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<
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-12/index.html
GCC 12 Release Series
Aug 19, 2022
The GCC developers are pleased to announce the release of GCC 12.2.
This release is a bug-fix release, containing fixes for regressions in
GCC 12.1 relative to previous releases of GCC.
Release History
GCC 12.2
Aug 19, 2022 ([1]changes, [2]documentation)
GCC 12.1
May 6, 2022 ([3]changes, [4]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 [5]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 [6]amazing group of volunteers is
what makes GCC successful.
For additional information about GCC please refer to the [7]GCC project
web site or contact the [8]GCC development mailing list.
To obtain GCC please use [9]our mirror sites or [10]our version control
system.
For questions related to the use of GCC, please consult these web
pages and the [11]GCC manuals. If that fails, the
[12]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 [13]gcc@gcc.gnu.org. All of [14]our lists have public
archives.
Copyright (C) [15]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 [16]maintained by the GCC team. Last modified
2022-08-19[17].
References
1. http://gcc.gnu.org/gcc-12/changes.html
2. http://gcc.gnu.org/onlinedocs/12.2.0/
3. http://gcc.gnu.org/gcc-12/changes.html
4. http://gcc.gnu.org/onlinedocs/12.1.0/
5. http://gcc.gnu.org/gcc-12/buildstat.html
6. http://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Contributors.html
7. http://gcc.gnu.org/index.html
8. mailto:gcc@gcc.gnu.org
9. http://gcc.gnu.org/mirrors.html
10. http://gcc.gnu.org/git.html
11. https://gcc.gnu.org/onlinedocs/
12. mailto:gcc-help@gcc.gnu.org
13. mailto:gcc@gcc.gnu.org
14. https://gcc.gnu.org/lists.html
15. https://www.fsf.org/
16. https://gcc.gnu.org/about.html
17. http://validator.w3.org/check/referer
======================================================================
http://gcc.gnu.org/gcc-12/changes.html
GCC 12 Release Series
Changes, New Features, and Fixes
This page is a "brief" summary of some of the huge number of
improvements in GCC 12. You may also want to check out our [1]Porting
to GCC 12 page and the [2]full GCC documentation.
Caveats
* An ABI incompatibility between C and C++ when passing or returning
by value certain aggregates containing zero width bit-fields has
been discovered on various targets. As mentioned in [3]PR102024,
since the [4]PR42217 fix in GCC 4.5 the C++ front-end has been
removing zero width bit-fields from the internal representation of
the aggregates after the layout of those aggregates, but the C
front-end kept them, so passing e.g. struct S { float a; int : 0;
float b; } or struct T { float c; int : 0; } by value could differ
between C and C++. Starting with GCC 12 the C++ front-end no longer
removes those bit-fields from the internal representation and per
clarified psABI some targets have been changed, so that they either
ignore those bit-fields in the argument passing by value decisions
in both C and C++, or they always take them into account. x86-64,
ARM and AArch64 will always ignore them (so there is a C ABI
incompatibility between GCC 11 and earlier with GCC 12 or later),
PowerPC64 ELFv2 and S/390 always take them into account (so there
is a C++ ABI incompatibility, GCC 4.4 and earlier compatible with
GCC 12 or later, incompatible with GCC 4.5 through GCC 11). RISC-V
has changed the handling of these already starting with GCC 10. As
the ABI requires, MIPS takes them into account handling function
return values so there is a C++ ABI incompatibility with GCC 4.5
through 11. For function arguments on MIPS, refer to [5]the MIPS
specific entry. GCC 12 on the above targets will report such
incompatibilities as warnings or other diagnostics unless
-Wno-psabi is used.
* C: Computed gotos require a pointer type now.
* C++: Two non-standard std::pair constructors have been deprecated.
These allowed the use of an rvalue and a literal 0 to construct a
pair containing a move-only type and a pointer. The nullptr keyword
should be used to initialize the pointer member instead of a
literal 0, as this is portable to other C++ implementations.
* The configuration option --enable-libstdcxx-allocator no longer
supports the bitmap, mt, and pool arguments. Those configurations
had been broken for some time.
* Fortran: OpenMP code using the omp_lib.h include file can no longer
be compiled with -std=f95 but now requires at least -std=f2003.
Alternatively, use the omp_lib module, which still supports
-std=f95 and is recommended to be used instead in general.
* OpenMP offloading to Intel MIC has been deprecated and will be
removed in a future release.
* The cr16 target with the cr16-*-* configuration has been obsoleted
and will be removed in a future release.
* The hppa[12]*-*-hpux10* and hppa[12]*-*-hpux11* configurations
targeting 32-bit PA-RISC with HP-UX have been obsoleted and will be
removed in a future release.
* The m32c*-*-rtems* configuration has been obsoleted and will be
removed in a future release.
* The support for the m32r-*-linux*, m32rle-*-linux*,
m68k*-*-openbsd* and vax-*-openbsd* configurations has been
removed.
* STABS: Support for emitting the STABS debugging format is
deprecated and will be removed in the next release. All ports now
default to emit DWARF (version 2 or later) debugging info or are
obsoleted.
* The optimization level -Ofast now implies
-fno-semantic-interposition.
General Improvements
* Vectorization is enabled at -O2 which is now equivalent to the
original -O2 -ftree-vectorize -fvect-cost-model=very-cheap. Note
that default vectorizer cost model has been changed which used to
behave as -fvect-cost-model=cheap were specified.
* GCC now supports the [6]ShadowCallStack sanitizer, which can be
enabled using the command-line option
[7]-fsanitize=shadow-call-stack. This sanitizer currently only
works on AArch64 targets and it requires an environment in which
all code has been compiled with -ffixed-r18. Its primary initial
user is the Linux kernel.
New Languages and Language specific improvements
* OpenMP
+ OpenMP 5.0 support has been extended: The close map modifier
and the affinity clause are now supported. In addition Fortran
gained additionally the following features which were
available in C and C++ before: declare variant is now
available, depobj, mutexinoutset and iterator can now also be
used with the depend clause, defaultmap has been updated for
OpenMP 5.0, and the loop directive and combined directives
involving the master directive have been added.
+ The following OpenMP 5.1 features have been added: support for
expressing OpenMP directives as C++ 11 attributes, the masked
and scope construct, the nothing and error directives, and
using primary with the proc_bind clause and OMP_PROC_BIND
environment variable, the reproducible and unconstrained
modifiers to the order clause, and, for C/C++ only, the align
and allocator modifiers to the allocate clause and the atomic
extensions are now available. The OMP_PLACE environment
variable supports the OpenMP 5.1 features. In addition the
OMP_NUM_TEAMS and OMP_TEAMS_THREAD_LIMIT environment variables
and their associated API routines are now supported as well as
the memory-allocation routines added for Fortran and extended
for C/C++ in OpenMP 5.1. In Fortran code, strictly structured
blocks can be used.
+ The [8]OpenMP Implementation Status can be found in the
libgomp manual.
* Version 2.6 of the [9]OpenACC specification continues to be
maintained and improved in the C, C++ and Fortran compilers. See
the [10]implementation status section on the OpenACC wiki page and
the [11]run-time library documentation for further information. In
addition to general performance tuning and bug fixing, new features
include:
+ OpenACC worker parallelism for [12]AMD GPUs (already for a
long time supported for [13]Nvidia GPUs).
+ Data privatization/sharing at the OpenACC gang level.
+ Considerable improvements for the experimental OpenACC
'kernels' decomposition ([14]--param
openacc-kernels=decompose).
+ A new warning flag [15]-Wopenacc-parallelism to warn about
potentially suboptimal choices related to OpenACC parallelism.
* The offload target code generation for OpenMP and OpenACC can now
be better adjusted using the new [16]-foffload-options= flag and
the pre-existing but now documented [17]-foffload= flag.
Ada
* Ada 2022
+ Added the -gnat2022 flag to indicate strict Ada 2022
compliance. The old -gnat2020 flag is now deprecated.
+ Support for Big Numbers (Annex G) has seen continuous
improvements. It is now considered complete. It is compatible
with SPARK, i.e. can be used from SPARK code.
+ Continuous improvements to the Ada 2022 standard since GCC 11.
+ Greatly improved compile time support. More functions can now
have the with Static aspect and can be used in more contexts.
* Ada 2022 extensions. The use of the -gnatX flag is necessary to
access these features as they are not considered stable or
standard.
+ Fixed lower bound for unconstrained arrays.
o type Matrix is array (Natural range 0 .. <>, Natural
range 0 .. <>) of Integer; is now valid.
o Subtypes can also specify a lower bound: subtype String_1
is String (1 .. <>);. Boundaries from slices will "slide"
to the correct lower bound of the subtype.
+ Generalized Object.Operand notation. The follwing code is now
valid V.Add_Element(42);, with V being a vector, for example.
+ Additional when constructs. Keywords return, goto and raise
can now use when in addition to the existing exit when. The
following expression is therefore now valid raise
Constraint_Error with "Element is null" when Element = null;
+ Pattern matching
o The case statement has been extended to cover records and
arrays as well as finer grained casing on scalar types.
In the future it is expected to provide more compile time
guarantees when accessing discriminated fields. Case
exhaustion is supported for pattern matching. An example
would be
type Sign is (Neg, Zero, Pos);
function Multiply (S1, S2 : Sign) return Sign is
(case (S1, S2) is
when (Neg, Neg) | (Pos, Pos) => Pos,
when (Zero, <>) | (<>, Zero) => Zero,
when (Neg, Pos) | (Pos, Neg) => Neg);
* gnatfind and gnatxref, which were already deprecated, have been
removed.
* Greatly expanded code covered by contracts. Thanks to this work,
there are now several Ada standard libraries fully proven in SPARK
which means they have no runtime nor logical errors. They are
mostly numeric and string handling libraries.
* Enable return-slot optimization for Pure functions.
* General optimizations, improvements and additions to the standard
library. Performance, correctness and in some cases stability was
improved. Memory pools have also seen some minor enhancements.
* Improvements to embedded-RTOS targets such as RTEMS, VxWorks and
QNX. Older targets were removed or cleaned.
* Added some [18]hardening features.
C family
* Support for __builtin_shufflevector compatible with the clang
language extension was added.
* Support for attribute unavailable was added.
* A new built-in function, __builtin_assoc_barrier, was added. It can
be used to inhibit re-association of floating-point expressions.
* Support for __builtin_dynamic_object_size compatible with the clang
language extension was added.
* New warnings:
+ [19]-Wbidi-chars warns about potentially misleading UTF-8
bidirectional control characters. The default is
-Wbidi-chars=unpaired ([20]PR103026)
+ [21]-Warray-compare warns about comparisons between two
operands of array type ([22]PR97573)
* Enhancements to existing warnings:
+ [23]-Wattributes has been extended so that it's possible to
use -Wno-attributes=ns::attr or -Wno-attributes=ns:: to
suppress warnings about unknown scoped attributes (in C++11
and C2X). Similarly, #pragma GCC diagnostic ignored_attributes
"vendor::attr" can be used to achieve the same effect
([24]PR101940)
C
* Some new features from the upcoming C2X revision of the ISO C
standard are supported with -std=c2x and -std=gnu2x. 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
-std=c2x -Wpedantic.
+ Digit separators (as in C++) are supported for C2X.
+ The #elifdef and #elifndef preprocessing directives are now
supported.
+ The printf and scanf format checking with [25]-Wformat now
supports the %b format specified by C2X for binary integers,
and the %B format recommended by C2X for printf.
