Adding upstream version 110.0.1.upstream/110.0.1upstream

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

1 files changed, 266 insertions, 0 deletions

diff --git a/third_party/rust/memchr/src/memmem/genericsimd.rs b/third_party/rust/memchr/src/memmem/genericsimd.rs
new file mode 100644
index 0000000000..28bfdab880
--- /dev/null
+++ b/third_party/rust/memchr/src/memmem/genericsimd.rs
@@ -0,0 +1,266 @@
+use core::mem::size_of;
+
+use crate::memmem::{util::memcmp, vector::Vector, NeedleInfo};
+
+/// The minimum length of a needle required for this algorithm. The minimum
+/// is 2 since a length of 1 should just use memchr and a length of 0 isn't
+/// a case handled by this searcher.
+pub(crate) const MIN_NEEDLE_LEN: usize = 2;
+
+/// The maximum length of a needle required for this algorithm.
+///
+/// In reality, there is no hard max here. The code below can handle any
+/// length needle. (Perhaps that suggests there are missing optimizations.)
+/// Instead, this is a heuristic and a bound guaranteeing our linear time
+/// complexity.
+///
+/// It is a heuristic because when a candidate match is found, memcmp is run.
+/// For very large needles with lots of false positives, memcmp can make the
+/// code run quite slow.
+///
+/// It is a bound because the worst case behavior with memcmp is multiplicative
+/// in the size of the needle and haystack, and we want to keep that additive.
+/// This bound ensures we still meet that bound theoretically, since it's just
+/// a constant. We aren't acting in bad faith here, memcmp on tiny needles
+/// is so fast that even in pathological cases (see pathological vector
+/// benchmarks), this is still just as fast or faster in practice.
+///
+/// This specific number was chosen by tweaking a bit and running benchmarks.
+/// The rare-medium-needle, for example, gets about 5% faster by using this
+/// algorithm instead of a prefilter-accelerated Two-Way. There's also a
+/// theoretical desire to keep this number reasonably low, to mitigate the
+/// impact of pathological cases. I did try 64, and some benchmarks got a
+/// little better, and others (particularly the pathological ones), got a lot
+/// worse. So... 32 it is?
+pub(crate) const MAX_NEEDLE_LEN: usize = 32;
+
+/// The implementation of the forward vector accelerated substring search.
+///
+/// This is extremely similar to the prefilter vector module by the same name.
+/// The key difference is that this is not a prefilter. Instead, it handles
+/// confirming its own matches. The trade off is that this only works with
+/// smaller needles. The speed up here is that an inlined memcmp on a tiny
+/// needle is very quick, even on pathological inputs. This is much better than
+/// combining a prefilter with Two-Way, where using Two-Way to confirm the
+/// match has higher latency.
+///
+/// So why not use this for all needles? We could, and it would probably work
+/// really well on most inputs. But its worst case is multiplicative and we
+/// want to guarantee worst case additive time. Some of the benchmarks try to
+/// justify this (see the pathological ones).
+///
+/// The prefilter variant of this has more comments. Also note that we only
+/// implement this for forward searches for now. If you have a compelling use
+/// case for accelerated reverse search, please file an issue.
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct Forward {
+    rare1i: u8,
+    rare2i: u8,
+}
+
+impl Forward {
+    /// Create a new "generic simd" forward searcher. If one could not be
+    /// created from the given inputs, then None is returned.
+    pub(crate) fn new(ninfo: &NeedleInfo, needle: &[u8]) -> Option<Forward> {
+        let (rare1i, rare2i) = ninfo.rarebytes.as_rare_ordered_u8();
+        // If the needle is too short or too long, give up. Also, give up
+        // if the rare bytes detected are at the same position. (It likely
+        // suggests a degenerate case, although it should technically not be
+        // possible.)
