User-visible Changes

This section 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 section News About GNU Fortran, for information on such changes to g77.

To find out about existing bugs and ongoing plans for GNU Fortran, retrieve ftp://alpha.gnu.org/g77.plan or, if you cannot do that, email fortran@gnu.org asking for a recent copy of the GNU Fortran `.plan' file.

In 0.5.23:

• This release contains several regressions against version 0.5.22 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. See section Actual Bugs We Haven't Fixed Yet, available in plain-text format in gcc/f/BUGS, for information on the known bugs in this version, including the regressions. 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:
  • Support for __restrict__ keyword, the options `-fargument-alias', `-fargument-noalias', and `-fargument-noalias-global', and the corresponding alias-analysis code. (Version 1.0.1 of 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.)
  • Support for the GNU compiler options `-fmove-all-movables', `-freduce-all-givs', and `-frerun-loop-opt'. (Version 1.0.1 of 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.)
  • Support for the `-W' option warning about integer division by zero.
  • The Intel x86-specific option `-malign-double' applying to stack-allocated data as well as statically-allocate data.
• Support gcc version 2.8, and remove support for prior versions of gcc.
• Remove support for the `--driver' option, as g77 now does all the driving, just like gcc.
• The g77 command now expects the run-time library to be named 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.
• g77's version of 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.
• Some diagnostics have been changed from warnings to errors, to prevent inadvertent use of the resulting, probably buggy, programs. These mostly include diagnostics about use of unsupported features in the OPEN, INQUIRE, READ, and WRITE statements, and about truncations of various sorts of constants.

In 0.5.22:

• Fix SIGNAL intrinsic so it offers portable support for 64-bit systems (such as Digital Alphas running GNU/Linux).
• Support `FORMAT(I<expr>)' when expr is a compile-time constant INTEGER expression.
• Fix g77 `-g' option so procedures that use `ENTRY' can be stepped through, line by line, in gdb.
• Allow any REAL argument to intrinsics Second and CPU_Time.
• Allow any numeric argument to intrinsics Int2 and Int8.
• Use tempnam, if available, to open scratch files (as in `OPEN(STATUS='SCRATCH')' so that the TMPDIR environment variable, if present, is used.
• Rename the gcc keyword restrict to __restrict__, to avoid rejecting valid, existing, C programs. Support for restrict is now more like support for complex.
• Fix `-fugly-comma' to affect invocations of only external procedures. Restore rejection of gratuitous trailing omitted arguments to intrinsics, as in `I=MAX(3,4,,)'.
• Fix compiler so it accepts `-fgnu-intrinsics-*' and `-fbadu77-intrinsics-*' options.

In 0.5.21:

• When the `-W' option is specified, gcc, g77, and other GNU compilers that incorporate the gcc back end as modified by g77, issue a warning about integer division by constant zero.
• New option `-Wno-globals' disables warnings about "suspicious" use of a name both as a global name and as the implicit name of an intrinsic, and warnings about disagreements over the number or natures of arguments passed to global procedures, or the natures of the procedures themselves. The default is to issue such warnings, which are new as of this version of g77.
• New option `-fno-globals' disables diagnostics about potentially fatal disagreements analysis problems, such as disagreements over the number or natures of arguments passed to global procedures, or the natures of those procedures themselves. 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.
• Fix libU77 routines that accept file names to strip trailing spaces from them, for consistency with other implementations.
• Fix SIGNAL intrinsic so it accepts an optional third `Status' argument.
• Make many changes to 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.
• Add options `-fbadu77-intrinsics-delete', `-fbadu77-intrinsics-hide', and so on.
• Add INT2 and INT8 intrinsics.
• Add CPU_TIME intrinsic.
• CTIME intrinsic now accepts any INTEGER argument, not just INTEGER(KIND=2).

In 0.5.20:

• The `-fno-typeless-boz' option is now the default. 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 section Options Controlling Fortran Dialect, for information on the `-ftypeless-boz' option.
• Options `-ff90-intrinsics-enable' and `-fvxt-intrinsics-enable' now are the defaults. 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.
• The `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 section Output Assumed To Flush, for more information.
• Dave Love's implementation of libU77 has been added to the version of libf2c distributed with and built by g77. g77 now knows about the routines in this library as intrinsics.
• New option `-fvxt' specifies that the source file is written in VXT Fortran, instead of GNU Fortran. See section VXT Fortran, for more information on the constructs recognized when the `-fvxt' option is specified.
• The `-fvxt-not-f90' option has been deleted, along with its inverse, `-ff90-not-vxt'. 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 section Other Dialects, for more information.
• The `-fugly' option now issues a warning, as it likely will be removed in a future version. (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.)
• The `-fugly-assumed' option, introduced in version 0.5.19, has been changed to better accommodate old and new code. See section Ugly Assumed-Size Arrays, for more information.
• Related to supporting Alpha (AXP) machines, the 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 systems, this won't make a noticeable 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).
• Emulate 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.
• Dummy arguments are no longer assumed to potentially alias (overlap) other dummy arguments or 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 section 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.
• New option `-fugly-assign' specifies that the same memory locations are to be used to hold the values assigned by both statements `I = 3' and `ASSIGN 10 TO I', for example. (Normally, g77 uses a separate memory location to hold assigned statement labels.) See section Ugly Assigned Labels, for more information.
• FORMAT and ENTRY statements now are allowed to precede IMPLICIT NONE statements.
• Enable full support of 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.
• Improve g77 driver and libf2c so that `g77 -v' yields version information on the library.
• The SNGL and FLOAT intrinsics now are specific intrinsics, instead of synonyms for the generic intrinsic REAL.
• New intrinsics have been added. These are REALPART, IMAGPART, COMPLEX, LONG, and SHORT.
• A new group of intrinsics, `gnu', has been added to contain the new REALPART, IMAGPART, and COMPLEX intrinsics. An old group, `dcp', has been removed.