C++
* Several C++23 features have been implemented:
+ [26]P1938R3, if consteval ([27]PR100974)
+ [28]P0849R8, auto(x): decay-copy in the language
([29]PR103049)
+ [30]P2242R3, Non-literal variables (and labels and gotos) in
constexpr functions ([31]PR102612)
+ [32]P2334R1, Support for preprocessing directives elifdef and
elifndef ([33]PR102616)
+ [34]P2360R0, Extend init-statement to allow alias-declaration
([35]PR102617)
+ [36]P2128R6, Multidimensional subscript operator
+ [37]DR 2397, auto specifier for pointers and references to
arrays ([38]PR100975)
* Several C++ Defect Reports have been resolved, e.g.:
+ [39]DR 960, Covariant functions and lvalue/rvalue references
+ [40]DR 1227, Mixing immediate and non-immediate contexts in
deduction failure
+ [41]DR 1315, Restrictions on non-type template arguments in
partial specializations
+ [42]DR 2082, Referring to parameters in unevaluated operands
of default arguments
+ [43]DR 2351, void{}
+ [44]DR 2374, Overly permissive specification of enum
direct-list-initialization
+ [45]DR 2397, auto specifier for pointers and references to
arrays
+ [46]DR 2446, Questionable type-dependency of concept-ids
* New command-line option -fimplicit-constexpr can be used to make
inline functions implicitly constexpr ([47]git)
* New command-line option -ffold-simple-inlines can be used to fold
calls to certain trivial inline functions (currently std::move,
std::forward, std::addressof and std::as_const). In contrast to
inlining such calls, folding means that no intermediate code or
debug information will be generated for them; this minimizes the
abstraction penalty incurred for using these functions versus using
the fundamental operations from which they're defined (e.g.
std::move versus static_cast). This flag is enabled by default when
-fno-inline is not active.
* Deduction guides can be declared at class scope ([48]PR79501)
* [49]-Wuninitialized warns about using uninitialized variables in
member initializer lists ([50]PR19808)
* [51]-Wint-in-bool-context is now disabled when instantiating a
template ([52]git)
* Stricter checking of attributes on friend declarations: if a friend
declaration has an attribute, that declaration must be a
definition. Moreover, a C++11 attribute cannot appear in the middle
of the decl-specifier-seq. ([53]PR99032)
* New warning options for C++ language mismatches:
-Wc++11-extensions, -Wc++14-extensions, -Wc++17-extensions,
-Wc++20-extensions, and -Wc++23-extensions. They are enabled by
default and can be used to control existing pedwarns about
occurrences of new C++ constructs in code using an old C++ standard
dialect.
* New warning [54]-Wmissing-requires warns about missing requires
([55]git)
* The existing std::is_constant_evaluated in if warning was extended
to warn in more cases ([56]PR100995)
* [57]-Waddress has been enhanced so that it now warns about, for
instance, comparing the address of a nonstatic member function to
null ([58]PR102103)
* Errors about narrowing are no longer hidden if they occur in system
headers
* Ordered comparison of null pointers is now rejected ([59]PR99701)
* Anonymous structs with bases are now rejected ([60]git)
* The compiler rejects taking the address of an immediate member
function ([61]PR102753)
* The compiler has support for C++20
__cpp_lib_is_pointer_interconvertible and
__cpp_lib_is_layout_compatible to help the C++ library implement
[62]P0466, Layout-compatibility and Pointer-interconvertibility
Traits ([63]PR101539)
* Memory usage of constraint subsumption has been improved
([64]PR100828)
* constinit thread_local variables are optimized better
([65]PR101786)
* Support for C++17 std::hardware_destructive_interference_size was
added, along with the [66]-Winterference-size warning ([67]git)
* Many bugs in the CTAD handling have been fixed ([68]PR101344,
[69]PR101883, [70]PR89062, [71]PR101233, [72]PR88252, [73]PR86439,
[74]PR98832, [75]PR102933 ...)
* Two-stage name lookup for dependent operator expressions has been
corrected ([76]PR51577)
* Several issues with constrained variable templates have been fixed
([77]PR98486)
* The compiler performs less instantiating when doing speculative
constant evaluation ([78]git)
* Various diagnostic improvements; e.g., a more precise caret
location for pointer-to-member expressions
* The new -fconstexpr-fp-except flag allows IEC559 floating point
exceptions in constant-expressions.
Runtime Library (libstdc++)
* Improved experimental C++20 support, including:
+ std::vector, std::basic_string, std::optional, and
std::variant can be used in constexpr functions.
+ std::make_shared for arrays with default initialization, and
std::atomic<std::shared_ptr<T>>.
+ Layout-compatibility and pointer-interconvertibility traits.
* Improved experimental C++23 support, including:
+ Monadic operations for std::optional.
+ std::move_only_function
+ <spanstream>
+ std::basic_string::resize_and_overwrite
+ std::unique_ptr can be used in constexpr functions.
+ <stacktrace> (not built by default, requires linking to an
extra library).
+ <stdatomic.h>
+ std::invoke_r
+ constexpr std::type_info::operator==
Fortran
* WG5/N1942, "TS 29113 Further Interoperability of Fortran with C",
is now fully supported. In addition to implementing previously
missing functionality, such as support for character arguments of
length greater than one in functions marked bind(c) and gaps in the
handling for assumed-rank arrays, numerous other bugs have been
fixed, and an extensive set of new conformance test cases has been
added.
* GCC 12 now uses OPERATION as the name of the function to the
CO_REDUCE intrinsic for the pairwise reduction, thus conforming to
the Fortran 2018 standard. Previous versions used OPERATOR which
conforms to TS 18508.
* On POWER systems which support it, the -mabi=ieeelongdouble option
now selects the IEEE 128-bit floating point format for
REAL(KIND=16). R16_IBM and R16_IEEE have been added to the
-fconvert option, the CONVERT specifyer of the OPEN statement and
the GFORTRAN_CONVERT_UNIT environment variable.
libgccjit
* The libgccjit API gained 30 new entry points:
+ 17 new "reflection" entrypoints for querying functions and
types ([79]LIBGCCJIT_ABI_16)
+ [80]gcc_jit_lvalue_set_tls_model for supporting thread-local
variables ([81]LIBGCCJIT_ABI_17)
+ [82]gcc_jit_lvalue_set_link_section for setting the link
section of global variables, analogous to
[83]__attribute__((section(".section")))
([84]LIBGCCJIT_ABI_18)
+ 4 new entrypoints for initializing global variables and
creating constructors for rvalues ([85]LIBGCCJIT_ABI_19)
+ Support for sized integer types, including 128-bit integers
and helper functions for such types ([86]LIBGCCJIT_ABI_20)
+ [87]gcc_jit_context_new_bitcast for reinterpreting the bits of
an rvalue as a different type ([88]LIBGCCJIT_ABI_21)
+ [89]gcc_jit_lvalue_set_register_name for setting a specific
register for a variable ([90]LIBGCCJIT_ABI_22)
+ [91]gcc_jit_context_set_bool_print_errors_to_stderr
([92]LIBGCCJIT_ABI_23)
+ 2 new entrypoints for setting the alignment of a variable
([93]LIBGCCJIT_ABI_24)
* libgccjit has gained support for the use of various atomic builtins
([94]PR96066, [95]PR96067)
* [96]gcc_jit_context_new_cast is now able to handle truncation and
extension between different integer types ([97]PR95498)
New Targets and Target Specific Improvements
AArch64 & arm
* Newer revisions of the Arm Architecture are supported as arguments
to the -march option: armv8.7-a, armv8.8-a, armv9-a.
* The Arm Cortex-A510 CPU is now supported through the cortex-a510
argument to the -mcpu and -mtune options.
* GCC can now auto-vectorize operations performing sign-differing
dot-product operations, taking advantage of instructions in the
Advanced SIMD (AArch64/AArch32) and SVE (AArch64) instruction sets.
AArch64
* A number of new CPUs are supported through the -mcpu and -mtune
options (GCC identifiers in parentheses).
+ Ampere-1 (ampere1).
+ Arm Cortex-A710 (cortex-a710).
+ Arm Cortex-X2 (cortex-x2).
* The 64-byte atomic load/store intrinsics to accelerator memory from
the [98]2020 Arm Architecture extensions are supported through the
+ls64 option extension.
* Initial code generation support is supported for hardware
instructions used to accelerate the memcpy,memmove and memset
standard functions. These instructions can be generated when
compiling with the +mopsoption extension.
* The ACLE Advanced SIMD intrinsics accessible through the arm_neon.h
header have been significantly reimplemented and generate
higher-performing code than previous GCC versions.
* The option -mtune=neoverse-512tvb is added to tune for Arm Neoverse
cores that have a total vector bandwidth of 512 bits. Please refer
to the documentation for more details.
AMD Radeon (GCN)
* Debug experience with ROCGDB has been improved.
* Support for the type __int128_t/integer(kind=16) was added.
* For offloading, the limitation of using only one wavefront per
compute unit (CU) has been lifted. Up to 40 workgroups per CU and
16 wavefronts per workgroup are supported (up to a limit of 40
wavefronts in total, per CU). Additionally, the number of used
wavefronts and workgroups was tuned for performance.
arm
* Support is added for accessing the stack canary value via the TLS
register through the -fstack-protector-guard=tls and
-mstack-protector-guard-offset= options. This intended for use in
Linux kernel development. Please refer to the documentation for
more details.
BPF
* Support for CO-RE (compile-once, run-everywhere) has been added to
the BPF backend. CO-RE allows to compile portable BPF programs that
are able to run among different versions of the Linux kernel.
IA-32/x86-64
* New ISA extension support for Intel AVX512-FP16 was added.
AVX512FP16 intrinsics are available via the -mavx512fp16 compiler
switch.
* For both C and C++ the _Float16 type is supported on x86 systems
with SSE2 enabled. Without {-mavx512fp16}, all operations will be
emulated in software and float instructions.
* Mitigation against straight line speculation (SLS) for function
return and indirect jump is supported via
-mharden-sls=[none|all|return|indirect-jmp].
* Add CS prefix to call and jmp to indirect thunk with branch target
in r8-r15 registers via -mindirect-branch-cs-prefix.
* Always use global offset table (GOT) to access external data and
function symbols when the new -mno-direct-extern-access
command-line option is specified.
LoongArch
* Support for the LoongArch architecture instruction set has been
added.
* The Loongson CPU codename LA464 and LoongArch 64-bit generic CPU
codename loongarch64 are supported through the -march= and -mtune=
options (GCC identifiers in parentheses).
+ Loongson LA464 core (la464).
+ LoongArch 64-bit generic core (loongarch64).
MIPS
* The ABI passing arguments containing zero-width fields (for
example, C/C++ zero-width bit-fields, GNU C/C++ zero-length arrays,
and GNU C empty structs) has changed. Now a zero-width field will
not prevent an aligned 64-bit floating-point field next to it from
being passed through FPR. This is compatible with LLVM, but
incompatible with previous GCC releases. GCC 12 on MIPS will report
such incompatibilities as an inform unless -Wno-psabi is used.
* The ABI returning values containing C++17 empty bases has changed.
Now an empty base will not prevent an aggregate containing only one
or two floating-point fields from being returned through FPR. This
is compatible with GCC 6 and earlier, but incompatible with GCC 7
through 11. GCC 12 on MIPS will report such incompatibilities as an
inform unless -Wno-psabi is used.
NVPTX
* The -march flag has been added. The -misa flag is now considered an
alias of the -march flag.
* Support for PTX ISA target architectures sm_53, sm_70, sm_75 and
sm_80 has been added. These can be specified using the -march flag.
* The default PTX ISA target architecture has been set back to sm_30,
to fix support for sm_30 boards.
* The -march-map flag has been added. The -march-map value will be
mapped to an valid -march flag value. For instance,
-march-map=sm_50 maps to -march=sm_35. This can be used to specify
that generated code is to be executed on a board with at least some
specific compute capability, without having to know the valid
values for the -march flag.
* The -mptx flag has been added to specify the PTX ISA version for
the generated code; permitted values are 3.1 (matches previous GCC
versions), 6.0, 6.3, and 7.0. If not specified, the used version is
the minimal version required for -march but at least 6.0.
* An mptx-3.1 multilib was added. This allows using older drivers
which do not support PTX ISA version 6.0.
* The new __PTX_SM__ predefined macro allows code to check the PTX
ISA target architecture being targeted by the compiler.
* The new __PTX_ISA_VERSION_MAJOR__ and __PTX_ISA_VERSION_MINOR__
predefined macros allows code to check the PTX ISA version being
targeted by the compiler.
PowerPC / PowerPC64 / RS6000
* The internal implementation of Power's target-specific built-in
functions has been rewritten to be easier and less error-prone to
maintain. Every attempt has been made to ensure that the new
behavior matches the old behavior, but inevitably some bugs can be
expected. Please report any problems via [99]GCC Bugzilla.
* The built-in functions __builtin_get_texasr, __builtin_get_texasru,
__builtin_get_tfhar, __builtin_get_tfiar, __builtin_set_texasr,
__builtin_set_texasru, __builtin_set_tfhar, and __builtin_set_tfiar
now behave as documented in all supported configurations. On prior
releases, the arguments and return values of these functions were
treated as unsigned long long instead of as unsigned long, when the
options -m32 -mpowerpc64 were in effect.
* The overloaded built-in functions vec_cntlz_lsbb and vec_cnttz_lsbb
now behave as documented. On prior releases, these built-in
functions had incorrect semantics on little-endian targets.
PRU
* The [100]__regio_symbol variable qualifier has been added. It
allows easier access in C programs to the __R30 and __R31 CPU I/O
registers.
RISC-V
* Default ISA spec version was bump to 20191213, more detail see this
[101]announcement
* New ISA extension support for zba, zbb, zbc, zbs was added.
* New ISA extension support for vector and scalar crypto was added,
only support architecture testing marco and -march= parsing.
* The option -mtune=thead-c906 is added to tune for T-HEAD c906
cores.
* libstdc++ no longer attempts to detect built-in atomics.
Distributions that have out-of-tree workarounds for -latomic should
check their ABIs again.
Operating Systems
Improvements to Static Analyzer
* The analyzer has gained a
[102]-Wanalyzer-use-of-uninitialized-value warning, similar to
[103]-Wuninitialized and [104]-Wmaybe-uninitialized, but based on
an interprocedural path-sensitive analysis ([105]PR95006).
Such warnings are not disabled by the new
[106]-ftrivial-auto-var-init (see below), as the latter is
considered a mitigation option.
* [107]-Wanalyzer-write-to-const and
[108]-Wanalyzer-write-to-string-literal will now check for
[109]__attribute__ ((access, ....)) on calls to externally-defined
functions, and complain about read-only regions pointed to by
arguments marked with a write_only or read_write attribute
([110]PR104793).
* The analyzer's "taint" mode, activated by
[111]-fanalyzer-checker=taint (in addition to [112]-fanalyzer), has
gained four new taint-based warnings:
+ [113]-Wanalyzer-tainted-allocation-size for e.g.
attacker-controlled malloc and alloca,
+ [114]-Wanalyzer-tainted-divisor for detecting where an
attacker can inject a divide-by-zero,
+ [115]-Wanalyzer-tainted-offset for attacker-controlled pointer
offsets,
+ [116]-Wanalyzer-tainted-size for attacker-controlled values
being used as a size parameter to calls to memset or to
functions marked with [117]__attribute__ ((access, ....)).
The existing [118]-Wanalyzer-tainted-array-index has been reworded
to talk about "attacker-controlled" rather than "tainted" values,
for consistency with the new warnings.
A new [119]__attribute__ ((tainted_args)) has been added to the C
and C++ frontends, usable on functions, and on function pointer
callback fields in structs. The analyzer's taint mode will treat
all parameters and buffers pointed to by parameters of such
functions as being attacked-controlled, such as for annotating
system calls in an operating system kernel as being an "attack
surface".
* The analyzer now respects [120]__attribute__((const)): it will
treat such functions as returning the same value when given the
same inputs ([121]PR104434), and as having no side effects
([122]PR104576).
* The analyzer is now able to split its analysis into multiple
execution paths in places where there isn't a split in the control
flow graph. For example, it now handles realloc calls by splitting
the execution path into three possible outcomes for the call:
+ failure, returning NULL
+ success, growing the buffer in-place without moving it
+ success, allocating a new buffer, copying the content of the
old buffer to it, and freeing the old buffer
* The analyzer's interprocedural path exploration logic is now able
to track calls through function pointers.
* The analyzer now makes the assumption that if we know PTR is
non-NULL, then (PTR + OFFSET) is also non-NULL. This isn't strictly
true, but eliminates false positives in practice ([123]PR101962).
* The analyzer has gained some initial support for inline assembler
code. This is extremely limited, and is purely to help suppress
false positives when analyzing the Linux kernel, which makes heavy
use of inline assembler ([124]PR101570).
* The way the analyzer tracks the state of memory along an execution
path has been improved in various ways for GCC 12:
+ An optimization for representing bulk updates to memory (e.g.
zero fills) has been removed as it never worked well. In GCC
12 it has been replaced with a simpler and more accurate
approach, eliminating many false positives ([125]PR95006).
+ Various optimizations have been added, speeding up the
analysis on a particularly problematic source file from 4
minutes down to 17 seconds ([126]PR104943, [127]PR104954, and
[128]PR104955).
+ The analyzer now tracks the sizes of dynamically-allocated
regions, both on the heap (via malloc etc) and stack (via
alloca), though none of the analyzer warnings make use of this
yet in GCC 12.
* The analyzer's handling of switch statements has been rewritten,
fixing various bugs.
Other significant improvements
Eliminating uninitialized variables
* GCC can now [129]initialize all stack variables implicitly,
including padding. This is intended to eliminate all classes of
uninitialized stack variable flaws. Lack of explicit initialization
will still warn when [130]-Wuninitialized is active. For best
debugging, use of the new command-line option
[131]-ftrivial-auto-var-init=pattern can be used to fill variables
with a repeated 0xFE pattern, which tends to illuminate many bugs
(e.g. pointers receive invalid addresses, sizes and indices are
very large). For best production results, the new command-line
option [132]-ftrivial-auto-var-init=zero can be used to fill
variables with 0x00, which tends to provide a safer state for bugs
(e.g. pointers are NULL, strings are NUL filled, and sizes and
indices are 0).
Debugging formats
* GCC can now generate debugging information in [133]CTF, a
lightweight debugging format that provides information about C
types and the association between functions and data symbols and
types. This format is designed to be embedded in ELF files and to
be very compact and simple. A new command-line option -gctf enables
the generation of CTF.
* GCC can now generate debugging information in BTF. This is a
debugging format mainly used in BPF programs and the Linux kernel.
The compiler can generate BTF for any target, when enabled with the
command-line option -gbtf
GCC 12.1
This is the [134]list of problem reports (PRs) from GCC's bug tracking
system that are known to be fixed in the 12.1 release. This list might
not be complete (that is, it is possible that some PRs that have been
fixed are not listed here).
GCC 12.2
This is the [135]list of problem reports (PRs) from GCC's bug tracking
system that are known to be fixed in the 12.2 release. This list might
not be complete (that is, it is possible that some PRs that have been
fixed are not listed here).
Target Specific Changes
LoongArch
* The default setting of -m[check|no-check]-zero-division is changed
for optimized code. Now -mno-check-zero-division is the default for
all optimization levels but -O0 and -Og. The old behavior can be
obtained by explicitly passing -mcheck-zero-division to GCC.
GCC 12.3
Note: GCC 12.3 has not been released yet, so this section is a
work-in-progress.
This is the [136]list of problem reports (PRs) from GCC's bug tracking
system that are known to be fixed in the 12.3 release. This list might
not be complete (that is, it is possible that some PRs that have been
fixed are not listed here).
For questions related to the use of GCC, please consult these web
pages and the [137]GCC manuals. If that fails, the
[138]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 [139]gcc@gcc.gnu.org. All of [140]our lists have public
archives.
Copyright (C) [141]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 [142]maintained by the GCC team. Last modified
2022-08-19[143].
References
1. http://gcc.gnu.org/gcc-12/porting_to.html
2. http://gcc.gnu.org/onlinedocs/index.html#current
3. https://gcc.gnu.org/PR102024
4. https://gcc.gnu.org/PR42217
5. http://gcc.gnu.org/gcc-12/changes.html#mips_zero_width_fields
6. https://clang.llvm.org/docs/ShadowCallStack.html
7. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Instrumentation-Options.html#index-fsanitize_003dshadow-call-stack
8. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/libgomp/OpenMP-Implementation-Status.html
9. https://www.openacc.org/
10. https://gcc.gnu.org/wiki/OpenACC/Implementation%20Status#status-12
11. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/libgomp/Enabling-OpenACC.html
12. http://gcc.gnu.org/gcc-12/changes.html#amdgcn
13. http://gcc.gnu.org/gcc-12/changes.html#nvptx
14. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Optimize-Options.html#index-param
15. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Wopenacc-parallelism
16. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/C-Dialect-Options.html#index-foffload-options
17. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/C-Dialect-Options.html#index-foffload
18. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gnat_rm/Security-Hardening-Features.html#Security-Hardening-Features
19. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Wbidi-chars
20. https://gcc.gnu.org/PR103026
21. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Warray-compare
22. https://gcc.gnu.org/PR97573
23. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Wattributes
24. https://gcc.gnu.org/PR101940
25. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Wformat
26. https://wg21.link/p1938
27. https://gcc.gnu.org/PR100974
28. https://wg21.link/p0849
29. https://gcc.gnu.org/PR103049
30. https://wg21.link/p2242
31. https://gcc.gnu.org/PR102612
32. https://wg21.link/p2334
33. https://gcc.gnu.org/PR102616
34. https://wg21.link/p2360
35. https://gcc.gnu.org/PR102617
36. https://wg21.link/p2128
37. https://wg21.link/cwg2397
38. https://gcc.gnu.org/PR100975
39. https://wg21.link/cwg960
40. https://wg21.link/cwg1227
41. https://wg21.link/cwg1315
42. https://wg21.link/cwg2082
43. https://wg21.link/cwg2351
44. https://wg21.link/cwg2374
45. https://wg21.link/cwg2397
46. https://wg21.link/cwg2446
47. https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=87c2080b
48. https://gcc.gnu.org/PR79501
49. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Wuninitialized
50. https://gcc.gnu.org/PR19808
51. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Wint-in-bool-context
52. https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=3a2b12bc
53. https://gcc.gnu.org/PR99032
54. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Wmissing-requires
55. https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=e18e56c7
56. https://gcc.gnu.org/PR100995
57. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Waddress
58. https://gcc.gnu.org/PR102103
59. https://gcc.gnu.org/PR99701
60. https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=3ead06c1
61. https://gcc.gnu.org/PR102753
62. https://wg21.link/p0466
63. https://gcc.gnu.org/PR101539
64. https://gcc.gnu.org/PR100828
65. https://gcc.gnu.org/PR101786
66. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Winterference-size
67. https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=76b75018
68. https://gcc.gnu.org/PR101344
69. https://gcc.gnu.org/PR101883
70. https://gcc.gnu.org/PR89062
71. https://gcc.gnu.org/PR101233
72. https://gcc.gnu.org/PR88252
73. https://gcc.gnu.org/PR86439
74. https://gcc.gnu.org/PR98832
75. https://gcc.gnu.org/PR102933
76. https://gcc.gnu.org/PR51577
77. https://gcc.gnu.org/PR98486
78. https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=1595fe44
79. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/compatibility.html#libgccjit-abi-16
80. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/expressions.html#c.gcc_jit_lvalue_set_tls_model
81. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/compatibility.html#libgccjit-abi-17
82. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/expressions.html#c.gcc_jit_lvalue_set_link_section
83. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Common-Variable-Attributes.html#index-section-variable-attribute
84. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/compatibility.html#libgccjit-abi-18
85. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/compatibility.html#libgccjit-abi-19
86. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/compatibility.html#libgccjit-abi-20
87. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/expressions.html#c.gcc_jit_context_new_bitcast
88. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/compatibility.html#libgccjit-abi-21
89. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/expressions.html#c.gcc_jit_lvalue_set_register_name
90. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/compatibility.html#libgccjit-abi-22
91. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/contexts.html#c.gcc_jit_context_set_bool_print_errors_to_stderr
92. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/compatibility.html#libgccjit-abi-23
93. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/compatibility.html#libgccjit-abi-24
94. https://gcc.gnu.org/PR96066
95. https://gcc.gnu.org/PR96067
96. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/jit/topics/expressions.html#c.gcc_jit_context_new_cast
97. https://gcc.gnu.org/PR95498
98. https://community.arm.com/arm-community-blogs/b/architectures-and-processors-blog/posts/arm-a-profile-architecture-developments-2020
99. https://gcc.gnu.org/bugzilla/
100. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Named-Address-Spaces.html#PRU-Named-Address-Spaces
101. https://groups.google.com/a/groups.riscv.org/g/sw-dev/c/aE1ZeHHCYf4
102. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-use-of-uninitialized-value
103. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Wuninitialized
104. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Wmaybe-uninitialized
105. https://gcc.gnu.org/PR95006
106. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Optimize-Options.html#index-ftrivial-auto-var-init
107. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-write-to-const
108. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-write-to-string-literal
109. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Common-Function-Attributes.html
110. https://gcc.gnu.org/PR104793
111. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Static-Analyzer-Options.html#index-fanalyzer-checker
112. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Static-Analyzer-Options.html#index-fanalyzer
113. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-tainted-allocation-size
114. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-tainted-divisor
115. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-tainted-offset
116. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-tainted-size
117. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Common-Function-Attributes.html
118. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-tainted-array-index
119. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Common-Function-Attributes.html#index-tainted_005fargs-function-attribute
120. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Common-Function-Attributes.html#index-const-function-attribute
121. https://gcc.gnu.org/PR104434
122. https://gcc.gnu.org/PR104576
123. https://gcc.gnu.org/PR101962
124. https://gcc.gnu.org/PR101570
125. https://gcc.gnu.org/PR95006
126. https://gcc.gnu.org/PR104943
127. https://gcc.gnu.org/PR104954
128. https://gcc.gnu.org/PR104955
129. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Optimize-Options.html#index-ftrivial-auto-var-init
130. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Warning-Options.html#index-Wuninitialized
131. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Optimize-Options.html#index-ftrivial-auto-var-init
132. https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Optimize-Options.html#index-ftrivial-auto-var-init
133. https://ctfstd.org/
134. https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=12.0
135. https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=12.2
136. https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=12.3
137. https://gcc.gnu.org/onlinedocs/
138. mailto:gcc-help@gcc.gnu.org
139. mailto:gcc@gcc.gnu.org
140. https://gcc.gnu.org/lists.html
141. https://www.fsf.org/
142. https://gcc.gnu.org/about.html
143. http://validator.w3.org/check/referer
======================================================================
http://gcc.gnu.org/gcc-11/index.html
GCC 11 Release Series
April 21, 2022
The GCC developers are pleased to announce the release of GCC 11.3.
