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GCC 10 Release Series &mdash; Changes, New Features, and Fixes
- GNU Project - Free Software Foundation (FSF)</title>
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<h1>GCC 10 Release Series<br/>Changes, New Features, and Fixes</h1>

<p>
This page is a "brief" summary of some of the huge number of improvements
in GCC 10.

You may also want to check out our
<a href="porting_to.html">Porting to GCC 10</a> page and the
<a href="../onlinedocs/index.html#current">full GCC documentation</a>.

</p>

<!-- .................................................................. -->
<h2>Caveats</h2>
<ul>
  <li>
    An ABI incompatibility between C++14 and C++17 has been fixed.  On some
    targets a class with a zero-sized subobject would be passed incorrectly
    when compiled as C++17 or C++20.
    See the <a href="#empty_base">C++ notes below</a> for more details.
  </li>
  <li>
    The deprecated Profile Mode and <code>array_allocator</code> extensions
    have been removed from libstdc++.
  </li>
  <li>
    The non-standard <code>std::__is_nullptr_t</code> type trait is deprecated
    and will be removed from libstdc++ in a future release.
    The standard trait <code>std::is_null_pointer</code> should be instead.
  </li>
  <li>
    The minimum version of the <a href="https://www.mpfr.org">MPFR</a>
    library required for building GCC has been increased to version
    3.1.0 (released 2011-10-03).
  </li>
  <li>
    The automatic template instantiation at link time (<code>-frepo</code>)
    has been removed.
  </li>
  <li>
    The <code>--param allow-store-data-races</code> internal parameter has
    been removed in favor of a new official option
    <code>-fallow-store-data-races</code>.  While default behavior is
    unchanged and the new option allows to correctly maintain a per
    compilation unit setting across link-time optimization, alteration
    of the default via <code>--param allow-store-data-races</code> will
    now be diagnosed and build systems have to be adjusted accordingly.
  </li>
  <li>
    Offloading to Heterogeneous System Architecture Intermediate
    Language (HSAIL) has been deprecated and will likely be removed in
    a future release.
  </li>
</ul>


<!-- .................................................................. -->
<h2 id="general">General Improvements</h2>
<ul>
  <li>New built-in functions:
    <ul>
      <li>The
	<a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/cpp/_005f_005fhas_005fbuiltin.html#g_t_005f_005fhas_005fbuiltin"><code>__has_builtin</code></a>
	built-in preprocessor operator can be used to query support
	for built-in functions provided by GCC and other compilers
	that support it.
      </li>
      <li><code>__builtin_roundeven</code> for the corresponding function from
	ISO/IEC TS 18661.
      </li>
    </ul>
  </li>
  <li>
    New command-line options:
    <ul>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Optimize-Options.html#index-fno-allocation-dce"><code>-fallocation-dce</code></a>
	removes unneeded pairs of <code>new</code> and <code>delete</code>
	operators.
      </li>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Optimize-Options.html#index-fprofile-partial-training"><code>-fprofile-partial-training</code></a>
	  can now be used to inform the compiler that code paths not covered by the
	  training run should not be optimized for size.
      </li>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Optimize-Options.html#index-fprofile-reproducible"><code>-fprofile-reproducible</code></a>
	  controls level of reproducibility of profile gathered by
	  <a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Optimize-Options.html#index-fprofile-generate"><code>-fprofile-generate</code></a>.
	  This makes it possible to rebuild program
	  with same outcome which is useful, for example, for distribution packages.
      </li>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Optimize-Options.html#index-fprofile-prefix-path"><code>-fprofile-prefix-path</code></a>
	  can be used in combination with <code>-fprofile-generate=profile_dir</code> and
	  <code>-fprofile-use=profile_dir</code> to inform GCC where the base
	  directory of build source tree is in case it differs between instrumentation
	  and optimized builds.
      </li>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Static-Analyzer-Options.html">-fanalyzer</a>
	enables a new static analysis pass and associated warnings.
	This pass performs a time-consuming exploration of paths through
	the code in the hope of detecting various common errors, such as
	double-free bugs.  This option should be regarded as
	<b>experimental</b> in this release.  In particular, analysis of non-C
	code is unlikely to work.
      </li>
    </ul>
  </li>
  <li>
    Inter-procedural optimization improvements:
    <ul>
      <li>The inter-procedural scalar replacement of aggregates (IPA-SRA) pass
	  was re-implemented to work at link-time and can now also remove
	  computing and returning unused return values.
      </li>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Optimize-Options.html#index-finline-functions"><code>-finline-functions</code></a>
	  is now enabled at <code>-O2</code> and was retuned for better code
	  size versus runtime performance trade-offs.  Inliner heuristics was
	  also significantly sped up to avoid negative impact to <code>-flto
	  -O2</code> compile times.
      </li>
      <li>Inliner heuristics and function cloning can now use value-range
	  information to predict effectivity of individual transformations.
      </li>
      <li>During link-time optimization the C++ One Definition Rule is used to
	  increase precision of type based alias analysis.
      </li>
    </ul>
  </li>
  <li>
    Link-time optimization improvements:
    <ul>
      <li>
        A new binary <a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/lto-dump.html"><code>lto-dump</code></a>
        has been added.  The program can dump various
        information about a LTO bytecode object file.
      </li>
      <li>
	Parallel phase of the LTO can automatically detect a running make's
	jobserver or can fall back to number of available cores.
      </li>
      <li>
        The LTO bytecode can be compressed with
        <a href="https://facebook.github.io/zstd/"><code>zstd</code></a>
        algorithm.  Configure script can automatically detect the <code>zstd</code> support.
      </li>
      <li>Most <code>--param</code> values can now be specified at
	  translation unit granularity. This includes all parameters controlling
	  the inliner and other inter-procedural optimizations.  Unlike earlier
	  releases, GCC 10 will ignore parameters controlling optimizations
	  specified at link-time and apply parameters specified at compile-time
	  in the same manner as done for optimization flags.
      </li>
    </ul>
  </li>
  <li>
    Profile driven optimization improvements:
    <ul>
      <li>Profile maintenance during compilation and hot/cold code
	  partitioning have been improved.
      </li>
      <li>
        Using <a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Optimize-Options.html#index-fprofile-values"><code>-fprofile-values</code></a>,
        an instrumented binary can track multiple
	values (up to 4) for e.g. indirect calls and provide more precise
	profile information.
      </li>
    </ul>
  </li>
</ul>
<!-- .................................................................. -->
<h2 id="languages">New Languages and Language-Specific Improvements</h2>

