Remove unnecessary string cloning from the parser

crates/ruff_python_parser/src/ascii.rs

@@ -0,0 +1,343 @@
+#![allow(
+    clippy::cast_possible_truncation,
+    clippy::cast_possible_wrap,
+    clippy::cast_ptr_alignment,
+    clippy::inline_always,
+    clippy::ptr_as_ptr,
+    unsafe_code
+)]
+
+//! Source: <https://github.com/BurntSushi/bstr/blob/d4aeee2eac5d5ef6ec4d2206f6ebffe7b3dd3e1f/src/ascii.rs>
+
+// The following ~400 lines of code exists for exactly one purpose, which is
+// to optimize this code:
+//
+//     byte_slice.iter().position(|&b| b > 0x7F).unwrap_or(byte_slice.len())
+//
+// Yes... Overengineered is a word that comes to mind, but this is effectively
+// a very similar problem to memchr, and virtually nobody has been able to
+// resist optimizing the crap out of that (except for perhaps the BSD and MUSL
+// folks). In particular, this routine makes a very common case (ASCII) very
+// fast, which seems worth it. We do stop short of adding AVX variants of the
+// code below in order to retain our sanity and also to avoid needing to deal
+// with runtime target feature detection. RESIST!
+//
+// In order to understand the SIMD version below, it would be good to read this
+// comment describing how my memchr routine works:
+// https://github.com/BurntSushi/rust-memchr/blob/b0a29f267f4a7fad8ffcc8fe8377a06498202883/src/x86/sse2.rs#L19-L106
+//
+// The primary difference with memchr is that for ASCII, we can do a bit less
+// work. In particular, we don't need to detect the presence of a specific
+// byte, but rather, whether any byte has its most significant bit set. That
+// means we can effectively skip the _mm_cmpeq_epi8 step and jump straight to
+// _mm_movemask_epi8.
+
+#[cfg(any(test, miri, not(target_arch = "x86_64")))]
+const USIZE_BYTES: usize = core::mem::size_of::<usize>();
+#[cfg(any(test, miri, not(target_arch = "x86_64")))]
+const FALLBACK_LOOP_SIZE: usize = 2 * USIZE_BYTES;
+
+// This is a mask where the most significant bit of each byte in the usize
+// is set. We test this bit to determine whether a character is ASCII or not.
+// Namely, a single byte is regarded as an ASCII codepoint if and only if it's
+// most significant bit is not set.
+#[cfg(any(test, miri, not(target_arch = "x86_64")))]
+const ASCII_MASK_U64: u64 = 0x8080_8080_8080_8080;
+#[cfg(any(test, miri, not(target_arch = "x86_64")))]
+const ASCII_MASK: usize = ASCII_MASK_U64 as usize;
+
+/// Returns the index of the first non ASCII byte in the given slice.
+///
+/// If slice only contains ASCII bytes, then the length of the slice is
+/// returned.
+pub(crate) fn first_non_ascii_byte(slice: &[u8]) -> usize {
+    #[cfg(any(miri, not(target_arch = "x86_64")))]
+    {
+        first_non_ascii_byte_fallback(slice)
+    }
+
+    #[cfg(all(not(miri), target_arch = "x86_64"))]
+    {
+        first_non_ascii_byte_sse2(slice)
+    }
+}
+
+#[cfg(any(test, miri, not(target_arch = "x86_64")))]
+fn first_non_ascii_byte_fallback(slice: &[u8]) -> usize {
+    let align = USIZE_BYTES - 1;
+    let start_ptr = slice.as_ptr();
+    let end_ptr = slice[slice.len()..].as_ptr();
+    let mut ptr = start_ptr;
+
+    unsafe {
+        if slice.len() < USIZE_BYTES {
+            return first_non_ascii_byte_slow(start_ptr, end_ptr, ptr);
+        }
+
+        let chunk = read_unaligned_usize(ptr);
+        let mask = chunk & ASCII_MASK;
+        if mask != 0 {
+            return first_non_ascii_byte_mask(mask);
+        }
+
+        ptr = ptr_add(ptr, USIZE_BYTES - (start_ptr as usize & align));
+        debug_assert!(ptr > start_ptr);
+        debug_assert!(ptr_sub(end_ptr, USIZE_BYTES) >= start_ptr);
+        if slice.len() >= FALLBACK_LOOP_SIZE {
+            while ptr <= ptr_sub(end_ptr, FALLBACK_LOOP_SIZE) {
+                debug_assert_eq!(0, (ptr as usize) % USIZE_BYTES);
+
+                let a = *ptr.cast::<usize>();
+                let b = *ptr_add(ptr, USIZE_BYTES).cast::<usize>();
+                if (a | b) & ASCII_MASK != 0 {
+                    // What a kludge. We wrap the position finding code into
+                    // a non-inlineable function, which makes the codegen in
+                    // the tight loop above a bit better by avoiding a
+                    // couple extra movs. We pay for it by two additional
+                    // stores, but only in the case of finding a non-ASCII
+                    // byte.
+                    #[inline(never)]
+                    unsafe fn findpos(start_ptr: *const u8, ptr: *const u8) -> usize {
+                        let a = *ptr.cast::<usize>();
+                        let b = *ptr_add(ptr, USIZE_BYTES).cast::<usize>();
+
+                        let mut at = sub(ptr, start_ptr);
+                        let maska = a & ASCII_MASK;
+                        if maska != 0 {
+                            return at + first_non_ascii_byte_mask(maska);
+                        }
+
+                        at += USIZE_BYTES;
+                        let maskb = b & ASCII_MASK;
+                        debug_assert!(maskb != 0);
+                        at + first_non_ascii_byte_mask(maskb)
+                    }
+                    return findpos(start_ptr, ptr);
+                }
+                ptr = ptr_add(ptr, FALLBACK_LOOP_SIZE);
+            }
+        }
+        first_non_ascii_byte_slow(start_ptr, end_ptr, ptr)
+    }
+}
+
+#[cfg(all(not(miri), target_arch = "x86_64"))]
+fn first_non_ascii_byte_sse2(slice: &[u8]) -> usize {
+    use core::arch::x86_64::*;
+
+    const VECTOR_SIZE: usize = core::mem::size_of::<__m128i>();
+    const VECTOR_ALIGN: usize = VECTOR_SIZE - 1;
+    const VECTOR_LOOP_SIZE: usize = 4 * VECTOR_SIZE;
+
+    let start_ptr = slice.as_ptr();
+    let end_ptr = slice[slice.len()..].as_ptr();
+    let mut ptr = start_ptr;
+
+    unsafe {
+        if slice.len() < VECTOR_SIZE {
+            return first_non_ascii_byte_slow(start_ptr, end_ptr, ptr);
+        }
+
+        let chunk = _mm_loadu_si128(ptr as *const __m128i);
+        let mask = _mm_movemask_epi8(chunk);
+        if mask != 0 {
+            return mask.trailing_zeros() as usize;
+        }
+
+        ptr = ptr.add(VECTOR_SIZE - (start_ptr as usize & VECTOR_ALIGN));
+        debug_assert!(ptr > start_ptr);
+        debug_assert!(end_ptr.sub(VECTOR_SIZE) >= start_ptr);
+        if slice.len() >= VECTOR_LOOP_SIZE {
+            while ptr <= ptr_sub(end_ptr, VECTOR_LOOP_SIZE) {
+                debug_assert_eq!(0, (ptr as usize) % VECTOR_SIZE);
+
+                let a = _mm_load_si128(ptr as *const __m128i);
+                let b = _mm_load_si128(ptr.add(VECTOR_SIZE) as *const __m128i);
+                let c = _mm_load_si128(ptr.add(2 * VECTOR_SIZE) as *const __m128i);
+                let d = _mm_load_si128(ptr.add(3 * VECTOR_SIZE) as *const __m128i);
+
+                let or1 = _mm_or_si128(a, b);
+                let or2 = _mm_or_si128(c, d);
+                let or3 = _mm_or_si128(or1, or2);
+                if _mm_movemask_epi8(or3) != 0 {
+                    let mut at = sub(ptr, start_ptr);
+                    let mask = _mm_movemask_epi8(a);
+                    if mask != 0 {
+                        return at + mask.trailing_zeros() as usize;
+                    }
+
+                    at += VECTOR_SIZE;
+                    let mask = _mm_movemask_epi8(b);
+                    if mask != 0 {
+                        return at + mask.trailing_zeros() as usize;
+                    }
+
+                    at += VECTOR_SIZE;
+                    let mask = _mm_movemask_epi8(c);
+                    if mask != 0 {
+                        return at + mask.trailing_zeros() as usize;
+                    }
+
+                    at += VECTOR_SIZE;
+                    let mask = _mm_movemask_epi8(d);
+                    debug_assert!(mask != 0);
+                    return at + mask.trailing_zeros() as usize;
+                }
+                ptr = ptr_add(ptr, VECTOR_LOOP_SIZE);
+            }
+        }
+        while ptr <= end_ptr.sub(VECTOR_SIZE) {
+            debug_assert!(sub(end_ptr, ptr) >= VECTOR_SIZE);
+
+            let chunk = _mm_loadu_si128(ptr as *const __m128i);
+            let mask = _mm_movemask_epi8(chunk);
+            if mask != 0 {
+                return sub(ptr, start_ptr) + mask.trailing_zeros() as usize;
+            }
+            ptr = ptr.add(VECTOR_SIZE);
+        }
+        first_non_ascii_byte_slow(start_ptr, end_ptr, ptr)
+    }
