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Avoid triggering uninitialized warning in RVec#22468

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vepadulano:rdf-gcc16-uninitialized-warning
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Avoid triggering uninitialized warning in RVec#22468
vepadulano wants to merge 2 commits into
root-project:masterfrom
vepadulano:rdf-gcc16-uninitialized-warning

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@vepadulano vepadulano commented Jun 3, 2026

Fixes #22467

For now the PR only contains the commit adding the test, to make sure we can see the failure in the CI as well.

@vepadulano vepadulano self-assigned this Jun 3, 2026
@vepadulano vepadulano added in:Math Libraries clean build Ask CI to do non-incremental build on PR labels Jun 3, 2026
@vepadulano vepadulano closed this Jun 3, 2026
@vepadulano vepadulano reopened this Jun 3, 2026
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github-actions Bot commented Jun 3, 2026 •
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Test Results

    22 files      22 suites   3d 14h 15m 24s ⏱️
 3 863 tests  3 863 ✅ 0 💤 0 ❌
76 238 runs  76 238 ✅ 0 💤 0 ❌

Results for commit b441aeb.

♻️ This comment has been updated with latest results.

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vepadulano commented Jun 3, 2026

Failing test visible at https://github.com/root-project/root/actions/runs/26879891828/job/79276912873?pr=22468#step:8:14757

 -- TEST COMMAND -- 
  cd /github/home/ROOT-CI/build/roottest/root/aclic/rvec_uninitialized
  /usr/sbin/timeout -s USR2 270s /github/home/ROOT-CI/build/bin/root.exe -e '#define CLING_WITH_ADAPTIVECPP' -e '#define ClingWorkAroundMissingDynamicScope' -e '#define ClingWorkAroundUnnamedInclude' -e '#define ClingWorkAroundMissingSmartInclude' -e '#define ClingWorkAroundNoDotInclude' -e '#define ClingWorkAroundMissingAutoLoadingForTemplates' -e '#define ClingWorkAroundTClassUpdateDouble32' -e '#define ClingWorkAroundAutoParseDeclaration' -e '#define ClingWorkAroundMissingUnloading' -e '#define ClingWorkAroundBrokenUnnamedReturn' -e '#define ClingWorkAroundUnnamedDetection2' -e '#define ClingWorkAroundNoPrivateClassIO' -e '#define ClingWorkAroundUnloadingVTABLES' -e 'gSystem->SetBuildDir("/github/home/ROOT-CI/build/roottest/root/aclic/rvec_uninitialized",true)' -e 'gSystem->AddDynamicPath("/github/home/ROOT-CI/build/roottest/root/aclic/rvec_uninitialized")' -e 'gROOT->SetMacroPath("/github/home/ROOT-CI/src/roottest/root/aclic/rvec_uninitialized")' -e 'gInterpreter->AddIncludePath("-I/github/home/ROOT-CI/build/roottest/root/aclic/rvec_uninitialized")' -e 'gSystem->AddIncludePath("-I/github/home/ROOT-CI/build/roottest/root/aclic/rvec_uninitialized")' -q -b /github/home/ROOT-CI/src/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized.C+
  -- BEGIN TEST OUTPUT --
  Processing /github/home/ROOT-CI/src/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized.C+...
  Info in <TUnixSystem::ACLiC>: creating shared library /github/home/ROOT-CI/build/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized_C.so
  In file included from /github/home/ROOT-CI/src/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized.C:1,
                   from /github/home/ROOT-CI/build/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized_C_ACLiC_dict.cxx:41:
  /github/home/ROOT-CI/build/include/ROOT/RVec.hxx: In constructor ‘ROOT::Internal::VecOps::SmallVectorTemplateCommon<T>::SmallVectorTemplateCommon(size_t) [with T = bool]’:
  /github/home/ROOT-CI/build/include/ROOT/RVec.hxx:222:68: warning: ‘<unknown>’ may be used uninitialized [-Wmaybe-uninitialized]
    222 |    SmallVectorTemplateCommon(size_t Size) : Base(getFirstEl(), Size) {}
        |                                                                    ^
  /github/home/ROOT-CI/build/include/ROOT/RVec.hxx:214:10: note: by argument 1 of type ‘const ROOT::Internal::VecOps::SmallVectorTemplateCommon<bool>*’ to ‘void* ROOT::Internal::VecOps::SmallVectorTemplateCommon<T>::getFirstEl() const [with T = bool]’ declared here
    214 |    void *getFirstEl() const
        |          ^~~~~~~~~~
  In file included from /github/home/ROOT-CI/src/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized.C:1,
                   from /github/home/ROOT-CI/build/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized_C_ACLiC_dict.cxx:41:
  /github/home/ROOT-CI/build/include/ROOT/RVec.hxx: In constructor ‘ROOT::Internal::VecOps::SmallVectorTemplateCommon<T>::SmallVectorTemplateCommon(size_t) [with T = bool]’:
  /github/home/ROOT-CI/build/include/ROOT/RVec.hxx:222:68: warning: ‘<unknown>’ may be used uninitialized [-Wmaybe-uninitialized]
    222 |    SmallVectorTemplateCommon(size_t Size) : Base(getFirstEl(), Size) {}
        |                                                                    ^
  /github/home/ROOT-CI/build/include/ROOT/RVec.hxx:214:10: note: by argument 1 of type ‘const ROOT::Internal::VecOps::SmallVectorTemplateCommon<bool>*’ to ‘void* ROOT::Internal::VecOps::SmallVectorTemplateCommon<T>::getFirstEl() const [with T = bool]’ declared here
    214 |    void *getFirstEl() const
        |          ^~~~~~~~~~
  
