+crate walk to grab *just* the hand-written documentation. Combined with the aforementioned
+"`find_testable_code`" in `html/markdown.rs`, it builds up a collection of tests to run before
+handing them off to the libtest test runner. One notable location in `test.rs` is the function
+`make_test`, which is where hand-written doctests get transformed into something that can be
+executed.
+
+## Dotting i's and crossing t's
+
+So that's rustdoc's code in a nutshell, but there's more things in the repo that deal with it. Since
+we have the full `compiletest` suite at hand, there's a set of tests in `src/test/rustdoc` that make
+sure the final HTML is what we expect in various situations. These tests also use a supplementary
+script, `src/etc/htmldocck.py`, that allows it to look through the final HTML using XPath notation
+to get a precise look at the output. The full description of all the commands available to rustdoc
+tests is in `htmldocck.py`.
+
+In addition, there are separate tests for the search index and rustdoc's ability to query it. The
+files in `src/test/rustdoc-js` each contain a different search query and the expected results,
+broken out by search tab. These files are processed by a script in `src/tools/rustdoc-js` and the
+Node.js runtime. These tests don't have as thorough of a writeup, but a broad example that features
+results in all tabs can be found in `basic.js`. The basic idea is that you match a given `QUERY`
+with a set of `EXPECTED` results, complete with the full item path of each item.

src/libstd/lib.rs

@@ -299,6 +299,7 @@
 #![feature(rand)]
 #![feature(raw)]
 #![feature(rustc_attrs)]
+#![feature(stdsimd)]
 #![feature(sip_hash_13)]
 #![feature(slice_bytes)]
 #![feature(slice_concat_ext)]
@@ -501,6 +502,35 @@ mod memchr;
 // compiler
 pub mod rt;
 
+// Pull in the the `stdsimd` crate directly into libstd. This is the same as
+// libcore's arch/simd modules where the source of truth here is in a different
+// repository, but we pull things in here manually to get it into libstd.
+//
+// Note that the #[cfg] here is intended to do two things. First it allows us to
+// change the rustc implementation of intrinsics in stage0 by not compiling simd
+// intrinsics in stage0. Next it doesn't compile anything in test mode as
+// stdsimd has tons of its own tests which we don't want to run.
+#[path = "../stdsimd/stdsimd/mod.rs"]
+#[allow(missing_debug_implementations, missing_docs, dead_code)]
+#[unstable(feature = "stdsimd", issue = "48556")]
+#[cfg(all(not(stage0), not(test)))]
+mod stdsimd;
+
+// A "fake" module needed by the `stdsimd` module to compile, not actually
+// exported though.
+#[cfg(not(stage0))]
+mod coresimd {
+    pub use core::arch;
+    pub use core::simd;
+}
+
+#[unstable(feature = "stdsimd", issue = "48556")]
+#[cfg(all(not(stage0), not(test)))]
+pub use stdsimd::simd;
+#[unstable(feature = "stdsimd", issue = "48556")]
+#[cfg(all(not(stage0), not(test)))]
+pub use stdsimd::arch;
+
 // Include a number of private modules that exist solely to provide
 // the rustdoc documentation for primitive types. Using `include!`
 // because rustdoc only looks for these modules at the crate level.

src/libstd_unicode/char.rs

@@ -59,7 +59,7 @@ pub use version::UnicodeVersion;
 /// [`to_lowercase`]: ../../std/primitive.char.html#method.to_lowercase
 /// [`char`]: ../../std/primitive.char.html
 #[stable(feature = "rust1", since = "1.0.0")]
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct ToLowercase(CaseMappingIter);
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -81,7 +81,7 @@ impl FusedIterator for ToLowercase {}
 /// [`to_uppercase`]: ../../std/primitive.char.html#method.to_uppercase
 /// [`char`]: ../../std/primitive.char.html
 #[stable(feature = "rust1", since = "1.0.0")]
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct ToUppercase(CaseMappingIter);
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -95,7 +95,7 @@ impl Iterator for ToUppercase {
 #[unstable(feature = "fused", issue = "35602")]
 impl FusedIterator for ToUppercase {}
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 enum CaseMappingIter {
     Three(char, char, char),
     Two(char, char),

src/stdsimd

@@ -0,0 +1 @@
+Subproject commit 678cbd325c84070c9dbe4303969fbd2734c0b4ee

src/tools/tidy/src/lib.rs

@@ -71,6 +71,7 @@ fn filter_dirs(path: &Path) -> bool {
         "src/librustc/mir/interpret",
         "src/librustc_mir/interpret",
         "src/target",
+        "src/stdsimd",
     ];
     skip.iter().any(|p| path.ends_with(p))
 }