Fix PR fortran/93500, ICE on invalid.

Returning &gfc_bad_expr when simplifying bounds after a divisin by zero
happened results in the division by zero error actually reaching the user.

2020-04-19  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/93500
	* resolve.c (resolve_operator): If both operands are
	NULL, return false.
	* simplify.c (simplify_bound): If a division by zero
	was seen during bound simplification, free the
	corresponcing expression and return &gfc_bad_expr.

2020-04-19  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/93500
	* arith_divide_3.f90: New test.

gcc/fortran/ChangeLog

+2020-04-19  Thomas Koenig  <tkoenig@gcc.gnu.org>
+
+	PR fortran/93500
+	* resolve.c (resolve_operator): If both operands are
+	NULL, return false.
+	* simplify.c (simplify_bound): If a division by zero
+	was seen during bound simplification, free the
+	corresponcing expression and return &gfc_bad_expr.
+
 2020-04-17  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
 	PR fortran/94090

gcc/fortran/resolve.c

@@ -3992,6 +3992,9 @@ resolve_operator (gfc_expr *e)
 
   op1 = e->value.op.op1;
   op2 = e->value.op.op2;
+  if (op1 == NULL && op2 == NULL)
+    return false;
+
   dual_locus_error = false;
 
   /* op1 and op2 cannot both be BOZ.  */

gcc/fortran/simplify.c

@@ -4251,7 +4251,11 @@ simplify_bound (gfc_expr *array, gfc_expr *dim, gfc_expr *kind, int upper)
 
 	      for (j = 0; j < d; j++)
 		gfc_free_expr (bounds[j]);
-	      return bounds[d];
+
+	      if (gfc_seen_div0)
+		return &gfc_bad_expr;
+	      else
+		return bounds[d];
 	    }
 	}
 

gcc/testsuite/ChangeLog

+2020-04-19  Thomas Koenig  <tkoenig@gcc.gnu.org>
+
+	PR fortran/93500
+	* arith_divide_3.f90: New test.
+
 2020-04-19  Jakub Jelinek  <jakub@redhat.com>
 
 	PR objc/94637

gcc/testsuite/gfortran.dg/arith_divide_3.f90

+! { dg-do compile }
+! { dg-options "-fcoarray=single" }
+! PR 93500 - this used to cause an ICE
+
+program p
+  integer :: a(min(2,0)/0) ! { dg-error "Division by zero" }
+  integer, save :: c[min(2,0)/0,*] ! { dg-error "Division by zero|must have constant shape" }
+  integer :: b = lbound(a) ! { dg-error "must be an array" }
+  print *,lcobound(c)
+end program p
+
+subroutine s
+  integer :: a(min(2,0)/0)  ! { dg-error "Division by zero" }
+  integer, save :: c[min(2,0)/0,*] ! { dg-error "Division by zero" }
+  integer :: b = lbound(a)
+  print *,lcobound(c)
+end subroutine s