In 0.5.19:

• A temporary kludge option provides bare-bones information on COMMON and EQUIVALENCE members at debug time. See section Options for Code Generation Conventions, for information on the `-fdebug-kludge' option.
• New `-fonetrip' option specifies FORTRAN-66-style one-trip DO loops.
• New `-fno-silent' option causes names of program units to be printed as they are compiled, in a fashion similar to UNIX f77 and f2c.
• New `-fugly-assumed' option specifies that arrays dimensioned via `DIMENSION X(1)', for example, are to be treated as assumed-size.
• New `-fno-typeless-boz' 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.
• New `-ff66' option is a "shorthand" option that specifies behaviors considered appropriate for FORTRAN 66 programs.
• New `-ff77' option is a "shorthand" option that specifies behaviors considered appropriate for UNIX f77 programs.
• New `-fugly-comma' and `-fugly-logint' options provided to perform some of what `-fugly' used to do. `-fugly' and `-fno-ugly' are now "shorthand" options, in that they do nothing more than enable (or disable) other `-fugly-*' options.
• Change code generation for list-directed I/O so it allows for new versions of libf2c that might return non-zero status codes for some operations previously assumed to always return zero. This change not only affects how IOSTAT= variables are set by list-directed I/O, it also affects whether END= and ERR= labels are reached by these operations.
• Add intrinsic support for new FTELL and FSEEK procedures in libf2c.
• Add options `--help' and `--version' to the g77 command, to conform to GNU coding guidelines. Also add printing of g77 version number when the `--verbose' (`-v') option is used.

In 0.5.18:

• The BYTE and WORD statements now are supported, to a limited extent.
• INTEGER*1, INTEGER*2, INTEGER*8, and their LOGICAL equivalents, now are supported to a limited extent. Among the missing elements are complete intrinsic and constant support.
• Support automatic arrays in procedures. For example, `REAL A(N)', where `A' is not a dummy argument, specifies that `A' is an automatic array. The size of `A' is calculated from the value of `N' each time the procedure is called, that amount of space is allocated, and that space is freed when the procedure returns to its caller.
• Add `-fno-zeros' option, enabled by default, to reduce compile-time CPU and memory usage for code that provides initial zero values for variables and arrays.
• Introduce three new options that apply to all compilations by g77-aware GNU compilers---`-fmove-all-movables', `-freduce-all-givs', and `-frerun-loop-opt'---which can improve the run-time performance of some programs.
• Replace much of the existing documentation with a single Info document.
• New option `-fno-second-underscore'.

In 0.5.17:

• The ERF() and ERFC() intrinsics now are generic intrinsics, mapping to ERF/DERF and ERFC/DERFC, respectively. Note: Use `INTRINSIC ERF,ERFC' in any code that might reference these as generic intrinsics, to improve the likelihood of diagnostics (instead of subtle run-time bugs) when using compilers that don't support these as intrinsics.
• New option `-Wsurprising'.
• DO loops with non-INTEGER variables now diagnosed only when `-Wsurprising' specified. Previously, this was diagnosed unless `-fpedantic' or `-fugly' was specified.

In 0.5.16:

• libf2c changed to output a leading zero (0) digit for floating-point values output via list-directed and formatted output (to bring g77 more into line with many existing Fortran implementations--the ANSI FORTRAN 77 standard leaves this choice to the implementation).
• libf2c no longer built with debugging information intact, making it much smaller.
• Automatic installation of the g77 command now works.
• Diagnostic messages now more informative, a la gcc, including messages like `In function `foo':' and `In file included from...:'.
• New group of intrinsics called `unix', including ABORT, DERF, DERFC, ERF, ERFC, EXIT, FLUSH, GETARG, GETENV, SIGNAL, and SYSTEM.
• `-funix-intrinsics-{delete,hide,disable,enable}' options added.
• `-fno-underscoring' option added.
• `--driver' option added to the g77 command.
• Support for the gcc options `-fident' and `-fno-ident' added.
• `g77 -v' returns much more version info, making the submission of better bug reports easily.
• Many improvements to the g77 command to better fulfill its role as a front-end to the gcc driver. For example, g77 now recognizes `--verbose' as a verbose way of specifying `-v'.
• Compiling preprocessed (`*.F' and `*.fpp') files now results in better diagnostics and debugging information, as the source-location info now is passed all the way through the compilation process instead of being lost.

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