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-7/index.html
                              GCC 7 Release Series

   May 2, 2017

   The [1]GNU project and the GCC developers are pleased to announce the
   release of GCC 7.1.

   This release is a major release, containing new features (as well as
   many other improvements) relative to GCC 6.x.

Release History

   GCC 7.1
          May 2, 2017 ([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
   2017-05-02[16].

References

   1. http://www.gnu.org/
   2. http://gcc.gnu.org/gcc-7/changes.html
   3. http://gcc.gnu.org/onlinedocs/7.1.0/
   4. http://gcc.gnu.org/gcc-7/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-7/changes.html
                              GCC 7 Release Series
                        Changes, New Features, and Fixes

   This page is a brief summary of some of the huge number of improvements
   in GCC 7. For more information, see the [1]Porting to GCC 7 page and
   the [2]full GCC documentation.

Disclaimer: GCC 7 has not been released yet, so this document is a
work-in-progress.

Caveats

     * GCC now uses [3]LRA (a new local register allocator) by default for
       new targets.
     * The non-standard C++0x type traits has_trivial_default_constructor,
       has_trivial_copy_constructor and has_trivial_copy_assign have been
       removed.
     * The libstdc++ [4]Profile Mode has been deprecated and will be
       removed in a future version.
     * The Cilk+ extensions to the C and C++ languages have been
       deprecated.

General Optimizer Improvements

     * GCC 7 can determine the return value or range of return values of
       some calls to the sprintf family of functions and make it available
       to other optimization passes. Some calls to the snprintf function
       with a zero size argument can be folded into constants. This
       optimization is included in -O1 and can be selectively controlled
       by the -fprintf-return-value option.
     * A new store merging pass has been added. It merges constant stores
       to adjacent memory locations into fewer, wider, stores. It is
       enabled by the -fstore-merging option and at the -O2 optimization
       level or higher (and -Os).
     * A new code hoisting optimization has been added to the partial
       redundancy elimination pass. It attempts to move evaluation of
       expressions executed on all paths to the function exit as early as
       possible, which helps primarily for code size, but can be useful
       for speed of generated code as well. It is enabled by the
       -fcode-hoisting option and at the -O2 optimization level or higher
       (and -Os).
     * A new interprocedural bitwise constant propagation optimization has
       been added, which propagates knowledge about which bits of
       variables are known to be zero (including pointer alignment
       information) across the call graph. It is enabled by the
       -fipa-bit-cp option if -fipa-cp is enabled as well, and is enabled
       at the -O2 optimization level and higher (and -Os). This
       optimization supersedes interprocedural alignment propagation of
       GCC 6, and therefore the option -fipa-cp-alignment is now
       deprecated and ignored.
     * A new interprocedural value range propagation optimization has been
       added, which propagates integral ranges that variable values can be
       proven to be within across the call graph. It is enabled by the
       -fipa-vrp option and at the -O2 optimization level and higher (and
       -Os).
     * A new loop splitting optimization pass has been added. It splits
       certain loops if they contain a condition that is always true on
       one side of the iteration space and always false on the other into
       two loops where each of the new two loops iterates just on one of
       the sides of the iteration space and the condition does not need to
       be checked inside of the loop. It is enabled by the -fsplit-loops
       option and at the -O3 optimization level or higher.
     * The shrink-wrapping optimization can now separate portions of
       prologues and epilogues to improve performance if some of the work
       done traditionally by prologues and epilogues is not needed on
       certain paths. This is controlled by the -fshrink-wrap-separate
       option, enabled by default. It requires target support, which is
       currently only implemented in the PowerPC and AArch64 ports.
     * AddressSanitizer gained a new sanitization option,
       -fsanitize-address-use-after-scope, which enables sanitization of
       variables whose address is taken and used after a scope where the
       variable is defined:

int
main (int argc, char **argv)
{
  char *ptr;
    {
      char my_char;
      ptr = &my_char;
    }

  *ptr = 123;
  return *ptr;
}

==28882==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fffb8dba99
0 at pc 0x0000004006d5 bp 0x7fffb8dba960 sp 0x7fffb8dba958
WRITE of size 1 at 0x7fffb8dba990 thread T0
    #0 0x4006d4 in main /tmp/use-after-scope-1.c:10
    #1 0x7f9c71943290 in __libc_start_main (/lib64/libc.so.6+0x20290)
    #2 0x400739 in _start (/tmp/a.out+0x400739)

Address 0x7fffb8dba990 is located in stack of thread T0 at offset 32 in frame
    #0 0x40067f in main /tmp/use-after-scope-1.c:3

  This frame has 1 object(s):
    [32, 33) 'my_char' <== Memory access at offset 32 is inside this variable

       The option is enabled by default with -fsanitize=address and
       disabled by default with -fsanitize=kernel-address. Compared to the
       LLVM compiler, where the option already exists, the implementation
       in the GCC compiler has couple of improvements and advantages:
          + A complex usage of gotos and case labels are properly handled
            and should not report any false positive or false negatives.
          + C++ temporaries are sanitized.
          + Sanitization can handle invalid memory stores that are
            optimized out by the LLVM compiler when using an optimization
            level.
     * The -fsanitize=signed-integer-overflow suboption of the
       UndefinedBehavior Sanitizer now diagnoses arithmetic overflows even
       on arithmetic operations with generic vectors.
     * Version 5 of the [5]DWARF debugging information standard is
       supported through the -gdwarf-5 option. The DWARF version 4
       debugging information remains the default until debugging
       information consumers are adjusted.

New Languages and Language specific improvements

   OpenACC support in C, C++, and Fortran continues to be maintained and
   improved. See the [6]OpenACC and [7]Offloading wiki pages for further
   information.

  Ada

     * On mainstream native platforms, Ada programs no longer require the
       stack to be made executable in order to run properly.

  BRIG (HSAIL)

   Support for processing BRIG 1.0 files was added in this release. BRIG
   is a binary format for HSAIL (Heterogeneous System Architecture
   Intermediate Language). The BRIG frontend can be used for implementing
   HSAIL "finalizers" (compilation of HSAIL to a native ISA) for
   gcc-supported targets. An implementation of an HSAIL runtime library,
   libhsail-rt is also included.

  C family

     * New command-line options have been added for the C and C++
       compilers:
          + -Wimplicit-fallthrough warns when a switch case falls through.
            This warning has five different levels. The compiler is able
            to parse a wide range of fallthrough comments, depending on
            the level. It also handles control-flow statements, such as
            ifs. It's possible to suppres the warning by either adding a
            fallthrough comment, or by using a null statement:
            __attribute__ ((fallthrough)); (C, C++), or [[fallthrough]];
            (C++17), or [[gnu::fallthrough]]; (C++11/C++14). This warning
            is enabled by -Wextra.
          + -Wpointer-compare warns when a pointer is compared with a zero
            character constant. Such code is now invalid in C++11 and GCC
            rejects it. This warning is enabled by default.
          + -Wduplicated-branches warns when an if-else has identical
            branches.
          + -Wrestrict warns when an argument passed to a
            restrict-qualified parameter aliases with another argument.
          + -Wmemset-elt-size warns for memset calls, when the first
            argument references an array, and the third argument is a
            number equal to the number of elements of the array, but not
            the size of the array. This warning is enabled by -Wall.
          + -Wint-in-bool-context warns about suspicious uses of integer
            values where boolean values are expected. This warning is
            enabled by -Wall.
          + -Wswitch-unreachable warns when a switch statement has
            statements between the controlling expression and the first
            case label which will never be executed. This warning is
            enabled by default.
          + -Wexpansion-to-defined warns when defined is used outside #if.
            This warning is enabled by -Wextra or -Wpedantic.
          + -Wregister warns about uses of the register storage specifier.
            In C++17 this keyword has been removed and for C++17 this is a
            pedantic warning enabled by default. The warning is not
            emitted for the GNU Explicit Register Variables extension.
          + -Wvla-larger-than=N warns about unbounded uses of
            variable-length arrays, and about bounded uses of
            variable-length arrays whose bound can be larger than N bytes.
          + -Wduplicate-decl-specifier warns when a declaration has
            duplicate const, volatile, restrict or _Atomic specifier. This
            warning is enabled by -Wall.
     * GCC 6's C and C++ frontends were able to 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;
               ^~~~~~

       GCC 7 greatly expands the scope of these suggestions. Firstly, it
       adds fix-it hints to such suggestions:

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

       The suggestions now cover many other things, such as misspelled
       function names:

spellcheck-identifiers.c:11:3: warning: implicit declaration of function 'gtk_wi
dget_showall'; did you mean 'gtk_widget_show_all'? [-Wimplicit-function-declarat
ion]
   gtk_widget_showall (w);
   ^~~~~~~~~~~~~~~~~~
   gtk_widget_show_all

       misspelled macro names and enum values:

spellcheck-identifiers.cc:85:11: error: 'MAX_ITEM' undeclared here (not in a fun
ction); did you mean 'MAX_ITEMS'?
 int array[MAX_ITEM];
           ^~~~~~~~
           MAX_ITEMS

       misspelled type names:

spellcheck-typenames.c:7:14: error: unknown type name 'singed'; did you mean 'si
gned'?
 void test (singed char e);
            ^~~~~~
            signed

       and, in the C frontend, named initializers:

test.c:7:20: error: 'struct s' has no member named 'colour'; did you mean 'color
'?
 struct s test = { .colour = 3 };
                    ^~~~~~
                    color

     * The preprocessor can now offer suggestions for misspelled
       directives, e.g.:

test.c:5:2: error:invalid preprocessing directive #endfi; did you mean #endif?
 #endfi
  ^~~~~
  endif

     * Warnings about format strings now underline the pertinent part of
       the string, and can offer suggested fixes. In some cases, the
       pertinent argument is underlined.

test.c:51:29: warning: format '%s' expects argument of type 'char *', but argume
nt 3 has type 'int' [-Wformat=]
   printf ("foo: %d  bar: %s baz: %d", 100, i + j, 102);
                          ~^                ~~~~~
                          %d

     * The new -Wdangling-else command-line option has been split out of
       -Wparentheses and warns about dangling else.
     * The -Wshadow warning has been split into three variants.
       -Wshadow=global warns for any shadowing. This is the default when
       using -Wshadow without any argument. -Wshadow=local only warns for
       a local variable shadowing another local variable or parameter.
       -Wshadow=compatible-local only warns for a local variable shadowing
       another local variable or parameter whose type is compatible (in
       C++ compatible means that the type of the shadowing variable can be
       converted to that of the shadowed variable).
       The following example shows the different kinds of shadow warnings:

enum operation { add, count };
struct container { int nr; };

int
container_count (struct container c, int count)
{
  int r = 0;
  for (int count = 0; count > 0; count--)
    {
      struct container count = c;
      r += count.nr;
    }
  return r;
}

       -Wshadow=compatible-local will warn for the parameter being
       shadowed with the same type:

warn-test.c:8:12: warning: declaration of 'count' shadows a parameter [-Wshadow=
compatible-local]
   for (int count = 0; count > 0; count--)
            ^~~~~
warn-test.c:5:42: note: shadowed declaration is here
 container_count (struct container c, int count)
                                          ^~~~~

       -Wshadow=local will warn for the above and for the shadowed
       declaration with incompatible type:

warn-test.c:10:24: warning: declaration of 'count' shadows a previous local [-Ws
hadow=local]
       struct container count = c;
                        ^~~~~
warn-test.c:8:12: note: shadowed declaration is here
   for (int count = 0; count > 0; count--)
            ^~~~~

       -Wshadow=global will warn for all of the above and the shadowing of
       the global declaration:

warn-test.c:5:42: warning: declaration of 'count' shadows a global declaration [
-Wshadow]
 container_count (struct container c, int count)
                                          ^~~~~
warn-test.c:1:23: note: shadowed declaration is here
 enum operation { add, count };
                       ^~~~~

     * GCC 7 contains a number of enhancements that help detect buffer
       overflow and other forms of invalid memory accesses.
          + The -Walloc-size-larger-than=size option detects calls to
            standard and user-defined memory allocation functions
            decorated with attribute alloc_size whose argument exceeds the
            specified size (PTRDIFF_MAX by default). The option also
            detects arithmetic overflow in the computation of the size in
            two-argument allocation functions like calloc where the total
            size is the product of the two arguments. Since calls with an
            excessive size cannot succeed they are typically the result of
            programming errors. Such bugs have been known to be the source
            of security vulnerabilities and a target of exploits.
            -Walloc-size-larger-than=PTRDIFF_MAX is included in -Wall.
            For example, the following call to malloc incorrectly tries to
            avoid passing a negative argument to the function and instead
            ends up unconditionally invoking it with an argument less than
            or equal to zero. Since after conversion to the type of the
            argument of the function (size_t) a negative argument results
            in a value in excess of the maximum PTRDIFF_MAX the call is
            diagnosed.

void* f (int n)
{
  return malloc (n > 0 ? 0 : n);
}

warning: argument 1 range [2147483648, 4294967295] exceeds maximum object size 2
147483647 [-Walloc-size-larger-than=]

          + The -Walloc-zero option detects calls to standard and
            user-defined memory allocation functions decorated with
            attribute alloc_size with a zero argument. -Walloc-zero is not
            included in either -Wall or -Wextra and must be explicitly
            enabled.
          + The -Walloca option detects all calls to the alloca function
            in the program. -Walloca is not included in either -Wall or
            -Wextra and must be explicitly enabled.
          + The -Walloca-larger-than=size option detects calls to the
            alloca function whose argument either may exceed the specified
            size, or that is not known to be sufficiently constrained to
            avoid exceeding it. -Walloca-larger-than is not included in
            either -Wall or -Wextra and must be explicitly enabled.
            For example, compiling the following snippet with
            -Walloca-larger-than=1024 results in a warning because even
            though the code appears to call alloca only with sizes of 1kb
            and less, since n is signed, a negative value would result in
            a call to the function well in excess of the limit.

void f (int n)
{
  char *d;
  if (n < 1025)
    d = alloca (n);
  else
    d = malloc (n);
  …
}

warning: argument to 'alloca may be too large due to conversion from 'int' to 'l
ong unsigned int' [-Walloca-larger-than=]

            In contrast, a call to alloca that isn't bounded at all such
            as in the following function will elicit the warning below
            regardless of the size argument to the option.

void f (size_t n)
{
  char *d = alloca (n);
  …
}

warning: unbounded use of 'alloca' [-Walloca-larger-than=]

          + The -Wformat-overflow=level option detects certain and likely
            buffer overflow in calls to the sprintf family of formatted
            output functions. Although the option is enabled even without
            optimization it works best with -O2 and higher.
            For example, in the following snippet the call to sprintf is
            diagnosed because even though its output has been constrained
            using the modulo operation it could result in as many as three
            bytes if mday were negative. The solution is to either
            allocate a larger buffer or make sure the argument is not
            negative, for example by changing mday's type to unsigned or
            by making the type of the second operand of the modulo
            expression unsigned: 100U.

void* f (int mday)
{
  char *buf = malloc (3);
  sprintf (buf, "%02i", mday % 100);
  return buf;
}

warning: 'sprintf may write a terminating nul past the end of the destination [-
Wformat-overflow=]
note: 'sprintf' output between 3 and 4 bytes into a destination of size 3

          + The -Wformat-truncation=level option detects certain and
            likely output truncation in calls to the snprintf family of
            formatted output functions. -Wformat-truncation=1 is included
            in -Wall and enabled without optimization but works best with
            -O2 and higher.
            For example, the following function attempts to format an
            integer between 0 and 255 in hexadecimal, including the 0x
            prefix, into a buffer of four charactars. But since the
            function must always terminate output by the null character
            ('\0') such a buffer is only big enough to fit just one digit
            plus the prefix. Therefore the snprintf call is diagnosed. To
            avoid the warning either use a bigger buffer or handle the
            function's return value which indicates whether or not its
            output has been truncated.

void f (unsigned x)
{
  char d[4];
  snprintf (d, sizeof d, "%#02x", x & 0xff);
  …
}

warning: 'snprintf' output may be truncated before the last format character [-W
format-truncation=]
note: 'snprintf' output between 3 and 5 bytes into a destination of size 4

          + The -Wnonnull option has been enhanced to detect a broader set
            of cases of passing null pointers to functions that expect a
            non-null argument (those decorated with attribute nonnull). By
            taking advantage of optimizations the option can detect many
            more cases of the problem than in prior GCC versions.
          + The -Wstringop-overflow=type option detects buffer overflow in
            calls to string handling functions like memcpy and strcpy. The
            option relies on [8]Object Size Checking and has an effect
            similar to defining the _FORTIFY_SOURCE macro.
            -Wstringop-overflow=2 is enabled by default.
            For example, in the following snippet, because the call to
            strncat specifies a maximum that allows the function to write
            past the end of the destination, it is diagnosed. To correct
            the problem and avoid the overflow the function should be
            called with a size of at most sizeof d - strlen(d) - 1.

void f (const char *fname)
{
  char d[8];
  strncpy (d, "/tmp/", sizeof d);
  strncat (d, fname, sizeof d);
  …
}

warning: specified bound 8 equals the size of the destination [-Wstringop-overfl
ow=]

     * The <limits.h> header provided by GCC defines macros such as
       INT_WIDTH for the width in bits of integer types, if
       __STDC_WANT_IEC_60559_BFP_EXT__ is defined before the header is
       included. The <stdint.h> header defines such macros as SIZE_WIDTH
       and INTMAX_WIDTH for the width of some standard typedef names for
       integer types, again if __STDC_WANT_IEC_60559_BFP_EXT__ is defined
       before the header is included; note that GCC's implementation of
       this header is only used for freestanding compilations, not hosted
       compilations, on most systems. These macros come from ISO/IEC TS
       18661-1:2014.
     * The <float.h> header provided by GCC defines the macro
       CR_DECIMAL_DIG, from ISO/IEC TS 18661-1:2014, if
       __STDC_WANT_IEC_60559_BFP_EXT__ is defined before the header is
       included. This represents the number of decimal digits for which
       conversions between decimal character strings and binary formats,
       in both directions, are correctly rounded, and currently has the
       value of UINTMAX_MAX on all systems, reflecting that GCC's
       compile-time conversions are correctly rounded for any number of
       digits.
     * New __builtin_add_overflow_p, __builtin_sub_overflow_p,
       __builtin_mul_overflow_p built-in functions have been added. These
       work similarly to their siblings without the _p suffix, but do not
       actually store the result of the arithmetics anywhere, just return
       whether the operation would overflow. Calls to these built-ins with
       integer constant arguments evaluate to integer constants
       expressions.
       For example, in the following, c is assigned the result of a * b
       only if the multiplication does not overflow, otherwise it is
       assigned the value zero. The multiplication is performed at
       compile-time and without triggering a -Woverflow warning.

enum {
  a = 12345678,
  b = 87654321,
  c = __builtin_mul_overflow_p (a, b, a) ? 0 : a * b
};

  C

     * The C front end now supports type names _FloatN for floating-point
       types with IEEE interchange formats and _FloatNx for floating-point
       types with IEEE extended formats. These type names come from
       ISO/IEC TS 18661-3:2015.
       The set of types supported depends on the target for which GCC is
       configured. Most targets support _Float32, _Float32x and _Float64.
       _Float128 is supported on targets where IEEE binary128 encoding was
       already supported as long double or __float128. _Float64x is
       supported on targets where a type with either binary128 or Intel
       extended precision format is available.
       Constants with these types are supported using suffixes fN, FN, fNx
       and FNx (e.g., 1.2f128 or 2.3F64x). Macros such as FLT128_MAX are
       defined in <float.h> if __STDC_WANT_IEC_60559_TYPES_EXT__ is
       defined before it is included.
       These new types are always distinct from each other and from float,
       double and long double, even if they have the same encoding.
       Complex types such as _Complex _Float128 are also supported.
       Type-generic built-in functions such as __builtin_isinf support the
       new types, and the following type-specific built-in functions have
       versions (suffixed fN or fNx) for the new types:
       __builtin_copysign, __builtin_fabs, __builtin_huge_val,
       __builtin_inf, __builtin_nan, __builtin_nans.
     * Compilation with -fopenmp is now compatible with the C11 _Atomic
       keyword.

  C++

     * The C++ front end has experimental support for all of the current
       C++17 draft with the -std=c++1z or -std=gnu++1z flags, including if
       constexpr, class template argument deduction, auto template
       parameters, and decomposition declarations. For a full list of new
       features, see [9]the C++ status page.
     * C++17 support for new of over-aligned types can be enabled in other
       modes with the -faligned-new flag.
     * The C++17 evaluation order requirements can be selected in other
       modes with the -fstrong-eval-order flag, or disabled in C++17 mode
       with -fno-strong-eval-order.
     * The default semantics of inherited constructors has changed in all
       modes, following [10]P0136. Essentially, overload resolution
       happens as if calling the inherited constructor directly, and the
       compiler fills in construction of the other bases and members as
       needed. Most uses should not need any changes. The old behavior can
       be restored with -fno-new-inheriting-ctors, or -fabi-version less
       than 11.
     * The resolution of DR 150 on matching of template template
       parameters, allowing default template arguments to make a template
       match a parameter, is currently enabled by default in C++17 mode
       only. The default can be overridden with -f{no-,}new-ttp-matching.
     * The C++ front end will now provide fix-it hints for some missing
       semicolons, allowing for automatic fixes by IDEs:

test.cc:4:11: error: expected ';' after class definition
 class a {}
           ^
           ;

     * -Waligned-new has been added to the C++ front end. It warns about
       new of type with extended alignment without -faligned-new.

    Runtime Library (libstdc++)

     * The type of exception thrown by iostreams, std::ios_base::failure,
       now uses the [11]cxx11 ABI.
     * Experimental support for C++17, including the following new
       features:
          + std::string_view;
          + std::any, std::optional, and std::variant;
          + std::invoke, std::is_invocable, std::is_nothrow_invocable, and
            invoke_result;
          + std::is_swappable, and std::is_nothrow_swappable;
          + std::apply, and std::make_from_tuple;
          + std::void_t, std::bool_constant, std::conjunction,
            std::disjunction, and std::negation;
          + Variable templates for type traits;
          + Mathematical Special Functions;
          + std::chrono::floor, std::chrono::ceil, std::chrono::round, and
            std::chrono::abs;
          + std::clamp, std::gcd, std::lcm, 3-dimensional std::hypot;
          + std::scoped_lock, std::shared_mutex,
            std::atomic<T>::is_always_lock_free;
          + std::sample, std::default_searcher, std::boyer_moore_searcher
            and std::boyer_moore_horspool_searcher;
          + Extraction and re-insertion of map and set nodes, try_emplace
            members for maps, and functions for accessing containers
            std::size, std::empty, and std::data;
          + std::shared_ptr support for arrays,
            std::shared_ptr<T>::weak_type,
            std::enable_shared_from_this<T>::weak_from_this(), and
            std::owner_less<void>;
          + std::byte;
          + std::as_const, std::not_fn,
            std::has_unique_object_representations, constexpr
            std::addressof.
       Thanks to Daniel Krügler, Tim Shen, Edward Smith-Rowland, and Ville
       Voutilainen for work on the C++17 support.
     * A new power-of-two rehashing policy for use with the _Hashtable
       internals, thanks to François Dumont.

  Fortran

     * Support for a number of extensions for compatibility with legacy
       code with new flags:
          + -fdec-structure Support for DEC STRUCTURE and UNION
          + -fdec-intrinsic-ints Support for new integer intrinsics with
            B/I/J/K prefixes such as BABS, JIAND...
          + -fdec-math Support for additional math intrinsics, including
            COTAN and degree-valued trigonometric functions such as TAND,
            ASIND...
          + -fdec Enable the -fdec-* family of extensions.
     * New flag -finit-derived to allow default initialization of
       derived-type variables.
     * Improved DO loops with step equal to 1 or -1, generates faster code
       without a loop preheader. A new warning, -Wundefined-do-loop, warns
       when a loop iterates either to HUGE(i) (with step equal to 1), or
       to -HUGE(i) (with step equal to -1). Invalid behavior can be caught
       at run time with -fcheck=do enabled:

program test
  implicit none
  integer(1) :: i
  do i = -HUGE(i)+10, -HUGE(i)-1, -1
    print *, i
  end do
end program test

At line 8 of file do_check_12.f90
Fortran runtime error: Loop iterates infinitely

     * Version 4.5 of the [12]OpenMP specification is now partially
       supported also in the Fortran compiler; the largest missing item is
       structure element mapping.
     * User-defined derived-type input/output (UDTIO) is added.
     * Derived type coarrays with allocable and pointer components is
       partially supported.
     * Non-constant stop codes and error stop codes (Fortran 2015
       feature).
     * Derived types with allocatable components of recursive type.
     * Intrinsic assignment to polymorphic variables.
     * Improved submodule support.
     * Improved diagnostics (polymorphic results in pure functions).

  Go

     * GCC 7 provides a complete implementation of the Go 1.8.1 user
       packages.
     * Compared to the Go 1.8.1 toolchain, the garbage collector is more
       conservative and less concurrent.
     * Escape analysis is available for experimental use via the
       -fgo-optimize-allocs option. The -fgo-debug-escape prints
       information useful for debugging escape analysis choices.

  Java (GCJ)

   The GCC Java frontend and associated libjava runtime library have been
   removed from GCC.

libgccjit

   The libgccjit API gained support for marking calls as requiring
   tail-call optimization via a new entrypoint:
   [13]gcc_jit_rvalue_set_bool_require_tail_call.

   libgccjit performs numerous checks at the API boundary, but if these
   succeed, it previously ignored errors and other diagnostics emitted
   within the core of GCC, and treated the compile of a gcc_jit_context as
   having succeeded. As of GCC 7 it now ensures that if any diagnostics
   are emitted, they are visible from the libgccjit API, and that the the
   context is flagged as having failed.

New Targets and Target Specific Improvements

  AArch64

     * The ARMv8.3-A architecture is now supported. It can be used by
       specifying the -march=armv8.3-a option.
     * The option -msign-return-address= is supported to enable return
       address protection using ARMv8.3-A Pointer Authentication
       Extensions. For more information on the arguments accepted by this
       option, please refer to [14]AArch64-Options.
     * The ARMv8.2-A architecture and the ARMv8.2-A 16-bit Floating-Point
       Extensions are now supported. They can be used by specifying the
       -march=armv8.2-a or -march=armv8.2-a+fp16 options. The 16-bit
       Floating-Point Extensions introduce new half-precision data
       processing floating-point instructions.
     * Support has been added for the following processors (GCC
       identifiers in parentheses): ARM Cortex-A73 (cortex-a73), Broadcom
       Vulcan (vulcan), Cavium ThunderX CN81xx (thunderxt81), Cavium
       ThunderX CN83xx (thunderxt83), Cavium ThunderX CN88xx
       (thunderxt88), Cavium ThunderX CN88xx pass 1.x (thunderxt88p1),
       Cavium ThunderX 2 CN99xx (thunderx2t99), Qualcomm Falkor (falkor).
       The GCC identifiers can be used as arguments to the -mcpu or -mtune
       options, for example: -mcpu=cortex-a73 or -mtune=vulcan or as
       arguments to the equivalent target attributes and pragmas.

  ARC

     * Add support for ARC HS and ARC EM processors.
     * Add support for ARC EM variation found in Intel QuarkSE SoCs.
     * Add support for NPS400 ARC700 based CPUs.
     * Thread Local Storage is now supported by ARC CPUs.
     * Fix errors for ARC600 when using 32x16 multiplier option.
     * Fix PIE for ARC CPUs.
     * New CPU templates are supported via multilib.

  ARM

     * Support for the ARMv5 and ARMv5E architectures has been deprecated
       (which have no known implementations) and will be removed in a
       future GCC release. Note that ARMv5T, ARMv5TE and ARMv5TEJ
       architectures remain supported. The values armv5 and armv5e of
       -march are thus deprecated.
     * The ARMv8.2-A architecture and the ARMv8.2-A 16-bit Floating-Point
       Extensions are now supported. They can be used by specifying the
       -march=armv8.2-a or -march=armv8.2-a+fp16 options. The 16-bit
       Floating-Point Extensions introduce new half-precision data
       processing floating-point instructions.
     * The ARMv8-M architecture is now supported in its two architecture
       profiles: ARMv8-M Baseline and ARMv8-M Mainline with its DSP and
       Floating-Point Extensions. They can be used by specifying the
       -march=armv8-m.base, armv8-m.main or armv8-m.main+dsp options.
     * Support has been added for the following processors (GCC
       identifiers in parentheses): ARM Cortex-A73 (cortex-a73), ARM
       Cortex-M23 (cortex-m23) and ARM Cortex-M33 (cortex-m33). The GCC
       identifiers can be used as arguments to the -mcpu or -mtune
       options, for example: -mcpu=cortex-a73 or -mtune=cortex-m33.
     * A new command-line option -mpure-code has been added. It does not
       allow constant data to be placed in code sections. This option is
       only available when generating non-pic code for ARMv7-M targets.
     * Support for the ACLE Coprocessor Intrinsics has been added. This
       enables the generation of coprocessor instructions through the use
       of intrinsics such as cdp, ldc, and others.
     * The configure option --with-multilib-list now accepts the value
       rmprofile to build multilib libraries for a range of embedded
       targets. See our [15]installation instructions for details.

  AVR

     * On the reduced Tiny cores, the progmem [16]variable attribute is
       now properly supported. Respective read-only variables are located
       in flash memory in section .progmem.data. No special code is needed
       to access such variables; the compiler automatically adds an offset
       of 0x4000 to all addresses, which is needed to access variables in
       flash memory. As opposed to ordinary cores where it is sufficient
       to specify the progmem attribute with definitions, on the reduced
       Tiny cores the attribute also has to be specified with (external)
       declarations:

extern const int array[] __attribute__((__progmem__));

int get_value2 (void)
{
  /* Access via addresses array + 0x4004 and array + 0x4005. */
  return array[2];
}

const int* get_address (unsigned idx)
{
  /* Returns array + 0x4000 + 2 * idx. */
  return &array[idx];
}

     * A new command-line option -Wmisspelled-isr has been added. It turns
       off — or turns into errors — warnings that are reported for
       interrupt service routines (ISRs) which don't follow AVR-LibC's
       naming convention of prefixing ISR names with __vector.
     * __builtin_avr_nops(n) is a new [17]built-in function that inserts n
       NOP instructions into the instruction stream. n must be a value
       known at compile time.

  IA-32/x86-64

     * Support for the AVX-512 Fused Multiply Accumulation Packed Single
       precision (4FMAPS), AVX-512 Vector Neural Network Instructions Word
       variable precision (4VNNIW), AVX-512 Vector Population Count
       (VPOPCNTDQ) and Software Guard Extensions (SGX) ISA extensions has
       been added.

  NVPTX

     * OpenMP target regions can now be offloaded to NVidia PTX GPGPUs.
       See the [18]Offloading Wiki on how to configure it.

  PowerPC / PowerPC64 / RS6000

     * The PowerPC port now uses LRA by default.
     * GCC now diagnoses inline assembly that clobbers register r2. This
       has always been invalid code, and is no longer quietly tolerated.
     * The PowerPC port's support for ISA 3.0 (-mcpu=power9) has been
       enhanced to generate more of the new instructions by default, and
       to provide more built-in functions to generate code for other new
       instructions.
     * The configuration option --enable-gnu-indirect-function is now
       enabled by default on PowerPC GNU/Linux builds.
     * The PowerPC port will now allow 64-bit and 32-bit integer types to
       be allocated to the VSX vector registers (ISA 2.06 and above). In
       addition, on ISA 3.0, 16-bit and 8-bit integer types can be
       allocated in the vector registers. Previously, only 64-bit integer
       types were allowed in the traditional floating point registers.
     * New options -mstack-protector-guard=global,
       -mstack-protector-guard=tls, -mstack-protector-guard-reg=, and
       -mstack-protector-guard-offset= change how the stack protector gets
       the value to use as canary.

  RISC-V

     * Support for the RISC-V instruction set has been added.

  SPARC

     * The SPARC port now uses LRA by default.
     * Support for the new Subtract-Extended-with-Carry instruction
       available in SPARC M7 (Niagara 7) has been added.

Operating Systems

  AIX

     * Visibility support has been enabled for AIX 7.1 and above.

  Fuchsia

     * Support has been added for the [19]Fuchsia OS.

  RTEMS

     * The ABI changes on ARM so that no short enums are used by default.

Other significant improvements

     * -fverbose-asm previously emitted information on the meanings of
       assembly expressions. This has been extended so that it now also
       prints comments showing the source lines that correspond to the
       assembly, making it easier to read the generated assembly
       (especially with larger functions). For example, given this C
       source file:

int test (int n)
{
  int i;
  int total = 0;

  for (i = 0; i < n; i++)
    total += i * i;
  return total;
}

       -fverbose-asm now gives output similar to this for the function
       body (when compiling for x86_64, with -Os):

       .text
       .globl  test
       .type   test, @@function
test:
.LFB0:
       .cfi_startproc
# example.c:4:   int total = 0;
       xorl    %eax, %eax      # <retval>
# example.c:6:   for (i = 0; i < n; i++)
       xorl    %edx, %edx      # i
.L2:
# example.c:6:   for (i = 0; i < n; i++)
       cmpl    %edi, %edx      # n, i
       jge     .L5     #,
# example.c:7:     total += i * i;
       movl    %edx, %ecx      # i, tmp92
       imull   %edx, %ecx      # i, tmp92
# example.c:6:   for (i = 0; i < n; i++)
       incl    %edx    # i
# example.c:7:     total += i * i;
       addl    %ecx, %eax      # tmp92, <retval>
       jmp     .L2     #
.L5:
# example.c:10: }
       ret
       .cfi_endproc

     * Two new options have been added for printing fix-it hints:
          + -fdiagnostics-parseable-fixits allows for fix-it hints to be
            emitted in a machine-readable form, suitable for consumption
            by IDEs. For example, given:

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

            it will emit:

fix-it:"spellcheck-fields.cc":{52:13-52:19}:"color"

          + -fdiagnostics-generate-patch will print a patch in "unified"
            format after any diagnostics are printed, showing the result
            of applying all fix-it hints. For the above example it would
            emit:

--- spellcheck-fields.cc
+++ spellcheck-fields.cc
@@ -49,5 +49,5 @@

 color get_color(struct s *ptr)
 {
-  return ptr->colour;
+  return ptr->color;
 }

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

$ gcc -c test.c -ftls-model=global-dinamic
gcc: error: unknown TLS model 'global-dinamic'
gcc: note: valid arguments to '-ftls-model=' are: global-dynamic initial-exec lo
cal-dynamic local-exec; did you mean 'global-dynamic'?

     * The compiler will now provide suggestions for misspelled
       parameters.

$ gcc -c test.c --param max-early-inliner-iteration=3
cc1: error: invalid --param name 'max-early-inliner-iteration'; did you mean 'ma
x-early-inliner-iterations'?

     * Profile-guided optimization (PGO) instrumentation, as well as test
       coverage (GCOV), can newly instrument constructors (functions marks
       with __attribute__((constructor))), destructors and C++
       constructors (and destructors) of classes that are used as a type
