[PATCH v2 7/9] diff --color-moved-ws: optimize allow-indentation-change
- From
- Phillip Wood <phillip.wood@talktalk.net>
- Date
- Nov 23, 2018, 11:16 UTC
- Message-ID
- <20181123111658.30342-8-phillip.wood@talktalk.net>
- In-Reply-To
- <20181123111658.30342-1-phillip.wood@talktalk.net>
From: Phillip Wood <phillip.wood@dunelm.org.uk>
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@dunelm.org.uk> --- 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;
-- 2.19.1.1690.g258b440b18