+        if needle.len() < MIN_NEEDLE_LEN
+            || needle.len() > MAX_NEEDLE_LEN
+            || rare1i == rare2i
+        {
+            return None;
+        }
+        Some(Forward { rare1i, rare2i })
+    }
+
+    /// Returns the minimum length of haystack that is needed for this searcher
+    /// to work for a particular vector. Passing a haystack with a length
+    /// smaller than this will cause `fwd_find` to panic.
+    #[inline(always)]
+    pub(crate) fn min_haystack_len<V: Vector>(&self) -> usize {
+        self.rare2i as usize + size_of::<V>()
+    }
+}
+
+/// Searches the given haystack for the given needle. The needle given should
+/// be the same as the needle that this searcher was initialized with.
+///
+/// # Panics
+///
+/// When the given haystack has a length smaller than `min_haystack_len`.
+///
+/// # Safety
+///
+/// Since this is meant to be used with vector functions, callers need to
+/// specialize this inside of a function with a `target_feature` attribute.
+/// Therefore, callers must ensure that whatever target feature is being used
+/// supports the vector functions that this function is specialized for. (For
+/// the specific vector functions used, see the Vector trait implementations.)
+#[inline(always)]
+pub(crate) unsafe fn fwd_find<V: Vector>(
+    fwd: &Forward,
+    haystack: &[u8],
+    needle: &[u8],
+) -> Option<usize> {
+    // It would be nice if we didn't have this check here, since the meta
+    // searcher should handle it for us. But without this, I don't think we
+    // guarantee that end_ptr.sub(needle.len()) won't result in UB. We could
+    // put it as part of the safety contract, but it makes it more complicated
+    // than necessary.
+    if haystack.len() < needle.len() {
+        return None;
+    }
+    let min_haystack_len = fwd.min_haystack_len::<V>();
+    assert!(haystack.len() >= min_haystack_len, "haystack too small");
+    debug_assert!(needle.len() <= haystack.len());
+    debug_assert!(
+        needle.len() >= MIN_NEEDLE_LEN,
+        "needle must be at least {} bytes",
+        MIN_NEEDLE_LEN,
+    );
+    debug_assert!(
+        needle.len() <= MAX_NEEDLE_LEN,
+        "needle must be at most {} bytes",
+        MAX_NEEDLE_LEN,
+    );
+
+    let (rare1i, rare2i) = (fwd.rare1i as usize, fwd.rare2i as usize);
+    let rare1chunk = V::splat(needle[rare1i]);
+    let rare2chunk = V::splat(needle[rare2i]);
+
+    let start_ptr = haystack.as_ptr();
+    let end_ptr = start_ptr.add(haystack.len());
+    let max_ptr = end_ptr.sub(min_haystack_len);
+    let mut ptr = start_ptr;
+
+    // N.B. I did experiment with unrolling the loop to deal with size(V)
+    // bytes at a time and 2*size(V) bytes at a time. The double unroll was
+    // marginally faster while the quadruple unroll was unambiguously slower.
+    // In the end, I decided the complexity from unrolling wasn't worth it. I
+    // used the memmem/krate/prebuilt/huge-en/ benchmarks to compare.
+    while ptr <= max_ptr {
+        let m = fwd_find_in_chunk(
+            fwd, needle, ptr, end_ptr, rare1chunk, rare2chunk, !0,
+        );
+        if let Some(chunki) = m {
+            return Some(matched(start_ptr, ptr, chunki));
+        }
+        ptr = ptr.add(size_of::<V>());
+    }
+    if ptr < end_ptr {
+        let remaining = diff(end_ptr, ptr);
+        debug_assert!(
+            remaining < min_haystack_len,
+            "remaining bytes should be smaller than the minimum haystack \
+             length of {}, but there are {} bytes remaining",
+            min_haystack_len,
+            remaining,
+        );
+        if remaining < needle.len() {
+            return None;
+        }
+        debug_assert!(
+            max_ptr < ptr,
+            "after main loop, ptr should have exceeded max_ptr",
+        );
+        let overlap = diff(ptr, max_ptr);
+        debug_assert!(
+            overlap > 0,
+            "overlap ({}) must always be non-zero",
+            overlap,
+        );
+        debug_assert!(
+            overlap < size_of::<V>(),
+            "overlap ({}) cannot possibly be >= than a vector ({})",
+            overlap,
+            size_of::<V>(),
+        );
+        // The mask has all of its bits set except for the first N least
+        // significant bits, where N=overlap. This way, any matches that
+        // occur in find_in_chunk within the overlap are automatically
+        // ignored.
