Auto merge of #74667 - Manishearth:rollup-s6k59sw, r=Manishearth

Rollup of 8 pull requests

Successful merges:

 - #74141 (libstd/libcore: fix various typos)
 - #74490 (add a Backtrace::disabled function)
 - #74548 (one more Path::with_extension example, to demonstrate behavior)
 - #74587 (Prefer constant over function)
 - #74606 (Remove Linux workarounds for missing CLOEXEC support)
 - #74637 (Make str point to primitive page)
 - #74654 (require type defaults to be after const generic parameters)
 - #74659 (Improve codegen for unchecked float casts on wasm)

Failed merges:

r? @ghost

36 files changed, 266 insertions, 302 deletions

diff --git a/src/liballoc/string.rs b/src/liballoc/string.rs
index 15f10df9a45..f41c8c5a559 100644
--- a/src/liballoc/string.rs
+++ b/src/liballoc/string.rs
@@ -65,7 +65,7 @@ use crate::vec::Vec;
 ///
 /// # Examples
 ///
-/// You can create a `String` from [a literal string][str] with [`String::from`]:
+/// You can create a `String` from [a literal string][`str`] with [`String::from`]:
 ///
 /// [`String::from`]: From::from
 ///
@@ -268,7 +268,8 @@ use crate::vec::Vec;
 ///
 /// Here, there's no need to allocate more memory inside the loop.
 ///
-/// [`&str`]: str
+/// [`str`]: type@str
+/// [`&str`]: type@str
 /// [`Deref`]: core::ops::Deref
 /// [`as_str()`]: String::as_str
 #[derive(PartialOrd, Eq, Ord)]
diff --git a/src/libcore/convert/mod.rs b/src/libcore/convert/mod.rs
index 94f7ff5c1f7..03b798d57db 100644
--- a/src/libcore/convert/mod.rs
+++ b/src/libcore/convert/mod.rs
@@ -677,7 +677,7 @@ impl AsRef<str> for str {
 ///
 ///
 /// However there is one case where `!` syntax can be used
-/// before `!` is stabilized as a full-fleged type: in the position of a function’s return type.
+/// before `!` is stabilized as a full-fledged type: in the position of a function’s return type.
 /// Specifically, it is possible implementations for two different function pointer types:
 ///
 /// ```
diff --git a/src/libcore/hash/sip.rs b/src/libcore/hash/sip.rs
index f2bbf646f32..a9882d54de4 100644
--- a/src/libcore/hash/sip.rs
+++ b/src/libcore/hash/sip.rs
@@ -43,7 +43,7 @@ struct SipHasher24 {
 ///
 /// SipHash is a general-purpose hashing function: it runs at a good
 /// speed (competitive with Spooky and City) and permits strong _keyed_
-/// hashing. This lets you key your hashtables from a strong RNG, such as
+/// hashing. This lets you key your hash tables from a strong RNG, such as
 /// [`rand::os::OsRng`](https://doc.rust-lang.org/rand/rand/os/struct.OsRng.html).
 ///
 /// Although the SipHash algorithm is considered to be generally strong,
diff --git a/src/libcore/intrinsics.rs b/src/libcore/intrinsics.rs
index 049f51fb103..1af4f1009d1 100644
--- a/src/libcore/intrinsics.rs
+++ b/src/libcore/intrinsics.rs
@@ -15,7 +15,7 @@
 //!
 //! If an intrinsic is supposed to be used from a `const fn` with a `rustc_const_stable` attribute,
 //! the intrinsic's attribute must be `rustc_const_stable`, too. Such a change should not be done
-//! without T-lang consulation, because it bakes a feature into the language that cannot be
+//! without T-lang consultation, because it bakes a feature into the language that cannot be
 //! replicated in user code without compiler support.
 //!
 //! # Volatiles
@@ -994,7 +994,7 @@ extern "rust-intrinsic" {
     /// [`std::mem::align_of`](../../std/mem/fn.align_of.html).
     #[rustc_const_stable(feature = "const_min_align_of", since = "1.40.0")]
     pub fn min_align_of<T>() -> usize;
-    /// The prefered alignment of a type.
+    /// The preferred alignment of a type.
     ///
     /// This intrinsic does not have a stable counterpart.
     #[rustc_const_unstable(feature = "const_pref_align_of", issue = "none")]
@@ -1246,14 +1246,14 @@ extern "rust-intrinsic" {
     ///     assert!(mid <= len);
     ///     unsafe {
     ///         let slice2 = mem::transmute::<&mut [T], &mut [T]>(slice);
-    ///         // first: transmute is not typesafe; all it checks is that T and
+    ///         // first: transmute is not type safe; all it checks is that T and
     ///         // U are of the same size. Second, right here, you have two
     ///         // mutable references pointing to the same memory.
     ///         (&mut slice[0..mid], &mut slice2[mid..len])
     ///     }
     /// }
     ///
-    /// // This gets rid of the typesafety problems; `&mut *` will *only* give
+    /// // This gets rid of the type safety problems; `&mut *` will *only* give
     /// // you an `&mut T` from an `&mut T` or `*mut T`.
     /// fn split_at_mut_casts<T>(slice: &mut [T], mid: usize)
     ///                          -> (&mut [T], &mut [T]) {
diff --git a/src/libcore/iter/traits/iterator.rs b/src/libcore/iter/traits/iterator.rs
index b8faeb488e7..3ea3eeed6b0 100644
--- a/src/libcore/iter/traits/iterator.rs
+++ b/src/libcore/iter/traits/iterator.rs
@@ -1069,7 +1069,7 @@ pub trait Iterator {
     /// let vec = iter.collect::<Vec<_>>();
     ///
     /// // We have more elements which could fit in u32 (4, 5), but `map_while` returned `None` for `-3`
-    /// // (as the `predicate` returned `None`) and `collect` stops at the first `None` entcountered.
+    /// // (as the `predicate` returned `None`) and `collect` stops at the first `None` encountered.
     /// assert_eq!(vec, vec![0, 1, 2]);
     /// ```
     ///
diff --git a/src/libcore/macros/mod.rs b/src/libcore/macros/mod.rs
index 4ac366ab164..3b9057b7e83 100644
--- a/src/libcore/macros/mod.rs
+++ b/src/libcore/macros/mod.rs
@@ -1047,7 +1047,7 @@ pub(crate) mod builtin {
         };
     }
 
