Improve performance let-binding `case-fold-search' (bug#66117)

* src/buffer.h: Remove case_fold_search_ buffer object slot.
* src/buffer.c (bset_case_fold_search): Remove - no longer needed.
(init_buffer_once): Remove removed buffer slot init.
(syms_of_buffer): Use DEFVAR_LISP to define `case-fold-search' and
declare it buffer-local.
* src/minibuf.c (syms_of_minibuf): Remove DEFSYM call for
`case-fold-search' symbol.  It now lives in `syms_of_buffer'.
* src/editfns.c (Fcompare_buffer_substrings):
(Fchar_equal):
* src/search.c (looking_at_1):
(string_match_1):
(search_command):
(Fre__describe_compiled): Adjust C queries to `case-fold-search' value
to use C globals instead of BVAR macro.
* doc/lispref/internals.texi (Buffer Internals): Do not list
`case_fold_search' slot.

See https://debbugs.gnu.org/cgi/bugreport.cgi?bug=66117#259

When used as buffer slot, let-binding `case-fold-search' would scale
with the number of live buffers and can be slow.  This change makes
let-binding much faster at the cost of slightly slower `set-buffer'.

doc/lispref/internals.texi

@@ -2519,7 +2519,6 @@ when the buffer is not current.
 
 @item mode_line_format
 @itemx header_line_format
-@itemx case_fold_search
 @itemx tab_width
 @itemx fill_column
 @itemx left_margin

src/buffer.c

@@ -210,11 +210,6 @@ bset_buffer_file_coding_system (struct buffer *b, Lisp_Object val)
   b->buffer_file_coding_system_ = val;
 }
 static void
-bset_case_fold_search (struct buffer *b, Lisp_Object val)
-{
-  b->case_fold_search_ = val;
-}
-static void
 bset_ctl_arrow (struct buffer *b, Lisp_Object val)
 {
   b->ctl_arrow_ = val;
@@ -4692,7 +4687,6 @@ init_buffer_once (void)
   XSETFASTINT (BVAR (&buffer_local_flags, mode_line_format), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, abbrev_mode), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, overwrite_mode), idx); ++idx;
-  XSETFASTINT (BVAR (&buffer_local_flags, case_fold_search), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, auto_fill_function), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, selective_display), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, selective_display_ellipses), idx); ++idx;
@@ -4785,7 +4779,6 @@ init_buffer_once (void)
   bset_tab_line_format (&buffer_defaults, Qnil);
   bset_abbrev_mode (&buffer_defaults, Qnil);
   bset_overwrite_mode (&buffer_defaults, Qnil);
-  bset_case_fold_search (&buffer_defaults, Qt);
   bset_auto_fill_function (&buffer_defaults, Qnil);
   bset_selective_display (&buffer_defaults, Qnil);
   bset_selective_display_ellipses (&buffer_defaults, Qt);
@@ -5215,10 +5208,6 @@ Format with `format-mode-line' to produce a string value.  */);
 		     doc: /*  Non-nil if Abbrev mode is enabled.
 Use the command `abbrev-mode' to change this variable.  */);
 
-  DEFVAR_PER_BUFFER ("case-fold-search", &BVAR (current_buffer, case_fold_search),
-		     Qnil,
-		     doc: /* Non-nil if searches and matches should ignore case.  */);
-
   DEFVAR_PER_BUFFER ("fill-column", &BVAR (current_buffer, fill_column),
 		     Qintegerp,
 		     doc: /* Column beyond which automatic line-wrapping should happen.
@@ -5951,6 +5940,12 @@ If `delete-auto-save-files' is nil, any autosave deletion is inhibited.  */);
 This is the default.  If nil, auto-save file deletion is inhibited.  */);
   delete_auto_save_files = 1;
 
+  DEFVAR_LISP ("case-fold-search", Vcase_fold_search,
+	       doc: /* Non-nil if searches and matches should ignore case.  */);
+  Vcase_fold_search = Qt;
+  DEFSYM (Qcase_fold_search, "case-fold-search");
+  Fmake_variable_buffer_local (Qcase_fold_search);
+
   DEFVAR_LISP ("clone-indirect-buffer-hook", Vclone_indirect_buffer_hook,
 	       doc: /* Normal hook to run in the new buffer at the end of `make-indirect-buffer'.
 

src/buffer.h

@@ -379,7 +379,6 @@ struct buffer
   /* Values of several buffer-local variables.  */
   /* tab-width is buffer-local so that redisplay can find it
      in buffers that are not current.  */
-  Lisp_Object case_fold_search_;
   Lisp_Object tab_width_;
   Lisp_Object fill_column_;
   Lisp_Object left_margin_;

src/editfns.c

@@ -1785,7 +1785,7 @@ determines whether case is significant or ignored.  */)
   register EMACS_INT begp1, endp1, begp2, endp2, temp;
   register struct buffer *bp1, *bp2;
   register Lisp_Object trt
-    = (!NILP (BVAR (current_buffer, case_fold_search))
+    = (!NILP (Vcase_fold_search)
        ? BVAR (current_buffer, case_canon_table) : Qnil);
   ptrdiff_t chars = 0;
   ptrdiff_t i1, i2, i1_byte, i2_byte;
@@ -4367,7 +4367,7 @@ Case is ignored if `case-fold-search' is non-nil in the current buffer.  */)
 
   if (XFIXNUM (c1) == XFIXNUM (c2))
     return Qt;
-  if (NILP (BVAR (current_buffer, case_fold_search)))
+  if (NILP (Vcase_fold_search))
     return Qnil;
 
   i1 = XFIXNAT (c1);

src/minibuf.c

@@ -2320,7 +2320,6 @@ syms_of_minibuf (void)
 
   DEFSYM (Qcurrent_input_method, "current-input-method");
   DEFSYM (Qactivate_input_method, "activate-input-method");
-  DEFSYM (Qcase_fold_search, "case-fold-search");
   DEFSYM (Qmetadata, "metadata");
   DEFSYM (Qcycle_sort_function, "cycle-sort-function");
 

src/search.c

@@ -281,7 +281,7 @@ looking_at_1 (Lisp_Object string, bool posix, bool modify_data)
   struct regexp_cache *cache_entry = compile_pattern (
     string,
     modify_match_data ? &search_regs : NULL,
-    (!NILP (BVAR (current_buffer, case_fold_search))
+    (!NILP (Vcase_fold_search)
      ? BVAR (current_buffer, case_canon_table) : Qnil),
     posix,
     !NILP (BVAR (current_buffer, enable_multibyte_characters)));
@@ -402,7 +402,7 @@ string_match_1 (Lisp_Object regexp, Lisp_Object string, Lisp_Object start,
   struct regexp_cache *cache_entry
     = compile_pattern (regexp,
 		       modify_match_data ? &search_regs : NULL,
-		       (!NILP (BVAR (current_buffer, case_fold_search))
+		       (!NILP (Vcase_fold_search)
 			? BVAR (current_buffer, case_canon_table)
 			: Qnil),
 		       posix,
@@ -1068,10 +1068,10 @@ search_command (Lisp_Object string, Lisp_Object bound, Lisp_Object noerror,
 			 BVAR (current_buffer, case_eqv_table));
 
   np = search_buffer (string, PT, PT_BYTE, lim, lim_byte, n, RE,
-		      (!NILP (BVAR (current_buffer, case_fold_search))
+		      (!NILP (Vcase_fold_search)
 		       ? BVAR (current_buffer, case_canon_table)
 		       : Qnil),
-		      (!NILP (BVAR (current_buffer, case_fold_search))
+		      (!NILP (Vcase_fold_search)
 		       ? BVAR (current_buffer, case_eqv_table)
 		       : Qnil),
 		      posix);
@@ -3402,7 +3402,7 @@ If RAW is non-nil, just return the actual bytecode.  */)
 {
   struct regexp_cache *cache_entry
     = compile_pattern (regexp, NULL,
-                       (!NILP (BVAR (current_buffer, case_fold_search))
+                       (!NILP (Vcase_fold_search)
                         ? BVAR (current_buffer, case_canon_table) : Qnil),
                        false,
                        !NILP (BVAR (current_buffer,