PileupJetId falling back to Muon::bestTrack for PFCandidate muon without a trackRef

[slava77]

Fixes a crash in PileupJetId https://cmssdt.cern.ch/SDT/cgi-bin/buildlogs/slc6_amd64_gcc491/CMSSW_7_4_X_2015-01-18-0200/pyRelValMatrixLogs/run/50202.0_TTbar_13+TTbar_13INPUT+DIGIUP15_PU50+RECOUP15_PU50+HARVESTUP15+MINIAODMCUP1550/step5_TTbar_13+TTbar_13INPUT+DIGIUP15_PU50+RECOUP15_PU50+HARVESTUP15+MINIAODMCUP1550.log

Recent change in
ce1863b#diff-34b721ce73bd0269273004088c8a715fL400

- reco::Track impactTrack = (lPack==nullptr)?(*pfTrk):(lPack->pseudoTrack());
+ const reco::Track& impactTrack = (lPack==nullptr)?(*pfTrk):(lPack->pseudoTrack());

exposed a problem with pfTrk being a nullptr and we
With the const ref used now we end up with an invalid reference and a segfault.

It's curious that the result of the following depends on optimization flags:

#include  <iostream>

class AS {
public:
  float x;
};

int main(){
  AS* anullP = nullptr;
  AS anullV = *anullP;
  std::cout<<"Really: "<<anullV.x<<std::endl;

  return 0;
}

gives:

gcc -o a.exe test_null.cc -lstdc++ -std=c++11 -O0
~>./a.exe 
Segmentation fault: 11
gcc -o a.exe test_null.cc -lstdc++ -std=c++11 -O1
~>./a.exe 
Really: 0

[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

A new Pull Request was created by @slava77 (Slava Krutelyov) for CMSSW_7_4_X.

PileupJetId falling back to Muon::bestTrack for PFCandidate muon without a trackRef

It involves the following packages:

RecoJets/JetProducers

@cmsbuild, @cvuosalo, @nclopezo, @slava77 can you please review it and eventually sign? Thanks.
@rappoccio, @ahinzmann, @TaiSakuma, @yslai, @nhanvtran, @schoef, @mariadalfonso this is something you requested to watch as well.
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[slava77]

+1

for #7273 c51260b
tested in CMSSW_7_4_X_2015-01-18-0200 test area sign492-devel
the affected producer runs only in the miniAOD step.
50202 now runs ok to completion.

@mmarionncern @TaiSakuma
Tai and Matthieu, please check that this king of muons actually make sense for the algorithm, the algorithm doesn't really give a way to skip the candidate, something should be done to every jet constituent in this case.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_4_X IBs unless changes or unless it breaks tests.

[cmsbuild]

+1
Tested at: c51260b
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7273/1997/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_4_X IBs unless changes (tests are also fine). This pull request will be automatically merged.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7273/1997/summary.html