[cfe-dev] [LLVMdev] [3.6 Release] RC3 has been tagged

Jack Howarth howarth.mailing.lists at gmail.com
Tue Feb 17 12:18:45 PST 2015


On Tue, Feb 17, 2015 at 2:44 PM, Hayden Livingston
<halivingston at gmail.com> wrote:
> In the interest of educating others, can someone explain what the regression
> is? Is it understood?
>
> I'm new to this area and would love to understand how we identified what is
> causing this regression? An optimization gone rogue? Some optimization
> missing, etc.
>

Hayden,
     See...

http://llvm.org/bugs/show_bug.cgi?id=22589#c5
http://llvm.org/bugs/show_bug.cgi?id=22589#c7
http://llvm.org/bugs/show_bug.cgi?id=22589#c9
http://llvm.org/bugs/show_bug.cgi?id=22589#c26
http://llvm.org/bugs/show_bug.cgi?id=22589#c27
http://llvm.org/bugs/show_bug.cgi?id=22589#c33
http://llvm.org/bugs/show_bug.cgi?id=22589#c36

which are the key postings on this bug. I would describe it as an
optimization no longer taken. As for identifying cause of regression,
the process is a brutal walk back through prior svn trunk until the
offending commit which cause the loss of optimization is pin-pointed.
             Jack

> On Tue, Feb 17, 2015 at 11:12 AM, Hans Wennborg <hans at chromium.org> wrote:
>>
>> Hi Jack,
>>
>> On Sun, Feb 15, 2015 at 6:05 AM, Jack Howarth
>> <howarth.mailing.lists at gmail.com> wrote:
>> >    What are the acceptable performance regressions in the generated
>> > code for a llvm release? We seem to be badly regressed in some
>> > benchmarks (which I first noticed from the review of 3.6-rc1 at
>> >
>> > http://www.phoronix.com/scan.php?page=article&item=llvm-clang-3.5-3.6-rc1).
>> > This same issue has also been reported in
>> > http://llvm.org/bugs/show_bug.cgi?id=22058. In the case of the 22%
>> > performance degradation in SciMark2's Sparse matmult benchmark, I have
>> > identified both commits that contribute equally to this regression in
>> > http://llvm.org/bugs/show_bug.cgi?id=22589...
>>
>> Thank you very much for trying out the release candidate.
>>
>> I asked a few of the other developers, and the consensus was that
>> while unfortunate, we won't block the release on a perf regression
>> like this, at least not at this stage in the release process.
>>
>> Having said that, we will be doing an rc4, and Hal said that he or
>> Sanjoy might be able to squeeze in a patch for the issue you pointed
>> out before that. Otherwise, it will have to wait to 3.6.1 or 3.7.
>>
>> Thanks,
>> Hans
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>



More information about the cfe-dev mailing list