[Bug c++/101371] New: constexpr expansions trigger internal Compiler Error

[Bug c++/101371] New: constexpr expansions trigger internal Compiler Error

[warren_graeme at yahoo dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371

            Bug ID: 101371
           Summary: constexpr expansions trigger internal Compiler Error
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: warren_graeme at yahoo dot co.uk
  Target Milestone: ---

Created attachment 51115
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51115&action=edit
preprocessed source code

Hello,

When attempting to compile a C++ function with gcc I have triggered an Internal
Compiler Error. I achieved this with the following commands:

g++-7 --std=c++17 -E init.cc > init.ii
g++-7 --std=c++17 -c init.ii



1) the peccant function (init.cc) follows:

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
#include <array>
#include <bitset>
using namespace std;

constexpr unsigned short N_citruss = 8;

enum class berry: unsigned{cran, straw, rasp, bil, black, huckle, elder,
goose};
constexpr berry operator++(berry& b, int) noexcept {
        return b = berry(static_cast<int>(b) + 1); }

struct berry_set_CX{
        bitset<8> bset;
        constexpr berry_set_CX(const bitset<8>& bits) noexcept: bset(bits) {}
        constexpr berry_set_CX(const char  bits) noexcept: bset(bits) {}
        constexpr berry_set_CX() noexcept : bset() {}
        constexpr berry_set_CX(const berry_set_CX& rhs) noexcept :
bset(rhs.bset) {}
};

struct bersets_by_citrus_CX{
        array<berry_set_CX, N_citruss> berrysets;
};

struct entree0_CX{
        bersets_by_citrus_CX passes;
        constexpr entree0_CX(const bersets_by_citrus_CX& bsbc) noexcept :
passes(bsbc) {}
};

struct berrybox_CX{
        constexpr entree0_CX make_entree() const noexcept {
                bersets_by_citrus_CX bsbc {};
                return entree0_CX(bsbc);
        }
        constexpr berrybox_CX(berry w, berry_set_CX hs) noexcept {}
};

void init() noexcept{
        const berry_set_CX fixed(bitset<8>(1));
        for (berry root_berry = berry::cran; root_berry <= berry::goose;
root_berry++){
                berrybox_CX nu_cs0(root_berry, fixed);
                const entree0_CX& pas = nu_cs0.make_entree();
        }
        return;
}
--------------------------------------------------------------------------

2) the preprocessed source file (init.ii) is attached;

3) the compiler version used (gcc -v output)  is:

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib64/gcc/x86_64-suse-linux/7/lto-wrapper
OFFLOAD_TARGET_NAMES=hsa:nvptx-none
Target: x86_64-suse-linux
Configured with: ../configure --prefix=/usr --infodir=/usr/share/info
--mandir=/usr/share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64
--enable-languages=c,c++,objc,fortran,obj-c++,ada,go
--enable-offload-targets=hsa,nvptx-none, --without-cuda-driver
--enable-checking=release --disable-werror
--with-gxx-include-dir=/usr/include/c++/7 --enable-ssp --disable-libssp
--disable-libvtv --disable-libcc1 --disable-plugin
--with-bugurl=https://bugs.opensuse.org/ --with-pkgversion='SUSE Linux'
--with-slibdir=/lib64 --with-system-zlib --enable-libstdcxx-allocator=new
--disable-libstdcxx-pch --enable-version-specific-runtime-libs
--with-gcc-major-version-only --enable-linker-build-id --enable-linux-futex
--enable-gnu-indirect-function --program-suffix=-7 --without-system-libunwind
--enable-multilib --with-arch-32=x86-64 --with-tune=generic
--build=x86_64-suse-linux --host=x86_64-suse-linux
Thread model: posix
gcc version 7.5.0 (SUSE Linux) 

