[PATCH][InstCombiner] Expose opportunities to merge subtract and comparison

[Quentin Colombet]

Ping^2?

-Quentin

On Sep 3, 2013, at 9:40 AM, Quentin Colombet <qcolombet at apple.com> wrote:

> Ping?
> 
> Evan, does it mean it looks good for you?
> 
> -Quentin
> 
> On Aug 27, 2013, at 1:58 PM, Evan Cheng <evan.cheng at apple.com> wrote:
> 
>> 
>> On Aug 27, 2013, at 1:41 PM, Quentin Colombet <qcolombet at apple.com> wrote:
>> 
>>> On Aug 27, 2013, at 1:30 PM, Evan Cheng <evan.cheng at apple.com> wrote:
>>> 
>>>> 
>>>> On Aug 27, 2013, at 12:34 PM, Quentin Colombet <qcolombet at apple.com> wrote:
>>>> 
>>>>> 
>>>>> ** Notes **
>>>>> 
>>>>> 1. Why LLVM IR for this “low-level” optimization?
>>>>> As already stated, several architectures expose such opportunities, therefore, I thought it may be best to do it as a target independent optimization. LLVM IR makes more sense for that. Doing this at MI IR level would require several additional target hooks or a specific pass for each target.
>>>> 
>>>> I'm not sure about this. Instcombine's primary responsibility is canonicalization. Is it possible for this to pessimize code on certain targets?
>>> Not that I am aware of, but I guess it might be possible.
>>> Do you think we should somehow guard this transformation with a target hook?
>>> 
>>>> Have you considered doing this at codegenprep time?
>>> No, I have not, and I think you are right, it would make more sense there.
>> 
>> Actually ignore me. After reading your original email more carefully I think instcombine is ok.
>> 
>> Evan
>> 
>>> 
>>> Thanks Evan.
>>> 
>>> -Quentin
>>>> 
>>>> Evan
>>>> 
>>>>> 
>>>>> 2. What about the canonical form?
>>>>> The optimization is only performed when both operands have the same complexity.
>>>>> We might want to break the complexity assumption (operands ordered from most to less complex) but I am not sure it will bring new opportunities.
>>>>> Thus, assuming we want to do that transformation at LLVM IR level, is it desirable to break that assumption and if yes, in which pass?
>>>>> 
>>>>> Cheers,
>>>>> -Quentin
>>>>> <scratch.cc>
>>>>> <InstCombineCSE.svndiff>
>>>>> _______________________________________________
>>>>> llvm-commits mailing list
>>>>> llvm-commits at cs.uiuc.edu
>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> 
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130909/09214f88/attachment.html>