Message ID | 20220926152258.20921-1-polacek@redhat.com |
---|---|
State | New |
Headers | show |
Series | c++: Instantiate less when evaluating __is_convertible | expand |
On Mon, 26 Sep 2022, Marek Polacek via Gcc-patches wrote: > Jon reported that evaluating __is_convertible in this test leads to > instantiating char_traits<char>::eq, which is invalid (because we > are trying to call a member function on a char) and so we fail to > compile the test. __is_convertible doesn't and shouldn't need to > instantiate so much, so let's limit it with a cp_unevaluated guard. > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? > > PR c++/106784 > > gcc/cp/ChangeLog: > > * method.cc (is_convertible): Use cp_unevaluated. I think is_nothrow_convertible would need cp_unevaluated too (or maybe we should define is_nothrow_convertible in terms of is_convertible). And the testcase can probably be minimized to something like: struct A; struct B { template<class T> B(const T&) noexcept { T::nonexistent; } }; static_assert(__is_convertible(const A&, B)); static_assert(__is_nothrow_convertible(const A&, B)); > > gcc/testsuite/ChangeLog: > > * g++.dg/ext/is_convertible3.C: New test. > --- > gcc/cp/method.cc | 1 + > gcc/testsuite/g++.dg/ext/is_convertible3.C | 66 ++++++++++++++++++++++ > 2 files changed, 67 insertions(+) > create mode 100644 gcc/testsuite/g++.dg/ext/is_convertible3.C > > diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc > index c35a59fe56c..45f70f5d3f3 100644 > --- a/gcc/cp/method.cc > +++ b/gcc/cp/method.cc > @@ -2246,6 +2246,7 @@ is_convertible (tree from, tree to) > { > if (VOID_TYPE_P (from) && VOID_TYPE_P (to)) > return true; > + cp_unevaluated u; > tree expr = build_stub_object (from); > expr = perform_implicit_conversion (to, expr, tf_none); > if (expr == error_mark_node) > diff --git a/gcc/testsuite/g++.dg/ext/is_convertible3.C b/gcc/testsuite/g++.dg/ext/is_convertible3.C > new file mode 100644 > index 00000000000..c817dc6f146 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/ext/is_convertible3.C > @@ -0,0 +1,66 @@ > +// PR c++/106784 > +// { dg-do compile { target c++11 } } > +// Make sure we don't reject this at runtime by trying to instantiate > +// char_traits<CharT>::eq(CharT, CharT) while evaluating __is_convertible. > + > +template<bool B> > +struct bool_constant { static constexpr bool value = B; }; > +using true_type = bool_constant<true>; > +using false_type = bool_constant<false>; > + > +template<typename T> struct is_void : false_type { }; > +template<> struct is_void<void> : true_type { }; > + > +template<typename T> T&& declval(); > + > +template<bool> struct enable_if { }; > +template<> struct enable_if<true> { using type = void; }; > +template<bool B> using enable_if_t = typename enable_if<B>::type; > + > +template<typename _From, typename _To> > + struct is_convertible > + : public bool_constant<__is_convertible(_From, _To)> > + { }; > + > +template<class CharT> > +struct char_traits > +{ > + static unsigned long length(const char* s) { eq(*s, *s); return 0; } > + > + static void eq(CharT l, CharT r) noexcept { l.f(r); } > +}; > + > +template<class CharT> > +struct basic_string_view > +{ > + using traits_type = char_traits<CharT>; > + > + constexpr basic_string_view() = default; > + constexpr basic_string_view(const basic_string_view&) = default; > + > + constexpr > + basic_string_view(const CharT* __str) noexcept > + : _M_len{traits_type::length(__str)} > + { } > + > + unsigned long _M_len = 0; > +}; > + > +template<class CharT> > +struct basic_string > +{ > + template<class T> > + enable_if_t<is_convertible<const T&, basic_string_view<CharT>>::value > + && !is_convertible<const T&, const char*>::value> > + replace(int, T) { } > + > + void replace(unsigned long, const char*) { } > + > + void replace(const char* s) { replace(1, s); } > +}; > + > +int main() > +{ > + basic_string<char> s; > + s.replace(""); > +} > > base-commit: 2460f7cdef7ef9c971de79271afc0db73687a272 > -- > 2.37.3 > >
On Mon, 26 Sept 2022 at 16:23, Marek Polacek wrote: > > Jon reported that evaluating __is_convertible in this test leads to > instantiating char_traits<char>::eq, which is invalid (because we > are trying to call a member function on a char) N.B. in the original code wasn't trying to do something dumb like call a member function on a char, but it was using basic_string_view<X> where X is a class type without an operator== and so char_traits<X>::eq was invalid. I changed it to just use basic_string_view<char> and changed char_traits::eq to do something different, that was invalid for char. I can provide a less silly test case if you like, but I don't think it matters for the purposes of the testsuite.