This release is a bug-fix release, containing fixes for regressions in
GCC 11.2 relative to previous releases of GCC.
Release History
GCC 11.3
April 21, 2022 ([1]changes, [2]documentation)
GCC 11.2
July 28, 2021 ([3]changes, [4]documentation)
GCC 11.1
April 27, 2021 ([5]changes, [6]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 [7]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 [8]amazing group of volunteers is
what makes GCC successful.
For additional information about GCC please refer to the [9]GCC project
web site or contact the [10]GCC development mailing list.
To obtain GCC please use [11]our mirror sites or [12]our version
control system.
For questions related to the use of GCC, please consult these web
pages and the [13]GCC manuals. If that fails, the
[14]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 [15]gcc@gcc.gnu.org. All of [16]our lists have public
archives.
Copyright (C) [17]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 [18]maintained by the GCC team. Last modified
2022-04-21[19].
References
1. http://gcc.gnu.org/gcc-11/changes.html
2. http://gcc.gnu.org/onlinedocs/11.3.0/
3. http://gcc.gnu.org/gcc-11/changes.html
4. http://gcc.gnu.org/onlinedocs/11.2.0/
5. http://gcc.gnu.org/gcc-11/changes.html
6. http://gcc.gnu.org/onlinedocs/11.1.0/
7. http://gcc.gnu.org/gcc-11/buildstat.html
8. http://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Contributors.html
9. http://gcc.gnu.org/index.html
10. mailto:gcc@gcc.gnu.org
11. http://gcc.gnu.org/mirrors.html
12. http://gcc.gnu.org/git.html
13. https://gcc.gnu.org/onlinedocs/
14. mailto:gcc-help@gcc.gnu.org
15. mailto:gcc@gcc.gnu.org
16. https://gcc.gnu.org/lists.html
17. https://www.fsf.org/
18. https://gcc.gnu.org/about.html
19. http://validator.w3.org/check/referer
======================================================================
http://gcc.gnu.org/gcc-11/changes.html
GCC 11 Release Series
Changes, New Features, and Fixes
This page is a "brief" summary of some of the huge number of
improvements in GCC 11. You may also want to check out our [1]Porting
to GCC 11 page and the [2]full GCC documentation.
Caveats
* The default mode for C++ is now -std=gnu++17 instead of
-std=gnu++14. Note that [3]C++17 changes to template template
parameter matching can be disabled independently of other features
with -fno-new-ttp-matching.
* When building GCC itself, the host compiler must now support C++11,
rather than C++98. In particular bootstrapping GCC 11 using an
older version of GCC requires a binary of GCC 4.8 or later, rather
than of GCC 3.4 or later as was the case for bootstrapping GCC 10.
* Naming and location of auxiliary and dump output files changed. If
you compile multiple input files in a single command, if you enable
Link Time Optimization, or if you use -dumpbase, -dumpdir,
-save-temps=*, and you expect any file other than the primary
output file(s) to be created as a side effect, watch out for
improvements and a few surprises. See [4]the patch, particularly
its textual description, for more details about the changes.
* -gsplit-dwarf no longer enables debug info generation on its own
but requires a separate -g for this.
* The libstdc++ configure option --enable-cheaders=c_std is
deprecated and will be removed in a future release. It should be
possible to use --enable-cheaders=c_global (the default) with no
change in behaviour.
* The front end for compiling BRIG format of Heterogeneous System
Architecture Intermediate Language (HSAIL) has been deprecated and
will likely be removed in a future release.
* Some short options of the gcov tool have been renamed: -i to -j and
-j to -H.
General Improvements
* [5]ThreadSanitizer improvements to support alternative runtimes and
environments. The [6]Linux Kernel Concurrency Sanitizer (KCSAN) is
now supported.
+ Add --param tsan-distinguish-volatile to optionally emit
instrumentation distinguishing volatile accesses.
+ Add --param tsan-instrument-func-entry-exit to optionally
control if function entries and exits should be instrumented.
* In previous releases of GCC, the "column numbers" emitted in
diagnostics were actually a count of bytes from the start of the
source line. This could be problematic, both because of:
+ multibyte characters (requiring more than one byte to encode),
and
+ multicolumn characters (requiring more than one column to
display in a monospace font)
For example, the character p ("GREEK SMALL LETTER PI (U+03C0)")
occupies one column, and its UTF-8 encoding requires two bytes; the
character &#x1F642; ("SLIGHTLY SMILING FACE (U+1F642)") occupies
two columns, and its UTF-8 encoding requires four bytes.
In GCC 11 the column numbers default to being column numbers,
respecting multi-column characters. The old behavior can be
restored using a new option [7]-fdiagnostics-column-unit=byte.
There is also a new option [8]-fdiagnostics-column-origin=,
allowing the pre-existing default of the left-hand column being
column 1 to be overridden if desired (e.g. for 0-based columns).
The output of [9]-fdiagnostics-format=json has been extended to
supply both byte counts and column numbers for all source
locations.
Additionally, in previous releases of GCC, tab characters in the
source would be emitted verbatim when quoting source code, but be
prefixed with whitespace or line number information, leading to
misalignments in the resulting output when compared with the actual
source. Tab characters are now printed as an appropriate number of
spaces, using the [10]-ftabstop option (which defaults to 8 spaces
per tab stop).
* Introduce [11]Hardware-assisted AddressSanitizer support. This
sanitizer currently only works for the AArch64 target. It helps
debug address problems similarly to [12]AddressSanitizer but is
based on partial hardware assistance and provides probabilistic
protection to use less RAM at run time. [13]Hardware-assisted
AddressSanitizer is not production-ready for user space, and is
provided mainly for use compiling the Linux Kernel.
To use this sanitizer the command line arguments are:
+ -fsanitize=hwaddress to instrument userspace code.
+ -fsanitize=kernel-hwaddress to instrument kernel code.
* For targets that produce DWARF debugging information GCC now
defaults to [14]DWARF version 5 (with the exception of VxWorks and
Darwin/Mac OS X which default to version 2 and AIX which defaults
to version 4). This can produce up to 25% more compact debug
information compared to earlier versions.
To take full advantage of DWARF version 5 GCC needs to be built
against binutils version 2.35.2 or higher. When GCC is built
against earlier versions of binutils GCC will still emit DWARF
version 5 for most debuginfo data, but will generate version 4
debug line tables (even when explicitly given -gdwarf-5).
The following debug information consumers can process DWARF version
5:
+ GDB 8.0, or higher
+ valgrind 3.17.0
+ elfutils 0.172, or higher (for use with systemtap,
dwarves/pahole, perf and libabigail)
+ dwz 0.14
Programs embedding libbacktrace are urged to upgrade to the version
shipping with GCC 11.
To make GCC 11 generate an older DWARF version use -g together with
-gdwarf-2, -gdwarf-3 or -gdwarf-4.
* Vectorizer improvements:
+ The straight-line code vectorizer now considers the whole
function when vectorizing and can handle opportunities
crossing CFG merges and backedges.
* A series of conditional expressions that compare the same variable
can be transformed into a switch statement if each of them contains
a comparison expression. Example:
int IsHTMLWhitespace(int aChar) {
return aChar == 0x0009 || aChar == 0x000A ||
aChar == 0x000C || aChar == 0x000D ||
aChar == 0x0020;
}
This statement can be transformed into a switch statement and then
expanded into a bit-test.
* New command-line options:
+ [15]-fbit-tests, enabled by default, can be used to enable or
disable switch expansion using bit-tests.
* Inter-procedural optimization improvements:
+ A new IPA-modref pass was added to track side effects of
function calls and improve precision of points-to-analysis.
The pass can be controlled by the [16]-fipa-modref option.
+ The identical code folding pass (controlled by [17]-fipa-icf)
was significantly improved to increase the number of unified
functions and to reduce compile-time memory use.
+ IPA-CP (Interprocedural constant propagation) heuristics
improved its estimation of potential usefulness of known loop
bounds and strides by taking the estimated frequency of these
loops into account.
* Link-time optimization improvements:
+ The LTO bytecode format was optimized for smaller object files
and faster streaming.
+ Memory allocation of the linking stage was improved to reduce
peak memory use.
* Profile driven optimization improvements:
+ Using [18]-fprofile-values, was improved by tracking more
target values for e.g. indirect calls.
+ GCOV data file format outputs smaller files by representing
zero counters in a more compact way.
New Languages and Language specific improvements
* GCC 11 adds support for non-rectangular loop nests in OpenMP
constructs and the allocator routines of [19]OpenMP 5.0, including
initial allocate clause support in C/C++. The OMP_TARGET_OFFLOAD
environment variable and the active-levels routines are now
supported. For C/C++, the declare variant and map support has been
extended. For Fortran, OpenMP 4.5 is now fully supported and OpenMP
5.0 support has been extended, including the following features
which were before only available in C and C++: order(concurrent),
device_type, memorder-clauses for flush, lastprivate with
conditional modifier, atomic construct and reduction clause
extensions of OpenMP 5.0, if clause with simd and cancel modifiers,
target data without map clause, and limited support for the
requires construct.
* Version 2.6 of the [20]OpenACC specification continues to be
maintained and improved in the C, C++ and Fortran compilers. See
the [21]implementation status section on the OpenACC wiki page and
the [22]run-time library documentation for further information.
C family
* New attributes:
+ The [23]no_stack_protector attribute has been added to mark
functions which should not be instrumented with stack
protection (-fstack-protector).
+ The existing [24]malloc attribute has been extended so that it
can be used to identify allocator/deallocator API pairs. A
pair of new [25]-Wmismatched-dealloc and
[26]-Wmismatched-new-delete warnings will complain about
mismatched calls, and [27]-Wfree-nonheap-object about
deallocation calls with pointers not obtained from allocation
functions. Additionally, the static analyzer will use these
attributes when checking for leaks, double-frees,
use-after-frees, and similar issues.
* New warnings:
+ [28]-Wmismatched-dealloc, enabled by default, warns about
calls to deallocation functions with pointers returned from
mismatched allocation functions.
+ [29]-Wsizeof-array-div, enabled by -Wall, warns about
divisions of two sizeof operators when the first one is
applied to an array and the divisor does not equal the size of
the array element.
+ [30]-Wstringop-overread, enabled by default, warns about calls
to string functions reading past the end of the arrays passed
to them as arguments. In prior GCC releases most instances of
his warning are diagnosed by -Wstringop-overflow.
+ [31]-Wtsan, enabled by default, warns about unsupported
features in ThreadSanitizer (currently
std::atomic_thread_fence).
