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diff --color-moved-ws: optimize allow-indentation-change

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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>
Reviewed-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Phillip Wood 2018-11-23 11:16:56 +00:00 committed by Junio C Hamano
parent b0a2ba4776
commit 7a4252c4df
1 changed files with 11 additions and 8 deletions
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19
diff.c
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@ -831,20 +831,23 @@ 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)
@ -872,7 +875,7 @@ 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;