path: root/debian/NEWS.gcc

GCC 4.7 Release Series -- Changes, New Features, and Fixes
==========================================================


Caveats
=======

 - The -fconserve-space flag has been deprecated.  The flag had no
   effect for most targets: only targets without a global .bss
   section and without support for switchable sections.  Furthermore,
   the flag only had an effect for G++, where it could result in
   wrong semantics (please refer to the GCC manual for further
   details).  The flag will be removed in GCC 4.8.

 - Support for a number of older systems and recently unmaintained or
   untested target ports of GCC has been declared obsolete in GCC 4.7.
   Unless there is activity to revive them, the next release of GCC
   will have their sources permanently removed.

 - All GCC ports for the following processor architectures have been
   declared obsolete:

   - picoChip (picochip-*)

  The following ports for individual systems on particular
  architectures have been obsoleted:

   - IRIX 6.5 (mips-sgi-irix6.5)
   - MIPS OpenBSD (mips*-*-openbsd*)
   - Solaris 8 (*-*-solaris2.8). Details can be found in the announcement.
   - Tru64 UNIX V5.1 (alpha*-dec-osf5.1*)

 - On ARM, when compiling for ARMv6 (but not ARMv6-M), ARMv7-A,
   ARMv7-R, or ARMv7-M, the new option -munaligned-access is active by
   default, which for some source codes generates code that accesses
   memory on unaligned addresses. This will require the kernel of
   those systems to enable such accesses (controlled by CP15 register
   c1, refer to ARM documentation). Alternatively or for compatibility
   with kernels where unaligned accesses are not supported, all code
   has to be compiled with -mno-unaligned-access. Linux/ARM in
   official releases has automatically and unconditionally supported
   unaligned accesses as emitted by GCC due to this option being
   active, since Linux version 2.6.28.

 - Support on ARM for the legacy floating-point accelerator (FPA) and
   the mixed-endian floating-point format that it used has been
   obsoleted. The ports that still use this format have been obsoleted
   as well. Many legacy ARM ports already provide an alternative that
   uses the VFP floating-point format. The obsolete ports will be
   deleted in the next release.  The obsolete ports with alternatives
   are:

   - arm*-*-rtems (use arm*-*-rtemseabi)
   - arm*-*-linux-gnu (use arm*-*-linux-gnueabi)
   - arm*-*-elf (use arm*-*-eabi)
   - arm*-*-uclinux* (use arm*-*-uclinux*eabi)

   Note, however, that these alternatives are not binary compatible
   with their legacy counterparts (although some can support running
   legacy applications).

   The obsolete ports that currently lack a modern alternative are:

   - arm*-*-ecos-elf
   - arm*-*-freebsd
   - arm*-wince-pe*

   New ports that support more recent versions of the architecture are
   welcome.

 - Support for the Maverick co-processor on ARM has been obsoleted. Code to
   support it will be deleted in the next release.

 - Support has been removed for Unix International threads on Solaris 2,
   so the --enable-threads=solaris configure option and the -threads
   compiler option don't work any longer.

 - Support has been removed for the Solaris BSD Compatibility Package,
   which lives in /usr/ucbinclude and /usr/ucblib. It has been removed
   from Solaris 11, and was only intended as a migration aid from
   SunOS 4 to SunOS 5. The -compat-bsd compiler option is not
   recognized any longer.

 - The AVR port's libgcc has been improved and its multilib structure
   has been enhanced. As a result, all objects contributing to an
   application must either be compiled with GCC versions up to 4.6.x
   or with GCC versions 4.7.0 or later.

 - The ARM port's -mwords-little-endian option has been deprecated. It will
   be removed in a future release.

 - Support has been removed for the NetWare x86 configuration obsoleted in
   GCC 4.6.

 - It is no longer possible to use the "l" constraint in MIPS16 asm statements.

 - GCC versions 4.7.0 and 4.7.1 had changes to the C++ standard
   library which affected the ABI in C++11 mode: a data member was
   added to std::list changing its size and altering the definitions
   of some member functions, and std::pair's move constructor was
   non-trivial which altered the calling convention for functions with
   std::pair arguments or return types. The ABI incompatibilities have
   been fixed for GCC version 4.7.2 but as a result C++11 code
   compiled with GCC 4.7.0 or 4.7.1 may be incompatible with C++11
   code compiled with different GCC versions and with C++98/C++03 code
   compiled with any version.

 - On ARM, a bug has been fixed in GCC's implementation of the AAPCS
   rules for the layout of vectors that could lead to wrong code being
   generated. Vectors larger than 8 bytes in size are now by default
   aligned to an 8-byte boundary. This is an ABI change: code that
   makes explicit use of vector types may be incompatible with binary
   objects built with older versions of GCC. Auto-vectorized code is
   not affected by this change. (This change affects GCC versions
   4.7.2 and later.)

 - More information on porting to GCC 4.7 from previous versions of GCC can
   be found in the porting_guide for this release.


General Optimizer Improvements
==============================

 - Support for a new parameter --param case-values-threshold=n was
   added to allow users to control the cutoff between doing switch
   statements as a series of if statements and using a jump table.

 - Link-time optimization (LTO) improvements:

   - Improved scalability and reduced memory usage. Link time
     optimization of Firefox now requires 3GB of RAM on a 64-bit
     system, while over 8GB was needed previously. Linking time has
     been improved, too. The serial stage of linking Firefox has been
     sped up by about a factor of 10.

   - Reduced size of object files and temporary storage used during linking.

   - Streaming performance (both outbound and inbound) has been improved.

   - ld -r is now supported with LTO.

   - Several bug fixes, especially in symbol table handling and merging.

 - Interprocedural optimization improvements:

   - Heuristics now take into account that after inlining code will be
     optimized out because of known values (or properties) of function
     parameters. For example:

       void foo(int a)
       {
         if (a > 10)
           ... huge code ...
       }
       void bar (void)
       {
         foo (0);
       }

     The call of foo will be inlined into bar even when optimizing for
     code size. Constructs based on __builtin_constant_p are now
     understood by the inliner and code size estimates are evaluated a
     lot more realistically.

   - The representation of C++ virtual thunks and aliases (both
     implicit and defined via the alias attribute) has been
     re-engineered.  Aliases no longer pose optimization barriers and
     calls to an alias can be inlined and otherwise optimized.

   - The inter-procedural constant propagation pass has been
     rewritten.  It now performs generic function specialization. For
     example when compiling the following:

       void foo(bool flag)
       {
         if (flag)
           ... do something ...
         else
           ... do something else ...
       }
       void bar (void)
       {
         foo (false);
         foo (true);
         foo (false);
         foo (true);
         foo (false);
         foo (true);
       }

     GCC will now produce two copies of foo. One with flag being true,
     while other with flag being false. This leads to performance
     improvements previously possible only by inlining all calls.
     Cloning causes a lot less code size growth.

   - A string length optimization pass has been added. It attempts to
     track string lengths and optimize various standard C string
     functions like strlen, strchr, strcpy, strcat, stpcpy and their
     _FORTIFY_SOURCE counterparts into faster alternatives. This pass
     is enabled by default at -O2 or above, unless optimizing for
     size, and can be disabled by the - fno-optimize-strlen
     option. The pass can e.g. optimize

       char *bar (const char *a)
       {
         size_t l = strlen (a) + 2;
         char *p = malloc (l); if (p == NULL) return p;
         strcpy (p, a); strcat (p, "/"); return p;
       }

     into:

       char *bar (const char *a)
       {
         size_t tmp = strlen (a);
         char *p = malloc (tmp + 2); if (p == NULL) return p;
         memcpy (p, a, tmp); memcpy (p + tmp, "/", 2); return p;
       }

     or for hosted compilations where stpcpy is available in the runtime
     and headers provide its prototype, e.g.

       void foo (char *a, const char *b, const char *c, const char *d)
       {
         strcpy (a, b); strcat (a, c); strcat (a, d);
       }

     can be optimized into:

       void foo (char *a, const char *b, const char *c, const char *d)
       {
         strcpy (stpcpy (stpcpy (a, b), c), d);
       }


New Languages and Language specific improvements
================================================

 - Version 3.1 of the OpenMP_specification is now supported for the C, C++,
   and Fortran compilers.


Ada
---

 - The command-line option -feliminate-unused-debug-types has been re-
   enabled by default, as it is for the other languages, leading to a
   reduction in debug info size of 12.5% and more for relevant cases,
   as well as to a small compilation speedup.


