https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117322
--- Comment #2 from Anton Kryukov <akryuk at gmail dot com> --- (In reply to Andrew Pinski from comment #1) > So adding: > if ((long)(len*4) <= 0) return; > > Fixes the warning. > > Looks like GCC does not realize len can't be too big to overflow. > > I am not 100% sure if the warning should be better worded or there is a > missed optimization here. But if I remove the heap allocation branch, leaving only the one with alloca with the possible overflow situation intact (https://godbolt.org/z/ne7bcsq6d), the warning goes away: //********************************************************** #include <memory> #include <alloca.h> #include <type_traits> using T = long long; //---------------------------------------------------------- void f(T const* data, size_t len); //---------------------------------------------------------- void h(int const* data, size_t len) { T* arr; size_t nbytes = len * sizeof(T); arr = reinterpret_cast<T*>(alloca(nbytes)); std::uninitialized_copy(data, data + len, arr); f(arr, len); } //*********************************************************
