[llvm-commits] [llvm] r171471 - /llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
mgottesman at apple.com
Fri Jan 4 15:23:32 PST 2013
Question. Which tests were run I.e. what is comprehensive? Also in order to know what are the "hot loops" we could use pgo.
On Jan 4, 2013, at 6:03 PM, Shuxin Yang <shuxin.llvm at gmail.com> wrote:
> I spot a defect that contribute the code size problem. I don't know to what ext it impacts the code sz.
> However, it is certainly easy to fix.
> The problem is that if a scalar constant, say s=2.0f, is broadcasted into a vector v=<2.0, 2.0, 2.0, 2.0>, and
> if the scalar is still referenced in the code, we will see the compiler creates read-only storage both for s and v.
> Actually the storage for the scalar is not necessary.
> On 1/4/13 10:09 AM, Nadav Rotem wrote:
>> Hi Hal,
>> I spoke with chandler last night and he said that he ran comprehensive testing and he found two interesting things:
>> 1. When vectorizing everything with O2, the code gets 3% bigger, and as a result slower. When it works it works really well, but most vectorizable loops are in the cold path.
>> 2. When disabling the pre-loop for loops that require: runtime checks, odd number of iterations, etc. Then the loop vectorizer does not catch much.
>> At the moment it looks like it is better to mimic the gcc behavior and enable the loop vectorizer only on O3.
>> On Jan 4, 2013, at 10:04 AM, Hal Finkel <hfinkel at anl.gov> wrote:
>>> ----- Original Message -----
>>>> From: "Nadav Rotem" <nrotem at apple.com>
>>>> To: llvm-commits at cs.uiuc.edu
>>>> Sent: Friday, January 4, 2013 11:57:44 AM
>>>> Subject: [llvm-commits] [llvm] r171471 - /llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
>>>> Author: nadav
>>>> Date: Fri Jan 4 11:57:44 2013
>>>> New Revision: 171471
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=171471&view=rev
>>>> Move the loop vectorizer from O2 to O3. It looks like the increase in
>>>> code size actually hurts the performance on many programs.
>>> Can you be specific about what code size increase? (runtime checks, if conversion, unrolling)? And what does this have to do with moving the vectorizer from -02 to -O3? To be clear, I don't object to the change (enabling autovectorization at -O3 seems pretty standard these days).
>>> Thanks again,
>>>> Modified: llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
>>>> --- llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp (original)
>>>> +++ llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp Fri Jan 4
>>>> 11:57:44 2013
>>>> @@ -187,7 +187,7 @@
>>>> MPM.add(createLoopIdiomPass()); // Recognize idioms
>>>> like memset.
>>>> MPM.add(createLoopDeletionPass()); // Delete dead loops
>>>> - if (LoopVectorize && OptLevel > 1)
>>>> + if (LoopVectorize && OptLevel > 2)
>>>> if (!DisableUnrollLoops)
>>>> llvm-commits mailing list
>>>> llvm-commits at cs.uiuc.edu
>>> Hal Finkel
>>> Postdoctoral Appointee
>>> Leadership Computing Facility
>>> Argonne National Laboratory
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