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From: "pascal_cuoq at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/97986] New: ICE in force_constant_size when applying va_arg
 to VLA type
Date: Wed, 25 Nov 2020 14:48:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97986

            Bug ID: 97986
           Summary: ICE in force_constant_size when applying va_arg to VLA
                    type
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pascal_cuoq at hotmail dot com
  Target Milestone: ---

This bug seems most similar to (but still different from)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D59711 (in which a comment sa=
ys
that it appears to have been fixed in GCC 6).

In GCC 10.2 and some earlier versions, compiling the following program
(Compiler Explorer link: https://gcc.godbolt.org/z/11ob5j ):

#include <stdarg.h>

int sum(int n, ...)
{
    va_list ap;
    va_start(ap, n);
    int *input =3D va_arg(ap, int[n]);
    int rc =3D 0;
    for (int i =3D 0; i < n; i++)
        rc +=3D input[i];
    return rc;
}

Produces the following error message:

In file included from <source>:1:
<source>: In function 'sum':
<source>:7:29: internal compiler error: in force_constant_size, at
gimplify.c:733
    7 |     int *input =3D va_arg(ap, int[n]);
      |                             ^~~
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://gcc.gnu.org/bugs/> for instructions.
Compiler returned: 1=