PR 53796 Improve INQUIRE(RECL=...) handling

The current F2018 draft (N2137) specifies behavior of the RECL=
specifier in the INQUIRE statement, where it previously was left as
undefined. Namely:

- If the unit is not connected, RECL= should be given the value -1.
- If the unit is connected with stream access, RECL= should be given
  the value -2.

Further, as PR 53796 describes, the handling of RECL= is poor in other
ways as well. When the recl is set to the maximum possible
(GFC_INTEGER_8_HUGE / LLONG_MAX), which it does by default except for
preconnected units, and when INQUIRE(RECL=) is used with a 4 byte
integer, the value is truncated and the 4 byte value is thus
-1. Fixing this to generate an error is a lot of work, as currently
the truncation is done by the frontend, the library sees only an 8
byte value with no indication that the frontend is going to copy it to
a 4 byte one. Instead, this patch does a bit twiddling trick such that
the truncated 4 byte value is GFC_INTEGER_4_HUGE while still being
0.99999999 * GFC_INTEGER_8_HUGE which is large enough for all
practical purposes.

Finally, the patch removes GFORTRAN_DEFAULT_RECL which was used only
for preconnected units, and instead uses the same approach as describe
above.

Regtested on x86_64-pc-linux-gnu, Ok for trunk.

gcc/fortran/ChangeLog:

2017-11-28  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/53796
	* gfortran.texi: Remove mentions of GFORTRAN_DEFAULT_RECL.

libgfortran/ChangeLog:

2017-11-28  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/53796
	* io/inquire.c (inquire_via_unit): Set recl to -1 for unconnected
	units.
	* io/io.h (default_recl): New variable.
	* io/open.c (new_unit): Set recl to default_recl for sequential,
	-2 for stream access.
	* io/transfer.c (read_block_form): Test against default_recl
	instead of DEFAULT_RECL.
	(write_block): Likewise.
	* io/unit.c (init_units): Calculate max_offset, default_recl.
	* libgfortran.h (DEFAULT_RECL): Remove.
	* runtime/environ.c: Remove GFORTRAN_DEFAULT_RECL.

gcc/testsuite/ChangeLog:

2017-11-28  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/53796
	* gfortran.dg/inquire_recl_f2018.f90: New test.

From-SVN: r255215

1 files changed, 4 insertions, 2 deletions

diff --git a/libgfortran/io/open.c b/libgfortran/io/open.c
index fab2065..05e1773 100644
--- a/libgfortran/io/open.c
+++ b/libgfortran/io/open.c
@@ -586,7 +586,7 @@ new_unit (st_parameter_open *opp, gfc_unit *u, unit_flags *flags)
   else
     {
       u->flags.has_recl = 0;
-      u->recl = max_offset;
+      u->recl = default_recl;
       if (compile_options.max_subrecord_length)
 	{
 	  u->recl_subrecord = compile_options.max_subrecord_length;
@@ -622,7 +622,9 @@ new_unit (st_parameter_open *opp, gfc_unit *u, unit_flags *flags)
   if (flags->access == ACCESS_STREAM)
     {
       u->maxrec = max_offset;
-      u->recl = 1;
+      /* F2018 (N2137) 12.10.2.26: If the connection is for stream
+	 access recl is assigned the value -2.  */
+      u->recl = -2;
       u->bytes_left = 1;
       u->strm_pos = stell (u->s) + 1;
     }