* Enhancements to existing warnings:
+ [32]-Wfree-nonheap-object detects many more instances of calls
to deallocation functions with pointers not returned from a
dynamic memory allocation function.
+ [33]-Wmaybe-uninitialized diagnoses passing pointers or
references to uninitialized memory to functions taking
const-qualified arguments.
+ [34]-Wuninitialized detects reads from uninitialized
dynamically allocated memory.
* For ELF targets that support the GNU or FreeBSD OSABIs, the used
attribute will now save the symbol declaration it is applied to
from linker garbage collection.
To support this behavior, used symbols that have not been placed in
specific sections (e.g. with the section attribute, or the
-f{function,data}-sections options) will be placed in new, unique
sections.
This functionality requires Binutils version 2.36 or later.
C
* Several new features from the upcoming C2X revision of the ISO C
standard are supported with -std=c2x and -std=gnu2x. 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
-std=c2x -Wpedantic.
+ The BOOL_MAX and BOOL_WIDTH macros are provided in <limits.h>.
+ As in C++, function definitions no longer need to give names
for unused function parameters.
+ The expansions of the true and false macros in <stdbool.h>
have changed so that they have type bool.
+ The [[nodiscard]] standard attribute is now supported.
+ The __has_c_attribute preprocessor operator is now supported.
+ Macros INFINITY, NAN, FLT_SNAN, DBL_SNAN, LDBL_SNAN,
DEC_INFINITY, DEC_NAN, and corresponding signaling NaN macros
for _FloatN, _FloatNx and _DecimalN types, are provided in
<float.h>. There are also corresponding built-in functions
__builtin_nansdN for decimal signaling NaNs.
+ Macros FLT_IS_IEC_60559, DBL_IS_IEC_60559 and
LDBL_IS_IEC_60559 are provided in <float.h>.
+ The feature test macro __STDC_WANT_IEC_60559_EXT__ is
supported by <float.h>.
+ Labels may appear before declarations and at the end of a
compound statement.
* New warnings:
+ [35]-Warray-parameter, enabled by -Wall, warns about
redeclarations of functions with ordinary array arguments
declared using inconsistent forms. The warning also enables
the detection of the likely out of bounds accesses in calls to
such functions with smaller arrays.
+ [36]-Wvla-parameter, enabled by -Wall, warns redeclarations of
functions with variable length array arguments declared using
inconsistent forms or with mismatched bounds. The warning also
enables the detection of the likely out of bounds accesses in
calls to such functions with smaller arrays.
C++
* The default mode has been changed to -std=gnu++17.
* Several C++20 features have been implemented:
+ the compiler now supports consteval virtual functions
+ P2082R1, Fixing CTAD for aggregates
+ P0593R6, Pseudo-destructors end object lifetimes
+ P1907R1, Inconsistencies with non-type template parameters
(complete implementation)
+ P1975R0, Fixing the wording of parenthesized
aggregate-initialization
+ P1009R2, Array size deduction in new-expressions
+ P1099R5, using enum
+ Modules, Requires -fmodules-ts and some aspects are
incomplete. Refer to [37]C++ 20 Status
* The C++ front end has experimental support for some of the upcoming
C++23 draft features with the -std=c++23, -std=gnu++23, -std=c++2b
or -std=gnu++2b flags, including
+ P0330R8, Literal Suffix for (signed) size_t.
For a full list of new features, see [38]the C++ status page.
* Several C++ Defect Reports have been resolved, e.g.:
+ DR 625, Use of auto as a template-argument
+ DR 1512, Pointer comparison vs qualification conversions
+ DR 1722, Should lambda to function pointer conversion function
be noexcept?
+ DR 1914, Duplicate standard attributes
+ DR 2032, Default template-arguments of variable templates
+ DR 2289, Uniqueness of decomposition declaration names
+ DR 2237, Can a template-id name a constructor?
+ DR 2303, Partial ordering and recursive variadic inheritance
+ DR 2369, Ordering between constraints and substitution
+ DR 2450, braced-init-list as a template-argument
* G++ now performs better access checking in templates ([39]PR41437).
* reinterpret_casts in constexpr evaluation are now checked more
completely ([40]PR95307).
* The diagnostic for static_assert has been improved: the compiler
now shows the expression including its template arguments (if there
were any), and can point to the failing clause if the condition
comprised of any logical AND operators ([41]PR97518).
* New warnings:
+ [42]-Wctad-maybe-unsupported, disabled by default, warns about
performing class template argument deduction on a type with no
deduction guides.
+ [43]-Wrange-loop-construct, enabled by -Wall, warns when a
range-based for-loop is creating unnecessary and expensive
copies.
+ [44]-Wdeprecated-enum-enum-conversion, enabled by default in
C++20, warns about deprecated arithmetic conversions on
operands of enumeration types, as outlined in
[depr.arith.conv.enum].
+ [45]-Wdeprecated-enum-float-conversion, enabled by default in
C++20, warns about deprecated arithmetic conversions on
operands where one is of enumeration type and the other is of
a floating-point type, as outlined in [depr.arith.conv.enum].
+ [46]-Wmismatched-new-delete, enabled by -Wall, warns about
calls to C++ operator delete with pointers returned from
mismatched forms of operator new or from other mismatched
allocation functions.
+ [47]-Wvexing-parse, enabled by default, warns about the most
vexing parse rule: the cases when a declaration looks like a
variable definition, but the C++ language requires it to be
interpreted as a function declaration.
* Enhancements to existing warnings:
+ [48]-Wnonnull considers the implicit this argument of every
C++ nonstatic member function to have been implicitly declared
with attribute nonnull and triggers warnings for calls where
the pointer is null.
Runtime Library (libstdc++)
* Improved C++17 support, including:
+ std::from_chars and std::to_chars for floating-point types.
* Improved experimental C++20 support, including:
+ Calendar additions to <chrono>. Thanks to Cassio Neri for
optimizations.
+ std::bit_cast
+ std::source_location
+ Atomic wait and notify operations.
+ <barrier>, <latch>, and <semaphore>
+ <syncstream>
+ Efficient access to basic_stringbuf's buffer.
+ Heterogeneous lookup in unordered containers.
* Experimental C++23 support, including:
+ contains member functions for strings, thanks to Paul Fee.
+ std::to_underlying, std::is_scoped_enum
* Experimental support for Data-Parallel Types (simd) from the
Parallelism 2 TS, thanks to Matthias Kretz.
* Faster std::uniform_int_distribution, thanks to Daniel Lemire.
D
* New features:
+ A new bottom type typeof(*null) has been added to represent
run-time errors and non-terminating functions. This also
introduces a new standard alias for the type named noreturn,
and is implicitly imported into every module.
+ Printf-like and scanf-like functions are now detected by
prefixing them with pragma(printf) for printf-like functions
or pragma(scanf) for scanf-like functions.
+ The __traits() expression now supports the extensions
isDeprecated, isDisabled, isFuture, isModule, isPackage,
child, isReturnOnStack, isZeroInit, getTargetInfo,
getLocation, hasPostblit, isCopyable, getVisibility, and
totype.
+ An expression-based contract syntax has been added to the
language.
+ Function literals can now return a value by reference with the
ref keyword.
+ A new syntax is available to declare aliases to function types
using the alias syntax based on the assignment operator.
+ New types __c_complex_float, __c_complex_double,
__c_complex_real, and __c_wchar_t have been added for
interfacing with C and C++ code, and are available from the
core.stdc.config module.
+ User-defined attributes can now be used to annotate enum
members, alias declarations, and function parameters.
+ Templates alias parameters can now be instantiated with basic
types such as int or void function().
+ The mixin construct can now be used as types in the form
mixin(string) var.
+ The mixin construct can now take an argument list, same as
pragma(msg).
* New intrinsics:
+ Bitwise rotate intrinsics core.bitop.rol and core.bitop.ror
have been added.
+ Byte swap intrinsic core.bitop.byteswap for swapping bytes in
a 2-byte ushort has been added.
+ Math intrinsics available from core.math now have overloads
for float and double types.
+ Volatile intrinsics core.volatile.volatileLoad and
core.volatile.volatileStore have been moved from the
core.bitop module.
* New attributes:
+ The following GCC attributes are now recognized and available
from the gcc.attributes module with short-hand aliases for
convenience:
o @attribute("alloc_size", arguments) or
@alloc_size(arguments).
o @attribute("always_inline") or @always_inline.
o @attribute("used") or @used.
o @attribute("optimize", arguments) or
@optimize(arguments).
o @attribute("cold") or @cold.
o @attribute("noplt") or @noplt.
o @attribute("target_clones", arguments) or
@target_clones(arguments).
o @attribute("no_icf") or @no_icf.
o @attribute("noipa") or @noipa.
o @attribute("symver", arguments) or @symver(arguments).
+ New aliases have been added to gcc.attributes for
compatibility with ldc.attributes.
o The @allocSize(arguments) attribute is the same as
@alloc_size(arguments), but uses a 0-based index for
function arguments.
o The @assumeUsed attribute is an alias for
@attribute("used").
o The @fastmath attribute is an alias for
@optimize("Ofast").
o The @naked attribute is an alias for @attribute("naked").
This attribute may not be available on all targets.
o The @restrict attribute has been added to specify that a
function parameter is to be restrict-qualified in the C99
sense of the term.
o The @optStrategy(strategy) attribute is an alias for
@optimize("O0") when the strategy is "none", otherwise
@optimize("Os") for the "optsize" and "minsize"
strategies.
o The @polly attribute is an alias for
@optimize("loop-parallelize-all").
o The @section(name) attribute is an alias for
@attribute("section", name).
o The @target(arguments) attribute is an alias for
attribute("target", arguments).
o The @weak attribute is an alias for @attribute("weak").
* New language options:
+ -fweak-templates, added to control whether declarations that
can be defined in multiple objects should be emitted as weak
symbols. The default is to emit all symbols with extern
linkage as weak, unless the target lacks support for weak
symbols.
+ -Wdeprecated, this option is now enabled by default.
+ -Wextra, this option now turns on all warnings that are not
part of the core D language front-end - -Waddress,
-Wcast-result, -Wunknown-pragmas.
+ -Wvarargs, added to turn on warnings about questionable usage
of the va_start intrinsic.
* Deprecated and removed features:
+ Compiler-recognized attributes are now made available from the
gcc.attributes module, the former module gcc.attribute has
been deprecated and will be removed in a future release.
+ The @attribute("alias") attribute has been removed, as it had
been superseded by pragma(mangle).
+ The @attribute("forceinline") attribute has been removed and
renamed to @always_inline.
+ __vector types that are not supported in hardware are now
rejected at compile-time. Previously all vector types were
accepted by the compiler and emulated when target support was
absent.
+ The extern(Pascal) linkage attribute has been removed.
+ The deprecation phase for -ftransition=import and
-ftransition=checkimports is finished. These switches no
longer have an effect and are now removed. Symbols that are
not visible in a particular scope will no longer be found by
the compiler.
+ It is now an error to use private variables selectively
imported from other modules. Due to a bug, some imported
private members were visible from other modules, violating the
specification.
+ The -fweak compiler switch has been removed, as it existed
only for testing.
Fortran
* Added DEPRECATED to !GCC$'s attributes directive.
Go
* GCC 11 provides a complete implementation of the Go 1.16.3 user
packages.
libgccjit
* libgccjit was marked as merely "Alpha" quality when [49]originally
added in GCC 5. Given that we have maintained [50]API and ABI
compatibility since then and it is in use by various projects, we
have removed that caveat.
* libgccjit can now be built for MinGW
* The libgccjit API gained 10 new entry points:
+ [51]gcc_jit_global_set_initializer
+ 9 entrypoints for [52]directly embedding asm statements into a
compile, analogous to inline asm in the C front end
New Targets and Target Specific Improvements
AArch64 & arm
* A number of new CPUs are supported through arguments to the -mcpu
and -mtune options in both the arm and aarch64 backends (GCC
identifiers in parentheses):
+ Arm Cortex-A78 (cortex-a78).
+ Arm Cortex-A78AE (cortex-a78ae).
+ Arm Cortex-A78C (cortex-a78c).
+ Arm Cortex-X1 (cortex-x1).
+ Arm Neoverse V1 (neoverse-v1).
+ Arm Neoverse N2 (neoverse-n2).
* GCC can now auto-vectorize operations performing addition,
subtraction, multiplication and the accumulate/subtract variants on
complex numbers, taking advantage of the Advanced SIMD instructions
in the Armv8.3-a (AArch64/AArch32), SVE (AArch64), SVE2 (AArch64)
and MVE (AArch32 M-profile) instruction sets.
AArch64
* In addition to the above, the following AArch64-only CPUs are now
supported:
+ Fujitsu A64FX (a64fx).
+ Arm Cortex-R82 (cortex-r82).
* The AArch64 Armv8-R architecture is now supported through the
-march=armv8-r option.
* Mitigation against the [53]Straight-line Speculation vulnerability
is supported with the -mharden-sls= option. Please refer to the
documentation for usage instructions.
* The availability of Advanced SIMD intrinsics available through the
arm_neon.h header is improved and GCC 11 supports the full set of
intrinsics defined by ACLE Q3 2020.
AMD Radeon (GCN)
* Initial support for gfx908 GPUs has been added.
arm
* Initial auto-vectorization is now available when targeting the MVE
instruction set.
* GCC can now make use of the Low Overhead Branch instruction in
Armv8.1-M to optimize loop counters and checks.
* The -mcpu=cortex-m55 option now supports the extensions +nomve and
+nomve.fp to control generation of MVE and MVE floating-point
instructions.
IA-32/x86-64
* New ISA extension support for Intel TSXLDTRK was added to GCC.
TSXLDTRK intrinsics are available via the -mtsxldtrk compiler
switch.
* New ISA extension support for Intel SERIALIZE was added to GCC.
SERIALIZE intrinsics are available via the -mserialize compiler
switch.
* New ISA extension support for Intel HRESET was added to GCC. HRESET
intrinsics are available via the -mhreset compiler switch.
* New ISA extension support for Intel UINTR was added to GCC. UINTR
intrinsics are available via the -muintr compiler switch.
* New ISA extension support for Intel KEYLOCKER was added to GCC.
KEYLOCKER intrinsics are available via the -mkeylocker compiler
switch.
* New ISA extension support for Intel AMX-TILE, AMX-INT8, AMX-BF16
was added to GCC. AMX-TILE, AMX-INT8, AMX-BF16 intrinsics are
available via the -mamx-tile, -mamx-int8, -mamx-bf16 compiler
switches.
* New ISA extension support for Intel AVX-VNNI was added to GCC.
AVX-VNNI intrinsics are available via the -mavxvnni compiler
switch.
* GCC now supports the Intel CPU named Sapphire Rapids through
-march=sapphirerapids. The switch enables the MOVDIRI, MOVDIR64B,
AVX512VP2INTERSECT, ENQCMD, CLDEMOTE, SERIALIZE, PTWRITE, WAITPKG,
TSXLDTRK, AMT-TILE, AMX-INT8, AMX-BF16, and AVX-VNNI ISA
extensions.
* GCC now supports the Intel CPU named Alderlake through
-march=alderlake. The switch enables the CLDEMOTE, PTWRITE,
WAITPKG, SERIALIZE, KEYLOCKER, AVX-VNNI, and HRESET ISA extensions.
* GCC now supports the Intel CPU named Rocketlake through
-march=rocketlake. Rocket Lake is based on Icelake client and minus
SGX.
* GCC now supports AMD CPUs based on the znver3 core via
-march=znver3.
* GCC now supports micro-architecture levels defined in the x86-64
psABI via -march=x86-64-v2, -march=x86-64-v3 and -march=x86-64-v4.
Nios II
* The options -mcustom-insn=N no longer produce compiler warnings if
the custom instruction is not generated due to missing optimization
options such as -fno-math-errno, -ffinite-math-only, or
-funsafe-math-optimizations. These warnings were not consistently
emitted for all custom instructions.
* The -mcustom-fpu-cfg=fph2 option has been added to enable the
custom instructions supported by the Nios II Floating Point
Hardware 2 Component.
NVPTX
* The -misa default has changed from sm_30 to sm_35.
* The -m32 compiler switch has been removed.
* The -msoft-stack-reserve-local format has been fixed. Previously,
it accepted -msoft-stack-reserve-local<n>. It now accepts
-msoft-stack-reserve-local=<n>.
S/390, System z, IBM Z Systems
* The behavior when compiling with -fexcess-precision=standard (e.g.,
implied by -std=c99) on s390(x) targets can now be controlled at
configure time with the flag --enable-s390-excess-float-precision.
When enabled, GCC will maintain previous behavior and evaluate
float expressions in double precision, which aligns with the
definition of float_t as double. With the flag disabled, GCC will
always evaluate float expressions in single precision. In native
builds and cross compiles that have target libc headers, GCC will
by default match the definition of float_t in the installed glibc.
RISC-V
* Support address sanitizer for RISC-V.
* Support big-endian for RISC-V, thanks to Marcus Comstedt.
* Implement new style of architecture extension test macros: each
architecture extension has a corresponding feature test macro,
which can be used to test its existence and version information.
* Legacy architecture extension test macros like __riscv_atomic are
deprecated, but will still be supported for at least 2 release
cycles.
* Support IFUNC for riscv*-*-linux*.
* Add new option -misa-spec=* to control ISA spec version. This
controls the default version of each extensions. It defaults to
2.2.
* Introduce the --with-multilib-generator configure time option. This
allows for flexible config multi-lib settings. Its syntax is the
same as RISC-V's multilib-generator.
* Extend the sytax for multilib-generator, support expansion operator
* to reduce the complexity of complicated multi-lib re-use rules.
* Support -mcpu=* option aligned with RISC-V clang/LLVM. It sets the
pipeline model and architecture extensions, like -mtune=* plus
-march=*.
* Support for TLS stack protector canary access, thanks to Cooper Qu.
* Support __builtin_thread_pointer for RISC-V.
* Introduce shorten_memrefs optimization, which reduces the code size
for memory access, thanks to Craig Blackmore.
Operating Systems
AIX
* GCC for AIX can be built as a 64 bit application and the runtime is
built as FAT libraries containing both 32 bit and 64 bit objects.
* Support AIX Vector Extended ABI with -mabi=vec-extabi.
* Thread-Local uninitiated data placed in local common section.
* Use thread-safe access in ctype.
* Link with libc128.a when long-double-128 enabled.
Improvements to Static Analyzer
* The implementation of how program state is tracked within
[54]-fanalyzer has been completely rewritten for GCC 11, fixing
numerous bugs, and allowing for the analyzer to scale to larger C
source files.
* The analysis of allocations and deallocations has been generalized
beyond malloc and free.
+ As preliminary work towards eventually supporting C++, the
malloc/free checking will also check new/delete and
new[]/delete[]. However, C++ is not yet properly supported by
[55]-fanalyzer (for example, exception-handling is
unimplemented).
+ As noted above, the existing [56]malloc attribute has been
extended so that it can be used to identify
allocator/deallocator API pairs. The analyzer will use these
attributes when checking for leaks, double-frees,
use-after-frees, and similar issues.
+ A new [57]-Wanalyzer-mismatching-deallocation warning has been
added, covering such mismatches as using scalar delete rather
vector delete[].
* The analyzer has gained warnings
[58]-Wanalyzer-shift-count-negative,
[59]-Wanalyzer-shift-count-overflow, [60]-Wanalyzer-write-to-const,
and [61]-Wanalyzer-write-to-string-literal, all enabled by default
when [62]-fanalyzer is enabled.
* The analyzer can now be extended by GCC plugins, allowing for
domain-specific path-sensitive warnings. An example of using a
[63]GCC plugin to check for misuses of CPython's global interpreter
lock can be seen in the test suite
* The analyzer has gained new debugging options
[64]-fdump-analyzer-json and [65]-fno-analyzer-feasibility.
Other significant improvements
* GCC has gained a new environment variable
[66]GCC_EXTRA_DIAGNOSTIC_OUTPUT which can be used by IDEs to
request machine-readable fix-it hints without needing to adjust
build flags.
GCC 11.1
This is the [67]list of problem reports (PRs) from GCC's bug tracking
system that are known to be fixed in the 11.1 release. This list might
not be complete (that is, it is possible that some PRs that have been
fixed are not listed here).
GCC 11.2
This is the [68]list of problem reports (PRs) from GCC's bug tracking
system that are known to be fixed in the 11.2 release. This list might
not be complete (that is, it is possible that some PRs that have been
fixed are not listed here).
GCC 11.3
This is the [69]list of problem reports (PRs) from GCC's bug tracking
system that are known to be fixed in the 11.3 release. This list might
not be complete (that is, it is possible that some PRs that have been
fixed are not listed here).
Target Specific Changes
x86-64
* The x86-64 ABI of passing and returning structure with a 64-bit
single precision vector changed in GCC 11.1 when 3DNOW is disabled.
Disabling 3DNOW no longer changes how they are passed nor returned.
This ABI change is now diagnosed with -Wpsabi.
* Mitigation against straight line speculation (SLS) for function
return and indirect jump is supported via
-mharden-sls=[none|all|return|indirect-jmp].
* Add CS prefix to call and jmp to indirect thunk with branch target
in r8-r15 registers via -mindirect-branch-cs-prefix.
For questions related to the use of GCC, please consult these web
pages and the [70]GCC manuals. If that fails, the
[71]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 [72]gcc@gcc.gnu.org. All of [73]our lists have public
archives.
Copyright (C) [74]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 [75]maintained by the GCC team. Last modified
2022-04-21[76].
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2. http://gcc.gnu.org/onlinedocs/index.html#current
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9. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Diagnostic-Message-Formatting-Options.html#index-fdiagnostics-format
10. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Preprocessor-Options.html#index-ftabstop
11. https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
12. https://github.com/google/sanitizers/wiki/AddressSanitizer
13. https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
14. https://dwarfstd.org/doc/DWARF5.pdf
15. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Code-Gen-Options.html#index-fno-bit-tests
16. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Optimize-Options.html#index-fipa-modref
17. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Optimize-Options.html#index-fipa-ocf
18. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Optimize-Options.html#index-fprofile-values
19. https://www.openmp.org/specifications/
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22. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/libgomp/Enabling-OpenACC.html
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24. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Common-Function-Attributes.html#index-malloc-function-attribute
25. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Wmismatched-dealloc
26. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/C_002b_002b-Dialect-Options.html#index-Wmismatched-new-delete
27. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Wfree-nonheap-object
28. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Wmismatched-dealloc
29. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Wsizeof-array-div
30. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Wstringop-overread
31. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Wtsan
32. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Wfree-nonheap-object
33. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Wmaybe-uninitialized
34. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Wuninitialized
35. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Warray-parameter
36. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Wvla-parameter
37. http://gcc.gnu.org/projects/cxx-status.html#cxx20
38. http://gcc.gnu.org/projects/cxx-status.html#cxx23
39. https://gcc.gnu.org/PR41437
40. https://gcc.gnu.org/PR95307
41. https://gcc.gnu.org/PR97518
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44. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/C_002b_002b-Dialect-Options.html#index-Wdeprecated-enum-enum-conversion
45. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/C_002b_002b-Dialect-Options.html#index-Wdeprecated-enum-float-conversion
46. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/C_002b_002b-Dialect-Options.html#index-Wmismatched-new-delete
47. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/C_002b_002b-Dialect-Options.html#index-Wvexing-parse
48. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html#index-Wnonnull
49. http://gcc.gnu.org/gcc-5/changes.html#jit
50. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/jit/topics/compatibility.html
51. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/jit/topics/expressions.html#c.gcc_jit_global_set_initializer
52. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/jit/topics/asm.html
53. https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/downloads/straight-line-speculation
54. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Static-Analyzer-Options.html
55. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Static-Analyzer-Options.html
56. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Common-Function-Attributes.html#index-malloc-function-attribute
57. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-mismatching-deallocation
58. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-shift-count-negative
59. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-shift-count-overflow
60. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Static-Analyzer-Options.html#index-Wanalyzer-write-to-const
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64. https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Static-Analyzer-Options.html#index-fdump-analyzer-json
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67. https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=11.0
68. https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=11.2
69. https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=11.3
70. https://gcc.gnu.org/onlinedocs/
71. mailto:gcc-help@gcc.gnu.org
72. mailto:gcc@gcc.gnu.org
73. https://gcc.gnu.org/lists.html
74. https://www.fsf.org/
75. https://gcc.gnu.org/about.html
76. http://validator.w3.org/check/referer
======================================================================
http://gcc.gnu.org/gcc-10/index.html
GCC 10 Release Series
June 28, 2022
The [1]GNU project and the GCC developers are pleased to announce the
release of GCC 10.4.
