diff options
Diffstat (limited to 'compiler/rustc_serialize/src/opaque.rs')
| -rw-r--r-- | compiler/rustc_serialize/src/opaque.rs | 277 |
1 files changed, 91 insertions, 186 deletions
diff --git a/compiler/rustc_serialize/src/opaque.rs b/compiler/rustc_serialize/src/opaque.rs index 0ffc537ee..552554390 100644 --- a/compiler/rustc_serialize/src/opaque.rs +++ b/compiler/rustc_serialize/src/opaque.rs @@ -3,10 +3,8 @@ use crate::serialize::{Decodable, Decoder, Encodable, Encoder}; use std::fs::File; use std::io::{self, Write}; use std::marker::PhantomData; -use std::mem::MaybeUninit; use std::ops::Range; use std::path::Path; -use std::ptr; // ----------------------------------------------------------------------------- // Encoder @@ -24,10 +22,12 @@ const BUF_SIZE: usize = 8192; /// size of the buffer, rather than the full length of the encoded data, and /// because it doesn't need to reallocate memory along the way. pub struct FileEncoder { - /// The input buffer. For adequate performance, we need more control over - /// buffering than `BufWriter` offers. If `BufWriter` ever offers a raw - /// buffer access API, we can use it, and remove `buf` and `buffered`. - buf: Box<[MaybeUninit<u8>]>, + // The input buffer. For adequate performance, we need to be able to write + // directly to the unwritten region of the buffer, without calling copy_from_slice. + // Note that our buffer is always initialized so that we can do that direct access + // without unsafe code. Users of this type write many more than BUF_SIZE bytes, so the + // initialization is approximately free. + buf: Box<[u8; BUF_SIZE]>, buffered: usize, flushed: usize, file: File, @@ -38,12 +38,13 @@ pub struct FileEncoder { impl FileEncoder { pub fn new<P: AsRef<Path>>(path: P) -> io::Result<Self> { - // Create the file for reading and writing, because some encoders do both - // (e.g. the metadata encoder when -Zmeta-stats is enabled) + // File::create opens the file for writing only. When -Zmeta-stats is enabled, the metadata + // encoder rewinds the file to inspect what was written. So we need to always open the file + // for reading and writing. let file = File::options().read(true).write(true).create(true).truncate(true).open(path)?; Ok(FileEncoder { - buf: Box::new_uninit_slice(BUF_SIZE), + buf: vec![0u8; BUF_SIZE].into_boxed_slice().try_into().unwrap(), buffered: 0, flushed: 0, file, @@ -54,94 +55,19 @@ impl FileEncoder { #[inline] pub fn position(&self) -> usize { // Tracking position this way instead of having a `self.position` field - // means that we don't have to update the position on every write call. + // means that we only need to update `self.buffered` on a write call, + // as opposed to updating `self.position` and `self.buffered`. self.flushed + self.buffered } + #[cold] + #[inline(never)] pub fn flush(&mut self) { - // This is basically a copy of `BufWriter::flush`. If `BufWriter` ever - // offers a raw buffer access API, we can use it, and remove this. - - /// Helper struct to ensure the buffer is updated after all the writes - /// are complete. It tracks the number of written bytes and drains them - /// all from the front of the buffer when dropped. - struct BufGuard<'a> { - buffer: &'a mut [u8], - encoder_buffered: &'a mut usize, - encoder_flushed: &'a mut usize, - flushed: usize, - } - - impl<'a> BufGuard<'a> { - fn new( - buffer: &'a mut [u8], - encoder_buffered: &'a mut usize, - encoder_flushed: &'a mut usize, - ) -> Self { - assert_eq!(buffer.len(), *encoder_buffered); - Self { buffer, encoder_buffered, encoder_flushed, flushed: 0 } - } - - /// The unwritten part of the buffer - fn remaining(&self) -> &[u8] { - &self.buffer[self.flushed..] - } - - /// Flag some bytes as removed from the front of the buffer - fn consume(&mut self, amt: usize) { - self.flushed += amt; - } - - /// true if all of the bytes have been written - fn done(&self) -> bool { - self.flushed >= *self.encoder_buffered - } - } - - impl Drop for BufGuard<'_> { - fn drop(&mut self) { - if self.flushed > 0 { - if self.done() { - *self.encoder_flushed += *self.encoder_buffered; - *self.encoder_buffered = 0; - } else { - self.buffer.copy_within(self.flushed.., 0); - *self.encoder_flushed += self.flushed; - *self.encoder_buffered -= self.flushed; - } - } - } - } - - // If we've already had an error, do nothing. It'll get reported after - // `finish` is called. - if self.res.is_err() { - return; - } - - let mut guard = BufGuard::new( - unsafe { MaybeUninit::slice_assume_init_mut(&mut self.buf[..self.buffered]) }, - &mut self.buffered, - &mut self.flushed, - ); - - while !guard.done() { - match self.file.write(guard.remaining()) { - Ok(0) => { - self.res = Err(io::Error::new( - io::ErrorKind::WriteZero, - "failed to write the buffered data", - )); - return; - } - Ok(n) => guard.consume(n), - Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {} - Err(e) => { - self.res = Err(e); - return; - } - } + if self.res.is_ok() { + self.res = self.file.write_all(&self.buf[..self.buffered]); } + self.flushed += self.buffered; + self.buffered = 0; } pub fn file(&self) -> &File { @@ -149,91 +75,89 @@ impl FileEncoder { } #[inline] - fn write_one(&mut self, value: u8) { - let mut buffered = self.buffered; - - if std::intrinsics::unlikely(buffered + 1 > BUF_SIZE) { - self.flush(); - buffered = 0; - } + fn buffer_empty(&mut self) -> &mut [u8] { + // SAFETY: self.buffered is inbounds as an invariant of the type + unsafe { self.buf.get_unchecked_mut(self.buffered..) } + } - // SAFETY: The above check and `flush` ensures that there is enough - // room to write the input to the buffer. - unsafe { - *MaybeUninit::slice_as_mut_ptr(&mut self.buf).add(buffered) = value; + #[cold] + #[inline(never)] + fn write_all_cold_path(&mut self, buf: &[u8]) { + self.flush(); + if let Some(dest) = self.buf.get_mut(..buf.len()) { + dest.copy_from_slice(buf); + self.buffered += buf.len(); + } else { + if self.res.is_ok() { + self.res = self.file.write_all(buf); + } + self.flushed += buf.len(); } - - self.buffered = buffered + 1; } #[inline] fn write_all(&mut self, buf: &[u8]) { - let buf_len = buf.len(); - - if std::intrinsics::likely(buf_len <= BUF_SIZE) { - let mut buffered = self.buffered; - - if std::intrinsics::unlikely(buffered + buf_len > BUF_SIZE) { - self.flush(); - buffered = 0; - } - - // SAFETY: The above check and `flush` ensures that there is enough - // room to write the input to the buffer. - unsafe { - let src = buf.as_ptr(); - let dst = MaybeUninit::slice_as_mut_ptr(&mut self.buf).add(buffered); - ptr::copy_nonoverlapping(src, dst, buf_len); - } - - self.buffered = buffered + buf_len; + if let Some(dest) = self.buffer_empty().get_mut(..buf.len()) { + dest.copy_from_slice(buf); + self.buffered += buf.len(); } else { - self.write_all_unbuffered(buf); + self.write_all_cold_path(buf); } } - fn write_all_unbuffered(&mut self, mut buf: &[u8]) { - // If we've already had an error, do nothing. It'll get reported after - // `finish` is called. - if self.res.is_err() { - return; - } - - if self.buffered > 0 { + /// Write up to `N` bytes to this encoder. + /// + /// This function can be used to avoid the overhead of calling memcpy for writes that + /// have runtime-variable length, but are small and have a small fixed upper bound. + /// + /// This can be used to do in-place encoding as is done for leb128 (without this function + /// we would need to write to a temporary buffer then memcpy into the encoder), and it can + /// also be used to implement the varint scheme we use for rmeta and dep graph encoding, + /// where we only want to encode the first few bytes of an integer. Copying in the whole + /// integer then only advancing the encoder state for the few bytes we care about is more + /// efficient than calling [`FileEncoder::write_all`], because variable-size copies are + /// always lowered to `memcpy`, which has overhead and contains a lot of logic we can bypass + /// with this function. Note that common architectures support fixed-size writes up to 8 bytes + /// with one instruction, so while this does in some sense do wasted work, we come out ahead. + #[inline] + pub fn write_with<const N: usize>(&mut self, visitor: impl FnOnce(&mut [u8; N]) -> usize) { + let