[PATCH v4 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 v3:

 * Changed Acked-by from Stolee to Reviewed-by.

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-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-962/newren/ort-perf-batch-12-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/962

Range-diff vs v3:

 1:  f63ffc2a7c22 ! 1:  140c1e89e0ec 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 <newren@gmail.com>
     -    Acked-by: Derrick Stolee <dstolee@microsoft.com>
     +    Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
      
       ## merge-ort.c ##
      @@ merge-ort.c: static int detect_and_process_renames(struct merge_options *opt,
 2:  cd13499a6ff5 ! 2:  be858c46cfe7 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 <newren@gmail.com>
     -    Acked-by: Derrick Stolee <dstolee@microsoft.com>
     +    Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
      
       ## diffcore-rename.c ##
      @@ diffcore-rename.c: static void register_rename_src(struct diff_filepair *p)
 3:  91c0962a7d75 ! 3:  55c0f2c4560a Fix various issues found in comments
     @@ Commit message
              function.  Update the comment now.
      
          Signed-off-by: Elijah Newren <newren@gmail.com>
     -    Acked-by: Derrick Stolee <dstolee@microsoft.com>
     +    Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
      
       ## diffcore-rename.c ##
      @@ diffcore-rename.c: void diffcore_rename_extended(struct diff_options *options,
 4:  01352fcdf3a9 ! 4:  6de569e6ac49 merge-ort: miscellaneous touch-ups
     @@ Commit message
          of pushing these changes upstream.
      
          Signed-off-by: Elijah Newren <newren@gmail.com>
     -    Acked-by: Derrick Stolee <dstolee@microsoft.com>
     +    Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
      
       ## merge-ort.c ##
      @@ merge-ort.c: static void add_pair(struct merge_options *opt,