This release is a bug-fix release, containing fixes for regressions in
GCC 10.3 relative to previous releases of GCC.
Release History
GCC 10.4
June 28, 2022 ([2]changes, [3]documentation)
GCC 10.3
April 8, 2021 ([4]changes, [5]documentation)
GCC 10.2
July 23, 2020 ([6]changes, [7]documentation)
GCC 10.1
May 7, 2020 ([8]changes, [9]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 [10]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 [11]amazing group of volunteers is
what makes GCC successful.
For additional information about GCC please refer to the [12]GCC
project web site or contact the [13]GCC development mailing list.
To obtain GCC please use [14]our mirror sites or [15]our version
control system.
For questions related to the use of GCC, please consult these web
pages and the [16]GCC manuals. If that fails, the
[17]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 [18]gcc@gcc.gnu.org. All of [19]our lists have public
archives.
Copyright (C) [20]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 [21]maintained by the GCC team. Last modified
2022-06-28[22].
References
1. http://www.gnu.org/
2. http://gcc.gnu.org/gcc-10/changes.html
3. http://gcc.gnu.org/onlinedocs/10.4.0/
4. http://gcc.gnu.org/gcc-10/changes.html
5. http://gcc.gnu.org/onlinedocs/10.3.0/
6. http://gcc.gnu.org/gcc-10/changes.html
7. http://gcc.gnu.org/onlinedocs/10.2.0/
8. http://gcc.gnu.org/gcc-10/changes.html
9. http://gcc.gnu.org/onlinedocs/10.1.0/
10. http://gcc.gnu.org/gcc-10/buildstat.html
11. http://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Contributors.html
12. http://gcc.gnu.org/index.html
13. mailto:gcc@gcc.gnu.org
14. http://gcc.gnu.org/mirrors.html
15. http://gcc.gnu.org/git.html
16. https://gcc.gnu.org/onlinedocs/
17. mailto:gcc-help@gcc.gnu.org
18. mailto:gcc@gcc.gnu.org
19. https://gcc.gnu.org/lists.html
20. https://www.fsf.org/
21. https://gcc.gnu.org/about.html
22. http://validator.w3.org/check/referer
======================================================================
http://gcc.gnu.org/gcc-10/changes.html
GCC 10 Release Series
Changes, New Features, and Fixes
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 [1]Porting
to GCC 10 page and the [2]full GCC documentation.
Caveats
* 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 [3]C++ notes
below for more details.
* The deprecated Profile Mode and array_allocator extensions have
been removed from libstdc++.
* The non-standard std::__is_nullptr_t type trait is deprecated and
will be removed from libstdc++ in a future release. The standard
trait std::is_null_pointer should be instead.
* The minimum version of the [4]MPFR library required for building
GCC has been increased to version 3.1.0 (released 2011-10-03).
* The automatic template instantiation at link time (-frepo) has been
removed.
* The --param allow-store-data-races internal parameter has been
removed in favor of a new official option -fallow-store-data-races.
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 --param
allow-store-data-races will now be diagnosed and build systems have
to be adjusted accordingly.
* Offloading to Heterogeneous System Architecture Intermediate
Language (HSAIL) has been deprecated and will likely be removed in
a future release.
* The type of the std::iterator base class of
std::istreambuf_iterator was changed in C++98 mode to be consistent
with C++11 and later standards. See the [5]libstdc++ notes below
for more details.
General Improvements
* New built-in functions:
+ The [6]__has_builtin built-in preprocessor operator can be
used to query support for built-in functions provided by GCC
and other compilers that support it.
+ __builtin_roundeven for the corresponding function from
ISO/IEC TS 18661.
* New command-line options:
+ [7]-fallocation-dce removes unneeded pairs of new and delete
operators.
+ [8]-fprofile-partial-training can now be used to inform the
compiler that code paths not covered by the training run
should not be optimized for size.
+ [9]-fprofile-reproducible controls level of reproducibility of
profile gathered by [10]-fprofile-generate. This makes it
possible to rebuild program with same outcome which is useful,
for example, for distribution packages.
+ [11]-fprofile-prefix-path can be used in combination with
-fprofile-generate=profile_dir and -fprofile-use=profile_dir
to inform GCC where the base directory of build source tree is
in case it differs between instrumentation and optimized
builds.
+ [12]-fanalyzer 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 experimental in this release. In
particular, analysis of non-C code is unlikely to work.
* Inter-procedural optimization improvements:
+ 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.
+ [13]-finline-functions is now enabled at -O2 and was retuned
for better code size versus runtime performance trade-offs.
Inliner heuristics was also significantly sped up to avoid
negative impact to -flto -O2 compile times.
+ Inliner heuristics and function cloning can now use
value-range information to predict effectivity of individual
transformations.
+ During link-time optimization the C++ One Definition Rule is
used to increase precision of type based alias analysis.
* Link-time optimization improvements:
+ A new binary [14]lto-dump has been added. It dumps various
information about LTO bytecode object files.
+ The parallel phase of the LTO can automatically detect a
running make's jobserver or fall back to number of available
cores.
+ The LTO bytecode can be compressed with the [15]zstd
algorithm. The configure script automatically detects zstd
support.
+ Most --param 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.
* Profile driven optimization improvements:
+ Profile maintenance during compilation and hot/cold code
partitioning have been improved.
+ Using [16]-fprofile-values, an instrumented binary can track
multiple values (up to 4) for e.g. indirect calls and provide
more precise profile information.
New Languages and Language-Specific Improvements
* Version 2.6 of the [17]OpenACC specification is now supported in
the C, C++ and Fortran compilers. See the [18]implementation status
section on the OpenACC wiki page and the [19]run-time library
documentation for further information.
* GCC 10 adds a number of newly implemented [20]OpenMP 5.0 features
on top of the GCC 9 release such as conditional lastprivate clause,
scan and loop directives, order(concurrent) and use_device_addr
clauses support, if clause on simd construct or partial support for
the declare variant directive, getting closer to full support of
the OpenMP 5.0 standard.
* OpenMP and OpenACC now support [21]offloading to AMD Radeon (GCN)
GPUs; supported are the third-generation Fiji (fiji) and the
fifth-generation VEGA 10/VEGA 20 (gfx900 or gfx906).
C family
* New attributes:
+ The access 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
-Wstringop-overflow.
+ The symver attribute can be used to bind symbols to specific
version nodes on ELF platforms. This is preferred to using
inline assembly with GNU as symver directive because the
latter is not compatible with link-time optimizations.
* New warnings:
+ [22]-Wstring-compare, enabled by -Wextra, warns about equality
and inequality expressions between zero and the result of a
call to either strcmp and strncmp 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.
+ [23]-Wzero-length-bounds, enabled by -Warray-bounds, warns
about accesses to elements of zero-length arrays that might
overlap other members of the same object.
* Enhancements to existing warnings:
+ [24]-Warray-bounds detects more out-of-bounds accesses to
member arrays as well as accesses to elements of zero-length
arrays.
+ [25]-Wformat-overflow makes full use of string length
information computed by the strlen optimization pass.
+ [26]-Wrestrict detects overlapping accesses to dynamically
allocated objects.
+ [27]-Wreturn-local-addr diagnoses more instances of return
statements returning addresses of automatic variables.
+ [28]-Wstringop-overflow 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 access.
+ [29]-Warith-conversion re-enables warnings from -Wconversion,
-Wfloat-conversion, and -Wsign-conversion that are now off by
default for an expression where the result of an arithmetic
operation will not fit in the target type due to promotion,
but the operands of the expression do fit in the target type.
* Extended characters in identifiers may now be specified directly in
the input encoding (UTF-8, by default), in addition to the UCN
syntax (\uNNNN or \UNNNNNNNN) that is already supported:
static const int p = 3;
int get_na<6E>ve_pi() {
return p;
}
C
* Several new features from the upcoming C2X revision of the ISO C
standard are supported with -std=c2x and -std=gnu2x. 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
-std=c2x -Wpedantic.
+ The [[]] attribute syntax is supported, as in C++. Existing
attributes can be used with this syntax in forms such as
[[gnu::const]]. The standard attributes [[deprecated]],
[[fallthrough]] and [[maybe_unused]] are supported.
+ UTF-8 character constants using the u8'' syntax are supported.
+ <float.h> defines macros FLT_NORM_MAX, DBL_NORM_MAX and
LDBL_NORM_MAX.
+ When decimal floating-point arithmetic is supported, <float.h>
defines macros DEC32_TRUE_MIN, DEC64_TRUE_MIN and
DEC128_TRUE_MIN, in addition to the macros that were
previously only defined if __STDC_WANT_DEC_FP__ was defined
before including <float.h>.
+ 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.
+ The strftime format checking supports the %OB and %Ob formats.
+ In C2X mode, -fno-fp-int-builtin-inexact is enabled by
default.
* GCC now defaults to -fno-common. 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 -fcommon such definitions are silently merged during
linking.
C++
* Several C++20 features have been implemented:
+ Concepts, including P0734R0, P0857R0, P1084R2, P1141R2,
P0848R3, P1616R1, P1452R2
+ P1668R1, Permitting Unevaluated inline-assembly in constexpr
Functions
+ P1161R3, Deprecate a[b,c]
+ P0848R3, Conditionally Trivial Special Member Functions
+ P1091R3, Extending structured bindings
+ P1143R2, Adding the constinit keyword
+ P1152R4, Deprecating volatile
+ P0388R4, Permit conversions to arrays of unknown bound
+ P0784R7, constexpr new
+ P1301R4, [[nodiscard("with reason")]]
+ P1814R0, class template argument deduction for alias templates
+ P1816R0, class template argument deduction for aggregates
+ P0960R3, Parenthesized initialization of aggregates
+ P1331R2, Allow trivial default initialization in constexpr
contexts
+ P1327R1, Allowing dynamic_cast and polymorphic typeid in
constexpr contexts
+ P0912R5, Coroutines (requires -fcoroutines)
* Several C++ Defect Reports have been resolved, e.g.:
+ DR 1560, lvalue-to-rvalue conversion in ?:
+ DR 1813, __is_standard_layout for a class with repeated bases
+ DR 2094, volatile scalars are trivially copyable,
+ DR 2096, constraints on literal unions
+ DR 2413, typename in conversion-function-ids
+ DR 2352, Similar types and reference binding
+ DR 1601, Promotion of enumeration with fixed underlying type
+ DR 330, Qualification conversions and pointers to arrays of
pointers
+ DR 1307, Overload resolution based on size of array
initializer-list
+ DR 1710, Missing template keyword in class-or-decltype
* New warnings:
+ [30]-Wmismatched-tags, 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.
+ [31]-Wredundant-tags, disabled by default, warns about
redundant class-key and enum-key in contexts where the key can
be eliminated without causing an syntactic ambiguity.
* G++ can now detect modifying constant objects in constexpr
evaluation (which is undefined behavior).
* G++ no longer emits bogus -Wsign-conversion warnings with explicit
casts.
* Narrowing is now detected in more contexts (e.g., case values).
* Memory consumption of the compiler has been reduced in constexpr
evaluation.
* The noexcept-specifier is now properly treated as a complete-class
context as per [class.mem].
* The attribute deprecated can now be used on namespaces too.
* The ABI of passing and returning certain C++ classes by value
changed on several targets in GCC 10, including [32]AArch64,
[33]ARM, [34]PowerPC ELFv2, [35]S/390 and [36]Itanium. These
changes affect classes with a zero-sized subobject (an empty base
class, or data member with the [[no_unique_address]] 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 -std=c++17
and -std=c++20 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 -std=c++17 and -std=c++14 ABI incompatible. This has
been corrected and the empty bases are ignored in those ABI
decisions, so functions compiled with -std=c++14 and -std=c++17 are
now ABI compatible again. Example: struct empty {}; struct S :
empty { float f; }; void f(S);. Similarly, in classes containing
non-static data members with empty class types using the C++20
[[no_unique_address]] 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 -Wpsabi.
Runtime Library (libstdc++)
* Improved experimental C++2a support, including:
+ Library concepts in <concepts> and <iterator>.