flush_threshold = const { BUF_SIZE.checked_sub(N).unwrap() }; + if std::intrinsics::unlikely(self.buffered > flush_threshold) { self.flush(); } - - // This is basically a copy of `Write::write_all` but also updates our - // `self.flushed`. It's necessary because `Write::write_all` does not - // return the number of bytes written when an error is encountered, and - // without that, we cannot accurately update `self.flushed` on error. - while !buf.is_empty() { - match self.file.write(buf) { - Ok(0) => { - self.res = Err(io::Error::new( - io::ErrorKind::WriteZero, - "failed to write whole buffer", - )); - return; - } - Ok(n) => { - buf = &buf[n..]; - self.flushed += n; - } - Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {} - Err(e) => { - self.res = Err(e); - return; - } - } + // SAFETY: We checked above that that N < self.buffer_empty().len(), + // and if isn't, flush ensures that our empty buffer is now BUF_SIZE. + // We produce a post-mono error if N > BUF_SIZE. + let buf = unsafe { self.buffer_empty().first_chunk_mut::<N>().unwrap_unchecked() }; + let written = visitor(buf); + // We have to ensure that an errant visitor cannot cause self.buffered to exeed BUF_SIZE. + if written > N { + Self::panic_invalid_write::<N>(written); } + self.buffered += written; + } + + #[cold] + #[inline(never)] + fn panic_invalid_write<const N: usize>(written: usize) { + panic!("FileEncoder::write_with::<{N}> cannot be used to write {written} bytes"); + } + + /// Helper for calls where [`FileEncoder::write_with`] always writes the whole array. + #[inline] + pub fn write_array<const N: usize>(&mut self, buf: [u8; N]) { + self.write_with(|dest| { + *dest = buf; + N + }) } pub fn finish(mut self) -> Result<usize, io::Error> { self.flush(); - - let res = std::mem::replace(&mut self.res, Ok(())); - res.map(|()| self.position()) + match std::mem::replace(&mut self.res, Ok(())) { + Ok(()) => Ok(self.position()), + Err(e) => Err(e), + } } } @@ -241,7 +165,7 @@ impl Drop for FileEncoder { fn drop(&mut self) { // Likely to be a no-op, because `finish` should have been called and // it also flushes. But do it just in case. - let _result = self.flush(); + self.flush(); } } @@ -249,26 +173,7 @@ macro_rules! write_leb128 { ($this_fn:ident, $int_ty:ty, $write_leb_fn:ident) => { #[inline] fn $this_fn(&mut self, v: $int_ty) { - const MAX_ENCODED_LEN: usize = $crate::leb128::max_leb128_len::<$int_ty>(); - - let mut buffered = self.buffered; - - // This can't overflow because BUF_SIZE and MAX_ENCODED_LEN are both - // quite small. - if std::intrinsics::unlikely(buffered + MAX_ENCODED_LEN > BUF_SIZE) { - self.flush(); - buffered = 0; - } - - // SAFETY: The above check and flush ensures that there is enough - // room to write the encoded value to the buffer. - let buf = unsafe { - &mut *(self.buf.as_mut_ptr().add(buffered) - as *mut [MaybeUninit<u8>; MAX_ENCODED_LEN]) - }; - - let encoded = leb128::$write_leb_fn(buf, v); - self.buffered = buffered + encoded.len(); + self.write_with(|buf| leb128::$write_leb_fn(buf, v)) } }; } @@ -281,12 +186,12 @@ impl Encoder for FileEncoder { #[inline] fn emit_u16(&mut self, v: u16) { - self.write_all(&v.to_le_bytes()); + self.write_array(v.to_le_bytes()); } #[inline] fn emit_u8(&mut self, v: u8) { - self.write_one(v); + self.write_array([v]); } write_leb128!(emit_isize, isize, write_isize_leb128); @@ -296,7 +201,7 @@ impl Encoder for FileEncoder { #[inline] fn emit_i16(&mut self, v: i16) { - self.write_all(&v.to_le_bytes()); + self.write_array(v.to_le_bytes()); } #[inline] @@ -353,7 +258,7 @@ impl<'a> MemDecoder<'a> { } #[inline] - fn read_array<const N: usize>(&mut self) -> [u8; N] { + pub fn read_array<const N: usize>(&mut self) -> [u8; N] { self.read_raw_bytes(N).try_into().unwrap() } @@ -495,7 +400,7 @@ impl Encodable<FileEncoder> for IntEncodedWithFixedSize { #[inline] fn encode(&self, e: &mut FileEncoder) { let _start_pos = e.position(); - e.emit_raw_bytes(&self.0.to_le_bytes()); + e.write_array(self.0.to_le_bytes()); let _end_pos = e.position(); debug_assert_eq!((_end_pos - _start_pos), IntEncodedWithFixedSize::ENCODED_SIZE); } |