-    /// Includes a utf8-encoded file as a string.
+    /// Includes a UTF-8 encoded file as a string.
     ///
     /// The file is located relative to the current file (similarly to how
     /// modules are found). The provided path is interpreted in a platform-specific
diff --git a/src/libcore/mem/mod.rs b/src/libcore/mem/mod.rs
index d62de7617a0..6ff7baab70f 100644
--- a/src/libcore/mem/mod.rs
+++ b/src/libcore/mem/mod.rs
@@ -348,11 +348,11 @@ pub fn size_of_val<T: ?Sized>(val: &T) -> usize {
 ///
 /// - If `T` is `Sized`, this function is always safe to call.
 /// - If the unsized tail of `T` is:
-///     - a [slice], then the length of the slice tail must be an intialized
+///     - a [slice], then the length of the slice tail must be an initialized
 ///       integer, and the size of the *entire value*
 ///       (dynamic tail length + statically sized prefix) must fit in `isize`.
 ///     - a [trait object], then the vtable part of the pointer must point
-///       to a valid vtable acquired by an unsizing coersion, and the size
+///       to a valid vtable acquired by an unsizing coercion, and the size
 ///       of the *entire value* (dynamic tail length + statically sized prefix)
 ///       must fit in `isize`.
 ///     - an (unstable) [extern type], then this function is always safe to
@@ -483,11 +483,11 @@ pub fn align_of_val<T: ?Sized>(val: &T) -> usize {
 ///
 /// - If `T` is `Sized`, this function is always safe to call.
 /// - If the unsized tail of `T` is:
-///     - a [slice], then the length of the slice tail must be an intialized
+///     - a [slice], then the length of the slice tail must be an initialized
 ///       integer, and the size of the *entire value*
 ///       (dynamic tail length + statically sized prefix) must fit in `isize`.
 ///     - a [trait object], then the vtable part of the pointer must point
-///       to a valid vtable acquired by an unsizing coersion, and the size
+///       to a valid vtable acquired by an unsizing coercion, and the size
 ///       of the *entire value* (dynamic tail length + statically sized prefix)
 ///       must fit in `isize`.
 ///     - an (unstable) [extern type], then this function is always safe to
diff --git a/src/libcore/num/f64.rs b/src/libcore/num/f64.rs
index bcb6cd40846..a5b1eb3f1fd 100644
--- a/src/libcore/num/f64.rs
+++ b/src/libcore/num/f64.rs
@@ -687,7 +687,7 @@ impl f64 {
     /// signaling NaNs on MIPS are quiet NaNs on x86, and vice-versa.
     ///
     /// Rather than trying to preserve signaling-ness cross-platform, this
-    /// implementation favours preserving the exact bits. This means that
+    /// implementation favors preserving the exact bits. This means that
     /// any payloads encoded in NaNs will be preserved even if the result of
     /// this method is sent over the network from an x86 machine to a MIPS one.
     ///
@@ -696,7 +696,7 @@ impl f64 {
     ///
     /// If the input isn't NaN, then there is no portability concern.
     ///
-    /// If you don't care about signalingness (very likely), then there is no
+    /// If you don't care about signaling-ness (very likely), then there is no
     /// portability concern.
     ///
     /// Note that this function is distinct from `as` casting, which attempts to
diff --git a/src/libcore/pin.rs b/src/libcore/pin.rs
index da299f026f8..9bcacd8ddcf 100644
--- a/src/libcore/pin.rs
+++ b/src/libcore/pin.rs
@@ -128,7 +128,7 @@
 //!
 //! Crucially, we have to be able to rely on [`drop`] being called. If an element
 //! could be deallocated or otherwise invalidated without calling [`drop`], the pointers into it
-//! from its neighbouring elements would become invalid, which would break the data structure.
+//! from its neighboring elements would become invalid, which would break the data structure.
 //!
 //! Therefore, pinning also comes with a [`drop`]-related guarantee.
 //!
diff --git a/src/libcore/ptr/const_ptr.rs b/src/libcore/ptr/const_ptr.rs
index 896ad740e1e..a2acc239bd3 100644
--- a/src/libcore/ptr/const_ptr.rs
+++ b/src/libcore/ptr/const_ptr.rs
@@ -331,13 +331,13 @@ impl<T: ?Sized> *const T {
         intrinsics::ptr_guaranteed_eq(self, other)
     }
 
-    /// Returns whether two pointers are guaranteed to be inequal.
+    /// Returns whether two pointers are guaranteed to be unequal.
     ///
     /// At runtime this function behaves like `self != other`.
     /// However, in some contexts (e.g., compile-time evaluation),
     /// it is not always possible to determine the inequality of two pointers, so this function may
-    /// spuriously return `false` for pointers that later actually turn out to be inequal.
-    /// But when it returns `true`, the pointers are guaranteed to be inequal.
+    /// spuriously return `false` for pointers that later actually turn out to be unequal.
+    /// But when it returns `true`, the pointers are guaranteed to be unequal.
     ///
     /// This function is the mirror of [`guaranteed_eq`], but not its inverse. There are pointer
     /// comparisons for which both functions return `false`.
diff --git a/src/libcore/ptr/mut_ptr.rs b/src/libcore/ptr/mut_ptr.rs
index 915dc3e45f6..17fa90ecc08 100644
--- a/src/libcore/ptr/mut_ptr.rs
+++ b/src/libcore/ptr/mut_ptr.rs
@@ -317,13 +317,13 @@ impl<T: ?Sized> *mut T {
         intrinsics::ptr_guaranteed_eq(self as *const _, other as *const _)
     }
 
-    /// Returns whether two pointers are guaranteed to be inequal.
+    /// Returns whether two pointers are guaranteed to be unequal.
     ///
     /// At runtime this function behaves like `self != other`.
     /// However, in some contexts (e.g., compile-time evaluation),
     /// it is not always possible to determine the inequality of two pointers, so this function may
-    /// spuriously return `false` for pointers that later actually turn out to be inequal.
-    /// But when it returns `true`, the pointers are guaranteed to be inequal.
+    /// spuriously return `false` for pointers that later actually turn out to be unequal.
+    /// But when it returns `true`, the pointers are guaranteed to be unequal.
     ///
     /// This function is the mirror of [`guaranteed_eq`], but not its inverse. There are pointer
     /// comparisons for which both functions return `false`.
diff --git a/src/libcore/ptr/non_null.rs b/src/libcore/ptr/non_null.rs
index b362a49d604..9f843a57099 100644
--- a/src/libcore/ptr/non_null.rs
+++ b/src/libcore/ptr/non_null.rs
@@ -172,7 +172,7 @@ impl<T> NonNull<[T]> {
     /// assert_eq!(unsafe { slice.as_ref()[2] }, 7);
     /// ```
     ///
-    /// (Note that this example artifically demonstrates a use of this method,
+    /// (Note that this example artificially demonstrates a use of this method,
     /// but `let slice = NonNull::from(&x[..]);` would be a better way to write code like this.)
     #[unstable(feature = "nonnull_slice_from_raw_parts", issue = "71941")]
     #[rustc_const_unstable(feature = "const_nonnull_slice_from_raw_parts", issue = "71941")]
diff --git a/src/librustc_ast_passes/ast_validation.rs b/src/librustc_ast_passes/ast_validation.rs
index 975881d9a0a..daf3e23d6a1 100644
--- a/src/librustc_ast_passes/ast_validation.rs
+++ b/src/librustc_ast_passes/ast_validation.rs
@@ -1118,13 +1118,26 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
     fn visit_generics(&mut self, generics: &'a Generics) {
         let mut prev_ty_default = None;
         for param in &generics.params {
-            if let GenericParamKind::Type { ref default, .. } = param.kind {
-                if default.is_some() {
+            match param.kind {
+                GenericParamKind::Lifetime => (),
+                GenericParamKind::Type { default: Some(_), .. } => {
                     prev_ty_default = Some(param.ident.span);
-                } else if let Some(span) = prev_ty_default {
-                    self.err_handler()
-                        .span_err(span, "type parameters with a default must be trailing");
-                    break;
+                }
+                GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
+                    if let Some(span) = prev_ty_default {
+                        let mut err = self.err_handler().struct_span_err(
+                            span,
+                            "type parameters with a default must be trailing",
+                        );
+                        if matches!(param.kind, GenericParamKind::Const { .. }) {
+                            err.note(
+                                "using type defaults and const parameters \
+                                 in the same parameter list is currently not permitted",
+                            );
+                        }
+                        err.emit();
+                        break;
+                    }
                 }
             }
         }
diff --git a/src/librustc_codegen_llvm/context.rs b/src/librustc_codegen_llvm/context.rs
index a07f6c64edc..33a3cdbfa9b 100644
--- a/src/librustc_codegen_llvm/context.rs
+++ b/src/librustc_codegen_llvm/context.rs
@@ -510,6 +510,14 @@ impl CodegenCx<'b, 'tcx> {
         ifn!("llvm.wasm.trunc.saturate.signed.i32.f64", fn(t_f64) -> t_i32);
         ifn!("llvm.wasm.trunc.saturate.signed.i64.f32", fn(t_f32) -> t_i64);
         ifn!("llvm.wasm.trunc.saturate.signed.i64.f64", fn(t_f64) -> t_i64);
+        ifn!("llvm.wasm.trunc.unsigned.i32.f32", fn(t_f32) -> t_i32);
+        ifn!("llvm.wasm.trunc.unsigned.i32.f64", fn(t_f64) -> t_i32);
+        ifn!("llvm.wasm.trunc.unsigned.i64.f32", fn(t_f32) -> t_i64);
+        ifn!("llvm.wasm.trunc.unsigned.i64.f64", fn(t_f64) -> t_i64);
+        ifn!("llvm.wasm.trunc.signed.i32.f32", fn(t_f32) -> t_i32);
+        ifn!("llvm.wasm.trunc.signed.i32.f64", fn(t_f64) -> t_i32);
+        ifn!("llvm.wasm.trunc.signed.i64.f32", fn(t_f32) -> t_i64);
+        ifn!("llvm.wasm.trunc.signed.i64.f64", fn(t_f64) -> t_i64);
 
         ifn!("llvm.trap", fn() -> void);
         ifn!("llvm.debugtrap", fn() -> void);
diff --git a/src/librustc_codegen_llvm/intrinsic.rs b/src/librustc_codegen_llvm/intrinsic.rs
index 2e5929a433d..11b1c95c58b 100644
--- a/src/librustc_codegen_llvm/intrinsic.rs
+++ b/src/librustc_codegen_llvm/intrinsic.rs
@@ -629,27 +629,24 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
             }
 
             sym::float_to_int_unchecked => {
-                if float_type_width(arg_tys[0]).is_none() {
-                    span_invalid_monomorphization_error(
-                        tcx.sess,
-                        span,
-                        &format!(
-                            "invalid monomorphization of `float_to_int_unchecked` \
+                let float_width = match float_type_width(arg_tys[0]) {
+                    Some(width) => width,
+                    None => {
+                        span_invalid_monomorphization_error(
+                            tcx.sess,
+                            span,
+                            &format!(
+                                "invalid monomorphization of `float_to_int_unchecked` \
                                   intrinsic: expected basic float type, \
                                   found `{}`",
-                            arg_tys[0]
-                        ),
-                    );
-                    return;
-                }
-                match int_type_width_signed(ret_ty, self.cx) {
-                    Some((width, signed)) => {
-                        if signed {
-                            self.fptosi(args[0].immediate(), self.cx.type_ix(width))
-                        } else {
-                            self.fptoui(args[0].immediate(), self.cx.type_ix(width))
-                        }
+                                arg_tys[0]
+                            ),
+                        );
+                        return;
                     }
+                };
+                let (width, signed) = match int_type_width_signed(ret_ty, self.cx) {
+                    Some(pair) => pair,
                     None => {
                         span_invalid_monomorphization_error(
                             tcx.sess,
@@ -663,7 +660,49 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
                         );
                         return;
                     }
+                };
+
+                // The LLVM backend can reorder and speculate `fptosi` and
+                // `fptoui`, so on WebAssembly the codegen for this instruction
+                // is quite heavyweight. To avoid this heavyweight codegen we
+                // instead use the raw wasm intrinsics which will lower to one
+                // instruction in WebAssembly (`iNN.trunc_fMM_{s,u}`). This one
+                // instruction will trap if the operand is out of bounds, but
+                // that's ok since this intrinsic is UB if the operands are out
+                // of bounds, so the behavior can be different on WebAssembly
+                // than other targets.
+                //
+                // Note, however, that when the `nontrapping-fptoint` feature is
+                // enabled in LLVM then LLVM will lower `fptosi` to
+                // `iNN.trunc_sat_fMM_{s,u}`, so if that's the case we don't
+                // bother with intrinsics.
+                let mut result = None;
+                if self.sess().target.target.arch == "wasm32"
+                    && !self.sess().target_features.contains(&sym::nontrapping_dash_fptoint)
+                {
+                    let name = match (width, float_width, signed) {
+                        (32, 32, true) => Some("llvm.wasm.trunc.signed.i32.f32"),
+                        (32, 64, true) => Some("llvm.wasm.trunc.signed.i32.f64"),
+                        (64, 32, true) => Some("llvm.wasm.trunc.signed.i64.f32"),
+                        (64, 64, true) => Some("llvm.wasm.trunc.signed.i64.f64"),
+                        (32, 32, false) => Some("llvm.wasm.trunc.unsigned.i32.f32"),
+                        (32, 64, false) => Some("llvm.wasm.trunc.unsigned.i32.f64"),
+                        (64, 32, false) => Some("llvm.wasm.trunc.unsigned.i64.f32"),
+                        (64, 64, false) => Some("llvm.wasm.trunc.unsigned.i64.f64"),
+                        _ => None,
+                    };
+                    if let Some(name) = name {
+                        let intrinsic = self.get_intrinsic(name);
+                        result = Some(self.call(intrinsic, &[args[0].immediate()], None));
+                    }
                 }
+                result.unwrap_or_else(|| {
+                    if signed {
+                        self.fptosi(args[0].immediate(), self.cx.type_ix(width))
+                    } else {
+                        self.fptoui(args[0].immediate(), self.cx.type_ix(width))
+                    }
+                })
             }
 
             sym::discriminant_value => {
diff --git a/src/libstd/backtrace.rs b/src/libstd/backtrace.rs
index e65775c1ced..09f83ea5fca 100644
--- a/src/libstd/backtrace.rs
+++ b/src/libstd/backtrace.rs
@@ -291,6 +291,12 @@ impl Backtrace {
         Backtrace::create(Backtrace::force_capture as usize)
     }
 
+    /// Forcibly captures a disabled backtrace, regardless of environment
+    /// variable configuration.
+    pub const fn disabled() -> Backtrace {
+        Backtrace { inner: Inner::Disabled }
+    }
+
     // Capture a backtrace which start just before the function addressed by
     // `ip`
     fn create(ip: usize) -> Backtrace {
diff --git a/src/libstd/f32.rs b/src/libstd/f32.rs
index b392d6e7226..c905bcf5e3d 100644
--- a/src/libstd/f32.rs
+++ b/src/libstd/f32.rs
@@ -1500,7 +1500,7 @@ mod tests {
         assert_approx_eq!(f32::from_bits(0x44a72000), 1337.0);
         assert_approx_eq!(f32::from_bits(0xc1640000), -14.25);
 
-        // Check that NaNs roundtrip their bits regardless of signalingness
+        // Check that NaNs roundtrip their bits regardless of signaling-ness
         // 0xA is 0b1010; 0x5 is 0b0101 -- so these two together clobbers all the mantissa bits
         let masked_nan1 = f32::NAN.to_bits() ^ 0x002A_AAAA;
         let masked_nan2 = f32::NAN.to_bits() ^ 0x0055_5555;
diff --git a/src/libstd/f64.rs b/src/libstd/f64.rs
index 72268d2cc2f..f09fc8d790b 100644
--- a/src/libstd/f64.rs
+++ b/src/libstd/f64.rs
@@ -1523,7 +1523,7 @@ mod tests {
         assert_approx_eq!(f64::from_bits(0x4094e40000000000), 1337.0);
         assert_approx_eq!(f64::from_bits(0xc02c800000000000), -14.25);
 
