On Tue, Jun 19, 2018 at 07:33:39PM +0200, René Scharfe wrote: > > The key thing about this iteration is that it doesn't regress > > performance, because we always short-circuit where we used to. The other > > obvious route is to stop short-circuiting only when "--column" is in > > effect, which would have the same property (at the expense of a little > > extra code in match_expr_eval()). > > The performance impact of the exhaustive search for --color scales with > the number of shown lines, while it would scale with the total number of > lines for --column. Coloring the results of highly selective patterns > is relatively cheap, short-circuiting them still helps significantly. I thought that at first, too, but I think we'd still scale with the number of shown lines. We're talking about short-circuiting OR, so by definition we stop the short-circuit because we matched the first half of the OR. If you stop short-circuiting AND, then yes, you incur a penalty for every line. But I don't think --column would need to do that. Although there are interesting cases around inversion. For example: git grep --not \( --not -e a --and --not -e b \) is equivalent to: git grep -e a --or -e b Do people care if we actually hunt down the exact column where we _didn't_ match "b" in the first case? The two are equivalent, but I have to wonder if somebody writing the first one really cares. > Disabling that optimization for --column wouldn't be a regression since > it's a new option.. Picking a random result (based on the order of > evaluation) seems sloppy and is probably going to surprise users. I don't see it as a random result; short-circuiting logic is well understood and we follow the user's ordering. I think the place where it's _most_ ugly is "--column --color", where we may color the short-circuited value in the second pass. > We could add an optimizer pass to reduce the number of regular > expressions in certain cases if that is really too slow. E.g. this: Yes, we actually discussed this kind of transformation. I think it's way out of scope for this patch series, though. If we do anything more, I think it should be to disable short-circuiting when --column is in use. -Peff
