gcc-4.8-source 4.8.5-4ubuntu2 / usr / src / gcc-4.8 / debian / NEWS.gcc

GCC 4.8 Release Series -- Changes, New Features, and Fixes
==========================================================


Caveats
=======

GCC now uses C++ as its implementation language. This means that to build GCC
from sources, you will need a C++ compiler that understands C++ 2003. For more
details on the rationale and specific changes, please refer to the C++
conversion page.

To enable the Graphite framework for loop optimizations you now need CLooG
version 0.18.0 and ISL version 0.11.1. Both can be obtained from the GCC
infrastructure directory. The installation manual contains more information
about requirements to build GCC.

GCC now uses a more aggressive analysis to derive an upper bound for the
number of iterations of loops using constraints imposed by language standards.
This may cause non-conforming programs to no longer work as expected, such as
SPEC CPU 2006 464.h264ref and 416.gamess. A new option, -fno-aggressive-loop-
optimizations, was added to disable this aggressive analysis. In some loops
that have known constant number of iterations, but undefined behavior is known
to occur in the loop before reaching or during the last iteration, GCC will
warn about the undefined behavior in the loop instead of deriving lower upper
bound of the number of iterations for the loop. The warning can be disabled
with -Wno-aggressive-loop-optimizations.

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.

On AVR, support has been removed for the command-line option -mshort-calls
deprecated in GCC 4.7.

On AVR, the configure option --with-avrlibc supported since GCC 4.7.2 is
turned on per default for all non-RTEMS configurations. This option arranges
for a better integration of AVR_Libc with avr-gcc. For technical details, see
PR54461. To turn off the option in non-RTEMS configurations, use --with-
avrlibc=no. If the compiler is configured for RTEMS, the option is always
turned off.

More information on porting to GCC 4.8 from previous versions of GCC can be
found in the porting guide (http://gcc.gnu.org/gcc-4.8/porting_to.html) for
this release.

General Optimizer Improvements (and Changes)
============================================

 - DWARF4 is now the default when generating DWARF debug information. When -g
   is used on a platform that uses DWARF debugging information, GCC will now
   default to -gdwarf-4 -fno-debug-types-section.
   GDB 7.5, Valgrind 3.8.0 and elfutils 0.154 debug information consumers
   support DWARF4 by default. Before GCC 4.8 the default version used was
   DWARF2. To make GCC 4.8 generate an older DWARF version use -g together with
   -gdwarf-2 or -gdwarf-3. The default for Darwin and VxWorks is still
   -gdwarf-2 -gstrict-dwarf.

 - A new general optimization level, -Og, has been introduced. It addresses the
   need for fast compilation and a superior debugging experience while
   providing a reasonable level of runtime performance. Overall experience for
   development should be better than the default optimization level -O0.

 - A new option -ftree-partial-pre was added to control the partial redundancy
   elimination (PRE) optimization. This option is enabled by default at the -O3
   optimization level, and it makes PRE more aggressive.

 - The option -fconserve-space has been removed; it was no longer useful on
   most targets since GCC supports putting variables into BSS without making
   them common.

 - The struct reorg and matrix reorg optimizations (command-line-options
   -fipa-struct-reorg and -fipa-matrix-reorg) have been -removed. They did not
   always work correctly, nor did they work -with link-time optimization (LTO),
   hence were only applicable to -programs consisting of a single translation
   unit.

 - Several scalability bottle-necks have been removed from GCC's optimization
   passes. Compilation of extremely large functions, e.g. due to the use of the
   flatten attribute in the "Eigen" C++ linear algebra templates library, is
   significantly faster than previous releases of GCC.

 - Link-time optimization (LTO) improvements:

   - LTO partitioning has been rewritten for better reliability and
     maintanibility. Several important bugs leading to link failures have been
     fixed.

 - Interprocedural optimization improvements:

   - A new symbol table has been implemented. It builds on existing callgraph
     and varpool modules and provide a new API. Unusual symbol visibilities and
     aliases are handled more consistently leading to, for example, more
     aggressive unreachable code removal with LTO.

   - The inline heuristic can now bypass limits on the size of of inlined
     functions when the inlining is particularly profitable. This happens, for
     example, when loop bounds or array strides get propagated.

   - Values passed through aggregates (either by value or reference) are now
     propagated at the inter-procedural level leading to better inlining
     decisions (for example in the case of Fortran array descriptors) and
     devirtualization.

