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# User-visible Changes

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 section 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.

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-2.95 version of `g77`, see section Known Bugs In GNU Fortran.

The following information was last updated on 1999-07-08:

## In 0.5.25, `GCC` 2.95 (`EGCS` 1.2) versus `EGCS` 1.1.2:

- The new ``-fbounds-check'` option causes `g77` to compile run-time bounds checks of array subscripts, as well as of substring start and end points.
- `libg2c` now supports building as multilibbed library, which provides better support for systems that require options such as ``-mieee'` to work properly.
- Source file names with the suffixes ``.FOR'` and ``.FPP'` now are recognized by `g77` as if they ended in ``.for'` and ``.fpp'`, respectively.
- The order of arguments to the subroutine forms of the `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.
- `g77` now warns about a reference to an intrinsic that has an interface that is not Year 2000 (Y2K) compliant. Also, `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 section Year 2000 (Y2K) Problems, for more information.
- ``-fno-emulate-complex'` is now the default option. This should result in improved performance of code that uses the `COMPLEX` data type.
- The ``-malign-double'` option now reliably aligns all double-precision variables and arrays on Intel x86 targets.
- `g77` no longer generates code to maintain `errno`, a C-language concept, when performing operations such as the `SqRt` intrinsic.
- Support for the ``-fugly'` option has been removed.

## In 0.5.24 versus 0.5.23:

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.

## In `EGCS` 1.1.2 versus `EGCS` 1.1.1:

## In `EGCS` 1.1.1 versus `EGCS` 1.1:

## In `EGCS` 1.1 versus `EGCS` 1.0.3:

- 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`.
- Use `tempnam`, if available, to open scratch files (as in ``OPEN(STATUS='SCRATCH')'`) so that the `TMPDIR` environment variable, if present, is used.
- `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.
- 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.
- 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 `EGCS` 1.1 versus `g77` 0.5.23:

- `g77` now treats ``%LOC(expr)'` and ``LOC(expr)'` as "ordinary" expressions when they are used as arguments in procedure calls. This change applies only to global (filewide) analysis, making it consistent with how `g77` actually generates code for these cases. Previously, `g77` treated these expressions as denoting special "pointer" arguments for the purposes of filewide analysis.
- Align static double-precision variables and arrays on Intel x86 targets regardless of whether ``-malign-double'` is specified. Generally, this affects only local variables and arrays having the `SAVE` attribute or given initial values via `DATA`.
- The `g77` driver now ensures that ``-lg2c'` is specified in the link phase prior to any occurrence of ``-lm'`. This prevents accidentally linking to a routine in the SunOS4 ``-lm'` library when the generated code wants to link to the one in `libf2c` (`libg2c`).
- `g77` emits more debugging information when ``-g'` is used. 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`.
- The F90 `Date_and_Time` intrinsic now is supported.
- The F90 `System_Clock` intrinsic allows the optional arguments (except for the `Count` argument) to be omitted.

## In 0.5.23 versus 0.5.22:

- 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. 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. (`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'`. (`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 versus 0.5.21:

- 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 `EGCS` 1.0.2 versus `EGCS` 1.0.1:

- Fix compiler so it accepts ``-fgnu-intrinsics-*'` and ``-fbadu77-intrinsics-*'` options.

## In `EGCS` 1.0.1 versus `EGCS` 1.0:

## In `EGCS` 1.0 versus `g77` 0.5.21:

- Version 1.0 of `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:
  - Support for the C-language `restrict` keyword.
  - 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.
- Remove support for the ``--driver'` option, as `g77` now does all the driving, just like `gcc`.
- Allow any numeric argument to intrinsics `Int2` and `Int8`.

## 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 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.
- Fix `CHMOD` intrinsic to work with file names that have embedded blanks, commas, and so on.
- 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.
- Add `ALARM` intrinsic.
- `CTIME` intrinsic now accepts any `INTEGER` argument, not just `INTEGER(KIND=2)`.
- `g77` driver now prints version information (such as produced by `g77 -v`) to `stderr` instead of `stdout`.
- The ``.r'` suffix now designates a Ratfor source file, to be preprocessed via the `ratfor` command, available separately.

## 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 as part of `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 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`).
- 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.
- Complain about industry-wide ambiguous references ``REAL(expr)'` and ``AIMAG(expr)'`, where expr is `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.

## In previous versions:

Information on previous versions is archived in ``egcs/gcc/f/news.texi'` following the test of the `DOC-OLDNEWS` macro.

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