-        // Check that NaNs roundtrip their bits regardless of signalingness
+        // Check that NaNs roundtrip their bits regardless of signaling-ness
         // 0xA is 0b1010; 0x5 is 0b0101 -- so these two together clobbers all the mantissa bits
         let masked_nan1 = f64::NAN.to_bits() ^ 0x000A_AAAA_AAAA_AAAA;
         let masked_nan2 = f64::NAN.to_bits() ^ 0x0005_5555_5555_5555;
diff --git a/src/libstd/os/linux/fs.rs b/src/libstd/os/linux/fs.rs
index d22b44a0666..657737394ab 100644
--- a/src/libstd/os/linux/fs.rs
+++ b/src/libstd/os/linux/fs.rs
@@ -285,7 +285,7 @@ pub trait MetadataExt {
     /// ```
     #[stable(feature = "metadata_ext2", since = "1.8.0")]
     fn st_ctime_nsec(&self) -> i64;
-    /// Returns the "preferred" blocksize for efficient filesystem I/O.
+    /// Returns the "preferred" block size for efficient filesystem I/O.
     ///
     /// # Examples
     ///
diff --git a/src/libstd/os/redox/fs.rs b/src/libstd/os/redox/fs.rs
index 6c87df534bd..61b5bff3805 100644
--- a/src/libstd/os/redox/fs.rs
+++ b/src/libstd/os/redox/fs.rs
@@ -289,7 +289,7 @@ pub trait MetadataExt {
     /// ```
     #[stable(feature = "metadata_ext2", since = "1.8.0")]
     fn st_ctime_nsec(&self) -> i64;
-    /// Returns the "preferred" blocksize for efficient filesystem I/O.
+    /// Returns the "preferred" block size for efficient filesystem I/O.
     ///
     /// # Examples
     ///
diff --git a/src/libstd/path.rs b/src/libstd/path.rs
index f14a9ff72f6..392c815ef28 100644
--- a/src/libstd/path.rs
+++ b/src/libstd/path.rs
@@ -2244,6 +2244,9 @@ impl Path {
     ///
     /// let path = Path::new("foo.rs");
     /// assert_eq!(path.with_extension("txt"), PathBuf::from("foo.txt"));
+    ///
+    /// let path = Path::new("foo.tar.gz");
+    /// assert_eq!(path.with_extension(""), PathBuf::from("foo.tar"));
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn with_extension<S: AsRef<OsStr>>(&self, extension: S) -> PathBuf {
diff --git a/src/libstd/sys/sgx/fd.rs b/src/libstd/sys/sgx/fd.rs
index 90158030c7f..e5dc5b5adaa 100644
--- a/src/libstd/sys/sgx/fd.rs
+++ b/src/libstd/sys/sgx/fd.rs
@@ -19,7 +19,7 @@ impl FileDesc {
         self.fd
     }
 
-    /// Extracts the actual filedescriptor without closing it.
+    /// Extracts the actual file descriptor without closing it.
     pub fn into_raw(self) -> Fd {
         let fd = self.fd;
         mem::forget(self);
diff --git a/src/libstd/sys/unix/ext/fs.rs b/src/libstd/sys/unix/ext/fs.rs
index 2b2bbc6e9d6..f174a59b49a 100644
--- a/src/libstd/sys/unix/ext/fs.rs
+++ b/src/libstd/sys/unix/ext/fs.rs
@@ -624,7 +624,7 @@ pub trait MetadataExt {
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn ctime_nsec(&self) -> i64;
-    /// Returns the blocksize for filesystem I/O.
+    /// Returns the block size for filesystem I/O.
     ///
     /// # Examples
     ///
@@ -635,7 +635,7 @@ pub trait MetadataExt {
     ///
     /// fn main() -> io::Result<()> {
     ///     let meta = fs::metadata("some_file")?;
-    ///     let blocksize = meta.blksize();
+    ///     let block_size = meta.blksize();
     ///     Ok(())
     /// }
     /// ```
diff --git a/src/libstd/sys/unix/fd.rs b/src/libstd/sys/unix/fd.rs
index c481ca8961f..84c4d662161 100644
--- a/src/libstd/sys/unix/fd.rs
+++ b/src/libstd/sys/unix/fd.rs
@@ -3,28 +3,28 @@
 use crate::cmp;
 use crate::io::{self, Initializer, IoSlice, IoSliceMut, Read};
 use crate::mem;
-use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sys::cvt;
 use crate::sys_common::AsInner;
 
-use libc::{c_int, c_void, ssize_t};
+use libc::{c_int, c_void};
 
 #[derive(Debug)]
 pub struct FileDesc {
     fd: c_int,
 }
 
-fn max_len() -> usize {
-    // The maximum read limit on most posix-like systems is `SSIZE_MAX`,
-    // with the man page quoting that if the count of bytes to read is
-    // greater than `SSIZE_MAX` the result is "unspecified".
-    //
-    // On macOS, however, apparently the 64-bit libc is either buggy or
-    // intentionally showing odd behavior by rejecting any read with a size
-    // larger than or equal to INT_MAX. To handle both of these the read
-    // size is capped on both platforms.
-    if cfg!(target_os = "macos") { <c_int>::MAX as usize - 1 } else { <ssize_t>::MAX as usize }
-}
+// The maximum read limit on most POSIX-like systems is `SSIZE_MAX`,
+// with the man page quoting that if the count of bytes to read is
+// greater than `SSIZE_MAX` the result is "unspecified".
+//
+// On macOS, however, apparently the 64-bit libc is either buggy or
+// intentionally showing odd behavior by rejecting any read with a size
+// larger than or equal to INT_MAX. To handle both of these the read
+// size is capped on both platforms.
+#[cfg(target_os = "macos")]
+const READ_LIMIT: usize = c_int::MAX as usize - 1;
+#[cfg(not(target_os = "macos"))]
+const READ_LIMIT: usize = libc::ssize_t::MAX as usize;
 
 impl FileDesc {
     pub fn new(fd: c_int) -> FileDesc {
@@ -44,7 +44,7 @@ impl FileDesc {
 
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
         let ret = cvt(unsafe {
-            libc::read(self.fd, buf.as_mut_ptr() as *mut c_void, cmp::min(buf.len(), max_len()))
+            libc::read(self.fd, buf.as_mut_ptr() as *mut c_void, cmp::min(buf.len(), READ_LIMIT))
         })?;
         Ok(ret as usize)
     }
@@ -92,7 +92,7 @@ impl FileDesc {
             cvt_pread64(
                 self.fd,
                 buf.as_mut_ptr() as *mut c_void,
-                cmp::min(buf.len(), max_len()),
+                cmp::min(buf.len(), READ_LIMIT),
                 offset as i64,
             )
             .map(|n| n as usize)
@@ -101,7 +101,7 @@ impl FileDesc {
 
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         let ret = cvt(unsafe {
-            libc::write(self.fd, buf.as_ptr() as *const c_void, cmp::min(buf.len(), max_len()))
+            libc::write(self.fd, buf.as_ptr() as *const c_void, cmp::min(buf.len(), READ_LIMIT))
         })?;
         Ok(ret as usize)
     }
@@ -144,7 +144,7 @@ impl FileDesc {
             cvt_pwrite64(
                 self.fd,
                 buf.as_ptr() as *const c_void,
-                cmp::min(buf.len(), max_len()),
+                cmp::min(buf.len(), READ_LIMIT),
                 offset as i64,
             )
             .map(|n| n as usize)
@@ -223,50 +223,9 @@ impl FileDesc {
     pub fn duplicate(&self) -> io::Result<FileDesc> {
         // We want to atomically duplicate this file descriptor and set the
         // CLOEXEC flag, and currently that's done via F_DUPFD_CLOEXEC. This
-        // flag, however, isn't supported on older Linux kernels (earlier than
-        // 2.6.24).
-        //
-        // To detect this and ensure that CLOEXEC is still set, we
-        // follow a strategy similar to musl [1] where if passing
-        // F_DUPFD_CLOEXEC causes `fcntl` to return EINVAL it means it's not
-        // supported (the third parameter, 0, is always valid), so we stop
-        // trying that.
-        //
-        // Also note that Android doesn't have F_DUPFD_CLOEXEC, but get it to
-        // resolve so we at least compile this.
-        //
-        // [1]: http://comments.gmane.org/gmane.linux.lib.musl.general/2963
-        #[cfg(any(target_os = "android", target_os = "haiku"))]
-        use libc::F_DUPFD as F_DUPFD_CLOEXEC;
-        #[cfg(not(any(target_os = "android", target_os = "haiku")))]
-        use libc::F_DUPFD_CLOEXEC;
-
-        let make_filedesc = |fd| {
-            let fd = FileDesc::new(fd);
-            fd.set_cloexec()?;
-            Ok(fd)
-        };
-        static TRY_CLOEXEC: AtomicBool = AtomicBool::new(!cfg!(target_os = "android"));
-        let fd = self.raw();
-        if TRY_CLOEXEC.load(Ordering::Relaxed) {
-            match cvt(unsafe { libc::fcntl(fd, F_DUPFD_CLOEXEC, 0) }) {
-                // We *still* call the `set_cloexec` method as apparently some
-                // linux kernel at some point stopped setting CLOEXEC even
-                // though it reported doing so on F_DUPFD_CLOEXEC.
-                Ok(fd) => {
-                    return Ok(if cfg!(target_os = "linux") {
-                        make_filedesc(fd)?
-                    } else {
-                        FileDesc::new(fd)
-                    });
-                }
-                Err(ref e) if e.raw_os_error() == Some(libc::EINVAL) => {
-                    TRY_CLOEXEC.store(false, Ordering::Relaxed);
-                }
-                Err(e) => return Err(e),
-            }
-        }
-        cvt(unsafe { libc::fcntl(fd, libc::F_DUPFD, 0) }).and_then(make_filedesc)
+        // is a POSIX flag that was added to Linux in 2.6.24.
+        let fd = cvt(unsafe { libc::fcntl(self.raw(), libc::F_DUPFD_CLOEXEC, 0) })?;
+        Ok(FileDesc::new(fd))
     }
 }
 
diff --git a/src/libstd/sys/unix/fs.rs b/src/libstd/sys/unix/fs.rs
index 29cdbf05354..acb18e6d064 100644
--- a/src/libstd/sys/unix/fs.rs
+++ b/src/libstd/sys/unix/fs.rs
@@ -708,56 +708,7 @@ impl File {
         // However, since this is a variadic function, C integer promotion rules mean that on
         // the ABI level, this still gets passed as `c_int` (aka `u32` on Unix platforms).
         let fd = cvt_r(|| unsafe { open64(path.as_ptr(), flags, opts.mode as c_int) })?;
-        let fd = FileDesc::new(fd);
-
-        // Currently the standard library supports Linux 2.6.18 which did not
-        // have the O_CLOEXEC flag (passed above). If we're running on an older
-        // Linux kernel then the flag is just ignored by the OS. After we open
-        // the first file, we check whether it has CLOEXEC set. If it doesn't,
-        // we will explicitly ask for a CLOEXEC fd for every further file we
-        // open, if it does, we will skip that step.
-        //
-        // The CLOEXEC flag, however, is supported on versions of macOS/BSD/etc
-        // that we support, so we only do this on Linux currently.
-        #[cfg(target_os = "linux")]
-        fn ensure_cloexec(fd: &FileDesc) -> io::Result<()> {
-            use crate::sync::atomic::{AtomicUsize, Ordering};
-
-            const OPEN_CLOEXEC_UNKNOWN: usize = 0;
-            const OPEN_CLOEXEC_SUPPORTED: usize = 1;
-            const OPEN_CLOEXEC_NOTSUPPORTED: usize = 2;
-            static OPEN_CLOEXEC: AtomicUsize = AtomicUsize::new(OPEN_CLOEXEC_UNKNOWN);
-
-            let need_to_set;
-            match OPEN_CLOEXEC.load(Ordering::Relaxed) {
-                OPEN_CLOEXEC_UNKNOWN => {
-                    need_to_set = !fd.get_cloexec()?;
-                    OPEN_CLOEXEC.store(
-                        if need_to_set {
-                            OPEN_CLOEXEC_NOTSUPPORTED
-                        } else {
-                            OPEN_CLOEXEC_SUPPORTED
-                        },
-                        Ordering::Relaxed,
-                    );
-                }
-                OPEN_CLOEXEC_SUPPORTED => need_to_set = false,
-                OPEN_CLOEXEC_NOTSUPPORTED => need_to_set = true,
-                _ => unreachable!(),
-            }
-            if need_to_set {
-                fd.set_cloexec()?;
-            }
-            Ok(())
-        }
-
-        #[cfg(not(target_os = "linux"))]
-        fn ensure_cloexec(_: &FileDesc) -> io::Result<()> {
-            Ok(())
-        }
-
-        ensure_cloexec(&fd)?;
-        Ok(File(fd))
+        Ok(File(FileDesc::new(fd)))
     }
 
     pub fn file_attr(&self) -> io::Result<FileAttr> {
diff --git a/src/libstd/sys/unix/net.rs b/src/libstd/sys/unix/net.rs
index 3717c660b57..011325fddc5 100644
--- a/src/libstd/sys/unix/net.rs
+++ b/src/libstd/sys/unix/net.rs
@@ -54,31 +54,26 @@ impl Socket {
 
     pub fn new_raw(fam: c_int, ty: c_int) -> io::Result<Socket> {
         unsafe {
-            // On linux we first attempt to pass the SOCK_CLOEXEC flag to
-            // atomically create the socket and set it as CLOEXEC. Support for
-            // this option, however, was added in 2.6.27, and we still support
-            // 2.6.18 as a kernel, so if the returned error is EINVAL we
-            // fallthrough to the fallback.
-            #[cfg(target_os = "linux")]
-            {
-                match cvt(libc::socket(fam, ty | libc::SOCK_CLOEXEC, 0)) {
-                    Ok(fd) => return Ok(Socket(FileDesc::new(fd))),
-                    Err(ref e) if e.raw_os_error() == Some(libc::EINVAL) => {}
-                    Err(e) => return Err(e),
-                }
-            }
-
-            let fd = cvt(libc::socket(fam, ty, 0))?;
-            let fd = FileDesc::new(fd);
-            fd.set_cloexec()?;
-            let socket = Socket(fd);
+            cfg_if::cfg_if! {
+                if #[cfg(target_os = "linux")] {
+                    // On Linux we pass the SOCK_CLOEXEC flag to atomically create
+                    // the socket and set it as CLOEXEC, added in 2.6.27.
+                    let fd = cvt(libc::socket(fam, ty | libc::SOCK_CLOEXEC, 0))?;
+                    Ok(Socket(FileDesc::new(fd)))
+                } else {
+                    let fd = cvt(libc::socket(fam, ty, 0))?;
+                    let fd = FileDesc::new(fd);
+                    fd.set_cloexec()?;
+                    let socket = Socket(fd);
 
