Auto merge of rust-lang#137110 - real-eren:rustc_span/remove-sse2-path, r=<try>

Remove SSE2 path from `rustc_span` `analyze_source_file`

Follow-up to  rust-lang#136460. When the SSE2 optimization was [introduced](https://github.com/michaelwoerister/rust/blob/a1f8a6ce80a340d51074071c0d9e30eb14f65d25/src/libsyntax_pos/analyze_filemap.rs), the generic path recorded `NonNarrowChar`s for ASCII control characters. Nowadays, `analyze_source_file` only deals with newlines and multi-byte chars.

The point of this PR is to see, via a perf run, whether the SSE2 path still provides a meaningful improvement over the generic path. If it doesn't, it could be removed.

The function can be simplified further after inlining; I left it as-is for the initial perf run so that it's easier to see that the behavior is unchanged.

r? `@Noratrieb`

Author: bors

compiler/rustc_span/src/analyze_source_file.rs

@@ -5,15 +5,17 @@ mod tests;
 
 /// Finds all newlines, multi-byte characters, and non-narrow characters in a
 /// SourceFile.
-///
-/// This function will use an SSE2 enhanced implementation if hardware support
-/// is detected at runtime.
 pub(crate) fn analyze_source_file(src: &str) -> (Vec<RelativeBytePos>, Vec<MultiByteChar>) {
     let mut lines = vec![RelativeBytePos::from_u32(0)];
     let mut multi_byte_chars = vec![];
 
-    // Calls the right implementation, depending on hardware support available.
-    analyze_source_file_dispatch(src, &mut lines, &mut multi_byte_chars);
+    analyze_source_file_generic(
+        src,
+        src.len(),
+        RelativeBytePos(0),
+        &mut lines,
+        &mut multi_byte_chars,
+    );
 
     // The code above optimistically registers a new line *after* each \n
     // it encounters. If that point is already outside the source_file, remove
@@ -29,256 +31,6 @@ pub(crate) fn analyze_source_file(src: &str) -> (Vec<RelativeBytePos>, Vec<Multi
     (lines, multi_byte_chars)
 }
 
