[llvm-commits] [llvm] r171471 - /llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp

[Michael Gottesman]

Of course. I am just saying that it might be a useful options for developers who wish to use vectorization but are afraid of the costs.

On Jan 4, 2013, at 6:37 PM, Nadav Rotem <nrotem at apple.com> wrote:

> Chandler ran the internal google test suite.  The problem with PGO is that you don't always have it.  
> 
> On Jan 4, 2013, at 3:23 PM, Michael Gottesman <mgottesman at apple.com> wrote:
> 
>> 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.
>>>> 
>>>> Nadav
>>>> 
>>>> 
>>>> 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
>>>>>> Log:
>>>>>> 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,
>>>>> Hal
>>>>> 
>>>>>> Modified:
>>>>>>  llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
>>>>>> 
>>>>>> Modified: llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
>>>>>> URL:
>>>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp?rev=171471&r1=171470&r2=171471&view=diff
>>>>>> ==============================================================================
>>>>>> --- 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)
>>>>>>   MPM.add(createLoopVectorizePass());
>>>>>> 
>>>>>> if (!DisableUnrollLoops)
>>>>>> 
>>>>>> 
>>>>>> _______________________________________________
>>>>>> llvm-commits mailing list
>>>>>> llvm-commits at cs.uiuc.edu
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>>>>> -- 
>>>>> Hal Finkel
>>>>> Postdoctoral Appointee
>>>>> Leadership Computing Facility
>>>>> Argonne National Laboratory
>>>> _______________________________________________
>>>> llvm-commits mailing list
>>>> llvm-commits at cs.uiuc.edu
>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>>> 
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