Re: [PATCH v2 1/3] diffcore-pickaxe: remove unnecessary call to get_textconv()

[Junio C Hamano <gitster@pobox.com>]

Junio C Hamano <gitster@pobox.com> writes:

> Perhaps...
>
> 	The fill_one() function is responsible for finding and
> 	filling the textconv filter as necessary, and is called by
> 	diff_grep() function that implements "git log -G<pattern>".
>
> 	The has_changes() function calls get_textconv() for two
> 	sides being compared, before it checks to see if it was
> 	asked to perform the pickaxe limiting with the -S option.
> 	Move the code around to avoid this wastage.  After that,
> 	fill_one() is called to use the textconv.
>
> 	By adding get_textconv() to diff_grep() and relieving
> 	fill_one() of responsibility to find the textconv filter, we
> 	can avoid calling get_textconv() twice.
>
> Explained that way, it makes me wonder why we cannot fix it the
> other way around, that is, not fetching textconv in has_changes()
> and instead letting fill_one() to find textconv as needed.
>
> The answer is because has_changes() itself looks at the textconv.
>
> But we have to wonder why it is so.  diff_grep() short-circuits when
> the two sides are identical and has_changes() has a similar but
> different logic to check if the identical two sides are processed
> with the same textconv filter before saying this filepair is
> uninteresting.
>
> Shouldn't that logic be unified as well?

That is, something along this line.  We may want to unify these two
functions even more, but I do not offhand see a good way to do so.

-- >8 --
Subject: [PATCH] log -S/-G: unify the short-cut logic a bit more

The fill_one() function is responsible for finding and filling the
textconv filter as necessary, and is called by diff_grep() function
that implements "git log -G<pattern>".

The has_changes() function calls get_textconv() for two sides being
compared, before it checks to see if it was asked to perform the
pickaxe limiting with the -S option.  Move the code around to avoid
this wastage.

By adding get_textconv() to diff_grep() and relieving fill_one() of
responsibility to find the textconv filter, we can avoid calling
get_textconv() twice; fill_one() no longer has to be passed a
pointer to a pointer to textconv.

The reason has_changes() calls get_textconv() early is because it
wants to compare two textconv filters on both sides.  When comparing
the two sides that are otherwise identical, if the same textconv
applies to both sides, we know pickaxe (either -S or -G) would not
find anything before applying the textconv and comparing the result.

Teach the same short-circuit logic to diff_grep() as well.  The code
in these two functions become more similar as the result.
---
 diffcore-pickaxe.c | 37 +++++++++++++++++++++++++++----------
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index b097fa7..6d285a7 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -75,11 +75,10 @@ static void diffgrep_consume(void *priv, char *line, unsigned long len)
 }
 
 static void fill_one(struct diff_filespec *one,
-		     mmfile_t *mf, struct userdiff_driver **textconv)
+		     mmfile_t *mf, struct userdiff_driver *textconv)
 {
 	if (DIFF_FILE_VALID(one)) {
-		*textconv = get_textconv(one);
-		mf->size = fill_textconv(*textconv, one, &mf->ptr);
+		mf->size = fill_textconv(textconv, one, &mf->ptr);
 	} else {
 		memset(mf, 0, sizeof(*mf));
 	}
@@ -94,11 +93,24 @@ static int diff_grep(struct diff_filepair *p, struct diff_options *o,
 	mmfile_t mf1, mf2;
 	int hit;
 
-	if (diff_unmodified_pair(p))
+	if (!o->pickaxe[0])
 		return 0;
 
-	fill_one(p->one, &mf1, &textconv_one);
-	fill_one(p->two, &mf2, &textconv_two);
+	textconv_one = get_textconv(p->one);
+	textconv_two = get_textconv(p->two);
+
+	/*
+	 * If we have an unmodified pair, we know that the count will be the
+	 * same and don't even have to load the blobs. Unless textconv is in
+	 * play, _and_ we are using two different textconv filters (e.g.,
+	 * because a pair is an exact rename with different textconv attributes
+	 * for each side, which might generate different content).
+	 */
+	if (textconv_one == textconv_two && diff_unmodified_pair(p))
+		return 0;
+
+	fill_one(p->one, &mf1, textconv_one);
+	fill_one(p->two, &mf2, textconv_two);
 
 	if (!mf1.ptr) {
 		if (!mf2.ptr)
@@ -131,6 +143,8 @@ static int diff_grep(struct diff_filepair *p, struct diff_options *o,
 		free(mf1.ptr);
 	if (textconv_two)
 		free(mf2.ptr);
+	diff_free_filespec_data(p->one);
+	diff_free_filespec_data(p->two);
 	return hit;
 }
 
@@ -201,14 +215,17 @@ static unsigned int contains(mmfile_t *mf, struct diff_options *o,
 static int has_changes(struct diff_filepair *p, struct diff_options *o,
 		       regex_t *regexp, kwset_t kws)
 {
-	struct userdiff_driver *textconv_one = get_textconv(p->one);
-	struct userdiff_driver *textconv_two = get_textconv(p->two);
+	struct userdiff_driver *textconv_one = NULL;
+	struct userdiff_driver *textconv_two = NULL;
 	mmfile_t mf1, mf2;
 	int ret;
 
 	if (!o->pickaxe[0])
 		return 0;
 
+	textconv_one = get_textconv(p->one);
+	textconv_two = get_textconv(p->two);
+
 	/*
 	 * If we have an unmodified pair, we know that the count will be the
 	 * same and don't even have to load the blobs. Unless textconv is in
@@ -219,8 +236,8 @@ static int has_changes(struct diff_filepair *p, struct diff_options *o,
 	if (textconv_one == textconv_two && diff_unmodified_pair(p))
 		return 0;
 
-	fill_one(p->one, &mf1, &textconv_one);
-	fill_one(p->two, &mf2, &textconv_two);
+	fill_one(p->one, &mf1, textconv_one);
+	fill_one(p->two, &mf2, textconv_two);
 
 	if (!mf1.ptr) {
 		if (!mf2.ptr)
-- 
1.8.2-634-g203ba97