[Bug fortran/105371] The result of the merge function is different when it's type of parameters is the extensions type of derived type

["sgk at troutmask dot apl.washington.edu" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105371

--- Comment #5 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Wed, Apr 27, 2022 at 07:51:10PM +0000, anlauf at gcc dot gnu.org wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105371
> 
> --- Comment #4 from anlauf at gcc dot gnu.org ---
> The following untested hackish patch leads to the same answer for both cases:
> 
> diff --git a/gcc/fortran/simplify.cc b/gcc/fortran/simplify.cc
> index 233cc42137f..abd93956217 100644
> --- a/gcc/fortran/simplify.cc
> +++ b/gcc/fortran/simplify.cc
> @@ -4946,7 +4946,8 @@ gfc_simplify_merge (gfc_expr *tsource, gfc_expr *fsource,
> gfc_expr *mask)
>      {
>        result = gfc_copy_expr (mask->value.logical ? tsource : fsource);
>        /* Parenthesis is needed to get lower bounds of 1.  */
> -      result = gfc_get_parentheses (result);
> +      if (result->rank)
> +       result = gfc_get_parentheses (result);
>        gfc_simplify_expr (result, 1);
>        return result;
>      }
> 
> Thing is, I have to find a compiler that gives the result the reporter expects.
> E.g. Intel 2021.5 prints
> 
>            1
> 
> for both cases.
> 

Harald,  thanks for looking at this!

I don't use polymorphism in my codes.

The "class(t) :: x, y, r" declaration clearly gives x, y, r the
type type(t).  I assume that the assignments "x = t2(1,-1)" and
"y = t2(2,-2)" now change the dynamic type of x and y to type(t2).
When "r = merge(x,y,...)" is evaluated and assigned the dynamic
type of r becomes type(t2).  So, the output should be

1 -1

But, again, I'm not polymorphic.