libstdc+: Eliminate usage of alloca for non-localized formatting

This patch eliminate the use of __builtin_alloca for non-localized formatting
of integers and pointers.

For integers, the transcoding to _CharT moved from _M_format_int function
to format. This makes the maximum size (that depends on sizeof(_Int)) of the
buffer known (__buf_size) and allows use local array of _CharT (__wbuf) for
the storage. The _M_format_int is modified to accept the string of _CharT.

For pointers, r16-7844-gbfc2b87f8244a1 modified _Pres_p and _Pres_P to have
same value as _Pres_x and _Pres_X, so format specifiers are subset of one
allowed for integers. In consequence we simply delegate to format method
of __formatter_int, reducing the code duplication. The set of allowed
specifiers is still limited per C++ standard by __formatter_ptr::parse.

This patch fix issue in __formatter_ptr::parse, where for 'p' and 'P' the value
of _M_alt was negated for _M_spec (result of previous parse) instead of __spec
(result of current parse), and adjust the __formatter_ptr default constructor
to set _M_spec._M_type and _M_spec._M_alt appropriately.

libstdc++-v3/ChangeLog:

	* include/std/format (__formatter_int::format): Handle transcoding
	to _CharT before calling _M_format_int.
	(__formatter_int::_M_format_int): Accept basic_string_view<_CharT>
	and remove transcoding.
	(__formatter_ptr::__formatter_ptr): Configure _M_spec member.
	(__formatter_ptr::parse): Negate _M_alt for __spec and not _M_spec.
	(__formatter_ptr::format): Delegate to __formatter_int.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>

diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 786edbe29b2038256a0704871aa19a8d9a0f76f3..cfb57f4a7a66b72f407b8ad6475073206ab61df7 100644 (file)
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -1647,7 +1647,8 @@ namespace __format
          if (_M_spec._M_type == _Pres_c)
            return _M_format_character(_S_to_character(__i), __fc);
 
-         char __buf[sizeof(_Int) * __CHAR_BIT__ + 3];
+         constexpr size_t __buf_size = sizeof(_Int) * __CHAR_BIT__ + 3;
+         char __buf[__buf_size];
          to_chars_result __res{};
 
          string_view __base_prefix;
@@ -1707,8 +1708,21 @@ namespace __format
            }
          __start = __format::__put_sign(__i, _M_spec._M_sign, __start - 1);
 
-         return _M_format_int(string_view(__start, __res.ptr - __start),
-                              __start_digits - __start, __fc);
+
+         string_view __narrow_str(__start, __res.ptr - __start);
+         size_t __prefix_len = __start_digits - __start;
+         if constexpr (is_same_v<char, _CharT>)
+           return _M_format_int(__narrow_str,  __prefix_len, __fc);
+#ifdef _GLIBCXX_USE_WCHAR_T
+         else
+           {
+             _CharT __wbuf[__buf_size];
+             size_t __n = __narrow_str.size();
+             std::__to_wstring_numeric(__narrow_str.data(), __n, __wbuf);
+             return _M_format_int(basic_string_view<_CharT>(__wbuf, __n),
+                                  __prefix_len, __fc);
+           }
+#endif
        }
 
