[LLVMdev] Upstreaming PNaCl's IR simplification passes

[Chris Lattner]

On Mar 4, 2014, at 3:17 PM, Chandler Carruth <chandlerc at google.com> wrote:

> On Tue, Mar 4, 2014 at 1:04 PM, Mark Seaborn <mseaborn at chromium.org> wrote:
> The PNaCl project has implemented various IR simplification passes that simplify LLVM IR by lowering complex features to simpler features.  We'd like to upstream some of these IR passes to LLVM.  We'd like to explore if this acceptable, and if so, how we should go about doing this.
> 
> My question is somewhat different. I'm not questioning whether these are acceptable, I'm questioning why these are interesting and important for the LLVM project.

I share Chandler's concern.  If these aren't actively used by something in tree, they will bit rot.  The way to counter the bit rot would be to add extensive testcases... but that would just add an even larger burden on core LLVM developers to keep them up to date.

We have seen similar "obviously useful" pieces of infrastructure fall to the same fate (e.g., the C backend, which incidentally had very similar utilities back when it was alive).  Why would this be any different?

-Chris

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