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GCC 13 Release Series
Changes, New Features, and Fixes

This page is a "brief" summary of some of the huge number of improvements in
GCC 13. You may also want to check out our Porting_to_GCC_13 page and the full
GCC_documentation.

Caveats

    * OpenMP offloading to Intel MIC has been removed.
    * The support for the cr16-elf, tilegx*-linux, tilepro*-linux, hppa[12]*-*-
      hpux10*, hppa[12]*-*-hpux11* and m32c-rtems configurations has been
      removed.
    * Support for Solaris 11.3 (*-*-solaris2.11.3) has been declared obsolete.
      The next release of GCC will have corresponding code permanently removed.
      Details can be found in the announcement.
    * Support for emitting the STABS debugging format (including the -gstabs
      and -gxcoff options) has been removed. (This means the dbx debugger is no
      longer supported, either.)
    * Legacy debug info compression option -gz=zlib-gnu was removed and the
      option is ignored right now.
    * -Warray-bounds=2 will no longer issue warnings for out of bounds accesses
      to trailing struct members of one-element array type anymore. Instead it
      diagnoses accesses to trailing arrays according to -fstrict-flex-arrays.
    * -fanalyzer is still only suitable for analyzing C code. In particular,
      using it on C++ is unlikely to give meaningful output.
    * In the arm port, support for the iWMMXt extensions, enabled through -
      mcpu=iwmmxt, has been deprecated and will be removed in a future release.
      This includes support for the iWMMXt_built-in_functions.

General Improvements

    * OpenMP
          o Reverse offload is now supported with AMD GCN and nvptx devices.
            Additionally, the requires handling has been improved and all
            clauses are now accepted. If a requirement cannot be fulfilled for
            an accessible device, this device is excluded from the list of
            available devices. This may imply that the only device left is the
            host (the initial device). In particular, unified_address and
            unified_shared_memory are unsupported by all non-host devices.
          o OpenMP 5.0: Fortran now supports some non-rectangular loop nests;
            for C/C++, the support was added in GCC 11.
          o The following OpenMP 5.1 features have been added: the
            omp_all_memory reserved locator, the inoutset modifier to the
            depend clause, the nowait clause for the taskwait directive and the
            omp_target_is_accessible, omp_target_memcpy_async,
            omp_target_memcpy_rect_async and omp_get_mapped_ptr API routines.
            The assume and assumes directives, the begin/end declare target
            syntax in C/C++ and device-specific ICV settings with environment
            variables are now supported.
          o Initial support for OpenMP 5.2 features has been added:
            firstprivate and allocate clauses on the scope construct; the
            OpenMP 5.2 syntax of the linear clause; new enum/constants
            omp_initial_device and omp_invalid_device; and optionally omitting
            the map-type in target enter/exit data. The enter clause (as alias
            for to) has been added to the declare target directive. Also added
            have been the omp_in_explicit_task routine and the doacross clause
            as alias for depend with source/sink modifier.
          o The _ALL suffix to the device-scope environment variables added in
            Technical Report (TR11) is already handled.
          o For user defined allocators requesting high bandwidth or large
            capacity memspaces or interleaved partitioning, the memkind library
            is used, if available at run time.
    * AddressSanitizer defaults to detect_stack_use_after_return=1 on GNU/Linux
      targets. For compatibility, it can be disabled with env
      ASAN_OPTIONS=detect_stack_use_after_return=0.
    * New debug info compression option value -gz=zstd has been added.
    * Link-time optimization improvements:
          o LTO supports the newly added jobserver of GNU make jobserver that
            uses named pipes (--jobserver-style=fifo) by default.
          o If make's jobserver is active, parallel LTO WPA streaming
            communicates with it and thus avoids system overcommitting.
    * -Ofast, -ffast-math and -funsafe-math-optimizations will no longer add
      startup code to alter the floating-point environment when producing a
      shared object with -shared.
    * GCC can now emit its diagnostics using SARIF. This is a JSON-based format
      suited for capturing the results of static analysis tools (like GCC's -
      fanalyzer), but it can also be used to capture other GCC warnings and
      errors in a machine-readable format. Specifically, the -fdiagnostics-
      format= option has been extended to support these new values:
          o -fdiagnostics-format=sarif-stderr
          o -fdiagnostics-format=sarif-file
          o -fdiagnostics-format=json-stderr, a synonym for the existing -
            fdiagnostics-format=json
          o -fdiagnostics-format=json-file
      where the json-prefixed variants refer to GCC's own JSON diagnostic
      format.

