[PATCH STABLE] revset: fix O(2^n) perf regression in addset

[Pierre-Yves David]

On 10/28/2014 09:20 PM, Durham Goode wrote:
> # HG changeset patch
> # User Durham Goode <durham at fb.com>
> # Date 1414530366 25200
> #      Tue Oct 28 14:06:06 2014 -0700
> # Branch stable
> # Node ID 247213e31a99056aa64b91d19592dcb72b436522
> # Parent  6df4bc39f6828e8aa74b33e51bc72eac621db2fe
> revset: fix O(2^n) perf regression in addset
>
> hg log -r 1 ... -r 100 was never returning due to a regression in the way addset
> computes __nonzero__.  It used 'bool(self._r1 or self._r2)' which required
> executing self._r1.__nonzero__ twice (once for the or, once for the bool).  hg
> log with a lot of -r's happens to build a one sided addset tree of N length,
> which ends up being 2^N performance.
>
> This patch fixes it by converting to bool before or'ing.
>
> This problem can be repro'd with something as simple as:
>
> hg log `for x in $(seq 1 50) ; do echo "-r $x "; done`

Good catch, thanks. It seems like it would be valuable to cache the 
__nonzero__ return too. If you agree I'll send a patch.

> Adding '1 + 2 + ... + 20' to the revsetbenchmark.txt didn't seem to repro the
> problem, so I wasn't able to add a revset benchmark for this issue.

The revset benchmar is only doing iteration testing. I'm adding more 
versatility to the benchmark but this is not ready yet.

-- 
Pierre-Yves David