first branch cache check

crates/polars-io/src/csv/read/parser.rs

@@ -438,12 +438,7 @@ impl<'a> Iterator for SplitLines<'a> {
     #[inline]
     #[cfg(feature = "simd")]
     fn next(&mut self) -> Option<&'a [u8]> {
-        if self.v.is_empty() {
-            return None;
-        }
-        self.total_index = 0;
-        let mut not_in_field_previous_iter = true;
-
+        // First check cached value
         if self.previous_valid_eols != 0 {
             let pos = self.previous_valid_eols.trailing_zeros() as usize;
             self.previous_valid_eols >>= (pos + 1) as u64;
@@ -458,6 +453,12 @@ impl<'a> Iterator for SplitLines<'a> {
                 return ret;
             }
         }
+        if self.v.is_empty() {
+            return None;
+        }
+
+        self.total_index = 0;
+        let mut not_in_field_previous_iter = true;
 
         loop {
             let bytes = unsafe { self.v.get_unchecked_release(self.total_index..) };

crates/polars-io/src/csv/read/splitfields.rs

@@ -214,12 +214,7 @@ mod inner {
 
         #[inline]
         fn next(&mut self) -> Option<(&'a [u8], bool)> {
-            if self.finished {
-                return None;
-            }
-            if self.v.is_empty() {
-                return self.finish(false);
-            }
+            // First check cached value as this is hot.
             if self.previous_valid_ends != 0 {
                 let pos = self.previous_valid_ends.trailing_zeros() as usize;
                 self.previous_valid_ends >>= (pos + 1) as u64;
@@ -241,6 +236,12 @@ mod inner {
                     return ret;
                 }
             }
+            if self.finished {
+                return None;
+            }
+            if self.v.is_empty() {
+                return self.finish(false);
+            }
 
             let mut needs_escaping = false;
             // There can be strings with separators: