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

2 files changed, 5 insertions, 9 deletions

diff --git a/gcc/fortran/ChangeLog b/gcc/fortran/ChangeLog
index 91c57e0..fc97158 100644
--- a/gcc/fortran/ChangeLog
+++ b/gcc/fortran/ChangeLog
@@ -1,3 +1,8 @@
+2017-11-28  Janne Blomqvist  <jb@gcc.gnu.org>
+
+	PR fortran/53796
+	* gfortran.texi: Remove mentions of GFORTRAN_DEFAULT_RECL.
+
 2017-11-28  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/83021
diff --git a/gcc/fortran/gfortran.texi b/gcc/fortran/gfortran.texi
index 4b4688c..36c7b94 100644
--- a/gcc/fortran/gfortran.texi
+++ b/gcc/fortran/gfortran.texi
@@ -600,7 +600,6 @@ Malformed environment variables are silently ignored.
 * GFORTRAN_UNBUFFERED_PRECONNECTED:: Do not buffer I/O for preconnected units.
 * GFORTRAN_SHOW_LOCUS::  Show location for runtime errors
 * GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted
-* GFORTRAN_DEFAULT_RECL:: Default record length for new files
 * GFORTRAN_LIST_SEPARATOR::  Separator for list output
 * GFORTRAN_CONVERT_UNIT::  Set endianness for unformatted I/O
 * GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors
@@ -683,14 +682,6 @@ where permitted by the Fortran standard.  If the first letter
 is @samp{n}, @samp{N} or @samp{0}, a plus sign is not printed
 in most cases.  Default is not to print plus signs.
 
-@node GFORTRAN_DEFAULT_RECL
-@section @env{GFORTRAN_DEFAULT_RECL}---Default record length for new files
-
-This environment variable specifies the default record length, in
-bytes, for files which are opened without a @code{RECL} tag in the
-@code{OPEN} statement.  This must be a positive integer.  The
-default value is 1073741824 bytes (1 GB).
-
 @node GFORTRAN_LIST_SEPARATOR
 @section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output