<ul>
  <li>
    Version 2.6 of the <a href="https://www.openacc.org/">OpenACC</a>
    specification is now supported in the C, C++ and Fortran compilers.
    See the <a href="https://gcc.gnu.org/wiki/OpenACC#status-10">implementation
    status</a> section on the OpenACC wiki page and the
    <a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/libgomp/#toc-Enabling-OpenACC-1">
    run-time library documentation</a> for further information.
  </li>
  <li>GCC 10 adds a number of newly implemented
      <a href="https://www.openmp.org/specifications/">OpenMP 5.0</a>
      features on top of the GCC 9 release such as <code>conditional</code>
      <code>lastprivate</code> clause, <code>scan</code> and <code>loop</code>
      directives, <code>order(concurrent)</code> and
      <code>use_device_addr</code> clauses support, <code>if</code>
      clause on <code>simd</code> construct or partial support for
      the <code>declare&nbsp;variant</code> directive, getting closer to
      full support of the OpenMP 5.0 standard.
  </li>
  <li>
    OpenMP and OpenACC now support
    <a href="https://gcc.gnu.org/wiki/Offloading">offloading</a> to AMD Radeon
    (GCN) GPUs; supported are the third-generation Fiji (<code>fiji</code>)
    and the fifth-generation VEGA 10/VEGA 20 (<code>gfx900</code> or
    <code>gfx906</code>).
  </li>
</ul>

<!-- <h3 id="ada">Ada</h3> -->

<!-- <h3 id="brig">BRIG (HSAIL)</h3> -->

<h3 id="c-family">C family</h3>
<ul>
  <li>New attributes:
    <ul>
     <li>
       The <code>access</code> function and type attribute has been added
       to describe how a function accesses objects passed to it by pointer
       or reference, and to associate such arguments with integer arguments
       denoting the objects' sizes.  The attribute is used to enable
       the detection of invalid accesses by user-defined functions, such
       as those diagnosed by <code>-Wstringop-overflow</code>.
     </li>
     <li>
       The <code>symver</code> attribute can be used to bind symbols to
       specific version nodes on ELF platforms. This is preferred to using
       inline assembly with GNU as <code>symver</code> directive because the
       latter is not compatible with link-time optimizations.
     </li>
    </ul>
  </li>
  <li>New warnings:
    <ul>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wstring-compare"><code>-Wstring-compare</code></a>, enabled
	by <code>-Wextra</code>, warns about equality and inequality
	expressions between zero and the result of a call to either
	<code>strcmp</code> and <code>strncmp</code> that evaluate to
	a constant as a result of the length of one argument being greater
	than the size of the array pointed to by the other.
      </li>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wzero-length-bounds"><code>-Wzero-length-bounds</code></a>,
	enabled by <code>-Warray-bounds</code>, warns about accesses to
	elements of zero-length arrays that might overlap other members
	of the same object.
      </li>
    </ul>
  </li>
  <li>Enhancements to existing warnings:
    <ul>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Warray-bounds"><code>-Warray-bounds</code></a>
	detects more out-of-bounds accesses to member arrays as well as
	accesses to elements of zero-length arrays.
      </li>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wformat-overflow"><code>-Wformat-overflow</code></a>
	makes full use of string length information computed by
	the <code>strlen</code> optimization pass.
      </li>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wrestrict"><code>-Wrestrict</code></a>
	detects overlapping accesses to dynamically allocated objects.
      </li>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wreturn-local-addr"><code>-Wreturn-local-addr</code></a>
	diagnoses more instances of <code>return</code> statements returning
	addresses of automatic variables.
      </li>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wstringop-overflow"><code>-Wstringop-overflow</code></a>
	detects more out-of-bounds stores to member arrays including
	zero-length arrays, dynamically allocated objects and variable length
	arrays, as well as more instances of reads of unterminated character
	arrays by string built-in functions.  The warning also detects
	out-of-bounds accesses by calls to user-defined functions declared
	with the new attribute <code>access</code>.
      </li>
    </ul>
  </li>
  <li>Extended characters in identifiers may now be specified directly in
  the input encoding (UTF-8, by default), in addition to the UCN syntax
  (<code>\uNNNN</code> or <code>\UNNNNNNNN</code>) that is already
  supported:
  <blockquote><pre>
static const int π = 3;
int get_naïve_pi() {
  return π;
}</pre></blockquote></li>
</ul>

