From: Junio C Hamano <gitster@pobox.com>
Date: Sun, 23 Nov 2025 07:09:22 GMT
Subject: Re: [PATCH v2] diff: disable rename detection with --quiet
Message-ID: <xmqqpl99z0m5.fsf@gitster.g>
In-Reply-To: <8cc12ef2-1d2c-4924-b130-bd740a975ce0@web.de>

René Scharfe <l.s.r@web.de> writes:

> --- >8 ---
> Subject: [PATCH] diff-index: don't queue unchanged filepairs with diff_change()
>
> diff_cache() queues unchanged filepairs if the flag find_copies_harder
> is set, and uses diff_change() for that.  This function does a few
> things that are unnecessary for unchanged filepairs and always sets the
> diff_flag has_changes, which is simply misleading in this case.
>
> Add a new streamlined function for queuing unchanged filepairs and
> use it in show_modified(), which is called by diff_cache() via
> oneway_diff() and do_oneway_diff().  It allocates only one half of each
> filepair, ...

It's a misleading thing to say.  It allocates a full filepair, but
because a filespec is reference counted, it can reuse the same
filespec to hold both preimage and postimage, halving the memory
requirement without leading to double freeing.  And having a
separete helper do so would make it almost trivial to avoid setting
the has_changes bit.

Cleverly done.

Thanks.

> ... which has a measurable effect if there are a lot of them, like
> in the Linux repo: