Using and Porting GNU Fortran (original) (raw)

News About GNU Fortran

Changes made to recent versions of GNU Fortran are listed below, with the most recent version first.

The changes are generally listed in order:

1. Code-generation and run-time-library bug-fixes
2. Compiler and run-time-library crashes involving valid code that have been fixed
3. New features
4. Fixes and enhancements to existing features
5. New diagnostics
6. Internal improvements
7. Miscellany

This order is not strict--for example, some items involve a combination of these elements.

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-3.1 version of g77, see Known Bugs In GNU Fortran.

An online, "live" version of this document (derived directly from the mainline, development version of g77 within gcc) is available athttp://www.gnu.org/software/gcc/onlinedocs/g77_news.html.

The following information was last updated on 2002-06-30:

In GCC 3.1 (formerly known as g77-0.5.27) versus GCC 3.0:

• Problem Reports fixed (in chronological order of submission):
  947
  Data statement initialization with subscript of kind INTEGER*2
  3743
  Reference to intrinsic `ISHFT' invalid
  3807
  Function BESJN(integer,double) problems
  3957
  g77 -pipe -xf77-cpp-input sends output to stdout
  4279
  g77 -h" gives bogus output
  4730
  ICE on valid input using CALL EXIT(%VAL(...))
  4752
  g77 -v -c -xf77-version /dev/null -xnone causes ice
  4885
  BACKSPACE example that doesn't work as of gcc/g77-3.0.x
  5122
  g77 rejects accepted use of INTEGER*2 as type of DATA statement loop index
  5397
  ICE on compiling source with 540 000 000 REAL array
  5473
  ICE on BESJN(integer*8,real)
  5837
  bug in loop unrolling
• g77 now has its man page generated from the texinfo documentation, to guarantee that it remains up to date.
• g77 used to reject the following program on 32-bit targets:
  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 programs that occupy more than 1 Gbyte statically, i.e. g77 -static ....

• Based on work done by Juergen Pfeifer (juergen.pfeifer@gmx.net) libf2c is now a shared library. One can still link in all objects with the program by specifying the -static option.
• Robert Anderson (rwa@alumni.princeton.edu) thought up a two line change that enables g77 to compile such code as:
  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.

• George Helffrich (george@geo.titech.ac.jp) implemented a change in substring index checking (when specifying -fbounds-check) that permits the use of zero length substrings of the formstring(1:0).
• Based on code developed by Pedro Vazquez (vazquez@penelope.iqm.unicamp.br), the 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.

In 0.5.26, GCC 3.0 versus GCC 2.95:

• When a REWIND was issued after a WRITE statement on an unformatted file, the implicit truncation was performed by copying the truncated file to /tmp and copying the result back. This has been fixed by using the ftruncate OS function. Thanks go to the GAMESS developers for bringing this to our attention.
• Using options -g, -ggdb or -gdwarf[-2] (where appropriate for your target) now also enables debugging information for COMMON BLOCK and EQUIVALENCE items to be emitted. Thanks go to Andrew Vaught (andy@xena.eas.asu.edu) and George Helffrich (george@geology.bristol.ac.uk) for fixing this longstanding problem.
• It is not necessary anymore to use the option -femulate-complexto compile Fortran code using COMPLEX arithmetic, even on 64-bit machines (like the Alpha). This will improve code generation.
• INTRINSIC arithmetic functions are now treated as routines that do not depend on anything but their argument(s). This enables further instruction scheduling, because it is known that they cannot read or modify arbitrary locations.
• Upgrade to libf2c as of 2000-12-05.
  This fixes a bug where a namelist containing initialization of LOGICAL items and a variable starting with T or F would be read incorrectly.
• The TtyNam intrinsics now set Name to all spaces (at run time) if the system has no ttyname implementation available.
• Upgrade to libf2c as of 1999-06-28.
  This fixes a bug whereby input to a NAMELIST read involving a repeat count, such as K(5)=10*3, was not properly handled by libf2c. The first item was written to K(5), but the remaining nine were written elsewhere (still within the array), not necessarily starting at K(6).