<h3 id="c">C</h3>
<ul>
  <li>Several new features from the upcoming C2X revision of the ISO C
  standard are supported with <code>-std=c2x</code>
  and <code>-std=gnu2x</code>.  Some of these features are also
  supported as extensions when compiling for older language versions.
  In addition to the features listed, some features previously
  supported as extensions and now added to the C standard are enabled
  by default in C2X mode and not diagnosed with <code>-std=c2x
  -Wpedantic</code>.
  <ul>
    <li>The <code>[[]]</code> attribute syntax is supported, as in
    C++.  Existing attributes can be used with this syntax in forms
    such as <code>[[gnu::const]]</code>.  The standard
    attributes <code>[[deprecated]]</code>, <code>[[fallthrough]]</code>
    and <code>[[maybe_unused]]</code> are supported.</li>
    <li>UTF-8 character constants using the <code>u8''</code> syntax
    are supported.</li>
    <li><code>&lt;float.h&gt;</code> defines
    macros <code>FLT_NORM_MAX</code>, <code>DBL_NORM_MAX</code>
    and <code>LDBL_NORM_MAX</code>.</li>
    <li>When decimal floating-point arithmetic is
    supported, <code>&lt;float.h&gt;</code> defines
    macros <code>DEC32_TRUE_MIN</code>, <code>DEC64_TRUE_MIN</code>
    and <code>DEC128_TRUE_MIN</code>, in addition to the macros that
    were previously only defined if <code>__STDC_WANT_DEC_FP__</code>
    was defined before including <code>&lt;float.h&gt;</code>.</li>
    <li>In C2X mode, empty parentheses in a function definition give
    that function a type with a prototype for subsequent calls; other
    old-style function definitions are diagnosed by default in C2X
    mode.</li>
    <li>The <code>strftime</code> format checking supports
    the <code>%OB</code> and <code>%Ob</code> formats.</li>
    <li>In C2X mode, <code>-fno-fp-int-builtin-inexact</code> is
    enabled by default.</li>
  </ul></li>

  <li>GCC now defaults to <code>-fno-common</code>.  As a result, global
      variable accesses are more efficient on various targets.  In C, global
      variables with multiple tentative definitions now result in linker errors.
      With <code>-fcommon</code> such definitions are silently merged during
      linking.
  </li>
</ul>

<h3 id="cxx">C++</h3>
<ul>
  <li>Several C++20 features have been implemented:
  <ul>
    <li>P1668R1, Permitting Unevaluated inline-assembly in constexpr Functions</li>
    <li>P1161R3, Deprecate <code>a[b,c]</code></li>
    <li>P0848R3, Conditionally Trivial Special Member Functions</li>
    <li>P1091R3, Extending structured bindings</li>
    <li>P1143R2, Adding the <code>constinit</code> keyword</li>
    <li>P1152R4, Deprecating <code>volatile</code></li>
    <li>P0388R4, Permit conversions to arrays of unknown bound</li>
    <li>P0784R7, <code>constexpr new</code></li>
    <li>Concepts, including P0734R0, P0857R0, P1084R2, P1141R2, P0848R3, P1616R1, P1452R2</li>
    <li>P1301R4, <code>[[nodiscard("with reason")]]</code></li>
    <li>P1814R0, class template argument deduction for alias templates</li>
    <li>P1816R0, class template argument deduction for aggregates</li>
    <li>P0960R3, Parenthesized initialization of aggregates</li>
    <li>P1331R2, Allow trivial default initialization in constexpr contexts</li>
    <li>P1327R1, Allowing dynamic_cast and polymorphic typeid in constexpr contexts</li>
    <li>P0912R5, Coroutines (requires <code>-fcoroutines</code>)</li>
  </ul>  
  </li>
  <li>Several C++ Defect Reports have been resolved, e.g.:
  <ul>
    <li>DR 1560, lvalue-to-rvalue conversion in <code>?:</code></li>
    <li>DR 1813, <code>__is_standard_layout</code> for a class with repeated
	bases</li>
    <li>DR 2094, volatile scalars are trivially copyable,</li>
    <li>DR 2096, constraints on literal unions</li>
    <li>DR 2413, <code>typename</code> in <code>conversion-function-id</code>s</li>
    <li>DR 2352, Similar types and reference binding</li>
    <li>DR 1601, Promotion of enumeration with fixed underlying type</li>
    <li>DR 330, Qualification conversions and pointers to arrays of pointers</li>
    <li>DR 1307, Overload resolution based on size of array
	<code>initializer-list</code></li>
    <li>DR 1710, Missing template keyword in <i>class-or-decltype</i></li>
  </ul>  
  </li>
  <li>New warnings:
    <ul>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/C_002b_002b-Dialect-Options.html#index-Wmismatched-tags"><code>-Wmismatched-tags</code></a>,
	disabled by default, warns about declarations of structs, classes,
	and class templates and their specializations with a class-key that
	does not match either the definition or the first declaration if no
	definition is provided.  The option is provided to ease portability
	to Windows-based compilers.
      </li>
      <li><a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/C_002b_002b-Dialect-Options.html#index-Wredundant-tags"><code>-Wredundant-tags</code></a>,
	disabled by default, warns about redundant <i>class-key</i> and
	<i>enum-key</i> in contexts where the key can be eliminated without
	causing an syntactic ambiguity.
      </li>
    </ul>
  </li>
  <li>
    G++ can now detect modifying constant objects in constexpr evaluation
    (which is undefined behavior).
  </li>
  <li>
    G++ no longer emits bogus <code>-Wsign-conversion</code> warnings with explicit
    casts.
  </li>
  <li>
    Narrowing is now detected in more contexts (e.g., <code>case</code>
    values).
  </li>
  <li>
    Memory consumption of the compiler has been reduced in constexpr evaluation.
  </li>
  <li>
    The <code>noexcept-specifier</code> is now properly treated as a
    <em>complete-class context</em> as per
    <a href="http://eel.is/c++draft/class.mem#def:complete-class_context">
    [class.mem]</a>.
  </li>
  <li>
    The attribute <code>deprecated</code> can now be used on
    <code>namespace</code>s too.
  </li>
  <li>
    <a name="empty_base">The ABI</a>
    of passing and returning certain C++ classes by value changed
    on several targets in GCC 10, including
    <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94383">AArch64</a>,
    <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94711">ARM</a>,
    <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94707">PowerPC ELFv2</a>,
    <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94704">S/390</a>
    and
    <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94706">Itanium</a>.
    These changes affect classes with a zero-sized
    subobject (an empty base class, or data member with the
    <code>[[no_unique_address]]</code> attribute) where all other non-static
    data members have the same type (this is called a "homogeneous aggregate"
    in some ABI specifications, or if there is only one such member,
    a "single element").
    In <code>-std=c++17</code> and <code>-std=c++20</code> modes, classes with
    an empty base class were not considered to have a single element or
    to be a homogeneous aggregate, and so could be passed differently
    (in the wrong registers or at the wrong stack address). This could make
    code compiled with <code>-std=c++17</code> and <code>-std=c++14</code>
    ABI incompatible.  This has been corrected and the empty bases are
    ignored in those ABI decisions, so functions compiled with
    <code>-std=c++14</code> and <code>-std=c++17</code> are now ABI compatible
    again.
    Example:
    <code>struct empty {}; struct S : empty { float f; }; void f(S);</code>.
    Similarly, in classes containing non-static data members with empty
    class types using the C++20 <code>[[no_unique_address]]</code> attribute,
    those members weren't ignored in the ABI argument passing decisions
    as they should be.  Both of these ABI changes are now diagnosed with
    <code>-Wpsabi</code>.
  </li>
</ul>

