[LLVMdev] Vectorization: Next Steps

Tobias Grosser tobias at grosser.es
Tue Feb 7 02:21:22 PST 2012

On 02/07/2012 01:17 AM, Hal Finkel wrote:
> 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
>> LLVM.
>> 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.

OK. I started looking into this.


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