This chapter describes changes to g77 that are visible to the programmers who actually write and maintain Fortran code they compile with g77. Information on changes to installation procedures, changes to the documentation, and bug fixes is not provided here, unless it is likely to affect how users use g77. See News About GNU Fortran, for information on such changes to g77.
Note that two variants of g77 are tracked below.
The egcs
variant is described vis-a-vis
previous versions of egcs
and/or
an official FSF version, as appropriate.
Note that all such variants are obsolete as of July 1999 -
the information is retained here only for its historical value.
Therefore, egcs
versions sometimes have multiple listings
to help clarify how they differ from other versions,
though this can make getting a complete picture
of what a particular egcs
version contains
somewhat more difficult.
For information on bugs in the GCC-3.3.6 version of g77, see Known Bugs In GNU Fortran.
The following information was last updated on 2003-05-18:
GCC
3.3 versus GCC
3.2:1832
3924
6286
6367
6491
6742
7113
7236
7278
7384
7388
8587
9038
9263
10197
10726
GCC
3.2 versus GCC
3.1:7681
8308
9258
GCC
3.1 (formerly known as g77-0.5.27) versus GCC
3.0:947
3743
3807
3957
4279
4730
4752
4885
5122
5397
5473
5837
6106
6138
6304
PROGRAM PROG DIMENSION A(140 000 000) END
with the message:
prog.f: In program `prog': prog.f:2: DIMENSION A(140 000 000) ^ Array `a' at (^) is too large to handle
because 140 000 000 REALs is larger than the largest bit-extent that can be
expressed in 32 bits. However, bit-sizes never play a role after offsets
have been converted to byte addresses. Therefore this check has been removed,
and the limit is now 2 Gbyte of memory (around 530 000 000 REALs).
Note: On GNU/Linux systems one has to compile and link programs that occupy
more than 1 Gbyte statically, i.e. g77 -static ...
.
SUBROUTINE SUB(A, N) DIMENSION N(2) DIMENSION A(N(1),N(2)) A(1,1) = 1. END
Note the use of array elements in the bounds of the adjustable array A.
string(1:0)
.
libf2c
library is now able to read and write files larger than
2 Gbyte on 32-bit target machines, if the operating system supports this.
GCC
3.0 versus GCC
2.95:ftruncate
OS function. Thanks go to the GAMESS developers
for bringing this to our attention.
GCC
2.95 (EGCS
1.2) versus EGCS
1.1.2:libg2c
now supports building as multilibbed library,
which provides better support for systems
that require options such as -mieee
to work properly.
CTime
, DTime
, ETime
, and TtyNam
intrinsics has been swapped.
The argument serving as the returned value
for the corresponding function forms
now is the second argument,
making these consistent with the other subroutine forms
of libU77
intrinsics.
libg2c
has been changed to increase the likelihood
of catching references to the implementations of these intrinsics
using the EXTERNAL
mechanism
(which would avoid the new warnings).
See Year 2000 (Y2K) Problems, for more information.
COMPLEX
data type.
errno
,
a C-language concept,
when performing operations such as the SqRt
intrinsic.
There is no g77 version 0.5.24 at this time, or planned. 0.5.24 is the version number designated for bug fixes and, perhaps, some new features added, to 0.5.23. Version 0.5.23 requires gcc 2.8.1, as 0.5.24 was planned to require.
Due to EGCS
becoming GCC
(which is now an acronym for “GNU Compiler Collection”),
and EGCS
1.2 becoming officially designated GCC
2.95,
there seems to be no need for an actual 0.5.24 release.
To reduce the confusion already resulting from use of 0.5.24
to designate g77 versions within EGCS
versions 1.0 and 1.1,
as well as in versions of g77 documentation and notices
during that period,
“mainline” g77 version numbering resumes
at 0.5.25 with GCC
2.95 (EGCS
1.2),
skipping over 0.5.24 as a placeholder version number.
To repeat, there is no g77 0.5.24, but there is now a 0.5.25. Please remain calm and return to your keypunch units.
EGCS
1.1.2 versus EGCS
1.1.1:EGCS
1.1.1 versus EGCS
1.1:EGCS
1.1 versus EGCS
1.0.3:INTEGER
expression.
ENTRY
can be stepped through, line by line,
in gdb.
REAL
argument to intrinsics
Second
and CPU_Time
.
tempnam
, if available, to open scratch files
(as in `OPEN(STATUS='SCRATCH')')
so that the TMPDIR
environment variable,
if present, is used.
libf2c
separates out
the setting of global state
(such as command-line arguments and signal handling)
from main.o into distinct, new library
archive members.
This should make it easier to write portable applications
that have their own (non-Fortran) main()
routine
properly set up the libf2c
environment, even
when libf2c
(now libg2c
) is a shared library.
libg2c.a
instead of libf2c.a
,
to ensure that a version other than the one built and
installed as part of the same g77 version is picked up.
OPEN
, INQUIRE
, READ
, and
WRITE
statements,
and about truncations of various sorts of constants.
EGCS
1.1 versus g77 0.5.23:Previously, g77 treated these expressions as denoting special “pointer” arguments for the purposes of filewide analysis.
Generally, this affects only local variables and arrays
having the SAVE
attribute
or given initial values via DATA
.
libf2c
(libg2c
).
This new information allows, for example,
which __g77_length_a to be used in gdb
to determine the type of the phantom length argument
supplied with CHARACTER
variables.
This information pertains to internally-generated
type, variable, and other information,
not to the longstanding deficiencies vis-a-vis
COMMON
and EQUIVALENCE
.
Date_and_Time
intrinsic now is
supported.
System_Clock
intrinsic allows
the optional arguments (except for the Count
argument) to be omitted.
Features that have been dropped from this version of g77 due to their being implemented via g77-specific patches to the gcc back end in previous releases include:
__restrict__
keyword,
the options -fargument-alias, -fargument-noalias,
and -fargument-noalias-global,
and the corresponding alias-analysis code.
(egcs
has the alias-analysis
code, but not the __restrict__
keyword.
egcs
g77 users benefit from the alias-analysis
code despite the lack of the __restrict__
keyword,
which is a C-language construct.)
(egcs
supports these options.
g77 users of egcs
benefit from them even if
they are not explicitly specified,
because the defaults are optimized for g77 users.)
libg2c.a
instead of libf2c.a
,
to ensure that a version other than the one built and
installed as part of the same g77 version is picked up.
libf2c
separates out
the setting of global state
(such as command-line arguments and signal handling)
from main.o into distinct, new library
archive members.
This should make it easier to write portable applications
that have their own (non-Fortran) main()
routine
properly set up the libf2c
environment, even
when libf2c
(now libg2c
) is a shared library.
OPEN
, INQUIRE
, READ
, and
WRITE
statements,
and about truncations of various sorts of constants.
Signal
intrinsic so it offers portable
support for 64-bit systems (such as Digital Alphas
running GNU/Linux).
INTEGER
expression.
ENTRY
can be stepped through, line by line,
in gdb.
REAL
argument to intrinsics
Second
and CPU_Time
.
Int2
and Int8
.
tempnam
, if available, to open scratch files
(as in `OPEN(STATUS='SCRATCH')')
so that the TMPDIR
environment variable,
if present, is used.
restrict
to
__restrict__
, to avoid rejecting valid, existing,
C programs.
Support for restrict
is now more like support
for complex
.
EGCS
1.0.2 versus EGCS
1.0.1:EGCS
1.0.1 versus EGCS
1.0:EGCS
1.0 versus g77 0.5.21:egcs
contains several regressions against
version 0.5.21 of g77,
due to using the
“vanilla” gcc back end instead of patching
it to fix a few bugs and improve performance in a
few cases.
Features that have been dropped from this version of g77 due to their being implemented via g77-specific patches to the gcc back end in previous releases include:
restrict
keyword.
Int2
and Int8
.
The default is to issue such warnings, which are new as of this version of g77.
The default is to issue such diagnostics and flag the compilation as unsuccessful. With this option, the diagnostics are issued as warnings, or, if -Wno-globals is specified, are not issued at all.
This option also disables inlining of global procedures, to avoid compiler crashes resulting from coding errors that these diagnostics normally would identify.
libU77
routines that accept file and other names
to strip trailing blanks from them, for consistency
with other implementations.
Blanks may be forcibly appended to such names by
appending a single null character (`CHAR(0)')
to the significant trailing blanks.
CHMOD
intrinsic to work with file names
that have embedded blanks, commas, and so on.
SIGNAL
intrinsic so it accepts an
optional third Status
argument.
libU77
intrinsics to
support existing code more directly.
Such changes include allowing both subroutine and
function forms of many routines, changing MCLOCK()
and TIME()
to return INTEGER(KIND=1)
values,
introducing MCLOCK8()
and TIME8()
to
return INTEGER(KIND=2)
values,
and placing functions that are intended to perform
side effects in a new intrinsic group, badu77
.