<h4 id="libstdcxx">Runtime Library (libstdc++)</h4>
<ul>
  <li>Improved experimental C++2a support, including:
    <ul>
      <li>
        Library concepts in <code>&lt;concepts&gt;</code> and
        <code>&lt;iterator&gt;</code>.
      </li>
      <li>
        Constrained algorithms in <code>&lt;ranges&gt;</code>,
        <code>&lt;algorithm&gt;</code>, and
        <code>&lt;memory&gt;</code> (thanks to Patrick Palka).
      </li>
      <li>
        New algorithms <code>shift_left</code> and <code>shift_right</code>
        (thanks to Patrick Palka).
      </li>
      <li> <code>std::span</code> (thanks to JeanHeyd Meneide). </li>
      <li>
        Three-way comparisons in <code>&lt;compare&gt;</code>
        and throughout the library.
      </li>
      <li>
        Constexpr support in <code>&lt;algorithm&gt;</code> and elsewhere
        (thanks to Edward Smith-Rowland).
      </li>
      <li>
        <code>&lt;stop_token&gt;</code> and <code>std::jthread</code>
        (thanks to Thomas Rodgers).
      </li>
      <li>
        <code>std::atomic_ref</code> and
        <code>std::atomic&lt;<i>floating point</i>&gt;</code>.
      </li>
      <li>
        Integer comparison functions
        (<code>cmp_equal</code>, <code>cmp_less</code> etc.).
      </li>
      <li> <code>std::ssize</code>, <code>std::to_array</code>. </li>
      <li>
        <code>std::construct_at</code>, <code>std::destroy</code>,
        constexpr <code>std::allocator</code>.
      </li>
      <li> Mathematical constants in <code>&lt;numbers&gt;</code>. </li>
    </ul>
  </li>
  <li>Support for RDSEED in <code>std::random_device</code>.</li>
  <li>
    Reduced header dependencies, leading to faster compilation for some code.
  </li>
</ul>

<h3 id="fortran">Fortran</h3>
<ul>
  <li><code>use_device_addr</code> of version 5.0 of the
      <a href="https://www.openmp.org/specifications/">OpenMP specification</a>
      is now supported. Note that otherwise OpenMP 4.5 is partially supported
      in the Fortran compiler; the largest missing item is structure element
      mapping.
  </li>
  <li>
    The default buffer size for I/O using unformatted files has been
    increased to 1048576.  The buffer size for can now be set at
    runtime via the environment
    variables <code>GFORTRAN_FORMATTED_BUFFER_SIZE</code> and
    <code>GFORTRAN_UNFORMATTED_BUFFER_SIZE</code> for formatted
    and unformatted files, respectively.
  </li>
  <li>
    Mismatches between actual and dummy argument lists in a single
    file are now rejected with an error. Use the new
    option <code>-fallow-argument-mismatch</code> to turn these
    errors into warnings; this option is implied
    with <code>-std=legacy</code>.  <code>-Wargument-mismatch</code>
    has been removed.
  </li>
  <li>
    The handling of a BOZ literal constant has been reworked to provide
    better conformance to the Fortran 2008 and 2018 standards.  In these
    Fortran standards, a BOZ literal constant is a typeless and kindless
    entity.  As a part of the rework, documented and undocumented
    extensions to the Fortran standard now emit errors during compilation.
    Some of these extensions are permitted with the
    <code>-fallow-invalid-boz</code>, where the error is degraded to a
    warning and the code is compiled as with older gfortran.
  </li>
  <li>
    At any optimization level except<code>-Os</code>, gfortran now
    uses inline packing for arguments instead of calling a library
    routine.  If the source contains a large number of arguments that
    need to be repacked, code size or time for compilation can become
    excessive. If that is the case, <code>-fno-inline-arg-packing</code>
    can be used to disable inline argument packing.
  </li>
  <li>
    Legacy extensions:
    <ul>
      <li>
        For formatted input/output, if the explicit widths after the data-edit
        descriptors <code>I</code>, <code>F</code> and <code>G</code> have been
        omitted, default widths are used.
      </li>
      <li>
        A blank format item at the end of a format specification, i.e. nothing
        following the final comma, is allowed.  Use the option
        <code>-fdec-blank-format-item</code>; this option is implied with
        <code>-fdec</code>.
      </li>
      <li>
        The existing support for <code>AUTOMATIC</code> and <code>STATIC</code>
        attributes has been extended to allow variables with the
        <code>AUTOMATIC</code> attribute to be used in <code>EQUIVALENCE</code>
        statements. Use <code>-fdec-static</code>; this option is implied by
        <code>-fdec</code>.
      </li>
      <li>
        Allow character literals in assignments and <code>DATA</code> statements
        for numeric (<code>INTEGER</code>, <code>REAL</code>, or
        <code>COMPLEX</code>) or <code>LOGICAL</code> variables.  Use the option
        <code>-fdec-char-conversions</code>; this option is implied with
        <code>-fdec</code>.
      </li>
      <li>
        DEC comparisons, i.e. allow Hollerith constants to be used in comparisons
        with <code>INTEGER</code>, <code>REAL</code>, <code>COMPLEX</code> and
        <code>CHARACTER</code> expressions. Use the option <code>-fdec</code>.
      </li>
    </ul>
  </li>
  <li>
    Character type names in errors and warnings now include <code>len</code>
    in addition to <code>kind</code>; <code>*</code> is used for assumed
    length. The kind is omitted if it is the default kind. Examples:
    <code>CHARACTER(12)</code>, <code>CHARACTER(6,4)</code>.
  </li>
  <li>
    <code>CO_BROADCAST</code> now supports derived type variables including
    objects with allocatable components. In this case, the optional arguments
    <code>STAT=</code> and <code>ERRMSG=</code> are currently ignored.
  </li>
  <li>
    The handling of module and submodule names has been reworked to allow the
    full 63-character length mandated by the standard. Previously symbol names
    were truncated if the combined length of module, submodule, and function
    name exceeded 126 characters. This change therefore breaks the ABI, but only
    for cases where this 126 character limit was exceeded.
  </li>

</ul>
<!-- <h3 id="go">Go</h3> -->

<!-- .................................................................. -->
<!-- <h2 id="jit">libgccjit</h2> -->

<!-- .................................................................. -->
<h2 id="targets">New Targets and Target Specific Improvements</h2>

<h3 id="arm-targets">AArch64 &amp; arm</h3>
<ul>
  <li>The AArch64 and arm ports now support condition flag output constraints
  in inline assembly, as indicated by the <code>__GCC_ASM_FLAG_OUTPUTS__</code>.
  On arm this feature is only available for A32 and T32 targets.
  Please refer to the documentation for more details. </li>
</ul>

