Minor comment and whitespace tweaks.

Author: nnethercote

compiler/rustc_abi/src/layout.rs

@@ -53,24 +53,24 @@ pub trait LayoutCalculator {
         kind: StructKind,
     ) -> Option<LayoutS> {
         let layout = univariant(self, dl, fields, repr, kind, NicheBias::Start);
-        // Enums prefer niches close to the beginning or the end of the variants so that other (smaller)
-        // data-carrying variants can be packed into the space after/before the niche.
+        // Enums prefer niches close to the beginning or the end of the variants so that other
+        // (smaller) data-carrying variants can be packed into the space after/before the niche.
         // If the default field ordering does not give us a niche at the front then we do a second
-        // run and bias niches to the right and then check which one is closer to one of the struct's
-        // edges.
+        // run and bias niches to the right and then check which one is closer to one of the
+        // struct's edges.
         if let Some(layout) = &layout {
             // Don't try to calculate an end-biased layout for unsizable structs,
             // otherwise we could end up with different layouts for
-            // Foo<Type> and Foo<dyn Trait> which would break unsizing
+            // Foo<Type> and Foo<dyn Trait> which would break unsizing.
             if !matches!(kind, StructKind::MaybeUnsized) {
                 if let Some(niche) = layout.largest_niche {
                     let head_space = niche.offset.bytes();
                     let niche_length = niche.value.size(dl).bytes();
                     let tail_space = layout.size.bytes() - head_space - niche_length;
 
-                    // This may end up doing redundant work if the niche is already in the last field
-                    // (e.g. a trailing bool) and there is tail padding. But it's non-trivial to get
-                    // the unpadded size so we try anyway.
+                    // This may end up doing redundant work if the niche is already in the last
+                    // field (e.g. a trailing bool) and there is tail padding. But it's non-trivial
+                    // to get the unpadded size so we try anyway.
                     if fields.len() > 1 && head_space != 0 && tail_space > 0 {
                         let alt_layout = univariant(self, dl, fields, repr, kind, NicheBias::End)
                             .expect("alt layout should always work");
@@ -684,7 +684,8 @@ pub trait LayoutCalculator {
                 // Also do not overwrite any already existing "clever" ABIs.
                 if variant.fields.count() > 0 && matches!(variant.abi, Abi::Aggregate { .. }) {
                     variant.abi = abi;
-                    // Also need to bump up the size and alignment, so that the entire value fits in here.
+                    // Also need to bump up the size and alignment, so that the entire value fits
+                    // in here.
                     variant.size = cmp::max(variant.size, size);
                     variant.align.abi = cmp::max(variant.align.abi, align.abi);
                 }
@@ -868,15 +869,15 @@ fn univariant(
 
         // If `-Z randomize-layout` was enabled for the type definition we can shuffle
         // the field ordering to try and catch some code making assumptions about layouts
-        // we don't guarantee
+        // we don't guarantee.
         if repr.can_randomize_type_layout() && cfg!(feature = "randomize") {
             #[cfg(feature = "randomize")]
             {
-                // `ReprOptions.layout_seed` is a deterministic seed that we can use to
-                // randomize field ordering with
+                // `ReprOptions.layout_seed` is a deterministic seed we can use to randomize field
+                // ordering.
                 let mut rng = Xoshiro128StarStar::seed_from_u64(repr.field_shuffle_seed.as_u64());
 
-                // Shuffle the ordering of the fields
+                // Shuffle the ordering of the fields.
                 optimizing.shuffle(&mut rng);
             }
             // Otherwise we just leave things alone and actually optimize the type's fields
@@ -892,27 +893,26 @@ fn univariant(
                 .max()
                 .unwrap_or(0);
 
