When fetching, Git will by default print a list of all updated refs in a
nicely formatted table. In order to come up with this table, Git needs
to iterate refs twice: first to determine the maximum column width, and
a second time to actually format these changed refs.

While this table will not be printed in case the user passes `--quiet`,
we still go out of our way and do all these steps. In fact, we even do
more work compared to not passing `--quiet`: without the flag, we will
skip all references in the column width computation which have not been
updated, but if it is set we will now compute widths for all refs.

Fix this issue by completely skipping both preparation of the format and
formatting data for display in case the user passes `--quiet`, improving
performance especially with many refs. The following benchmark shows a
nice speedup for a quiet mirror-fetch in a repository with 2.3M refs:

    Benchmark #1: HEAD~: git-fetch
      Time (mean ± σ):     26.929 s ±  0.145 s    [User: 24.194 s, System: 4.656 s]
      Range (min … max):   26.692 s … 27.068 s    5 runs

    Benchmark #2: HEAD: git-fetch
      Time (mean ± σ):     25.189 s ±  0.094 s    [User: 22.556 s, System: 4.606 s]
      Range (min … max):   25.070 s … 25.314 s    5 runs

    Summary
      'HEAD: git-fetch' ran
        1.07 ± 0.01 times faster than 'HEAD~: git-fetch'

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/fetch.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index e064687dbd..d064b66512 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -757,6 +757,9 @@ static void prepare_format_display(struct ref *ref_map)
 		die(_("configuration fetch.output contains invalid value %s"),
 		    format);
 
+	if (verbosity < 0)
+		return;
+
 	for (rm = ref_map; rm; rm = rm->next) {
 		if (rm->status == REF_STATUS_REJECT_SHALLOW ||
 		    !rm->peer_ref ||
@@ -827,7 +830,12 @@ static void format_display(struct strbuf *display, char code,
 			   const char *remote, const char *local,
 			   int summary_width)
 {
-	int width = (summary_width + strlen(summary) - gettext_width(summary));
+	int width;
+
+	if (verbosity < 0)
+		return;
+
+	width = (summary_width + strlen(summary) - gettext_width(summary));
 
 	strbuf_addf(display, "%c %-*s ", code, width, summary);
 	if (!compact_format)
-- 
2.33.0