Optimize search for composable characters in redisplay

* src/composite.c (composition_compute_stop_pos): Accept new
argument INCLUDE_STATIC, and look for potential static
compositions only if this argument is non-zero.
* src/xdisp.c:
* src/composite.c:
* src/indent.c: All callers adjusted.
* src/xdisp.c (compute_stop_pos): Don't search for static
compositions.  Search for automatic compositions only after the
iterator gets past the composition stop_pos computed last time.
Use a better position for limiting search for automatic
compositions.  (Bug#62780)

4 files changed, 41 insertions, 20 deletions

diff --git a/src/composite.c b/src/composite.c
index 164eeb39598..34f369d167a 100644
--- a/src/composite.c
+++ b/src/composite.c
@@ -1040,7 +1040,9 @@ inhibit_auto_composition (void)
    composition closest to CHARPOS is found, set cmp_it->stop_pos to
    the last character of the composition.  STRING, if non-nil, is
    the string (as opposed to a buffer) whose characters should be
-   tested for being composable.
+   tested for being composable.  INCLUDE_STATIC non-zero means
+   consider both static and automatic compositions; if zero, look
+   only for potential automatic compositions.
 
    If no composition is found, set cmp_it->ch to -2.  If a static
    composition is found, set cmp_it->ch to -1.  Otherwise, set
@@ -1050,7 +1052,7 @@ inhibit_auto_composition (void)
 void
 composition_compute_stop_pos (struct composition_it *cmp_it, ptrdiff_t charpos,
                               ptrdiff_t bytepos, ptrdiff_t endpos,
-                              Lisp_Object string)
+                              Lisp_Object string, bool include_static)
 {
   ptrdiff_t start, end;
   int c;
@@ -1084,8 +1086,10 @@ composition_compute_stop_pos (struct composition_it *cmp_it, ptrdiff_t charpos,
   cmp_it->stop_pos = endpos;
   if (charpos == endpos)
     return;
+  /* Look for static compositions.  */
   /* FIXME: Bidi is not yet handled well in static composition.  */
-  if (charpos < endpos
+  if (include_static
+      && charpos < endpos
       && find_composition (charpos, endpos, &start, &end, &prop, string)
       && start >= charpos
       && composition_valid_p (start, end, prop))
@@ -1106,6 +1110,7 @@ composition_compute_stop_pos (struct composition_it *cmp_it, ptrdiff_t charpos,
         bytepos = string_char_to_byte (string, charpos);
     }
 
+  /* Look for automatic compositions.  */
   start = charpos;
   if (charpos < endpos)
     {
@@ -1285,7 +1290,8 @@ composition_reseat_it (struct composition_it *cmp_it, ptrdiff_t charpos,
 {
   if (cmp_it->ch == -2)
     {
-      composition_compute_stop_pos (cmp_it, charpos, bytepos, endpos, string);
+      composition_compute_stop_pos (cmp_it, charpos, bytepos, endpos, string,
+                                    true);
       if (cmp_it->ch == -2 || cmp_it->stop_pos != charpos)
         /* The current position is not composed.  */
         return 0;
@@ -1424,7 +1430,7 @@ composition_reseat_it (struct composition_it *cmp_it, ptrdiff_t charpos,
     }
   if (cmp_it->reversed_p)
     endpos = -1;
-  composition_compute_stop_pos (cmp_it, charpos, bytepos, endpos, string);
+  composition_compute_stop_pos (cmp_it, charpos, bytepos, endpos, string, true);
   return 0;
 }
 
diff --git a/src/composite.h b/src/composite.h
index e81465d90cc..0f791c1ea62 100644
--- a/src/composite.h
+++ b/src/composite.h
@@ -348,7 +348,7 @@ extern bool find_automatic_composition (ptrdiff_t, ptrdiff_t, ptrdiff_t,
 
 extern void composition_compute_stop_pos (struct composition_it *,
                                           ptrdiff_t, ptrdiff_t, ptrdiff_t,
-                                          Lisp_Object);
+                                          Lisp_Object, bool);
 extern bool composition_reseat_it (struct composition_it *, ptrdiff_t,
                                    ptrdiff_t, ptrdiff_t, struct window *,
                                    signed char, struct face *, Lisp_Object);
diff --git a/src/indent.c b/src/indent.c
index 08d2bf5ea28..16285ce84e2 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -616,7 +616,7 @@ scan_for_column (ptrdiff_t *endpos, EMACS_INT *goalcol,
 
   memset (&cmp_it, 0, sizeof cmp_it);
   cmp_it.id = -1;
-  composition_compute_stop_pos (&cmp_it, scan, scan_byte, end, Qnil);
+  composition_compute_stop_pos (&cmp_it, scan, scan_byte, end, Qnil, true);
 
   /* Scan forward to the target position.  */
   while (scan < end)
@@ -681,7 +681,7 @@ scan_for_column (ptrdiff_t *endpos, EMACS_INT *goalcol,
             {
               cmp_it.id = -1;
               composition_compute_stop_pos (&cmp_it, scan, scan_byte, end,
-                                            Qnil);
+                                            Qnil, true);
             }
           else
             cmp_it.from = cmp_it.to;
@@ -1290,7 +1290,7 @@ compute_motion (ptrdiff_t from, ptrdiff_t frombyte, EMACS_INT fromvpos,
   prev_tab_offset = tab_offset;
   memset (&cmp_it, 0, sizeof cmp_it);
   cmp_it.id = -1;
-  composition_compute_stop_pos (&cmp_it, pos, pos_byte, to, Qnil);
+  composition_compute_stop_pos (&cmp_it, pos, pos_byte, to, Qnil, true);
 
   unsigned short int quit_count = 0;
 
@@ -1600,7 +1600,7 @@ compute_motion (ptrdiff_t from, ptrdiff_t frombyte, EMACS_INT fromvpos,
                 {
                   cmp_it.id = -1;
                   composition_compute_stop_pos (&cmp_it, pos, pos_byte, to,
-                                                Qnil);
+                                                Qnil, true);
                 }
               else
                 cmp_it.from = cmp_it.to;
diff --git a/src/xdisp.c b/src/xdisp.c
index 76d6592bf00..18ea042e212 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -4056,7 +4056,7 @@ compute_stop_pos (struct it *it)
 {
   register INTERVAL iv, next_iv;
   Lisp_Object object, limit, position;
-  ptrdiff_t charpos, bytepos;
+  ptrdiff_t charpos, bytepos, cmp_limit_pos = -1;
 
   if (STRINGP (it->string))
     {
@@ -4126,7 +4126,10 @@ compute_stop_pos (struct it *it)
                 }
             }
           if (found)
-            pos--;
+            {
+              pos--;
+              cmp_limit_pos = pos;
+            }
           else if (it->stop_charpos < endpos)
             pos = it->stop_charpos;
           else
@@ -4184,14 +4187,25 @@ compute_stop_pos (struct it *it)
         }
     }
 
-  if (it->cmp_it.id < 0)
+  if (it->cmp_it.id < 0
+      && (STRINGP (it->string)
+          || ((!it->bidi_p || it->bidi_it.scan_dir >= 0)
+              && it->cmp_it.stop_pos <= IT_CHARPOS (*it))))
     {
       ptrdiff_t stoppos = it->end_charpos;
 
+      /* If we found, above, a buffer position that cannot be part of
+         an automatic composition, limit the search of composable
+         characters to that position.  */
       if (it->bidi_p && it->bidi_it.scan_dir < 0)
         stoppos = -1;
+      else if (cmp_limit_pos > 0)
+        stoppos = cmp_limit_pos;
+      /* Force composition_compute_stop_pos avoid the costly search
+         for static compositions, since those were already found by
+         looking at text properties, above.  */
       composition_compute_stop_pos (&it->cmp_it, charpos, bytepos,
-                                    stoppos, it->string);
+                                    stoppos, it->string, false);
     }
 
   eassert (STRINGP (it->string)
@@ -7716,7 +7730,7 @@ reseat_to_string (struct it *it, const char *s, Lisp_Object string,
       if (endpos > it->end_charpos)
         endpos = it->end_charpos;
       composition_compute_stop_pos (&it->cmp_it, charpos, -1, endpos,
-                                    it->string);
+                                    it->string, true);
     }
   CHECK_IT (it);
 }
@@ -8404,7 +8418,7 @@ set_iterator_to_next (struct it *it, bool reseat_p)
                    where to stop.  */
                 stop = -1;
               composition_compute_stop_pos (&it->cmp_it, IT_CHARPOS (*it),
-                                            IT_BYTEPOS (*it), stop, Qnil);
+                                            IT_BYTEPOS (*it), stop, Qnil, true);
             }
         }
       else
@@ -8435,7 +8449,8 @@ set_iterator_to_next (struct it *it, bool reseat_p)
                   if (it->bidi_it.scan_dir < 0)
                     stop = -1;
                   composition_compute_stop_pos (&it->cmp_it, IT_CHARPOS (*it),
-                                                IT_BYTEPOS (*it), stop, Qnil);
+                                                IT_BYTEPOS (*it), stop, Qnil,
+                                                true);
                 }
             }
           eassert (IT_BYTEPOS (*it) == CHAR_TO_BYTE (IT_CHARPOS (*it)));
@@ -8591,7 +8606,7 @@ set_iterator_to_next (struct it *it, bool reseat_p)
               composition_compute_stop_pos (&it->cmp_it,
                                             IT_STRING_CHARPOS (*it),
                                             IT_STRING_BYTEPOS (*it), stop,
-                                            it->string);
+                                            it->string, true);
             }
         }
       else
@@ -8628,7 +8643,7 @@ set_iterator_to_next (struct it *it, bool reseat_p)
                   composition_compute_stop_pos (&it->cmp_it,
                                                 IT_STRING_CHARPOS (*it),
                                                 IT_STRING_BYTEPOS (*it), stop,
-                                                it->string);
+                                                it->string, true);
                 }
             }
         }
@@ -8879,7 +8894,7 @@ get_visually_first_element (struct it *it)
       if (it->bidi_it.scan_dir < 0)
         stop = -1;
       composition_compute_stop_pos (&it->cmp_it, charpos, bytepos, stop,
-                                    it->string);
+                                    it->string, true);
     }
 }