On 17/02/20 15:32 +0000, Jonathan Wakely wrote:
Many uses of std::numeric_limits in C++17 and C++20 features only really need the min(), max() and digits constants for integral types. By adding __detail::__int_limits we can avoid including the whole <limits> header.The <limits> header isn't especially large, but avoiding it still gives small savings in compilation time and memory usage for the compiler. There are also C++11 features that could benefit from this change (e.g. <bits/hashtable_policy.h> and <bits/uniform_int_dist.h>) but I won't change those until stage 1. The implementation of __int_limits assumes two's complement integers, which is true for all targets supported by GCC. PR libstdc++/92546 (partial) * include/Makefile.am: Add new header. * include/Makefile.in: Regenerate. * include/bits/int_limits.h: New header. * include/bits/parse_numbers.h (__select_int::_Select_int): Replace numeric_limits with __detail::__int_limits. * include/std/bit (__rotl, __rotr, __countl_zero, __countl_one) (__countr_zero, __countr_one, __popcount, __ceil2, __floor2, __log2p1): Likewise. * include/std/charconv (__to_chars_8, __from_chars_binary) (__from_chars_alpha_to_num, from_chars): Likewise. * include/std/memory_resource (polymorphic_allocator::allocate) (polymorphic_allocator::allocate_object): Likewise. * include/std/string_view (basic_string_view::_S_compare): Likewise. * include/std/utility (in_range): Likewise. * testsuite/20_util/integer_comparisons/in_range_neg.cc: Adjust for extra error about incomplete type __int_limits<bool>. * testsuite/26_numerics/bit/bit.count/countl_one.cc: Include <limits>. * testsuite/26_numerics/bit/bit.count/countl_zero.cc: Likewise. * testsuite/26_numerics/bit/bit.count/countr_one.cc: Likewise. * testsuite/26_numerics/bit/bit.count/countr_zero.cc: Likewise. * testsuite/26_numerics/bit/bit.count/popcount.cc: Likewise. * testsuite/26_numerics/bit/bit.pow.two/ceil2_neg.cc: Likewise. * testsuite/26_numerics/bit/bit.pow.two/ceil2.cc: Likewise. * testsuite/26_numerics/bit/bit.pow.two/floor2.cc: Likewise. * testsuite/26_numerics/bit/bit.pow.two/ispow2.cc: Likewise. * testsuite/26_numerics/bit/bit.pow.two/log2p1.cc: Likewise. * testsuite/26_numerics/bit/bit.rotate/rotl.cc: Likewise. * testsuite/26_numerics/bit/bit.rotate/rotr.cc: Likewise. Tested powerpc64le-linux, committed to master.
I think I probably should have just used __gnu_cxx::__numeric_traits instead of adding a new trait. That already has min, max and digits and is much smaller than the whole of <limits>.
