use simd on supported platforms

compiler/parse/src/blankspace.rs

@@ -226,11 +226,11 @@ fn fast_eat_spaces(state: &State) -> FastSpaceState {
     use FastSpaceState::*;
 
     let mut newlines = 0;
-    let mut index = 0;
     let mut line_start = state.line_start.offset as usize;
     let base_offset = state.pos().offset as usize;
 
-    let bytes = state.bytes();
+    let mut index = base_offset;
+    let bytes = state.original_bytes();
     let length = bytes.len();
 
     'outer: while index < length {
@@ -241,18 +241,50 @@ fn fast_eat_spaces(state: &State) -> FastSpaceState {
             b'\n' => {
                 newlines += 1;
                 index += 1;
-                line_start = base_offset + index;
+                line_start = index;
             }
             b'\r' => {
                 index += 1;
-                line_start = base_offset + index;
+                line_start = index;
             }
             b'\t' => {
-                return HasTab(Position::new((base_offset + index) as u32));
+                return HasTab(Position::new(index as u32));
             }
             b'#' => {
                 index += 1;
 
+                // try to use SIMD instructions explicitly
+                if cfg!(target_arch = "x86_64") {
+                    use std::arch::x86_64::*;
+
+                    // a bytestring with the three characters we're looking for (the rest is ignored)
+                    let needle = b"\r\n\t=============";
+                    let needle = unsafe { _mm_loadu_si128(needle.as_ptr() as *const _) };
+
+                    while index < length {
+                        let remaining = length - index;
+                        let length = if remaining < 16 { remaining as i32 } else { 16 };
+
+                        // the source bytes we'll be looking at
+                        let haystack =
+                            unsafe { _mm_loadu_si128(bytes.as_ptr().add(index) as *const _) };
+
+                        // use first 3 characters of needle, first `length` characters of haystack
+                        // finds the first index where one of the `needle` characters occurs
+                        // or 16 when none of the needle characters occur
+                        let first_special_char = unsafe {
+                            _mm_cmpestri(needle, 3, haystack, length, _SIDD_CMP_EQUAL_ANY)
+                        };
+
+                        // we've made `first_special_char` characters of progress
+                        index += first_special_char as usize;
+
+                        // if we found a special char, let the outer loop handle it
+                        if first_special_char != 16 {
+                            continue 'outer;
+                        }
+                    }
+                } else {
                     while index < length {
                         match bytes[index] {
                             b'\n' | b'\t' | b'\r' => {
@@ -265,14 +297,15 @@ fn fast_eat_spaces(state: &State) -> FastSpaceState {
                         }
                     }
                 }
+            }
             _ => break,
         }
     }
 
     Good {
         newlines,
-        consumed: index,
-        column: ((base_offset + index) - line_start) as u32,
+        consumed: index - base_offset,
+        column: (index - line_start) as u32,
     }
 }