-            // macOS and iOS use `SO_NOSIGPIPE` as a `setsockopt`
-            // flag to disable `SIGPIPE` emission on socket.
-            #[cfg(target_vendor = "apple")]
-            setsockopt(&socket, libc::SOL_SOCKET, libc::SO_NOSIGPIPE, 1)?;
+                    // macOS and iOS use `SO_NOSIGPIPE` as a `setsockopt`
+                    // flag to disable `SIGPIPE` emission on socket.
+                    #[cfg(target_vendor = "apple")]
+                    setsockopt(&socket, libc::SOL_SOCKET, libc::SO_NOSIGPIPE, 1)?;
 
-            Ok(socket)
+                    Ok(socket)
+                }
+            }
         }
     }
 
@@ -86,24 +81,20 @@ impl Socket {
         unsafe {
             let mut fds = [0, 0];
 
-            // Like above, see if we can set cloexec atomically
-            #[cfg(target_os = "linux")]
-            {
-                match cvt(libc::socketpair(fam, ty | libc::SOCK_CLOEXEC, 0, fds.as_mut_ptr())) {
-                    Ok(_) => {
-                        return Ok((Socket(FileDesc::new(fds[0])), Socket(FileDesc::new(fds[1]))));
-                    }
-                    Err(ref e) if e.raw_os_error() == Some(libc::EINVAL) => {}
-                    Err(e) => return Err(e),
+            cfg_if::cfg_if! {
+                if #[cfg(target_os = "linux")] {
+                    // Like above, set cloexec atomically
+                    cvt(libc::socketpair(fam, ty | libc::SOCK_CLOEXEC, 0, fds.as_mut_ptr()))?;
+                    Ok((Socket(FileDesc::new(fds[0])), Socket(FileDesc::new(fds[1]))))
+                } else {
+                    cvt(libc::socketpair(fam, ty, 0, fds.as_mut_ptr()))?;
+                    let a = FileDesc::new(fds[0]);
+                    let b = FileDesc::new(fds[1]);
+                    a.set_cloexec()?;
+                    b.set_cloexec()?;
+                    Ok((Socket(a), Socket(b)))
                 }
             }
-
-            cvt(libc::socketpair(fam, ty, 0, fds.as_mut_ptr()))?;
-            let a = FileDesc::new(fds[0]);
-            let b = FileDesc::new(fds[1]);
-            a.set_cloexec()?;
-            b.set_cloexec()?;
-            Ok((Socket(a), Socket(b)))
         }
     }
 
@@ -177,30 +168,20 @@ impl Socket {
     pub fn accept(&self, storage: *mut sockaddr, len: *mut socklen_t) -> io::Result<Socket> {
         // Unfortunately the only known way right now to accept a socket and
         // atomically set the CLOEXEC flag is to use the `accept4` syscall on
-        // Linux. This was added in 2.6.28, however, and because we support
-        // 2.6.18 we must detect this support dynamically.
-        #[cfg(target_os = "linux")]
-        {
-            syscall! {
-                fn accept4(
-                    fd: c_int,
-                    addr: *mut sockaddr,
-                    addr_len: *mut socklen_t,
-                    flags: c_int
-                ) -> c_int
-            }
-            let res = cvt_r(|| unsafe { accept4(self.0.raw(), storage, len, libc::SOCK_CLOEXEC) });
-            match res {
-                Ok(fd) => return Ok(Socket(FileDesc::new(fd))),
-                Err(ref e) if e.raw_os_error() == Some(libc::ENOSYS) => {}
-                Err(e) => return Err(e),
+        // Linux. This was added in 2.6.28, glibc 2.10 and musl 0.9.5.
+        cfg_if::cfg_if! {
+            if #[cfg(target_os = "linux")] {
+                let fd = cvt_r(|| unsafe {
+                    libc::accept4(self.0.raw(), storage, len, libc::SOCK_CLOEXEC)
+                })?;
+                Ok(Socket(FileDesc::new(fd)))
+            } else {
+                let fd = cvt_r(|| unsafe { libc::accept(self.0.raw(), storage, len) })?;
+                let fd = FileDesc::new(fd);
+                fd.set_cloexec()?;
+                Ok(Socket(fd))
             }
         }
-
-        let fd = cvt_r(|| unsafe { libc::accept(self.0.raw(), storage, len) })?;
-        let fd = FileDesc::new(fd);
-        fd.set_cloexec()?;
-        Ok(Socket(fd))
     }
 
     pub fn duplicate(&self) -> io::Result<Socket> {
diff --git a/src/libstd/sys/unix/os.rs b/src/libstd/sys/unix/os.rs
index a9cd5094997..2fcb5b9c4e6 100644
--- a/src/libstd/sys/unix/os.rs
+++ b/src/libstd/sys/unix/os.rs
@@ -71,6 +71,7 @@ pub fn errno() -> i32 {
 
 /// Sets the platform-specific value of errno
 #[cfg(all(not(target_os = "linux"), not(target_os = "dragonfly")))] // needed for readdir and syscall!
+#[allow(dead_code)] // but not all target cfgs actually end up using it
 pub fn set_errno(e: i32) {
     unsafe { *errno_location() = e as c_int }
 }
diff --git a/src/libstd/sys/unix/pipe.rs b/src/libstd/sys/unix/pipe.rs
index f2a2eabef91..7ae37bdda70 100644
--- a/src/libstd/sys/unix/pipe.rs
+++ b/src/libstd/sys/unix/pipe.rs
@@ -1,11 +1,8 @@
 use crate::io::{self, IoSlice, IoSliceMut};
 use crate::mem;
-use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sys::fd::FileDesc;
 use crate::sys::{cvt, cvt_r};
 
-use libc::c_int;
-
 ////////////////////////////////////////////////////////////////////////////////
 // Anonymous pipes
 ////////////////////////////////////////////////////////////////////////////////
@@ -13,46 +10,32 @@ use libc::c_int;
 pub struct AnonPipe(FileDesc);
 
 pub fn anon_pipe() -> io::Result<(AnonPipe, AnonPipe)> {
-    syscall! { fn pipe2(fds: *mut c_int, flags: c_int) -> c_int }
-    static INVALID: AtomicBool = AtomicBool::new(false);
-
     let mut fds = [0; 2];
 