On 9/26/22 11:51, Patrick Palka wrote: > On Mon, 26 Sep 2022, Marek Polacek via Gcc-patches wrote: > >> Jon reported that evaluating __is_convertible in this test leads to >> instantiating char_traits<char>::eq, which is invalid (because we >> are trying to call a member function on a char) and so we fail to >> compile the test. __is_convertible doesn't and shouldn't need to >> instantiate so much, so let's limit it with a cp_unevaluated guard. >> >> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? >> >> PR c++/106784 >> >> gcc/cp/ChangeLog: >> >> * method.cc (is_convertible): Use cp_unevaluated. > > I think is_nothrow_convertible would need cp_unevaluated too (or maybe we > should define is_nothrow_convertible in terms of is_convertible). Agreed. > And the testcase can probably be minimized to something like: > > struct A; > struct B { template<class T> B(const T&) noexcept { T::nonexistent; } }; > > static_assert(__is_convertible(const A&, B)); > static_assert(__is_nothrow_convertible(const A&, B)); > >> >> gcc/testsuite/ChangeLog: >> >> * g++.dg/ext/is_convertible3.C: New test. >> --- >> gcc/cp/method.cc | 1 + >> gcc/testsuite/g++.dg/ext/is_convertible3.C | 66 ++++++++++++++++++++++ >> 2 files changed, 67 insertions(+) >> create mode 100644 gcc/testsuite/g++.dg/ext/is_convertible3.C >> >> diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc >> index c35a59fe56c..45f70f5d3f3 100644 >> --- a/gcc/cp/method.cc >> +++ b/gcc/cp/method.cc >> @@ -2246,6 +2246,7 @@ is_convertible (tree from, tree to) >> { >> if (VOID_TYPE_P (from) && VOID_TYPE_P (to)) >> return true; >> + cp_unevaluated u; >> tree expr = build_stub_object (from); >> expr = perform_implicit_conversion (to, expr, tf_none); >> if (expr == error_mark_node) >> diff --git a/gcc/testsuite/g++.dg/ext/is_convertible3.C b/gcc/testsuite/g++.dg/ext/is_convertible3.C >> new file mode 100644 >> index 00000000000..c817dc6f146 >> --- /dev/null >> +++ b/gcc/testsuite/g++.dg/ext/is_convertible3.C >> @@ -0,0 +1,66 @@ >> +// PR c++/106784 >> +// { dg-do compile { target c++11 } } >> +// Make sure we don't reject this at runtime by trying to instantiate >> +// char_traits<CharT>::eq(CharT, CharT) while evaluating __is_convertible. >> + >> +template<bool B> >> +struct bool_constant { static constexpr bool value = B; }; >> +using true_type = bool_constant<true>; >> +using false_type = bool_constant<false>; >> + >> +template<typename T> struct is_void : false_type { }; >> +template<> struct is_void<void> : true_type { }; >> + >> +template<typename T> T&& declval(); >> + >> +template<bool> struct enable_if { }; >> +template<> struct enable_if<true> { using type = void; }; >> +template<bool B> using enable_if_t = typename enable_if<B>::type; >> + >> +template<typename _From, typename _To> >> + struct is_convertible >> + : public bool_constant<__is_convertible(_From, _To)> >> + { }; >> + >> +template<class CharT> >> +struct char_traits >> +{ >> + static unsigned long length(const char* s) { eq(*s, *s); return 0; } >> + >> + static void eq(CharT l, CharT r) noexcept { l.f(r); } >> +}; >> + >> +template<class CharT> >> +struct basic_string_view >> +{ >> + using traits_type = char_traits<CharT>; >> + >> + constexpr basic_string_view() = default; >> + constexpr basic_string_view(const basic_string_view&) = default; >> + >> + constexpr >> + basic_string_view(const CharT* __str) noexcept >> + : _M_len{traits_type::length(__str)} >> + { } >> + >> + unsigned long _M_len = 0; >> +}; >> + >> +template<class CharT> >> +struct basic_string >> +{ >> + template<class T> >> + enable_if_t<is_convertible<const T&, basic_string_view<CharT>>::value >> + && !is_convertible<const T&, const char*>::value> >> + replace(int, T) { } >> + >> + void replace(unsigned long, const char*) { } >> + >> + void replace(const char* s) { replace(1, s); } >> +}; >> + >> +int main() >> +{ >> + basic_string<char> s; >> + s.replace(""); >> +} >> >> base-commit: 2460f7cdef7ef9c971de79271afc0db73687a272 >> -- >> 2.37.3 >> >> >
