name-hash: precompute hash values during preload-index

Precompute the istate.name_hash and istate.dir_hash values
for each cache-entry during the preload-index phase.

Move the expensive memihash() calculations from lazy_init_name_hash()
to the multi-threaded preload-index phase.

Signed-off-by: Jeff Hostetler <[email protected]>

cache.h

@@ -173,6 +173,9 @@ struct cache_entry {
 	unsigned int ce_flags;
 	unsigned int ce_namelen;
 	unsigned int index;	/* for link extension */
+	unsigned int precompute_hash_state;
+	unsigned int precompute_hash_name;
+	unsigned int precompute_hash_dir;
 	struct object_id oid;
 	char name[FLEX_ARRAY]; /* more */
 };
@@ -229,6 +232,19 @@ struct cache_entry {
 #error "CE_EXTENDED_FLAGS out of range"
 #endif
 
+/*
+ * Bit set if preload-index precomputed the hash value(s)
+ * for this cache-entry.
+ */ 
+#define CE_PRECOMPUTE_HASH_STATE__SET   (1 << 0)
+/*
+ * Bit set if precompute-index also precomputed the hash value
+ * for the parent directory.
+ */ 
+#define CE_PRECOMPUTE_HASH_STATE__DIR   (1 << 1)
+
+void precompute_istate_hashes(struct cache_entry *ce);
+
 /* Forward structure decls */
 struct pathspec;
 struct child_process;

preload-index.c

@@ -47,6 +47,8 @@ static void *preload_thread(void *_data)
 		struct cache_entry *ce = *cep++;
 		struct stat st;
 
+		precompute_istate_hashes(ce);
+
 		if (ce_stage(ce))
 			continue;
 		if (S_ISGITLINK(ce->ce_mode))

read-cache.c

@@ -73,6 +73,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
 	copy_cache_entry(new, old);
 	new->ce_flags &= ~CE_HASHED;
 	new->ce_namelen = namelen;
+	new->precompute_hash_state = 0;
 	new->index = 0;
 	memcpy(new->name, new_name, namelen + 1);
 
@@ -614,6 +615,7 @@ static struct cache_entry *create_alias_ce(struct index_state *istate,
 	new = xcalloc(1, cache_entry_size(len));
 	memcpy(new->name, alias->name, len);
 	copy_cache_entry(new, ce);
+	new->precompute_hash_state = 0;
 	save_or_free_index_entry(istate, ce);
 	return new;
 }
@@ -1446,6 +1448,7 @@ static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *on
 	ce->ce_stat_data.sd_size  = get_be32(&ondisk->size);
 	ce->ce_flags = flags & ~CE_NAMEMASK;
 	ce->ce_namelen = len;
+	ce->precompute_hash_state = 0;
 	ce->index = 0;
 	hashcpy(ce->oid.hash, ondisk->sha1);
 	memcpy(ce->name, name, len);