[PATCH v3 0/4] Optimization batch 12: miscellaneous unthemed stuff

This series depends on en/ort-perf-batch-11 textually, but is semantically
independent of it.

Changes since v2:

 * Made suggested minor tweaks from Stolee on Patch 1
 * Dropped patch 3, for now
 * Added Stolee's Acked-by

Changes since v1 (all for the first patch):

 * Add more comments explaining the sorting function, its purpose, and how
   its expected to be called
 * Small style fixup
 * Switch back to using string_list_sort() instead of direct QSORT()

This short series has a few optimizations, but only one of which affects the
testcases of interest (namely, reducing our time spent on sorting an array).
It also fixes a few comments.

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28), the
changes in just this series improves the performance as follows:

                     Before Series           After Series
no-renames:        5.622 s ±  0.059 s     5.235 s ±  0.042 s
mega-renames:     10.127 s ±  0.073 s     9.419 s ±  0.107 s
just-one-mega:   500.3  ms ±  3.8  ms   480.1  ms ±  3.9  ms


As a reminder, before any merge-ort/diffcore-rename performance work, the
performance results we started with were:

no-renames-am:      6.940 s ±  0.485 s
no-renames:        18.912 s ±  0.174 s
mega-renames:    5964.031 s ± 10.459 s
just-one-mega:    149.583 s ±  0.751 s


Elijah Newren (4):
  merge-ort: replace string_list_df_name_compare with faster alternative
  diffcore-rename: avoid unnecessary strdup'ing in break_idx
  Fix various issues found in comments
  merge-ort: miscellaneous touch-ups

 diffcore-rename.c                   |  4 +-
 merge-ort.c                         | 80 ++++++++++++++++++++---------
 t/t6423-merge-rename-directories.sh |  2 +-
 3 files changed, 60 insertions(+), 26 deletions(-)


base-commit: 76e253793c9a1d7fdd1836d5e4db26dabd3d713a
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-962%2Fnewren%2Fort-perf-batch-12-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-962/newren/ort-perf-batch-12-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/962

Range-diff vs v2:

 1:  c4a0f6a9510c ! 1:  f63ffc2a7c22 merge-ort: replace string_list_df_name_compare with faster alternative
     @@ Commit message
              just-one-mega:   500.3  ms ±  3.8  ms   480.1  ms ±  3.9  ms
      
          Signed-off-by: Elijah Newren [off-list ref]
     +    Acked-by: Derrick Stolee [off-list ref]
      
       ## merge-ort.c ##
      @@ merge-ort.c: static int detect_and_process_renames(struct merge_options *opt,
     @@ merge-ort.c: static int detect_and_process_renames(struct merge_options *opt,
      -	 * sorting cause no problems for us.
      +	 * The reason to not use df_name_compare directly was that it was
      +	 * just too expensive (we don't have the string lengths handy), so
     -+	 * I had to reimplement it.
     ++	 * it was reimplemented.
       	 */
      -	int cmp = df_name_compare(one, onelen, S_IFDIR,
      -				  two, twolen, S_IFDIR);
     @@ merge-ort.c: static int detect_and_process_renames(struct merge_options *opt,
      +		two++;
      +	}
      +
     -+	c1 = *one;
     -+	if (!c1)
     -+		c1 = '/';
     -+
     -+	c2 = *two;
     -+	if (!c2)
     -+		c2 = '/';
     ++	c1 = *one ? *one : '/';
     ++	c2 = *two ? *two : '/';
      +
      +	if (c1 == c2) {
      +		/* Getting here means one is a leading directory of the other */
      +		return (*one) ? 1 : -1;
      +	} else
     -+		return c1-c2;
     ++		return c1 - c2;
       }
       
       static int read_oid_strbuf(struct merge_options *opt,
 2:  38713ed48273 ! 2:  cd13499a6ff5 diffcore-rename: avoid unnecessary strdup'ing in break_idx
     @@ Commit message
          unrelated optimization noted in passing while looking at the code.
      
          Signed-off-by: Elijah Newren [off-list ref]
     +    Acked-by: Derrick Stolee [off-list ref]
      
       ## diffcore-rename.c ##
      @@ diffcore-rename.c: static void register_rename_src(struct diff_filepair *p)
 3:  45e1de5fe780 < -:  ------------ diffcore-rename: enable limiting rename detection to relevant destinations
 4:  2f26d7e935c0 ! 3:  91c0962a7d75 Fix various issues found in comments
     @@ Commit message
              function.  Update the comment now.
      
          Signed-off-by: Elijah Newren [off-list ref]
     +    Acked-by: Derrick Stolee [off-list ref]
      
       ## diffcore-rename.c ##
      @@ diffcore-rename.c: void diffcore_rename_extended(struct diff_options *options,
 5:  7156f26ab299 ! 4:  01352fcdf3a9 merge-ort: miscellaneous touch-ups
     @@ Commit message
          of pushing these changes upstream.
      
          Signed-off-by: Elijah Newren [off-list ref]
     +    Acked-by: Derrick Stolee [off-list ref]
      
       ## merge-ort.c ##
      @@ merge-ort.c: static void add_pair(struct merge_options *opt,

-- 
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