[Bug tree-optimization/91470] [10 Regression] bogus uninitialized warning in trans-intrinsic.c

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91470

--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> ---
On Tue, 27 Aug 2019, marxin at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91470
> 
> Martin Liška <marxin at gcc dot gnu.org> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>            Keywords|needs-reduction             |
>              Status|UNCONFIRMED                 |NEW
>    Last reconfirmed|                            |2019-08-27
>                  CC|                            |marxin at gcc dot gnu.org
>      Ever confirmed|0                           |1
> 
> --- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
> There's a reduced test-case:
> 
> $ cat pr91470.ii
> int input_location, global_trees_0, gfc_conv_intrinsic_findloc_body,
>     gfc_conv_intrinsic_findloc_loopblock, gfc_conv_intrinsic_findloc_tmp,
>     gfc_conv_intrinsic_findloc_found, gfc_conv_intrinsic_findloc_loop;
> enum tree_code { COND_EXPR };
> struct A {};
> struct B {
>   int pre;
>   int expr;
> };
> void fn1(B *, B *);
> void fn2(int *, int *);
> int *fn3(int *);
> void fn4(int, tree_code, int *, int *, int *, int);
> void fn5(B *, int *);
> void fn6() {
>   A array_arg, value_arg, dim_arg, mask_arg, kind_arg, back_arg;
>   int *forward_branch;
>   B arrayse, valuese, maskse, backse;
>   int i;
>   value_arg = array_arg;
>   mask_arg = dim_arg;
>   back_arg = kind_arg;
>   for (i = 0; i < 2; i++) {
>     fn5(&maskse, &gfc_conv_intrinsic_findloc_loop);
>     fn1(&arrayse, __null);
>     fn2(&gfc_conv_intrinsic_findloc_body, &valuese.pre);
>     fn4(input_location, COND_EXPR, &global_trees_0,
>         &gfc_conv_intrinsic_findloc_tmp, &gfc_conv_intrinsic_findloc_found, 0);
>     if (i == 0)
>       forward_branch = fn3(&gfc_conv_intrinsic_findloc_loopblock);
>   }
>   fn4(input_location, COND_EXPR, &global_trees_0, &backse.expr, forward_branch,
>       0);
> }

So this is basically

  int x;
  for (int i = 0; i < 2; ++i)
   if (i == 0) x = bar();
  baz(x);

with making sure we do _not_ thread / header copy / unroll this.
The uninit pass warns about the default def flowing into the loop PHI
node here.