https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110057
Bug ID: 110057 Summary: Missed devirtualization opportunities Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: yongxiangng at gmail dot com Target Milestone: --- There are some missed devirtualization opportunities involving vectors. The issue is discussed in the stackoverflow here. https://stackoverflow.com/questions/73257739/missed-optimization-stdvectortpop-back-not-qualifying-destructor-call/ Because we know the type of the objects in the vector (they have to be _Tp), there is no need to invoke the virtual methods and we can devirtualize them. I believe this applies not just to the destructor, but also other member functions. This missed optimization does not only affect vector. When creating an array, the virtual destructor is invoked even though it should be quite clear to the compiler that it can resolve the type of the object in the array at compile time. There is a possibility of using placement new and "spoofing" the type https://godbolt.org/z/3MdMsdKha (thanks Jonathan Wakely), but I'm not sure if this is legal c++ and if this applies to raw arrays I think this might be a problem with the IPA component, I might have mislabelled the issue because there isn't an option for IPA. Please let me know if this makes sense or I have some misconception. A sample program that shows this behavior is below. /* { dg-do run } */ /* Virtual calls should be devirtualized because we know dynamic type of object in vector at compile time */ /* { dg-options "-O3 -fdump-tree-ssa" } */ #include <vector> using std::vector; class A { public: virtual ~A() { } }; class B : public A { public: virtual ~B() { } }; int main() { vector<B> arr; // B b[40]; return 0; } /* { dg-final { scan-tree-dump-times "OBJ_TYPE_REF" 0 "ssa"} } */