Auto merge of #83465 - michaelwoerister:safe-read_raw_bytes, r=cjgillot

Allow for reading raw bytes from rustc_serialize::Decoder without unsafe code

The current `read_raw_bytes` method requires using `MaybeUninit` and `unsafe`. I don't think this is necessary. Let's see if a safe interface has any performance drawbacks.

This is a followup to #83273 and will make it easier to rebase #82183.

r? `@cjgillot`
This commit is contained in:
bors 2021-03-26 01:28:59 +00:00
commit 0ced530534
5 changed files with 48 additions and 45 deletions

View File

@ -1,7 +1,7 @@
use crate::stable_hasher;
use rustc_serialize::{Decodable, Encodable};
use std::convert::TryInto;
use std::hash::{Hash, Hasher};
use std::mem::{self, MaybeUninit};
#[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Clone, Copy)]
#[repr(C)]
@ -60,6 +60,29 @@ impl Fingerprint {
pub fn to_hex(&self) -> String {
format!("{:x}{:x}", self.0, self.1)
}
#[inline]
pub fn to_le_bytes(&self) -> [u8; 16] {
// This seems to optimize to the same machine code as
// `unsafe { mem::transmute(*k) }`. Well done, LLVM! :)
let mut result = [0u8; 16];
let first_half: &mut [u8; 8] = (&mut result[0..8]).try_into().unwrap();
*first_half = self.0.to_le_bytes();
let second_half: &mut [u8; 8] = (&mut result[8..16]).try_into().unwrap();
*second_half = self.1.to_le_bytes();
result
}
#[inline]
pub fn from_le_bytes(bytes: [u8; 16]) -> Fingerprint {
Fingerprint(
u64::from_le_bytes(bytes[0..8].try_into().unwrap()),
u64::from_le_bytes(bytes[8..16].try_into().unwrap()),
)
}
}
impl std::fmt::Display for Fingerprint {
@ -119,8 +142,7 @@ impl_stable_hash_via_hash!(Fingerprint);
impl<E: rustc_serialize::Encoder> Encodable<E> for Fingerprint {
#[inline]
fn encode(&self, s: &mut E) -> Result<(), E::Error> {
let bytes: [u8; 16] = unsafe { mem::transmute([self.0.to_le(), self.1.to_le()]) };
s.emit_raw_bytes(&bytes)?;
s.emit_raw_bytes(&self.to_le_bytes()[..])?;
Ok(())
}
}
@ -128,11 +150,9 @@ impl<E: rustc_serialize::Encoder> Encodable<E> for Fingerprint {
impl<D: rustc_serialize::Decoder> Decodable<D> for Fingerprint {
#[inline]
fn decode(d: &mut D) -> Result<Self, D::Error> {
let mut bytes: [MaybeUninit<u8>; 16] = MaybeUninit::uninit_array();
d.read_raw_bytes(&mut bytes)?;
let [l, r]: [u64; 2] = unsafe { mem::transmute(bytes) };
Ok(Fingerprint(u64::from_le(l), u64::from_le(r)))
let mut bytes = [0u8; 16];
d.read_raw_bytes_into(&mut bytes[..])?;
Ok(Fingerprint::from_le_bytes(bytes))
}
}

View File

@ -473,8 +473,8 @@ macro_rules! implement_ty_decoder {
}
#[inline]
fn read_raw_bytes(&mut self, bytes: &mut [std::mem::MaybeUninit<u8>]) -> Result<(), Self::Error> {
self.opaque.read_raw_bytes(bytes)
fn read_raw_bytes_into(&mut self, bytes: &mut [u8]) -> Result<(), Self::Error> {
self.opaque.read_raw_bytes_into(bytes)
}
fn error(&mut self, err: &str) -> Self::Error {

View File

@ -188,7 +188,6 @@ use std::collections::{BTreeMap, HashMap};
use std::io;
use std::io::prelude::*;
use std::mem::swap;
use std::mem::MaybeUninit;
use std::num::FpCategory as Fp;
use std::ops::Index;
use std::str::FromStr;
@ -2367,10 +2366,9 @@ impl crate::Decoder for Decoder {
expect!(self.pop(), String).map(Cow::Owned)
}
fn read_raw_bytes(&mut self, s: &mut [MaybeUninit<u8>]) -> Result<(), Self::Error> {
fn read_raw_bytes_into(&mut self, s: &mut [u8]) -> Result<(), Self::Error> {
for c in s.iter_mut() {
let h = self.read_u8()?;
unsafe { *c.as_mut_ptr() = h };
*c = self.read_u8()?;
}
Ok(())
}

