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From: "slyfox at inbox dot ru" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/95942] New: [11 regression] offsetof on an array: error:
 'e' is not a constant expression
Date: Sat, 27 Jun 2020 18:22:43 +0000
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X-Bugzilla-Version: 10.1.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95942

            Bug ID: 95942
           Summary: [11 regression] offsetof on an array: error: 'e' is
                    not a constant expression
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at inbox dot ru
  Target Milestone: ---

The original error is seen on https://www.dolphin-emu.org/ project as a bui=
ld
error. Minimized example looks the following:

"""
  // $ cat.bug.cc
  struct a {
    int b;
    char c[100];
  };
  unsigned long d(long e) { return __builtin_offsetof(a, c[e]); }
"""

OK:
  $ LANG=3DC g++-10.1.0 -c bug.cc -o bug.o

OK:
  $ LANG=3DC clang++-10 -c bug.cc -o bug.o

FAIL:
  $ LANG=3DC g++-11.0.0 -c bug.cc -o bug.o
  bug.cc: In function 'void d(long int)':
  bug.cc:8:42: error: 'e' is not a constant expression
      8 | void d(long e) { __builtin_offsetof(a, c[e]); }
        |

Who is wrong here? gcc-10 or gcc-11?=