On Mon, Sep 26, 2022 at 05:02:36PM +0100, Jonathan Wakely wrote: > On Mon, 26 Sept 2022 at 16:23, Marek Polacek wrote: > > > > Jon reported that evaluating __is_convertible in this test leads to > > instantiating char_traits<char>::eq, which is invalid (because we > > are trying to call a member function on a char) > > N.B. in the original code wasn't trying to do something dumb like call > a member function on a char, but it was using basic_string_view<X> > where X is a class type without an operator== and so > char_traits<X>::eq was invalid. I changed it to just use > basic_string_view<char> and changed char_traits::eq to do something > different, that was invalid for char. Ack. > I can provide a less silly test case if you like, but I don't think it > matters for the purposes of the testsuite. I think no need to, I'm going to use Patrick's short test. Thanks, Marek
diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc index c35a59fe56c..45f70f5d3f3 100644 --- a/gcc/cp/method.cc +++ b/gcc/cp/method.cc @@ -2246,6 +2246,7 @@ is_convertible (tree from, tree to) { if (VOID_TYPE_P (from) && VOID_TYPE_P (to)) return true; + cp_unevaluated u; tree expr = build_stub_object (from); expr = perform_implicit_conversion (to, expr, tf_none); if (expr == error_mark_node) diff --git a/gcc/testsuite/g++.dg/ext/is_convertible3.C b/gcc/testsuite/g++.dg/ext/is_convertible3.C new file mode 100644 index 00000000000..c817dc6f146 --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/is_convertible3.C @@ -0,0 +1,66 @@ +// PR c++/106784 +// { dg-do compile { target c++11 } } +// Make sure we don't reject this at runtime by trying to instantiate +// char_traits<CharT>::eq(CharT, CharT) while evaluating __is_convertible. + +template<bool B> +struct bool_constant { static constexpr bool value = B; }; +using true_type = bool_constant<true>; +using false_type = bool_constant<false>; + +template<typename T> struct is_void : false_type { }; +template<> struct is_void<void> : true_type { }; + +template<typename T> T&& declval(); + +template<bool> struct enable_if { }; +template<> struct enable_if<true> { using type = void; }; +template<bool B> using enable_if_t = typename enable_if<B>::type; + +template<typename _From, typename _To> + struct is_convertible + : public bool_constant<__is_convertible(_From, _To)> + { }; + +template<class CharT> +struct char_traits +{ + static unsigned long length(const char* s) { eq(*s, *s); return 0; } + + static void eq(CharT l, CharT r) noexcept { l.f(r); } +}; + +template<class CharT> +struct basic_string_view +{ + using traits_type = char_traits<CharT>; + + constexpr basic_string_view() = default; + constexpr basic_string_view(const basic_string_view&) = default; + + constexpr + basic_string_view(const CharT* __str) noexcept + : _M_len{traits_type::length(__str)} + { } + + unsigned long _M_len = 0; +}; + +template<class CharT> +struct basic_string +{ + template<class T> + enable_if_t<is_convertible<const T&, basic_string_view<CharT>>::value + && !is_convertible<const T&, const char*>::value> + replace(int, T) { } + + void replace(unsigned long, const char*) { } + + void replace(const char* s) { replace(1, s); } +}; + +int main() +{ + basic_string<char> s; + s.replace(""); +}