Micro-optimize prepare_alt_odb

Calling getenv() is not that expensive, but its also not free,
and its certainly not cheaper than testing to see if alt_odb_tail
is not null.

Because we are calling prepare_alt_odb() from within find_sha1_file
every time we cannot find an object file locally we want to skip out
of prepare_alt_odb() as early as possible once we have initialized
our alternate list.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/sha1_file.c b/sha1_file.c
index 6a5ba635003858d70e449122351b502b823de13a..a3637d7e5b7763b97b5325923e586722f5e431bf 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -376,11 +376,12 @@ void prepare_alt_odb(void)
 {
        const char *alt;
 
+       if (alt_odb_tail)
+               return;
+
        alt = getenv(ALTERNATE_DB_ENVIRONMENT);
        if (!alt) alt = "";
 
-       if (alt_odb_tail)
-               return;
        alt_odb_tail = &alt_odb_list;
        link_alt_odb_entries(alt, alt + strlen(alt), ':', NULL, 0);