[LLVMdev] Upstreaming PNaCl's IR simplification passes

[Sean Silva]

On Mar 4, 2014 8:22 PM, "Chris Lattner" <clattner at apple.com> wrote:
>
>
> 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?
>
My reading of the OP suggests that there are at least two projects that
depend on these passes in production (and will for the foreseeable future).
I wasn't around when the CBE was added; were there such users for it then?
If not, then I would consider that a major difference in the situation.

-- Sean Silva

> -Chris
>
>
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