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- To: Eigen <eigen@xxxxxxxxxxxxxxxxxxx>
- Subject: Re: [eigen] nesting
- From: Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>
- Date: Thu, 4 Feb 2010 16:01:21 +0100
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Well, specializing the product is a bad idea. Actually, we need to
deduce expressions that have products nested (or heavy weight objects
in general), those must then be nested by reference in order to
prevent copies.
- Hauke
On Thu, Feb 4, 2010 at 2:35 PM, Hauke Heibel
<hauke.heibel@xxxxxxxxxxxxxx> wrote:
> Hi,
>
> While looking into the "performance degradation" issue from the forum
> I found out that it is due to temporaries - as Benoit already guessed.
>
> I am a little bit afraid, that what I once proposed, namely copying
> expressions by value, is now backfiring. The reason is that initially
> I assumed expressions to be tiny little objects with close to no copy
> costs. The issue is related to those expressions holding temporaries.
> Copying them (e.g. a product expression) means copying all the data
> including the temporary and that will happen as many times as we nest
> expressions.
>
> The only solution I can think about at the moment is the
> specialization of ei_nested for those types and to go back to nesting
> by reference for these heavy weight guys.
>
> - Hauke
>