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Make it easier to fold MakeString usages to reduce binary size. (#6754)

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* Decay char[n] to char* so that we get better re-use of MakeString invocations.
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Scott McKay 2021-02-20 20:41:19 +10:00 committed by GitHub
parent 3bda7f4d36
commit 9f7dffb109
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1 changed files with 47 additions and 3 deletions
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50
include/onnxruntime/core/common/make_string.h
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@ -19,10 +19,12 @@
#include <locale>
#include <sstream>
#include <type_traits>
namespace onnxruntime {
namespace detail {
inline void MakeStringImpl(std::ostringstream& /*ss*/) noexcept {
}
@ -36,6 +38,39 @@ inline void MakeStringImpl(std::ostringstream& ss, const T& t, const Args&... ar
MakeStringImpl(ss, t);
MakeStringImpl(ss, args...);
}
// see MakeString comments for explanation of why this is necessary
template <typename... Args>
inline std::string MakeStringImpl(const Args&... args) noexcept {
std::ostringstream ss;
MakeStringImpl(ss, args...);
return ss.str();
}
//
// Infrastructure to convert char[n] to char* to reduce binary size
//
// default is to leave the type as is
template <class T>
struct if_char_array_make_ptr {
using type = T;
};
// specialization that matches an array reference, which is what the char array from a string literal
// used in a call to MakeString will be.
// if the type is a char[n] array we 'decay' it to a char* so that the usages can be folded.
template <class T, size_t N>
struct if_char_array_make_ptr<T (&)[N]> {
// remove a single extent (T[x] -> T, but T[x][y] -> T[y]) so we only match char[x],
// and get the type name without the 'const' so both 'const char (&)[n]' and 'char (&)[n]' are matched.
using element_type = typename std::remove_const<typename std::remove_extent<T>::type>::type;
using type = typename std::conditional<std::is_same<char, element_type>::value, T*, T (&)[N]>::type;
};
// helper to make usage simpler in MakeString
template <class T>
using if_char_array_make_ptr_t = typename if_char_array_make_ptr<T>::type;
} // namespace detail
/**
@ -44,9 +79,18 @@ inline void MakeStringImpl(std::ostringstream& ss, const T& t, const Args&... ar
*/
template <typename... Args>
std::string MakeString(const Args&... args) {
std::ostringstream ss;
detail::MakeStringImpl(ss, args...);
return ss.str();
// We need to update the types from the MakeString template instantiation to decay any char[n] to char*.
// e.g. MakeString("in", "out") goes from MakeString<char[2], char[3]> to MakeStringImpl<char*, char*>
// so that MakeString("out", "in") will also match MakeStringImpl<char*, char*> instead of requiring
// MakeStringImpl<char[3], char[2]>.
//
// We have to do the type processing before any actual work, so this function purely implements the type processing.
// If we do not do it this way we do not get the full binary size reduction.
//
// See https://stackoverflow.com/a/29418212/684911 for overall details of the approach, but note it does not cover
// the need to do the type processing as a separate step.
return detail::MakeStringImpl(detail::if_char_array_make_ptr_t<Args const&>(args)...);
}
/**