Commit: patch 9.2.0240: syn_name2id() is slow due to linear search

[Christian Brabandt]

patch 9.2.0240: syn_name2id() is slow due to linear search

Commit: https://github.com/vim/vim/commit/b435da0b4fea339be51616cc846055d5bd0a2a62
Author: Yasuhiro Matsumoto <matt...@gmail.com>
Date: Tue Mar 24 20:47:27 2026 +0000

patch 9.2.0240: syn_name2id() is slow due to linear search

Problem: Looking up highlight group names uses a linear scan of the
highlight table, which is slow at startup when many groups
are defined.
Solution: Use a hashtable for O(1) highlight group name lookup.
(Yasuhiro Matsumoto).

Benchmark (523 highlight groups, :highlight + highlight link + syntax
keyword + hlID() + redraw, 20 iterations):

master: 0.057 sec (~295,000 ops/sec)
this branch: 0.036 sec (~463,000 ops/sec)
speedup: ~1.57x

closes: #19788

Signed-off-by: Yasuhiro Matsumoto <matt...@gmail.com>
Signed-off-by: Christian Brabandt <c...@256bit.org>

diff --git a/src/highlight.c b/src/highlight.c
index 0accfe9be..19d13907a 100644
--- a/src/highlight.c
+++ b/src/highlight.c
@@ -207,6 +207,21 @@ static int hl_flags[HLF_COUNT] = HL_FLAGS;
static garray_T highlight_ga;
#define HL_TABLE() ((hl_group_T *)((highlight_ga.ga_data)))

+// Wrapper struct for hashtable entries: stores the highlight group ID alongside
+// the uppercase name used as a hash key. Uses the same offsetof pattern as
+// signgroup_T / HI2SG.
+typedef struct {
+ int hn_id; // highlight group ID (1-based)
+ char_u hn_key[1]; // uppercase name (stretchable array)
+} hlname_T;
+
+#define HLNAME_KEY_OFF offsetof(hlname_T, hn_key)
+#define HI2HLNAME(hi) ((hlname_T *)((hi)->hi_key - HLNAME_KEY_OFF))
+
+// hashtable for quick highlight group name lookup
+static hashtab_T highlight_ht;
+static bool highlight_ht_inited = false;
+
/*
* An attribute number is the index in attr_table plus ATTR_OFF.
*/
@@ -217,6 +232,7 @@ static void set_hl_attr(int idx);
static void highlight_list_one(int id);
static int highlight_list_arg(int id, int didh, int type, int iarg, char_u *sarg, char *name);
static int syn_add_group(char_u *name);
+static int syn_name2id_len(char_u *name, int len);
static int hl_has_settings(int idx, int check_link);
static void highlight_clear(int idx);

@@ -2034,9 +2050,11 @@ free_highlight(void)
{
highlight_clear(i);
vim_free(HL_TABLE()[i].sg_name);
- vim_free(HL_TABLE()[i].sg_name_u);
+ vim_free(HL_TABLE()[i].sg_name_u - HLNAME_KEY_OFF);
}
ga_clear(&highlight_ga);
+ hash_clear(&highlight_ht);
+ highlight_ht_inited = false;
}
#endif

@@ -3810,25 +3828,37 @@ syn_override(int id)
}

/*
- * Lookup a highlight group name and return its ID.
+ * Lookup a highlight group name by pointer and length.
* If it is not found, 0 is returned.
*/
- int
-syn_name2id(char_u *name)
+ static int
+syn_name2id_len(char_u *name, int len)
{
- int i;
char_u name_u[MAX_SYN_NAME + 1];
+ hashitem_T *hi;

- // Avoid using stricmp() too much, it's slow on some systems
- // Avoid alloc()/free(), these are slow too. ID names over 200 chars
- // don't deserve to be found!
- vim_strncpy(name_u, name, MAX_SYN_NAME);
+ if (len > MAX_SYN_NAME)
+ len = MAX_SYN_NAME;
+ mch_memmove(name_u, name, len);
+ name_u[len] = NUL;
vim_strup(name_u);
- for (i = highlight_ga.ga_len; --i >= 0; )
- if (HL_TABLE()[i].sg_name_u != NULL
- && STRCMP(name_u, HL_TABLE()[i].sg_name_u) == 0)
- break;
- return i + 1;
+ if (!highlight_ht_inited)
+ return 0;
+ hi = hash_find(&highlight_ht, name_u);
+ if (HASHITEM_EMPTY(hi))
+ return 0;
+ return HI2HLNAME(hi)->hn_id;
+}
+
+/*
+ * Lookup a highlight group name and return its ID.
+ * If it is not found, 0 is returned.
+ */
+ int
+syn_name2id(char_u *name)
+{
+ // Avoid using stricmp() too much, it's slow on some systems.
+ return syn_name2id_len(name, (int)STRLEN(name));
}

