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

- Acked-by: Derrick Stolee <[email protected]>
+ Reviewed-by: Derrick Stolee <[email protected]>

## 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.

- Acked-by: Derrick Stolee <[email protected]>
+ Reviewed-by: Derrick Stolee <[email protected]>

## 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.

- Acked-by: Derrick Stolee <[email protected]>
+ Reviewed-by: Derrick Stolee <[email protected]>

## 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.

- Acked-by: Derrick Stolee <[email protected]>
+ Reviewed-by: Derrick Stolee <[email protected]>

## merge-ort.c ##
@@ merge-ort.c: static void add_pair(struct merge_options *opt,

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