[Bug fortran/31279] Uninitialized warning for call-by-reference arguments with known intent(in)

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31279

--- Comment #8 from Richard Biener  ---
The original testcase hides everything behind array descriptors, even with
unrolling and vectorization disabled we end up with

   [local count: 214748368]:
  parm.0.data = [0];
  parm.0.offset = -1;
  parm.0.dtype.elem_len = 4;
  MEM  [(void *) + 24B] = 1103806595072;
  parm.0.span = 4;
  parm.0.dim[0].stride = 1;
  parm.0.dim[0].lbound = 1;
  parm.0.dim[0].ubound = 4;
  atmp.1.data = 
  atmp.1.offset = 0;
  atmp.1.dtype.elem_len = 4;
  MEM  [(void *) + 24B] = 1103806595072;
  atmp.1.span = 4;
  atmp.1.dim[0].stride = 1;
  atmp.1.dim[0].lbound = 0;
  atmp.1.dim[0].ubound = 3;
  _gfortran_cshift0_4 (, , , 0B);

the frontend might set the fnspec correctly to r (read-only, even transitively)
which we might use here but then the actual use is the intrinsic and the
fnspec does not say that the function acrually reads from the uninitialized
storage.

[Bug fortran/31279] Uninitialized warning for call-by-reference arguments with known intent(in)

[msebor at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31279

Martin Sebor  changed:

   What|Removed |Added

  Component|middle-end  |fortran

--- Comment #7 from Martin Sebor  ---
GCC added the attributes mentioned in comment #4 under the name access -- see
below.  Getting the middle end to issue a warning for the cases described in
comment #0 should be a matter of the Fortran front end making use of the
attribute.

$ cat x.c && gcc -S -Wall x.c
__attribute__ ((access (read_only, 1))) void f (int*);

void g (void)
{
  int x;
  f ();
}
x.c: In function ‘g’:
x.c:6:3: warning: ‘x’ is used uninitialized [-Wuninitialized]
6 |   f ();
  |   ^~
x.c:1:46: note: in a call to ‘f’ declared with attribute ‘access (read_only,
1)’ here
1 | __attribute__ ((access (read_only, 1))) void f (int*);
  |  ^
x.c:5:7: note: ‘x’ declared here
5 |   int x;
  |   ^