<h3 id="aarch64">AArch64</h3>
<ul>
  <li>There have been several improvements related to the Scalable
  Vector Extension (SVE):
    <ul>
      <li>The SVE ACLE types and intrinsics are now supported.  They can
      be accessed using the header file <code>arm_sve.h</code>.
      </li>
      <li>It is now possible to create fixed-length SVE types using
      the <code>arm_sve_vector_bits</code> attribute.  For example:
<pre>#if __ARM_FEATURE_SVE_BITS==512
typedef svint32_t vec512 __attribute__((arm_sve_vector_bits(512)));
typedef svbool_t pred512 __attribute__((arm_sve_vector_bits(512)));
#endif</pre>
      </li>
      <li><code>-mlow-precision-div</code>, <code>-mlow-precision-sqrt</code>
      and <code>-mlow-precision-recip-sqrt</code> now work for SVE.
      </li>
      <li><code>-msve-vector-bits=128</code> now generates
      vector-length-specific code for little-endian targets.  It continues
      to generate vector-length-agnostic code for big-endian targets,
      just as previous releases did for all targets.
      </li>
      <li>The vectorizer is now able to use extending loads and truncating
      stores, including gather loads and scatter stores.
      </li>
      <li>The vectorizer now compares the cost of vectorizing with SVE
      and vectorizing with Advanced SIMD and tries to pick the best one.
      Previously it would always use SVE if possible.
      </li>
      <li>If a vector loop uses Advanced SIMD rather than SVE, the vectorizer
      now considers using SVE to vectorize the left-over elements (the
      “scalar tail” or “epilog”).
      </li>
      <li>Besides these specific points, there have been many general
      improvements to the way that the vectorizer uses SVE.
      </li>
    </ul>
  </li>
  <li>The <code>-mbranch-protection=pac-ret</code> option now accepts the
  optional argument <code>+b-key</code> extension to perform return address
  signing with the B-key instead of the A-key.
  </li>
  <li>The option <code>-moutline-atomics</code> has been added to aid
  deployment of the Large System Extensions (LSE) on GNU/Linux systems built
  with a baseline architecture targeting Armv8-A.  When the option is
  specified code is emitted to detect the presence of LSE instructions at
  runtime and use them for standard atomic operations.
  For more information please refer to the documentation.
  </li>
  <li>The Transactional Memory Extension is now supported through ACLE
  intrinsics.  It can be enabled through the <code>+tme</code> option
  extension (for example, <code>-march=armv8.5-a+tme</code>).
  </li>
  <li>A number of features from Armv8.5-A are now supported through ACLE
  intrinsics.  These include:
    <ul>
	<li>The random number instructions that can be enabled
	through the (already present in GCC 9.1) <code>+rng</code> option
	extension.</li>
	<li>Floating-point intrinsics to round to integer instructions from
	Armv8.5-A when targeting <code>-march=armv8.5-a</code> or later.</li>
	<li>Memory Tagging Extension intrinsics enabled through the
	<code>+memtag</code> option extension.</li>
    </ul>
  </li>
  <li>Similarly, the following Armv8.6-A features are now supported
  through ACLE intrinsics:
    <ul>
      <li>The bfloat16 extension.  This extension is enabled automatically
      when Armv8.6-A is selected (such as by <code>-march=armv8.6-a</code>).
      It can also be enabled for Armv8.2-A and later using the
      <code>+bf16</code> option extension.
      </li>
      <li>The Matrix Multiply extension.  This extension is split into
      three parts, one for each supported data type:
	<ul>
	  <li>Support for 8-bit integer matrix multiply instructions.
	  This extension is enabled automatically when Armv8.6-A is
	  selected.  It can also be enabled for Armv8.2-A and later using
	  the <code>+i8mm</code> option extension.
	  </li>
	  <li>Support for 32-bit floating-point matrix multiply instructions.
	  This extension can be enabled using the <code>+f32mm</code>
	  option extension, which also has the effect of enabling SVE.
	  </li>
	  <li>Support for 64-bit floating-point matrix multiply instructions.
	  This extension can be enabled using the <code>+f64mm</code>
	  option extension, which likewise has the effect of enabling SVE.
	  </li>
	</ul>
      </li>
    </ul>
  </li>
  <li>SVE2 is now supported through ACLE intrinsics and (to a limited extent)
  through autovectorization.  It can be enabled through the <code>+sve2</code>
  option extension (for example, <code>-march=armv8.5-a+sve2</code>).
  Additional extensions can be enabled through <code>+sve2-sm4</code>,
  <code>+sve2-aes</code>, <code>+sve2-sha3</code> and
  <code>+sve2-bitperm</code>.
  </li>
  <li>
       Support has been added for the following processors
       (GCC identifiers in parentheses):
       <ul>
         <li>Arm Cortex-A77 (<code>cortex-a77</code>).</li>
	 <li>Arm Cortex-A76AE (<code>cortex-a76ae</code>).</li>
	 <li>Arm Cortex-A65 (<code>cortex-a65</code>).</li>
	 <li>Arm Cortex-A65AE (<code>cortex-a65ae</code>).</li>
	 <li>Arm Cortex-A34 (<code>cortex-a34</code>).</li>
	 <li>Marvell ThunderX3 (<code>thunderx3t110</code>).</li>
       </ul>
       The GCC identifiers can be used
       as arguments to the <code>-mcpu</code> or <code>-mtune</code> options,
       for example: <code>-mcpu=cortex-a77</code> or
       <code>-mtune=cortex-a65ae</code> or as arguments to the equivalent target
       attributes and pragmas.
  </li>
</ul>

<h3 id="arm">arm</h3>
<ul>
  <li>Support for the FDPIC ABI has been added. It uses 64-bit
  function descriptors to represent pointers to functions, and enables
  code sharing on MMU-less systems. The corresponding target triple is
  <code>arm-uclinuxfdpiceabi</code>, and the C library is uclibc-ng.
  </li>
  <li>Support has been added for the Arm EABI on NetBSD through the
  <code>arm*-*-netbsdelf-*eabi*</code> triplet.
  </li>
  <li>The handling of 64-bit integer operations has been significantly reworked
  and improved leading to improved performance and reduced stack usage when using
  64-bit integral data types.  The option <code>-mneon-for-64bits</code> is now
  deprecated and will be removed in a future release.</li>
  <li>
       Support has been added for the following processors
       (GCC identifiers in parentheses):
       <ul>
         <li>Arm Cortex-A77 (<code>cortex-a77</code>).</li>
         <li>Arm Cortex-A76AE (<code>cortex-a76ae</code>).</li>
         <li>Arm Cortex-M35P (<code>cortex-m35p</code>).</li>
       </ul>
       The GCC identifiers can be used
       as arguments to the <code>-mcpu</code> or <code>-mtune</code> options,
       for example: <code>-mcpu=cortex-a77</code> or
       <code>-mtune=cortex-m35p</code>.
  </li>
  <li>Support has been extended for the ACLE
  <a href="https://developer.arm.com/docs/101028/0009/data-processing-intrinsics">
  data-processing intrinsics</a> to include 32-bit SIMD, saturating arithmetic,
  16-bit multiplication and other related intrinsics aimed at DSP algorithm
  optimization.
  </li>
  <li>Support for <code>-mpure-code</code> in Thumb-1 (v6m) has been
  added: this M-profile feature is no longer restricted to targets
  with <code>MOVT</code>. For example, <code>-mcpu=cortex-m0</code>
  now supports this option.</li>
  <li>Support for the Custom Datapath Extension beta ACLE
  <a href="https://developer.arm.com/docs/101028/0010/custom-datapath-extension">
  intrinsics</a> has been added.</li>
</ul>


