From c3a7ca1125e017ecf5e46685f8ee6feccceec0c7 Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Sun, 6 Nov 2022 13:44:50 +0100 Subject: [PATCH] move InitMask to its own module --- compiler/rustc_codegen_llvm/src/consts.rs | 4 +- .../rustc_const_eval/src/interpret/memory.rs | 6 +- .../src/mir/interpret/allocation.rs | 619 +----------------- .../src/mir/interpret/allocation/init_mask.rs | 530 +++++++++++++++ .../interpret/allocation/provenance_map.rs | 3 - .../rustc_middle/src/mir/interpret/mod.rs | 2 +- compiler/rustc_middle/src/mir/pretty.rs | 16 +- 7 files changed, 582 insertions(+), 598 deletions(-) create mode 100644 compiler/rustc_middle/src/mir/interpret/allocation/init_mask.rs diff --git a/compiler/rustc_codegen_llvm/src/consts.rs b/compiler/rustc_codegen_llvm/src/consts.rs index b58b47df65f..b23074935e1 100644 --- a/compiler/rustc_codegen_llvm/src/consts.rs +++ b/compiler/rustc_codegen_llvm/src/consts.rs @@ -38,9 +38,7 @@ fn append_chunks_of_init_and_uninit_bytes<'ll, 'a, 'b>( alloc: &'a Allocation, range: Range, ) { - let chunks = alloc - .init_mask() - .range_as_init_chunks(Size::from_bytes(range.start), Size::from_bytes(range.end)); + let chunks = alloc.init_mask().range_as_init_chunks(range.clone().into()); let chunk_to_llval = move |chunk| match chunk { InitChunk::Init(range) => { diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs index 19e8dd660f0..4eda9882da3 100644 --- a/compiler/rustc_const_eval/src/interpret/memory.rs +++ b/compiler/rustc_const_eval/src/interpret/memory.rs @@ -1089,7 +1089,7 @@ pub fn mem_copy_repeatedly( .prepare_copy(src_range, dest_offset, num_copies, self) .map_err(|e| e.to_interp_error(dest_alloc_id))?; // Prepare a copy of the initialization mask. - let init = src_alloc.compress_uninit_range(src_range); + let init = src_alloc.init_mask().prepare_copy(src_range); // Destination alloc preparations and access hooks. let (dest_alloc, extra) = self.get_alloc_raw_mut(dest_alloc_id)?; @@ -1155,8 +1155,8 @@ pub fn mem_copy_repeatedly( } // now fill in all the "init" data - dest_alloc.mark_compressed_init_range( - &init, + dest_alloc.init_mask_apply_copy( + init, alloc_range(dest_offset, size), // just a single copy (i.e., not full `dest_range`) num_copies, ); diff --git a/compiler/rustc_middle/src/mir/interpret/allocation.rs b/compiler/rustc_middle/src/mir/interpret/allocation.rs index 62c822ae080..4a80088ca2f 100644 --- a/compiler/rustc_middle/src/mir/interpret/allocation.rs +++ b/compiler/rustc_middle/src/mir/interpret/allocation.rs @@ -1,12 +1,11 @@ //! The virtual memory representation of the MIR interpreter. +mod init_mask; mod provenance_map; use std::borrow::Cow; -use std::convert::{TryFrom, TryInto}; use std::fmt; use std::hash; -use std::iter; use std::ops::Range; use std::ptr; @@ -21,8 +20,11 @@ UnsupportedOpInfo, }; use crate::ty; +use init_mask::*; use provenance_map::*; +pub use init_mask::{InitChunk, InitChunkIter}; + /// This type represents an Allocation in the Miri/CTFE core engine. /// /// Its public API is rather low-level, working directly with allocation offsets and a custom error @@ -110,7 +112,7 @@ pub struct ConstAllocation<'tcx, Prov = AllocId, Extra = ()>( impl<'tcx> fmt::Debug for ConstAllocation<'tcx> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - // The debug-representation of this is very verbose and basically useless, + // The debug representation of this is very verbose and basically useless, // so don't print it. write!(f, "ConstAllocation {{ .. }}") } @@ -185,12 +187,21 @@ pub fn alloc_range(start: Size, size: Size) -> AllocRange { AllocRange { start, size } } -impl AllocRange { +impl From> for AllocRange { #[inline] - pub fn from(r: Range) -> Self { + fn from(r: Range) -> Self { alloc_range(r.start, r.end - r.start) // `Size` subtraction (overflow-checked) } +} + +impl From> for AllocRange { + #[inline] + fn from(r: Range) -> Self { + AllocRange::from(Size::from_bytes(r.start)..Size::from_bytes(r.end)) + } +} +impl AllocRange { #[inline(always)] pub fn end(self) -> Size { self.start + self.size // This does overflow checking. @@ -351,7 +362,12 @@ pub fn get_bytes_strip_provenance( cx: &impl HasDataLayout, range: AllocRange, ) -> AllocResult<&[u8]> { - self.check_init(range)?; + self.init_mask.is_range_initialized(range).map_err(|uninit_range| { + AllocError::InvalidUninitBytes(Some(UninitBytesAccess { + access: range, + uninit: uninit_range, + })) + })?; if !Prov::OFFSET_IS_ADDR { if !self.provenance.range_empty(range, cx) { return Err(AllocError::ReadPointerAsBytes); @@ -395,6 +411,15 @@ pub fn get_bytes_mut_ptr( /// Reading and writing. impl Allocation { + /// Sets the init bit for the given range. + fn mark_init(&mut self, range: AllocRange, is_init: bool) { + if range.size.bytes() == 0 { + return; + } + assert!(self.mutability == Mutability::Mut); + self.init_mask.set_range(range, is_init); + } + /// Reads a *non-ZST* scalar. /// /// If `read_provenance` is `true`, this will also read provenance; otherwise (if the machine @@ -412,7 +437,7 @@ pub fn read_scalar( read_provenance: bool, ) -> AllocResult> { // First and foremost, if anything is uninit, bail. - if self.is_init(range).is_err() { + if self.init_mask.is_range_initialized(range).is_err() { return Err(AllocError::InvalidUninitBytes(None)); } @@ -505,7 +530,7 @@ pub fn write_uninit(&mut self, cx: &impl HasDataLayout, range: AllocRange) -> Al return Ok(()); } - /// Applies a provenance copy. + /// Applies a previously prepared provenance copy. /// The affected range, as defined in the parameters to `provenance().prepare_copy` is expected /// to be clear of provenance. /// @@ -514,584 +539,12 @@ pub fn write_uninit(&mut self, cx: &impl HasDataLayout, range: AllocRange) -> Al pub fn provenance_apply_copy(&mut self, copy: ProvenanceCopy) { self.provenance.apply_copy(copy) } -} - -//////////////////////////////////////////////////////////////////////////////// -// Uninitialized byte tracking -//////////////////////////////////////////////////////////////////////////////// - -type Block = u64; - -/// A bitmask where each bit refers to the byte with the same index. If the bit is `true`, the byte -/// is initialized. If it is `false` the byte is uninitialized. -// Note: for performance reasons when interning, some of the `InitMask` fields can be partially -// hashed. (see the `Hash` impl below for more details), so the impl is not derived. -#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable)] -#[derive(HashStable)] -pub struct InitMask { - blocks: Vec, - len: Size, -} - -// Const allocations are only hashed for interning. However, they can be large, making the hashing -// expensive especially since it uses `FxHash`: it's better suited to short keys, not potentially -// big buffers like the allocation's init mask. We can partially hash some fields when they're -// large. -impl hash::Hash for InitMask { - fn hash(&self, state: &mut H) { - const MAX_BLOCKS_TO_HASH: usize = MAX_BYTES_TO_HASH / std::mem::size_of::(); - const MAX_BLOCKS_LEN: usize = MAX_HASHED_BUFFER_LEN / std::mem::size_of::(); - - // Partially hash the `blocks` buffer when it is large. To limit collisions with common - // prefixes and suffixes, we hash the length and some slices of the buffer. - let block_count = self.blocks.len(); - if block_count > MAX_BLOCKS_LEN { - // Hash the buffer's length. - block_count.hash(state); - - // And its head and tail. - self.blocks[..MAX_BLOCKS_TO_HASH].hash(state); - self.blocks[block_count - MAX_BLOCKS_TO_HASH..].hash(state); - } else { - self.blocks.hash(state); - } - - // Hash the other fields as usual. - self.len.hash(state); - } -} - -impl InitMask { - pub const BLOCK_SIZE: u64 = 64; - - #[inline] - fn bit_index(bits: Size) -> (usize, usize) { - // BLOCK_SIZE is the number of bits that can fit in a `Block`. - // Each bit in a `Block` represents the initialization state of one byte of an allocation, - // so we use `.bytes()` here. - let bits = bits.bytes(); - let a = bits / InitMask::BLOCK_SIZE; - let b = bits % InitMask::BLOCK_SIZE; - (usize::try_from(a).unwrap(), usize::try_from(b).unwrap()) - } - - #[inline] - fn size_from_bit_index(block: impl TryInto, bit: impl TryInto) -> Size { - let block = block.try_into().ok().unwrap(); - let bit = bit.try_into().ok().unwrap(); - Size::from_bytes(block * InitMask::BLOCK_SIZE + bit) - } - - pub fn new(size: Size, state: bool) -> Self { - let mut m = InitMask { blocks: vec![], len: Size::ZERO }; - m.grow(size, state); - m - } - - pub fn set_range(&mut self, start: Size, end: Size, new_state: bool) { - let len = self.len; - if end > len { - self.grow(end - len, new_state); - } - self.set_range_inbounds(start, end, new_state); - } - - pub fn set_range_inbounds(&mut self, start: Size, end: Size, new_state: bool) { - let (blocka, bita) = Self::bit_index(start); - let (blockb, bitb) = Self::bit_index(end); - if blocka == blockb { - // First set all bits except the first `bita`, - // then unset the last `64 - bitb` bits. - let range = if bitb == 0 { - u64::MAX << bita - } else { - (u64::MAX << bita) & (u64::MAX >> (64 - bitb)) - }; - if new_state { - self.blocks[blocka] |= range; - } else { - self.blocks[blocka] &= !range; - } - return; - } - // across block boundaries - if new_state { - // Set `bita..64` to `1`. - self.blocks[blocka] |= u64::MAX << bita; - // Set `0..bitb` to `1`. - if bitb != 0 { - self.blocks[blockb] |= u64::MAX >> (64 - bitb); - } - // Fill in all the other blocks (much faster than one bit at a time). - for block in (blocka + 1)..blockb { - self.blocks[block] = u64::MAX; - } - } else { - // Set `bita..64` to `0`. - self.blocks[blocka] &= !(u64::MAX << bita); - // Set `0..bitb` to `0`. - if bitb != 0 { - self.blocks[blockb] &= !(u64::MAX >> (64 - bitb)); - } - // Fill in all the other blocks (much faster than one bit at a time). - for block in (blocka + 1)..blockb { - self.blocks[block] = 0; - } - } - } - - #[inline] - pub fn get(&self, i: Size) -> bool { - let (block, bit) = Self::bit_index(i); - (self.blocks[block] & (1 << bit)) != 0 - } - - #[inline] - pub fn set(&mut self, i: Size, new_state: bool) { - let (block, bit) = Self::bit_index(i); - self.set_bit(block, bit, new_state); - } - - #[inline] - fn set_bit(&mut self, block: usize, bit: usize, new_state: bool) { - if new_state { - self.blocks[block] |= 1 << bit; - } else { - self.blocks[block] &= !(1 << bit); - } - } - - pub fn grow(&mut self, amount: Size, new_state: bool) { - if amount.bytes() == 0 { - return; - } - let unused_trailing_bits = - u64::try_from(self.blocks.len()).unwrap() * Self::BLOCK_SIZE - self.len.bytes(); - if amount.bytes() > unused_trailing_bits { - let additional_blocks = amount.bytes() / Self::BLOCK_SIZE + 1; - self.blocks.extend( - // FIXME(oli-obk): optimize this by repeating `new_state as Block`. - iter::repeat(0).take(usize::try_from(additional_blocks).unwrap()), - ); - } - let start = self.len; - self.len += amount; - self.set_range_inbounds(start, start + amount, new_state); // `Size` operation - } - - /// Returns the index of the first bit in `start..end` (end-exclusive) that is equal to is_init. - fn find_bit(&self, start: Size, end: Size, is_init: bool) -> Option { - /// A fast implementation of `find_bit`, - /// which skips over an entire block at