Auto merge of #66121 - pietroalbini:rollup-8zrwe7l, r=pietroalbini

Rollup of 8 pull requests

Successful merges:

 - #65948 (Improve MaybeUninit::get_{ref,mut} documentation)
 - #65953 (Allow specifying LLVM's MCTargetOptions::ABIName in target specification files)
 - #66012 (De-querify `trivial_dropck_outlives`.)
 - #66025 (`Span` cannot represent `span.hi < span.lo`)
 - #66047 (Don't double-count `simd_shuffle` promotion candidates)
 - #66053 (when Miri tests are not passing, do not add Miri component)
 - #66082 (clean highlightSourceLines code)
 - #66091 (Implemented the home_dir for VxWorks)

Failed merges:

r? @ghost

Cargo.lock

@@ -208,6 +208,7 @@ name = "build-manifest"
 version = "0.1.0"
 dependencies = [
  "serde",
+ "serde_json",
  "toml",
 ]
 

src/libcore/mem/maybe_uninit.rs

@@ -509,32 +509,183 @@ impl<T> MaybeUninit<T> {
         self.as_ptr().read()
     }
 
-    /// Gets a reference to the contained value.
+    /// Gets a shared reference to the contained value.
+    ///
+    /// This can be useful when we want to access a `MaybeUninit` that has been
+    /// initialized but don't have ownership of the `MaybeUninit` (preventing the use
+    /// of `.assume_init()`).
     ///
     /// # Safety
     ///
-    /// It is up to the caller to guarantee that the `MaybeUninit<T>` really is in an initialized
-    /// state. Calling this when the content is not yet fully initialized causes undefined
-    /// behavior.
+    /// Calling this when the content is not yet fully initialized causes undefined
+    /// behavior: it is up to the caller to guarantee that the `MaybeUninit<T>` really
+    /// is in an initialized state.
+    ///
+    /// # Examples
+    ///
+    /// ### Correct usage of this method:
+    ///
+    /// ```rust
+    /// #![feature(maybe_uninit_ref)]
+    /// use std::mem::MaybeUninit;
+    ///
+    /// let mut x = MaybeUninit::<Vec<u32>>::uninit();
+    /// // Initialize `x`:
+    /// unsafe { x.as_mut_ptr().write(vec![1, 2, 3]); }
+    /// // Now that our `MaybeUninit<_>` is known to be initialized, it is okay to
+    /// // create a shared reference to it:
+    /// let x: &Vec<u32> = unsafe {
+    ///     // Safety: `x` has been initialized.
+    ///     x.get_ref()
+    /// };
+    /// assert_eq!(x, &vec![1, 2, 3]);
+    /// ```
+    ///
+    /// ### *Incorrect* usages of this method:
+    ///
+    /// ```rust,no_run
+    /// #![feature(maybe_uninit_ref)]
+    /// use std::mem::MaybeUninit;
+    ///
+    /// let x = MaybeUninit::<Vec<u32>>::uninit();
+    /// let x_vec: &Vec<u32> = unsafe { x.get_ref() };
+    /// // We have created a reference to an uninitialized vector! This is undefined behavior.
+    /// ```
+    ///
+    /// ```rust,no_run
+    /// #![feature(maybe_uninit_ref)]
+    /// use std::{cell::Cell, mem::MaybeUninit};
+    ///
+    /// let b = MaybeUninit::<Cell<bool>>::uninit();
+    /// // Initialize the `MaybeUninit` using `Cell::set`:
+    /// unsafe {
+    ///     b.get_ref().set(true);
+    ///  // ^^^^^^^^^^^
+    ///  // Reference to an uninitialized `Cell<bool>`: UB!
+    /// }
+    /// ```
     #[unstable(feature = "maybe_uninit_ref", issue = "63568")]
     #[inline(always)]
     pub unsafe fn get_ref(&self) -> &T {
+        intrinsics::panic_if_uninhabited::<T>();
         &*self.value
     }
 
