Re: Performance problems in diffcore rename

[Shawn Pearce <spearce@spearce.org>]

Junio C Hamano <junkio@cox.net> wrote:
> Shawn Pearce <spearce@spearce.org> writes:
> 
> > But looking at is_exact_match I'm now wondering why we bother
> > to open the working tree file at all here.
> 
> You are right.  When we _know_ both SHA-1 can be trusted, we
> should be able to do just this, regardless of contents_too
> (whose only purpose is to delay comparing a cache dirty working
> tree file with something else):
> 
> diff --git a/diffcore-rename.c b/diffcore-rename.c
> index 57a74b6..677db85 100644
> --- a/diffcore-rename.c
> +++ b/diffcore-rename.c
> @@ -100,9 +100,8 @@ static int is_exact_match(struct diff_filespec *src,
>  			  struct diff_filespec *dst,
>  			  int contents_too)
>  {
> -	if (src->sha1_valid && dst->sha1_valid &&
> -	    !hashcmp(src->sha1, dst->sha1))
> -		return 1;
> +	if (src->sha1_valid && dst->sha1_valid)
> +		return !hashcmp(src->sha1, dst->sha1);
>  	if (!contents_too)
>  		return 0;
>  	if (diff_populate_filespec(src, 1) || diff_populate_filespec(dst, 1))
> 

Have you tested the above patch?  I have the exact same one in
my working directory right now and its failing a huge number of
the tests.  At least great minds think alike that we can make this
optimization here, but there's something amiss...

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