a time if it's all 0s (resp. 1s), - /// and finds the first 1 (resp. 0) bit inside a block using `trailing_zeros` instead of a loop. - /// - /// Note that all examples below are written with 8 (instead of 64) bit blocks for simplicity, - /// and with the least significant bit (and lowest block) first: - /// ```text - /// 00000000|00000000 - /// ^ ^ ^ ^ - /// index: 0 7 8 15 - /// ``` - /// Also, if not stated, assume that `is_init = true`, that is, we are searching for the first 1 bit. - fn find_bit_fast( - init_mask: &InitMask, - start: Size, - end: Size, - is_init: bool, - ) -> Option { - /// Search one block, returning the index of the first bit equal to `is_init`. - fn search_block( - bits: Block, - block: usize, - start_bit: usize, - is_init: bool, - ) -> Option { - // For the following examples, assume this function was called with: - // bits = 0b00111011 - // start_bit = 3 - // is_init = false - // Note that, for the examples in this function, the most significant bit is written first, - // which is backwards compared to the comments in `find_bit`/`find_bit_fast`. - - // Invert bits so we're always looking for the first set bit. - // ! 0b00111011 - // bits = 0b11000100 - let bits = if is_init { bits } else { !bits }; - // Mask off unused start bits. - // 0b11000100 - // & 0b11111000 - // bits = 0b11000000 - let bits = bits & (!0 << start_bit); - // Find set bit, if any. - // bit = trailing_zeros(0b11000000) - // bit = 6 - if bits == 0 { - None - } else { - let bit = bits.trailing_zeros(); - Some(InitMask::size_from_bit_index(block, bit)) - } - } - - if start >= end { - return None; - } - - // Convert `start` and `end` to block indexes and bit indexes within each block. - // We must convert `end` to an inclusive bound to handle block boundaries correctly. - // - // For example: - // - // (a) 00000000|00000000 (b) 00000000| - // ^~~~~~~~~~~^ ^~~~~~~~~^ - // start end start end - // - // In both cases, the block index of `end` is 1. - // But we do want to search block 1 in (a), and we don't in (b). - // - // We subtract 1 from both end positions to make them inclusive: - // - // (a) 00000000|00000000 (b) 00000000| - // ^~~~~~~~~~^ ^~~~~~~^ - // start end_inclusive start end_inclusive - // - // For (a), the block index of `end_inclusive` is 1, and for (b), it's 0. - // This provides the desired behavior of searching blocks 0 and 1 for (a), - // and searching only block 0 for (b). - // There is no concern of overflows since we checked for `start >= end` above. - let (start_block, start_bit) = InitMask::bit_index(start); - let end_inclusive = Size::from_bytes(end.bytes() - 1); - let (end_block_inclusive, _) = InitMask::bit_index(end_inclusive); - - // Handle first block: need to skip `start_bit` bits. - // - // We need to handle the first block separately, - // because there may be bits earlier in the block that should be ignored, - // such as the bit marked (1) in this example: - // - // (1) - // -|------ - // (c) 01000000|00000000|00000001 - // ^~~~~~~~~~~~~~~~~~^ - // start end - if let Some(i) = - search_block(init_mask.blocks[start_block], start_block, start_bit, is_init) - { - // If the range is less than a block, we may find a matching bit after `end`. - // - // For example, we shouldn't successfully find bit (2), because it's after `end`: - // - // (2) - // -------| - // (d) 00000001|00000000|00000001 - // ^~~~~^ - // start end - // - // An alternative would be to mask off end bits in the same way as we do for start bits, - // but performing this check afterwards is faster and simpler to implement. - if i < end { - return Some(i); - } else { - return None; - } - } - - // Handle remaining blocks. - // - // We can skip over an entire block at once if it's all 0s (resp. 1s). - // The block marked (3) in this example is the first block that will be handled by this loop, - // and it will be skipped for that reason: - // - // (3) - // -------- - // (e) 01000000|00000000|00000001 - // ^~~~~~~~~~~~~~~~~~^ - // start end - if start_block < end_block_inclusive { - // This loop is written in a specific way for performance. - // Notably: `..end_block_inclusive + 1` is used for an inclusive range instead of `..=end_block_inclusive`, - // and `.zip(start_block + 1..)` is used to track the index instead of `.enumerate().skip().take()`, - // because both alternatives result in significantly worse codegen. - // `end_block_inclusive + 1` is guaranteed not to wrap, because `end_block_inclusive <= end / BLOCK_SIZE`, - // and `BLOCK_SIZE` (the number of bits per block) will always be at least 8 (1 byte). - for (&bits, block) in init_mask.blocks[start_block + 1..end_block_inclusive + 1] - .iter() - .zip(start_block + 1..) - { - if let Some(i) = search_block(bits, block, 0, is_init) { - // If this is the last block, we may find a matching bit after `end`. - // - // For example, we shouldn't successfully find bit (4), because it's after `end`: - // - // (4) - // -------| - // (f) 00000001|00000000|00000001 - // ^~~~~~~~~~~~~~~~~~^ - // start end - // - // As above with example (d), we could handle the end block separately and mask off end bits, - // but unconditionally searching an entire block at once and performing this check afterwards - // is faster and much simpler to implement. - if i < end { - return Some(i); - } else { - return None; - } - } - } - } - - None - } - - #[cfg_attr(not(debug_assertions), allow(dead_code))] - fn find_bit_slow( - init_mask: &InitMask, - start: Size, - end: Size, - is_init: bool, - ) -> Option { - (start..end).find(|&i| init_mask.get(i) == is_init) - } - - let result = find_bit_fast(self, start, end, is_init); - - debug_assert_eq!