/usr/src/gcc-6/debian/NEWS.gcc

This file contains information about GCC releases which has been generated
automatically from the online release notes. It covers releases of GCC
(and the former EGCS project) since EGCS 1.0, on the line of development
that led to GCC 3. For information on GCC 2.8.1 and older releases of GCC 2,
see ONEWS.

======================================================================
http://gcc.gnu.org/gcc-6/index.html
GCC 6 Release Series

April 27, 2015

The [1]GNU project and the GCC developers are pleased to announce the
release of GCC 6.1.

This release is a major release, containing new features (as well as
many other improvements) relative to GCC 5.x.

Release History

GCC 6.1
April 27, 2015 ([2]changes, [3]documentation)

References and Acknowledgements

GCC used to stand for the GNU C Compiler, but since the compiler
supports several other languages aside from C, it now stands for the
GNU Compiler Collection.

A list of [4]successful builds is updated as new information becomes
available.

The GCC developers would like to thank the numerous people that have
contributed new features, improvements, bug fixes, and other changes as
well as test results to GCC. This [5]amazing group of volunteers is
what makes GCC successful.

For additional information about GCC please refer to the [6]GCC project
web site or contact the [7]GCC development mailing list.

To obtain GCC please use [8]our mirror sites or [9]our SVN server.

For questions related to the use of GCC, please consult these web
pages and the [10]GCC manuals. If that fails, the
[11]gcc-help@gcc.gnu.org mailing list might help. Comments on these
web pages and the development of GCC are welcome on our developer
list at [12]gcc@gcc.gnu.org. All of [13]our lists have public
archives.

Copyright (C) [14]Free Software Foundation, Inc. Verbatim copying and
distribution of this entire article is permitted in any medium,
provided this notice is preserved.

These pages are [15]maintained by the GCC team. Last modified
2016-04-27[16].

References

1. http://www.gnu.org/
2. http://gcc.gnu.org/gcc-6/changes.html
3. http://gcc.gnu.org/onlinedocs/6.1.0/
4. http://gcc.gnu.org/gcc-6/buildstat.html
5. http://gcc.gnu.org/onlinedocs/gcc/Contributors.html
6. http://gcc.gnu.org/index.html
7. mailto:gcc@gcc.gnu.org
8. http://gcc.gnu.org/mirrors.html
9. http://gcc.gnu.org/svn.html
10. https://gcc.gnu.org/onlinedocs/
11. mailto:gcc-help@gcc.gnu.org
12. mailto:gcc@gcc.gnu.org
13. https://gcc.gnu.org/lists.html
14. http://www.fsf.org/
15. https://gcc.gnu.org/about.html
16. http://validator.w3.org/check/referer
======================================================================
http://gcc.gnu.org/gcc-6/changes.html
GCC 6 Release Series
Changes, New Features, and Fixes

This page is a brief summary of some of the huge number of improvements
in GCC 6. For more information, see the [1]Porting to GCC 6 page and
the [2]full GCC documentation.

Caveats

* The default mode for C++ is now -std=gnu++14 instead of
-std=gnu++98.
* Support for a number of older systems and recently unmaintained or
untested target ports of GCC has been declared obsolete in GCC 6.
Unless there is activity to revive them, the next release of GCC
will have their sources permanently removed.
The following ports for individual systems on particular
architectures have been obsoleted:
+ SH5 / SH64 (sh64-*-*) as announced [3]here.

General Optimizer Improvements

* UndefinedBehaviorSanitizer gained a new sanitization option,
-fsanitize=bounds-strict, which enables strict checking of array
bounds. In particular, it enables -fsanitize=bounds as well as
instrumentation of flexible array member-like arrays.
* Type-based alias analysis now disambiguates accesses to different
pointers. This improves precision of the alias oracle by about
20-30% on higher-level C++ programs. Programs doing invalid type
punning of pointer types may now need -fno-strict-aliasing to work
correctly.
* Alias analysis now correctly supports weakref and alias attributes.
This makes it possible to access both a variable and its alias in
one translation unit which is common with link-time optimization.
* Value range propagation now assumes that the this pointer of C++
member functions is non-null. This eliminates common null pointer
checks but also breaks some non-conforming code-bases (such as
Qt-5, Chromium, KDevelop). As a temporary work-around
-fno-delete-null-pointer-checks can be used. Wrong code can be
identified by using -fsanitize=undefined.
* Link-time optimization improvements:
+ warning and error attributes are now correctly preserved by
declaration linking and thus -D_FORTIFY_SOURCE=2 is now
supported with -flto.
+ Type merging was fixed to handle C and Fortran
interoperability rules as defined by the Fortran 2008 language
standard.
As an exception, CHARACTER(KIND=C_CHAR) is not inter-operable
with char in all cases because it is an array while char is
scalar. INTEGER(KIND=C_SIGNED_CHAR) should be used instead. In
general, this inter-operability cannot be implemented, for
example, on targets where function passing conventions of
arrays differs from scalars.
+ More type information is now preserved at link time reducing
the loss of accuracy of the type based alias analysis compared
to builds without link-time optimization.
+ Invalid type punning on global variables and declarations is
now reported with -Wodr-type-mismatch.
+ The size of LTO object files was reduced by about 11%
(measured by compiling Firefox 46.0).
+ Link-time parallelization (enabled using -flto=n) was
significantly improved by decreasing the size of streamed data
when partitioning programs. The size of streamed IL while
compiling Firefox 46.0 was reduced by 66%.
+ The linker plugin was extended to pass information about type
of binary produced to GCC back end (that can be also manually
controlled by -flinker-output). This makes it possible to
properly configure the code generator and support incremental
linking. Incremental linking of LTO objects by gcc -r is now
supported on plugin-enabled setups.
There are two ways to perform incremental linking:
1. Linking by ld -r will result in an object file with all
sections from individual object files mechanically
merged. This delays the actual link time optimization to
final linking step and thus permits whole program
optimization. Linking final binary with such object files
is however slower.
2. Linking by gcc -r will lead to link time optimization and
produce final binary into the object file. Linking such
object file is fast but avoids any benefits from whole
program optimization.
GCC 7 will support incremental link-time optimization with gcc
-r.
* Inter-procedural optimization improvements:
+ Basic jump threading is now performed before profile
construction and inline analysis, resulting in more realistic
size and time estimates that drive the heuristics of the of
inliner and function cloning passes.
+ Function cloning now more aggressively eliminates unused
function parameters.

New Languages and Language specific improvements

Compared to GCC 5, the GCC 6 release series includes a much improved
implementation of the [4]OpenACC 2.0a specification. Highlights are:
* In addition to single-threaded host-fallback execution, offloading
is supported for nvptx (Nvidia GPUs) on x86_64 and PowerPC 64-bit
little-endian GNU/Linux host systems. For nvptx offloading, with
the OpenACC parallel construct, the execution model allows for an
arbitrary number of gangs, up to 32 workers, and 32 vectors.
* Initial support for parallelized execution of OpenACC kernels
constructs:
+ Parallelization of a kernels region is switched on by
-fopenacc combined with -O2 or higher.
+ Code is offloaded onto multiple gangs, but executes with just
one worker, and a vector length of 1.
+ Directives inside a kernels region are not supported.
+ Loops with reductions can be parallelized.
+ Only kernels regions with one loop nest are parallelized.
+ Only the outer-most loop of a loop nest can be parallelized.
+ Loop nests containing sibling loops are not parallelized.
Typically, using the OpenACC parallel construct gives much better
performance, compared to the initial support of the OpenACC kernels
construct.
* The device_type clause is not supported. The bind and nohost
clauses are not supported. The host_data directive is not supported
in Fortran.
* Nested parallelism (cf. CUDA dynamic parallelism) is not supported.
* Usage of OpenACC constructs inside multithreaded contexts (such as
created by OpenMP, or pthread programming) is not supported.
* If a call to the acc_on_device function has a compile-time constant
argument, the function call evaluates to a compile-time constant
value only for C and C++ but not for Fortran.

See the [5]OpenACC and [6]Offloading wiki pages for further
information.

C family

* Version 4.5 of the [7]OpenMP specification is now supported in the
C and C++ compilers.
* The C and C++ compilers now support attributes on enumerators. For
instance, it is now possible to mark enumerators as deprecated:

enum {
newval,
oldval __attribute__ ((deprecated ("too old")))
};

* Source locations for the C and C++ compilers are now tracked as
ranges, rather than just points, making it easier to identify the
subexpression of interest within a complicated expression. For
example:

test.cc: In function 'int test(int, int, foo, int, int)':
test.cc:5:16: error: no match for 'operator*' (operand types are 'int' and 'foo'
)
return p + q * r * s + t;
~~^~~

In addition, there is now initial support for precise diagnostic
locations within strings:

format-strings.c:3:14: warning: field width specifier '*' expects a matching 'in
t' argument [-Wformat=]
printf("%*d");
^

* Diagnostics can now contain "fix-it hints", which are displayed in
context underneath the relevant source code. For example:

fixits.c: In function 'bad_deref':
fixits.c:11:13: error: 'ptr' is a pointer; did you mean to use '->'?
return ptr.x;
^
->

* The C and C++ compilers now offer suggestions for misspelled field
names:

spellcheck-fields.cc:52:13: error: 'struct s' has no member named 'colour'; did
you mean 'color'?
return ptr->colour;
^~~~~~

* New command-line options have been added for the C and C++
compilers:
+ -Wshift-negative-value warns about left shifting a negative
value.
+ -Wshift-overflow warns about left shift overflows. This
warning is enabled by default. -Wshift-overflow=2 also warns
about left-shifting 1 into the sign bit.
+ -Wtautological-compare warns if a self-comparison always
evaluates to true or false. This warning is enabled by -Wall.
+ -Wnull-dereference warns if the compiler detects paths that
trigger erroneous or undefined behavior due to dereferencing a
null pointer. This option is only active when
-fdelete-null-pointer-checks is active, which is enabled by
optimizations in most targets. The precision of the warnings
depends on the optimization options used.
+ -Wduplicated-cond warns about duplicated conditions in an
if-else-if chain.
+ -Wmisleading-indentation warns about places where the
indentation of the code gives a misleading idea of the block
structure of the code to a human reader. For example, given
[8]CVE-2014-1266:

sslKeyExchange.c: In function 'SSLVerifySignedServerKeyExchange':
sslKeyExchange.c:629:3: warning: this 'if' clause does not guard... [-Wmisleadin
g-indentation]
if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0)
^~
sslKeyExchange.c:631:5: note: ...this statement, but the latter is misleadingly
indented as if it is guarded by the 'if'
goto fail;
^~~~

This warning is enabled by -Wall.
* The C and C++ compilers now emit saner error messages if
merge-conflict markers are present in a source file.

test.c:3:1: error: version control conflict marker in file
<<<<<<< HEAD
^~~~~~~

* It is possible to disable warnings when an initialized field of a
structure or a union with side effects is being overridden when
using designated initializers via a new warning option
-Woverride-init-side-effects.
* A new type attribute scalar_storage_order applying to structures
and unions has been introduced. It specifies the storage order (aka
endianness) in memory of scalar fields in structures or unions.

C++

* The default mode has been changed to -std=gnu++14.
* [9]C++ Concepts are now supported when compiling with -fconcepts.
* -flifetime-dse is more aggressive in dead-store elimination in
situations where a memory store to a location precedes a
constructor to the memory location.
* G++ now supports [10]C++17 fold expressions, u8 character literals,
extended static_assert, and nested namespace definitions.
* G++ now allows constant evaluation for all non-type template
arguments.
* G++ now supports C++ Transactional Memory when compiling with
-fgnu-tm.

Runtime Library (libstdc++)

* Extensions to the C++ Library to support mathematical special
functions (ISO/IEC 29124:2010), thanks to Edward Smith-Rowland.
* Experimental support for C++17, including the following new
features:
+ std::uncaught_exceptions function (this is also available for
-std=gnu++NN modes);
+ new member functions try_emplace and insert_or_assign for
unique_key maps;
+ non-member functions std::size, std::empty, and std::data for
accessing containers and arrays;
+ std::invoke;
+ std::shared_mutex;
+ std::void_t and std::bool_constant metaprogramming utilities.
Thanks to Ville Voutilainen for contributing many of the C++17
features.
* An experimental implementation of the File System TS.
* Experimental support for most features of the second version of the
Library Fundamentals TS. This includes polymorphic memory resources
and array support in shared_ptr, thanks to Fan You.
* Some assertions checked by Debug Mode can now also be enabled by
_GLIBCXX_ASSERTIONS. The subset of checks enabled by the new macro
have less run-time overhead than the full _GLIBCXX_DEBUG checks and
don't affect the library ABI, so can be enabled per-translation
unit.
* Timed mutex types are supported on more targets, including Darwin.
* Improved std::locale support for DragonFly and FreeBSD, thanks to
John Marino and Andreas Tobler.

Fortran

* The MATMUL intrinsic is now inlined for straightforward cases if
front-end optimization is active. The maximum size for inlining can
be set to n with the -finline-matmul-limit=n option and turned off
with -finline-matmul-llimit=0.
* The -Wconversion-extra option will warn about REAL constants which
have excess precision for their kind.
* The -Winteger-division option has been added, which warns about
divisions of integer constants which are truncated. This option is
included in -Wall by default.

libgccjit

* The driver code is now run in-process within libgccjit, providing a
small speed-up of the compilation process.
* The API has gained entrypoints for
+ [11]timing how long was spent in different parts of code,
+ [12]creating switch statements,
+ [13]allowing unreachable basic blocks in a function, and
+ [14]adding arbitrary command-line options to a compilation.

New Targets and Target Specific Improvements

AArch64

* The new command line options -march=native, -mcpu=native and
-mtune=native are now available on native AArch64 GNU/Linux
systems. Specifying these options will cause GCC to auto-detect the
host CPU and rewrite these options to the optimal setting for that
system. If GCC is unable to detect the host CPU these options have
no effect.
* -fpic is now supported by the AArch64 target when generating code
for the small code model (-mcmodel=small). The size of the global
offset table (GOT) is limited to 28KiB under the LP64 SysV ABI ,
and 15KiB under the ILP32 SysV ABI.
* The AArch64 port now supports target attributes and pragmas. Please
refer to the [15]documentation for details of available attributes
and pragmas as well as usage instructions.
* Link-time optimization across translation units with different
target-specific options is now supported.

ARM

* Support for revisions of the ARM architecture prior to ARMv4t has
been deprecated and will be removed in a future GCC release. The
-mcpu and -mtune values that are deprecated are: arm2, arm250,
arm3, arm6, arm60, arm600, arm610, arm620, arm7, arm7d, arm7di,
arm70, arm700, arm700i, arm710, arm720, arm710c, arm7100, arm7500,
arm7500fe, arm7m, arm7dm, arm7dmi, arm8, arm810, strongarm,
strongarm110, strongarm1100, strongarm1110, fa526, fa626. The value
arm7tdmi is still supported. The values of -march that are
deprecated are: armv2,armv2a,armv3,armv3m,armv4.
* The ARM port now supports target attributes and pragmas. Please
refer to the [16]documentation for details of available attributes
and pragmas as well as usage instructions.
* Support has been added for the following processors (GCC
identifiers in parentheses): ARM Cortex-A32 (cortex-a32), ARM
Cortex-A35 (cortex-a35). The GCC identifiers can be used as
arguments to the -mcpu or -mtune options, for example:
-mcpu=cortex-a32 or -mtune=cortex-a35.

Heterogeneous Systems Architecture

* GCC can now generate HSAIL (Heterogeneous System Architecture
Intermediate Language) for simple OpenMP device constructs if
configured with --enable-offload-targets=hsa. A new libgomp plugin
then runs the HSA GPU kernels implementing these constructs on HSA
capable GPUs via a standard HSA run time.
If the HSA compilation back end determines it cannot output HSAIL
for a particular input, it gives a warning by default. These
warnings can be suppressed with -Wno-hsa. To give a few examples,
the HSA back end does not implement compilation of code using
function pointers, automatic allocation of variable sized arrays,
functions with variadic arguments as well as a number of other less
common programming constructs.
When compilation for HSA is enabled, the compiler attempts to
compile composite OpenMP constructs

#pragma omp target teams distribute parallel for

into parallel HSA GPU kernels.

IA-32/x86-64

* GCC now supports the Intel CPU named Skylake with AVX-512
extensions through -march=skylake-avx512. The switch enables the
following ISA extensions: AVX-512F, AVX512VL, AVX-512CD, AVX-512BW,
AVX-512DQ.
* Support for new AMD instructions monitorx and mwaitx has been
added. This includes new intrinsic and built-in support. It is
enabled through option -mmwaitx. The instructions monitorx and
mwaitx implement the same functionality as the old monitor and
mwait instructions. In addition mwaitx adds a configurable timer.
The timer value is received as third argument and stored in
register %ebx.
* x86-64 targets now allow stack realignment from a word-aligned
stack pointer using the command-line option -mstackrealign or
__attribute__ ((force_align_arg_pointer)). This allows functions
compiled with a vector-aligned stack to be invoked from objects
that keep only word-alignment.
* Support for address spaces __seg_fs, __seg_gs, and __seg_tls. These
can be used to access data via the %fs and %gs segments without
having to resort to inline assembly. Please refer to the
[17]documentation for usage instructions.
* Support for AMD Zen (family 17h) processors is now available
through the -march=znver1 and -mtune=znver1 options.

MeP

* Support for the MeP (mep-elf) architecture has been deprecated and
will be removed in a future GCC release.

MSP430

* The MSP430 compiler now has the ability to automatically distribute
code and data between low memory (addresses below 64K) and high
memory. This only applies to parts that actually have both memory
regions and only if the linker script for the part has been
specifically set up to support this feature.
A new attribute of either can be applied to both functions and
data, and this tells the compiler to place the object into low
memory if there is room and into high memory otherwise. Two other
new attributes - lower and upper - can be used to explicitly state
that an object should be placed in the specified memory region. If
there is not enough left in that region the compilation will fail.
Two new command-line options - -mcode-region=[lower|upper|either]
and -mdata-region=[lower|upper|either] - can be used to tell the
compiler what to do with objects that do not have one of these new
attributes.

PowerPC / PowerPC64 / RS6000

* PowerPC64 now supports IEEE 128-bit floating-point using the
__float128 data type. In GCC 6, this is NOT enabled by default, but
you can enable it with -mfloat128. The IEEE 128-bit floating-point
support requires the use of the VSX instruction set. IEEE 128-bit
floating-point values are passed and returned as a single vector
value. The software emulator for IEEE 128-bit floating-point
support is only built on PowerPC Linux systems where the default
cpu is at least power7. On future ISA 3.0 systems (power9 and
later), you will be able to use the -mfloat128-hardware option to
use the ISA 3.0 instructions that support IEEE 128-bit
floating-point. An additional type (__ibm128) has been added to
refer to the IBM extended double type that normally implements long
double. This will allow for a future transition to implementing
long double with IEEE 128-bit floating-point.
* Basic support has been added for POWER9 hardware that will use the
recently published OpenPOWER ISA 3.0 instructions. The following
new switches are available:
+ -mcpu=power9: Implement all of the ISA 3.0 instructions
supported by the compiler.
+ -mtune=power9: In the future, apply tuning for POWER9 systems.
Currently, POWER8 tunings are used.
+ -mmodulo: Generate code using the ISA 3.0 integer instructions
(modulus, count trailing zeros, array index support, integer
multiply/add).
+ -mpower9-fusion: Generate code to suitably fuse instruction
sequences for a POWER9 system.
+ -mpower9-dform: Generate code to use the new D-form (register
+offset) memory instructions for the vector registers.
+ -mpower9-vector: Generate code using the new ISA 3.0 vector
(VSX or Altivec) instructions.
+ -mpower9-minmax: Reserved for future development.
+ -mtoc-fusion: Keep TOC entries together to provide more fusion
opportunities.
* New constraints have been added to support IEEE 128-bit
floating-point and ISA 3.0 instructions:
+ wb: Altivec register if -mpower9-dform is enabled.
+ we: VSX register if -mpower9-vector is enabled for 64-bit code
generation.
+ wo: VSX register if -mpower9-vector is enabled.
+ wp: Reserved for future use if long double is implemented with
IEEE 128-bit floating-point instead of IBM extended double.
+ wq: VSX register if -mfloat128 is enabled.
+ wF: Memory operand suitable for POWER9 fusion load/store.
+ wG: Memory operand suitable for TOC fusion memory references.
+ wL: Integer constant identifying the element number mfvsrld
accesses within a vector.
* Support has been added for __builtin_cpu_is () and
__builtin_cpu_supports (), allowing for very fast access to
AT_PLATFORM, AT_HWCAP, and AT_HWCAP2 values. This requires use of
glibc 2.23 or later.
* All hardware transactional memory builtins now correctly behave as
memory barriers. Programmers can use #ifdef __TM_FENCE__ to
determine whether their "old" compiler treats the builtins as
barriers.
* Split-stack support has been added for gccgo on PowerPC64 for both
big- and little-endian (but NOT for 32-bit). The gold linker from
at least binutils 2.25.1 must be available in the PATH when
configuring and building gccgo to enable split stack. (The
requirement for binutils 2.25.1 applies to PowerPC64 only.) The
split-stack feature allows a small initial stack size to be
allocated for each goroutine, which increases as needed.
* GCC on PowerPC now supports the standard lround function.
* A new configuration option ---with-advance-toolchain=at was added
for PowerPC 64-bit GNU/Linux systems to use the header files,
library files, and the dynamic linker from a specific Advance
Toolchain release instead of the default versions that are provided
by the GNU/Linux distribution. In general, this option is intended
for the developers of GCC, and it is not intended for general use.
* The "q", "S", "T", and "t" asm-constraints have been removed.
* The "b", "B", "m", "M", and "W" format modifiers have been removed.

S/390, System z, IBM z Systems

* Support for the IBM z13 processor has been added. When using the
-march=z13 option, the compiler will generate code making use of
the new instructions and registers introduced with the vector
extension facility. The -mtune=z13 option enables z13 specific
instruction scheduling without making use of new instructions.
Compiling code with -march=z13 reduces the default alignment of
vector types bigger than 8 bytes to 8. This is an ABI change and
care must be taken when linking modules compiled with different
arch levels which interchange variables containing vector type
values. For newly compiled code the GNU linker will emit a warning.
* The -mzvector option enables a C/C++ language extension. This
extension provides a new keyword vector which can be used to define
vector type variables. (Note: This is not available when enforcing
strict standard compliance e.g. with -std=c99. Either enable GNU
extensions with e.g. -std=gnu99 or use __vector instead of vector.)
Additionally a set of overloaded builtins is provided which is
partially compatible to the PowerPC Altivec builtins. In order to
make use of these builtins the vecintrin.h header file needs to be
included.
* The new command line options -march=native, and -mtune=native are
now available on native IBM z Systems. Specifying these options
will cause GCC to auto-detect the host CPU and rewrite these
options to the optimal setting for that system. If GCC is unable to
detect the host CPU these options have no effect.
* The IBM z Systems port now supports target attributes and pragmas.
Please refer to the [18]documentation for details of available
attributes and pragmas as well as usage instructions.
* -fsplit-stack is now supported as part of the IBM z Systems port.
This feature requires a recent gold linker to be used.
* Support for the g5 and g6 -march=/-mtune= CPU level switches has
been deprecated and will be removed in a future GCC release. -m31
from now on defaults to -march=z900 if not specified otherwise.
-march=native on a g5/g6 machine will default to -march=z900.

* Support for SH5 / SH64 has been declared obsolete and will be
removed in future releases.
* Support for the FDPIC ABI has been added. It can be enabled using
the new -mfdpic target option and --enable-fdpic configure option.

SPARC

* An ABI bug has been fixed in 64-bit mode. Unfortunately, this
change will break binary compatibility with earlier releases for
code it affects, but this should be pretty rare in practice. The
conditions are: a 16-byte structure containing a double or a 8-byte
vector in the second half is passed to a subprogram in slot #15,
for example as 16th parameter if the first 15 ones have at most 8
bytes. The double or vector was wrongly passed in floating-point
register %d32 in lieu of on the stack as per the SPARC calling
conventions.

Operating Systems

Linux

* Support for the [19]musl C library was added for the AArch64, ARM,
MicroBlaze, MIPS, MIPS64, PowerPC, PowerPC64, SH, i386, x32 and
x86_64 targets. It can be selected using the new -mmusl option in
case musl is not the default libc. GCC defaults to musl libc if it
is built with a target triplet matching the *-linux-musl* pattern.

RTEMS

* The RTEMS thread model implementation changed. Mutexes now use
self-contained objects defined in Newlib <sys/lock.h> instead of
Classic API semaphores. The keys for thread specific data and the
once function are directly defined via <pthread.h>. Self-contained
condition variables are provided via Newlib <sys/lock.h>. The RTEMS
thread model also supports C++11 threads.
* OpenMP support now uses self-contained objects provided by Newlib
<sys/lock.h> and offers a significantly better performance compared
to the POSIX configuration of libgomp. It is possible to configure
thread pools for each scheduler instance via the environment
variable GOMP_RTEMS_THREAD_POOLS.

AIX

* DWARF debugging support for AIX 7.1 has been enabled as an optional
debugging format. A more recent Technology Level (TL) and GCC built
with that level are required for full exploitation of DWARF
debugging capabilities.

Solaris

* Solaris 12 is now fully supported. Minimal support had already been
present in GCC 5.3.
* Solaris 12 provides a full set of startup files (crt1.o, crti.o,
crtn.o), which GCC now prefers over its own ones.
* Position independent executables (PIE) are now supported on Solaris
12.
* Constructor priority is now supported on Solaris 12 with the system
linker.
* libvtv has been ported to Solaris 11 and up.

Windows

* The option -mstackrealign is now automatically activated in 32-bit
mode whenever the use of SSE instructions is requested.

Other significant improvements

* The gcc and g++ driver programs will now provide suggestions for
misspelled command line options.

$ gcc -static-libfortran test.f95
gcc: error: unrecognized command line option '-static-libfortran'; did you mean
'-static-libgfortran'?

* The --enable-default-pie configure option enables generation of PIE
by default.

For questions related to the use of GCC, please consult these web
pages and the [20]GCC manuals. If that fails, the
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web pages and the development of GCC are welcome on our developer
list at [22]gcc@gcc.gnu.org. All of [23]our lists have public
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Copyright (C) [24]Free Software Foundation, Inc. Verbatim copying and
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These pages are [25]maintained by the GCC team. Last modified
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References

1. http://gcc.gnu.org/gcc-6/porting_to.html
2. http://gcc.gnu.org/onlinedocs/index.html#current
3. https://gcc.gnu.org/ml/gcc/2015-08/msg00101.html
4. http://www.openacc.org/
5. https://gcc.gnu.org/wiki/OpenACC
6. https://gcc.gnu.org/wiki/Offloading
7. http://openmp.org/wp/openmp-specifications/
8. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-1266
9. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4377.pdf
10. https://gcc.gnu.org/projects/cxx-status.html#cxx1z.html
11. https://gcc.gnu.org/onlinedocs/jit/topics/performance.html
12. https://gcc.gnu.org/onlinedocs/jit/topics/functions.html#gcc_jit_block_end_with_switch
13. https://gcc.gnu.org/onlinedocs/jit/topics/contexts.html#gcc_jit_context_set_bool_allow_unreachable_blocks
14. https://gcc.gnu.org/onlinedocs/jit/topics/contexts.html#gcc_jit_context_add_command_line_option
15. https://gcc.gnu.org/onlinedocs/gcc/AArch64-Function-Attributes.html#AArch64-Function-Attributes
16. https://gcc.gnu.org/onlinedocs/gcc/ARM-Function-Attributes.html#ARM-Function-Attributes
17. https://gcc.gnu.org/onlinedocs/gcc/Named-Address-Spaces.html#Named-Address-Spaces
18. https://gcc.gnu.org/onlinedocs/gcc/S_002f390-Function-Attributes.html#S_002f390-Function-Attributes
19. http://www.musl-libc.org/
20. https://gcc.gnu.org/onlinedocs/
21. mailto:gcc-help@gcc.gnu.org
22. mailto:gcc@gcc.gnu.org
23. https://gcc.gnu.org/lists.html
24. http://www.fsf.org/
25. https://gcc.gnu.org/about.html
26. http://validator.w3.org/check/referer

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