 - AddressSanitizer, a fast memory error detector, has been added and can be
   enabled via -fsanitize=address. Memory access instructions will be
   instrumented to detect heap-, stack-, and global-buffer overflow as well as
   use-after-free bugs. To get nicer stacktraces, use -fno-omit-frame-pointer.
   The AddressSanitizer is available on IA-32/x86-64/x32/PowerPC/PowerPC64 GNU/
   Linux and on x86-64 Darwin.

 - ThreadSanitizer has been added and can be enabled via -fsanitize=thread.
   Instructions will be instrumented to detect data races. The ThreadSanitizer
   is available on x86-64 GNU/Linux.


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


C family
--------

 - Each diagnostic emitted now includes the original source line and a caret
   '^' indicating the column. The option -fno-diagnostics-show-caret suppresses
   this information.

 - The option -ftrack-macro-expansion=2 is now enabled by default. This allows
   the compiler to display the macro expansion stack in diagnostics. Combined
   with the caret information, an example diagnostic showing these two features
   is:

     t.c:1:94: error: invalid operands to binary < (have ‘struct mystruct’ and ‘float’)
     #define MYMAX(A,B)    __extension__ ({ __typeof__(A) __a = (A);
                                            __typeof__(B) __b = (B);
                                             __a < __b ? __b : __a; })
                                                 ^
     t.c:7:7: note: in expansion of macro 'MYMAX'
        X = MYMAX(P, F);
            ^

 - A new -Wsizeof-pointer-memaccess warning has been added (also enabled by
   -Wall) to warn about suspicious length parameters to certain string and
   memory built-in functions if the argument uses sizeof. This warning warns
   e.g. about memset (ptr, 0, sizeof (ptr)); if ptr is not an array, but a
   pointer, and suggests a possible fix, or about
   memcpy (&foo, ptr, sizeof (&foo));.

 - The new option -Wpedantic is an alias for -pedantic, which is now
   deprecated. The forms -Wno-pedantic, -Werror=pedantic, and -Wno-
   error=pedantic work in the same way as for any other -W option. One caveat
   is that -Werror=pedantic is not equivalent to -pedantic-errors, since the
   latter makes into errors some warnings that are not controlled by
   -Wpedantic, and the former only affects diagnostics that are disabled when
   using -Wno-pedantic.

 - The option -Wshadow no longer warns if a declaration shadows a function
   declaration, unless the former declares a function or pointer to function,
   because this is a_common_and_valid_case_in_real-world_code.


C++
---

 - G++ now implements the C++11 thread_local keyword; this differs from the GNU
   __thread keyword primarily in that it allows dynamic initialization and
   destruction semantics. Unfortunately, this support requires a run-time
   penalty for references to non-function-local thread_local variables defined
   in a different translation unit even if they don't need dynamic
   initialization, so users may want to continue to use __thread for TLS
   variables with static initialization semantics.

   If the programmer can be sure that no use of the variable in a non-defining
   TU needs to trigger dynamic initialization (either because the variable is
   statically initialized, or a use of the variable in the defining TU will be
   executed before any uses in another TU), they can avoid this overhead with
   the -fno-extern-tls-init option.

   OpenMP threadprivate variables now also support dynamic initialization and
   destruction by the same mechanism.

 - G++ now implements the C++11 attribute syntax, e.g.

     [[noreturn]] void f();

   and also the alignment specifier, e.g.

     alignas(double) int i;

 - G++ now implements C++11 inheriting constructors, e.g.

     struct A { A(int); };
     struct B: A { using A::A; }; // defines B::B(int)
     B b(42); // OK

 - As of GCC 4.8.1, G++ implements the change to decltype semantics from N3276.

     struct A f();
     decltype(f()) g();    // OK, return type of f() is not required
     to be complete.

 - G++ now supports a -std=c++1y option for experimentation with features
   proposed for the next revision of the standard, expected around 2017.
   Currently the only difference from -std=c++11 is support for return type
   deduction in normal functions, as proposed in N3386.

 - The G++ namespace association extension, __attribute ((strong)), has been
   deprecated. Inline namespaces should be used instead.

 - G++ now supports a -fext-numeric-literal option to control whether GNU
   numeric literal suffixes are accepted as extensions or processed as C++11
   user-defined numeric literal suffixes. The flag is on (use suffixes for GNU
   literals) by default for -std=gnu++*, and -std=c++98. The flag is off (use
   suffixes for user-defined literals) by default for -std=c++11 and later.


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

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

   - forward_list meets the allocator-aware container requirements;

   - this_thread::sleep_for(), this_thread::sleep_until() and this_thread::
     yield() are defined without requiring the configure option
     --enable-libstdcxx-time;

 - Improvements to <random>:

   - SSE optimized normal_distribution.

   - Use of hardware RNG instruction for random_device on new x86 processors
     (requires the assembler to support the instruction.)

   and <ext/random>:

   - New random number engine simd_fast_mersenne_twister_engine with an
     optimized SSE implementation.

   - New random number distributions beta_distribution, normal_mv_distribution,
     rice_distribution, nakagami_distribution, pareto_distribution,
     k_distribution, arcsine_distribution, hoyt_distribution.

 - Added --disable-libstdcxx-verbose configure option to disable diagnostic
   messages issued when a process terminates abnormally. This may be useful for
   embedded systems to reduce the size of executables that link statically to
   the library.


Fortran
-------

 - Compatibility notice:

   - Module files: The version of module files (.mod) has been incremented.
     Fortran MODULEs compiled by earlier GCC versions have to be recompiled,
     when they are USEd by files compiled with GCC 4.8. GCC 4.8 is not able to
     read .mod files created by earlier versions; attempting to do so gives an
     error message.
     Note: The ABI of the produced assembler data itself has not changed;
     object files and libraries are fully compatible with older versions except
     as noted below.

   - ABI: Some internal names (used in the assembler/object file) have changed
     for symbols declared in the specification part of a module. If an affected
     module - or a file using it via use association - is recompiled, the
     module and all files which directly use such symbols have to be recompiled
     as well. This change only affects the following kind of module symbols:

     - Procedure pointers. Note: C-interoperable function pointers (type
       (c_funptr)) are not affected nor are procedure-pointer components.
     - Deferred-length character strings.

 - The BACKTRACE intrinsic subroutine has been added. It shows a backtrace at
   an arbitrary place in user code; program execution continues normally
   afterwards.

 - The -Wc-binding-type warning option has been added (disabled by default). It
   warns if the a variable might not be C interoperable; in particular, if the
   variable has been declared using an intrinsic type with default kind instead
   of using a kind parameter defined for C interoperability in the intrinsic
   ISO_C_Binding module. Before, this warning was always printed. The
   -Wc-binding-type option is enabled by -Wall.

 - The -Wrealloc-lhs and -Wrealloc-lhs-all warning command-line options have
   been added, which diagnose when code to is inserted for automatic
   (re)allocation of a variable during assignment. This option can be used to
   decide whether it is safe to use -fno-realloc-lhs. Additionally, it can be
   used to find automatic (re)allocation in hot loops. (For arrays, replacing
   var= by var(:)= disables the automatic reallocation.)

 - The -Wcompare-reals command-line option has been added. When this is set,
   warnings are issued when comparing REAL or COMPLEX types for equality and
   inequality; consider replacing a == b by abs(a-b) < eps with a suitable eps.
   -Wcompare-reals is enabled by -Wextra.

 - The -Wtarget-lifetime command-line option has been added (enabled with
   -Wall), which warns if the pointer in a pointer assignment might outlive its
   target.

 - Reading floating point numbers which use q for the exponential (such as
   4.0q0) is now supported as vendor extension for better compatibility with
   old data files. It is strongly recommended to use for I/O the equivalent but
   standard conforming e (such as 4.0e0).
   (For Fortran source code, consider replacing the q in floating-point
   literals by a kind parameter (e.g. 4.0e0_qp with a suitable qp). Note that -
   in Fortran source code - replacing q by a simple e is not equivalent.)

 - The GFORTRAN_TMPDIR environment variable for specifying a non-default
   directory for files opened with STATUS="SCRATCH", is not used anymore.
   Instead gfortran checks the POSIX/GNU standard TMPDIR environment variable.
   If TMPDIR is not defined, gfortran falls back to other methods to determine
   the directory for temporary files as documented in the user_manual.

 - Fortran_2003:

   - Support for unlimited polymorphic variables (CLASS(*)) has been added.
     Nonconstant character lengths are not yet supported.

 - TS_29113:

   - Assumed types (TYPE(*)) are now supported.

   - Experimental support for assumed-rank arrays (dimension(..)) has been
     added. Note that currently gfortran's own array descriptor is used, which
     is different from the one defined in TS29113, see gfortran's_header_file
     or use the Chasm_Language_Interoperability_Tools.


Go
--

 - GCC 4.8.0 implements a preliminary version of the upcoming Go 1.1 release.
   The library support is not quite complete, due to release timing.

 - Go has been tested on GNU/Linux and Solaris platforms for various processors
   including x86, x86_64, PowerPC, SPARC, and Alpha. It may work on other
   platforms as well.


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


AArch64
-------

 - A new port has been added to support AArch64, the new 64-bit architecture
   from ARM. Note that this is a separate port from the existing 32-bit ARM
   port.
 - The port provides initial support for the Cortex-A53 and the Cortex-A57
   processors with the command line options -mcpu=cortex-a53 and
   -mcpu=cortex-a57.


ARM
---

 - Initial support has been added for the AArch32 extensions defined in the
   ARMv8 architecture.

 - Code generation improvements for the Cortex-A7 and Cortex-A15 CPUs.

 - A new option, -mcpu=marvell-pj4, has been added to generate code for the
   Marvell PJ4 processor.

 - The compiler can now automatically generate the VFMA, VFMS, REVSH and REV16
   instructions.

 - A new vectorizer cost model for Advanced SIMD configurations to improve the
   auto-vectorization strategies used.

 - The scheduler now takes into account the number of live registers to reduce
   the amount of spilling that can occur. This should improve code performance
   in large functions. The limit can be removed by using the option -fno-sched-
   pressure.

 - Improvements have been made to the Marvell iWMMX code generation and support
   for the iWMMX2 SIMD unit has been added. The option -mcpu=iwmmxt2 can be
   used to enable code generation for the latter.

 - A number of code generation improvements for Thumb2 to reduce code size when
   compiling for the M-profile processors.

 - The RTEMS (arm-rtems) port has been updated to use the EABI.

 - Code generation support for the old FPA and Maverick floating-point
   architectures has been removed. Ports that previously relied on these
   features have also been removed. This includes the targets:

   - arm*-*-linux-gnu (use arm*-*-linux-gnueabi)
   - arm*-*-elf (use arm*-*-eabi)
   - arm*-*-uclinux* (use arm*-*-uclinux*eabi)
   - arm*-*-ecos-elf (no alternative)
   - arm*-*-freebsd (no alternative)
   - arm*-wince-pe* (no alternative).


AVR
---

 - Support for the "Embedded C" fixed-point has been added. For details, see
   the GCC_wiki and the user_manual. The support is not complete.
 - A new print modifier %r for register operands in inline assembler is
   supported. It will print the raw register number without the register prefix
   'r':

     /* Return the most significant byte of 'val', a 64-bit value.  */

     unsigned char msb (long long val)
       {
         unsigned char c;
         __asm__ ("mov %0, %r1+7" : "=r" (c) : "r" (val));
         return c;
       }

   The inline assembler in this example will generate code like

     mov r24, 8+7

   provided c is allocated to R24 and val is allocated to R8...R15. This works
   because the GNU assembler accepts plain register numbers without register
   prefix.

 - Static initializers with 3-byte symbols are supported now:

     extern const __memx char foo;
     const __memx void *pfoo = &foo;

   This requires at least Binutils 2.23.


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

 - Allow -mpreferred-stack-boundary=3 for the x86-64 architecture with SSE
   extensions disabled. Since the x86-64 ABI requires 16 byte stack alignment,
   this is ABI incompatible and intended to be used in controlled environments
   where stack space is an important limitation. This option will lead to wrong
   code when functions compiled with 16 byte stack alignment (such as functions
   from a standard library) are called with misaligned stack. In this case, SSE
   instructions may lead to misaligned memory access traps. In addition,
   variable arguments will be handled incorrectly for 16 byte aligned objects
   (including x87 long double and __int128), leading to wrong results. You must
   build all modules with -mpreferred-stack-boundary=3, including any
   libraries. This includes the system libraries and startup modules.

 - Support for the new Intel processor codename Broadwell with RDSEED, ADCX,
   ADOX, PREFETCHW is available through -madx, -mprfchw, -mrdseed command-line
   options.

 - Support for the Intel RTM and HLE intrinsics, built-in functions and code
   generation is available via -mrtm and -mhle.

 - Support for the Intel FXSR, XSAVE and XSAVEOPT instruction sets. Intrinsics
   and built-in functions are available via -mfxsr, -mxsave and -mxsaveopt
   respectively.

