Noteworthy change in GCC version 2.5.4:

A bug fix in passing of structure arguments for the HP-PA architecture
makes code compiled with GCC 2.5.4 incompatible with code compiled
with earlier versions (if it passes struct arguments of 33 to 64 bits,
interspersed with other types of arguments).

Noteworthy change in gcc version 2.5.3:

The method of "mangling" C++ function names has been changed.  So you
must recompile all C++ programs completely when you start using GCC
2.5.  Also, GCC 2.5 requires libg++ version 2.5.  Earlier libg++
versions won't work with GCC 2.5.  (This is generally true--GCC
version M.N requires libg++ version M.N.)

Noteworthy GCC changes in version 2.5:

* There is now support for the IBM 370 architecture as a target.
Currently the only operating system supported is MVS; GCC does not run
on MVS, so you must produce .s files using GCC as a cross compiler,
then transfer them to MVS to assemble them.  This port is not reliable
yet.

* The Power PC is now supported.

* The i860-based Paragon machine is now supported.

* The Hitachi 3050 (an HP-PA machine) is now supported.

* The variable __GNUC_MINOR__ holds the minor version number of GCC, as
an integer.  For version 2.5.X, the value is 5.

* In C, initializers for static and global variables are now processed
an element at a time, so that they don't need a lot of storage.

* The C syntax for specifying which structure field comes next in an
initializer is now `.FIELDNAME='.  The corresponding syntax for
array initializers is now `[INDEX]='.  For example,

  char whitespace[256]
    = { [' '] = 1, ['\t'] = 1, ['\n'] = 1 };

This was changed to accord with the syntax proposed by the Numerical
C Extensions Group (NCEG).

* Complex numbers are now supported in C.  Use the keyword __complex__
to declare complex data types.  See the manual for details.

* GCC now supports `long double' meaningfully on the Sparc (128-bit
floating point) and on the 386 (96-bit floating point).  The Sparc
support is enabled on on Solaris 2.x because earlier system versions
(SunOS 4) have bugs in the emulation.

* All targets now have assertions for cpu, machine and system.  So you
can now use assertions to distinguish among all supported targets.

* Nested functions in C may now be inline.  Just declare them inline
in the usual way.

* Packed structure members are now supported fully; it should be possible 
to access them on any supported target, no matter how little alignment
they have.

* To declare that a function does not return, you must now write
something like this (works only in 2.5):

    void fatal () __attribute__ ((noreturn));

or like this (works in older versions too):

    typedef void voidfn ();

    volatile voidfn fatal;

It used to be possible to do so by writing this:

    volatile void fatal ();

but it turns out that ANSI C requires that to mean something
else (which is useless).

Likewise, to declare that a function is side-effect-free
so that calls may be deleted or combined, write
something like this (works only in 2.5):

    int computation () __attribute__ ((const));

or like this (works in older versions too):

    typedef int intfn ();

    const intfn computation;

* The new option -iwithprefixbefore specifies a directory to add to 
the search path for include files in the same position where -I would
put it, but uses the specified prefix just like -iwithprefix.

* Basic block profiling has been enhanced to record the function the
basic block comes from, and if the module was compiled for debugging,
the line number and filename.  A default version of the basic block
support module has been added to libgcc2 that appends the basic block
information to a text file 'bb.out'.  Machine descriptions can now
override the basic block support module in the target macro file.

New features in g++:

* The new flag `-fansi-overloading' for C++.  Use a newly implemented
scheme of argument matching for C++.  It makes g++ more accurately
obey the rules set down in Chapter 13 of the Annotated C++ Reference
Manual (the ARM).  This option will be turned on by default in a
future release.

* The -finline-debug flag is now gone (it was never really used by the
  compiler).

* Recognizing the syntax for pointers to members, e.g., "foo::*bar", has been
  dramatically improved.  You should not get any syntax errors or incorrect
  runtime results while using pointers to members correctly; if you do, it's
  a definite bug.

* Forward declaration of an enum is now flagged as an error.

* Class-local typedefs are now working properly.

* Nested class support has been significantly improved.  The compiler
  will now (in theory) support up to 240 nested classes before hitting
  other system limits (like memory size).

* There is a new C version of the `g++' driver, to replace the old
  shell script.  This should significantly improve the performance of
  executing g++ on a system where a user's PATH environment variable
  references many NFS-mounted filesystems.  This driver also works
  under MS-DOS and OS/2.

* The ANSI committee working on the C++ standard has adopted a new
  keyword `mutable'.  This will allow you to make a specific member be
  modifiable in an otherwise const class.

Noteworthy GCC changes in version 2.4.4:

  A crash building g++ on various hosts (including m68k) has been
  fixed.  Also the g++ compiler no longer reports incorrect
  ambiguities in some situations where they do not exist, and
  const template member functions are now being found properly.

Noteworthy GCC changes in version 2.4:

* On each target, the default is now to return short structures
compatibly with the "usual" compiler on that target.

For most targets, this means the default is to return all structures
in memory, like long structures, in whatever way is used on that
target.  Use -freg-struct-return to enable returning short structures
(and unions) in registers.

This change means that newly compiled binaries are incompatible with
binaries compiled with previous versions of GCC.

On some targets, GCC is itself the usual compiler.  On these targets,
the default way to return short structures is still in registers.
Use -fpcc-struct-return to tell GCC to return them in memory.

* There is now a floating point emulator which can imitate the way all
supported target machines do floating point arithmetic.

This makes it possible to have cross compilation to and from the VAX,
and between machines of different endianness.  However, this works
only when the target machine description is updated to use the new
facilities, and not all have been updated.

This also makes possible support for longer floating point types.
GCC 2.4 supports extended format on the 68K if you use `long double',
for targets that have a 68881.  (When we have run time library
routines for extended floating point, then `long double' will use
extended format on all 68K targets.)

We expect to support extended floating point on the i386 and Sparc in
future versions.

* Building GCC now automatically fixes the system's header files.
This should require no attention.

* GCC now installs an unsigned data type as size_t when it fixes the
header files (on all but a handful of old target machines).
Therefore, the bug that size_t failed to be unsigned is fixed.

* Building and installation are now completely separate.
All new files are constructed during the build process; 
installation just copies them.

* New targets supported: Clipper, Hitachi SH, Hitachi 8300, and Sparc
Lite.

* A totally new and much better Objective C run time system is included.

* Objective C supports many new features.  Alas, I can't describe them
since I don't use that language; however, they are the same ones 
supported in recent versions of the NeXT operating system.

* The builtin functions __builtin_apply_args, __builtin_apply and
__builtin_return let you record the arguments and returned
value of a function without knowing their number or type.

* The builtin string variables __FUNCTION__ and __PRETTY_FUNCTION__
give the name of the function in the source, and a pretty-printed
version of the name.  The two are the same in C, but differ in C++.

* Casts to union types do not yield lvalues.

* ## before an empty rest argument discards the preceding sequence
of non-whitespace characters from the macro definition.
(This feature is subject to change.)


New features specific to C++:

* The manual contains a new section ``Common Misunderstandings with
GNU C++'' that C++ users should read.

* #pragma interface and #pragma implementation let you use the same
C++ source file for both interface and implementation.
However, this mechanism is still in transition.

* Named returned values let you avoid an extra constructor call
when a function result has a class type.

* The C++ operators <? and >? yield min and max, respectively.

* C++ gotos can exit a block safely even if the block has
aggregates that require destructors.

* gcc defines the macro __GNUG__ when compiling C++ programs.

* GNU C++ now correctly distinguishes between the prefix and postfix
forms of overloaded operator ++ and --.  To avoid breaking old
code, if a class defines only the prefix form, the compiler
accepts either ++obj or obj++, unless -pedantic is used.

* If you are using version 2.3 of libg++, you need to rebuild it with
`make CC=gcc' to avoid mismatches in the definition of `size_t'.

Newly documented compiler options:

-fnostartfiles
	Omit the standard system startup files when linking.

-fvolatile-global
	Consider memory references to extern and global data items to
	be volatile.

-idirafter DIR
	Add DIR to the second include path.

-iprefix PREFIX
	Specify PREFIX for later -iwithprefix options.

-iwithprefix DIR
	Add PREFIX/DIR to the second include path.

-mv8
	Emit Sparc v8 code (with integer multiply and divide).
-msparclite
	Emit Sparclite code (roughly v7.5).

-print-libgcc-file-name
	Search for the libgcc.a file, print its absolute file name, and exit.

-Woverloaded-virtual
	Warn when a derived class function declaration may be an error
	in defining a C++ virtual function. 

-Wtemplate-debugging
	When using templates in a C++ program, warn if debugging is
	not yet fully available.

+eN
	Control how C++ virtual function definitions are used
	(like cfront 1.x).