--------------------------------------------------------------------------

4) the compiler output is:

i+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
init.cc: In function ‘void init()’:
init.cc:40:46:   in constexpr expansion of ‘berrybox_CX::make_entree() const()’
init.cc:40:46:   in constexpr expansion of ‘entree0_CX(((const
bersets_by_citrus_CX&)(& bsbc)))’
init.cc:25:79:   in constexpr expansion of
‘((entree0_CX*)this)->entree0_CX::passes.bersets_by_citrus_CX::bersets_by_citrus_CX(bsbc)’
init.cc:19:8:   in constexpr expansion of
‘((bersets_by_citrus_CX*)this)->bersets_by_citrus_CX::berrysets.std::array<berry_set_CX,
8>::array(bersets_by_citrus_CX::berrysets)’
init.cc:40:46:   in constexpr expansion of
‘berry_set_CX(std::array<berry_set_CX, 8>::_M_elems[0])’
init.cc:40:46: internal compiler error: in cxx_eval_component_reference, at
cp/constexpr.c:2479
   const entree0_CX& pas = nu_cs0.make_entree();
                                              ^
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://bugs.opensuse.org/> for instructions.

--------------------------------------------------------------------------

Initially the program which incorporated this function was developed under
OpenSuse Leap 42.3 . The default compiler on that OS did not support the
constexpr functionality I needed, so I installed g++-7 and used that. The code,
including this function, compiled (and ran) correctly.

Later I upgraded to OpenSuse Leap 15.2, my present OS; and as I had not changed
my code I was not expecting trouble. But it fell over as described. I was
puzzled as I was using the 15.2 default compiler, namely  g++-7. 

However I see now that there has been more than one edition of gcc-7, so if I
had silently changed from an earlier to a later version, there could be changes
which trigger the ICE. Unfortunately I no longer have Leap 42.3 so have no
record of which edition of gcc-7 I used then. 

I have tried compiling with gccs -8, -9 and -10: they all produce the same
output as gcc-7 above, except with different line numbers in "constexpr.c".

Yours faithfully,

Graeme A. Warren

[Bug c++/101371] constexpr expansions trigger internal Compiler Error

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-07-08
             Status|UNCONFIRMED                 |NEW
      Known to fail|                            |12.0
     Ever confirmed|0                           |1
            Version|unknown                     |10.3.1
           Keywords|                            |ice-on-valid-code

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  Also fails on trunk.  clang accepts it.

[Bug c++/101371] constexpr expansions trigger internal Compiler Error

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Reduced, even g++ 7 ICEs.  We only ICE with -std=c++14.

struct berry_set_CX;
template <int _Nm> struct __array_traits { typedef berry_set_CX _Type[_Nm]; };
template <int _Nm> struct array {
  typename __array_traits<_Nm>::_Type _M_elems;
};
struct _Base_bitset {
  long _M_w;
};
struct berry_set_CX {
  _Base_bitset bset;
  constexpr berry_set_CX() : bset() {}
  constexpr berry_set_CX(berry_set_CX &rhs) : bset(rhs.bset) {}
};
struct bersets_by_citrus_CX {
  array<8> berrysets;
};
struct entree0_CX {
  constexpr entree0_CX(bersets_by_citrus_CX) {}
};
struct berrybox_CX {
  constexpr entree0_CX make_entree() const {
    bersets_by_citrus_CX bsbc{};
    return bsbc;
  }
  berrybox_CX(berry_set_CX);
};
void init() {
  berry_set_CX fixed;
  berrybox_CX nu_cs0(fixed);
  entree0_CX pas = nu_cs0.make_entree();
}

[Bug c++/101371] constexpr expansions trigger internal Compiler Error

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
The ICE started with r247813.

[Bug c++/101371] constexpr expansions trigger internal Compiler Error

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Reduced more:

struct A {
  int i;
};
struct B {
  A a{};
  constexpr B() : a() {}
  constexpr B(const B &rhs) : a(rhs.a) {}
};
struct C {
  B arr[1];
};

constexpr C
fn ()
{
  C c{};
  return c;
}

C c = fn();

[Bug c++/101371] [9/10/11/12 Regression] constexpr expansions trigger internal Compiler Error

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |9.5
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org
            Summary|constexpr expansions        |[9/10/11/12 Regression]
                   |trigger internal Compiler   |constexpr expansions
                   |Error                       |trigger internal Compiler
                   |                            |Error

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
...which started with my r272217.

