[LLVMdev] Vectorization: Next Steps
hfinkel at anl.gov
Mon Feb 6 16:17:07 PST 2012
On Tue, 2012-02-07 at 00:47 +0100, Tobias Grosser wrote:
> On 02/06/2012 11:28 PM, Chris Lattner wrote:
> > On Feb 6, 2012, at 1:56 PM, Hal Finkel wrote:
> >>> If you do not want to use polly, you could use ISL
> >>> http://freecode.com/projects/isl to set up the dependence problem and
> >>> use ISL's ILP to solve it.
> >> isl is an LGPL project. It is not clear to me what the general consensus
> >> would be on having a core analysis pass carry an LGPL dependency.
> > This is fine for something that wants to live out of tree or be a secondary subproject, but isn't acceptable for something that wants to go into the mainline llvm repository and be a default part of the compiler.
> If there is consensus that parts of Polly should be included in the core
> compiler, I am sure there are ways to solve these issues. Polly itself
> is BSD anyways, ISL and GMP are LGPL. As isl is using just a tiny subset
> of GMP I am pretty sure we can either rewrite this subset ourselves or
> extend the existing arbitrary (but fixed) width integer functionality in
> This leaves us with ISL and CLooG. For both the copyright situation is
> pretty clear. The more complex library here is ISL. To my knowledge it
> is the only competitive open source integer set library. Rewriting it
> will be hard*. However, it was developed by one person (Sven
> Verdoolaege) and some smaller patches of me. AFAIK the copyrights are
> hold by the academic institutions he was working for. This means the
> copyright situation is clear. It cannot be changed overnight, but the
> institutions that need to be addressed are known.
In my experience, it is better to investigate these kinds of things
sooner rather than later. The more contributors a project acquires the
harder it is to get the license changed.
> The main reason I did not look into this earlier is that I prioritized
> the development of Polly itself and I postponed copyright issues to the
> point where they actually need to be solved. This was not the case for
> Polly as a pure research project, but if parts of it may also be used in
> production that is obviously different.
> If there is a consensus that people want isl being used within core
> LLVM, I am very glad to investigate this further. (Otherwise it is still
> on my TODO list, but not highest priority). For now I must admit I am
> very comfortable having Polly as a side project, but I can also see that
> it might be useful to move more mature parts of it into LLVM.
> * Developing an equivalent library from scratch within LLVM will be at
> least as hard.
Leadership Computing Facility
Argonne National Laboratory
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