On Fri, Oct 30, 2020 at 02:36:00AM +0000, Marek Polacek via Gcc-patches wrote:
> We may not call value_dependent_expression_p on expressions that are
> not potential constant expressions, otherwise value_d could crash,
> as I saw recently (in C++98). So beef up the checking in i_d_e_p.
>
> This revealed a curious issue: when we have __PRETTY_FUNCTION__ in
> a template function, we set its DECL_VALUE_EXPR to error_mark_node
> (cp_make_fname_decl), so potential_c_e returns false when it gets it,
> but value_dependent_expression_p handles it specially and says true.
> This broke lambda-generic-pretty1.C. So take care of that.
>
> And then also tweak uses_template_parms.
>
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
Hi,
This breaks the GCC build for msp430-elf. The large memory model
(-mlarge) uses __int20 pointers.
In file included from
/home/jozef/msp430/gcc/build-msp430/msp430-elf/large/libstdc++-v3/include/sstream:38,
from
../../../../../../libstdc++-v3/src/c++20/sstream-inst.cc:30:
/home/jozef/msp430/gcc/build-msp430/msp430-elf/large/libstdc++-v3/include/istream:
In function 'std::basic_istream<_CharT, _Traits>&
std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT (&)[_Num])':
/home/jozef/msp430/gcc/build-msp430/msp430-elf/large/libstdc++-v3/include/istream:840:26:
error: non-constant condition for static assertion
840 | static_assert(_Num <=
__gnu_cxx::__numeric_traits<streamsize>::__max);
|
~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/jozef/msp430/gcc/build-msp430/msp430-elf/large/libstdc++-v3/include/istream:840:26:
error: the value of '__gnu_cxx::__numeric_traits_integer<__int20>::__max' is
not usable in a constant expression
In file included from
/home/jozef/msp430/gcc/build-msp430/msp430-elf/large/libstdc++-v3/include/bits/stl_algobase.h:63,
from
/home/jozef/msp430/gcc/build-msp430/msp430-elf/large/libstdc++-v3/include/bits/char_traits.h:39,
from
/home/jozef/msp430/gcc/build-msp430/msp430-elf/large/libstdc++-v3/include/ios:40,
from
/home/jozef/msp430/gcc/build-msp430/msp430-elf/large/libstdc++-v3/include/istream:38,
from
/home/jozef/msp430/gcc/build-msp430/msp430-elf/large/libstdc++-v3/include/sstream:38,
from
../../../../../../libstdc++-v3/src/c++20/sstream-inst.cc:30:
/home/jozef/msp430/gcc/build-msp430/msp430-elf/large/libstdc++-v3/include/ext/numeric_traits.h:78:27:
note: '__gnu_cxx::__numeric_traits_integer<__int20>::__max' was not
initialized with a constant expression
78 | static const _Value __max = __glibcxx_max(_Value);
| ^~~~~
make[9]: *** [Makefile:550: sstream-inst.lo] Error 1
>
> gcc/cp/ChangeLog:
>
> * constexpr.c (potential_constant_expression_1): Treat
> __PRETTY_FUNCTION__ inside a template function as
> potentially-constant.
> * pt.c (uses_template_parms): Call
> instantiation_dependent_expression_p instead of
> value_dependent_expression_p.
> (instantiation_dependent_expression_p): Check
> potential_constant_expression before calling
> value_dependent_expression_p.
> ---
> gcc/cp/constexpr.c | 5 +++++
> gcc/cp/pt.c | 5 +++--
> 2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
> index b46824f128d..c257dfcb2e6 100644
> --- a/gcc/cp/constexpr.c
> +++ b/gcc/cp/constexpr.c
> @@ -7716,6 +7716,11 @@ potential_constant_expression_1 (tree t, bool
> want_rval, bool strict, bool now,
> }
> return false;
> }
> + /* Treat __PRETTY_FUNCTION__ inside a template function as
> + potentially-constant. */
> + else if (DECL_PRETTY_FUNCTION_P (t)
> + && DECL_VALUE_EXPR (t) == error_mark_node)
> + return true;
> return RECUR (DECL_VALUE_EXPR (t), rval);
> }
> if (want_rval
> diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
> index b569644514c..c419fb470ee 100644
> --- a/gcc/cp/pt.c
> +++ b/gcc/cp/pt.c
> @@ -10755,7 +10755,7 @@ uses_template_parms (tree t)
> else if (t == error_mark_node)
> dependent_p = false;
> else
> - dependent_p = value_dependent_expression_p (t);
> + dependent_p = instantiation_dependent_expression_p (t);
>
> processing_template_decl = saved_processing_template_decl;
>
> @@ -27293,7 +27293,8 @@ bool
> instantiation_dependent_expression_p (tree expression)
> {
> return (instantiation_dependent_uneval_expression_p (expression)
> - || value_dependent_expression_p (expression));
> + || (potential_constant_expression (expression)
> + && value_dependent_expression_p (expression)));
> }
>
> /* Like type_dependent_expression_p, but it also works while not processing
>
> base-commit: 4f0606fe4bbf1346f83dd4d0c9060c6b46672a7d
> --
> 2.28.0