-#[cfg(bootstrap)]
-cfg_match! {
-    cfg(any(target_arch = "x86", target_arch = "x86_64")) => {
-        fn analyze_source_file_dispatch(
-            src: &str,
-            lines: &mut Vec<RelativeBytePos>,
-            multi_byte_chars: &mut Vec<MultiByteChar>,
-        ) {
-            if is_x86_feature_detected!("sse2") {
-                unsafe {
-                    analyze_source_file_sse2(src, lines, multi_byte_chars);
-                }
-            } else {
-                analyze_source_file_generic(
-                    src,
-                    src.len(),
-                    RelativeBytePos::from_u32(0),
-                    lines,
-                    multi_byte_chars,
-                );
-            }
-        }
-
-        /// Checks 16 byte chunks of text at a time. If the chunk contains
-        /// something other than printable ASCII characters and newlines, the
-        /// function falls back to the generic implementation. Otherwise it uses
-        /// SSE2 intrinsics to quickly find all newlines.
-        #[target_feature(enable = "sse2")]
-        unsafe fn analyze_source_file_sse2(
-            src: &str,
-            lines: &mut Vec<RelativeBytePos>,
-            multi_byte_chars: &mut Vec<MultiByteChar>,
-        ) {
-            #[cfg(target_arch = "x86")]
-            use std::arch::x86::*;
-            #[cfg(target_arch = "x86_64")]
-            use std::arch::x86_64::*;
-
-            const CHUNK_SIZE: usize = 16;
-
-            let src_bytes = src.as_bytes();
-
-            let chunk_count = src.len() / CHUNK_SIZE;
-
-            // This variable keeps track of where we should start decoding a
-            // chunk. If a multi-byte character spans across chunk boundaries,
-            // we need to skip that part in the next chunk because we already
-            // handled it.
-            let mut intra_chunk_offset = 0;
-
-            for chunk_index in 0..chunk_count {
-                let ptr = src_bytes.as_ptr() as *const __m128i;
-                // We don't know if the pointer is aligned to 16 bytes, so we
-                // use `loadu`, which supports unaligned loading.
-                let chunk = unsafe { _mm_loadu_si128(ptr.add(chunk_index)) };
-
-                // For character in the chunk, see if its byte value is < 0, which
-                // indicates that it's part of a UTF-8 char.
-                let multibyte_test = unsafe { _mm_cmplt_epi8(chunk, _mm_set1_epi8(0)) };
-                // Create a bit mask from the comparison results.
-                let multibyte_mask = unsafe { _mm_movemask_epi8(multibyte_test) };
-
-                // If the bit mask is all zero, we only have ASCII chars here:
-                if multibyte_mask == 0 {
-                    assert!(intra_chunk_offset == 0);
-
-                    // Check for newlines in the chunk
-                    let newlines_test = unsafe { _mm_cmpeq_epi8(chunk, _mm_set1_epi8(b'\n' as i8)) };
-                    let mut newlines_mask = unsafe { _mm_movemask_epi8(newlines_test) };
-
-                    let output_offset = RelativeBytePos::from_usize(chunk_index * CHUNK_SIZE + 1);
-
-                    while newlines_mask != 0 {
-                        let index = newlines_mask.trailing_zeros();
-
-                        lines.push(RelativeBytePos(index) + output_offset);
-
-                        // Clear the bit, so we can find the next one.
-                        newlines_mask &= newlines_mask - 1;
-                    }
-                } else {
-                    // The slow path.
-                    // There are multibyte chars in here, fallback to generic decoding.
-                    let scan_start = chunk_index * CHUNK_SIZE + intra_chunk_offset;
-                    intra_chunk_offset = analyze_source_file_generic(
-                        &src[scan_start..],
-                        CHUNK_SIZE - intra_chunk_offset,
-                        RelativeBytePos::from_usize(scan_start),
-                        lines,
-                        multi_byte_chars,
-                    );
-                }
-            }
-
-            // There might still be a tail left to analyze
-            let tail_start = chunk_count * CHUNK_SIZE + intra_chunk_offset;
-            if tail_start < src.len() {
-                analyze_source_file_generic(
-                    &src[tail_start..],
-                    src.len() - tail_start,
-                    RelativeBytePos::from_usize(tail_start),
-                    lines,
-                    multi_byte_chars,
-                );
-            }
-        }
-    }
-    _ => {
-        // The target (or compiler version) does not support SSE2 ...
-        fn analyze_source_file_dispatch(
-            src: &str,
-            lines: &mut Vec<RelativeBytePos>,
-            multi_byte_chars: &mut Vec<MultiByteChar>,
-        ) {
-            analyze_source_file_generic(
-                src,
-                src.len(),
-                RelativeBytePos::from_u32(0),
-                lines,
-                multi_byte_chars,
-            );
-        }
-    }
-}
-
-#[cfg(not(bootstrap))]
-cfg_match! {
-    any(target_arch = "x86", target_arch = "x86_64") => {