( - result, - find_bit_slow(self, start, end, is_init), - "optimized implementation of find_bit is wrong for start={:?} end={:?} is_init={} init_mask={:#?}", - start, - end, - is_init, - self - ); - - result - } -} - -/// A contiguous chunk of initialized or uninitialized memory. -pub enum InitChunk { - Init(Range), - Uninit(Range), -} - -impl InitChunk { - #[inline] - pub fn is_init(&self) -> bool { - match self { - Self::Init(_) => true, - Self::Uninit(_) => false, - } - } - - #[inline] - pub fn range(&self) -> Range { - match self { - Self::Init(r) => r.clone(), - Self::Uninit(r) => r.clone(), - } - } -} - -impl InitMask { - /// Checks whether the range `start..end` (end-exclusive) is entirely initialized. - /// - /// Returns `Ok(())` if it's initialized. Otherwise returns a range of byte - /// indexes for the first contiguous span of the uninitialized access. - #[inline] - pub fn is_range_initialized(&self, start: Size, end: Size) -> Result<(), AllocRange> { - if end > self.len { - return Err(AllocRange::from(self.len..end)); - } - - let uninit_start = self.find_bit(start, end, false); - - match uninit_start { - Some(uninit_start) => { - let uninit_end = self.find_bit(uninit_start, end, true).unwrap_or(end); - Err(AllocRange::from(uninit_start..uninit_end)) - } - None => Ok(()), - } - } - - /// Returns an iterator, yielding a range of byte indexes for each contiguous region - /// of initialized or uninitialized bytes inside the range `start..end` (end-exclusive). - /// - /// The iterator guarantees the following: - /// - Chunks are nonempty. - /// - Chunks are adjacent (each range's start is equal to the previous range's end). - /// - Chunks span exactly `start..end` (the first starts at `start`, the last ends at `end`). - /// - Chunks alternate between [`InitChunk::Init`] and [`InitChunk::Uninit`]. - #[inline] - pub fn range_as_init_chunks(&self, start: Size, end: Size) -> InitChunkIter<'_> { - assert!(end <= self.len); - - let is_init = if start < end { - self.get(start) - } else { - // `start..end` is empty: there are no chunks, so use some arbitrary value - false - }; - - InitChunkIter { init_mask: self, is_init, start, end } - } -} - -/// Yields [`InitChunk`]s. See [`InitMask::range_as_init_chunks`]. -#[derive(Clone)] -pub struct InitChunkIter<'a> { - init_mask: &'a InitMask, - /// Whether the next chunk we will return is initialized. - /// If there are no more chunks, contains some arbitrary value. - is_init: bool, - /// The current byte index into `init_mask`. - start: Size, - /// The end byte index into `init_mask`. - end: Size, -} - -impl<'a> Iterator for InitChunkIter<'a> { - type Item = InitChunk; - - #[inline] - fn next(&mut self) -> Option { - if self.start >= self.end { - return None; - } - - let end_of_chunk = - self.init_mask.find_bit(self.start, self.end, !self.is_init).unwrap_or(self.end); - let range = self.start..end_of_chunk; - - let ret = - Some(if self.is_init { InitChunk::Init(range) } else { InitChunk::Uninit(range) }); - - self.is_init = !self.is_init; - self.start = end_of_chunk; - - ret - } -} -/// Uninitialized bytes. -impl Allocation { - /// Checks whether the given range is entirely initialized. - /// - /// Returns `Ok(())` if it's initialized. Otherwise returns the range of byte - /// indexes of the first contiguous uninitialized access. - fn is_init(&self, range: AllocRange) -> Result<(), AllocRange> { - self.init_mask.is_range_initialized(range.start, range.end()) // `Size` addition - } - - /// Checks that a range of bytes is initialized. If not, returns the `InvalidUninitBytes` - /// error which will report the first range of bytes which is uninitialized. - fn check_init(&self, range: AllocRange) -> AllocResult { - self.is_init(range).map_err(|uninit_range| { - AllocError::InvalidUninitBytes(Some(UninitBytesAccess { - access: range, - uninit: uninit_range, - })) - }) - } - - fn mark_init(&mut self, range: AllocRange, is_init: bool) { - if range.size.bytes() == 0 { - return; - } - assert!(self.mutability == Mutability::Mut); - self.init_mask.set_range(range.start, range.end(), is_init); - } -} - -/// Run-length encoding of the uninit mask. -/// Used to copy parts of a mask multiple times to another allocation. -pub struct InitMaskCompressed { - /// Whether the first range is initialized. - initial: bool, - /// The lengths of ranges that are run-length encoded. - /// The initialization state of the ranges alternate starting with `initial`. - ranges: smallvec::SmallVec<[u64; 1]>, -} - -impl InitMaskCompressed { - pub fn no_bytes_init(&self) -> bool { - // The `ranges` are run-length encoded and of alternating initialization state. - // So if `ranges.len() > 1` then the second block is an initialized range. - !self.initial && self.ranges.len() == 1 - } -} - -/// Transferring the initialization mask to other allocations. -impl Allocation { - /// Creates a run-length encoding of the initialization mask; panics if range is empty. - /// - /// This is essentially a more space-efficient version of - /// `InitMask::range_as_init_chunks(...).collect::>()`. - pub fn compress_uninit_range(&self, range: AllocRange) -> InitMaskCompressed { - // Since we are copying `size` bytes from `src` to `dest + i * size` (`for i in 0..repeat`), - // a naive initialization mask copying algorithm would repeatedly have to read the initialization mask from - // the source and write it to the destination. Even if we optimized the memory accesses, - // we'd be doing all of this `repeat` times. - // Therefore we precompute a compressed version of the initialization mask of the source value