perf(events): store autocommands in flat vectors (#23256)

Instead of nested linked lists, store autocommands in a flat, contiguous
kvec_t, with one kvec_t per event type. Previously patterns were stored
in each node of the outer linked list, so they can be matched only once
on repeating patterns. They are now reference counted and referenced in
each autocommand, and matching is skipped if the pattern repeats. Speeds
up creation and deletion, execution is not affected.

Co-authored-by: ii14 <ii14@users.noreply.github.com>

src/nvim/autocmd.h

@@ -12,9 +12,7 @@
 #include "nvim/regexp_defs.h"
 #include "nvim/types.h"
 
-struct AutoCmd_S;
 struct AutoPatCmd_S;
-struct AutoPat_S;
 
 // event_T definition
 #ifdef INCLUDE_GENERATED_DECLARATIONS
@@ -35,49 +33,45 @@ typedef struct {
   int save_State;                 ///< saved State
 } aco_save_T;
 
-typedef struct AutoCmd_S AutoCmd;
-struct AutoCmd_S {
-  AucmdExecutable exec;
-  bool once;                            // "One shot": removed after execution
-  bool nested;                          // If autocommands nest here
-  bool last;                            // last command in list
-  int64_t id;                           // ID used for uniquely tracking an autocmd.
-  sctx_T script_ctx;                    // script context where it is defined
-  char *desc;                           // Description for the autocmd.
-  AutoCmd *next;                        // Next AutoCmd in list
-};
+typedef struct {
+  size_t refcount;          ///< Reference count (freed when reaches zero)
+  char *pat;                ///< Pattern as typed
+  regprog_T *reg_prog;      ///< Compiled regprog for pattern
+  int group;                ///< Group ID
+  int patlen;               ///< strlen() of pat
+  int buflocal_nr;          ///< !=0 for buffer-local AutoPat
+  char allow_dirs;          ///< Pattern may match whole path
+} AutoPat;
 
-typedef struct AutoPat_S AutoPat;
-struct AutoPat_S {
-  AutoPat *next;                        // next AutoPat in AutoPat list; MUST
-                                        // be the first entry
-  char *pat;                            // pattern as typed (NULL when pattern
-                                        // has been removed)
-  regprog_T *reg_prog;                  // compiled regprog for pattern
-  AutoCmd *cmds;                        // list of commands to do
-  int group;                            // group ID
-  int patlen;                           // strlen() of pat
-  int buflocal_nr;                      // !=0 for buffer-local AutoPat
-  char allow_dirs;                      // Pattern may match whole path
-  char last;                            // last pattern for apply_autocmds()
-};
+typedef struct {
+  AucmdExecutable exec;     ///< Command or callback function
+  AutoPat *pat;             ///< Pattern reference (NULL when autocmd was removed)
+  int64_t id;               ///< ID used for uniquely tracking an autocmd
+  char *desc;               ///< Description for the autocmd
+  sctx_T script_ctx;        ///< Script context where it is defined
+  bool once;                ///< "One shot": removed after execution
+  bool nested;              ///< If autocommands nest here
+} AutoCmd;
 
 /// Struct used to keep status while executing autocommands for an event.
 typedef struct AutoPatCmd_S AutoPatCmd;
 struct AutoPatCmd_S {
-  AutoPat *curpat;          // next AutoPat to examine
-  AutoCmd *nextcmd;         // next AutoCmd to execute
-  int group;                // group being used
-  char *fname;              // fname to match with
-  char *sfname;             // sfname to match with
-  char *tail;               // tail of fname
-  event_T event;            // current event
-  sctx_T script_ctx;        // script context where it is defined
-  int arg_bufnr;            // initially equal to <abuf>, set to zero when buf is deleted
-  Object *data;             // arbitrary data
-  AutoPatCmd *next;         // chain of active apc-s for auto-invalidation
+  AutoPat *lastpat;         ///< Last matched AutoPat
+  size_t auidx;             ///< Current autocmd index to execute
+  size_t ausize;            ///< Saved AutoCmd vector size
+  char *fname;              ///< Fname to match with
+  char *sfname;             ///< Sfname to match with
+  char *tail;               ///< Tail of fname
+  int group;                ///< Group being used
+  event_T event;            ///< Current event
+  sctx_T script_ctx;        ///< Script context where it is defined
+  int arg_bufnr;            ///< Initially equal to <abuf>, set to zero when buf is deleted
+  Object *data;             ///< Arbitrary data
+  AutoPatCmd *next;         ///< Chain of active apc-s for auto-invalidation
 };
 
+typedef kvec_t(AutoCmd) AutoCmdVec;
+
 // Set by the apply_autocmds_group function if the given event is equal to
 // EVENT_FILETYPE. Used by the readfile function in order to determine if
 // EVENT_BUFREADPOST triggered the EVENT_FILETYPE.