Re: [PATCH] Fix _GLIBCXX_DEBUG tests

[Jonathan Wakely <jwakely@redhat.com>]

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On 15/12/20 15:20 +0000, Jonathan Wakely wrote:
>On 14/12/20 22:36 +0100, François Dumont wrote:
>>On 14/12/20 11:08 am, Jonathan Wakely wrote:
>>>
>>>
>>>On Mon, 14 Dec 2020, 06:51 François Dumont via Libstdc++, 
>>><libstdc++@gcc.gnu.org <mailto:libstdc%2B%2B@gcc.gnu.org>> wrote:
>>>
>>>   On 13/12/20 11:17 pm, Jonathan Wakely wrote:
>>>   > On 13/12/20 15:52 +0100, François Dumont via Libstdc++ wrote:
>>>   >> Some tests are XPASS because array assertions have been
>>>   disabled for
>>>   >> a good reason in C++11.
>>>   >>
>>>   >> I wonder if the respective non-constexpr _GLIBCXX_ASSERTION checks
>>>   >> shouldn't target C++14 too. At the moment they are failing as
>>>   >> expected but because of an Undefined Behavior no ?
>>>   >
>>>   > Hmm, maybe my "fix" for the bug was too hasty, and I should have
>>>   done
>>>   > this instead:
>>>   >
>>>   > --- a/libstdc++-v3/include/bits/c++config
>>>   > +++ b/libstdc++-v3/include/bits/c++config
>>>   > @@ -684,7 +684,7 @@ namespace std
>>>   >
>>>   >  #undef _GLIBCXX_HAS_BUILTIN
>>>   >
>>>   > -#if _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
>>>   > +#if _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED && __cplusplus >=
>>>   > 201402L
>>>   >  # define __glibcxx_assert_1(_Condition)                \
>>>   >      if (__builtin_is_constant_evaluated())     \
>>>   >       {                                         \
>>>   >
>>>   > That would allow us to keep the std::array runtime assertions for
>>>   > C++11, and only disable them in constexpr contexts.
>>>
>>>   I already tried to restore this check in C++11 runtime without
>>>   success
>>>   but I didn't try this approach.
>>>
>>>   I'll have a try but C++11 forces constexpr to be just a return
>>>   statement
>>>   so I fear that it won't appreciate the additional assertion.
>>>
>>>
>>>
>>>Ah yes, we'd need something like Daniel suggested, and it's not 
>>>worth it just for C++11.
>>>
>>>Just limiting the tests to c++14 is fine.
>>>
>>>
>>Attached patch committed then.
>
>Thanks.

I'm committing this anyway, because although it won't fix those tests,
it is useless to check __builtin_is_constant_evaluated() in C++11
mode.

Tested powerpc64le-linux, normal mode and debug mode. Pushed to trunk.



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commit f072d1021e3e80539afe58ba0019fafa9a0bb7a6
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Dec 15 15:39:58 2020

    libstdc++: Do not define constexpr assertions for C++11
    
    There's no point even checking is_constant_evaluated() in C++11 mode,
    because the 'if' statement used for the assertion wouldn't be valid in a
    C++11 constexpr function anyway.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/c++config (__glibcxx_assert_1): Define as empty
            for C++11.

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index 27302ed392e..155d0f46b16 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -684,7 +684,7 @@ namespace std
 
 #undef _GLIBCXX_HAS_BUILTIN
 
-#if _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
+#if _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED && __cplusplus >= 201402L
 # define __glibcxx_assert_1(_Condition)		\
     if (__builtin_is_constant_evaluated())	\
      {						\