http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57242
Bug ID: 57242 Summary: gcc ignores precompiled headers unless the .gch and TU's are compiled with certain combinations of -g flag Product: gcc Version: 4.8.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: pch Assignee: unassigned at gcc dot gnu.org Reporter: scottbaldwin at gmail dot com In GCC 4.7.2 and 4.8.x, precompiled headers (PCH) .gch file is ignored unless a certain combination of '-gN' debug options are used. To demonstrate, consider the following g++ commands to generate PCH (my_pch.hpp.gch) and compile a TU (foo.cpp) using the PCH cache: g++ $(PCH_DEBUG_FLAGS) -std=c++11 -m64 -Wall -Werror -Wno-unused -Wno-unused-variable -I./dbg-mt -I. -I. ./dbg-mt/my_pch.hpp -o ./dbg-mt/my_pch.hpp.gch g++ $(CPP_DEBUG_FLAGS) -std=c++11 -m64 -Wall -Werror -Wno-unused -Wno-unused-variable -I./dbg-mt -I. -I. -c foo.cpp -o dbg-mt/foo.o The only difference between these two commands (other than the input file) is the $(PCH_DEBUG_FLAGS) vs $(CPP_DEBUG_FLAGS). However, in order for the precompiled headers (.gch file) to be used when compiling the source files (e.g., foo.cpp), both of the following conditions must be met: 1) The '-g' or '-g2' or '-g3' flag must be used when building the precompiled headers (.gch file). 2) The '-g3' flag (and no less) must be used when compiling each TU (.c/.cpp file), and In other words: PCH_DEBUG_FLAGS = -g3 or -g2 or -g (specifying no 'g' at all will cause PCH cache to be ignored) CPP_DEBUG_FLAGS = -g3 (specifying -g2 or -g or no 'g' at all will cause PCH cache to be ignored) I put a #warning in the my_pch.hpp file to be sure of when PCH were being ignored (though, the long delay also made it quite obvious). This bug is present in all 3 versions of gcc I tested (4.7.2, 4.8.0, 4.8.1_20130427).