[LLVMdev] Upstreaming PNaCl's IR simplification passes

[Chandler Carruth]

On Tue, Mar 4, 2014 at 3:11 PM, Sean Silva <chisophugis at gmail.com> wrote:

> On Tue, Mar 4, 2014 at 4:04 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.
>>
>> The immediate reason is that Emscripten is reusing PNaCl's IR passes for
>> its new "fastcomp" backend [1].  It would be really useful if PNaCl and
>> Emscripten could collaborate via upstream LLVM rather than a branch.
>>
>> Some background:  There are two related use cases for these IR
>> simplification passes:
>>
>>  1) Simplifying the task of writing a new LLVM backend.  This is
>> Emscripten's use case.  The IR simplification passes reduce the number of
>> cases a backend has to handle, so they would be useful for anyone else
>> creating a new backend.
>>
>
> FWIW, this sounds to me like a sufficiently compelling use case to support
> getting this in-tree.
>

Just in case it gets lost in my longer reply, I want to emphasize that if
these will be used to simplify the in-tree backends and those backend
maintainers are on board, then I am *totally* in favor of this going into
the tree. My concerns are heavily based on the fact that as proposed, none
of that seems likely to happen.
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