PR fortran/95500 - Segfault compiling extra interface on intrinsic

Converting an expression so that it can be passed by reference could
result in a NULL pointer dereference.

2020-06-04  Steven G. Kargl  <kargl@gcc.gnu.org>
	    Harald Anlauf  <anlauf@gmx.de>

gcc/fortran/
	PR fortran/95500
	* trans-expr.c (gfc_conv_expr_reference): Do not dereference NULL
	pointer.

gcc/testsuite/
	PR fortran/95500
	* gfortran.dg/pr95500.f90: New test.

(cherry picked from commit 8c727bdf4acf28c8315b119a1c8f6d6af745c2af)

gcc/fortran/trans-expr.c

@@ -8810,6 +8810,7 @@ gfc_conv_expr_reference (gfc_se * se, gfc_expr * expr, bool add_clobber)
 
   if (expr->expr_type == EXPR_FUNCTION
       && ((expr->value.function.esym
+	   && expr->value.function.esym->result
 	   && expr->value.function.esym->result->attr.pointer
 	   && !expr->value.function.esym->result->attr.dimension)
 	  || (!expr->value.function.esym && !expr->ref

gcc/testsuite/gfortran.dg/pr95500.f90

+! { dg-do compile }
+! PR fortran/95500 - ICE compiling extra interface on intrinsic
+
+program test_intrinsic
+  implicit none
+  intrinsic :: alog
+  intrinsic :: dlog
+  real (4), parameter :: one = 1
+
+  interface ln
+     procedure :: alog, dlog
+  end interface ln
+
+  write (*,*) 'ln  1', ln (one)
+end program test_intrinsic