From: Phillip Wood <phillip.wood@xxxxxxxxxxxxx>
When running
git diff --color-moved-ws=allow-indentation-change v2.18.0 v2.19.0
cmp_in_block_with_wsd() is called 694908327 times. Of those 42.7%
return after comparing a and b. By comparing the lengths first we can
return early in all but 0.03% of those cases without dereferencing the
string pointers. The comparison between a and c fails in 6.8% of
calls, by comparing the lengths first we reject all the failing calls
without dereferencing the string pointers.
This reduces the time to run the command above by by 42% from 14.6s to
8.5s. This is still much slower than the normal --color-moved which
takes ~0.6-0.7s to run but is a significant improvement.
The next commits will replace the current implementation with one that
works with mixed tabs and spaces in the indentation. I think it is
worth optimizing the current implementation first to enable a fair
comparison between the two implementations.
Signed-off-by: Phillip Wood <phillip.wood@xxxxxxxxxxxxx>
---
diff.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)
diff --git a/diff.c b/diff.c
index 8c08dd68df..c378ce3daf 100644
--- a/diff.c
+++ b/diff.c
@@ -829,20 +829,23 @@ static int cmp_in_block_with_wsd(const struct diff_options *o,
int n)
{
struct emitted_diff_symbol *l = &o->emitted_symbols->buf[n];
- int al = cur->es->len, cl = l->len;
+ int al = cur->es->len, bl = match->es->len, cl = l->len;
const char *a = cur->es->line,
*b = match->es->line,
*c = l->line;
-
+ const char *orig_a = a;
int wslen;
/*
- * We need to check if 'cur' is equal to 'match'.
- * As those are from the same (+/-) side, we do not need to adjust for
- * indent changes. However these were found using fuzzy matching
- * so we do have to check if they are equal.
+ * We need to check if 'cur' is equal to 'match'. As those
+ * are from the same (+/-) side, we do not need to adjust for
+ * indent changes. However these were found using fuzzy
+ * matching so we do have to check if they are equal. Here we
+ * just check the lengths. We delay calling memcmp() to check
+ * the contents until later as if the length comparison for a
+ * and c fails we can avoid the call all together.
*/
- if (strcmp(a, b))
+ if (al != bl)
return 1;
if (!pmb->wsd.string)
@@ -870,7 +873,7 @@ static int cmp_in_block_with_wsd(const struct diff_options *o,
al -= wslen;
}
- if (al != cl || memcmp(a, c, al))
+ if (al != cl || memcmp(orig_a, b, bl) || memcmp(a, c, al))
return 1;
return 0;
--
2.19.1