+}
+
+#[inline(always)]
+unsafe fn first_non_ascii_byte_slow(
+    start_ptr: *const u8,
+    end_ptr: *const u8,
+    mut ptr: *const u8,
+) -> usize {
+    debug_assert!(start_ptr <= ptr);
+    debug_assert!(ptr <= end_ptr);
+
+    while ptr < end_ptr {
+        if *ptr > 0x7F {
+            return sub(ptr, start_ptr);
+        }
+        ptr = ptr.offset(1);
+    }
+    sub(end_ptr, start_ptr)
+}
+
+/// Compute the position of the first ASCII byte in the given mask.
+///
+/// The mask should be computed by `chunk & ASCII_MASK`, where `chunk` is
+/// 8 contiguous bytes of the slice being checked where *at least* one of those
+/// bytes is not an ASCII byte.
+///
+/// The position returned is always in the inclusive range [0, 7].
+#[cfg(any(test, miri, not(target_arch = "x86_64")))]
+fn first_non_ascii_byte_mask(mask: usize) -> usize {
+    #[cfg(target_endian = "little")]
+    {
+        mask.trailing_zeros() as usize / 8
+    }
+    #[cfg(target_endian = "big")]
+    {
+        mask.leading_zeros() as usize / 8
+    }
+}
+
+/// Increment the given pointer by the given amount.
+unsafe fn ptr_add(ptr: *const u8, amt: usize) -> *const u8 {
+    debug_assert!(amt < ::core::isize::MAX as usize);
+    ptr.add(amt)
+}
+
+/// Decrement the given pointer by the given amount.
+unsafe fn ptr_sub(ptr: *const u8, amt: usize) -> *const u8 {
+    debug_assert!(amt < ::core::isize::MAX as usize);
+    ptr.offset((amt as isize).wrapping_neg())
+}
+
+#[cfg(any(test, miri, not(target_arch = "x86_64")))]
+unsafe fn read_unaligned_usize(ptr: *const u8) -> usize {
+    use core::ptr;
+
+    let mut n: usize = 0;
+    ptr::copy_nonoverlapping(ptr, std::ptr::addr_of_mut!(n) as *mut u8, USIZE_BYTES);
+    n
+}
+
+/// Subtract `b` from `a` and return the difference. `a` should be greater than
+/// or equal to `b`.
+fn sub(a: *const u8, b: *const u8) -> usize {
+    debug_assert!(a >= b);
+    (a as usize) - (b as usize)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Our testing approach here is to try and exhaustively test every case.
+    // This includes the position at which a non-ASCII byte occurs in addition
+    // to the alignment of the slice that we're searching.
+
+    #[test]
+    fn positive_fallback_forward() {
+        for i in 0..517 {
+            let s = "a".repeat(i);
+            assert_eq!(
+                i,
+                first_non_ascii_byte_fallback(s.as_bytes()),
+                "i: {:?}, len: {:?}, s: {:?}",
+                i,
+                s.len(),
+                s
+            );
+        }
+    }
+
+    #[test]
+    #[cfg(target_arch = "x86_64")]
+    #[cfg(not(miri))]
+    fn positive_sse2_forward() {
+        for i in 0..517 {
+            let b = "a".repeat(i).into_bytes();
+            assert_eq!(b.len(), first_non_ascii_byte_sse2(&b));
+        }
+    }
+
+    #[test]
+    #[cfg(not(miri))]
+    fn negative_fallback_forward() {
+        for i in 0..517 {
+            for align in 0..65 {
+                let mut s = "a".repeat(i);
+                s.push_str("☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃");
+                let s = s.get(align..).unwrap_or("");
+                assert_eq!(
+                    i.saturating_sub(align),
+                    first_non_ascii_byte_fallback(s.as_bytes()),
+                    "i: {:?}, align: {:?}, len: {:?}, s: {:?}",
+                    i,
+                    align,
+                    s.len(),
+                    s
+                );
+            }
+        }
+    }
+
+    #[test]
+    #[cfg(target_arch = "x86_64")]
+    #[cfg(not(miri))]
+    fn negative_sse2_forward() {
+        for i in 0..517 {
+            for align in 0..65 {
+                let mut s = "a".repeat(i);
+                s.push_str("☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃");
+                let s = s.get(align..).unwrap_or("");
+                assert_eq!(
+                    i.saturating_sub(align),
+                    first_non_ascii_byte_sse2(s.as_bytes()),
+                    "i: {:?}, align: {:?}, len: {:?}, s: {:?}",
+                    i,
+                    align,
+                    s.len(),
+                    s
+                );
+            }
+        }
+    }
+}

