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From: "iains at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/94897] New: range-for produces a variable initialiser with
 use of a forward decl.
Date: Thu, 30 Apr 2020 20:48:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94897

            Bug ID: 94897
           Summary: range-for produces a variable initialiser with use of
                    a forward decl.
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: iains at gcc dot gnu.org
  Target Milestone: ---

It seems that parser.c:cp_convert_range_for () is not implementing the lowe=
ring
that its header comment outlines.

for this:
#include <array>

void
foo ()
{
  const std::array<int, 5> expectedValues =3D {{0, 3, 1, 4, 2}};

  for (int expectedValue : expectedValues) {
    ;
  }
}

we are getting the statement tree below, the key being (V =3D Var decl, Va =
=3D
artificial var decl) where the first entry initialiser contains a forward r=
ef.

----

 V int expectedValue =3D E (std::array<int, E <cst>5>::value_type)E *VD
foo::__for_begin;
 Va const std::array<int, E <cst>5>& __for_range =3D E (const std::array<in=
t, E
<cst>5>&)E &foo::expectedValues;
 Va const std::array<int, E <cst>5>::value_type* __for_begin;
 Va const std::array<int, E <cst>5>::value_type* __for_end;

=3D=3D=3D=3D=3D

FD foo ()=20

- <STATEMENT_LIST>{
  S BIND_EXPR [scope 0x10399a3c0] BLOCK #0 not outer [ao] 0x0=20
    [super-ctx] 0x0 SUBBLOCKS 0x10399a360
  VARS {
    V const std::array<int, E <cst>5>expectedValues =3D {E CE {E <cst>0, E
<cst>3, E <cst>1, E <cst>4, E <cst>2}};
  }
  BODY {
    - <STATEMENT_LIST>{
      CPs<<sD const std::array<int, E <cst>5>expectedValues =3D {E CE {E <c=
st>0,
E <cst>3, E <cst>1, E <cst>4, E <cst>2}}; CPE>>
      S BIND_EXPR [scope 0x10399a360] BLOCK #0 not outer [ao] 0x0=20
        [super-ctx] 0x10399a3c0 SUBBLOCKS 0x0
      VARS {
        V int expectedValue =3D E (std::array<int, E <cst>5>::value_type)E =
*VD
foo::__for_begin;
        Va const std::array<int, E <cst>5>& __for_range =3D E (const
std::array<int, E <cst>5>&)E &foo::expectedValues;
        Va const std::array<int, E <cst>5>::value_type* __for_begin;
        Va const std::array<int, E <cst>5>::value_type* __for_end;
      }
      BODY {
        - <STATEMENT_LIST>{
          sD const std::array<int, E <cst>5>& __for_range =3D E (const
std::array<int, E <cst>5>&)E &foo::expectedValues;
          sD const std::array<int, E <cst>5>::value_type* __for_begin;
          CPs<<S xE (void)E foo::__for_begin =3D=20
foo::__for_range.std::array<int, E <cst>5>::begin (); CPE>>
          sD const std::array<int, E <cst>5>::value_type* __for_end;
          CPs<<S xE (void)E foo::__for_end =3D  foo::__for_range.std::array=
<int,
E <cst>5>::end (); CPE>>
          sS for (; E CE foo::__for_begin !=3D foo::__for_end; CPe<<E (void=
)E CE
++foo::__for_begin CPE>>)
             sD int expectedValue =3D E (std::array<int, E <cst>5>::value_t=
ype)E
*VD foo::__for_begin;
        }
      }
    }
  }=