[Bug c++/63249] New: [OpenMP] Spurious »set but not used« warnings when actually used in OpenMP target's array section's lower-bound and length

["tschwinge at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63249

            Bug ID: 63249
           Summary: [OpenMP] Spurious »set but not used« warnings when
                    actually used in OpenMP target's array section's
                    lower-bound and length
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Keywords: openmp
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tschwinge at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org
        Depends on: 63248

This is similar to what has previously been addressed in
<https://gcc.gnu.org/PR51360>,
<http://news.gmane.org/find-root.php?message_id=%3C20111215173852.GT1957%40tyan-ft48-01.lab.bos.redhat.com%3E>:

    int f(int A, int B)
    {
      int r = 0;
      extern int *v;
      int a = 2;
      int b = 4;
      int n = 3;

      v[n] = 0;

    #pragma omp target map(to: v[a:b])
      r |= v[n];

    #pragma omp target map(to: v[A:B])
      r |= v[n];

      return r;
    }

    ../../openacc/w.c: In function 'f':
    ../../openacc/w.c:6:7: warning: variable 'b' set but not used
[-Wunused-but-set-variable]
       int b = 4;
       ^
    ../../openacc/w.c:5:7: warning: variable 'a' set but not used
[-Wunused-but-set-variable]
       int a = 2;
       ^
    ../../openacc/w.c:1:11: warning: parameter 'A' set but not used
[-Wunused-but-set-parameter]
     int f(int A, int B)
           ^
    ../../openacc/w.c:1:18: warning: parameter 'B' set but not used
[-Wunused-but-set-parameter]
     int f(int A, int B)
              ^
Patch (for C) submitted in
<http://news.gmane.org/find-root.php?message_id=%3C87y4trrcsk.fsf%40schwinge.name%3E>,
C++ blocked on PR63248.
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Subject: [Bug target/34777] uClibc-0.9.29 compilation error for sh4 arch with gcc-4.x
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id4777

Oleg Endo <olegendo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |55212

--- Comment #12 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Oleg Endo from comment #11)
>
> seems to fix the test case of PR 34807.  However, I've not tested it any
> further and probably the fix is incomplete and works only for mem loads and
> not stores.
> In fact it can be broken again quite easily by inserting another insn that
> requires R0 (tst #imm,r0 in this case):
>
> int glob, glob1;
>
> static int _dl_mmap (int xx)
>  {
>    register int __sc0 __asm__ ("r0") = glob1;
>    register int __sc1 __asm__ ("r1") = glob;
>
>    if (xx & 3)
>      __asm__  ("trapa %1 " : "=z" (__sc0) : "i" (0x10), "0" (__sc0), "r"
> (__sc1));
>
>    return (__sc0);
>  }
>
>  void _start(int xx)
>  {
>    static int buf;
>    buf = _dl_mmap(xx);
>  }

I've tried that test case with the sh-lra branch and the problems seem to be
gone.