New Languages and Language specific improvements

Ada

    * Traceback support added in RTEMS for the PPC ELF and ARM architectures.
    * Support for versions older than VxWorks 7 has been removed.
    * General improvements to the contracts in the standard libraries.
    * Addition of GNAT.Binary_Search.
    * Further additions and fixes for the Ada 2022 specification.
    * The Pragma SPARK_Mode=>Auto is now accepted. Contract analysis has been
      further improved.
    * Documentation improvements.

C family

    * New warnings:
          o -Wxor-used-as-pow warns about uses of ^, the exclusive or operator,
            where it appears the user meant exponentiation (PR90885)
    * Three new function attributes for documenting int arguments that are file
      descriptors:
          o __attribute__((fd_arg(N)))
          o __attribute__((fd_arg_read(N)))
          o __attribute__((fd_arg_write(N)))
      These are used by -fanalyzer to detect misuses of file descriptors.
    * A new statement attribute for C++23 P1774R8 Portable assumptions support
      also in C or older C++: __attribute__((assume(EXPR)));
    * GCC can now control when to treat the trailing array of a structure as a
      flexible array member for the purpose of accessing the elements of such
      an array. By default, all trailing arrays in aggregates are treated as
      flexible array members. Use the new command-line option -fstrict-flex-
      arrays to control which array members are treated as flexible arrays.

C

    * Several C23 features have been implemented:
          o N3042, Introduce the nullptr constant
          o N2963, Enhanced Enumerations (fixed underlying types)
          o N2975, Relax requirements for variadic parameter lists
          o N3007, Type inference for object definitions (auto)
          o N3018, The constexpr specifier for object definitions
          o N3038, Introduce storage-class specifiers for compound literals
          o typeof (previously supported as an extension) and typeof_unqual
          o New keywords alignas, alignof, bool, false, static_assert,
            thread_local, true
          o N2764, The noreturn attribute
          o Support for empty initializer braces
          o __STDC_VERSION_*_H__ header version macros
          o Removal of ATOMIC_VAR_INIT
          o unreachable macro in <stddef.h>
          o Removal of trigraphs
          o Removal of unprototyped functions
          o printf and scanf format checking with -Wformat for %wN and %wfN
            format length modifiers
          o N2836, Identifier Syntax using Unicode Standard Annex 31
    * In addition to those C23 features, existing features adopted in C23 have
      been adjusted to follow C23 requirements and are not diagnosed with -
      std=c2x -Wpedantic.
    * New warnings:
          o -Wenum-int-mismatch warns about mismatches between an enumerated
            type and an integer type (PR105131)

C++

    * Excess precision support (which has been available in C since GCC 4.5)
      has been implemented for C++ as well. It is enabled by default in strict
      standard modes like -std=c++17, where it defaults to -fexcess-
      precision=standard, while in GNU standard modes like -std=gnu++20 it
      defaults to -fexcess-precision=fast. The option mainly affects IA-32/x86-
      64 using x87 math and in some cases on Motorola 68000, where float and
      double expressions are evaluated in long double precision and S/390,
      System z, IBM z Systems where float expressions are evaluated in double
      precision. Also, on several architectures where std::float16_t or std::
      bfloat16_t types are supported those are evaluated in float precision. -
      fexcess-precision=fast restores previous behavior.
    * Several C++23 features have been implemented:
          o P2324R1, Labels at the end of compound statements (PR103539)
          o P2255R2, A type trait to detect reference binding to temporary
            (PR104477)
          o P2327R1, De-deprecating volatile compound operations
          o P2437R1, Support for #warning (PR106646)
          o P2290R3, Delimited escape sequences (PR106645)
          o P2071R2, Named universal character escapes (PR106648)
          o P2513R3, char8_t Compatibility and Portability Fix (PR106656)
          o P1169R4, static operator() (PR106651)
          o P2266R3, Simpler implicit move (PR101165)
          o P2468R2, The Equality Operator You Are Looking For (PR106644)
          o P2362R3, Remove non-encodable
            wide character literals and multicharacter wide character literals
            (PR106647)
          o P2448R2, Relaxing some constexpr restrictions (PR106649)
          o P1467R9, Extended floating-point types and standard names
            (PR106652)
          o P1774R8, Portable assumptions (PR106654)
          o P2295R6, Support for UTF-8 as a portable source file encoding
            (PR106655)
          o P2589R1, static operator[] (PR107684)
    * New warnings:
          o -Wself-move warns when a value is moved to itself with std::move
            (PR81159)
          o -Wdangling-reference warns when a reference is bound to a temporary
            whose lifetime has ended (PR106393)
    * The -Wpessimizing-move and -Wredundant-move warnings have been extended
      to warn in more contexts.
    * The -nostdlib++ option has been added, to enable linking with g++ without
      implicitly linking in the C++ standard library.

Runtime Library (libstdc++)

    * Improved experimental support for C++20, including:
          o <format> header and std::format.
          o std::chrono::utc_clock and other clocks, time zones, and std::
            format support in the <chrono> header.
    * Improved experimental support for C++23, including:
          o Additions to the <ranges> header: views::zip, views::zip_transform,
            views::adjacent, views::adjacent_transform views::pairwise, views::
            slide, views::chunk, views::chunk_by, views::repeat, views::
            chunk_by, views::cartesian_product, views::as_rvalue, views::
            enumerate, views::as_const.
          o Additions to the <algorithm> header: ranges::contains, ranges::
            contains_subrange, ranges::iota, ranges::find_last, ranges::
            find_last_if, ranges::find_last_if_not, ranges::fold_left, ranges::
            fold_left_first, ranges::fold_right, ranges::fold_right_last,
            ranges::fold_left_with_iter, ranges::fold_left_first_with_iter.
          o Monadic operations for std::expected.
          o Constexpr std::bitset, std::to_chars and std::from_chars.
          o Library support for extended floating-point types.
    * Support for the <experimental/scope> header from v3 of the Library
      Fundamentals Technical Specification.
    * Support for the <experimental/synchronized_value> header from v2 of the
      Concurrency Technical Specification.

Fortran

    * Finalization is now fully supported.

Go
    * GCC 13, like GCC 12, provides a complete implementation of the Go 1.18
      user packages.
    * Although Go 1.18 includes support for generic programming, that support
      is not yet available in GCC.

Modula-2
    * Support for the language Modula-2 has been added. This includes support
      for the ISO/IEC 10514-1, PIM2, PIM3, PIM4 dialects together with a
      complete set of ISO/IEC 10514-1 and PIM libraries.
    * The <* noreturn *> attribute is supported with the -Wreturn-type option.

New Targets and Target Specific Improvements

AArch64

    * The AArch64 target now supports Decimal Floating-point in the BID format
      through the libbid library.
    * A number of new CPUs are supported through the -mcpu and -mtune options
      (GCC identifiers in parentheses).
          o Ampere-1A (ampere1a).
          o Arm Cortex-A715 (cortex-a715).
          o Arm Cortex-X1C (cortex-x1c).
          o Arm Cortex-X3 (cortex-x3).
          o Arm Neoverse V2 (neoverse-v2).
    * Support has been added for the armv9.1-a, armv9.2-a and armv9.3-
      a arguments to the -march= option.
    * The FEAT_LRCPC feature is now supported by generating the LDAPR
      instructions for C and C++ atomic loads with an acquire memory model.
      This is enabled when compiling with the +rcpc extension to -march or a
      CPU target that supports this feature.
    * The FEAT_CSSC feature from the 2022 Arm Architecture extensions is
      supported through the +cssc extension option. When enabled, scalar
      operations like integer minimum, maximum, absolute value, count trailing
      zeroes (__builtin_ctz), population count (__builtin_popcount) can be
      implemented in a single instruction.
    * The FEAT_LSE2 feature is now supported through libatomic and provides
      lockless 16-byte atomics on systems that implement it.