-    /// Gets a mutable reference to the contained value.
+    /// Gets a mutable (unique) reference to the contained value.
+    ///
+    /// This can be useful when we want to access a `MaybeUninit` that has been
+    /// initialized but don't have ownership of the `MaybeUninit` (preventing the use
+    /// of `.assume_init()`).
     ///
     /// # Safety
     ///
-    /// It is up to the caller to guarantee that the `MaybeUninit<T>` really is in an initialized
-    /// state. Calling this when the content is not yet fully initialized causes undefined
-    /// behavior.
+    /// Calling this when the content is not yet fully initialized causes undefined
+    /// behavior: it is up to the caller to guarantee that the `MaybeUninit<T>` really
+    /// is in an initialized state. For instance, `.get_mut()` cannot be used to
+    /// initialize a `MaybeUninit`.
+    ///
+    /// # Examples
+    ///
+    /// ### Correct usage of this method:
+    ///
+    /// ```rust
+    /// #![feature(maybe_uninit_ref)]
+    /// use std::mem::MaybeUninit;
+    ///
+    /// # unsafe extern "C" fn initialize_buffer(buf: *mut [u8; 2048]) { *buf = [0; 2048] }
+    /// # #[cfg(FALSE)]
+    /// extern "C" {
+    ///     /// Initializes *all* the bytes of the input buffer.
+    ///     fn initialize_buffer(buf: *mut [u8; 2048]);
+    /// }
+    ///
+    /// let mut buf = MaybeUninit::<[u8; 2048]>::uninit();
+    ///
+    /// // Initialize `buf`:
+    /// unsafe { initialize_buffer(buf.as_mut_ptr()); }
+    /// // Now we know that `buf` has been initialized, so we could `.assume_init()` it.
+    /// // However, using `.assume_init()` may trigger a `memcpy` of the 2048 bytes.
+    /// // To assert our buffer has been initialized without copying it, we upgrade
+    /// // the `&mut MaybeUninit<[u8; 2048]>` to a `&mut [u8; 2048]`:
+    /// let buf: &mut [u8; 2048] = unsafe {
+    ///     // Safety: `buf` has been initialized.
+    ///     buf.get_mut()
+    /// };
+    ///
+    /// // Now we can use `buf` as a normal slice:
+    /// buf.sort_unstable();
+    /// assert!(
+    ///     buf.chunks(2).all(|chunk| chunk[0] <= chunk[1]),
+    ///     "buffer is sorted",
+    /// );
+    /// ```
+    ///
+    /// ### *Incorrect* usages of this method:
+    ///
+    /// You cannot use `.get_mut()` to initialize a value:
+    ///
+    /// ```rust,no_run
+    /// #![feature(maybe_uninit_ref)]
+    /// use std::mem::MaybeUninit;
+    ///
+    /// let mut b = MaybeUninit::<bool>::uninit();
+    /// unsafe {
+    ///     *b.get_mut() = true;
+    ///     // We have created a (mutable) reference to an uninitialized `bool`!
+    ///     // This is undefined behavior.
+    /// }
+    /// ```
+    ///
+    /// For instance, you cannot [`Read`] into an uninitialized buffer:
+    ///
+    /// [`Read`]: https://doc.rust-lang.org/std/io/trait.Read.html
+    ///
+    /// ```rust,no_run
+    /// #![feature(maybe_uninit_ref)]
+    /// use std::{io, mem::MaybeUninit};
+    ///
+    /// fn read_chunk (reader: &'_ mut dyn io::Read) -> io::Result<[u8; 64]>
+    /// {
+    ///     let mut buffer = MaybeUninit::<[u8; 64]>::uninit();
+    ///     reader.read_exact(unsafe { buffer.get_mut() })?;
+    ///                             // ^^^^^^^^^^^^^^^^
+    ///                             // (mutable) reference to uninitialized memory!
+    ///                             // This is undefined behavior.
+    ///     Ok(unsafe { buffer.assume_init() })
+    /// }
+    /// ```
+    ///
+    /// Nor can you use direct field access to do field-by-field gradual initialization:
+    ///
+    /// ```rust,no_run
+    /// #![feature(maybe_uninit_ref)]
+    /// use std::{mem::MaybeUninit, ptr};
+    ///
+    /// struct Foo {
+    ///     a: u32,
+    ///     b: u8,
+    /// }
+    ///
+    /// let foo: Foo = unsafe {
+    ///     let mut foo = MaybeUninit::<Foo>::uninit();
+    ///     ptr::write(&mut foo.get_mut().a as *mut u32, 1337);
+    ///                  // ^^^^^^^^^^^^^
+    ///                  // (mutable) reference to uninitialized memory!
+    ///                  // This is undefined behavior.
+    ///     ptr::write(&mut foo.get_mut().b as *mut u8, 42);
+    ///                  // ^^^^^^^^^^^^^
+    ///                  // (mutable) reference to uninitialized memory!
+    ///                  // This is undefined behavior.
+    ///     foo.assume_init()
+    /// };
+    /// ```
     // FIXME(#53491): We currently rely on the above being incorrect, i.e., we have references
     // to uninitialized data (e.g., in `libcore/fmt/float.rs`).  We should make
     // a final decision about the rules before stabilization.
     #[unstable(feature = "maybe_uninit_ref", issue = "63568")]
     #[inline(always)]
     pub unsafe fn get_mut(&mut self) -> &mut T {
+        intrinsics::panic_if_uninhabited::<T>();
         &mut *self.value
     }
 

src/librustc/ich/hcx.rs

@@ -309,11 +309,6 @@ impl<'a> HashStable<StableHashingContext<'a>> for Span {
         // position that belongs to it, as opposed to hashing the first
         // position past it.
         let span = self.data();
-
-        if span.hi < span.lo {
-            return std_hash::Hash::hash(&TAG_INVALID_SPAN, hasher);
-        }
-
         let (file_lo, line_lo, col_lo) = match hcx.source_map()
                                                   .byte_pos_to_line_and_col(span.lo) {
             Some(pos) => pos,

src/librustc/query/mod.rs

@@ -228,12 +228,6 @@ rustc_queries! {
             cycle_delay_bug
         }
 
-        query trivial_dropck_outlives(ty: Ty<'tcx>) -> bool {
-            anon
-            no_force
-            desc { "checking if `{:?}` has trivial dropck", ty }
-        }
-
         query adt_dtorck_constraint(
             _: DefId
         ) -> Result<DtorckConstraint<'tcx>, NoSolution> {}

src/librustc/traits/query/dropck_outlives.rs

@@ -5,7 +5,6 @@ use std::iter::FromIterator;
 use syntax::source_map::Span;
 use crate::ty::subst::GenericArg;
 use crate::ty::{self, Ty, TyCtxt};
-use crate::ty::query::Providers;
 
 impl<'cx, 'tcx> At<'cx, 'tcx> {
     /// Given a type `ty` of some value being dropped, computes a set
@@ -34,7 +33,7 @@ impl<'cx, 'tcx> At<'cx, 'tcx> {
         // Quick check: there are a number of cases that we know do not require
         // any destructor.
         let tcx = self.infcx.tcx;
-        if tcx.trivial_dropck_outlives(ty) {
+        if trivial_dropck_outlives(tcx, ty) {
             return InferOk {
                 value: vec![],
                 obligations: vec![],
@@ -208,15 +207,15 @@ pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
         | ty::Error => true,
 
         // [T; N] and [T] have same properties as T.
-        ty::Array(ty, _) | ty::Slice(ty) => tcx.trivial_dropck_outlives(ty),
+        ty::Array(ty, _) | ty::Slice(ty) => trivial_dropck_outlives(tcx, ty),
 
         // (T1..Tn) and closures have same properties as T1..Tn --
         // check if *any* of those are trivial.
-        ty::Tuple(ref tys) => tys.iter().all(|t| tcx.trivial_dropck_outlives(t.expect_ty())),
+        ty::Tuple(ref tys) => tys.iter().all(|t| trivial_dropck_outlives(tcx, t.expect_ty())),
         ty::Closure(def_id, ref substs) => substs
             .as_closure()
             .upvar_tys(def_id, tcx)
-            .all(|t| tcx.trivial_dropck_outlives(t)),
+            .all(|t| trivial_dropck_outlives(tcx, t)),
 
         ty::Adt(def, _) => {
             if Some(def.did) == tcx.lang_items().manually_drop() {
@@ -244,10 +243,3 @@ pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
         ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
     }
 }
-
-crate fn provide(p: &mut Providers<'_>) {
-    *p = Providers {
-        trivial_dropck_outlives,
-        ..*p
-    };
-}

src/librustc/traits/query/type_op/outlives.rs

@@ -1,5 +1,5 @@
 use crate::infer::canonical::{Canonicalized, CanonicalizedQueryResponse};
-use crate::traits::query::dropck_outlives::DropckOutlivesResult;
+use crate::traits::query::dropck_outlives::{DropckOutlivesResult, trivial_dropck_outlives};
 use crate::traits::query::Fallible;
 use crate::ty::{ParamEnvAnd, Ty, TyCtxt};
 
@@ -21,7 +21,7 @@ impl super::QueryTypeOp<'tcx> for DropckOutlives<'tcx> {
         tcx: TyCtxt<'tcx>,
         key: &ParamEnvAnd<'tcx, Self>,
     ) -> Option<Self::QueryResponse> {
-        if tcx.trivial_dropck_outlives(key.value.dropped_ty) {
+        if trivial_dropck_outlives(tcx, key.value.dropped_ty) {
             Some(DropckOutlivesResult::default())
         } else {
             None

src/librustc/ty/mod.rs

@@ -3407,7 +3407,6 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
     layout::provide(providers);
     util::provide(providers);
     constness::provide(providers);
-    crate::traits::query::dropck_outlives::provide(providers);
     *providers = ty::query::Providers {
         asyncness,
         associated_item,

