[PATCH 2/3] 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 <redacted>
---
 sha1_file.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/sha1_file.c b/sha1_file.c
index 6a5ba63..a3637d7 100644
--- 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);
 

-- 
1.5.2.789.g8ee1