and - // then write it back `repeat` times without computing any more information from the source. - - // A precomputed cache for ranges of initialized / uninitialized bits - // 0000010010001110 will become - // `[5, 1, 2, 1, 3, 3, 1]`, - // where each element toggles the state. - - let mut ranges = smallvec::SmallVec::<[u64; 1]>::new(); - - let mut chunks = self.init_mask.range_as_init_chunks(range.start, range.end()).peekable(); - - let initial = chunks.peek().expect("range should be nonempty").is_init(); - - // Here we rely on `range_as_init_chunks` to yield alternating init/uninit chunks. - for chunk in chunks { - let len = chunk.range().end.bytes() - chunk.range().start.bytes(); - ranges.push(len); - } - - InitMaskCompressed { ranges, initial } - } - - /// Applies multiple instances of the run-length encoding to the initialization mask. + /// Applies a previously prepared copy of the init mask. /// /// This is dangerous to use as it can violate internal `Allocation` invariants! /// It only exists to support an efficient implementation of `mem_copy_repeatedly`. - pub fn mark_compressed_init_range( - &mut self, - defined: &InitMaskCompressed, - range: AllocRange, - repeat: u64, - ) { - // An optimization where we can just overwrite an entire range of initialization - // bits if they are going to be uniformly `1` or `0`. - if defined.ranges.len() <= 1 { - self.init_mask.set_range_inbounds( - range.start, - range.start + range.size * repeat, // `Size` operations - defined.initial, - ); - return; - } - - for mut j in 0..repeat { - j *= range.size.bytes(); - j += range.start.bytes(); - let mut cur = defined.initial; - for range in &defined.ranges { - let old_j = j; - j += range; - self.init_mask.set_range_inbounds( - Size::from_bytes(old_j), - Size::from_bytes(j), - cur, - ); - cur = !cur; - } - } + pub fn init_mask_apply_copy(&mut self, copy: InitCopy, range: AllocRange, repeat: u64) { + self.init_mask.apply_copy(copy, range, repeat) } } diff --git a/compiler/rustc_middle/src/mir/interpret/allocation/init_mask.rs b/compiler/rustc_middle/src/mir/interpret/allocation/init_mask.rs new file mode 100644 index 00000000000..4f406cc5ef8 --- /dev/null +++ b/compiler/rustc_middle/src/mir/interpret/allocation/init_mask.rs @@ -0,0 +1,530 @@ +use std::hash; +use std::iter; +use std::ops::Range; + +use rustc_target::abi::Size; + +use super::AllocRange; + +type Block = u64; + +/// A bitmask where each bit refers to the byte with the same index. If the bit is `true`, the byte +/// is initialized. If it is `false` the byte is uninitialized. +// Note: for performance reasons when interning, some of the `InitMask` fields can be partially +// hashed. (see the `Hash` impl below for more details), so the impl is not derived. +#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable)] +#[derive(HashStable)] +pub struct InitMask { + blocks: Vec, + len: Size, +} + +// Const allocations are only hashed for interning. However, they can be large, making the hashing +// expensive especially since it uses `FxHash`: it's better suited to short keys, not potentially +// big buffers like the allocation's init mask. We can partially hash some fields when they're +// large. +impl hash::Hash for InitMask { + fn hash(&self, state: &mut H) { + const MAX_BLOCKS_TO_HASH: usize = super::MAX_BYTES_TO_HASH / std::mem::size_of::(); + const MAX_BLOCKS_LEN: usize = super::MAX_HASHED_BUFFER_LEN / std::mem::size_of::(); + + // Partially hash the `blocks` buffer when it is large. To limit collisions with common + // prefixes and suffixes, we hash the length and some slices of the buffer. + let block_count = self.blocks.len(); + if block_count > MAX_BLOCKS_LEN { + // Hash the buffer's length. + block_count.hash(state); + + // And its head and tail. + self.blocks[..MAX_BLOCKS_TO_HASH].hash(state); + self.blocks[block_count - MAX_BLOCKS_TO_HASH..].hash(state); + } else { + self.blocks.hash(state); + } + + // Hash the other fields as usual. + self.len.hash(state); + } +} + +impl InitMask { + pub const BLOCK_SIZE: u64 = 64; + + pub fn new(size: Size, state: bool) -> Self { + let mut m = InitMask { blocks: vec![], len: Size::ZERO }; + m.grow(size, state); + m + } + + #[inline] + fn bit_index(bits: Size) -> (usize, usize) { + // BLOCK_SIZE is the number of bits that can fit in a `Block`. + // Each bit in a `Block` represents the initialization state of one byte of an allocation, + // so we use `.bytes()` here. + let bits = bits.bytes(); + let a = bits / InitMask::BLOCK_SIZE; + let b = bits % InitMask::BLOCK_SIZE; + (usize::try_from(a).unwrap(), usize::try_from(b).unwrap()) + } + + #[inline] + fn size_from_bit_index(block: impl TryInto, bit: impl TryInto) -> Size { + let block = block.try_into().ok().unwrap(); + let bit = bit.try_into().ok().unwrap(); + Size::from_bytes(block * InitMask::BLOCK_SIZE + bit) + } + + /// Checks whether the `range` is entirely initialized. + /// + /// Returns `Ok(())` if it's initialized. Otherwise returns a range of byte + /// indexes for the first contiguous span of the uninitialized access. + #[inline] + pub fn is_range_initialized(&self, range: AllocRange) -> Result<(), AllocRange> { + let end = range.end(); + if end > self.len { + return Err(AllocRange::from(self.len..end)); + } + + let uninit_start = self.find_bit(range.start, end, false); + + match uninit_start { + Some(uninit_start) => { + let uninit_end = self.find_bit(uninit_start, end, true).unwrap_or(end); + Err(AllocRange::from(uninit_start..uninit_end)) + } + None => Ok(()), + } + } + + pub fn set_range(&mut self, range: AllocRange, new_state: bool) { + let end = range.end(); + let