Fix excessive calls to bidi_shelve_cache reported in bug #15555.

 src/xdisp.c (move_it_in_display_line_to): Save the iterator state in ppos_it
 only once per call.  Reimplement the method used to return to the
 best candidate position if all the positions found in display line
 are beyond TO_CHARPOS.  This cuts down the number of calls to
 bidi_shelve_cache, which moves a lot of stuff when lines are long
 and include bidirectional text.

2 files changed, 38 insertions, 17 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 3c063ca3c0b..4bb47197106 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -5,6 +5,12 @@
         (try_cursor_movement): Don't use cursor position if
         set_cursor_from_row failed to compute it.  This avoids assertion
         violations in MATRIX_ROW.
+        (move_it_in_display_line_to): Save the iterator state in ppos_it
+        only once per call.  Reimplement the method used to return to the
+        best candidate position if all the positions found in display line
+        are beyond TO_CHARPOS.  This cuts down the number of calls to
+        bidi_shelve_cache, which moves a lot of stuff when lines are long
+        and include bidirectional text.  (Bug#15555)
 
 2014-02-20  Glenn Morris  <rgm@gnu.org>
 
diff --git a/src/xdisp.c b/src/xdisp.c
index 94dd65c5d0b..840ff1288e5 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -8313,7 +8313,7 @@ move_it_in_display_line_to (struct it *it,
   void *ppos_data = NULL;
   int may_wrap = 0;
   enum it_method prev_method = it->method;
-  ptrdiff_t prev_pos = IT_CHARPOS (*it);
+  ptrdiff_t closest_pos, prev_pos = IT_CHARPOS (*it);
   int saw_smaller_pos = prev_pos < to_charpos;
 
   /* Don't produce glyphs in produce_glyphs.  */
@@ -8330,16 +8330,21 @@ move_it_in_display_line_to (struct it *it,
   atx_it.sp = -1;
 
   /* Use ppos_it under bidi reordering to save a copy of IT for the
-     position > CHARPOS that is the closest to CHARPOS.  We restore
-     that position in IT when we have scanned the entire display line
-     without finding a match for CHARPOS and all the character
-     positions are greater than CHARPOS.  */
+     initial position.  We restore that position in IT when we have
+     scanned the entire display line without finding a match for
+     TO_CHARPOS and all the character positions are greater than
+     TO_CHARPOS.  We then restart the scan from the initial position,
+     and stop at CLOSEST_POS, which is a position > TO_CHARPOS that is
+     the closest to TO_CHARPOS.  */
   if (it->bidi_p)
     {
-      SAVE_IT (ppos_it, *it, ppos_data);
-      SET_TEXT_POS (ppos_it.current.pos, ZV, ZV_BYTE);
       if ((op & MOVE_TO_POS) && IT_CHARPOS (*it) >= to_charpos)
-        SAVE_IT (ppos_it, *it, ppos_data);
+        {
+          SAVE_IT (ppos_it, *it, ppos_data);
+          closest_pos = IT_CHARPOS (*it);
+        }
+      else
+        closest_pos = ZV;
     }
 
 #define BUFFER_POS_REACHED_P()                                  \
@@ -8483,8 +8488,8 @@ move_it_in_display_line_to (struct it *it,
           if (it->bidi_p
               && (op & MOVE_TO_POS)
               && IT_CHARPOS (*it) > to_charpos
-              && IT_CHARPOS (*it) < IT_CHARPOS (ppos_it))
-            SAVE_IT (ppos_it, *it, ppos_data);
+              && IT_CHARPOS (*it) < closest_pos)
+            closest_pos = IT_CHARPOS (*it);
           continue;
         }
 
@@ -8706,9 +8711,11 @@ move_it_in_display_line_to (struct it *it,
             {
               if (!saw_smaller_pos && IT_CHARPOS (*it) > to_charpos)
                 {
-                  if (IT_CHARPOS (ppos_it) < ZV)
+                  if (closest_pos < ZV)
                     {
                       RESTORE_IT (it, &ppos_it, ppos_data);
+                      move_it_in_display_line_to (it, closest_pos, -1,
+                                                  MOVE_TO_POS);
                       result = MOVE_POS_MATCH_OR_ZV;
                     }
                   else
@@ -8738,8 +8745,8 @@ move_it_in_display_line_to (struct it *it,
       if (it->bidi_p
           && (op & MOVE_TO_POS)
           && IT_CHARPOS (*it) >= to_charpos
-          && IT_CHARPOS (*it) < IT_CHARPOS (ppos_it))
-        SAVE_IT (ppos_it, *it, ppos_data);
+          && IT_CHARPOS (*it) < closest_pos)
+        closest_pos = IT_CHARPOS (*it);
 
       /* Stop if lines are truncated and IT's current x-position is
          past the right edge of the window now.  */
@@ -8765,8 +8772,13 @@ move_it_in_display_line_to (struct it *it,
                       && IT_CHARPOS (*it) > to_charpos))
                 {
                   if (it->bidi_p
-                      && !at_eob_p && IT_CHARPOS (ppos_it) < ZV)
-                    RESTORE_IT (it, &ppos_it, ppos_data);
+                      && !BUFFER_POS_REACHED_P ()
+                      && !at_eob_p && closest_pos < ZV)
+                    {
+                      RESTORE_IT (it, &ppos_it, ppos_data);
+                      move_it_in_display_line_to (it, closest_pos, -1,
+                                                  MOVE_TO_POS);
+                    }
                   result = MOVE_POS_MATCH_OR_ZV;
                   break;
                 }
@@ -8780,8 +8792,11 @@ move_it_in_display_line_to (struct it *it,
                    && !saw_smaller_pos
                    && IT_CHARPOS (*it) > to_charpos)
             {
-              if (IT_CHARPOS (ppos_it) < ZV)
-                RESTORE_IT (it, &ppos_it, ppos_data);
+              if (closest_pos < ZV)
+                {
+                  RESTORE_IT (it, &ppos_it, ppos_data);
+                  move_it_in_display_line_to (it, closest_pos, -1, MOVE_TO_POS);
+                }
               result = MOVE_POS_MATCH_OR_ZV;
               break;
             }