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Use AttrVec in more places.

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In some places we use `Vec<Attribute>` and some places we use
`ThinVec<Attribute>` (a.k.a. `AttrVec`). This results in various points
where we have to convert between `Vec` and `ThinVec`.

This commit changes the places that use `Vec<Attribute>` to use
`AttrVec`. A lot of this is mechanical and boring, but there are
some interesting parts:
- It adds a few new methods to `ThinVec`.
- It implements `MapInPlace` for `ThinVec`, and introduces a macro to
  avoid the repetition of this trait for `Vec`, `SmallVec`, and
  `ThinVec`.

Overall, it makes the code a little nicer, and has little effect on
performance. But it is a precursor to removing
`rustc_data_structures::thin_vec::ThinVec` and replacing it with
`thin_vec::ThinVec`, which is implemented more efficiently.
This commit is contained in:
Nicholas Nethercote 2022-08-17 12:34:33 +10:00
parent 650bff80a6
commit 619b8abaa6
49 changed files with 352 additions and 392 deletions
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129
compiler/rustc_data_structures/src/map_in_place.rs
View file

@ -1,3 +1,4 @@
use crate::thin_vec::ThinVec;
use smallvec::{Array, SmallVec};
use std::ptr;
@ -15,94 +16,64 @@ pub trait MapInPlace<T>: Sized {
I: IntoIterator<Item = T>;
}
impl<T> MapInPlace<T> for Vec<T> {
fn flat_map_in_place<F, I>(&mut self, mut f: F)
where
F: FnMut(T) -> I,
I: IntoIterator<Item = T>,
{
let mut read_i = 0;
let mut write_i = 0;
unsafe {
let mut old_len = self.len();
self.set_len(0); // make sure we just leak elements in case of panic
// The implementation of this method is syntactically identical for all the
// different vector types.
macro_rules! flat_map_in_place {
() => {
fn flat_map_in_place<F, I>(&mut self, mut f: F)
where
F: FnMut(T) -> I,
I: IntoIterator<Item = T>,
{
let mut read_i = 0;
let mut write_i = 0;
unsafe {
let mut old_len = self.len();
self.set_len(0); // make sure we just leak elements in case of panic
while read_i < old_len {
// move the read_i'th item out of the vector and map it
// to an iterator
let e = ptr::read(self.as_ptr().add(read_i));
let iter = f(e).into_iter();
read_i += 1;
while read_i < old_len {
// move the read_i'th item out of the vector and map it
// to an iterator
let e = ptr::read(self.as_ptr().add(read_i));
let iter = f(e).into_iter();
read_i += 1;
for e in iter {
if write_i < read_i {
ptr::write(self.as_mut_ptr().add(write_i), e);
write_i += 1;
} else {
// If this is reached we ran out of space
// in the middle of the vector.
// However, the vector is in a valid state here,
// so we just do a somewhat inefficient insert.
self.set_len(old_len);
self.insert(write_i, e);
for e in iter {
if write_i < read_i {
ptr::write(self.as_mut_ptr().add(write_i), e);
write_i += 1;
} else {
// If this is reached we ran out of space
// in the middle of the vector.
// However, the vector is in a valid state here,
// so we just do a somewhat inefficient insert.
self.set_len(old_len);
self.insert(write_i, e);
old_len = self.len();
self.set_len(0);
old_len = self.len();
self.set_len(0);
read_i += 1;
write_i += 1;
read_i += 1;
write_i += 1;
}
}
}
}
// write_i tracks the number of actually written new items.
self.set_len(write_i);
// write_i tracks the number of actually written new items.
self.set_len(write_i);
}
}
}
};
}
impl<T> MapInPlace<T> for Vec<T> {
flat_map_in_place!();
}
impl<T, A: Array<Item = T>> MapInPlace<T> for SmallVec<A> {
fn flat_map_in_place<F, I>(&mut self, mut f: F)
where
F: FnMut(T) -> I,
I: IntoIterator<Item = T>,
{
let mut read_i = 0;
let mut write_i = 0;
unsafe {
let mut old_len = self.len();
self.set_len(0); // make sure we just leak elements in case of panic
while read_i < old_len {
// move the read_i'th item out of the vector and map it
// to an iterator
let e = ptr::read(self.as_ptr().add(read_i));
let iter = f(e).into_iter();
read_i += 1;
for e in iter {
if write_i < read_i {
ptr::write(self.as_mut_ptr().add(write_i), e);
write_i += 1;
} else {
// If this is reached we ran out of space
// in the middle of the vector.
// However, the vector is in a valid state here,
// so we just do a somewhat inefficient insert.
self.set_len(old_len);
self.insert(write_i, e);
old_len = self.len();
self.set_len(0);
read_i += 1;
write_i += 1;
}
}
}
// write_i tracks the number of actually written new items.
self.set_len(write_i);
}
}
flat_map_in_place!();
}
impl<T> MapInPlace<T> for ThinVec<T> {
flat_map_in_place!();
}

45
compiler/rustc_data_structures/src/thin_vec.rs
View file

@ -27,6 +27,51 @@ impl<T> ThinVec<T> {
ThinVec(None) => *self = vec![item].into(),
}
}
/// Note: if `set_len(0)` is called on a non-empty `ThinVec`, it will
/// remain in the `Some` form. This is required for some code sequences
/// (such as the one in `flat_map_in_place`) that call `set_len(0)` before
/// an operation that might panic, and then call `set_len(n)` again
/// afterwards.
pub unsafe fn set_len(&mut self, new_len: usize) {
match *self {
ThinVec(None) => {
// A prerequisite of `Vec::set_len` is that `new_len` must be
// less than or equal to capacity(). The same applies here.
if new_len != 0 {
panic!("unsafe ThinVec::set_len({})", new_len);
}
}
ThinVec(Some(ref mut vec)) => vec.set_len(new_len),
}
}
pub fn insert(&mut self, index: usize, value: T) {
match *self {
ThinVec(None) => {
if index == 0 {
*self = vec![value].into();
} else {
panic!("invalid ThinVec::insert");
}
}
ThinVec(Some(ref mut vec)) => vec.insert(index, value),
}
}
pub fn remove(&mut self, index: usize) -> T {
match self {
ThinVec(None) => panic!("invalid ThinVec::remove"),
ThinVec(Some(vec)) => vec.remove(index),
}
}
pub fn as_slice(&self) -> &[T] {
match self {
ThinVec(None) => &[],
ThinVec(Some(vec)) => vec.as_slice(),
}
}
}
impl<T> From<Vec<T>> for ThinVec<T> {