[LLVMdev] LLVM 2.8 and MMX

Nicolas Capens
Tue, 21 Sep 2010 22:13:56 -0000

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.