master 8c81818673a 6/7: Tune volatile in read_char

[Paul Eggert]

branch: master
commit 8c81818673ae9ff788c6e65fb90984f327b27964
Author: Paul Eggert <eggert@cs.ucla.edu>
Commit: Paul Eggert <eggert@cs.ucla.edu>

    Tune volatile in read_char
    
    * src/keyboard.c (read_char): Optimize access to a local volatile.
---
 src/keyboard.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/keyboard.c b/src/keyboard.c
index b519ccdf9f0..0d3506bc59b 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -2517,7 +2517,7 @@ read_char (int commandflag, Lisp_Object map,
           Lisp_Object prev_event,
           bool *used_mouse_menu, struct timespec *end_time)
 {
-  Lisp_Object volatile c;
+  Lisp_Object c;
   sys_jmp_buf local_getcjmp;
   sys_jmp_buf save_jump;
   Lisp_Object tem, save;
@@ -2752,8 +2752,10 @@ read_char (int commandflag, Lisp_Object map,
      it *must not* be in effect when we call redisplay.  */
 
   specpdl_ref jmpcount = SPECPDL_INDEX ();
+  Lisp_Object volatile c_volatile;
   if (sys_setjmp (local_getcjmp))
     {
+      c = c_volatile;
       /* Handle quits while reading the keyboard.  */
       /* We must have saved the outer value of getcjmp here,
         so restore it now.  */
@@ -2798,6 +2800,13 @@ read_char (int commandflag, Lisp_Object map,
       goto non_reread;
     }
 
+  c_volatile = c;
+#if GCC_LINT && __GNUC__ && !__clang__
+  /* This useless assignment pacifies GCC 14.2.1 x86-64
+     <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=21161>.  */
+  c = c_volatile;
+#endif
+
   /* Start idle timers if no time limit is supplied.  We don't do it
      if a time limit is supplied to avoid an infinite recursion in the
      situation where an idle timer calls `sit-for'.  */
@@ -2959,6 +2968,8 @@ read_char (int commandflag, Lisp_Object map,
            }
          reread = true;
        }
+
+      c_volatile = c;
     }
 
   /* Read something from current KBOARD's side queue, if possible.  */
@@ -2970,6 +2981,7 @@ read_char (int commandflag, Lisp_Object map,
          if (!CONSP (KVAR (current_kboard, kbd_queue)))
            emacs_abort ();
          c = XCAR (KVAR (current_kboard, kbd_queue));
+         c_volatile = c;
          kset_kbd_queue (current_kboard,
                          XCDR (KVAR (current_kboard, kbd_queue)));
          if (NILP (KVAR (current_kboard, kbd_queue)))
@@ -3025,6 +3037,8 @@ read_char (int commandflag, Lisp_Object map,
          c = XCDR (c);
          recorded = true;
        }
+
+      c_volatile = c;
   }
 
  non_reread:
@@ -3108,7 +3122,7 @@ read_char (int commandflag, Lisp_Object map,
          d = Faref (KVAR (current_kboard, Vkeyboard_translate_table), c);
          /* nil in keyboard-translate-table means no translation.  */
          if (!NILP (d))
-           c = d;
+           c_volatile = c = d;
        }
     }
 
@@ -3148,6 +3162,7 @@ read_char (int commandflag, Lisp_Object map,
              Vunread_command_events = Fcons (c, Vunread_command_events);
            }
          c = posn;
+         c_volatile = c;
        }
     }
 
@@ -3273,6 +3288,7 @@ read_char (int commandflag, Lisp_Object map,
        }
       /* It returned one event or more.  */
       c = XCAR (tem);
+      c_volatile = c;
       Vunread_post_input_method_events
        = nconc2 (XCDR (tem), Vunread_post_input_method_events);
     }
@@ -3347,6 +3363,7 @@ read_char (int commandflag, Lisp_Object map,
       do
        {
          c = read_char (0, Qnil, Qnil, 0, NULL);
+         c_volatile = c;
          if (EVENT_HAS_PARAMETERS (c)
              && EQ (EVENT_HEAD_KIND (EVENT_HEAD (c)), Qmouse_click))
            XSETCAR (help_form_saved_window_configs, Qnil);
@@ -3360,7 +3377,7 @@ read_char (int commandflag, Lisp_Object map,
        {
          cancel_echoing ();
          do
-           c = read_char (0, Qnil, Qnil, 0, NULL);
+           c_volatile = c = read_char (0, Qnil, Qnil, 0, NULL);
          while (BUFFERP (c));
        }
     }