  -- END TEST OUTPUT --
  -- BEGIN OUTDIFF OUTPUT --
  --- /github/home/ROOT-CI/src/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized.ref	Wed Jun  3 10:49:51 2026
  +++ /github/home/ROOT-CI/build/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized.log	Wed Jun  3 11:55:33 2026
  @@ -0,0 +1,18 @@
  +In file included from /github/home/ROOT-CI/src/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized.C:1,
  +                 from /github/home/ROOT-CI/build/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized_C_ACLiC_dict.cxx:41:
  +/github/home/ROOT-CI/build/include/ROOT/RVec.hxx: In constructor ‘ROOT::Internal::VecOps::SmallVectorTemplateCommon<T>::SmallVectorTemplateCommon(size_t) [with T = bool]’:
  +/github/home/ROOT-CI/build/include/ROOT/RVec.hxx:222:68: warning: ‘<unknown>’ may be used uninitialized [-Wmaybe-uninitialized]
  +  222 |    SmallVectorTemplateCommon(size_t Size) : Base(getFirstEl(), Size) {}
  +      |                                                                    ^
  +/github/home/ROOT-CI/build/include/ROOT/RVec.hxx:214:10: note: by argument 1 of type ‘const ROOT::Internal::VecOps::SmallVectorTemplateCommon<bool>*’ to ‘void* ROOT::Internal::VecOps::SmallVectorTemplateCommon<T>::getFirstEl() const [with T = bool]’ declared here
  +  214 |    void *getFirstEl() const
  +      |          ^~~~~~~~~~
  +In file included from /github/home/ROOT-CI/src/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized.C:1,
  +                 from /github/home/ROOT-CI/build/roottest/root/aclic/rvec_uninitialized/rvec_uninitialized_C_ACLiC_dict.cxx:41:
  +/github/home/ROOT-CI/build/include/ROOT/RVec.hxx: In constructor ‘ROOT::Internal::VecOps::SmallVectorTemplateCommon<T>::SmallVectorTemplateCommon(size_t) [with T = bool]’:
  +/github/home/ROOT-CI/build/include/ROOT/RVec.hxx:222:68: warning: ‘<unknown>’ may be used uninitialized [-Wmaybe-uninitialized]
  +  222 |    SmallVectorTemplateCommon(size_t Size) : Base(getFirstEl(), Size) {}
  +      |                                                                    ^
  +/github/home/ROOT-CI/build/include/ROOT/RVec.hxx:214:10: note: by argument 1 of type ‘const ROOT::Internal::VecOps::SmallVectorTemplateCommon<bool>*’ to ‘void* ROOT::Internal::VecOps::SmallVectorTemplateCommon<T>::getFirstEl() const [with T = bool]’ declared here
  +  214 |    void *getFirstEl() const
  +      |          ^~~~~~~~~~
  
  -- END OUTDIFF OUTPUT --

@vepadulano vepadulano force-pushed the rdf-gcc16-uninitialized-warning branch from fa99249 to b441aeb Compare June 3, 2026 14:10
@vepadulano vepadulano marked this pull request as ready for review June 3, 2026 14:11
@vepadulano vepadulano mentioned this pull request Jun 3, 2026
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guitargeek approved these changes Jun 4, 2026
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LGTM!

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hahnjo commented Jun 4, 2026

I don't see LLVM upstream doing anything similar, but can't see a difference in our code. What is triggering this for us?

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vepadulano commented Jun 4, 2026 •
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I don't see LLVM upstream doing anything similar, but can't see a difference in our code. What is triggering this for us?

Happens if a struct with RVec<bool> is involved in the generation and subsequent usage of a ROOT dictionary, with GCC16.

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vepadulano commented Jun 4, 2026

The issue is much more widespread, as demonstrated by https://github.com/root-project/root/actions/runs/26955003387/job/79529828759?pr=22480#step:8:4508

The missing part to make it that much visible was compiling ROOT with CMAKE_BUILD_TYPE=Debug, then the warnings appear pretty much everywhere that uses RVec

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ACLiC on Fedora 44 and GCC 16 in debug mode triggers uninitialized warning in RVec

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