From: Jonathan Wakely Date: Tue, 1 Sep 2020 17:18:26 +0000 (+0100) Subject: libstdc++: Constrain chrono::duration conversions [LWG 2094] X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=b1850c617b14eedaf60b358f3b7d4707cff73b8a;p=gcc.git libstdc++: Constrain chrono::duration conversions [LWG 2094] The chrono::duration constructor that converts from another duration type is meant to be constrained so that it doesn't participate in overload resolution if the ratio of the periods cannot be represented as a std::ratio. Because our std::ratio_divide is not SFINAE-friendly the evaluation of __is_harmonic results in an error outside the immediate context when an overflow occurs. I intend to make ratio_divide (and ratio_multiply) SFINAE-friendly in a future patch, but for now this patch just introduces a new SFINAE-friendly alias template for the division. The standard doesn't require it, but it also seems right to constrain the constructor with std::is_convertible_v<_Rep2, rep>. libstdc++-v3/ChangeLog: * include/std/chrono (duration::_S_gcd(intmax_t, intmax_t)): New helper function for finding GCD of two positive intmax_t values. (duration::__divide): New helper alias for dividing one period by another. (duration::__is_harmonic): Use __divide not ratio_divide. (duration(const duration&)): Require the duration rep types to be convertible. * testsuite/20_util/duration/cons/dr2094.cc: New test. * testsuite/20_util/duration/requirements/reduced_period.cc: Fix definition of unused member functions in test type. * testsuite/20_util/duration/requirements/typedefs_neg2.cc: Adjust expected errors. --- diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono index 524d23ea6a7..1682263fd9f 100644 --- a/libstdc++-v3/include/std/chrono +++ b/libstdc++-v3/include/std/chrono @@ -424,10 +424,28 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION template using __is_float = treat_as_floating_point<_Rep2>; + static constexpr intmax_t + _S_gcd(intmax_t __m, intmax_t __n) noexcept + { + // Duration only allows positive periods so we don't need to + // support negative values here (unlike __static_gcd and std::gcd). + return (__m == 0) ? __n : (__n == 0) ? __m : _S_gcd(__n, __m % __n); + } + + // _GLIBCXX_RESOLVE_LIB_DEFECTS + // 2094. overflow shouldn't participate in overload resolution + // 3090. What is [2094] intended to mean? + // This only produces a valid type if no overflow occurs. + template + using __divide = ratio<(_R1::num / __gcd1) * (_R2::den / __gcd2), + (_R1::den / __gcd2) * (_R2::num / __gcd1)>; + // _Period2 is an exact multiple of _Period template using __is_harmonic - = __bool_constant::den == 1>; + = __bool_constant<__divide<_Period2, _Period>::den == 1>; public: @@ -453,6 +471,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION : __r(static_cast(__rep)) { } template, __or_<__is_float, __and_<__is_harmonic<_Period2>, __not_<__is_float<_Rep2>>>>>> diff --git a/libstdc++-v3/testsuite/20_util/duration/cons/dr2094.cc b/libstdc++-v3/testsuite/20_util/duration/cons/dr2094.cc new file mode 100644 index 00000000000..859c14fe693 --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/duration/cons/dr2094.cc @@ -0,0 +1,64 @@ +// Copyright (C) 2020 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// . + +// { dg-do compile { target c++11 } } + +#include + +void +test01() +{ + using namespace std::chrono; + using std::exa; + + // LWG 2094 + // duration conversion overflow shouldn't participate in overload resolution + bool f(milliseconds); + void f(seconds); + duration r(1); + f(r); +} + +void +test02() +{ + struct Number + { + explicit + Number(int t = 0) : i(t) + { } + + int i = 0; + + Number& operator+=(Number n) { i += n.i; return *this; } + Number& operator-=(Number n) { i -= n.i; return *this; } + Number& operator*=(Number n) { i *= n.i; return *this; } + Number& operator/=(Number n) { i /= n.i; return *this; } + Number& operator%=(Number n) { i %= n.i; return *this; } + + Number operator+(Number n) { return Number{ i + n.i }; } + Number operator-(Number n) { return Number{ i - n.i }; } + Number operator*(Number n) { return Number{ i * n.i }; } + Number operator/(Number n) { return Number{ i / n.i }; } + Number operator%(Number n) { return Number{ i % n.i }; } + }; + + using std::chrono::duration; + + static_assert( ! std::is_constructible, duration>(), + "duration(const duration&) constrained on R2 -> R conversion" ); +} diff --git a/libstdc++-v3/testsuite/20_util/duration/requirements/reduced_period.cc b/libstdc++-v3/testsuite/20_util/duration/requirements/reduced_period.cc index 4c7472699d2..87124e526b3 100644 --- a/libstdc++-v3/testsuite/20_util/duration/requirements/reduced_period.cc +++ b/libstdc++-v3/testsuite/20_util/duration/requirements/reduced_period.cc @@ -151,11 +151,11 @@ struct Number Number& operator/=(Number n) { i /= n.i; return *this; } Number& operator%=(Number n) { i %= n.i; return *this; } - Number operator+(Number n) { return { i + n.i }; } - Number operator-(Number n) { return { i - n.i }; } - Number operator*(Number n) { return { i * n.i }; } - Number operator/(Number n) { return { i / n.i }; } - Number operator%(Number n) { return { i % n.i }; } + Number operator+(Number n) { return Number{ i + n.i }; } + Number operator-(Number n) { return Number{ i - n.i }; } + Number operator*(Number n) { return Number{ i * n.i }; } + Number operator/(Number n) { return Number{ i / n.i }; } + Number operator%(Number n) { return Number{ i % n.i }; } }; namespace std diff --git a/libstdc++-v3/testsuite/20_util/duration/requirements/typedefs_neg2.cc b/libstdc++-v3/testsuite/20_util/duration/requirements/typedefs_neg2.cc index 02dab73b0eb..e44b01c4c82 100644 --- a/libstdc++-v3/testsuite/20_util/duration/requirements/typedefs_neg2.cc +++ b/libstdc++-v3/testsuite/20_util/duration/requirements/typedefs_neg2.cc @@ -32,4 +32,5 @@ void test01() // { dg-error "must be a specialization of ratio" "" { target *-*-* } 0 } // { dg-prune-output "'num' is not a member of 'int'" } +// { dg-prune-output "'den' is not a member of 'int'" } // { dg-prune-output "'int' is not a class, struct, or union type" }