From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 17 Aug 2024 02:02:55 +0000 (-0700)
Subject: Tune volatile in read_char
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=79d8ebf2dbcdf013594982b13c5e9381d2ad63fa;p=emacs.git

Tune volatile in read_char

* src/keyboard.c (read_char): Optimize access to a local volatile.

(cherry picked from commit 8c81818673ae9ff788c6e65fb90984f327b27964)
---

diff --git a/src/keyboard.c b/src/keyboard.c
index 6e088372fcf..6438e9cacb4 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));
 	}
     }