[PATCH] dirstate._walkexplicit: don't bother normalizing ''

[Martin von Zweigbergk]

On Sun, Mar 29, 2015 at 8:41 PM Siddharth Agarwal <sid0 at fb.com> wrote:

> # HG changeset patch
> # User Siddharth Agarwal <sid0 at fb.com>
> # Date 1427678928 25200
> #      Sun Mar 29 18:28:48 2015 -0700
> # Node ID da9074bcbd34008b2615f019fd57d203b80425e1
> # Parent  efa094701a05d58d505c3b0c3b3c73dba4e51e97
> dirstate._walkexplicit: don't bother normalizing ''
>
> The overwhelmingly common case is running commands like 'hg diff' with no
> arguments. Therefore the only file that'll be listed is the root directory.
> Normalizing that's just a waste of time.
>
> This means that for a plain 'hg diff' we'll never need to construct the
> foldmap, saving us a significant chunk of time.
>
> On case-insensitive HFS+ on OS X, for a large repository with over 200,000
> files, this brings down 'hg diff' from 2.97 seconds to 2.36.
>
> diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py
> --- a/mercurial/dirstate.py
> +++ b/mercurial/dirstate.py
> @@ -635,10 +635,15 @@
>
>          alldirs = None
>          for ff in files:
> -            if normalize:
> -                nf = normalize(normpath(ff), False, True)
> +            # constructing the foldmap is expensive, so don't do it for
> the
> +            # common case where files is ['']
> +            if ff != '':
> +                if normalize:
> +                    nf = normalize(normpath(ff), False, True)
> +                else:
> +                    nf = normpath(ff)
>              else:
> -                nf = normpath(ff)
> +                nf = '.'
>

Nit: It might be simpler to call normpath() first:

nf = normpath(ff)
if nf != '.' and normalize:
  nf = normalize(nf, False, True)

Slightly off topic: When does normpath have any effect anyway? The paths
get here through a matcher and the matcher seems to normalize all paths.
The only effect normpath seems to have is to convert '' to '.' (i.e. back
to what it was before we converted from '.' to '' a few lines up).


>              if nf in results:
>                  continue
>
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