/*
@@ -3876,16 +3906,7 @@ syn_id2name(int id)
int
syn_namen2id(char_u *linep, int len)
{
- char_u *name;
- int id = 0;
-
- name = vim_strnsave(linep, len);
- if (name == NULL)
- return 0;
-
- id = syn_name2id(name);
- vim_free(name);
- return id;
+ return syn_name2id_len(linep, len);
}

/*
@@ -3905,15 +3926,14 @@ syn_check_group(char_u *pp, int len)
emsg(_(e_highlight_group_name_too_long));
return 0;
}
- name = vim_strnsave(pp, len);
- if (name == NULL)
- return 0;
-
- id = syn_name2id(name);
+ id = syn_name2id_len(pp, len);
if (id == 0) // doesn't exist yet
+ {
+ name = vim_strnsave(pp, len);
+ if (name == NULL)
+ return 0;
id = syn_add_group(name);
- else
- vim_free(name);
+ }
return id;
}

@@ -3952,6 +3972,8 @@ syn_add_group(char_u *name)
{
highlight_ga.ga_itemsize = sizeof(hl_group_T);
highlight_ga.ga_growsize = 10;
+ hash_init(&highlight_ht);
+ highlight_ht_inited = true;
}

if (highlight_ga.ga_len >= MAX_HL_ID)
@@ -3968,11 +3990,20 @@ syn_add_group(char_u *name)
return 0;
}

- name_up = vim_strsave_up(name);
- if (name_up == NULL)
{
- vim_free(name);
- return 0;
+ hlname_T *hn;
+ int len = (int)STRLEN(name);
+
+ hn = alloc(offsetof(hlname_T, hn_key) + len + 1);
+ if (hn == NULL)
+ {
+ vim_free(name);
+ return 0;
+ }
+ vim_strncpy(hn->hn_key, name, len);
+ vim_strup(hn->hn_key);
+ hn->hn_id = highlight_ga.ga_len + 1; // ID is index plus one
+ name_up = hn->hn_key;
}

CLEAR_POINTER(&(HL_TABLE()[highlight_ga.ga_len]));
@@ -3983,6 +4014,7 @@ syn_add_group(char_u *name)
HL_TABLE()[highlight_ga.ga_len].sg_gui_fg = INVALCOLOR;
HL_TABLE()[highlight_ga.ga_len].sg_gui_sp = INVALCOLOR;
#endif
+ hash_add(&highlight_ht, name_up, "highlight");
++highlight_ga.ga_len;

return highlight_ga.ga_len; // ID is index plus one
@@ -3995,9 +4027,14 @@ syn_add_group(char_u *name)
static void
syn_unadd_group(void)
{
+ hashitem_T *hi;
+
--highlight_ga.ga_len;
+ hi = hash_find(&highlight_ht, HL_TABLE()[highlight_ga.ga_len].sg_name_u);
+ if (!HASHITEM_EMPTY(hi))
+ hash_remove(&highlight_ht, hi, "highlight");
vim_free(HL_TABLE()[highlight_ga.ga_len].sg_name);
- vim_free(HL_TABLE()[highlight_ga.ga_len].sg_name_u);
+ vim_free(HL_TABLE()[highlight_ga.ga_len].sg_name_u - HLNAME_KEY_OFF);
}

/*
@@ -4246,6 +4283,7 @@ highlight_changed(void)
int hlf;
int i;
char_u *p;
+ char_u *default_hl;
int attr;
char_u *end;
int id;
@@ -4278,14 +4316,22 @@ highlight_changed(void)
highlight_ids[hlf] = 0;
}

+ default_hl = get_highlight_default();
+
// First set all attributes to their default value.
- // Then use the attributes from the 'highlight' option.
+ // Then use the attributes from the 'highlight' option, unless it already
+ // matches the default and would repeat the same work.
for (i = 0; i < 2; ++i)
{
if (i)
+ {
+ if (default_hl != NULL && p_hl != NULL
+ && STRCMP(default_hl, p_hl) == 0)
+ continue;
p = p_hl;
+ }
else
- p = get_highlight_default();
+ p = default_hl;
if (p == NULL) // just in case
continue;

diff --git a/src/version.c b/src/version.c
index c8c3fbc59..2e9145cfe 100644
--- a/src/version.c
+++ b/src/version.c
@@ -734,6 +734,8 @@ static char *(features[]) =

static int included_patches[] =
{ /* Add new patch number below this line */
+/**/
+ 240,
/**/
239,
/**/