len = self.len; + if end > len { + self.grow(end - len, new_state); + } + self.set_range_inbounds(range.start, end, new_state); + } + + fn set_range_inbounds(&mut self, start: Size, end: Size, new_state: bool) { + let (blocka, bita) = Self::bit_index(start); + let (blockb, bitb) = Self::bit_index(end); + if blocka == blockb { + // First set all bits except the first `bita`, + // then unset the last `64 - bitb` bits. + let range = if bitb == 0 { + u64::MAX << bita + } else { + (u64::MAX << bita) & (u64::MAX >> (64 - bitb)) + }; + if new_state { + self.blocks[blocka] |= range; + } else { + self.blocks[blocka] &= !range; + } + return; + } + // across block boundaries + if new_state { + // Set `bita..64` to `1`. + self.blocks[blocka] |= u64::MAX << bita; + // Set `0..bitb` to `1`. + if bitb != 0 { + self.blocks[blockb] |= u64::MAX >> (64 - bitb); + } + // Fill in all the other blocks (much faster than one bit at a time). + for block in (blocka + 1)..blockb { + self.blocks[block] = u64::MAX; + } + } else { + // Set `bita..64` to `0`. + self.blocks[blocka] &= !(u64::MAX << bita); + // Set `0..bitb` to `0`. + if bitb != 0 { + self.blocks[blockb] &= !(u64::MAX >> (64 - bitb)); + } + // Fill in all the other blocks (much faster than one bit at a time). + for block in (blocka + 1)..blockb { + self.blocks[block] = 0; + } + } + } + + #[inline] + fn get(&self, i: Size) -> bool { + let (block, bit) = Self::bit_index(i); + (self.blocks[block] & (1 << bit)) != 0 + } + + fn grow(&mut self, amount: Size, new_state: bool) { + if amount.bytes() == 0 { + return; + } + let unused_trailing_bits = + u64::try_from(self.blocks.len()).unwrap() * Self::BLOCK_SIZE - self.len.bytes(); + if amount.bytes() > unused_trailing_bits { + let additional_blocks = amount.bytes() / Self::BLOCK_SIZE + 1; + self.blocks.extend( + // FIXME(oli-obk): optimize this by repeating `new_state as Block`. + iter::repeat(0).take(usize::try_from(additional_blocks).unwrap()), + ); + } + let start = self.len; + self.len += amount; + self.set_range_inbounds(start, start + amount, new_state); // `Size` operation + } + + /// Returns the index of the first bit in `start..end` (end-exclusive) that is equal to is_init. + fn find_bit(&self, start: Size, end: Size, is_init: bool) -> Option { + /// A fast implementation of `find_bit`, + /// which skips over an entire block at a time if it's all 0s (resp. 1s), + /// and finds the first 1 (resp. 0) bit inside a block using `trailing_zeros` instead of a loop. + /// + /// Note that all examples below are written with 8 (instead of 64) bit blocks for simplicity, + /// and with the least significant bit (and lowest block) first: + /// ```text + /// 00000000|00000000 + /// ^ ^ ^ ^ + /// index: 0 7 8 15 + /// ``` + /// Also, if not stated, assume that `is_init = true`, that is, we are searching for the first 1 bit. + fn find_bit_fast( + init_mask: &InitMask, + start: Size, + end: Size, + is_init: bool, + ) -> Option { + /// Search one block, returning the index of the first bit equal to `is_init`. + fn search_block( + bits: Block, + block: usize, + start_bit: usize, + is_init: bool, + ) -> Option { + // For the following examples, assume this function was called with: + // bits = 0b00111011 + // start_bit = 3 + // is_init = false + // Note that, for the examples in this function, the most significant bit is written first, + // which is backwards compared to the comments in `find_bit`/`find_bit_fast`. + + // Invert bits so we're always looking for the first set bit. + // ! 0b00111011 + // bits = 0b11000100 + let bits = if is_init { bits } else { !bits }; + // Mask off unused start bits. + // 0b11000100 + // & 0b11111000 + // bits = 0b11000000 + let bits = bits & (!0 << start_bit); + // Find set bit, if any. + // bit = trailing_zeros(0b11000000) + // bit = 6 + if bits == 0 { + None + } else { + let bit = bits.trailing_zeros(); + Some(InitMask::size_from_bit_index(block, bit)) + } + } + + if start >= end { + return None; + } + + // Convert `start` and `end` to block indexes and bit indexes within each block. + // We must convert `end` to an inclusive bound to handle block boundaries correctly. + // + // For example: + // + // (a) 00000000|00000000 (b) 00000000| + // ^~~~~~~~~~~^ ^~~~~~~~~^ + // start end start end + // + // In both cases, the block index of `end` is 1. + // But we do want to search block 1 in (a), and we don't in (b). + // + // We subtract 1 from both end positions to make them inclusive: + // + // (a) 00000000|00000000 (b) 00000000| + // ^~~~~~~~~~^ ^~~~~~~^ + // start end_inclusive start end_inclusive + // + // For (a), the block index of `end_inclusive` is 1, and for (b), it's 0. + // This provides the desired behavior of searching blocks 0 and 1 for (a), + // and searching only block 0 for (b). + // There is no concern of overflows since we checked for `start >= end` above. + let (start_block, start_bit) = InitMask::bit_index(start); + let end_inclusive = Size::from_bytes(end.bytes() - 1); + let (end_block_inclusive, _) = InitMask::bit_index(end_inclusive); + + // Handle first block: need to skip `start_bit` bits. + // + // We need to handle the first block separately, + // because there may be bits earlier in the block that should be ignored, + // such as the bit marked (1) in this example: + // + // (1) + // -|------ + // (c) 01000000|00000000|00000001 + // ^~~~~~~~~~~~~~~~~~^ + // start end + if let Some(i) = + search_block(init_mask.blocks[start_block], start_block, start_bit, is_init) + { + // If the range is less than a block, we may find a matching bit after `end`. + // + // For example, we shouldn't successfully find