[llvm-dev] Would a spreadsheet be a good project using LLVM?

Jason Glazer via llvm-dev llvm-dev at lists.llvm.org
Fri Aug 21 07:19:16 PDT 2015


Thanks for your feedback. I guess I should elaborate on one 
of the features I would like to implement. In today's 
spreadsheets if you want to crunch a lot of data, you 
usually put the data in rows and put expressions in cells to 
the right of the data and repeat those cells for every row 
of the data. I would like to create a spreadsheet system 
that can process the same quantity of data but only has the 
a single instance of those cells with expressions. In other 
words, I do expect that that the same expressions get used 
over and over with the same data, perhaps thousands (or 
more) times.

Would LLVM be a good fit now?

Thanks again,


On 8/21/2015 8:58 AM, mats petersson wrote:
> This sounds like an interesting project, but I'm far from 
> convinced that LLVM will help much:
> I have not TRIED to solve this, but my guess is that of 
> the time to recalculate a large spreadsheet, the majority 
> of the time is not actually spent calculating the values 
> of the content, but actually inferring the dependencies 
> and other "work out what needs to be (re-)calculated". And 
> whilst LLVM can probably help in doing that, I'm far from 
> convinced that it will speed up the things you actually 
> want to speed up.
> Compilers (I'm including LLVM in "compilers" for this 
> discussing) are really best at dealing with things where 
> you repeat the same exact thing over and over. In a 
> spreadsheet, the common case is that you calculate all the 
> fields ONCE, then only recalculate based on changes. Of 
> course, some change that is used EVERYWHERE (like if you 
> change the base-interest rate in your spreadsheet for 
> calculating bank-rates and the earnings on various 
> bank-accounts, then ALL your cells will depend on that in 
> some way, and everything gets recalculated). And whilst 
> the dependancy graph DOESN'T change (except when you 
> change the formulae in the cells). So you'd end up 
> spending a lot of time compiling the spreadsheet code, and 
> probably lose time rather than gain on the competing 
> solutions.
> So my feeling, without testing it, is that LLVM probably 
> won't give you a huge amount of benefit in the general 
> case of spreadsheets.
> If it was my project, I think it would be worth writing 
> something that simulates the general principle of 
> spreadsheet calculations, and first of all, figure out 
> where the majority of the time is spent. I don't think 
> this experiment needs to have full support of all the 
> different data types, functons, etc, just the dependency 
> and (basic) formula support.
> No, I can't back up this with any facts - just my thoughts 
> - hopefully it's of some help, and I haven't just rambled 
> away completely aimlessly.
> --
> Mats
> On 21 August 2015 at 14:23, Jason Glazer via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> 
> wrote:
>     I am thinking about writing a new open source
>     spreadsheet application since I think the spreadsheet
>     applications out there (Microsoft Excel, LibreOffice
>     Calc, etc.) do not have some features that I would
>     really like to use. I would like the spreadsheet to
>     recalculate very fast and wondered if it would make
>     sense to use LLVM to calculate the cell values
>     quickly. Each cell of a spreadsheet contains an
>     expression, much like an expression in any programming
>     language. The big difference is that the ordering of
>     the expression evaluations is governed by the
>     dependencies of each cell on other cells and end up
>     being turned into a directed acyclic graph (DAG). It
>     would be good if the actual conversion of cell
>     expressions from strings that the user enters into a
>     cell, would be converted into a representation that
>     can be recalculated very quickly. I was thinking that
>     LLVM machine code might be a good target.
>     Overall, is this a good project to use LLVM?
>     Is there existing open source code for compiling
>     expressions using LLVM that you would recommend for
>     this project?
>     Any suggestions or concerns about this approach?
>     Is anyone interested in helping out?
>     Thanks
>     Jason
>     -- 
>     Jason Glazer, P.E., GARD Analytics, 90.1 ECB chair
>     Admin for onebuilding.org <http://onebuilding.org>
>     building performance mailing lists
>     _______________________________________________
>     LLVM Developers mailing list
>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
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Jason Glazer, P.E., GARD Analytics, 90.1 ECB chair
Admin for onebuilding.org building performance mailing lists

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