Merging upstream version 1.67.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

3 files changed, 870 insertions, 0 deletions

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 000000000..82e9a961a
--- /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, TyEncodable, TyDecodable)]
+#[derive(HashStable)]
+pub struct InitMask {
+    blocks: Vec<Block>,
+    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<H: hash::Hasher>(&self, state: &mut H) {
+        const MAX_BLOCKS_TO_HASH: usize = super::MAX_BYTES_TO_HASH / std::mem::size_of::<Block>();
+        const MAX_BLOCKS_LEN: usize = super::MAX_HASHED_BUFFER_LEN / std::mem::size_of::<Block>();
+
+        // 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<u64>, bit: impl TryInto<u64>) -> 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]
+    pub 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<Size> {
+        /// 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<Size> {
+            /// 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<Size> {
+                // 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<Size> {
+            (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<Size>),
+    Uninit(Range<Size>),
+}
+
+impl InitChunk {
+    #[inline]
+    pub fn is_init(&self) -> bool {
+        match self {
+            Self::Init(_) => true,
+            Self::Uninit(_) => false,
+        }
+    }
+
+    #[inline]
+    pub fn range(&self) -> Range<Size> {
+        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<Self::Item> {
+        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::<Vec<_>>()`.
+    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
new file mode 100644
index 000000000..ddd3f3943
--- /dev/null
+++ b/compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs
@@ -0,0 +1,321 @@
+//! Store the provenance for each byte in the range, with a more efficient
+//! representation for the common case where PTR_SIZE consecutive bytes have the same provenance.
+
+use std::cmp;
+
+use rustc_data_structures::sorted_map::SortedMap;
+use rustc_target::abi::{HasDataLayout, Size};
+
+use super::{alloc_range, AllocError, AllocId, AllocRange, AllocResult, Provenance};
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
+
+/// Stores the provenance information of pointers stored in memory.
+#[derive(Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(HashStable)]
+pub struct ProvenanceMap<Prov = AllocId> {
+    /// Provenance in this map applies from the given offset for an entire pointer-size worth of
+    /// bytes. Two entires in this map are always at least a pointer size apart.
+    ptrs: SortedMap<Size, Prov>,
+    /// Provenance in this map only applies to the given single byte.
+    /// This map is disjoint from the previous. It will always be empty when
+    /// `Prov::OFFSET_IS_ADDR` is false.
+    bytes: Option<Box<SortedMap<Size, Prov>>>,
+}
+
+impl<D: Decoder, Prov: Provenance + Decodable<D>> Decodable<D> for ProvenanceMap<Prov> {
+    fn decode(d: &mut D) -> Self {
+        assert!(!Prov::OFFSET_IS_ADDR); // only `AllocId` is ever serialized
+        Self { ptrs: Decodable::decode(d), bytes: None }
+    }
+}
+
+impl<S: Encoder, Prov: Provenance + Encodable<S>> Encodable<S> for ProvenanceMap<Prov> {
+    fn encode(&self, s: &mut S) {
+        let Self { ptrs, bytes } = self;
+        assert!(!Prov::OFFSET_IS_ADDR); // only `AllocId` is ever serialized
+        debug_assert!(bytes.is_none());
+        ptrs.encode(s)
+    }
+}
+
+impl<Prov> ProvenanceMap<Prov> {
+    pub fn new() -> Self {
+        ProvenanceMap { ptrs: SortedMap::new(), bytes: None }
+    }
+
+    /// The caller must guarantee that the given provenance list is already sorted
+    /// by address and contain no duplicates.
+    pub fn from_presorted_ptrs(r: Vec<(Size, Prov)>) -> Self {
+        ProvenanceMap { ptrs: SortedMap::from_presorted_elements(r), bytes: None }
+    }
+}
+
+impl ProvenanceMap {
+    /// Give access to the ptr-sized provenances (which can also be thought of as relocations, and
+    /// indeed that is how codegen treats them).
+    ///
+    /// Only exposed with `AllocId` provenance, since it panics if there is bytewise provenance.
+    #[inline]
+    pub fn ptrs(&self) -> &SortedMap<Size, AllocId> {
+        debug_assert!(self.bytes.is_none()); // `AllocId::OFFSET_IS_ADDR` is false so this cannot fail
+        &self.ptrs
+    }
+}
+
+impl<Prov: Provenance> ProvenanceMap<Prov> {
+    /// Returns all ptr-sized provenance in the given range.