bit (2), because it's after `end`: + // + // (2) + // -------| + // (d) 00000001|00000000|00000001 + // ^~~~~^ + // start end + // + // An alternative would be to mask off end bits in the same way as we do for start bits, + // but performing this check afterwards is faster and simpler to implement. + if i < end { + return Some(i); + } else { + return None; + } + } + + // Handle remaining blocks. + // + // We can skip over an entire block at once if it's all 0s (resp. 1s). + // The block marked (3) in this example is the first block that will be handled by this loop, + // and it will be skipped for that reason: + // + // (3) + // -------- + // (e) 01000000|00000000|00000001 + // ^~~~~~~~~~~~~~~~~~^ + // start end + if start_block < end_block_inclusive { + // This loop is written in a specific way for performance. + // Notably: `..end_block_inclusive + 1` is used for an inclusive range instead of `..=end_block_inclusive`, + // and `.zip(start_block + 1..)` is used to track the index instead of `.enumerate().skip().take()`, + // because both alternatives result in significantly worse codegen. + // `end_block_inclusive + 1` is guaranteed not to wrap, because `end_block_inclusive <= end / BLOCK_SIZE`, + // and `BLOCK_SIZE` (the number of bits per block) will always be at least 8 (1 byte). + for (&bits, block) in init_mask.blocks[start_block + 1..end_block_inclusive + 1] + .iter() + .zip(start_block + 1..) + { + if let Some(i) = search_block(bits, block, 0, is_init) { + // If this is the last block, we may find a matching bit after `end`. + // + // For example, we shouldn't successfully find bit (4), because it's after `end`: + // + // (4) + // -------| + // (f) 00000001|00000000|00000001 + // ^~~~~~~~~~~~~~~~~~^ + // start end + // + // As above with example (d), we could handle the end block separately and mask off end bits, + // but unconditionally searching an entire block at once and performing this check afterwards + // is faster and much simpler to implement. + if i < end { + return Some(i); + } else { + return None; + } + } + } + } + + None + } + + #[cfg_attr(not(debug_assertions), allow(dead_code))] + fn find_bit_slow( + init_mask: &InitMask, + start: Size, + end: Size, + is_init: bool, + ) -> Option { + (start..end).find(|&i| init_mask.get(i) == is_init) + } + + let result = find_bit_fast(self, start, end, is_init); + + debug_assert_eq!( + result, + find_bit_slow(self, start, end, is_init), + "optimized implementation of find_bit is wrong for start={:?} end={:?} is_init={} init_mask={:#?}", + start, + end, + is_init, + self + ); + + result + } +} + +/// A contiguous chunk of initialized or uninitialized memory. +pub enum InitChunk { + Init(Range), + Uninit(Range), +} + +impl InitChunk { + #[inline] + pub fn is_init(&self) -> bool { + match self { + Self::Init(_) => true, + Self::Uninit(_) => false, + } + } + + #[inline] + pub fn range(&self) -> Range { + match self { + Self::Init(r) => r.clone(), + Self::Uninit(r) => r.clone(), + } + } +} + +impl InitMask { + /// Returns an iterator, yielding a range of byte indexes for each contiguous region + /// of initialized or uninitialized bytes inside the range `start..end` (end-exclusive). + /// + /// The iterator guarantees the following: + /// - Chunks are nonempty. + /// - Chunks are adjacent (each range's start is equal to the previous range's end). + /// - Chunks span exactly `start..end` (the first starts at `start`, the last ends at `end`). + /// - Chunks alternate between [`InitChunk::Init`] and [`InitChunk::Uninit`]. + #[inline] + pub fn range_as_init_chunks(&self, range: AllocRange) -> InitChunkIter<'_> { + let start = range.start; + let end = range.end(); + assert!(end <= self.len); + + let is_init = if start < end { + self.get(start) + } else { + // `start..end` is empty: there are no chunks, so use some arbitrary value + false + }; + + InitChunkIter { init_mask: self, is_init, start, end } + } +} + +/// Yields [`InitChunk`]s. See [`InitMask::range_as_init_chunks`]. +#[derive(Clone)] +pub struct InitChunkIter<'a> { + init_mask: &'a InitMask, + /// Whether the next chunk we will return is initialized. + /// If there are no more chunks, contains some arbitrary value. + is_init: bool, + /// The current byte index into `init_mask`. + start: Size, + /// The end byte index into `init_mask`. + end: Size, +} + +impl<'a> Iterator for InitChunkIter<'a> { + type Item = InitChunk; + + #[inline] + fn next(&mut self) -> Option { + if self.start >= self.end { + return None; + } + + let end_of_chunk = + self.init_mask.find_bit(self.start, self.end, !self.is_init).unwrap_or(self.end); + let range = self.start..end_of_chunk; + + let ret = + Some(if self.is_init { InitChunk::Init(range) } else { InitChunk::Uninit(range) }); + + self.is_init = !self.is_init; + self.start = end_of_chunk; + + ret + } +} + +/// Run-length encoding of the uninit mask. +/// Used to copy parts of a mask multiple times to another allocation. +pub struct InitCopy { + /// Whether the first range is initialized. + initial: bool, + /// The lengths of ranges that are run-length encoded. + /// The initialization state of the ranges alternate starting with `initial`. + ranges: smallvec::SmallVec<[u64; 1]>, +} + +impl InitCopy { + pub fn no_bytes_init(&self) -> bool { + // The `ranges` are run-length encoded and of alternating initialization state. + // So if `ranges.len() > 1` then the second block is an initialized range. + !self.initial && self.ranges.len() == 1 + } +} + +/// Transferring the initialization mask to other allocations. +impl InitMask { + /// Creates a run-length encoding of the initialization