https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70723
Bug ID: 70723
Summary: Missed optimization opportunity for lambda converted
to fun-ptr
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: m.cencora at gmail dot com
Target Milestone: ---
Hi,
the following code gets properly optimized-out if erasedTypeVTable is
initialized with &dtor<T> (case [2]), but it is not optimized if initialized
with lambda (case [1]).
#include <type_traits>
#include <new>
namespace
{
struct ErasedTypeVTable
{
using destructor_t = void (*)(void *obj);
destructor_t dtor;
};
template <typename T>
void dtor(void *obj)
{
return static_cast<T *>(obj)->~T();
}
template <typename T>
static const ErasedTypeVTable erasedTypeVTable = {
/* 1 */ [] (void *obj) { return static_cast<T *>(obj)->~T(); }
/* 2 */ // &dtor<T>
};
struct myType
{
int a;
};
void meow()
{
std::aligned_storage<sizeof(myType)>::type storage;
auto *ptr = new ((char *)(&storage)) myType{5};
ptr->a = 10;
erasedTypeVTable<myType>.dtor(ptr);
}
}
int main()
{
meow();
}
Compiled with -O3 -std=c++14 flags.
g++ --version:
g++ (Ubuntu 6-20160405-0ubuntu1) 6.0.0 20160405 (experimental) [trunk revision
234749]
FWIW, clang 3.8 optimizes both versions.