-        fn analyze_source_file_dispatch(
-            src: &str,
-            lines: &mut Vec<RelativeBytePos>,
-            multi_byte_chars: &mut Vec<MultiByteChar>,
-        ) {
-            if is_x86_feature_detected!("sse2") {
-                unsafe {
-                    analyze_source_file_sse2(src, lines, multi_byte_chars);
-                }
-            } else {
-                analyze_source_file_generic(
-                    src,
-                    src.len(),
-                    RelativeBytePos::from_u32(0),
-                    lines,
-                    multi_byte_chars,
-                );
-            }
-        }
-
-        /// Checks 16 byte chunks of text at a time. If the chunk contains
-        /// something other than printable ASCII characters and newlines, the
-        /// function falls back to the generic implementation. Otherwise it uses
-        /// SSE2 intrinsics to quickly find all newlines.
-        #[target_feature(enable = "sse2")]
-        unsafe fn analyze_source_file_sse2(
-            src: &str,
-            lines: &mut Vec<RelativeBytePos>,
-            multi_byte_chars: &mut Vec<MultiByteChar>,
-        ) {
-            #[cfg(target_arch = "x86")]
-            use std::arch::x86::*;
-            #[cfg(target_arch = "x86_64")]
-            use std::arch::x86_64::*;
-
-            const CHUNK_SIZE: usize = 16;
-
-            let src_bytes = src.as_bytes();
-
-            let chunk_count = src.len() / CHUNK_SIZE;
-
-            // This variable keeps track of where we should start decoding a
-            // chunk. If a multi-byte character spans across chunk boundaries,
-            // we need to skip that part in the next chunk because we already
-            // handled it.
-            let mut intra_chunk_offset = 0;
-
-            for chunk_index in 0..chunk_count {
-                let ptr = src_bytes.as_ptr() as *const __m128i;
-                // We don't know if the pointer is aligned to 16 bytes, so we
-                // use `loadu`, which supports unaligned loading.
-                let chunk = unsafe { _mm_loadu_si128(ptr.add(chunk_index)) };
-
-                // For character in the chunk, see if its byte value is < 0, which
-                // indicates that it's part of a UTF-8 char.
-                let multibyte_test = unsafe { _mm_cmplt_epi8(chunk, _mm_set1_epi8(0)) };
-                // Create a bit mask from the comparison results.
-                let multibyte_mask = unsafe { _mm_movemask_epi8(multibyte_test) };
-
-                // If the bit mask is all zero, we only have ASCII chars here:
-                if multibyte_mask == 0 {
-                    assert!(intra_chunk_offset == 0);
-
-                    // Check for newlines in the chunk
-                    let newlines_test = unsafe { _mm_cmpeq_epi8(chunk, _mm_set1_epi8(b'\n' as i8)) };
-                    let mut newlines_mask = unsafe { _mm_movemask_epi8(newlines_test) };
-
-                    let output_offset = RelativeBytePos::from_usize(chunk_index * CHUNK_SIZE + 1);
-
-                    while newlines_mask != 0 {
-                        let index = newlines_mask.trailing_zeros();
-
-                        lines.push(RelativeBytePos(index) + output_offset);
-
-                        // Clear the bit, so we can find the next one.
-                        newlines_mask &= newlines_mask - 1;
-                    }
-                } else {
-                    // The slow path.
-                    // There are multibyte chars in here, fallback to generic decoding.
-                    let scan_start = chunk_index * CHUNK_SIZE + intra_chunk_offset;
-                    intra_chunk_offset = analyze_source_file_generic(
-                        &src[scan_start..],
-                        CHUNK_SIZE - intra_chunk_offset,
-                        RelativeBytePos::from_usize(scan_start),
-                        lines,
-                        multi_byte_chars,
-                    );
-                }
-            }
-
-            // There might still be a tail left to analyze
-            let tail_start = chunk_count * CHUNK_SIZE + intra_chunk_offset;
-            if tail_start < src.len() {
-                analyze_source_file_generic(
-                    &src[tail_start..],
-                    src.len() - tail_start,
-                    RelativeBytePos::from_usize(tail_start),
-                    lines,
-                    multi_byte_chars,
-                );
-            }
-        }
-    }
-    _ => {
-        // The target (or compiler version) does not support SSE2 ...
-        fn analyze_source_file_dispatch(
-            src: &str,
-            lines: &mut Vec<RelativeBytePos>,
-            multi_byte_chars: &mut Vec<MultiByteChar>,
-        ) {
-            analyze_source_file_generic(
-                src,
-                src.len(),
-                RelativeBytePos::from_u32(0),
-                lines,
-                multi_byte_chars,
-            );
-        }
-    }
-}
-
 // `scan_len` determines the number of bytes in `src` to scan. Note that the
 // function can read past `scan_len` if a multi-byte character start within the
 // range but extends past it. The overflow is returned by the function.