re PR fortran/27958 (assignments to and from zero-sized string selections not handled)

	PR fortran/27958

	* trans-expr.c (gfc_conv_substring): If the substring start is
	greater than its end, the length of the substring is zero, and
	not negative.
	(gfc_trans_string_copy): Don't generate a call to
	_gfortran_copy_string when destination length is zero.

	* gcc/testsuite/gfortran.dg/substr_2.f: New test.

From-SVN: r114496

gcc/fortran/ChangeLog

+2006-06-08  Francois-Xavier Coudert  <coudert@clipper.ens.fr>
+
+	PR fortran/27958
+	* trans-expr.c (gfc_conv_substring): If the substring start is
+	greater than its end, the length of the substring is zero, and
+	not negative.
+	(gfc_trans_string_copy): Don't generate a call to
+	_gfortran_copy_string when destination length is zero.
+
 2006-06-08  Asher Langton  <langton2@llnl.gov>
 	
 	PR fortran/27786

gcc/fortran/trans-expr.c

@@ -275,6 +275,8 @@ gfc_conv_substring (gfc_se * se, gfc_ref * ref, int kind)
 		     build_int_cst (gfc_charlen_type_node, 1),
 		     start.expr);
   tmp = fold_build2 (PLUS_EXPR, gfc_charlen_type_node, end.expr, tmp);
+  tmp = fold_build2 (MAX_EXPR, gfc_charlen_type_node, tmp,
+		     build_int_cst (gfc_charlen_type_node, 0));
   se->string_length = tmp;
 }
 
@@ -2196,6 +2198,7 @@ gfc_trans_string_copy (stmtblock_t * block, tree dlen, tree dest,
   tree tmp;
   tree dsc;
   tree ssc;
+  tree cond;
 
   /* Deal with single character specially.  */
   dsc = gfc_to_single_character (dlen, dest);
@@ -2206,12 +2209,16 @@ gfc_trans_string_copy (stmtblock_t * block, tree dlen, tree dest,
       return;
     }
 
+  cond = fold_build2 (GT_EXPR, boolean_type_node, dlen,
+		      build_int_cst (gfc_charlen_type_node, 0));
+
   tmp = NULL_TREE;
   tmp = gfc_chainon_list (tmp, dlen);
   tmp = gfc_chainon_list (tmp, dest);
   tmp = gfc_chainon_list (tmp, slen);
   tmp = gfc_chainon_list (tmp, src);
   tmp = build_function_call_expr (gfor_fndecl_copy_string, tmp);
+  tmp = fold_build3 (COND_EXPR, void_type_node, cond, tmp, build_empty_stmt ());
   gfc_add_expr_to_block (block, tmp);
 }
 

gcc/testsuite/ChangeLog

+2006-06-08  Francois-Xavier Coudert  <coudert@clipper.ens.fr>
+
+	PR fortran/27958
+	* gcc/testsuite/gfortran.dg/substr_2.f: New test.
+
 2006-06-08  Asher Langton  <langton2@llnl.gov>
 	
 	PR fortran/27786

gcc/testsuite/gfortran.dg/substr_2.f

+! { dg-do run }
+! Check that substrings behave correctly even when zero-sized
+      implicit none
+      character(len=10) :: s, t
+      integer :: i, j
+
+      s = "abcdefghij"
+      t(:10) = s(1:)
+      s(6:5) = "foo"
+      if (s /= t) call abort
+      i = 2
+      j = -1
+      s(i:i+j) = "foo"
+      if (s /= t) call abort
+      i = 20
+      s(i+1:i) = "foo"
+      if (s /= t) call abort
+      s(6:5) = s(7:5)
+      if (s /= t) call abort
+      s = t(7:6)
+      if (len(trim(s)) /= 0) call abort
+      if (len(t(8:4)) /= 0) call abort
+      if (len(trim(t(8:4))) /= 0) call abort
+      end