Auto merge of #52680 - Mark-Simulacrum:rollup, r=Mark-Simulacrum

Rollup of 7 pull requests

Successful merges:

 - #52391 (Add unaligned volatile intrinsics)
 - #52402 (impl PartialEq+Eq for BuildHasherDefault)
 - #52645 (Allow declaring existential types inside blocks)
 - #52656 (Stablize Redox Unix Sockets)
 - #52658 (Prefer `Option::map`/etc over `match` wherever it improves clarity)
 - #52668 (clarify pointer offset function safety concerns)
 - #52677 (Release notes: add some missing 1.28 libs stabilization)

Failed merges:

r? @ghost

RELEASES.md

@@ -52,6 +52,16 @@ Stabilized APIs
 ---------------
 - [`Iterator::step_by`]
 - [`Path::ancestors`]
+- [`SystemTime::UNIX_EPOCH`]
+- [`alloc::GlobalAlloc`]
+- [`alloc::Layout`]
+- [`alloc::LayoutErr`]
+- [`alloc::System`]
+- [`alloc::alloc`]
+- [`alloc::alloc_zeroed`]
+- [`alloc::dealloc`]
+- [`alloc::realloc`]
+- [`alloc::handle_alloc_error`]
 - [`btree_map::Entry::or_default`]
 - [`fmt::Alignment`]
 - [`hash_map::Entry::or_default`]
@@ -122,6 +132,16 @@ Compatibility Notes
 [cargo/5584]: https://github.com/rust-lang/cargo/pull/5584/
 [`Iterator::step_by`]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.step_by
 [`Path::ancestors`]: https://doc.rust-lang.org/std/path/struct.Path.html#method.ancestors
+[`SystemTime::UNIX_EPOCH`]: https://doc.rust-lang.org/std/time/struct.SystemTime.html#associatedconstant.UNIX_EPOCH
+[`alloc::GlobalAlloc`]: https://doc.rust-lang.org/std/alloc/trait.GlobalAlloc.html
+[`alloc::Layout`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html
+[`alloc::LayoutErr`]: https://doc.rust-lang.org/std/alloc/struct.LayoutErr.html
+[`alloc::System`]: https://doc.rust-lang.org/std/alloc/struct.System.html
+[`alloc::alloc`]: https://doc.rust-lang.org/std/alloc/fn.alloc.html
+[`alloc::alloc_zeroed`]: https://doc.rust-lang.org/std/alloc/fn.alloc_zeroed.html
+[`alloc::dealloc`]: https://doc.rust-lang.org/std/alloc/fn.dealloc.html
+[`alloc::realloc`]: https://doc.rust-lang.org/std/alloc/fn.realloc.html
+[`alloc::handle_alloc_error`]: https://doc.rust-lang.org/std/alloc/fn.handle_alloc_error.html
 [`btree_map::Entry::or_default`]: https://doc.rust-lang.org/std/collections/btree_map/enum.Entry.html#method.or_default
 [`fmt::Alignment`]: https://doc.rust-lang.org/std/fmt/enum.Alignment.html
 [`hash_map::Entry::or_default`]: https://doc.rust-lang.org/std/collections/btree_map/enum.Entry.html#method.or_default
@@ -3162,7 +3182,7 @@ Stabilized APIs
 * [`UnixDatagram::shutdown`](http://doc.rust-lang.org/std/os/unix/net/struct.UnixDatagram.html#method.shutdown)
 * RawFd impls for `UnixDatagram`
 * `{BTree,Hash}Map::values_mut`
-* [`<[_]>::binary_search_by_key`](http://doc.rust-lang.org/beta/std/primitive.slice.html#method.binary_search_by_key)
+* [`<[_]>::binary_search_by_key`](http://doc.rust-lang.org/std/primitive.slice.html#method.binary_search_by_key)
 
 Libraries
 ---------
@@ -4080,7 +4100,7 @@ Compatibility Notes
 [1.6bh]: https://github.com/rust-lang/rust/pull/29811
 [1.6c]: https://github.com/rust-lang/cargo/pull/2192
 [1.6cc]: https://github.com/rust-lang/cargo/pull/2131
-[1.6co]: http://doc.rust-lang.org/beta/core/index.html
+[1.6co]: http://doc.rust-lang.org/core/index.html
 [1.6dv]: https://github.com/rust-lang/rust/pull/30000
 [1.6f]: https://github.com/rust-lang/rust/pull/29129
 [1.6m]: https://github.com/rust-lang/rust/pull/29828

src/libcore/hash/mod.rs

@@ -542,6 +542,16 @@ impl<H> Default for BuildHasherDefault<H> {
     }
 }
 
+#[stable(since = "1.29.0", feature = "build_hasher_eq")]
+impl<H> PartialEq for BuildHasherDefault<H> {
+    fn eq(&self, _other: &BuildHasherDefault<H>) -> bool {
+        true
+    }
+}
+
+#[stable(since = "1.29.0", feature = "build_hasher_eq")]
+impl<H> Eq for BuildHasherDefault<H> {}
+
 //////////////////////////////////////////////////////////////////////////////
 
 mod impls {

src/libcore/intrinsics.rs

@@ -1085,6 +1085,15 @@ extern "rust-intrinsic" {
     /// [`std::ptr::write_volatile`](../../std/ptr/fn.write_volatile.html).
     pub fn volatile_store<T>(dst: *mut T, val: T);
 
+    /// Perform a volatile load from the `src` pointer
+    /// The pointer is not required to be aligned.
+    #[cfg(not(stage0))]
+    pub fn unaligned_volatile_load<T>(src: *const T) -> T;
+    /// Perform a volatile store to the `dst` pointer.
+    /// The pointer is not required to be aligned.
+    #[cfg(not(stage0))]
+    pub fn unaligned_volatile_store<T>(dst: *mut T, val: T);
+
     /// Returns the square root of an `f32`
     pub fn sqrtf32(x: f32) -> f32;
     /// Returns the square root of an `f64`

src/libcore/ptr.rs

@@ -591,7 +591,7 @@ impl<T: ?Sized> *const T {
     /// Behavior:
     ///
     /// * Both the starting and resulting pointer must be either in bounds or one
-    ///   byte past the end of an allocated object.
+    ///   byte past the end of *the same* allocated object.
     ///
     /// * The computed offset, **in bytes**, cannot overflow an `isize`.
     ///
@@ -643,9 +643,15 @@ impl<T: ?Sized> *const T {
     ///
     /// The resulting pointer does not need to be in bounds, but it is
     /// potentially hazardous to dereference (which requires `unsafe`).
+    /// In particular, the resulting pointer may *not* be used to access a
+    /// different allocated object than the one `self` points to. In other
+    /// words, `x.wrapping_offset(y.wrapping_offset_from(x))` is
+    /// *not* the same as `y`, and dereferencing it is undefined behavior
+    /// unless `x` and `y` point into the same allocated object.
     ///
     /// Always use `.offset(count)` instead when possible, because `offset`
-    /// allows the compiler to optimize better.
+    /// allows the compiler to optimize better.  If you need to cross object
+    /// boundaries, cast the pointer to an integer and do the arithmetic there.
     ///
     /// # Examples
     ///
@@ -1340,7 +1346,7 @@ impl<T: ?Sized> *mut T {
     /// Behavior:
     ///
     /// * Both the starting and resulting pointer must be either in bounds or one
-    ///   byte past the end of an allocated object.
+    ///   byte past the end of *the same* allocated object.
     ///
     /// * The computed offset, **in bytes**, cannot overflow an `isize`.
     ///
@@ -1391,9 +1397,15 @@ impl<T: ?Sized> *mut T {
     ///
     /// The resulting pointer does not need to be in bounds, but it is
     /// potentially hazardous to dereference (which requires `unsafe`).
+    /// In particular, the resulting pointer may *not* be used to access a
+    /// different allocated object than the one `self` points to. In other
+    /// words, `x.wrapping_offset(y.wrapping_offset_from(x))` is
+    /// *not* the same as `y`, and dereferencing it is undefined behavior
+    /// unless `x` and `y` point into the same allocated object.
     ///
     /// Always use `.offset(count)` instead when possible, because `offset`
-    /// allows the compiler to optimize better.
+    /// allows the compiler to optimize better.  If you need to cross object
+    /// boundaries, cast the pointer to an integer and do the arithmetic there.
     ///
     /// # Examples
     ///