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

• g77 no longer generates bad code for assignments, or other conversions, of REAL or COMPLEX constant expressions to type INTEGER(KIND=2)(often referred to as INTEGER*8).
  For example, INTEGER*8 J; J = 4E10 now works as documented.
• g77 no longer truncates INTEGER(KIND=2)(usually INTEGER*8) subscript expressions when evaluating array references on systems with pointers widers than INTEGER(KIND=1)(such as Alphas).
• g77 no longer generates bad code for an assignment to a COMPLEX variable or array that partially overlaps one or more of the sources of the same assignment (a very rare construction). It now assigns through a temporary, in cases where such partial overlap is deemed possible.
• libg2c (libf2c) no longer loses track of the file being worked on during a BACKSPACE operation.
• libg2c (libf2c) fixes a bug whereby input to a NAMELIST read involving a repeat count, such as K(5)=10*3, was not properly handled by libf2c. The first item was written to K(5), but the remaining nine were written elsewhere (still within the array), not necessarily starting at K(6).
• Automatic arrays now seem to be working on HP-UX systems.
• The Date intrinsic now returns the correct result on big-endian systems.
• Fix g77 so it no longer crashes when compiling I/O statements using keywords that define INTEGER values, such as IOSTAT=j``, where j is other than default INTEGER(such as INTEGER*2). Instead, it issues a diagnostic.
• Fix g77 so it properly handles DATA A/rpt*val/, where rpt is not default INTEGER, such as INTEGER*2, instead of producing a spurious diagnostic. Also fix DATA (A(I),I=1,N), where N is not default INTEGERto work instead of crashing g77.
• The -ax option is now obeyed when compiling Fortran programs. (It is passed to the f771 driver.)
• 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 -mieeeto work properly.
• Source file names with the suffixes .FOR and .FPPnow are recognized by g77as if they ended in .for and .fpp, respectively.
• The order of arguments to the subroutine forms of theCTime, DTime, ETime, and TtyNamintrinsics 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 Year 2000 (Y2K) Problems, for more information.
• g77 now warns about a reference to a function when the corresponding subsequent function program unit disagrees with the reference concerning the type of the function.
• -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.
• Even without the -malign-double option,g77 reliably aligns local double-precision variables that are not in EQUIVALENCE areas and not SAVE'd.
• g77 now open-codes ("inlines") division of COMPLEX operands instead of generating a run-time call to the libf2c routines c_div or z_div, unless the -Os option is specified.
• g77 no longer generates code to maintain errno, a C-language concept, when performing operations such as the SqRt intrinsic.
• g77 developers can temporarily use the -fflatten-arrays option to compare how the compiler handles code generation using C-like constructs as compared to the Fortran-like method constructs normally used.
• A substantial portion of the g77 front end's code-generation component was rewritten. It now generates code using facilities more robustly supported by the gcc back end. One effect of this rewrite is that some codes no longer produce a spurious "label lab used before containing binding contour" message.
• Support for the -fugly option has been removed.
• Improve documentation and indexing, including information on Year 2000 (Y2K) compliance, and providing more information on internals of the front end.
• Upgrade to libf2c as of 1999-05-10.

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:

• Fix the IDate intrinsic (VXT) (in libg2c) so the returned year is in the documented, non-Y2K-compliant range of 0-99, instead of being returned as 100 in the year 2000.
  See IDate Intrinsic (VXT), for more information.
• Fix the Date_and_Time intrinsic (in libg2c) to return the milliseconds value properly in Values(8).
• Fix the LStat intrinsic (in libg2c) to return device-ID information properly in SArray(7).
• Improve documentation.

In EGCS 1.1.1 versus EGCS 1.1:

• Fix libg2c so it performs an implicit ENDFILE operation (as appropriate) whenever a REWIND is done.
  (This bug was introduced in 0.5.23 and egcs 1.1 ing77's version of libf2c.)
• Fix libg2c so it no longer crashes with a spurious diagnostic upon doing any I/O following a direct formatted write.
  (This bug was introduced in 0.5.23 and egcs 1.1 ing77's version of libf2c.)
• Fix g77 so it no longer crashes compiling references to the Rand intrinsic on some systems.
• Fix g77 portion of installation process so it works better on some systems (those with shells requiring else true clauses on if constructs for the completion code to be set properly).

In EGCS 1.1 versus EGCS 1.0.3:

• Fix bugs in the libU77 intrinsic HostNmthat wrote one byte beyond the end of its CHARACTERargument, and in the libU77 intrinsicsGMTime and LTimethat overwrote their arguments.
• Assumed arrays with negative bounds (such as REAL A(-1:*)) no longer elicit spurious diagnostics from g77, even on systems with pointers having different sizes than integers.
  This bug is not known to have existed in any recent version of gcc. It was introduced in an early release of egcs.
• Valid combinations of EXTERNAL, passing that external as a dummy argument without explicitly giving it a type, and, in a subsequent program unit, referencing that external as an external function with a different type no longer crash g77.
• CASE DEFAULT no longer crashes g77.
• The -Wunused option no longer issues a spurious warning about the "master" procedure generated byg77 for procedures containing ENTRY statements.
• 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 intrinsicsSecond 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.
• g77 no longer installs the f77 command and f77.1 man page in the /usr or /usr/local hierarchy, even if the f77-install-ok file exists in the source or build directory. See the installation documentation for more information.
• g77 no longer installs the libf2c.a library and f2c.h include file in the /usr or /usr/local hierarchy, even if the f2c-install-ok or f2c-exists-ok files exist in the source or build directory. See the installation documentation for more information.
• The libf2c.a library produced by g77 has been renamed to libg2c.a. It is installed only in the gcc "private" directory hierarchy, gcc-lib. This allows system administrators and users to choose which version of the libf2c library from netlib they wish to use on a case-by-case basis. See the installation documentation for more information.
• The f2c.h include (header) file produced by g77has been renamed to g2c.h. It is installed only in the gcc "private" directory hierarchy, gcc-lib. This allows system administrators and users to choose which version of the include file from netlib they wish to use on a case-by-case basis. See the installation documentation for more information.
• 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.
• During the configuration and build process,g77 creates subdirectories it needs only as it needs them. Other cleaning up of the configuration and build process has been performed as well.
• install-info now used to update the directory of Info documentation to contain an entry for g77(during installation).
• 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, andWRITE statements, and about truncations of various sorts of constants.
• Improve compilation of FORMAT expressions so that a null byte is appended to the last operand if it is a constant. This provides a cleaner run-time diagnostic as provided by libf2c for statements like PRINT '(I1', 42.
• Improve documentation and indexing.
• The upgrade to libf2c as of 1998-06-18 should fix a variety of problems, including those involving some uses of the T format specifier, and perhaps some build (porting) problems as well.

In EGCS 1.1 versus g77 0.5.23:

• Fix a code-generation bug that afflicted Intel x86 targets when -O2 was specified compiling, for example, an old version of the DNRM2 routine.
  The x87 coprocessor stack was being mismanaged in cases involving assigned GOTOand ASSIGN.
• g77 no longer produces incorrect code and initial values for EQUIVALENCE and COMMONaggregates that, due to "unnatural" ordering of members vis-a-vis their types, require initial padding.
• Fix g77 crash compiling code containing the construct CMPLX(0.) or similar.
• g77 no longer crashes when compiling code containing specification statements such asINTEGER(KIND=7) PTR.
• g77 no longer crashes when compiling code such as J = SIGNAL(1, 2).
• g77 now treats %LOC(expr) andLOC(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.
• Fix g77 crash (or apparently infinite run-time) when compiling certain complicated expressions involving COMPLEX arithmetic (especially multiplication).
• 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 -lg2cis 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 gdbto 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-visCOMMON and EQUIVALENCE.
• The F90 Date_and_Time intrinsic now is supported.
• The F90 System_Clock intrinsic allows the optional arguments (except for the Countargument) to be omitted.
• Upgrade to libf2c as of 1998-06-18.
• Improve documentation and indexing.

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 gccback 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-doubleapplying to stack-allocated data as well as statically-allocate data.
    Note that the gcc/f/gbe/ subdirectory has been removed from this distribution as a result of g77 no longer including patches for the gcc back end.
• Fix bugs in the libU77 intrinsic HostNmthat wrote one byte beyond the end of its CHARACTERargument, and in the libU77 intrinsicsGMTime and LTimethat overwrote their arguments.
• 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.
• CASE DEFAULT no longer crashes g77.
• Valid combinations of EXTERNAL, passing that external as a dummy argument without explicitly giving it a type, and, in a subsequent program unit, referencing that external as an external function with a different type no longer crash g77.
• g77 no longer installs the f77 command and f77.1 man page in the /usr or /usr/local hierarchy, even if the f77-install-ok file exists in the source or build directory. See the installation documentation for more information.
• g77 no longer installs the libf2c.a library and f2c.h include file in the /usr or /usr/local hierarchy, even if the f2c-install-ok or f2c-exists-ok files exist in the source or build directory. See the installation documentation for more information.
• The libf2c.a library produced by g77 has been renamed to libg2c.a. It is installed only in the gcc "private" directory hierarchy, gcc-lib. This allows system administrators and users to choose which version of the libf2c library from netlib they wish to use on a case-by-case basis. See the installation documentation for more information.
• The f2c.h include (header) file produced by g77has been renamed to g2c.h. It is installed only in the gcc "private" directory hierarchy, gcc-lib. This allows system administrators and users to choose which version of the include file from netlib they wish to use on a case-by-case basis. See the installation documentation for more information.
• 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.
• The -Wunused option no longer issues a spurious warning about the "master" procedure generated byg77 for procedures containing ENTRY statements.
• 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.
• During the configuration and build process,g77 creates subdirectories it needs only as it needs them, thus avoiding unnecessary creation of, for example,stage1/f/runtime when doing a non-bootstrap build. Other cleaning up of the configuration and build process has been performed as well.
• install-info now used to update the directory of Info documentation to contain an entry for g77(during installation).
• 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, andWRITE statements, and about truncations of various sorts of constants.
• Improve documentation and indexing.
• Upgrade to libf2c as of 1998-04-20.
  This should fix a variety of problems, including those involving some uses of the T format specifier, and perhaps some build (porting) problems as well.

In 0.5.22 versus 0.5.21:

• Fix code generation for iterative DO loops that have one or more references to the iteration variable, or to aliases of it, in their control expressions. For example, DO 10 J=2,J now is compiled correctly.
• Fix a code-generation bug that afflicted Intel x86 targets when -O2 was specified compiling, for example, an old version of the DNRM2 routine.
  The x87 coprocessor stack was being mismanaged in cases involving assigned GOTOand ASSIGN.
• Fix DTime intrinsic so as not to truncate results to integer values (on some systems).
• Fix Signal intrinsic so it offers portable support for 64-bit systems (such as Digital Alphas running GNU/Linux).
• Fix run-time crash involving NAMELIST on 64-bit machines such as Alphas.
• Fix g77 version of libf2c so it no longer produces a spurious I/O recursion diagnostic at run time when an I/O operation (such as READ *,I) is interrupted in a manner that causes the program to be terminated via the f_exit routine (such as via C-c).
• Fix g77 crash triggered by CASE statement with an omitted lower or upper bound.
• Fix g77 crash compiling references to CPU_Timeintrinsic.
• Fix g77 crash (or apparently infinite run-time) when compiling certain complicated expressions involving COMPLEX arithmetic (especially multiplication).
• Fix g77 crash on statements such asPRINT *, (REAL(Z(I)),I=1,2), whereZ is DOUBLE COMPLEX.
• Fix a g++ crash.
• 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.
• Fix a profiling-related bug in gcc back end for Intel x86 architecture.
• Allow any REAL argument to intrinsicsSecond and CPU_Time.
• Allow any numeric argument to intrinsicsInt2 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 -fpedantic to not reject procedure invocations such as I=J() and CALL FOO().
• 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.
• Improve diagnostic messages from libf2cso it is more likely that the printing of the active format string is limited to the string, with no trailing garbage being printed.
  (Unlike f2c, g77 did not append a null byte to its compiled form of every format string specified via a FORMAT statement. However, f2c would exhibit the problem anyway for a statement like PRINT '(I)garbage', 1by printing (I)garbage as the format string.)
• Improve compilation of FORMAT expressions so that a null byte is appended to the last operand if it is a constant. This provides a cleaner run-time diagnostic as provided by libf2c for statements like PRINT '(I1', 42.
• Fix various crashes involving code with diagnosed errors.
• Fix cross-compilation bug when configuring libf2c.
• Improve diagnostics.
• Improve documentation and indexing.
• Upgrade to libf2c as of 1997-09-23. This fixes a formatted-I/O bug that afflicted 64-bit systems with 32-bit integers (such as Digital Alpha running GNU/Linux).

In EGCS 1.0.2 versus EGCS 1.0.1:

• Fix g77 crash triggered by CASE statement with an omitted lower or upper bound.
• Fix g77 crash on statements such asPRINT *, (REAL(Z(I)),I=1,2), whereZ is DOUBLE COMPLEX.
• Fix -fPIC (such as compiling for ELF targets) on the Intel x86 architecture target so invalid assembler code is no longer produced.
• Fix -fpedantic to not reject procedure invocations such as I=J() and CALL FOO().
• 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 1.0.1 versus EGCS 1.0:

• Fix run-time crash involving NAMELIST on 64-bit machines such as Alphas.

In EGCS 1.0 versus g77 0.5.21:

• Version 1.0 of egcscontains 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 gccback 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-doubleapplying to stack-allocated data as well as statically-allocate data.
    Note that the gcc/f/gbe/ subdirectory has been removed from this distribution as a result of g77being fully integrated with the egcs variant of the gcc back end.
• Fix code generation for iterative DO loops that have one or more references to the iteration variable, or to aliases of it, in their control expressions. For example, DO 10 J=2,J now is compiled correctly.
• Fix DTime intrinsic so as not to truncate results to integer values (on some systems).
• Some Fortran code, miscompiled by g77 built on gcc version 2.8.1 on m68k-next-nextstep3 configurations when using the -O2 option, is now compiled correctly. It is believed that a C function known to miscompile on that configuration when using the -O2 -funroll-loops options also is now compiled correctly.
• Remove support for non-egcs versions of gcc.
• Remove support for the --driver option, as g77 now does all the driving, just like gcc.
• Allow any numeric argument to intrinsicsInt2 and Int8.
• Improve diagnostic messages from libf2cso it is more likely that the printing of the active format string is limited to the string, with no trailing garbage being printed.
  (Unlike f2c, g77 did not append a null byte to its compiled form of every format string specified via a FORMAT statement. However, f2c would exhibit the problem anyway for a statement like PRINT '(I)garbage', 1by printing (I)garbage as the format string.)
• Upgrade to libf2c as of 1997-09-23. This fixes a formatted-I/O bug that afflicted 64-bit systems with 32-bit integers (such as Digital Alpha running GNU/Linux).

In 0.5.21:

• Fix a code-generation bug introduced by 0.5.20 caused by loop unrolling (by specifying-funroll-loops or similar). This bug afflicted all code compiled by version 2.7.2.2.f.2 of gcc (C, C++, Fortran, and so on).
• Fix a code-generation bug manifested when combining local EQUIVALENCE with aDATA statement that follows the first executable statement (or is treated as an executable-context statement as a result of using the -fpedanticoption).
• Fix a compiler crash that occurred when an integer division by a constant zero is detected. Instead, when the -W option is specified, the gcc back end issues a warning about such a case. This bug afflicted all code compiled by version 2.7.2.2.f.2 of gcc (C, C++, Fortran, and so on).
• Fix a compiler crash that occurred in some cases of procedure inlining. (Such cases became more frequent in 0.5.20.)
• Fix a compiler crash resulting from using DATAor similar to initialize a COMPLEX variable or array to zero.
• Fix compiler crashes involving use of AND, OR, or XOR intrinsics.
• Fix compiler bug triggered when using a COMMONor EQUIVALENCE variable as the target of an ASSIGNor assigned-GOTO statement.
• Fix compiler crashes due to using the name of a some non-standard intrinsics (such as FTell orFPutC) as such and as the name of a procedure or common block. Such dual use of a name in a program is allowed by the standard.
• Place automatic arrays on the stack, even ifSAVE or the -fno-automatic option is in effect. This avoids a compiler crash in some cases.
• The -malign-double option now reliably alignsDOUBLE PRECISION optimally on Pentium and Pentium Pro architectures (586 and 686 in gcc).
• 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.
• Diagnose cases where a reference to a procedure disagrees with the type of that procedure, or where disagreements about the number or nature of arguments exist. This avoids a compiler crash.
• Fix parsing bug whereby g77 rejected a second initialization specification immediately following the first's closing / without an intervening comma in a DATA statement, and the second specification was an implied-DO list.
• Improve performance of the gcc back end so certain complicated expressions involving COMPLEXarithmetic (especially multiplication) don't appear to take forever to compile.
• Fix a couple of profiling-related bugs in gccback end.
• Integrate GNU Ada's (GNAT's) changes to the back end, which consist almost entirely of bug fixes. These fixes are circa version 3.10p of GNAT.
• Include some other gcc fixes that seem useful ing77's version of gcc. (See gcc/ChangeLog for details--compare it to that file in the vanilla gcc-2.7.2.3.tar.gzdistribution.)
• 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.
• Fix IDATE() intrinsic subroutine (VXT form) so it accepts arguments in the correct order. Documentation fixed accordingly, and forGMTIME() and LTIME() as well.
• 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.
• Improve libU77 so it is more portable.
• Add options -fbadu77-intrinsics-delete,-fbadu77-intrinsics-hide, and so on.
• Fix crashes involving diagnosed or invalid code.
• g77 and gcc now do a somewhat better job detecting and diagnosing arrays that are too large to handle before these cause diagnostics during the assembler or linker phase, a compiler crash, or generation of incorrect code.
• Make some fixes to alias analysis code.
• Add support for restrict keyword in gccfront end.
• Support gcc version 2.7.2.3 (modified by g77 into version 2.7.2.3.f.1), and remove support for prior versions of gcc.
• Incorporate GNAT's patches to the gcc back end into g77's, so GNAT users do not need to apply GNAT's patches to build both GNAT and g77from the same source tree.
• Modify make rules and related code so that generation of Info documentation doesn't require compilation using gcc. Now, any ANSI C compiler should be adequate to produce the g77 documentation (in particular, the tables of intrinsics) from scratch.
• Add INT2 and INT8 intrinsics.
• Add CPU_TIME intrinsic.
• Add ALARM intrinsic.
• CTIME intrinsic now accepts any INTEGERargument, not just INTEGER(KIND=2).
• Warn when explicit type declaration disagrees with the type of an intrinsic invocation.
• Support *f771 entry in gcc specs file.
• Fix typo in make rule g77-cross, used only for cross-compiling.
• Fix libf2c build procedure to re-archive library if previous attempt to archive was interrupted.
• Change gcc to unroll loops only during the last invocation (of as many as two invocations) of loop optimization.
• Improve handling of -fno-f2c so that code that attempts to pass an intrinsic as an actual argument, such as CALL FOO(ABS), is rejected due to the fact that the run-time-library routine is, effectively, compiled with -ff2c in effect.
• Fix g77 driver to recognize -fsyntax-onlyas an option that inhibits linking, just like -c or-S, and to recognize and properly handle the-nostdlib, -M, -MM, -nodefaultlibs, and -Xlinker options.
• Upgrade to libf2c as of 1997-08-16.
• Modify libf2c to consistently and clearly diagnose recursive I/O (at run time).
• 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.
• Fix some aspects of how gcc determines what kind of system is being configured and what kinds are supported. For example, GNU Linux/Alpha ELF systems now are directly supported.
• Improve diagnostics.
• Improve documentation and indexing.
• Include all pertinent files for libf2c that come from netlib.bell-labs.com; give any such files that aren't quite accurate in g77's version oflibf2c the suffix .netlib.
• Reserve INTEGER(KIND=0) for future use.

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 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 EXTERNALstatements 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 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 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 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 Ugly Assumed-Size Arrays, for more information.
• Make a number of fixes to the g77 front end and the gcc back end to better support Alpha (AXP) machines. This includes providing at least one bug-fix to thegcc back end for Alphas.
• 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 thegcc back end. New option -fno-emulate-complexcauses g77 to revert the 0.5.19 behavior.
• Fix bug whereby REAL A(1), for example, caused a compiler crash if -fugly-assumed was in effect and A was a local (automatic) array. That case is no longer affected by the new handling of -fugly-assumed.
• Fix g77 command driver so that g77 -o foo.fno longer deletes foo.f before issuing other diagnostics, and so the -x option is properly handled.
• Enable inlining of subroutines and functions by the gccback end. This works as it does for gcc itself--program units may be inlined for invocations that follow them in the same program unit, as long as the appropriate compile-time options are specified.
• 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-addralso 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.
• The CONJG() and DCONJG() intrinsics now are compiled in-line.
• The bug-fix for 0.5.19.1 has been re-done. The g77 compiler has been changed back to assume libf2c has no aliasing problems in its implementations of the COMPLEX (andDOUBLE COMPLEX) intrinsics. The libf2c has been changed to have no such problems.
  As a result, 0.5.20 is expected to offer improved performance over 0.5.19.1, perhaps as good as 0.5.19 in most or all cases, due to this change alone.
  Note: This change requires version 0.5.20 oflibf2c, at least, when linking code produced by any versions of g77 other than 0.5.19.1. Use g77 -v to determine the version numbers of the libF77, libI77, and libU77components of the libf2c library. (If these version numbers are not printed--in particular, if the linker complains about unresolved references to names like g77__fvers__--that strongly suggests your installation has an obsolete version of libf2c.)
• New option -fugly-assign specifies that the same memory locations are to be used to hold the values assigned by both statements I = 3 andASSIGN 10 TO I, for example. (Normally, g77 uses a separate memory location to hold assigned statement labels.)
  See Ugly Assigned Labels, for more information.
• FORMAT and ENTRY statements now are allowed to precede IMPLICIT NONE statements.
• Produce diagnostic for unsupported SELECT CASE onCHARACTER type, instead of crashing, at compile time.
• Fix crashes involving diagnosed or invalid code.
• Change approach to building libf2c archive (libf2c.a) so that members are added to it only when truly necessary, so the user that installs an already-built g77 doesn't need to have write access to the build tree (whereas the user doing the build might not have access to install new software on the system).
• Support gcc version 2.7.2.2 (modified by g77 into version 2.7.2.2.f.2), and remove support for prior versions of gcc.
• Upgrade to libf2c as of 1997-02-08, and fix up some of the build procedures.
• Improve general build procedures for g77, fixing minor bugs (such as deletion of any file named f771 in the parent directory of gcc/).
• Enable full support of INTEGER(KIND=2)(often referred to as INTEGER*8) available inlibf2c and f2c.h so that f2c users may make full use of its features via the g77version of f2c.h and the INTEGER(KIND=2)support routines in the g77 version of libf2c.
• Improve g77 driver and libf2c so that g77 -vyields 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 referencesREAL(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.
• Make improvements to diagnostics.
• Speed up compiler a bit.
• Improvements to documentation and indexing, including a new chapter containing information on one, later more, diagnostics that users are directed to pull up automatically via a message in the diagnostic itself.
  (Hence the menu item M for the nodeDiagnostics in the top-level menu of the Info documentation.)

In previous versions:

Information on previous versions is archived in gcc/gcc/f/news.texifollowing the test of the DOC-OLDNEWS macro.