AMD Radeon (GCN)

    * Support for the Instinct MI200 series devices (gfx90a) has been added.
    * SIMD vectorization support has been improved; this and stack-handling
      changes require newlib 4.3.0 (or newer).

arm
    * A number of new CPUs are supported through the -mcpu and -mtune options
      (GCC identifiers in parentheses).
          o STAR-MC1 (star-mc1).
          o Arm Cortex-X1C (cortex-x1c).
          o Arm Cortex-M85 (cortex-m85).
    * Support has been added for the M-profile PACBTI extension that can help
      harden the generated code against return-oriented and jump-oriented
      attacks. It can be enabled through the -mbranch-protection= option.

IA-32/x86-64
    * For both C and C++ the __bf16 type is supported on x86 systems with SSE2
      and above enabled.
    * Use real __bf16 type for AVX512BF16 intrinsics. Previously we use
      __bfloat16 which is typedef of short. Now we introduced real __bf16 type
      to x86 psABI. Users need to adjust their AVX512BF16-related source code
      when upgrading GCC12 to GCC13.
    * New ISA extension support for Intel AVX-IFMA was added. AVX-IFMA
      intrinsics are available via the -mavxifma compiler switch.
    * New ISA extension support for Intel AVX-VNNI-INT8 was added. AVX-VNNI-
      INT8 intrinsics are available via the -mavxvnniint8 compiler switch.
    * New ISA extension support for Intel AVX-NE-CONVERT was added. AVX-NE-
      CONVERT intrinsics are available via the -mavxneconvert compiler switch.
    * New ISA extension support for Intel CMPccXADD was added. CMPccXADD
      intrinsics are available via the -mcmpccxadd compiler switch.
    * New ISA extension support for Intel AMX-FP16 was added. AMX-FP16
      intrinsics are available via the -mamx-fp16 compiler switch.
    * New ISA extension support for Intel PREFETCHI was added. PREFETCHI
      intrinsics are available via the -mprefetchi compiler switch.
    * New ISA extension support for Intel RAO-INT was added. RAO-INT intrinsics
      are available via the -mraoint compiler switch.
    * New ISA extension support for Intel AMX-COMPLEX was added. AMX-COMPLEX
      intrinsics are available via the -mamx-complex compiler switch.
    * GCC now supports the Intel CPU named Raptor Lake through -
      march=raptorlake. Raptor Lake is based on Alder Lake.
    * GCC now supports the Intel CPU named Meteor Lake through -
      march=meteorlake. Meteor Lake is based on Alder Lake.
    * GCC now supports the Intel CPU named Sierra Forest through -
      march=sierraforest. The switch enables the AVX-IFMA, AVX-VNNI-INT8, AVX-
      NE-CONVERT and CMPccXADD ISA extensions.
    * GCC now supports the Intel CPU named Grand Ridge through -
      march=grandridge. The switch enables the AVX-IFMA, AVX-VNNI-INT8, AVX-NE-
      CONVERT, CMPccXADD and RAO-INT ISA extensions.
    * GCC now supports the Intel CPU named Emerald Rapids through -
      march=emeraldrapids. Emerald Rapids is based on Sapphire Rapids.
    * GCC now supports the Intel CPU named Granite Rapids through -
      march=graniterapids. The switch enables the AMX-FP16, PREFETCHI and AMX-
      COMPLEX ISA extensions.
    * GCC now supports AMD CPUs based on the znver4 core via -march=znver4. The
      switch makes GCC consider using 512 bit vectors when auto-vectorizing.

LoongArch

    * New features
          o The new command-line option -mexplicit-relocs decides whether to
            use the assembler relocation operator when dealing with symbolic
            addresses. It is enabled by default if a compatible assembler
            (binutils 2.40 or later) is present at GCC build time.
          o The new command-line option -mdirect-extern-access can be used to
            prevent accessing external symbols through GOT.
          o The new variable attribute model has been added.
    * Built-in functions
          o The rint and copysign mathematical builtins (and their float
            variants) are now implemented as inline LoongArch intrinsics.
          o The lrint, logb, scalbln, scalbn and ldexp mathematical builtins
            (and their float variants) are now implemented as inline LoongArch
            intrinsics when using -fno-math-errno.
          o The lceil and lfloor mathematical builtins (and their float
            variants) are now implemented as inline LoongArch intrinsics when
            using -ffp-int-builtin-inexact.
    * Subprojects Support
          o libvtv now supports LoongArch.
          o libitm now supports LoongArch.
          o Address sanitizers other than HWASan and TSan are now supported on
            LoongArch.

