On Sep 21, 2010, at 5:30 PMPDT, Bill Wendling wrote:
> LLVM isn't going to stop generating MMX instructions all together. We
can't do that. :-) If the user specifically wants MMX (by, say, using the
builtins), we have to support that still. The plan to cease generating MMX for
generic vectors is a work-in-progress right now. It's not in 2.8.
>
> -bw
Right, early on there was speculation that the early phases of this work were
causing the problem Nicolas is seeing, but it now appears that that problem is
unrelated.
> On Sep 21, 2010, at 4:24 PM, Reid Kleckner wrote:
>
>> This thread confuses me. I thought Chris said that LLVM 2.8 will not
>> lower generic vectors to MMX because it breaks x87 code, and I
didn't
>> see an answer to your question about a switch to tell the code
>> generator otherwise. However, you're complaining that MMX
performance
>> is subpar, even though LLVM 2.8 isn't supposed to generate MMX
>> instructions.
>>
>> Can someone clarify the situation for me?
>>
>> Thanks,
>> Reid
>>
>> On Tue, Sep 21, 2010 at 6:13 PM, Nicolas Capens
>> <nicolas.capens at gmail.com> wrote:
>>> Hi Dale,
>>>
>>> I suspect that these patches were intended to improve 128-bit
vector
>>> performance but caused certain 64-bit vector operations to no
longer lower
>>> to MMX instructions. Anyway, now that I've narrowed it down to
these patches
>>> I think I can narrow it down further to a specific case so I can
file a
>>> bug...
>>>
>>> Will Bruno be back soon or is he no longer working on the project
for good?
>>>
>>> Cheers,
>>>
>>> Nicolas
>>>
>>>
>>> -----Original Message-----
>>> From: Dale Johannesen [mailto:dalej at apple.com]
>>> Sent: Tuesday, September 21, 2010 20:12
>>> To: Nicolas Capens
>>> Cc: Dale Johannesen; 'Chris Lattner'; 'Eli
Friedman'; llvmdev at cs.uiuc.edu
>>> Subject: Re: [LLVMdev] LLVM 2.8 and MMX
>>>
>>>
>>> On Sep 21, 2010, at 10:23 AMPDT, Nicolas Capens wrote:
>>>
>>>> Hi all,
>>>>
>>>> Sorry for the late reply. I got sidetracked by other fun
projects. ;-)
>>>>
>>>> I found that the performance regression is caused by revisions
112804,
>>>> 112805 and 112806. Those changes were made 2 days prior to the
2.8
>>>> branching, so it may have not been the intention to include
them there?
>>>> Either way they make my vector-intensive code two times slower
so it would
>>>> be much appreciated to revert these changes for the 2.8
release.
>>>>
>>>> Thanks,
>>>>
>>>> Nicolas
>>>
>>> Interesting. These are all Bruno's patches, and I'm pretty
sure they
>>> weren't intended to affect MMX. I doubt reverting them is
right since the
>>> effect on SSE is presumably positive. Unfortunately Bruno is not
here any
>>> more.
>>>
>>>> -----Original Message-----
>>>> From: Chris Lattner [mailto:clattner at apple.com]
>>>>>
>>>>> I think some changes related to MMX landed before 2.8
branched which
>>>>> shouldn't have... please file a bug.
>>>
>>> So please file a bug, with example.
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev