On Mon, 17 Oct 2022 at 17:27, Patrick Palka via Libstdc++ <libstd...@gcc.gnu.org> wrote: > > It looks like the constexpr <charconv> commit r13-3313-g378a0f1840e694 > caused some modules regressions: > > FAIL: g++.dg/modules/xtreme-header-4_b.C -std=c++2b (test for excess errors) > FAIL: g++.dg/modules/xtreme-header_b.C -std=c++2b (test for excess errors) > > Like PR105297, the problem seems to be the local class from > __from_chars_alnum_to_val ending up as the type of a namespace-scope > entity (the variable template __detail::__table in this case). > > This patch works around this modules issue by using an ordinary class > instead of a local class. Also, I suppose we might as well use a static > data member to define the table once for all dialects instead of having > to define it twice in C++23 mode, once as a static local variable (which > isn't usable during constexpr evaluation) and again as a variable template > (which is). > > Tested on x86_64-pc-linux-gnu, does this look OK for trunk? Diff > generated with -w to ignore noisy whitespace changes.
OK, thanks. > > libstdc++-v3/ChangeLog: > > * include/std/charconv (__detail::__from_chars_alnum_to_val_table): > Redefine as a class template containing type, value and _S_table > members. Don't use a local class as the table type. > (__detail::__table): Remove. > (__detail::__from_chars_alnum_to_val): Adjust after the above. > --- > libstdc++-v3/include/std/charconv | 31 ++++++++++++++----------------- > 1 file changed, 14 insertions(+), 17 deletions(-) > > diff --git a/libstdc++-v3/include/std/charconv > b/libstdc++-v3/include/std/charconv > index 7aefdd3298c..c157d4c74ab 100644 > --- a/libstdc++-v3/include/std/charconv > +++ b/libstdc++-v3/include/std/charconv > @@ -413,14 +413,19 @@ namespace __detail > return true; > } > > + template<bool _DecOnly> > + struct __from_chars_alnum_to_val_table > + { > + struct type { unsigned char __data[1u << __CHAR_BIT__] = {}; }; > + > // Construct and return a lookup table that maps 0-9, A-Z and a-z to > their > // corresponding base-36 value and maps all other characters to 127. > - constexpr auto > - __from_chars_alnum_to_val_table() > + static constexpr type > + _S_table() > { > constexpr unsigned char __lower_letters[27] = > "abcdefghijklmnopqrstuvwxyz"; > constexpr unsigned char __upper_letters[27] = > "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; > - struct { unsigned char __data[1u << __CHAR_BIT__] = {}; } __table; > + type __table; > for (auto& __entry : __table.__data) > __entry = 127; > for (int __i = 0; __i < 10; ++__i) > @@ -433,10 +438,11 @@ namespace __detail > return __table; > } > > -#if __cpp_lib_constexpr_charconv > - template<bool _DecOnly> > - inline constexpr auto __table = __from_chars_alnum_to_val_table(); > -#endif > + // This initializer is made superficially dependent in order > + // to prevent the compiler from wastefully constructing the > + // table ahead of time when it's not needed. > + static constexpr type value = (_DecOnly, _S_table()); > + }; > > // If _DecOnly is true: if the character is a decimal digit, then > // return its corresponding base-10 value, otherwise return a value >= 127. > @@ -449,16 +455,7 @@ namespace __detail > if _GLIBCXX17_CONSTEXPR (_DecOnly) > return static_cast<unsigned char>(__c - '0'); > else > - { > -#if __cpp_lib_constexpr_charconv > - if (std::__is_constant_evaluated()) > - return __table<_DecOnly>.__data[__c]; > -#endif > - // This initializer is deliberately made dependent in order to work > - // around modules bug PR105322. > - static constexpr auto __table = (_DecOnly, > __from_chars_alnum_to_val_table()); > - return __table.__data[__c]; > - } > + return __from_chars_alnum_to_val_table<_DecOnly>::value.__data[__c]; > } > > /// std::from_chars implementation for integers in a power-of-two base. > -- > 2.38.0.68.ge85701b4af >