+    /// If the range has length 0, returns provenance that crosses the edge between `start-1` and
+    /// `start`.
+    fn range_get_ptrs(&self, range: AllocRange, cx: &impl HasDataLayout) -> &[(Size, Prov)] {
+        // We have to go back `pointer_size - 1` bytes, as that one would still overlap with
+        // the beginning of this range.
+        let adjusted_start = Size::from_bytes(
+            range.start.bytes().saturating_sub(cx.data_layout().pointer_size.bytes() - 1),
+        );
+        self.ptrs.range(adjusted_start..range.end())
+    }
+
+    /// Returns all byte-wise provenance in the given range.
+    fn range_get_bytes(&self, range: AllocRange) -> &[(Size, Prov)] {
+        if let Some(bytes) = self.bytes.as_ref() {
+            bytes.range(range.start..range.end())
+        } else {
+            &[]
+        }
+    }
+
+    /// Get the provenance of a single byte.
+    pub fn get(&self, offset: Size, cx: &impl HasDataLayout) -> Option<Prov> {
+        let prov = self.range_get_ptrs(alloc_range(offset, Size::from_bytes(1)), cx);
+        debug_assert!(prov.len() <= 1);
+        if let Some(entry) = prov.first() {
+            // If it overlaps with this byte, it is on this byte.
+            debug_assert!(self.bytes.as_ref().map_or(true, |b| b.get(&offset).is_none()));
+            Some(entry.1)
+        } else {
+            // Look up per-byte provenance.
+            self.bytes.as_ref().and_then(|b| b.get(&offset).copied())
+        }
+    }
+
+    /// Check if here is ptr-sized provenance at the given index.
+    /// Does not mean anything for bytewise provenance! But can be useful as an optimization.
+    pub fn get_ptr(&self, offset: Size) -> Option<Prov> {
+        self.ptrs.get(&offset).copied()
+    }
+
+    /// Returns whether this allocation has provenance overlapping with the given range.
+    ///
+    /// Note: this function exists to allow `range_get_provenance` to be private, in order to somewhat
+    /// limit access to provenance outside of the `Allocation` abstraction.
+    ///
+    pub fn range_empty(&self, range: AllocRange, cx: &impl HasDataLayout) -> bool {
+        self.range_get_ptrs(range, cx).is_empty() && self.range_get_bytes(range).is_empty()
+    }
+
+    /// Yields all the provenances stored in this map.
+    pub fn provenances(&self) -> impl Iterator<Item = Prov> + '_ {
+        let bytes = self.bytes.iter().flat_map(|b| b.values());
+        self.ptrs.values().chain(bytes).copied()
+    }
+
+    pub fn insert_ptr(&mut self, offset: Size, prov: Prov, cx: &impl HasDataLayout) {
+        debug_assert!(self.range_empty(alloc_range(offset, cx.data_layout().pointer_size), cx));
+        self.ptrs.insert(offset, prov);
+    }
+
+    /// Removes all provenance inside the given range.
+    /// If there is provenance overlapping with the edges, might result in an error.
+    pub fn clear(&mut self, range: AllocRange, cx: &impl HasDataLayout) -> AllocResult {
+        let start = range.start;
+        let end = range.end();
+        // Clear the bytewise part -- this is easy.
+        if Prov::OFFSET_IS_ADDR {
+            if let Some(bytes) = self.bytes.as_mut() {
+                bytes.remove_range(start..end);
+            }
+        } else {
+            debug_assert!(self.bytes.is_none());
+        }
+
+        // For the ptr-sized part, find the first (inclusive) and last (exclusive) byte of
+        // provenance that overlaps with the given range.
+        let (first, last) = {
+            // Find all provenance overlapping the given range.
+            let provenance = self.range_get_ptrs(range, cx);
+            if provenance.is_empty() {
+                // No provenance in this range, we are done.
+                return Ok(());
+            }
+
+            (
+                provenance.first().unwrap().0,
+                provenance.last().unwrap().0 + cx.data_layout().pointer_size,
+            )
+        };
+
+        // We need to handle clearing the provenance from parts of a pointer.
+        if first < start {
+            if !Prov::OFFSET_IS_ADDR {
+                // We can't split up the provenance into less than a pointer.
