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, 22 insertions, 11 deletions

diff --git a/libgfortran/io/unit.c b/libgfortran/io/unit.c
index e62f9b8..fbb3304 100644
--- a/libgfortran/io/unit.c
+++ b/libgfortran/io/unit.c
@@ -95,7 +95,10 @@ static int newunit_lwi;
 
 #define CACHE_SIZE 3
 static gfc_unit *unit_cache[CACHE_SIZE];
+
 gfc_offset max_offset;
+gfc_offset default_recl;
+
 gfc_unit *unit_root;
 #ifdef __GTHREAD_MUTEX_INIT
 __gthread_mutex_t unit_lock = __GTHREAD_MUTEX_INIT;
@@ -575,7 +578,6 @@ void
 init_units (void)
 {
   gfc_unit *u;
-  unsigned int i;
 
 #ifdef HAVE_NEWLOCALE
   c_locale = newlocale (0, "C", 0);
@@ -589,6 +591,22 @@ init_units (void)
   __GTHREAD_MUTEX_INIT_FUNCTION (&unit_lock);
 #endif
 
+  if (sizeof (max_offset) == 8)
+    {
+      max_offset = GFC_INTEGER_8_HUGE;
+      /* Why this weird value? Because if the recl specifier in the
+	 inquire statement is a 4 byte value, u->recl is truncated,
+	 and this trick ensures it becomes HUGE(0) rather than -1.
+	 The full 8 byte value of default_recl is still 0.99999999 *
+	 max_offset which is large enough for all practical
+	 purposes.  */
+      default_recl = max_offset & ~(1LL<<31);
+    }
+  else if (sizeof (max_offset) == 4)
+    max_offset = default_recl = GFC_INTEGER_4_HUGE;
+  else
+    internal_error (NULL, "sizeof (max_offset) must be 4 or 8");
+
   if (options.stdin_unit >= 0)
     {				/* STDIN */
       u = insert_unit (options.stdin_unit);
@@ -611,7 +629,7 @@ init_units (void)
       u->flags.share = SHARE_UNSPECIFIED;
       u->flags.cc = CC_LIST;
 
-      u->recl = options.default_recl;
+      u->recl = default_recl;
       u->endfile = NO_ENDFILE;
 
       u->filename = strdup (stdin_name);
@@ -642,7 +660,7 @@ init_units (void)
       u->flags.share = SHARE_UNSPECIFIED;
       u->flags.cc = CC_LIST;
 
-      u->recl = options.default_recl;
+      u->recl = default_recl;
       u->endfile = AT_ENDFILE;
 
       u->filename = strdup (stdout_name);
@@ -672,7 +690,7 @@ init_units (void)
       u->flags.share = SHARE_UNSPECIFIED;
       u->flags.cc = CC_LIST;
 
-      u->recl = options.default_recl;
+      u->recl = default_recl;
       u->endfile = AT_ENDFILE;
 
       u->filename = strdup (stderr_name);
@@ -682,13 +700,6 @@ init_units (void)
 
       __gthread_mutex_unlock (&u->lock);
     }
-
-  /* Calculate the maximum file offset in a portable manner.
-     max will be the largest signed number for the type gfc_offset.
-     set a 1 in the LSB and keep a running sum, stopping at MSB-1 bit.  */
-  max_offset = 0;
-  for (i = 0; i < sizeof (max_offset) * 8 - 1; i++)
-    max_offset = max_offset + ((gfc_offset) 1 << i);
 }