INT2
and INT8
intrinsics.
CPU_TIME
intrinsic.
ALARM
intrinsic.
CTIME
intrinsic now accepts any INTEGER
argument, not just INTEGER(KIND=2)
.
stderr
instead of stdout
.
This option specifies that non-decimal-radix
constants using the prefixed-radix form (such as `Z'1234'')
are to be interpreted as INTEGER(KIND=1)
constants.
Specify -ftypeless-boz to cause such
constants to be interpreted as typeless.
(Version 0.5.19 introduced -fno-typeless-boz and its inverse.)
See Options Controlling Fortran Dialect, for information on the -ftypeless-boz option.
Some programs might use names that clash with
intrinsic names defined (and now enabled) by these
options or by the new libU77
intrinsics.
Users of such programs might need to compile them
differently (using, for example, -ff90-intrinsics-disable)
or, better yet, insert appropriate EXTERNAL
statements specifying that these names are not intended
to be names of intrinsics.
ALWAYS_FLUSH
macro is no longer defined when
building libf2c
, which should result in improved
I/O performance, especially over NFS.
Note: If you have code that depends on the behavior
of libf2c
when built with ALWAYS_FLUSH
defined,
you will have to modify libf2c
accordingly before
building it from this and future versions of g77.
See Output Assumed To Flush, for more information.
libU77
has been
added to the version of libf2c
distributed with
and built as part of g77.
g77 now knows about the routines in this library
as intrinsics.
See VXT Fortran, for more information on the constructs recognized when the -fvxt option is specified.
If you used one of these deleted options, you should re-read the pertinent documentation to determine which options, if any, are appropriate for compiling your code with this version of g77.
See Other Dialects, for more information.
(Enabling all the -fugly-* options is unlikely to be feasible, or sensible, in the future, so users should learn to specify only those -fugly-* options they really need for a particular source file.)
See Ugly Assumed-Size Arrays, for more information.
LOC()
intrinsic and %LOC()
construct now return
values of INTEGER(KIND=0)
type,
as defined by the GNU Fortran language.
This type is wide enough (holds the same number of bits) as the character-pointer type on the machine.
On most machines, this won't make a difference,
whereas, on Alphas and other systems with 64-bit pointers,
the INTEGER(KIND=0)
type is equivalent to INTEGER(KIND=2)
(often referred to as INTEGER*8
)
instead of the more common INTEGER(KIND=1)
(often referred to as INTEGER*4
).
COMPLEX
arithmetic in the g77 front
end, to avoid bugs in complex
support in the
gcc back end.
New option -fno-emulate-complex
causes g77 to revert the 0.5.19 behavior.
COMMON
areas when any of
these are defined (assigned to) by Fortran code.
This can result in faster and/or smaller programs when compiling with optimization enabled, though on some systems this effect is observed only when -fforce-addr also is specified.
New options -falias-check, -fargument-alias, -fargument-noalias, and -fno-argument-noalias-global control the way g77 handles potential aliasing.
See Aliasing Assumed To Work, for detailed information on why the new defaults might result in some programs no longer working the way they did when compiled by previous versions of g77.
See Ugly Assigned Labels, for more information.
FORMAT
and ENTRY
statements now are allowed to
precede IMPLICIT NONE
statements.
INTEGER(KIND=2)
(often referred to as INTEGER*8
)
available in
libf2c
and f2c.h so that f2c users
may make full use of its features via the g77
version of f2c.h and the INTEGER(KIND=2)
support routines in the g77 version of libf2c
.
libf2c
so that `g77 -v'
yields version information on the library.
SNGL
and FLOAT
intrinsics now are
specific intrinsics, instead of synonyms for the
generic intrinsic REAL
.
REALPART
, IMAGPART
,
COMPLEX
,
LONG
, and SHORT
.
gnu
, has been added
to contain the new REALPART
, IMAGPART
,
and COMPLEX
intrinsics.
An old group, dcp
, has been removed.
DOUBLE COMPLEX
(or any
complex type other than COMPLEX
), unless
-ff90 option specifies Fortran 90 interpretation
or new -fugly-complex option, in conjunction with
-fnot-f90, specifies f2c interpretation.
Information on previous versions is archived
in gcc/gcc/f/news.texi
following the test of the DOC-OLDNEWS
macro.