[Bug fortran/107874] New: merge not using all its arguments

["john.harper at vuw dot ac.nz" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107874

            Bug ID: 107874
           Summary: merge not using all its arguments
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: john.harper at vuw dot ac.nz
  Target Milestone: ---

The F2018 standard 15.5.3 requires all actual arguments in a function reference
to be evaluated.

In the program below, merge has three scalar arguments; ifort evaluates
all three, gfortran evaluates only the useful two, which violates 15.5.3.

program testmerge9
  implicit none
  integer i
  logical:: x(2)=(/.true., .false./), y ! avoiding [ ] allows f95 option
  do i = 1,2
     y = merge(tstuff(),fstuff(),x(i))
     print *,y
  end do
contains
  logical function tstuff()
    print *,'tstuff'
    tstuff = .true.
  end function tstuff

  logical function fstuff()
    print *,'fstuff'
    fstuff = .false.
  end function fstuff
end program testmerge9

Steve Kargl said "Looks like a bug. Feel free to send a bug report with this
patch."

diff --git a/gcc/fortran/trans-intrinsic.cc b/gcc/fortran/trans-intrinsic.cc
index bb938026828..c5b63d356e1 100644
--- a/gcc/fortran/trans-intrinsic.cc
+++ b/gcc/fortran/trans-intrinsic.cc
@@ -7538,9 +7538,9 @@ gfc_conv_intrinsic_merge (gfc_se * se, gfc_expr * expr)
   gfc_conv_intrinsic_function_args (se, expr, args, num_args);
   if (expr->ts.type != BT_CHARACTER)
     {
-      tsource = args[0];
-      fsource = args[1];
-      mask = args[2];
+      tsource = gfc_evaluate_now (args[0], &se->pre);
+      fsource = gfc_evaluate_now (args[1], &se->pre);
+      mask = gfc_evaluate_now (args[2], &se->pre);
     }
   else
     {