On Fri, Apr 20, 2018 at 10:02 AM, Elijah Newren [off-list ref] wrote:

On Fri, Apr 20, 2018 at 6:36 AM, Ben Peart [off-list ref] wrote:

quoted

--- a/Documentation/merge-config.txt
+++ b/Documentation/merge-config.txt

@@ -37,6 +37,11 @@ merge.renameLimit::
        during a merge; if not specified, defaults to the value of
        diff.renameLimit.

+merge.renames::
+       Whether and how Git detects renames.  If set to "false",
+       rename detection is disabled. If set to "true", basic rename
+       detection is enabled. This is the default.

One can already control o->detect_rename via the -Xno-renames and
-Xfind-renames options.  I think the documentation should mention that
"false" is the same as passing -Xno-renames, and "true" is the same as
passing -Xfind-renames.  However, find-renames does take similarity
threshold as a parameter, so there's a question whether this option
should provide some way to do the same.  I'm not sure the answer to
that; it may be that we'd want a separate config option for that, and
we can wait to add it until someone actually wants it.

I just realized another issue, though it also affects -Xno-renames.
Even if rename detection is turned off for the merge, it is
unconditionally turned on for the diffstat.  In builtin/merge.c,
function finish(), there is the code:

    if (new_head && show_diffstat) {
        ...
        opts.detect_rename = DIFF_DETECT_RENAME;

It seems that this option should affect that line as well.  (Do you
have diffstat turned off by chance?  If not, you may be able to
improve your performance even more...)