<h3 id="amdgcn">AMD Radeon (GCN)</h3>
<ul>
  <li>The code generation and in particular the vectorization support has been
  much improved.</li>
</ul>

<h3 id="arc">ARC</h3>
<ul>
  <li>The interrupt service routine functions save all used
  registers, including extension registers and auxiliary registers
  used by Zero Overhead Loops.</li>
  <li>Improve code size by using multiple short instructions instead of
  a single long <code>mov</code> or <code>ior</code> instruction when its
  long immediate constant is known.</li>
  <li>Fix usage of the accumulator register for ARC600.</li>
  <li>Fix issues with <code>uncached</code> attribute.</li>
  <li>Remove <code>-mq-class</code> option.</li>
  <li>Improve 64-bit integer addition and subtraction operations.</li>
</ul>

<h3 id="avr">AVR</h3>
<ul>
  <li>Support for the XMEGA-like devices
    <blockquote>
      ATtiny202, ATtiny204, ATtiny402, ATtiny404, ATtiny406, ATtiny804,
      ATtiny806, ATtiny807, ATtiny1604, ATtiny1606, ATtiny1607, ATmega808,
      ATmega809, ATmega1608, ATmega1609, ATmega3208, ATmega3209,
      ATmega4808, ATmega4809
    </blockquote>
    has been added.
  </li>
  <li>
    A new command-line option <code>-nodevicespecs</code> has been added.
    It allows to provide a custom device-specs file by means of
    <blockquote><code>
	avr-gcc -nodevicespecs -specs=<em>my-spec-file</em> &lt;options&gt;
    </code></blockquote>
    and without the need to provide options <code>-B</code> and
    <code>-mmcu=</code>.
    See
    <a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/AVR-Options.html#index-nodevicespecs">AVR
      command-line options</a> for details.
    This feature is also available in GCC 9.3+ and GCC 8.4+.
  </li>
  <li>
    New command-line options <code>-mdouble=[32,64]</code> and
    <code>-mlong-double=[32,64]</code> have been added.  They allow
    to choose the size (in bits) of the <code>double</code> and
    <code>long double</code> types, respectively.  Whether or not the
    mentioned layouts are available, whether the options act
    as a multilib option, and the default for either option
    are controlled by the new
    <a href="https://gcc.gnu.org/install/configure.html#avr">AVR configure
      options</a>
    <code>--with-double=</code> and <code>--with-long-double=</code>.
  </li>
  <li>
    A new configure option <code>--with-libf7=</code> has been added.
    It controls to which level avr-libgcc provides 64-bit floating point
    support by means of
    <a href="https://gcc.gnu.org/wiki/avr-gcc#Libf7">Libf7</a>.
  </li>
  <li>
    A new configure option <code>--with-double-comparison=</code> has been
    added. It's unlikely you need to set this option by hand.
  </li>
</ul>

<!-- <h3 id="hsa">Heterogeneous Systems Architecture</h3> -->

<h3 id="x86">IA-32/x86-64</h3>
<ul>
  <li>Support to expand <code>__builtin_roundeven</code> into the appropriate
    SSE 4.1 instruction has been added.
  </li>
  <li>New ISA extension support for Intel ENQCMD was added to GCC.  ENQCMD
      intrinsics are available via the <code>-menqcmd</code> compiler switch.
  </li>
  <li>GCC now supports the Intel CPU named Cooperlake through
    <code>-march=cooperlake</code>.
    The switch enables the AVX512BF16 ISA extensions.
  </li>
  <li>GCC now supports the Intel CPU named Tigerlake through
    <code>-march=tigerlake</code>.
    The switch enables the MOVDIRI MOVDIR64B AVX512VP2INTERSECT ISA extensions.
  </li>
</ul>


 <h3 id="mips">MIPS</h3>
 <ul>
    <li>The <code>mips*-*-linux*</code> targets now mark object files with
      appropriate GNU-stack note, facilitating use of non-executable stack
      hardening on GNU/Linux.
      The soft-float targets have this feature enabled by default, while
      for hard-float targets it is required for GCC to be configured with
      <code>--with-glibc-version=2.31</code>
      against glibc 2.31 or later.
   </li>
 </ul>