+                return Err(AllocError::PartialPointerOverwrite(first));
+            }
+            // Insert the remaining part in the bytewise provenance.
+            let prov = self.ptrs[&first];
+            let bytes = self.bytes.get_or_insert_with(Box::default);
+            for offset in first..start {
+                bytes.insert(offset, prov);
+            }
+        }
+        if last > end {
+            let begin_of_last = last - cx.data_layout().pointer_size;
+            if !Prov::OFFSET_IS_ADDR {
+                // We can't split up the provenance into less than a pointer.
+                return Err(AllocError::PartialPointerOverwrite(begin_of_last));
+            }
+            // Insert the remaining part in the bytewise provenance.
+            let prov = self.ptrs[&begin_of_last];
+            let bytes = self.bytes.get_or_insert_with(Box::default);
+            for offset in end..last {
+                bytes.insert(offset, prov);
+            }
+        }
+
+        // Forget all the provenance.
+        // Since provenance do not overlap, we know that removing until `last` (exclusive) is fine,
+        // i.e., this will not remove any other provenance just after the ones we care about.
+        self.ptrs.remove_range(first..last);
+
+        Ok(())
+    }
+}
+
+/// A partial, owned list of provenance to transfer into another allocation.
+///
+/// Offsets are already adjusted to the destination allocation.
+pub struct ProvenanceCopy<Prov> {
+    dest_ptrs: Option<Box<[(Size, Prov)]>>,
+    dest_bytes: Option<Box<[(Size, Prov)]>>,
+}
+
+impl<Prov: Provenance> ProvenanceMap<Prov> {
+    pub fn prepare_copy(
+        &self,
+        src: AllocRange,
+        dest: Size,
+        count: u64,
+        cx: &impl HasDataLayout,
+    ) -> AllocResult<ProvenanceCopy<Prov>> {
+        let shift_offset = move |idx, offset| {
+            // compute offset for current repetition
+            let dest_offset = dest + src.size * idx; // `Size` operations
+            // shift offsets from source allocation to destination allocation
+            (offset - src.start) + dest_offset // `Size` operations
+        };
+        let ptr_size = cx.data_layout().pointer_size;
+
+        // # Pointer-sized provenances
+        // Get the provenances that are entirely within this range.
+        // (Different from `range_get_ptrs` which asks if they overlap the range.)
+        // Only makes sense if we are copying at least one pointer worth of bytes.
+        let mut dest_ptrs_box = None;
+        if src.size >= ptr_size {
+            let adjusted_end = Size::from_bytes(src.end().bytes() - (ptr_size.bytes() - 1));
+            let ptrs = self.ptrs.range(src.start..adjusted_end);
+            // If `count` is large, this is rather wasteful -- we are allocating a big array here, which
+            // is mostly filled with redundant information since it's just N copies of the same `Prov`s
+            // at slightly adjusted offsets. The reason we do this is so that in `mark_provenance_range`
+            // we can use `insert_presorted`. That wouldn't work with an `Iterator` that just produces
+            // the right sequence of provenance for all N copies.
+            // Basically, this large array would have to be created anyway in the target allocation.
+            let mut dest_ptrs = Vec::with_capacity(ptrs.len() * (count as usize));
+            for i in 0..count {
+                dest_ptrs
+                    .extend(ptrs.iter().map(|&(offset, reloc)| (shift_offset(i, offset), reloc)));
+            }
+            debug_assert_eq!(dest_ptrs.len(), dest_ptrs.capacity());
+            dest_ptrs_box = Some(dest_ptrs.into_boxed_slice());
+        };
+
+        // # Byte-sized provenances
+        // This includes the existing bytewise provenance in the range, and ptr provenance
+        // that overlaps with the begin/end of the range.
+        let mut dest_bytes_box = None;
+        let begin_overlap = self.range_get_ptrs(alloc_range(src.start, Size::ZERO), cx).first();
+        let end_overlap = self.range_get_ptrs(alloc_range(src.end(), Size::ZERO), cx).first();
+        if !Prov::OFFSET_IS_ADDR {
+            // There can't be any bytewise provenance, and we cannot split up the begin/end overlap.