crates/ruff_python_parser/src/lib.rs

@@ -121,6 +121,7 @@ use crate::lexer::LexResult;
 
 mod function;
 // Skip flattening lexer to distinguish from full ruff_python_parser
+mod ascii;
 mod context;
 mod invalid;
 pub mod lexer;

crates/ruff_python_parser/src/python.lalrpop

@@ -1606,7 +1606,7 @@ StringLiteralOrFString: StringType = {
 StringLiteral: StringType = {
     <location:@L> <string:string> <end_location:@R> =>? {
         let (source, kind, triple_quoted) = string;
-        Ok(parse_string_literal(&source, kind, triple_quoted, (location..end_location).into())?)
+        Ok(parse_string_literal(source, kind, triple_quoted, (location..end_location).into())?)
     }
 };
 
@@ -1623,7 +1623,7 @@ FStringMiddlePattern: ast::FStringElement = {
     FStringReplacementField,
     <location:@L> <fstring_middle:fstring_middle> <end_location:@R> =>? {
         let (source, is_raw, _) = fstring_middle;
-        Ok(parse_fstring_literal_element(&source, is_raw, (location..end_location).into())?)
+        Ok(parse_fstring_literal_element(source, is_raw, (location..end_location).into())?)
     }
 };
 

crates/ruff_python_parser/src/python.rs

@@ -1,5 +1,5 @@
 // auto-generated: "lalrpop 0.20.0"
-// sha3: aa0540221d25f4eadfc9e043fb4fc631d537b672b8a96785dfec2407e0524b79
+// sha3: 83dd2ba251ff635b813dfe48854debd5935c1a506789893ac1c2638639f27353
 use ruff_text_size::{Ranged, TextLen, TextRange, TextSize};
 use ruff_python_ast::{self as ast, Int, IpyEscapeKind};
 use crate::{
@@ -36369,7 +36369,7 @@ fn __action217<
 {
     {
         let (source, kind, triple_quoted) = string;
-        Ok(parse_string_literal(&source, kind, triple_quoted, (location..end_location).into())?)
+        Ok(parse_string_literal(source, kind, triple_quoted, (location..end_location).into())?)
     }
 }
 
@@ -36419,7 +36419,7 @@ fn __action220<
 {
     {
         let (source, is_raw, _) = fstring_middle;
-        Ok(parse_fstring_literal_element(&source, is_raw, (location..end_location).into())?)
+        Ok(parse_fstring_literal_element(source, is_raw, (location..end_location).into())?)
     }
 }