<!-- <h3 id="mep">MeP</h3> -->

<!-- <h3 id="msp430">MSP430</h3> -->

<!-- <h3 id="nds32">NDS32</h3> -->

<!-- <h3 id="nios2">Nios II</h3> -->

<!-- <h3 id="nvptx">NVPTX</h3> -->

<!-- <h3 id="hppa">PA-RISC</h3> -->

<h3 id="powerpc">PowerPC / PowerPC64 / RS6000</h3>
<ul>
  <li>
    Many vector builtins have been listed as deprecated in the
    <a href="https://openpowerfoundation.org/?resource_lib=64-bit-elf-v2-abi-specification-power-architecture">64-Bit ELF V2 ABI Specification</a>
    for quite a number of years.  The vector builtins listed in Tables A.8
    through A.10 are now deprecated for GCC 10, and will likely be removed
    from support in GCC 11.
  </li>
</ul>

<h3 id="pru">PRU</h3>
<ul>
  <li>
    A new back end targeting TI PRU I/O processors has been contributed to GCC.
  </li>
</ul>

<h3 id="riscv">RISC-V</h3>
<ul>
  <li>
    The <code>riscv*-*-*</code> targets now require GNU binutils version 2.30
    or later, to support new assembly instructions produced by GCC.
  </li>
</ul>

<!-- <h3 id="rx">RX</h3> -->

<!-- <h3 id="s390">S/390, System z, IBM z Systems</h3> -->

<!-- <h3 id="sh">SH</h3> -->

<!-- <h3 id="sparc">SPARC</h3> -->

<!-- <h3 id="Tile">Tile</h3> -->

<h3 id="v850">V850</h3>
<ul>
  <li>The ABI for V850 nested functions has been changed.  Previously
      the V850 port used %r20 for the static chain pointer, now the
      port uses %r19.  This corrects a long standing latent bug in the
      v850 port where a call to a nested function would unexpectedly
      change the value in %r20.
  </li>
</ul>

<!-- .................................................................. -->
<h2 id="os">Operating Systems</h2>

<!-- <h3 id="aix">AIX</h3> -->

<!-- <h3 id="fuchsia">Fuchsia</h3> -->

<!-- <h3 id="dragonfly">DragonFly BSD</h3> -->

<!-- <h3 id="freebsd">FreeBSD</h3> -->

<!-- <h3 id="gnulinux">GNU/Linux</h3> -->

<!-- <h3 id="rtems">RTEMS</h3> -->

<!-- <h3 id="solaris">Solaris</h3> -->

<!-- <h3 id="vxmils">VxWorks MILS</h3> -->

<!-- <h3 id="windows">Windows</h3> -->


<!-- .................................................................. -->
<!-- <h2>Documentation improvements</h2> -->


<!-- .................................................................. -->
<h2 id="plugins">Improvements for plugin authors</h2>
<ul>
  <li>
    GCC diagnostics can now have a chain of events associated with them,
    describing a path through the code that triggers the problem.
    These can be printed by the diagnostics subsystem in various ways,
    controlled by the
    <a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Diagnostic-Message-Formatting-Options.html#index-fdiagnostics-path-format">-fdiagnostics-path-format</a>
    option, or captured in JSON form via
    <a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Diagnostic-Message-Formatting-Options.html#index-fdiagnostics-format">-fdiagnostics-format=json</a>.</li>
  <li>
    GCC diagnostics can now be associated with
    <a href="https://cwe.mitre.org">CWE weakness identifiers</a>, which
    will appear on the standard error stream, and in the JSON output from
    <a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Diagnostic-Message-Formatting-Options.html#index-fdiagnostics-format">-fdiagnostics-format=json</a>.
  </li>
</ul>

<!-- .................................................................. -->
<h2>Other significant improvements</h2>
<ul>
  <li>
    To allow inline expansion of both <code>memcpy</code>
    and <code>memmove</code>, the existing <code>movmem</code> instruction
    patterns used for non-overlapping memory copies have been renamed to
    <code>cpymem</code>. The <code>movmem</code> name is now used
    for overlapping memory moves, consistent with the
    library functions <code>memcpy</code> and <code>memmove</code>.
  </li>
  <li>
    For many releases, when GCC emits a warning it prints the option
    controlling that warning.  As of GCC 10, that option text is now a
    clickable hyperlink for the documentation of that option (assuming a
    <a href="https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda">sufficiently capable terminal</a>).
    This behavior can be controlled via a new
    <a href="https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Diagnostic-Message-Formatting-Options.html#index-fdiagnostics-urls">-fdiagnostics-urls</a>
    option (along with various environment variables and heuristics
    documented with that option).
  </li>
</ul>

<!-- .................................................................. -->
<h2><a name="10.1">GCC 10.1</a></h2>

<p>This is the <a href="https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&amp;resolution=FIXED&amp;target_milestone=10.0">list
of problem reports (PRs)</a> from GCC's bug tracking system that are
known to be fixed in the 10.1 release. This list might not be
complete (that is, it is possible that some PRs that have been fixed
are not listed here).</p>

<!-- .................................................................. -->




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<address>For questions related to the use of GCC,
please consult these web pages and the
<a href="https://gcc.gnu.org/onlinedocs/">GCC manuals</a>. If that fails,
the <a href="mailto:gcc-help@gcc.gnu.org">gcc-help@gcc.gnu.org</a>
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Comments on these web pages and the development of GCC are welcome on our
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All of <a href="https://gcc.gnu.org/lists.html">our lists</a>
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</address>

<p>Copyright (C)
<a href="https://www.fsf.org">Free Software Foundation, Inc.</a>
Verbatim copying and distribution of this entire article is
permitted in any medium, provided this notice is preserved.</p>

<p>These pages are
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