mask; panics if range is empty. + /// + /// This is essentially a more space-efficient version of + /// `InitMask::range_as_init_chunks(...).collect::>()`. + pub fn prepare_copy(&self, range: AllocRange) -> InitCopy { + // Since we are copying `size` bytes from `src` to `dest + i * size` (`for i in 0..repeat`), + // a naive initialization mask copying algorithm would repeatedly have to read the initialization mask from + // the source and write it to the destination. Even if we optimized the memory accesses, + // we'd be doing all of this `repeat` times. + // Therefore we precompute a compressed version of the initialization mask of the source value and + // then write it back `repeat` times without computing any more information from the source. + + // A precomputed cache for ranges of initialized / uninitialized bits + // 0000010010001110 will become + // `[5, 1, 2, 1, 3, 3, 1]`, + // where each element toggles the state. + + let mut ranges = smallvec::SmallVec::<[u64; 1]>::new(); + + let mut chunks = self.range_as_init_chunks(range).peekable(); + + let initial = chunks.peek().expect("range should be nonempty").is_init(); + + // Here we rely on `range_as_init_chunks` to yield alternating init/uninit chunks. + for chunk in chunks { + let len = chunk.range().end.bytes() - chunk.range().start.bytes(); + ranges.push(len); + } + + InitCopy { ranges, initial } + } + + /// Applies multiple instances of the run-length encoding to the initialization mask. + pub fn apply_copy(&mut self, defined: InitCopy, range: AllocRange, repeat: u64) { + // An optimization where we can just overwrite an entire range of initialization + // bits if they are going to be uniformly `1` or `0`. + if defined.ranges.len() <= 1 { + self.set_range_inbounds( + range.start, + range.start + range.size * repeat, // `Size` operations + defined.initial, + ); + return; + } + + for mut j in 0..repeat { + j *= range.size.bytes(); + j += range.start.bytes(); + let mut cur = defined.initial; + for range in &defined.ranges { + let old_j = j; + j += range; + self.set_range_inbounds(Size::from_bytes(old_j), Size::from_bytes(j), cur); + cur = !cur; + } + } + } +} diff --git a/compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs b/compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs index f0f990f4e9d..15bd151bc06 100644 --- a/compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs +++ b/compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs @@ -264,9 +264,6 @@ pub fn prepare_copy( /// Applies a provenance copy. /// The affected range, as defined in the parameters to `prepare_copy` is expected /// to be clear of provenance. - /// - /// This is dangerous to use as it can violate internal `Allocation` invariants! - /// It only exists to support an efficient implementation of `mem_copy_repeatedly`. pub fn apply_copy(&mut self, copy: ProvenanceCopy) { self.ptrs.insert_presorted(copy.dest_ptrs); self.bytes.insert_presorted(copy.dest_bytes); diff --git a/compiler/rustc_middle/src/mir/interpret/mod.rs b/compiler/rustc_middle/src/mir/interpret/mod.rs index 9c8ab44cfd6..e247a79339d 100644 --- a/compiler/rustc_middle/src/mir/interpret/mod.rs +++ b/compiler/rustc_middle/src/mir/interpret/mod.rs @@ -128,7 +128,7 @@ macro_rules! throw_machine_stop { pub use self::allocation::{ alloc_range, AllocError, AllocRange, AllocResult, Allocation, ConstAllocation, InitChunk, - InitChunkIter, InitMask, + InitChunkIter, }; pub use self::pointer::{Pointer, PointerArithmetic, Provenance}; diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs index 7965a9499a1..72035319b8b 100644 --- a/compiler/rustc_middle/src/mir/pretty.rs +++ b/compiler/rustc_middle/src/mir/pretty.rs @@ -12,8 +12,8 @@ use rustc_hir::def_id::DefId; use rustc_index::vec::Idx; use rustc_middle::mir::interpret::{ - read_target_uint, AllocId, Allocation, ConstAllocation, ConstValue, GlobalAlloc, Pointer, - Provenance, + alloc_range, read_target_uint, AllocId, Allocation, ConstAllocation, ConstValue, GlobalAlloc, + Pointer, Provenance, }; use rustc_middle::mir::visit::Visitor; use rustc_middle::mir::MirSource; @@ -884,7 +884,7 @@ fn write_allocation_bytes<'tcx, Prov: Provenance, Extra>( } if let Some(prov) = alloc.provenance().get_ptr(i) { // Memory with provenance must be defined - assert!(alloc.init_mask().is_range_initialized(i, i + ptr_size).is_ok()); + assert!(alloc.init_mask().is_range_initialized(alloc_range(i, ptr_size)).is_ok()); let j = i.bytes_usize(); let offset = alloc .inspect_with_uninit_and_ptr_outside_interpreter(j..j + ptr_size.bytes_usize()); @@ -943,7 +943,9 @@ fn write_allocation_bytes<'tcx, Prov: Provenance, Extra>( } } else if let Some(prov) = alloc.provenance().get(i, &tcx) { // Memory with provenance must be defined - assert!(alloc.init_mask().is_range_initialized(i, i + Size::from_bytes(1)).is_ok()); + assert!( + alloc.init_mask().is_range_initialized(alloc_range(i, Size::from_bytes(1))).is_ok() + ); ascii.push('━'); // HEAVY HORIZONTAL // We have two characters to display this, which is obviously not enough. // Format is similar to "oversized" above. @@ -951,7 +953,11 @@ fn write_allocation_bytes<'tcx, Prov: Provenance, Extra>( let c = alloc.inspect_with_uninit_and_ptr_outside_interpreter(j..j + 1)[0]; write!(w, "╾{:02x}{:#?} (1 ptr byte)╼", c, prov)?; i += Size::from_bytes(1); - } else if alloc.init_mask().is_range_initialized(i, i + Size::from_bytes(1)).is_ok() { + } else if alloc + .init_mask() + .is_range_initialized(alloc_range(i, Size::from_bytes(1))) + .is_ok() + { let j = i.bytes_usize(); // Checked definedness (and thus range) and provenance. This access also doesn't -- 2.44.0