 - New -maddress-mode=[short|long] options for x32. -maddress-mode=short
   overrides default 64-bit addresses to 32-bit by emitting the 0x67 address-
   size override prefix. This is the default address mode for x32.

 - New built-in functions to detect run-time CPU type and ISA:

   - A built-in function __builtin_cpu_is has been added to detect if the run-
     time CPU is of a particular type. It returns a positive integer on a match
     and zero otherwise. It accepts one string literal argument, the CPU name.
     For example, __builtin_cpu_is("westmere") returns a positive integer if
     the run-time CPU is an Intel Core i7 Westmere processor. Please refer to
     the user_manual for the list of valid CPU names recognized.

   - A built-in function __builtin_cpu_supports has been added to detect if the
     run-time CPU supports a particular ISA feature. It returns a positive
     integer on a match and zero otherwise. It accepts one string literal
     argument, the ISA feature. For example, __builtin_cpu_supports("ssse3")
     returns a positive integer if the run-time CPU supports SSSE3
     instructions. Please refer to the user_manual for the list of valid ISA
     names recognized.

   Caveat: If these built-in functions are called before any static
   constructors are invoked, like during IFUNC initialization, then the CPU
   detection initialization must be explicitly run using this newly provided
   built-in function, __builtin_cpu_init. The initialization needs to be done
   only once. For example, this is how the invocation would look like inside an
   IFUNC initializer:

        static void (*some_ifunc_resolver(void))(void)
        {
          __builtin_cpu_init();
          if (__builtin_cpu_is("amdfam10h") ...
          if (__builtin_cpu_supports("popcnt") ...
        }

 - Function Multiversioning Support with G++:
   It is now possible to create multiple function versions each targeting a
   specific processor and/or ISA. Function versions have the same signature but
   different target attributes. For example, here is a program with function
   versions:

     __attribute__ ((target ("default")))
     int foo(void)
       {
         return 1;
       }

     __attribute__ ((target ("sse4.2")))
     int foo(void)
       {
         return 2;
       }

     int main (void)
     {
       int (*p) = &foo;
       assert ((*p)() == foo());
       return 0;
     }

   Please refer to this wiki for more information.

 - The x86 backend has been improved to allow option -fschedule-insns to work
   reliably. This option can be used to schedule instructions better and leads
   to improved performace in certain cases.

 - Windows MinGW-w64 targets (*-w64-mingw*) require at least r5437 from the
   Mingw-w64 trunk.

 - Support for new AMD family 15h processors (Steamroller core) is now
   available through the -march=bdver3 and -mtune=bdver3 options.

 - Support for new AMD family 16h processors (Jaguar core) is now available
   through the -march=btver2 and -mtune=btver2 options.


FRV
---

 - This target now supports the -fstack-usage command-line option.


MIPS
----

 - GCC can now generate code specifically for the R4700, Broadcom XLP and MIPS
   34kn processors. The associated -march options are -march=r4700, -march=xlp
   and -march=34kn respectively.

 - GCC now generates better DSP code for MIPS 74k cores thanks to further
   scheduling optimizations.

 - The MIPS port now supports the -fstack-check option.

 - GCC now passes the -mmcu and -mno-mcu options to the assembler.

 - Previous versions of GCC would silently accept -fpic and -fPIC for
   -mno-abicalls targets like mips*-elf. This combination was not intended or
   supported, and did not generate position-independent code. GCC 4.8 now
   reports an error when this combination is used.


PowerPC / PowerPC64 / RS6000
----------------------------

 - SVR4 configurations (GNU/Linux, FreeBSD, NetBSD) no longer save, restore or
   update the VRSAVE register by default. The respective operating systems
   manage the VRSAVE register directly.

 - Large TOC support has been added for AIX through the command line option
   -mcmodel=large.

 - Native Thread-Local Storage support has been added for AIX.

 - VMX (Altivec) and VSX instruction sets now are enabled implicitly when
   targetting processors that support those hardware features on AIX 6.1 and
   above.


RX
--

 - This target will now issue a warning message whenever multiple fast
   interrupt handlers are found in the same cpmpilation unit. This feature can
   be turned off by the new -mno-warn-multiple-fast-interrupts command-line
   option.


S/390, System z
---------------

 - Support for the IBM zEnterprise zEC12 processor has been added. When using
   the -march=zEC12 option, the compiler will generate code making use of the
   following new instructions:

   - load and trap instructions
   - 2 new compare and trap instructions
   - rotate and insert selected bits - without CC clobber

   The -mtune=zEC12 option enables zEC12 specific instruction scheduling
   without making use of new instructions.

 - Register pressure sensitive instruction scheduling is enabled by default.

 - The ifunc function attribute is enabled by default.

 - memcpy and memcmp invokations on big memory chunks or with run time lengths
   are not generated inline anymore when tuning for z10 or higher. The purpose
   is to make use of the IFUNC optimized versions in Glibc.


SH
--

 - The default alignment settings have been reduced to be less aggressive. This
   results in more compact code for optimization levels other than -Os.

 - Improved support for the __atomic built-in functions:

   - A new option -matomic-model=model selects the model for the generated
     atomic sequences. The following models are supported:

     soft-gusa
         Software gUSA sequences (SH3* and SH4* only). On SH4A targets this
         will now also partially utilize the movco.l and movli.l
         instructions. This is the default when the target is sh3*-*-linux*
         or sh4*-*-linux*.
     hard-llcs
         Hardware movco.l / movli.l sequences (SH4A only).
     soft-tcb
         Software thread control block sequences.
     soft-imask
         Software interrupt flipping sequences (privileged mode only). This
         is the default when the target is sh1*-*-linux* or sh2*-*-linux*.
     none
         Generates function calls to the respective __atomic built-in
         functions. This is the default for SH64 targets or when the target
         is not sh*-*-linux*.

   - The option -msoft-atomic has been deprecated. It is now an alias for
     -matomic-model=soft-gusa.

   - A new option -mtas makes the compiler generate the tas.b instruction for
     the __atomic_test_and_set built-in function regardless of the selected
     atomic model.

   - The __sync functions in libgcc now reflect the selected atomic model when
     building the toolchain.

 - Added support for the mov.b and mov.w instructions with displacement
   addressing.

 - Added support for the SH2A instructions movu.b and movu.w.

 - Various improvements to code generated for integer arithmetic.

 - Improvements to conditional branches and code that involves the T bit. A new
   option -mzdcbranch tells the compiler to favor zero-displacement branches.
   This is enabled by default for SH4* targets.

 - The pref instruction will now be emitted by the __builtin_prefetch built-in
   function for SH3* targets.

 - The fmac instruction will now be emitted by the fmaf standard function and
   the __builtin_fmaf built-in function.

 - The -mfused-madd option has been deprecated in favor of the machine-
   independent -ffp-contract option. Notice that the fmac instruction will now
   be generated by default for expressions like a * b + c. This is due to the
   compiler default setting -ffp-contract=fast.

 - Added new options -mfsrra and -mfsca to allow the compiler using the fsrra
   and fsca instructions on targets other than SH4A (where they are already
   enabled by default).

 - Added support for the __builtin_bswap32 built-in function. It is now
   expanded as a sequence of swap.b and swap.w instructions instead of a
   library function call.

 - The behavior of the -mieee option has been fixed and the negative form
   -mno-ieee has been added to control the IEEE conformance of floating point
   comparisons. By default -mieee is now enabled and the option -ffinite-math-
   only implicitly sets -mno-ieee.

 - Added support for the built-in functions __builtin_thread_pointer and
   __builtin_set_thread_pointer. This assumes that GBR is used to hold the
   thread pointer of the current thread. Memory loads and stores relative to
   the address returned by __builtin_thread_pointer will now also utilize GBR
   based displacement address modes.


SPARC
-----

 - Added optimized instruction scheduling for Niagara4.


TILE-Gx
-------

 - Added support for the -mcmodel=MODEL command-line option. The models
   supported are small and large.


V850
----

 - This target now supports the E3V5 architecture via the use of the new
   -mv850e3v5 command-line option. It also has experimental support for the e3v5
   LOOP instruction which can be enabled via the new -mloop command-line
   option.


XStormy16
---------

 - This target now supports the -fstack-usage command-line option.


Operating Systems
=================


Windows (Cygwin)
----------------

 - Executables are now linked against shared libgcc by default. The previous
   default was to link statically, which can still be done by explicitly
   specifying -static or -static-libgcc on the command line. However it is
   strongly advised against, as it will cause problems for any application that
   makes use of DLLs compiled by GCC. It should be alright for a monolithic
   stand-alone application that only links against the Windows OS DLLs, but
   offers little or no benefit.


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mailing list might help.  Please send comments on these web pages and
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Last modified 2013-03-23.