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Implement an optimization that David Abrahams and myself came up with,

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where Boost.Function uses a bit in the vtable pointer to indicate when
the target function object has a trivial copy constructor, trivial
destructor, and fits within the small object buffer. In this case, we
just copy the bits of the function object rather than performing an
indirect call to the manager.

This results in a 60% speedup on a micro-benchmark that copies and
calls such function objects repeatedly.



[SVN r51743]
This commit is contained in:
Douglas Gregor
2009-03-13 05:23:53 +00:00
parent 678fb133f0
commit 6f8ec5c8c5
2 changed files with 55 additions and 16 deletions
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18
include/boost/function/function_base.hpp
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@ -18,6 +18,9 @@
#include <typeinfo>
#include <boost/config.hpp>
#include <boost/assert.hpp>
#include <boost/integer.hpp>
#include <boost/type_traits/has_trivial_copy.hpp>
#include <boost/type_traits/has_trivial_destructor.hpp>
#include <boost/type_traits/is_const.hpp>
#include <boost/type_traits/is_integral.hpp>
#include <boost/type_traits/is_volatile.hpp>
@ -625,7 +628,7 @@ public:
if (!vtable) return typeid(void);
detail::function::function_buffer type;
vtable->manager(functor, type, detail::function::get_functor_type_tag);
get_vtable()->manager(functor, type, detail::function::get_functor_type_tag);
return *type.type.type;
}
@ -638,7 +641,7 @@ public:
type_result.type.type = &typeid(Functor);
type_result.type.const_qualified = is_const<Functor>::value;
type_result.type.volatile_qualified = is_volatile<Functor>::value;
vtable->manager(functor, type_result,
get_vtable()->manager(functor, type_result,
detail::function::check_functor_type_tag);
return static_cast<Functor*>(type_result.obj_ptr);
}
@ -656,7 +659,7 @@ public:
type_result.type.type = &typeid(Functor);
type_result.type.const_qualified = true;
type_result.type.volatile_qualified = is_volatile<Functor>::value;
vtable->manager(functor, type_result,
get_vtable()->manager(functor, type_result,
detail::function::check_functor_type_tag);
// GCC 2.95.3 gets the CV qualifiers wrong here, so we
// can't do the static_cast that we should do.
@ -702,6 +705,15 @@ public:
#endif
public: // should be protected, but GCC 2.95.3 will fail to allow access
detail::function::vtable_base* get_vtable() const {
return reinterpret_cast<detail::function::vtable_base*>(
reinterpret_cast<std::size_t>(vtable) & ~(std::size_t)0x01);
}
bool has_trivial_copy_and_destroy() const {
return reinterpret_cast<std::size_t>(vtable) & 0x01;
}
detail::function::vtable_base* vtable;
mutable detail::function::function_buffer functor;
};