-    // Unfortunately the only known way right now to create atomically set the
-    // CLOEXEC flag is to use the `pipe2` syscall on Linux. This was added in
-    // 2.6.27, however, and because we support 2.6.18 we must detect this
-    // support dynamically.
-    if cfg!(any(
-        target_os = "dragonfly",
-        target_os = "freebsd",
-        target_os = "linux",
-        target_os = "netbsd",
-        target_os = "openbsd",
-        target_os = "redox"
-    )) && !INVALID.load(Ordering::SeqCst)
-    {
-        // Note that despite calling a glibc function here we may still
-        // get ENOSYS. Glibc has `pipe2` since 2.9 and doesn't try to
-        // emulate on older kernels, so if you happen to be running on
-        // an older kernel you may see `pipe2` as a symbol but still not
-        // see the syscall.
-        match cvt(unsafe { pipe2(fds.as_mut_ptr(), libc::O_CLOEXEC) }) {
-            Ok(_) => {
-                return Ok((AnonPipe(FileDesc::new(fds[0])), AnonPipe(FileDesc::new(fds[1]))));
-            }
-            Err(ref e) if e.raw_os_error() == Some(libc::ENOSYS) => {
-                INVALID.store(true, Ordering::SeqCst);
-            }
-            Err(e) => return Err(e),
+    // The only known way right now to create atomically set the CLOEXEC flag is
+    // to use the `pipe2` syscall. This was added to Linux in 2.6.27, glibc 2.9
+    // and musl 0.9.3, and some other targets also have it.
+    cfg_if::cfg_if! {
+        if #[cfg(any(
+            target_os = "dragonfly",
+            target_os = "freebsd",
+            target_os = "linux",
+            target_os = "netbsd",
+            target_os = "openbsd",
+            target_os = "redox"
+        ))] {
+            cvt(unsafe { libc::pipe2(fds.as_mut_ptr(), libc::O_CLOEXEC) })?;
+            Ok((AnonPipe(FileDesc::new(fds[0])), AnonPipe(FileDesc::new(fds[1]))))
+        } else {
+            cvt(unsafe { libc::pipe(fds.as_mut_ptr()) })?;
+
+            let fd0 = FileDesc::new(fds[0]);
+            let fd1 = FileDesc::new(fds[1]);
+            fd0.set_cloexec()?;
+            fd1.set_cloexec()?;
+            Ok((AnonPipe(fd0), AnonPipe(fd1)))
         }
     }
-    cvt(unsafe { libc::pipe(fds.as_mut_ptr()) })?;
-
-    let fd0 = FileDesc::new(fds[0]);
-    let fd1 = FileDesc::new(fds[1]);
-    fd0.set_cloexec()?;
-    fd1.set_cloexec()?;
-    Ok((AnonPipe(fd0), AnonPipe(fd1)))
 }
 
 impl AnonPipe {
diff --git a/src/libstd/sys/unix/weak.rs b/src/libstd/sys/unix/weak.rs
index 08cbe596174..f4b33a00f7c 100644
--- a/src/libstd/sys/unix/weak.rs
+++ b/src/libstd/sys/unix/weak.rs
@@ -16,6 +16,11 @@
 //! symbol, but that caused Debian to detect an unnecessarily strict versioned
 //! dependency on libc6 (#23628).
 
+// There are a variety of `#[cfg]`s controlling which targets are involved in
+// each instance of `weak!` and `syscall!`. Rather than trying to unify all of
+// that, we'll just allow that some unix targets don't use this module at all.
+#![allow(dead_code, unused_macros)]
+
 use crate::ffi::CStr;
 use crate::marker;
 use crate::mem;
diff --git a/src/libstd/sys/vxworks/fd.rs b/src/libstd/sys/vxworks/fd.rs
index 7fa86f0db04..ea186846929 100644
--- a/src/libstd/sys/vxworks/fd.rs
+++ b/src/libstd/sys/vxworks/fd.rs
@@ -13,12 +13,10 @@ pub struct FileDesc {
     fd: c_int,
 }
 
-fn max_len() -> usize {
-    // The maximum read limit on most posix-like systems is `SSIZE_MAX`,
-    // with the man page quoting that if the count of bytes to read is
-    // greater than `SSIZE_MAX` the result is "unspecified".
-    <ssize_t>::MAX as usize
-}
+// The maximum read limit on most POSIX-like systems is `SSIZE_MAX`,
+// with the man page quoting that if the count of bytes to read is
+// greater than `SSIZE_MAX` the result is "unspecified".
+const READ_LIMIT: usize = ssize_t::MAX as usize;
 
 impl FileDesc {
     pub fn new(fd: c_int) -> FileDesc {
@@ -29,7 +27,7 @@ impl FileDesc {
         self.fd
     }
 
-    /// Extracts the actual filedescriptor without closing it.
+    /// Extracts the actual file descriptor without closing it.
     pub fn into_raw(self) -> c_int {
         let fd = self.fd;
         mem::forget(self);
@@ -38,7 +36,7 @@ impl FileDesc {
 
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
         let ret = cvt(unsafe {
-            libc::read(self.fd, buf.as_mut_ptr() as *mut c_void, cmp::min(buf.len(), max_len()))
+            libc::read(self.fd, buf.as_mut_ptr() as *mut c_void, cmp::min(buf.len(), READ_LIMIT))
         })?;
         Ok(ret as usize)
     }
@@ -79,7 +77,7 @@ impl FileDesc {
             cvt_pread(
                 self.fd,
                 buf.as_mut_ptr() as *mut c_void,
-                cmp::min(buf.len(), max_len()),
+                cmp::min(buf.len(), READ_LIMIT),
                 offset as i64,
             )
             .map(|n| n as usize)
@@ -88,7 +86,7 @@ impl FileDesc {
 
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         let ret = cvt(unsafe {
-            libc::write(self.fd, buf.as_ptr() as *const c_void, cmp::min(buf.len(), max_len()))
+            libc::write(self.fd, buf.as_ptr() as *const c_void, cmp::min(buf.len(), READ_LIMIT))
         })?;
         Ok(ret as usize)
     }
@@ -124,7 +122,7 @@ impl FileDesc {
             cvt_pwrite(
                 self.fd,
                 buf.as_ptr() as *const c_void,
-                cmp::min(buf.len(), max_len()),
+                cmp::min(buf.len(), READ_LIMIT),
                 offset as i64,
             )
             .map(|n| n as usize)
diff --git a/src/libstd/sys/vxworks/time.rs b/src/libstd/sys/vxworks/time.rs
index 8365c9ee9c9..8f46f4d284f 100644
--- a/src/libstd/sys/vxworks/time.rs
+++ b/src/libstd/sys/vxworks/time.rs
@@ -1,6 +1,6 @@
 use crate::cmp::Ordering;
 use crate::time::Duration;
-use ::core::hash::{Hash, Hasher};
+use core::hash::{Hash, Hasher};
 
