LI75114: -QTEMPLATEREGISTRY CAUSING REPEATED COMPILES

October 2009 Update for XL C/C++ for Linux, V10.1
June 2011 Update for XL C/C++ for Linux, V10.1
XL C/C++ for Linux Fix Pack 8 (January 2014 Update) for 10.1
August 2010 Update for XL C/C++ for Linux, V10.1
January 2011 Update for XL C/C++ for Linux, V10.1
January 2012 Update for XL C/C++ for Linux, V10.1
July 2012 Update for XL C/C++ for Linux, V10.1

APAR status

• Closed as program error.

Error description

• The issue comes from compiling a project that uses
  implicit and explicit instantiations of a template with the
  -qtemplateregistry option.  When compiled twice, the template
  registry may register an incorrect record, thus causing an extra
  recompile, or in some cases, an unending loop of compilation.
  
  =====  TEST CASE  =====
  
  The scenario is:
  file A has an implicit instantiation of foo<int>
  file B has an explicit instantiation of foo<int>
  file C has an implicit instantiation of foo<int>
  compile in the following order:
  file A
  file B
  file C
  recompile file A
  
  
  To reproduce - Build this project twice:
  
  all:
    xlC_r -qtemplateregistry -I. -c -o filea.o filea.cpp
    xlC_r -qtemplateregistry -I. -c -o fileb.o fileb.cpp
    xlC_r -qtemplateregistry -I. -c -o filec.o filec.cpp
    xlC_r -qmkshrobj -qtemplateregistry -I. -o libTest.so filea.o
      fileb.o filec.o
  
  
  --------   filea.cpp   --------
  #include "temp.h"
  
  void filea()
  {
          mytemplate<int> asdf (5);
          int temp = asdf.getfoo();
  }
  
  
  --------   fileb.cpp   --------
  #include "temp.h"
  
  template class mytemplate<int>;
  
  void fileb()
  {
          mytemplate<int> asdf (5);
  }
  
  
  --------   filec.cpp   --------
  #include "temp.h"
  
  void filec()
  {
          mytemplate<int> asdf (5);
          int temp = asdf.getfoo();
  }
  
  
  --------   temp.h      --------
  #ifndef Template_Included
  #define Template_Included
  
  template <class T>
  class mytemplate
  {
          T foo;
          public:
                  mytemplate(T arg) { foo=arg; }
                  T getfoo();
  };
  
  template <class T>
  T mytemplate<T>::getfoo()
  {
          return foo;
  }
  
  #endif
  

Local fix

• Turn off -qtemplateregistry
  

Problem summary

• USERS AFFECTED:
  Users who are using -qtemplateregistry and have some explicit
  instantiations in their code.  Encountering the problem will
  depend on the order of compilation.
  
  PROBLEM DESCRIPTION:
  If the user compiles an implicit instantiation before an
  explicit instantiation, the registry will record the implicit
  and explicit instantiation and the compiler will create a
  recompile record.  When the file with the implicit
  instantiation is recompiled, the compiler will try to eliminate
  the implicit one.  However it is creating a recompile record
  instead of using the explicit instantiation.  This will cause a
  source file to be recompiled that doesn't need to be.  In some
  cases this can cause an unending loop of alternating between
  recompiles of files with implicit instantiations.
  

Problem conclusion

• The -qtemplateregistry code needs to check for explicit
  instantiations before creating a recompile record for an
  implicit instantiation that is no longer defined in the object
  file.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

  IZ52119

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  XL C/C++ SLES10

• Fixed component ID

  5724U8300

Applicable component levels

• RA10 PSN IZ52119

     UP06/09/13