src/librustc/ty/query/on_disk_cache.rs

@@ -796,11 +796,6 @@ where
         }
 
         let span_data = span.data();
-
-        if span_data.hi < span_data.lo {
-            return TAG_INVALID_SPAN.encode(self);
-        }
-
         let (file_lo, line_lo, col_lo) = match self.source_map
                                                    .byte_pos_to_line_and_col(span_data.lo) {
             Some(pos) => pos,

src/librustc_codegen_llvm/back/write.rs

@@ -161,6 +161,7 @@ pub fn target_machine_factory(sess: &Session, optlvl: config::OptLevel, find_fea
     let cpu = SmallCStr::new(llvm_util::target_cpu(sess));
     let features = features.join(",");
     let features = CString::new(features).unwrap();
+    let abi = SmallCStr::new(&sess.target.target.options.llvm_abiname);
     let is_pie_binary = !find_features && is_pie_binary(sess);
     let trap_unreachable = sess.target.target.options.trap_unreachable;
     let emit_stack_size_section = sess.opts.debugging_opts.emit_stack_sizes;
@@ -170,7 +171,7 @@ pub fn target_machine_factory(sess: &Session, optlvl: config::OptLevel, find_fea
     Arc::new(move || {
         let tm = unsafe {
             llvm::LLVMRustCreateTargetMachine(
-                triple.as_ptr(), cpu.as_ptr(), features.as_ptr(),
+                triple.as_ptr(), cpu.as_ptr(), features.as_ptr(), abi.as_ptr(),
                 code_model,
                 reloc_model,
                 opt_level,

src/librustc_codegen_llvm/llvm/ffi.rs

@@ -1684,6 +1684,7 @@ extern "C" {
     pub fn LLVMRustCreateTargetMachine(Triple: *const c_char,
                                        CPU: *const c_char,
                                        Features: *const c_char,
+                                       Abi: *const c_char,
                                        Model: CodeModel,
                                        Reloc: RelocMode,
                                        Level: CodeGenOptLevel,

src/librustc_mir/transform/promote_consts.rs

@@ -199,6 +199,8 @@ impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
                             bb: location.block,
                             index: 2,
                         });
+
+                        return; // Don't double count `simd_shuffle` candidates
                     }
                 }
 

src/librustc_target/spec/mod.rs

@@ -793,7 +793,10 @@ pub struct TargetOptions {
     pub merge_functions: MergeFunctions,
 
     /// Use platform dependent mcount function
-    pub target_mcount: String
+    pub target_mcount: String,
+
+    /// LLVM ABI name, corresponds to the '-mabi' parameter available in multilib C compilers
+    pub llvm_abiname: String,
 }
 
 impl Default for TargetOptions {
@@ -880,6 +883,7 @@ impl Default for TargetOptions {
             override_export_symbols: None,
             merge_functions: MergeFunctions::Aliases,
             target_mcount: "mcount".to_string(),
+            llvm_abiname: "".to_string(),
         }
     }
 }
@@ -1196,6 +1200,7 @@ impl Target {
         key!(override_export_symbols, opt_list);
         key!(merge_functions, MergeFunctions)?;
         key!(target_mcount);
+        key!(llvm_abiname);
 
         if let Some(array) = obj.find("abi-blacklist").and_then(Json::as_array) {
             for name in array.iter().filter_map(|abi| abi.as_string()) {
@@ -1414,6 +1419,7 @@ impl ToJson for Target {
         target_option_val!(override_export_symbols);
         target_option_val!(merge_functions);
         target_option_val!(target_mcount);
+        target_option_val!(llvm_abiname);
 
         if default.abi_blacklist != self.options.abi_blacklist {
             d.insert("abi-blacklist".to_string(), self.options.abi_blacklist.iter()

src/librustc_traits/dropck_outlives.rs

@@ -1,6 +1,7 @@
 use rustc::hir::def_id::DefId;
 use rustc::infer::canonical::{Canonical, QueryResponse};
 use rustc::traits::query::dropck_outlives::{DropckOutlivesResult, DtorckConstraint};
+use rustc::traits::query::dropck_outlives::trivial_dropck_outlives;
 use rustc::traits::query::{CanonicalTyGoal, NoSolution};
 use rustc::traits::{TraitEngine, Normalized, ObligationCause, TraitEngineExt};
 use rustc::ty::query::Providers;
@@ -172,7 +173,7 @@ fn dtorck_constraint_for_ty<'tcx>(
         return Ok(());
     }
 
-    if tcx.trivial_dropck_outlives(ty) {
+    if trivial_dropck_outlives(tcx, ty) {
         return Ok(());
     }