LLVM can't optimize out a global constructor - once it's in the list of functions to call, LLVM has to leave it there. There are uses of such global constructors that require them to stay. The only way to prevent it is to not include it in the first place.
On Thu, May 5, 2016 at 8:07 PM, Jian Huang <[email protected]> wrote: > Thanks Alon. But due to the linking order of .a is somehow tricky as we > discussed before( > https://groups.google.com/forum/#!searchin/emscripten-discuss/jian$20huang/emscripten-discuss/_4qYN_7dvVs/hrf05GesCAAJ), > we prefer .bc. Here's the follow-up questions. Why .bc cannot work? Even > so, should these unnecessary obj can be detected and optimized out in > linking stage or stage of generating js? > > On Friday, May 6, 2016 at 4:48:58 AM UTC+8, Alon Zakai wrote: >> >> Archive files (.a suffix) can do this. They contain separate .o files, >> and only the ones with symbols that are actually required are linked in. >> The rest are not, and that means their global constructors would not appear >> in the final output. >> >> >> On Wed, May 4, 2016 at 8:51 PM, Jian Huang <[email protected]> wrote: >> >>> Let say we have 3 .cpp in our project as below: >>> >>> //abc.cpp >>> #include <iostream> >>> class abc >>> { >>> public: >>> static int sabc; >>> }; >>> >>> int abc::sabc = [](){std::cout << "init abc" << std::endl; return 0;}(); >>> >>> //abcd.cpp >>> #include <iostream> >>> class abcd >>> { >>> public: >>> static int sabcd; >>> }; >>> >>> int abcd::sabcd = [](){std::cout << "init abcd" << std::endl; return >>> 0;}(); >>> >>> //test.cpp >>> int main() >>> { >>> return 0; >>> } >>> >>> Given above .cpp, I build the test executable and run it by following >>> typing: >>> >>> >em++ -std=c++11 abc.cpp abcd.cpp -o abc.bc >>> >em++ -std=c++11 abc.bc test.cpp -o test.js >>> >node test.js >>> init abc >>> init abcd >>> >>> As we see in the output, those static class variables will be >>> initialized ahead due to unused abc.obj and abcd.obj will be linked to >>> final executable. Is there any way to prevent these unused objs to be >>> linked into final executable so that those global variables in them will >>> not be initialized? >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "emscripten-discuss" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> -- > You received this message because you are subscribed to the Google Groups > "emscripten-discuss" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "emscripten-discuss" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