-            // Calculates a sort key to group fields by their alignment or possibly some size-derived
-            // pseudo-alignment.
+            // Calculates a sort key to group fields by their alignment or possibly some
+            // size-derived pseudo-alignment.
             let alignment_group_key = |layout: Layout<'_>| {
                 if let Some(pack) = pack {
-                    // return the packed alignment in bytes
+                    // Return the packed alignment in bytes.
                     layout.align().abi.min(pack).bytes()
                 } else {
-                    // returns log2(effective-align).
-                    // This is ok since `pack` applies to all fields equally.
-                    // The calculation assumes that size is an integer multiple of align, except for ZSTs.
-                    //
+                    // Returns `log2(effective-align)`. This is ok since `pack` applies to all
+                    // fields equally. The calculation assumes that size is an integer multiple of
+                    // align, except for ZSTs.
                     let align = layout.align().abi.bytes();
                     let size = layout.size().bytes();
                     let niche_size = layout.largest_niche().map(|n| n.available(dl)).unwrap_or(0);
-                    // group [u8; 4] with align-4 or [u8; 6] with align-2 fields
+                    // Group [u8; 4] with align-4 or [u8; 6] with align-2 fields.
                     let size_as_align = align.max(size).trailing_zeros();
                     let size_as_align = if largest_niche_size > 0 {
                         match niche_bias {
-                            // Given `A(u8, [u8; 16])` and `B(bool, [u8; 16])` we want to bump the array
-                            // to the front in the first case (for aligned loads) but keep the bool in front
-                            // in the second case for its niches.
+                            // Given `A(u8, [u8; 16])` and `B(bool, [u8; 16])` we want to bump the
+                            // array to the front in the first case (for aligned loads) but keep
+                            // the bool in front in the second case for its niches.
                             NicheBias::Start => max_field_align.trailing_zeros().min(size_as_align),
                             // When moving niches towards the end of the struct then for
                             // A((u8, u8, u8, bool), (u8, bool, u8)) we want to keep the first tuple
@@ -931,14 +931,14 @@ fn univariant(
 
             match kind {
                 StructKind::AlwaysSized | StructKind::MaybeUnsized => {
-                    // Currently `LayoutS` only exposes a single niche so sorting is usually sufficient
-                    // to get one niche into the preferred position. If it ever supported multiple niches
-                    // then a more advanced pick-and-pack approach could provide better results.
-                    // But even for the single-niche cache it's not optimal. E.g. for
-                    // A(u32, (bool, u8), u16) it would be possible to move the bool to the front
-                    // but it would require packing the tuple together with the u16 to build a 4-byte
-                    // group so that the u32 can be placed after it without padding. This kind
-                    // of packing can't be achieved by sorting.
+                    // Currently `LayoutS` only exposes a single niche so sorting is usually
+                    // sufficient to get one niche into the preferred position. If it ever
+                    // supported multiple niches then a more advanced pick-and-pack approach could
+                    // provide better results. But even for the single-niche cache it's not
+                    // optimal. E.g. for A(u32, (bool, u8), u16) it would be possible to move the
+                    // bool to the front but it would require packing the tuple together with the
+                    // u16 to build a 4-byte group so that the u32 can be placed after it without
+                    // padding. This kind of packing can't be achieved by sorting.
                     optimizing.sort_by_key(|&x| {
                         let f = fields[x];
                         let field_size = f.size().bytes();

compiler/rustc_abi/src/lib.rs

@@ -53,10 +53,11 @@ bitflags! {
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 #[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_Generic))]
 pub enum IntegerType {
-    /// Pointer sized integer type, i.e. isize and usize. The field shows signedness, that
-    /// is, `Pointer(true)` is isize.
+    /// Pointer-sized integer type, i.e. `isize` and `usize`. The field shows signedness, e.g.
+    /// `Pointer(true)` means `isize`.
     Pointer(bool),
-    /// Fix sized integer type, e.g. i8, u32, i128 The bool field shows signedness, `Fixed(I8, false)` means `u8`
+    /// Fixed-sized integer type, e.g. `i8`, `u32`, `i128`. The bool field shows signedness, e.g.
+    /// `Fixed(I8, false)` means `u8`.
     Fixed(Integer, bool),
 }
 
@@ -69,7 +70,7 @@ impl IntegerType {
     }
 }
 
-/// Represents the repr options provided by the user,
+/// Represents the repr options provided by the user.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Default)]
 #[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_Generic))]
 pub struct ReprOptions {
@@ -139,7 +140,7 @@ impl ReprOptions {
     }
 
     /// Returns `true` if this type is valid for reordering and `-Z randomize-layout`
-    /// was enabled for its declaration crate
+    /// was enabled for its declaration crate.
     pub fn can_randomize_type_layout(&self) -> bool {
         !self.inhibit_struct_field_reordering_opt()
             && self.flags.contains(ReprFlags::RANDOMIZE_LAYOUT)
@@ -217,7 +218,8 @@ pub enum TargetDataLayoutErrors<'a> {
 }
 
 impl TargetDataLayout {
-    /// Parse data layout from an [llvm data layout string](https://llvm.org/docs/LangRef.html#data-layout)
+    /// Parse data layout from an
+    /// [llvm data layout string](https://llvm.org/docs/LangRef.html#data-layout)
     ///
     /// This function doesn't fill `c_enum_min_size` and it will always be `I32` since it can not be
     /// determined from llvm string.
@@ -747,7 +749,6 @@ impl Align {
 /// A pair of alignments, ABI-mandated and preferred.
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 #[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
-
 pub struct AbiAndPrefAlign {
     pub abi: Align,
     pub pref: Align,
@@ -773,7 +774,6 @@ impl AbiAndPrefAlign {
 /// Integers, also used for enum discriminants.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
 #[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_Generic))]
-
 pub enum Integer {
     I8,
     I16,
@@ -937,8 +937,7 @@ impl Primitive {
 }
 
 /// Inclusive wrap-around range of valid values, that is, if
-/// start > end, it represents `start..=MAX`,
-/// followed by `0..=end`.
+/// start > end, it represents `start..=MAX`, followed by `0..=end`.
 ///
 /// That is, for an i8 primitive, a range of `254..=2` means following
 /// sequence:
@@ -1066,15 +1065,17 @@ impl Scalar {
     }
 
     #[inline]
-    /// Allows the caller to mutate the valid range. This operation will panic if attempted on a union.
+    /// Allows the caller to mutate the valid range. This operation will panic if attempted on a
+    /// union.
     pub fn valid_range_mut(&mut self) -> &mut WrappingRange {
         match self {
             Scalar::Initialized { valid_range, .. } => valid_range,
             Scalar::Union { .. } => panic!("cannot change the valid range of a union"),
         }
     }
 
-    /// Returns `true` if all possible numbers are valid, i.e `valid_range` covers the whole layout
+    /// Returns `true` if all possible numbers are valid, i.e `valid_range` covers the whole
+    /// layout.
     #[inline]
     pub fn is_always_valid<C: HasDataLayout>(&self, cx: &C) -> bool {
         match *self {
@@ -1252,7 +1253,6 @@ impl AddressSpace {
 /// in terms of categories of C types there are ABI rules for.
 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
 #[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
-
 pub enum Abi {
     Uninhabited,
     Scalar(Scalar),
@@ -1457,17 +1457,19 @@ impl Niche {
             return None;
         }
 
-        // Extend the range of valid values being reserved by moving either `v.start` or `v.end` bound.
-        // Given an eventual `Option<T>`, we try to maximize the chance for `None` to occupy the niche of zero.
-        // This is accomplished by preferring enums with 2 variants(`count==1`) and always taking the shortest path to niche zero.
-        // Having `None` in niche zero can enable some special optimizations.
+        // Extend the range of valid values being reserved by moving either `v.start` or `v.end`
+        // bound. Given an eventual `Option<T>`, we try to maximize the chance for `None` to occupy
+        // the niche of zero. This is accomplished by preferring enums with 2 variants(`count==1`)
+        // and always taking the shortest path to niche zero. Having `None` in niche zero can
+        // enable some special optimizations.
         //
         // Bound selection criteria:
         // 1. Select closest to zero given wrapping semantics.
         // 2. Avoid moving past zero if possible.
         //
-        // In practice this means that enums with `count > 1` are unlikely to claim niche zero, since they have to fit perfectly.
-        // If niche zero is already reserved, the selection of bounds are of little interest.
+        // In practice this means that enums with `count > 1` are unlikely to claim niche zero,
+        // since they have to fit perfectly. If niche zero is already reserved, the selection of
+        // bounds are of little interest.
         let move_start = |v: WrappingRange| {
             let start = v.start.wrapping_sub(count) & max_value;
             Some((start, Scalar::Initialized { value, valid_range: v.with_start(start) }))