 pub use self::inner::{Instant, SystemTime, UNIX_EPOCH};
 use crate::convert::TryInto;
diff --git a/src/libstd/sys/wasi/fs.rs b/src/libstd/sys/wasi/fs.rs
index 793daea43c2..2eed9e436a9 100644
--- a/src/libstd/sys/wasi/fs.rs
+++ b/src/libstd/sys/wasi/fs.rs
@@ -597,14 +597,14 @@ fn open_at(fd: &WasiFd, path: &Path, opts: &OpenOptions) -> io::Result<File> {
 ///
 /// WASI has no fundamental capability to do this. All syscalls and operations
 /// are relative to already-open file descriptors. The C library, however,
-/// manages a map of preopened file descriptors to their path, and then the C
+/// manages a map of pre-opened file descriptors to their path, and then the C
 /// library provides an API to look at this. In other words, when you want to
 /// open a path `p`, you have to find a previously opened file descriptor in a
 /// global table and then see if `p` is relative to that file descriptor.
 ///
 /// This function, if successful, will return two items:
 ///
-/// * The first is a `ManuallyDrop<WasiFd>`. This represents a preopened file
+/// * The first is a `ManuallyDrop<WasiFd>`. This represents a pre-opened file
 ///   descriptor which we don't have ownership of, but we can use. You shouldn't
 ///   actually drop the `fd`.
 ///
@@ -619,7 +619,7 @@ fn open_at(fd: &WasiFd, path: &Path, opts: &OpenOptions) -> io::Result<File> {
 /// appropriate rights for performing `rights` actions.
 ///
 /// Note that this can fail if `p` doesn't look like it can be opened relative
-/// to any preopened file descriptor.
+/// to any pre-opened file descriptor.
 fn open_parent(p: &Path) -> io::Result<(ManuallyDrop<WasiFd>, PathBuf)> {
     let p = CString::new(p.as_os_str().as_bytes())?;
     unsafe {
@@ -627,7 +627,7 @@ fn open_parent(p: &Path) -> io::Result<(ManuallyDrop<WasiFd>, PathBuf)> {
         let fd = __wasilibc_find_relpath(p.as_ptr(), &mut ret);
         if fd == -1 {
             let msg = format!(
-                "failed to find a preopened file descriptor \
+                "failed to find a pre-opened file descriptor \
                  through which {:?} could be opened",
                 p
             );
diff --git a/src/test/codegen/unchecked-float-casts.rs b/src/test/codegen/unchecked-float-casts.rs
index 789feea12d6..4e3bfcd4397 100644
--- a/src/test/codegen/unchecked-float-casts.rs
+++ b/src/test/codegen/unchecked-float-casts.rs
@@ -2,6 +2,7 @@
 // unchecked intrinsics.
 
 // compile-flags: -C opt-level=3
+// ignore-wasm32 the wasm target is tested in `wasm_casts_*`
 
 #![crate_type = "lib"]
 
diff --git a/src/test/codegen/wasm_casts_trapping.rs b/src/test/codegen/wasm_casts_trapping.rs
index 45b90519049..b7f8522fdfb 100644
--- a/src/test/codegen/wasm_casts_trapping.rs
+++ b/src/test/codegen/wasm_casts_trapping.rs
@@ -38,7 +38,6 @@ pub fn cast_f32_i32(a: f32) -> i32 {
     a as _
 }
 
-
 // CHECK-LABEL: @cast_f64_u64
 #[no_mangle]
 pub fn cast_f64_u64(a: f64) -> u64 {
@@ -84,13 +83,10 @@ pub fn cast_f32_u8(a: f32) -> u8 {
     a as _
 }
 
-
-
 // CHECK-LABEL: @cast_unchecked_f64_i64
 #[no_mangle]
 pub unsafe fn cast_unchecked_f64_i64(a: f64) -> i64 {
-    // CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
-    // CHECK: fptosi double {{.*}} to i64
+    // CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.signed.{{.*}}
     // CHECK-NEXT: ret i64 {{.*}}
     a.to_int_unchecked()
 }
@@ -98,8 +94,7 @@ pub unsafe fn cast_unchecked_f64_i64(a: f64) -> i64 {
 // CHECK-LABEL: @cast_unchecked_f64_i32
 #[no_mangle]
 pub unsafe fn cast_unchecked_f64_i32(a: f64) -> i32 {
-    // CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
-    // CHECK: fptosi double {{.*}} to i32
+    // CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.signed.{{.*}}
     // CHECK-NEXT: ret i32 {{.*}}
     a.to_int_unchecked()
 }
@@ -107,8 +102,7 @@ pub unsafe fn cast_unchecked_f64_i32(a: f64) -> i32 {
 // CHECK-LABEL: @cast_unchecked_f32_i64
 #[no_mangle]
 pub unsafe fn cast_unchecked_f32_i64(a: f32) -> i64 {
-    // CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
-    // CHECK: fptosi float {{.*}} to i64
+    // CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.signed.{{.*}}
     // CHECK-NEXT: ret i64 {{.*}}
     a.to_int_unchecked()
 }
@@ -116,18 +110,15 @@ pub unsafe fn cast_unchecked_f32_i64(a: f32) -> i64 {
 // CHECK-LABEL: @cast_unchecked_f32_i32
 #[no_mangle]
 pub unsafe fn cast_unchecked_f32_i32(a: f32) -> i32 {
-    // CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
-    // CHECK: fptosi float {{.*}} to i32
+    // CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.signed.{{.*}}
     // CHECK-NEXT: ret i32 {{.*}}
     a.to_int_unchecked()
 }
 
-
 // CHECK-LABEL: @cast_unchecked_f64_u64
 #[no_mangle]
 pub unsafe fn cast_unchecked_f64_u64(a: f64) -> u64 {
-    // CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
-    // CHECK: fptoui double {{.*}} to i64
+    // CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.unsigned.{{.*}}
     // CHECK-NEXT: ret i64 {{.*}}
     a.to_int_unchecked()
 }
@@ -135,8 +126,7 @@ pub unsafe fn cast_unchecked_f64_u64(a: f64) -> u64 {
 // CHECK-LABEL: @cast_unchecked_f64_u32
 #[no_mangle]
 pub unsafe fn cast_unchecked_f64_u32(a: f64) -> u32 {
-    // CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
-    // CHECK: fptoui double {{.*}} to i32
+    // CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.unsigned.{{.*}}
     // CHECK-NEXT: ret i32 {{.*}}
     a.to_int_unchecked()
 }
@@ -144,8 +134,7 @@ pub unsafe fn cast_unchecked_f64_u32(a: f64) -> u32 {
 // CHECK-LABEL: @cast_unchecked_f32_u64
 #[no_mangle]
 pub unsafe fn cast_unchecked_f32_u64(a: f32) -> u64 {
-    // CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
-    // CHECK: fptoui float {{.*}} to i64
+    // CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.unsigned.{{.*}}
     // CHECK-NEXT: ret i64 {{.*}}
     a.to_int_unchecked()
 }
@@ -153,8 +142,7 @@ pub unsafe fn cast_unchecked_f32_u64(a: f32) -> u64 {
 // CHECK-LABEL: @cast_unchecked_f32_u32
 #[no_mangle]
 pub unsafe fn cast_unchecked_f32_u32(a: f32) -> u32 {
-    // CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
-    // CHECK: fptoui float {{.*}} to i32
+    // CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.unsigned.{{.*}}
     // CHECK-NEXT: ret i32 {{.*}}
     a.to_int_unchecked()
 }
diff --git a/src/test/ui/const-generics/defaults/wrong-order.rs b/src/test/ui/const-generics/defaults/wrong-order.rs
new file mode 100644
index 00000000000..7f17c6358b7
--- /dev/null
+++ b/src/test/ui/const-generics/defaults/wrong-order.rs
@@ -0,0 +1,8 @@
+#![feature(const_generics)] //~ WARN the feature `const_generics` is incomplete
+
+struct A<T = u32, const N: usize> {
+    //~^ ERROR type parameters with a default must be trailing
+    arg: T,
+}
+
+fn main() {}
diff --git a/src/test/ui/const-generics/defaults/wrong-order.stderr b/src/test/ui/const-generics/defaults/wrong-order.stderr
new file mode 100644
index 00000000000..283f6656121
--- /dev/null
+++ b/src/test/ui/const-generics/defaults/wrong-order.stderr
@@ -0,0 +1,19 @@
+error: type parameters with a default must be trailing
+  --> $DIR/wrong-order.rs:3:10
+   |
+LL | struct A<T = u32, const N: usize> {
+   |          ^
+   |
+   = note: using type defaults and const parameters in the same parameter list is currently not permitted
+
+warning: the feature `const_generics` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/wrong-order.rs:1:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
+
+error: aborting due to previous error; 1 warning emitted
+