[llvm] r255530 - Remove the successor probabilities normalization in tail duplication pass.

[Cong Hou via llvm-commits]

On Mon, Dec 14, 2015 at 4:50 PM, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Tue, Dec 15, 2015 at 6:11 AM, Cong Hou via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: conghou
>> Date: Mon Dec 14 13:11:54 2015
>> New Revision: 255530
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=255530&view=rev
>> Log:
>> Remove the successor probabilities normalization in tail duplication pass.
>>
>> The normalization may cause assertion failures on SystemZ and some
>> out-of-tree
>> tests.
>
>
> Sounds like you have test coverage - please commit such a test to go with
> this change.
>

Actually I haven't got reduced test cases from others. I have requested but
haven't got replied.

Cong


>
>
>> The root cause is that unknown probabilities are materialized into known
>> ones by calling getSuccProbability(), which is then used to add another
>> successor to the same MBB which results in mixed known and unknown
>> probabilities. But currently those mixed probabilities cannot be
>> normalized.
>>
>> I will compose another patch to fix the root issue.
>>
>>
>>
>> Modified:
>>     llvm/trunk/lib/CodeGen/TailDuplication.cpp
>>
>> Modified: llvm/trunk/lib/CodeGen/TailDuplication.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/TailDuplication.cpp?rev=255530&r1=255529&r2=255530&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/CodeGen/TailDuplication.cpp (original)
>> +++ llvm/trunk/lib/CodeGen/TailDuplication.cpp Mon Dec 14 13:11:54 2015
>> @@ -751,7 +751,6 @@ TailDuplicatePass::duplicateSimpleBB(Mac
>>      assert(NumSuccessors <= 1);
>>      if (NumSuccessors == 0 || *PredBB->succ_begin() != NewTarget)
>>        PredBB->addSuccessor(NewTarget, Prob);
>> -    PredBB->normalizeSuccProbs();
>>
>>      TDBBs.push_back(PredBB);
>>    }
>>
>>
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>>
>
>
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