View File

@ -1,6 +1,7 @@
use crate::leb128::{self, max_leb128_len};
use crate::serialize::{self, Decoder as _, Encoder as _};
use crate::serialize::{self, Encoder as _};
use std::borrow::Cow;
use std::convert::TryInto;
use std::fs::File;
use std::io::{self, Write};
use std::mem::MaybeUninit;
@ -539,6 +540,13 @@ impl<'a> Decoder<'a> {
pub fn advance(&mut self, bytes: usize) {
self.position += bytes;
}
#[inline]
pub fn read_raw_bytes(&mut self, bytes: usize) -> &'a [u8] {
let start = self.position;
self.position += bytes;
&self.data[start..self.position]
}
}
macro_rules! read_leb128 {
@ -659,22 +667,10 @@ impl<'a> serialize::Decoder for Decoder<'a> {
}
#[inline]
fn read_raw_bytes(&mut self, s: &mut [MaybeUninit<u8>]) -> Result<(), String> {
fn read_raw_bytes_into(&mut self, s: &mut [u8]) -> Result<(), String> {
let start = self.position;
let end = start + s.len();
assert!(end <= self.data.len());
// SAFETY: Both `src` and `dst` point to at least `s.len()` elements:
// `src` points to at least `s.len()` elements by above assert, and
// `dst` points to `s.len()` elements by derivation from `s`.
unsafe {
let src = self.data.as_ptr().add(start);
let dst = s.as_mut_ptr() as *mut u8;
ptr::copy_nonoverlapping(src, dst, s.len());
}
self.position = end;
self.position += s.len();
s.copy_from_slice(&self.data[start..self.position]);
Ok(())
}
}
@ -705,16 +701,7 @@ impl serialize::Encodable<FileEncoder> for [u8] {
impl<'a> serialize::Decodable<Decoder<'a>> for Vec<u8> {
fn decode(d: &mut Decoder<'a>) -> Result<Self, String> {
let len = serialize::Decoder::read_usize(d)?;
let mut v = Vec::with_capacity(len);
let buf = &mut v.spare_capacity_mut()[..len];
d.read_raw_bytes(buf)?;
unsafe {
v.set_len(len);
}
Ok(v)
Ok(d.read_raw_bytes(len).to_owned())
}
}
@ -750,13 +737,12 @@ impl serialize::Encodable<FileEncoder> for IntEncodedWithFixedSize {
impl<'a> serialize::Decodable<Decoder<'a>> for IntEncodedWithFixedSize {
#[inline]
fn decode(decoder: &mut Decoder<'a>) -> Result<IntEncodedWithFixedSize, String> {
let mut bytes = MaybeUninit::uninit_array();
let _start_pos = decoder.position();
decoder.read_raw_bytes(&mut bytes)?;
let bytes = decoder.read_raw_bytes(IntEncodedWithFixedSize::ENCODED_SIZE);
let _end_pos = decoder.position();
debug_assert_eq!((_end_pos - _start_pos), IntEncodedWithFixedSize::ENCODED_SIZE);
let value = u64::from_le_bytes(unsafe { MaybeUninit::array_assume_init(bytes) });
let value = u64::from_le_bytes(bytes.try_into().unwrap());
Ok(IntEncodedWithFixedSize(value))
}
}

View File

@ -7,7 +7,6 @@ Core encoding and decoding interfaces.
use std::borrow::Cow;
use std::cell::{Cell, RefCell};
use std::marker::PhantomData;
use std::mem::MaybeUninit;
use std::path;
use std::rc::Rc;
use std::sync::Arc;
@ -226,7 +225,7 @@ pub trait Decoder {
fn read_f32(&mut self) -> Result<f32, Self::Error>;
fn read_char(&mut self) -> Result<char, Self::Error>;
fn read_str(&mut self) -> Result<Cow<'_, str>, Self::Error>;
fn read_raw_bytes(&mut self, s: &mut [MaybeUninit<u8>]) -> Result<(), Self::Error>;
fn read_raw_bytes_into(&mut self, s: &mut [u8]) -> Result<(), Self::Error>;
// Compound types:
#[inline]