+        let mask = !((1 << overlap) - 1);
+        ptr = max_ptr;
+        let m = fwd_find_in_chunk(
+            fwd, needle, ptr, end_ptr, rare1chunk, rare2chunk, mask,
+        );
+        if let Some(chunki) = m {
+            return Some(matched(start_ptr, ptr, chunki));
+        }
+    }
+    None
+}
+
+/// Search for an occurrence of two rare bytes from the needle in the chunk
+/// pointed to by ptr, with the end of the haystack pointed to by end_ptr. When
+/// an occurrence is found, memcmp is run to check if a match occurs at the
+/// corresponding position.
+///
+/// rare1chunk and rare2chunk correspond to vectors with the rare1 and rare2
+/// bytes repeated in each 8-bit lane, respectively.
+///
+/// mask should have bits set corresponding the positions in the chunk in which
+/// matches are considered. This is only used for the last vector load where
+/// the beginning of the vector might have overlapped with the last load in
+/// the main loop. The mask lets us avoid visiting positions that have already
+/// been discarded as matches.
+///
+/// # Safety
+///
+/// It must be safe to do an unaligned read of size(V) bytes starting at both
+/// (ptr + rare1i) and (ptr + rare2i). It must also be safe to do unaligned
+/// loads on ptr up to (end_ptr - needle.len()).
+#[inline(always)]
+unsafe fn fwd_find_in_chunk<V: Vector>(
+    fwd: &Forward,
+    needle: &[u8],
+    ptr: *const u8,
+    end_ptr: *const u8,
+    rare1chunk: V,
+    rare2chunk: V,
+    mask: u32,
+) -> Option<usize> {
+    let chunk0 = V::load_unaligned(ptr.add(fwd.rare1i as usize));
+    let chunk1 = V::load_unaligned(ptr.add(fwd.rare2i as usize));
+
+    let eq0 = chunk0.cmpeq(rare1chunk);
+    let eq1 = chunk1.cmpeq(rare2chunk);
+
+    let mut match_offsets = eq0.and(eq1).movemask() & mask;
+    while match_offsets != 0 {
+        let offset = match_offsets.trailing_zeros() as usize;
+        let ptr = ptr.add(offset);
+        if end_ptr.sub(needle.len()) < ptr {
+            return None;
+        }
+        let chunk = core::slice::from_raw_parts(ptr, needle.len());
+        if memcmp(needle, chunk) {
+            return Some(offset);
+        }
+        match_offsets &= match_offsets - 1;
+    }
+    None
+}
+
+/// Accepts a chunk-relative offset and returns a haystack relative offset
+/// after updating the prefilter state.
+///
+/// See the same function with the same name in the prefilter variant of this
+/// algorithm to learned why it's tagged with inline(never). Even here, where
+/// the function is simpler, inlining it leads to poorer codegen. (Although
+/// it does improve some benchmarks, like prebuiltiter/huge-en/common-you.)
+#[cold]
+#[inline(never)]
+fn matched(start_ptr: *const u8, ptr: *const u8, chunki: usize) -> usize {
+    diff(ptr, start_ptr) + chunki
+}
+
+/// Subtract `b` from `a` and return the difference. `a` must be greater than
+/// or equal to `b`.
+fn diff(a: *const u8, b: *const u8) -> usize {
+    debug_assert!(a >= b);
+    (a as usize) - (b as usize)
+}