C family
--------

 - A new built-in, __builtin_assume_aligned, has been added, through which
   the compiler can be hinted about pointer alignment and can use it to
   improve generated code.

 - A new -Wunused-local-typedefs warning was added for C, C++,
   Objective-C and Objective-C++.  This warning diagnoses typedefs
   locally defined in a function, and otherwise not used.

 - A new experimental -ftrack-macro-expansion option was added for C,
   C++, Objective-C, Objective-C++ and Fortran.  It allows the
   compiler to emit diagnostic about the current macro expansion
   stack when a compilation error occurs in a macro expansion.

 - Experimental support for transactional memory has been added. It includes
   support in the compiler, as well as a supporting runtime library called
   libitm. To compile code with transactional memory constructs, use the -
   fgnu-tm option.

   Support is currently available for Alpha, ARM, PowerPC, SH, SPARC, and
   32-bit/64-bit x86 platforms.

   For more details on transactional memory see the_GCC_WiKi.

 - Support for atomic operations specifying the C++11/C11 memory model has
   been added. These new __atomic routines replace the existing __sync
   built-in routines.

   Atomic support is also available for memory blocks. Lock-free
   instructions will be used if a memory block is the same size and
   alignment as a supported integer type. Atomic operations which do not
   have lock-free support are left as function calls. A set of library
   functions is available on the GCC atomic wiki in the "External Atomics
   Library" section.

   For more details on the memory models and features, see the atomic_wiki.

 - When a binary operation is performed on vector types and one of the
   operands is a uniform vector, it is possible to replace the vector with
   the generating element. For example:

     typedef int v4si __attribute__ ((vector_size (16)));
     v4si res, a = {1,2,3,4};
     int x;

     res = 2 + a;  /* means {2,2,2,2} + a  */
     res = a - x;  /* means a - {x,x,x,x}  */


C
-

 - There is support for some more features from the C11 revision of the ISO
   C standard. GCC now accepts the options -std=c11 and -std=gnu11, in
   addition to the previous -std=c1x and -std=gnu1x.

   - Unicode strings (previously supported only with options such as
     -std=gnu11, now supported with -std=c11), and the predefined macros
     __STDC_UTF_16__ and __STDC_UTF_32__.

   - Nonreturning functions (_Noreturn and <stdnoreturn.h>).

   - Alignment support (_Alignas, _Alignof, max_align_t, <stdalign.h>).

   - A built-in function __builtin_complex is provided to support C
     library implementation of the CMPLX family of macros.


C++
---

 - G++ now accepts the -std=c++11, -std=gnu++11, and -Wc++11-compat options,
   which are equivalent to -std=c++0x, -std=gnu++0x, and -Wc++0x-compat,
   respectively.

 - G++ now implements C++11 extended friend syntax:

     template<class W>
     class Q
     {
       static const int I = 2;
     public:
       friend W;
     };

     struct B
     {
       int ar[Q<B>::I];
     };

 - Thanks to Ville Voutilainen, G++ now implements C++11 explicit override
   control.

     struct B {
       virtual void f() const final;
       virtual void f(int);
     };

     struct D : B {
       void f() const;            // error: D::f attempts to
     override final B::f
       void f(long) override;     // error: doesn't override
     anything
       void f(int) override;      // ok
     };

     struct E final { };
     struct F: E { }; // error: deriving from final class

 - G++ now implements C++11 non-static data member initializers.

     struct A {
       int i = 42;
     } a; // initializes a.i to 42

 - Thanks to Ed Smith-Rowland, G++ now implements C++11 user-defined
   literals.

     // Not actually a good approximation.  :)
     constexpr long double operator"" _degrees (long double d)
     { return d * 0.0175; }
     long double pi = 180.0_degrees;

 - G++ now implements C++11 alias-declarations.

     template <class T> using Ptr = T*;
     Ptr<int> ip;  // decltype(ip) is int*

 - Thanks to Ville Voutilainen and Pedro Lamarão, G++ now implements C++11
   delegating constructors.

     struct A {
       A(int);
       A(): A(42) { } // delegate to the A(int) constructor
     };

 - G++ now fully implements C++11 atomic classes rather than just integer
   derived classes.

     class POD {
       int a;
       int b;
     };
     std::atomic<POD> my_atomic_POD;

 - G++ now sets the predefined macro __cplusplus to the correct value,
   199711L for C++98/03, and 201103L for C++11.

 - G++ now correctly implements the two-phase lookup rules such that an
   unqualified name used in a template must have an appropriate declaration
   found either in scope at the point of definition of the template or by
   argument-dependent lookup at the point of instantiation. As a result,
   code that relies on a second unqualified lookup at the point of
   instantiation to find functions declared after the template or in
   dependent bases will be rejected. The compiler will suggest ways to fix
   affected code, and using the -fpermissive compiler flag will allow the
   code to compile with a warning.

     template <class T>
     void f() { g(T()); } // error, g(int) not found by argument-
     dependent lookup
     void g(int) { } // fix by moving this declaration before the
     declaration of f

     template <class T>
     struct A: T {
       // error, B::g(B) not found by argument-dependent lookup
       void f() { g(T()); } // fix by using this->g or A::g
     };

     struct B { void g(B); };

     int main()
     {
       f<int>();
       A<B>().f();
     }

 - G++ now properly re-uses stack space allocated for temporary objects when
   their lifetime ends, which can significantly lower stack consumption for
   some C++ functions. As a result of this, some code with undefined
   behavior will now break:

     const int &amp;f(const int &amp;i) { return i; }
     ....
     const int &amp;x = f(1);
     const int &amp;y = f(2);

   Here, x refers to the temporary allocated to hold the 1 argument, which
   only lives until the end of the initialization; it immediately becomes a
   dangling reference. So the next statement re-uses the stack slot to hold
   the 2 argument, and users of x get that value instead.
   Note that this should not cause any change of behavior for temporaries of
   types with non-trivial destructors, as they are already destroyed at end
   of full-expression; the change is that now the storage is released as
   well.

 - A new command-line option -Wdelete-non-virtual-dtor has been added to
   warn when delete is used to destroy an instance of a class which has
   virtual functions and non-virtual destructor. It is unsafe to delete an
   instance of a derived class through a pointer to a base class if the base
   class does not have a virtual destructor. This warning is enabled by -Wall.

 - A new command-line option -Wzero-as-null-pointer-constant has been added
   to warn when a literal '0' is used as null pointer constant. It can be
   useful to facilitate the conversion to nullptr in C++11.

 - As per C++98, access-declarations are now deprecated by G++. Using-
   declarations are to be used instead. Furthermore, some efforts have been
   made to improve the support of class scope using-declarations. In
   particular, using-declarations referring to a dependent type now work as
   expected (bug_c++/14258).

 - The ELF symbol visibility of a template instantiation is now properly
   constrained by the visibility of its template arguments (bug_c++/35688).


Runtime Library (libstdc++)
---------------------------

 - Improved_experimental_support_for_the_new_ISO_C++_standard,_C++11,
   including:

   - using noexcept in most of the library;

   - implementations of pointer_traits, allocator_traits and
     scoped_allocator_adaptor;

   - uses-allocator construction for tuple;

   - vector meets the allocator-aware container requirements;

   - replacing monotonic_clock with steady_clock;

   - enabling the thread support library on most POSIX targets;

   - many small improvements to conform to the FDIS.

 - Added --enable-clocale=newlib configure option.

 - Debug Mode iterators for unordered associative containers.

 - Avoid polluting the global namespace and do not include <unistd.h>.


Fortran
-------

 - The compile flag -fstack-arrays has been added, which causes all local
   arrays to be put on stack memory. For some programs this will improve the
   performance significantly. If your program uses very large local arrays,
   it is possible that you will have to extend your runtime limits for stack
   memory.

 - The -Ofast flag now also implies -fno-protect-parens and -fstack-arrays.

 - Front-end optimizations can now be selected by the -ffrontend-optimize
   option and deselected by the -fno-frontend-optimize option.

 - When front-end optimization removes a function call, -Wfunction-
   elimination warns about that.

 - When performing front-end-optimization, the -faggressive-function-
   elimination option allows the removal of duplicate function calls even
   for impure functions.

 - The flag -Wreal-q-constant has been added, which warns if floating-point
   literals have been specified using q (such as 1.0q0); the q marker is now
   supported as a vendor extension to denote quad precision (REAL(16) or, if
   not available, REAL(10)). Consider using a kind parameter (such as in
   1.0_qp) instead, which can be obtained via SELECTED_REAL_KIND.

 - The GFORTRAN_USE_STDERR environment variable has been removed. GNU
   Fortran now always prints error messages to standard error. If you wish
   to redirect standard error, please consult the manual for your OS, shell,
   batch environment etc. as appropriate.

 - The -fdump-core option and GFORTRAN_ERROR_DUMPCORE environment variable
   have been removed. When encountering a serious error, gfortran will now
   always abort the program. Whether a core dump is generated depends on the
   user environment settings; see the ulimit -c setting for POSIX shells,
   limit coredumpsize for C shells, and the WER_user-mode_dumps_settings on
   Windows.

 - The -fbacktrace option is now enabled by default. When encountering a
   fatal error, gfortran will attempt to print a backtrace to standard error
   before aborting. It can be disabled with -fno-backtrace. Note: On POSIX
   targets with the addr2line utility from GNU binutils, GNU Fortran can
   print a backtrace with function name, file name, line number information
   in addition to the addresses; otherwise only the addresses are printed.

 - Fortran_2003:

   - Generic interface names which have the same name as derived types
     are now supported, which allows to write constructor functions.
     Note that Fortran does not support static constructor functions;
     only default initialization or an explicit structure-constructor
     initialization are available.

   - Polymorphic (class) arrays are now supported.

 - Fortran_2008:

   - Support for the DO CONCURRENT construct has been added, which
     allows the user to specify that individual loop iterations have no
     interdependencies.

   - Coarrays: Full single-image support except for polymorphic
     coarrays. Additionally, preliminary support for multiple images via
     an MPI-based coarray_communication_library has been added. Note:
     The library version is not yet usable as remote coarray access is
     not yet possible.

 - TS_29113:

   - New flag -std=f2008ts permits programs that are expected to conform
     to the Fortran 2008 standard and the draft Technical Specification
     (TS) 29113 on Further Interoperability of Fortran with C.

   - The OPTIONAL attribute is now allowed for dummy arguments of BIND
     (C) procedures.
     
   - The RANK intrinsic has been added.

   - The implementation of the ASYNCHRONOUS attribute in GCC is
     compatible with the candidate draft of TS 29113 (since GCC 4.6).


Go
--

 - GCC 4.7 implements the Go_1_language_standard. The library support in
   4.7.0 is not quite complete, due to release timing. Release 4.7.1 is
   expected to include complete support.

 - Go has been tested on GNU/Linux and Solaris platforms. It may work on
   other platforms as well.


New Targets and Target Specific Improvements
============================================

ARM
---

 - GCC now supports the Cortex-A7 processor implementing the v7-a version of
   the architecture using the option -mcpu=cortex-a7.

 - The default vector size in auto-vectorization for NEON is now 128 bits.
   If vectorization fails thusly, the vectorizer tries again with 64-bit
   vectors.

 - A new option -mvectorize-with-neon-double was added to allow users to
   change the vector size to 64 bits.


AVR
---

 - GCC now supports the XMEGA architecture. This requires GNU binutils 2.22
   or later.

 - Support for the named_address_spaces __flash, __flash1, …, __flash5 and
   __memx has been added. These address spaces locate read-only data in
   flash memory and allow reading from flash memory by means of ordinary C
   code, i.e. without the need of (inline) assembler code:

     const __flash int values[] = { 42, 31 };

     int add_values (const __flash int *p, int i)
     {
         return values[i] + *p;
     }

 - Support has been added for a new AVR-specific configure option
   --with-avrlibc=yes in order to arrange for better integration of
   AVR-Libc. This configure option is supported in avr-gcc 4.7.2 and
   newer and will only take effect in non-RTEMS configurations. If
   avr-gcc is configured for RTEMS, the option will be ignored which is
   the same as specifying --with-avrlibc=no. See PR54461 for more
   technical details.

 - Support for AVR-specific built-in_functions has been added.

 - Support has been added for the signed and unsigned 24-bit scalar integer
   types __int24 and __uint24.

 - New command-line options -maccumulate-args, -mbranch-cost=cost and
   -mstrict-X were added to allow better fine-tuning of code optimization.

 - Many optimizations to:

   - 64-bit integer arithmetic

   - Widening multiplication

   - Integer division by a constant

   - Avoid constant reloading in multi-byte instructions.

   - Micro-optimizations for special instruction sequences.

   - Generic built-in functions like __builtin_ffs*, __builtin_clz*, etc.

   - If-else decision trees generated by switch instructions

   - Merging of data located in flash memory

   - New libgcc variants for devices with 8-bit wide stack pointer

 - Better documentation:

   - Handling of EIND and indirect jumps on devices with more than 128
     KiB of program memory.

   - Handling of the RAMPD, RAMPX, RAMPY and RAMPZ special function
     registers.

   - Function attributes OS_main and OS_task.
   - AVR-specific built-in macros.


C6X
---

 - Support has been added for the Texas Instruments C6X family of processors.


CR16
----

 - Support has been added for National Semiconductor's CR16 architecture.


Epiphany
--------

 - Support has been added for Adapteva's Epiphany architecture.


IA-32/x86-64
------------

 - Support for Intel AVX2 intrinsics, built-in functions and code generation
   is available via -mavx2.

 - Support for Intel BMI2 intrinsics, built-in functions and code generation
   is available via -mbmi2.

 - Implementation and automatic generation of __builtin_clz* using the lzcnt
   instruction is available via -mlzcnt.

 - Support for Intel FMA3 intrinsics and code generation is available via
   -mfma.

 - A new -mfsgsbase command-line option is available that makes GCC generate
   new segment register read/write instructions through dedicated built-ins.

 - Support for the new Intel rdrnd instruction is available via -mrdrnd.

 - Two additional AVX vector conversion instructions are available via
   -mf16c.

 - Support for new Intel processor codename IvyBridge with RDRND, FSGSBASE
   and F16C is available through -march=core-avx-i.

 - Support for the new Intel processor codename Haswell with AVX2, FMA, BMI,
   BMI2, LZCNT is available through -march=core-avx2.

 - Support for new AMD family 15h processors (Piledriver core) is now
   available through -march=bdver2 and -mtune=bdver2 options.

 - Support for the_x32_psABI is now available through the -mx32 option.

 - Windows mingw targets are using the -mms-bitfields option by default.

 - Windows x86 targets are using the __thiscall calling convention for C++
   class-member functions.

 - Support for the configure option --with-threads=posix for Windows mingw
   targets.


MIPS
----

 - GCC now supports thread-local storage (TLS) for MIPS16. This requires GNU
   binutils 2.22 or later.

 - GCC can now generate code specifically for the Cavium Octeon+ and Octeon2
   processors. The associated command-line options are -march=octeon+ and
   -march=octeon2 respectively. Both options require GNU binutils 2.22 or
   later.

 - GCC can now work around certain 24k errata, under the control of the
   command-line option -mfix-24k. These workarounds require GNU binutils
   2.20 or later.

 - 32-bit MIPS GNU/Linux targets such as mips-linux-gnu can now build n32
   and n64 multilibs. The result is effectively a 64-bit GNU/Linux toolchain
   that generates 32-bit code by default. Use the configure-time option
   --enable-targets=all to select these extra multilibs.

 - Passing -fno-delayed-branch now also stops the assembler from
   automatically filling delay slots.


PowerPC/PowerPC64
-----------------

 - Vectors of type vector long long or vector long are passed and returned
   using the same method as other vectors with the VSX instruction set.
   Previously the GCC compiler did not adhere to the ABI for 128-bit vectors
   with 64-bit integer base types (PR 48857). This will also be fixed in the
   GCC 4.6.1 and 4.5.4 releases.

 - A new option -mno-pointers-to-nested-functions was added to allow AIX 32-
   bit/64-bit and GNU/Linux 64-bit PowerPC users to specify that the
   compiler should not load up the chain register (r11) before calling a
   function through a pointer. If you use this option, you cannot call
   nested functions through a pointer, or call other languages that might
   use the static chain.

 - A new option msave-toc-indirect was added to allow AIX 32-bit/64-bit and
   GNU/Linux 64-bit PowerPC users control whether we save the TOC in the
   prologue for indirect calls or generate the save inline. This can speed
   up some programs that call through a function pointer a lot, but it can
   slow down other functions that only call through a function pointer in
   exceptional cases.

 - The PowerPC port will now enable machine-specific built-in functions when
   the user switches the target machine using the #pragma GCC target or
   __attribute__ ((__target__ ("target"))) code sequences. In addition, the
   target macros are updated. However, due to the way the -save-temps switch
   is implemented, you won't see the effect of these additional macros being
   defined in preprocessor output.


SH
--

 - A new option -msoft-atomic has been added. When it is specified, GCC will
   generate GNU/Linux-compatible gUSA atomic sequences for the new __atomic
   routines.

 - Since it is neither supported by GAS nor officially documented, code
   generation for little endian SH2A has been disabled. Specifying -ml with
   -m2a* will now result in a compiler error.

 - The defunct -mbranch-cost option has been fixed.

 - Some improvements to the generated code of:

   - Utilization of the tst #imm,R0 instruction.

   - Dynamic shift instructions on SH2A.

   - Integer absolute value calculations.


SPARC
-----

 - The option -mflat has been reinstated. When it is specified, the compiler
   will generate code for a single register window model. This is
   essentially a new implementation and the corresponding debugger support
   has been added to GDB 7.4.

 - Support for the options -mtune=native and -mcpu=native has been added on
   selected native platforms (GNU/Linux and Solaris).

 - Support for the SPARC T3 (Niagara 3) processor has been added.

 - VIS:

   - An intrinsics header visintrin.h has been added.
   - Builtin intrinsics for the VIS 1.0 edge handling and pixel compare
     instructions have been added.
   - The little-endian version of alignaddr is now supported.
   - When possible, VIS builtins are marked const, which should increase
     the compiler's ability to optimize VIS operations.
   - The compiler now properly tracks the %gsr register and how it
     behaves as an input for various VIS instructions.
   - Akin to fzero, the compiler can now generate fone instructions in
     order to set all of the bits of a floating-point register to 1.
   - The documentation for the VIS intrinsics in the GCC manual has been
     brought up to date and many inaccuracies were fixed.
   - Intrinsics for the VIS 2.0 bmask, bshuffle, and non-condition-code
     setting edge instructions have been added. Their availability is
     controlled by the new -mvis2 and -mno-vis2 options. They are
     enabled by default on UltraSPARC-III and later CPUs.

 - Support for UltraSPARC Fused Multiply-Add floating-point extensions has
   been added. These instructions are enabled by default on SPARC T3
  (Niagara 3) and later CPUs.


TILE-Gx/TILEPro
---------------

 - Support has been added for the Tilera TILE-Gx and TILEPro families of
   processors.


Other significant improvements
==============================

 - A new option (-grecord-gcc-switches) was added that appends compiler
   command-line options that might affect code generation to the
   DW_AT_producer attribute string in the DWARF debugging information.

 - GCC now supports various new GNU extensions to the DWARF debugging
   information format, like entry_value and call_site information, typed
   DWARF_stack or a_more_compact_macro_representation. Support for these
   extensions has been added to GDB 7.4. They can be disabled through the
   -gstrict-dwarf command-line option.


GCC 4.7.1
=========

This is the list of problem reports (PRs) from GCC's bug tracking
system that are known to be fixed in the 4.7.1 release. This list
might not be complete (that is, it is possible that some PRs that have
been fixed are not listed here).

http://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&amp;resolution=FIXED&amp;target_milestone=4.7.1

The Go frontend in the 4.7.1 release fully supports the Go 1 language
standard (http://weekly.golang.org/doc/go1.html).


GCC 4.7.2
=========

This is the list of problem reports (PRs) from GCC's bug tracking
system that are known to be fixed in the 4.7.2 release. This list
might not be complete (that is, it is possible that some PRs that have
been fixed are not listed here).

http://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&amp;resolution=FIXED&amp;target_milestone=4.7.2


For questions related to the use of GCC, please consult these web
pages and the GCC manuals. If that fails, the gcc-help@gcc.gnu.org
mailing list might help.  Please send comments on these web pages and
the development of GCC to our developer list at gcc@gcc.gnu.org.  All
of our lists have public archives.

Copyright (C) Free Software Foundation, Inc.

Verbatim copying and distribution of this entire article is
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Last modified 2012-03-26.