[Bug c++/101371] [9/10/11/12 Regression] constexpr expansions trigger internal Compiler Error

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/101371] [9/10/11/12 Regression] constexpr expansions trigger internal Compiler Error

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
And this should compile fine but doesn't since r269078:

struct A {
  int i;
};
struct B {
  A a{};
  constexpr B() : a() {}
  constexpr B(const B &rhs) : a(rhs.a) {}
};
struct C {
  B arr[1];
};

constexpr C
fn ()
{
  C c{};
  return c;
}

constexpr C c = fn();

$ ./cc1plus -quiet 101371.C
101371.C:20:20:   in ‘constexpr’ expansion of ‘fn()()’
101371.C:17:10:   in ‘constexpr’ expansion of ‘C(c)’
101371.C:20:20:   in ‘constexpr’ expansion of ‘B(<anonymous>.C::arr[0])’
101371.C:20:20:   in ‘constexpr’ expansion of ‘B()’
101371.C:20:20: error: accessing value of ‘<anonymous>.B::a’ through a ‘B’
glvalue in a constant expression
   20 | constexpr C c = fn();
      |                    ^

[Bug c++/101371] [9/10/11 Regression] constexpr expansions trigger internal Compiler Error

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[9/10/11/12 Regression]     |[9/10/11 Regression]
                   |constexpr expansions        |constexpr expansions
                   |trigger internal Compiler   |trigger internal Compiler
                   |Error                       |Error

--- Comment #7 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed on trunk so far.

[Bug c++/101371] [9/10/11 Regression] constexpr expansions trigger internal Compiler Error

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Marek Polacek
<mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:da47a84e277c7fbeebbf9c1e7dc1e8ba3277fe53

commit r11-9710-gda47a84e277c7fbeebbf9c1e7dc1e8ba3277fe53
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Jul 13 17:16:54 2021 -0400

    c++: constexpr array reference and value-initialization [PR101371]

    This PR gave me a hard time: I saw multiple issues starting with
    different revisions.  But ultimately the root cause seems to be
    the following, and the attached patch fixes all issues I've found
    here.

    In cxx_eval_array_reference we create a new constexpr context for the
    CP_AGGREGATE_TYPE_P case, but we also have to create it for the
    non-aggregate case.  In this test, we are evaluating

      ((B *)this)->a = rhs->a

    which means that we set ctx.object to ((B *)this)->a.  Then we proceed
    to evaluate the initializer, rhs->a.  For *rhs, we eval rhs, a PARM_DECL,
    for which we have (const B &) &c.arr[0] in the hash table.  Then
    cxx_fold_indirect_ref gives us c.arr[0].  c is evaluated to {.arr={}} so
    c.arr is {}.  Now we want c.arr[0], so we end up in
cxx_eval_array_reference
    and since we're initializing from {}, we call build_value_init which
    gives us an AGGR_INIT_EXPR that calls 'constexpr B::B()'.  Then we
    evaluate this AGGR_INIT_EXPR and since its first argument is dummy,
    we take ctx.object instead.  But that is the wrong object, we're not
    initializing ((B *)this)->a here.  And so we wound up with an
    initializer for A, and then crash in cxx_eval_component_reference:

      gcc_assert (DECL_CONTEXT (part) == TYPE_MAIN_VARIANT (TREE_TYPE
(whole)));

    where DECL_CONTEXT (part) is B (as it should be) but the type of whole
    was A.

    So create a new object, if there already was one, and the element type
    is not a scalar.

            PR c++/101371

    gcc/cp/ChangeLog:

            * constexpr.c (cxx_eval_array_reference): Create a new .object
            and .ctor for the non-aggregate non-scalar case too when
            value-initializing.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1y/constexpr-101371-2.C: New test.
            * g++.dg/cpp1y/constexpr-101371.C: New test.

    (cherry picked from commit a42f8120442cf3ba25d621bed857b5be19019d0c)

[Bug c++/101371] [9/10 Regression] constexpr expansions trigger internal Compiler Error

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED
            Summary|[9/10/11 Regression]        |[9/10 Regression] constexpr
                   |constexpr expansions        |expansions trigger internal
                   |trigger internal Compiler   |Compiler Error
                   |Error                       |

--- Comment #9 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed.