[Bug c++/58848] New: constexpr function allows throw

[Bug c++/58848] New: constexpr function allows throw

[mib.bugzilla at gmail dot com]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58848

            Bug ID: 58848
           Summary: constexpr function allows throw
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mib.bugzilla at gmail dot com

Created attachment 31072
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31072&action=edit
should get compilation error

A simple test case rejects throw inside constexpr function, but a more
complicated test case allows the throw.  Attaching 2 test cases

Bad:

 g++ constexp_error.cpp -std=c++0x
-bash-4.1$ ./a.out
fail, exception raised

Good:
 g++ constexp_ok.cpp -std=c++0x
constexp_ok.cpp: In function âint main()â:
constexp_ok.cpp:15:47:   in constexpr expansion of
âfum<DUMMY>::numSubEntities<int>(5)â
constexp_ok.cpp:8:73: error: expression â<throw-expression>â is not a
constant-expression
        throw std::out_of_range("a point has only subentities of codim=0");

gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/rdrive/ref/gcc/4.8.1/rhel60/efi2/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.8.1/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with:
/rusers/sys_cron/grab_gcc/downloads_rel/4.8.1/gcc-4.8.1/configure
--prefix=/rdrive/ref/gcc/4.8.1/rhel60/efi2
--enable-languages=c,c++,objc,fortran --disable-multilib --enable-bootstrap
--target=x86_64-unknown-linux-gnu --disable-bootstrap --enable-decimal-float
--with-gmp=/rusers/sys_cron/grab_gcc/downloads_rel/lib/efi2
--with-mpfr=/rusers/sys_cron/grab_gcc/downloads_rel/lib/efi2
--with-mpc=/rusers/sys_cron/grab_gcc/downloads_rel/lib/efi2
Thread model: posix
gcc version 4.8.1 (GCC)
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Subject: [Bug c++/58848] constexpr function allows throw
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idX848

--- Comment #1 from mib.bugzilla at gmail dot com ---
Created attachment 31073
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id1073&actioníit
simpler test case gets compilation error (good)

both test cases should get a compilation error because of the throw.

[Bug c++/58848] constexpr function allows throw

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58848

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler@googlemail.
                   |                            |com

--- Comment #2 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
I cannot follow your argumentation for constexp_error.cpp: The main function
invokes

ReferenceElement<RefElType::POINT>::numSubEntities(7)

This function is declared as

  static inline unsigned numSubEntities(int codim) {
    return typeTraits_<RefElType::POINT>::numSubEntities(codim);
  }

Note in particular that this is *not* a constexpr function. Now it delegates to
typeTraits_<RefElType::POINT>::numSubEntities, which is defined as:

  static constexpr unsigned numSubEntities(int codim) {
    return codim==0 ? 11 : throw 20;
  }

This is a constexpr function, but it is not called with constant arguments that
require the evaluation of this function in a constexpr context. Thus, throwing
an exception is valid here.

So what is the problem?
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From: "schwab@linux-m68k.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug testsuite/58851] New: FAIL: gfortran.dg/unlimited_polymorphic_13.f90  -O0  execution test
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idX851

            Bug ID: 58851
           Summary: FAIL: gfortran.dg/unlimited_polymorphic_13.f90  -O0
                    execution test
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: testsuite
          Assignee: unassigned at gcc dot gnu.org
          Reporter: schwab@linux-m68k.org
            Blocks: 58793
            Target: i386-*-*, m68k-*-*

The storage size of real(kind\x10) is target-dependent.  On i386 and m68k it is
96, not 128.

[Bug c++/58848] constexpr function allows throw

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58848

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The initializer for ReferenceElement<RefElType::POINT>::v calls the function in
a constant expression, but G++ doesn't diagnose it unless you instantiate that
member.

You get an error if you do:

int main() {
  return ReferenceElement<RefElType::POINT>::v;
}