src/libcore/str/mod.rs

@@ -696,13 +696,10 @@ impl<'a> Iterator for CharIndices<'a> {
 impl<'a> DoubleEndedIterator for CharIndices<'a> {
     #[inline]
     fn next_back(&mut self) -> Option<(usize, char)> {
-        match self.iter.next_back() {
-            None => None,
-            Some(ch) => {
-                let index = self.front_offset + self.iter.iter.len();
-                Some((index, ch))
-            }
-        }
+        self.iter.next_back().map(|ch| {
+            let index = self.front_offset + self.iter.iter.len();
+            (index, ch)
+        })
     }
 }
 

src/librustc/traits/on_unimplemented.rs

@@ -190,11 +190,10 @@ impl<'a, 'gcx, 'tcx> OnUnimplementedDirective {
         for command in self.subcommands.iter().chain(Some(self)).rev() {
             if let Some(ref condition) = command.condition {
                 if !attr::eval_condition(condition, &tcx.sess.parse_sess, &mut |c| {
-                    options.contains(&(c.name().as_str().to_string(),
-                                      match c.value_str().map(|s| s.as_str().to_string()) {
-                                          Some(s) => Some(s),
-                                          None => None
-                                      }))
+                    options.contains(&(
+                        c.name().as_str().to_string(),
+                        c.value_str().map(|s| s.as_str().to_string())
+                    ))
                 }) {
                     debug!("evaluate: skipping {:?} due to condition", command);
                     continue

src/librustc/ty/mod.rs

@@ -2697,15 +2697,12 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             self.opt_associated_item(def_id)
         };
 
-        match item {
-            Some(trait_item) => {
-                match trait_item.container {
-                    TraitContainer(_) => None,
-                    ImplContainer(def_id) => Some(def_id),
-                }
+        item.and_then(|trait_item|
+            match trait_item.container {
+                TraitContainer(_) => None,
+                ImplContainer(def_id) => Some(def_id),
             }
-            None => None
-        }
+        )
     }
 
     /// Looks up the span of `impl_did` if the impl is local; otherwise returns `Err`

src/librustc_codegen_llvm/builder.rs

@@ -54,6 +54,7 @@ bitflags! {
     pub struct MemFlags: u8 {
         const VOLATILE = 1 << 0;
         const NONTEMPORAL = 1 << 1;
+        const UNALIGNED = 1 << 2;
     }
 }
 
@@ -602,7 +603,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let ptr = self.check_store(val, ptr);
         unsafe {
             let store = llvm::LLVMBuildStore(self.llbuilder, val, ptr);
-            llvm::LLVMSetAlignment(store, align.abi() as c_uint);
+            let align = if flags.contains(MemFlags::UNALIGNED) {
+                1
+            } else {
+                align.abi() as c_uint
+            };
+            llvm::LLVMSetAlignment(store, align);
             if flags.contains(MemFlags::VOLATILE) {
                 llvm::LLVMSetVolatile(store, llvm::True);
             }

src/librustc_codegen_llvm/intrinsic.rs

@@ -234,15 +234,20 @@ pub fn codegen_intrinsic_call<'a, 'tcx>(bx: &Builder<'a, 'tcx>,
             memset_intrinsic(bx, true, substs.type_at(0),
                              args[0].immediate(), args[1].immediate(), args[2].immediate())
         }
-        "volatile_load" => {
+        "volatile_load" | "unaligned_volatile_load" => {
             let tp_ty = substs.type_at(0);
             let mut ptr = args[0].immediate();
             if let PassMode::Cast(ty) = fn_ty.ret.mode {
                 ptr = bx.pointercast(ptr, ty.llvm_type(cx).ptr_to());
             }
             let load = bx.volatile_load(ptr);
+            let align = if name == "unaligned_volatile_load" {
+                1
+            } else {
+                cx.align_of(tp_ty).abi() as u32
+            };
             unsafe {
-                llvm::LLVMSetAlignment(load, cx.align_of(tp_ty).abi() as u32);
+                llvm::LLVMSetAlignment(load, align);
             }
             to_immediate(bx, load, cx.layout_of(tp_ty))
         },
@@ -251,6 +256,11 @@ pub fn codegen_intrinsic_call<'a, 'tcx>(bx: &Builder<'a, 'tcx>,
             args[1].val.volatile_store(bx, dst);
             return;
         },
+        "unaligned_volatile_store" => {
+            let dst = args[0].deref(bx.cx);
+            args[1].val.unaligned_volatile_store(bx, dst);
+            return;
+        },
         "prefetch_read_data" | "prefetch_write_data" |
         "prefetch_read_instruction" | "prefetch_write_instruction" => {
             let expect = cx.get_intrinsic(&("llvm.prefetch"));

src/librustc_codegen_llvm/mir/operand.rs

@@ -276,6 +276,10 @@ impl<'a, 'tcx> OperandValue {
         self.store_with_flags(bx, dest, MemFlags::VOLATILE);
     }
 
+    pub fn unaligned_volatile_store(self, bx: &Builder<'a, 'tcx>, dest: PlaceRef<'tcx>) {
+        self.store_with_flags(bx, dest, MemFlags::VOLATILE | MemFlags::UNALIGNED);
+    }
+
     pub fn nontemporal_store(self, bx: &Builder<'a, 'tcx>, dest: PlaceRef<'tcx>) {
         self.store_with_flags(bx, dest, MemFlags::NONTEMPORAL);
     }

src/librustc_metadata/locator.rs

@@ -824,17 +824,14 @@ impl<'a> Context<'a> {
         if rlib.is_none() && rmeta.is_none() && dylib.is_none() {
             return None;
         }
-        match slot {
-            Some((_, metadata)) => {
-                Some(Library {
-                    dylib,
-                    rlib,
-                    rmeta,
-                    metadata,
-                })
+        slot.map(|(_, metadata)|
+            Library {
+                dylib,
+                rlib,
+                rmeta,
+                metadata,
             }
-            None => None,
-        }
+        )
     }
 }
 

src/librustc_typeck/check/intrinsic.rs

@@ -270,9 +270,9 @@ pub fn check_intrinsic_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             "roundf32"     => (0, vec![ tcx.types.f32 ], tcx.types.f32),
             "roundf64"     => (0, vec![ tcx.types.f64 ], tcx.types.f64),
 
-            "volatile_load" =>
+            "volatile_load" | "unaligned_volatile_load" =>
                 (1, vec![ tcx.mk_imm_ptr(param(0)) ], param(0)),
-            "volatile_store" =>
+            "volatile_store" | "unaligned_volatile_store" =>
                 (1, vec![ tcx.mk_mut_ptr(param(0)), param(0) ], tcx.mk_nil()),
 
             "ctpop" | "ctlz" | "ctlz_nonzero" | "cttz" | "cttz_nonzero" |

src/libstd/net/parser.rs

@@ -53,10 +53,7 @@ impl<'a> Parser<'a> {
         F: FnOnce(&mut Parser) -> Option<T>,
     {
         self.read_atomically(move |p| {
-            match cb(p) {
-                Some(x) => if p.is_eof() {Some(x)} else {None},
-                None => None,
-            }
+            cb(p).filter(|_| p.is_eof())
         })
     }
 

src/libstd/path.rs

@@ -1065,10 +1065,7 @@ impl<'a> Iterator for Ancestors<'a> {
 
     fn next(&mut self) -> Option<Self::Item> {
         let next = self.next;
-        self.next = match next {
-            Some(path) => path.parent(),
-            None => None,
-        };
+        self.next = next.and_then(Path::parent);
         next
     }
 }