       template<typename _Out>
@@ -1795,24 +1809,10 @@ namespace __format
 
       template<typename _Out>
        typename basic_format_context<_Out, _CharT>::iterator
-       _M_format_int(string_view __narrow_str, size_t __prefix_len,
+       _M_format_int(basic_string_view<_CharT> __str, size_t __prefix_len,
                      basic_format_context<_Out, _CharT>& __fc) const
        {
          size_t __width = _M_spec._M_get_width(__fc);
-
-         basic_string_view<_CharT> __str;
-         if constexpr (is_same_v<char, _CharT>)
-           __str = __narrow_str;
-#ifdef _GLIBCXX_USE_WCHAR_T
-         else
-           {
-             size_t __n = __narrow_str.size();
-             auto __p = (_CharT*)__builtin_alloca(__n * sizeof(_CharT));
-             std::__to_wstring_numeric(__narrow_str.data(), __n, __p);
-             __str = {__p, __n};
-           }
-#endif
-
          if (_M_spec._M_localized)
            {
              const auto& __l = __fc.locale();
@@ -2433,7 +2433,13 @@ namespace __format
   template<__format::__char _CharT>
     struct __formatter_ptr
     {
-      __formatter_ptr() = default;
+      constexpr
+      __formatter_ptr() noexcept
+      : _M_spec()
+      {
+       _M_spec._M_type = _Pres_p;
+       _M_spec._M_alt = true;
+      }
 
       constexpr
       __formatter_ptr(_Spec<_CharT> __spec) noexcept
@@ -2483,14 +2489,14 @@ namespace __format
        if (*__first == 'p')
          {
            __spec._M_type = _Pres_p;
-           _M_spec._M_alt = !_M_spec._M_alt;
+           __spec._M_alt = !__spec._M_alt;
            ++__first;
          }
 #if __glibcxx_format >= 202304L
        else if (*__first == 'P')
          {
            __spec._M_type = _Pres_P;
-           _M_spec._M_alt = !_M_spec._M_alt;
+           __spec._M_alt = !__spec._M_alt;
            ++__first;
          }
 #endif
@@ -2506,57 +2512,7 @@ namespace __format
        format(const void* __v, basic_format_context<_Out, _CharT>& __fc) const
        {
          auto __u = reinterpret_cast<__UINTPTR_TYPE__>(__v);
-         char __buf[2 + sizeof(__v) * 2];
-         auto [__ptr, __ec] = std::to_chars(__buf + 2, std::end(__buf),
-                                            __u, 16);
-         int __n = __ptr - __buf;
-         __buf[0] = '0';
-         __buf[1] = 'x';
-#if __glibcxx_format >= 202304L
-         if (_M_spec._M_type == __format::_Pres_P)
-           {
-             __buf[1] = 'X';
-             for (auto __p = __buf + 2; __p != __ptr; ++__p)
-#if __has_builtin(__builtin_toupper)
-               *__p = __builtin_toupper(*__p);
-#else
-               *__p = std::toupper(*__p);
-#endif
-           }
-#endif
-
-         basic_string_view<_CharT> __str;
-         if constexpr (is_same_v<_CharT, char>)
-           __str = string_view(__buf, __n);
-#ifdef _GLIBCXX_USE_WCHAR_T
-         else
-           {
-             auto __p = (_CharT*)__builtin_alloca(__n * sizeof(_CharT));
-             std::__to_wstring_numeric(__buf, __n, __p);
-             __str = wstring_view(__p, __n);
-           }
-#endif
-
-#if __glibcxx_format >= 202304L
-         if (_M_spec._M_zero_fill)
-           {
-             size_t __width = _M_spec._M_get_width(__fc);
-             if (__width <= __str.size())
-               return __format::__write(__fc.out(), __str);
-
-             auto __out = __fc.out();
-             // Write "0x" or "0X" prefix before zero-filling.
-             __out = __format::__write(std::move(__out), __str.substr(0, 2));
-             __str.remove_prefix(2);
-             size_t __nfill = __width - __n;
-             return __format::__write_padded(std::move(__out), __str,
-                                             __format::_Align_right,
-                                             __nfill, _CharT('0'));
-           }
-#endif
-
-         return __format::__write_padded_as_spec(__str, __n, __fc, _M_spec,
-                                                 __format::_Align_right);
+         return __formatter_int<_CharT>(_M_spec).format(__u, __fc);
        }
 
     private:
@@ -2571,7 +2527,7 @@ namespace __format
        }
       }
 
-      __format::_Spec<_CharT> _M_spec{};
+      __format::_Spec<_CharT> _M_spec;
     };
 
 } // namespace __format