+            if let Some(entry) = begin_overlap {
+                return Err(AllocError::PartialPointerCopy(entry.0));
+            }
+            if let Some(entry) = end_overlap {
+                return Err(AllocError::PartialPointerCopy(entry.0));
+            }
+            debug_assert!(self.bytes.is_none());
+        } else {
+            let mut bytes = Vec::new();
+            // First, if there is a part of a pointer at the start, add that.
+            if let Some(entry) = begin_overlap {
+                trace!("start overlapping entry: {entry:?}");
+                // For really small copies, make sure we don't run off the end of the `src` range.
+                let entry_end = cmp::min(entry.0 + ptr_size, src.end());
+                for offset in src.start..entry_end {
+                    bytes.push((offset, entry.1));
+                }
+            } else {
+                trace!("no start overlapping entry");
+            }
+            // Then the main part, bytewise provenance from `self.bytes`.
+            if let Some(all_bytes) = self.bytes.as_ref() {
+                bytes.extend(all_bytes.range(src.start..src.end()));
+            }
+            // And finally possibly parts of a pointer at the end.
+            if let Some(entry) = end_overlap {
+                trace!("end overlapping entry: {entry:?}");
+                // For really small copies, make sure we don't start before `src` does.
+                let entry_start = cmp::max(entry.0, src.start);
+                for offset in entry_start..src.end() {
+                    if bytes.last().map_or(true, |bytes_entry| bytes_entry.0 < offset) {
+                        // The last entry, if it exists, has a lower offset than us.
+                        bytes.push((offset, entry.1));
+                    } else {
+                        // There already is an entry for this offset in there! This can happen when the
+                        // start and end range checks actually end up hitting the same pointer, so we
+                        // already added this in the "pointer at the start" part above.
+                        assert!(entry.0 <= src.start);
+                    }
+                }
+            } else {
+                trace!("no end overlapping entry");
+            }
+            trace!("byte provenances: {bytes:?}");
+
+            // And again a buffer for the new list on the target side.
+            let mut dest_bytes = Vec::with_capacity(bytes.len() * (count as usize));
+            for i in 0..count {
+                dest_bytes
+                    .extend(bytes.iter().map(|&(offset, reloc)| (shift_offset(i, offset), reloc)));
+            }
+            debug_assert_eq!(dest_bytes.len(), dest_bytes.capacity());
+            dest_bytes_box = Some(dest_bytes.into_boxed_slice());
+        }
+
+        Ok(ProvenanceCopy { dest_ptrs: dest_ptrs_box, dest_bytes: dest_bytes_box })
+    }
+
+    /// Applies a provenance copy.
+    /// The affected range, as defined in the parameters to `prepare_copy` is expected
+    /// to be clear of provenance.
+    pub fn apply_copy(&mut self, copy: ProvenanceCopy<Prov>) {
+        if let Some(dest_ptrs) = copy.dest_ptrs {
+            self.ptrs.insert_presorted(dest_ptrs.into());
+        }
+        if Prov::OFFSET_IS_ADDR {
+            if let Some(dest_bytes) = copy.dest_bytes && !dest_bytes.is_empty() {
+                self.bytes.get_or_insert_with(Box::default).insert_presorted(dest_bytes.into());
+            }
+        } else {
+            debug_assert!(copy.dest_bytes.is_none());
+        }
+    }
+}
diff --git a/compiler/rustc_middle/src/mir/interpret/allocation/tests.rs b/compiler/rustc_middle/src/mir/interpret/allocation/tests.rs
new file mode 100644
index 000000000..c9c3c50c5
--- /dev/null
+++ b/compiler/rustc_middle/src/mir/interpret/allocation/tests.rs
@@ -0,0 +1,19 @@
+use super::*;
+
+#[test]
+fn uninit_mask() {
+    let mut mask = InitMask::new(Size::from_bytes(500), false);
+    assert!(!mask.get(Size::from_bytes(499)));
+    mask.set_range(alloc_range(Size::from_bytes(499), Size::from_bytes(1)), true);
+    assert!(mask.get(Size::from_bytes(499)));
+    mask.set_range((100..256).into(), true);
+    for i in 0..100 {
+        assert!(!mask.get(Size::from_bytes(i)), "{i} should not be set");
+    }
+    for i in 100..256 {
+        assert!(mask.get(Size::from_bytes(i)), "{i} should be set");
+    }
+    for i in 256..499 {
+        assert!(!mask.get(Size::from_bytes(i)), "{i} should not be set");
+    }
+}