NVPTX

    * The default value for the -march option can be now changed when building
      GCC using the --with-arch= configure option. GCC's target libraries are
      then build both with sm_30 and the specified target architecture. If not
      specified, GCC defaults to sm_30.

RISC-V

    * Support for vector intrinsics as specified in version_0.11_of_the_RISC-
      V_vector_intrinsic_specification, thanks Ju-Zhe Zhong from RiVAI for
      contributing most of implementation.
    * Support for the following standard extensions has been added:
          o Zawrs
          o Zbkb
          o Zbkc
          o Zbkx
          o Zdinx
          o Zfinx
          o Zfh
          o Zfhmin
          o Zhinx
          o Zhinxmin
          o Zicbom
          o Zicbop
          o Zicboz
          o Zknd
          o Zkne
          o Zksed
          o Zksh
          o Zmmul
    * Support for the following vendor extensions has been added:
          o XTheadBa
          o XTheadBb
          o XTheadBs
          o XTheadCmo
          o XTheadCondMov
          o XTheadFMemIdx
          o XTheadFmv
          o XTheadInt
          o XTheadMac
          o XTheadMemIdx
          o XTheadMemPair
          o XTheadSync
    * The following new CPUs are supported through the -mcpu option (GCC
      identifiers in parentheses).
          o T-Head's XuanTie C906 (thead-c906).
    * Improves the multi-lib selection mechanism for the bare-metal toolchain
      (riscv*-elf*). GCC will now automatically select the best-fit multi-lib
      candidate instead of requiring all possible reuse rules to be listed at
      build time.

Operating Systems

Improvements to Static Analyzer

    * The analyzer has gained 20 new warnings:
          o -Wanalyzer-allocation-size
          o -Wanalyzer-deref-before-check
          o -Wanalyzer-exposure-through-uninit-copy
          o Seven new warnings relating to misuse of file descriptors:
                # -Wanalyzer-fd-access-mode-mismatch
                # -Wanalyzer-fd-double-close
                # -Wanalyzer-fd-leak
                # -Wanalyzer-fd-phase-mismatch (e.g. calling accept on a socket
                  before calling listen on it)
                # -Wanalyzer-fd-type-mismatch (e.g. using a stream socket
                  operation on a datagram socket)
                # -Wanalyzer-fd-use-after-close
                # -Wanalyzer-fd-use-without-check
            along with special-casing handling of the behavior of open, close,
            creat, dup, dup2, dup3, pipe, pipe2, read, and write.
          o -Wanalyzer-imprecise-fp-arithmetic
          o -Wanalyzer-infinite-recursion
          o -Wanalyzer-jump-through-null
          o -Wanalyzer-out-of-bounds
          o -Wanalyzer-putenv-of-auto-var
          o -Wanalyzer-tainted-assertion
          o Four new warnings for misuses of <stdarg.h>:
                # -Wanalyzer-va-list-leak for complaining about missing va_end
                  after a va_start or va_copy
                # -Wanalyzer-va-list-use-after-va-end for complaining about
                  va_arg or va_copy used on a va_list that's had va_end called
                  on it
                # -Wanalyzer-va-arg-type-mismatch for type-checking of va_arg
                  usage in interprocedural execution paths against the types of
                  the parameters that were actually passed to the variadic call
                # -Wanalyzer-va-list-exhausted for complaining in
                  interprocedural execution paths if va_arg is used too many
                  times on a va_list
      along with numerous other improvements.

Improvements for plugin authors
    * GCC diagnostics can now be associated_with_rules such as from coding
      standards documents, or specifications. Such rules have a code name and
      can have a URL, which GCC can print in text form or capture in its SARIF
      output when emitting diagnostics.

Other significant improvements

GCC 13.1

This is the list_of_problem_reports_(PRs) from GCC's bug tracking system that
are known to be fixed in the 13.1 release. This list might not be complete
(that is, it is possible that some PRs that have been fixed are not listed
here).
https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=13.0