+ Constrained algorithms in <ranges>, <algorithm>, and <memory>
(thanks to Patrick Palka).
+ New algorithms shift_left and shift_right (thanks to Patrick
Palka).
+ std::span (thanks to JeanHeyd Meneide).
+ Three-way comparisons in <compare> and throughout the library.
+ Constexpr support in <algorithm> and elsewhere (thanks to
Edward Smith-Rowland).
+ <stop_token> and std::jthread (thanks to Thomas Rodgers).
+ std::atomic_ref and std::atomic<floating point>.
+ Integer comparison functions (cmp_equal, cmp_less etc.).
+ std::ssize, std::to_array.
+ std::construct_at, std::destroy, constexpr std::allocator.
+ Mathematical constants in <numbers>.
* Support for RDSEED in std::random_device.
* Reduced header dependencies, leading to faster compilation for some
code.
* The std::iterator base class of std::istreambuf_iterator was
changed in C++98 mode to be consistent with C++11 and later
standards. This is expected to have no noticeable effect except in
the unlikely case of a class which has potentially overlapping
subobjects of type std::istreambuf_iterator<C> and another iterator
type with a std::iterator<input_iterator_tag, C, ...> base class.
The layout of such a type might change when compiled as C++98.
[37]Bug 92285 has more details and concrete examples.
D
* Support for static foreach has been implemented.
* Aliases can now be created directly from any __traits that return
symbols or tuples. Previously, an AliasSeq was necessary in order
to alias their return.
* It is now possible to detect the language ABI specified for a
struct, class, or interface using __traits(getLinkage, ...).
* Support for core.math.toPrec intrinsics has been added. These
intrinsics guarantee the rounding to specific floating-point
precisions at specified points in the code.
* Support for pragma(inline) has been implemented. Previously the
pragma was recognized, but had no effect on the compilation.
* Optional parentheses in asm operands are deprecated and will be
removed in a future release.
* All content imported files are now included in the make dependency
list when compiling with -M.
* Compiler recognized attributes provided by the gcc.attribute module
will now take effect when applied to function prototypes as well as
when applied to full function declarations.
* Added a --enable-libphobos-checking configure option to control
whether run-time checks are compiled into the D runtime library.
* Added a --with-libphobos-druntime-only configure option to indicate
whether to build only the core D runtime library, or both the core
and standard libraries into libphobos.
Fortran
* use_device_addr of version 5.0 of the [38]OpenMP specification is
now supported. Note that otherwise OpenMP 4.5 is partially
supported in the Fortran compiler; the largest missing item is
structure element mapping.
* 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 GFORTRAN_FORMATTED_BUFFER_SIZE and
GFORTRAN_UNFORMATTED_BUFFER_SIZE for formatted and unformatted
files, respectively.
* Mismatches between actual and dummy argument lists in a single file
are now rejected with an error. Use the new option
-fallow-argument-mismatch to turn these errors into warnings; this
option is implied with -std=legacy. -Wargument-mismatch has been
removed.
* 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
-fallow-invalid-boz option, which degrades the error to a warning
and the code is compiled as with older gfortran.
* At any optimization level except-Os, 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, -fno-inline-arg-packing can be used to disable
inline argument packing.
* Legacy extensions:
+ For formatted input/output, if the explicit widths after the
data-edit descriptors I, F and G have been omitted, default
widths are used.
+ A blank format item at the end of a format specification, i.e.
nothing following the final comma, is allowed. Use the option
-fdec-blank-format-item; this option is implied with -fdec.
+ The existing support for AUTOMATIC and STATIC attributes has
been extended to allow variables with the AUTOMATIC attribute
to be used in EQUIVALENCE statements. Use -fdec-static; this
option is implied by -fdec.
+ Allow character literals in assignments and DATA statements
for numeric (INTEGER, REAL, or COMPLEX) or LOGICAL variables.
Use the option -fdec-char-conversions; this option is implied
with -fdec.
+ DEC comparisons, i.e. allow Hollerith constants to be used in
comparisons with INTEGER, REAL, COMPLEX and CHARACTER
expressions. Use the option -fdec.
* Character type names in errors and warnings now include len in
addition to kind; * is used for assumed length. The kind is omitted
if it is the default kind. Examples: CHARACTER(12), CHARACTER(6,4).
* CO_BROADCAST now supports derived type variables including objects
with allocatable components. In this case, the optional arguments
STAT= and ERRMSG= are currently ignored.
* 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.
Go
* GCC 10 provides a complete implementation of the Go 1.14.6 user
packages.
libgccjit
* The libgccjit API gained four new entry points:
+ [39]gcc_jit_version_major, [40]gcc_jit_version_minor, and
[41]gcc_jit_version_patchlevel for programmatically checking
the libgccjit version from client code, and
+ [42]gcc_jit_context_new_bitfield
New Targets and Target Specific Improvements
AArch64 & arm
* The AArch64 and arm ports now support condition flag output
constraints in inline assembly, as indicated by the
__GCC_ASM_FLAG_OUTPUTS__. On arm this feature is only available for
A32 and T32 targets. Please refer to the documentation for more
details.
AArch64
* There have been several improvements related to the Scalable Vector
Extension (SVE):
+ The SVE ACLE types and intrinsics are now supported. They can
be accessed using the header file arm_sve.h.
+ It is now possible to create fixed-length SVE types using the
arm_sve_vector_bits attribute. For example:
#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
+ -mlow-precision-div, -mlow-precision-sqrt and
-mlow-precision-recip-sqrt now work for SVE.
+ -msve-vector-bits=128 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.
+ The vectorizer is now able to use extending loads and
truncating stores, including gather loads and scatter stores.
+ 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.
+ 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").
+ Besides these specific points, there have been many general
improvements to the way that the vectorizer uses SVE.
* The -mbranch-protection=pac-ret option now accepts the optional
argument +b-key extension to perform return address signing with
the B-key instead of the A-key.
* The option -moutline-atomics 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.
* The Transactional Memory Extension is now supported through ACLE
intrinsics. It can be enabled through the +tme option extension
(for example, -march=armv8.5-a+tme).
* A number of features from Armv8.5-A are now supported through ACLE
intrinsics. These include:
+ The random number instructions that can be enabled through the
(already present in GCC 9.1) +rng option extension.
+ Floating-point intrinsics to round to integer instructions
from Armv8.5-A when targeting -march=armv8.5-a or later.
+ Memory Tagging Extension intrinsics enabled through the
+memtag option extension.
* Similarly, the following Armv8.6-A features are now supported
through ACLE intrinsics:
+ The bfloat16 extension. This extension is enabled
automatically when Armv8.6-A is selected (such as by
-march=armv8.6-a). It can also be enabled for Armv8.2-A and
later using the +bf16 option extension.
+ The Matrix Multiply extension. This extension is split into
three parts, one for each supported data type:
o 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 +i8mm option extension.
o Support for 32-bit floating-point matrix multiply
instructions. This extension can be enabled using the
+f32mm option extension, which also has the effect of
enabling SVE.
o Support for 64-bit floating-point matrix multiply
instructions. This extension can be enabled using the
+f64mm option extension, which likewise has the effect of
enabling SVE.
* SVE2 is now supported through ACLE intrinsics and (to a limited
extent) through autovectorization. It can be enabled through the
+sve2 option extension (for example, -march=armv8.5-a+sve2).
Additional extensions can be enabled through +sve2-sm4, +sve2-aes,
+sve2-sha3 and +sve2-bitperm.
* Support has been added for the following processors (GCC
identifiers in parentheses):
+ Arm Cortex-A77 (cortex-a77).
+ Arm Cortex-A76AE (cortex-a76ae).
+ Arm Cortex-A65 (cortex-a65).
+ Arm Cortex-A65AE (cortex-a65ae).
+ Arm Cortex-A34 (cortex-a34).
+ Marvell ThunderX3 (thunderx3t110).
The GCC identifiers can be used as arguments to the -mcpu or -mtune
options, for example: -mcpu=cortex-a77 or -mtune=cortex-a65ae or as
arguments to the equivalent target attributes and pragmas.
arm
* 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
arm-uclinuxfdpiceabi, and the C library is uclibc-ng.
* Support has been added for the Arm EABI on NetBSD through the
arm*-*-netbsdelf-*eabi* triplet.
* 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
-mneon-for-64bits is now deprecated and will be removed in a future
release.
* Support has been added for the following processors (GCC
identifiers in parentheses):
+ Arm Cortex-A77 (cortex-a77).
+ Arm Cortex-A76AE (cortex-a76ae).
+ Arm Cortex-M35P (cortex-m35p).
+ Arm Cortex-M55 (cortex-m55).
The GCC identifiers can be used as arguments to the -mcpu or -mtune
options, for example: -mcpu=cortex-a77 or -mtune=cortex-m35p.
* Support has been extended for the ACLE [43]data-processing
intrinsics to include 32-bit SIMD, saturating arithmetic, 16-bit
multiplication and other related intrinsics aimed at DSP algorithm
optimization.
* Support for -mpure-code in Thumb-1 (v6m) has been added: this
M-profile feature is no longer restricted to targets with MOVT. For
example, -mcpu=cortex-m0 now supports this option.
* Support for the [44]Armv8.1-M Mainline Architecture has been added.
+ Armv8.1-M Mainline can be enabled by using the
-march=armv8.1-m.main command-line option.
* Support for the [45]MVE beta ACLE intrinsics has been added. These
intrinsics can be enabled by including the arm_mve.h header file
and passing the +mve or +mve.fp option extensions (for example:
-march=armv8.1-m.main+mve).
* Support for the Custom Datapath Extension beta ACLE [46]intrinsics
has been added.
* Support for Armv8.1-M Mainline Security Extensions architecture has
been added. The -mcmse option, when used in combination with an
Armv8.1-M Mainline architecture (for example: -march=armv8.1-m.main
-mcmse), now leads to the generation of improved code sequences
when changing security states.
AMD Radeon (GCN)
* The code generation and in particular the vectorization support has
been much improved.
ARC
* The interrupt service routine functions save all used registers,
including extension registers and auxiliary registers used by Zero
Overhead Loops.
* Improve code size by using multiple short instructions instead of a
single long mov or ior instruction when its long immediate constant
is known.
* Fix usage of the accumulator register for ARC600.
* Fix issues with uncached attribute.
* Remove -mq-class option.
* Improve 64-bit integer addition and subtraction operations.
AVR
* Support for the XMEGA-like devices
ATtiny202, ATtiny204, ATtiny402, ATtiny404, ATtiny406, ATtiny804,
ATtiny806, ATtiny807, ATtiny1604, ATtiny1606, ATtiny1607, ATmega808,
ATmega809, ATmega1608, ATmega1609, ATmega3208, ATmega3209,
ATmega4808, ATmega4809
has been added.
* A new command-line option -nodevicespecs has been added. It allows
to provide a custom device-specs file by means of
avr-gcc -nodevicespecs -specs=my-spec-file <options>
and without the need to provide options -B and -mmcu=. See [47]AVR
command-line options for details. This feature is also available in
GCC 9.3+ and GCC 8.4+.
* New command-line options -mdouble=[32,64] and -mlong-double=[32,64]
have been added. They allow to choose the size (in bits) of the
double and long double 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 [48]AVR configure options --with-double= and
--with-long-double=.
* A new configure option --with-libf7= has been added. It controls to
which level avr-libgcc provides 64-bit floating point support by
means of [49]Libf7.
* A new configure option --with-double-comparison= has been added.
It's unlikely you need to set this option by hand.
IA-32/x86-64
* Support to expand __builtin_roundeven into the appropriate SSE 4.1
instruction has been added.
* New ISA extension support for Intel ENQCMD was added to GCC. ENQCMD
intrinsics are available via the -menqcmd compiler switch.
* GCC now supports the Intel CPU named Cooperlake through
-march=cooperlake. The switch enables the AVX512BF16 ISA
extensions.
* GCC now supports the Intel CPU named Tigerlake through
-march=tigerlake. The switch enables the MOVDIRI MOVDIR64B
AVX512VP2INTERSECT ISA extensions.
MIPS
* The mips*-*-linux* 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 --with-glibc-version=2.31 against glibc 2.31 or
later.
PowerPC / PowerPC64 / RS6000
* Many vector builtins have been listed as deprecated in the
[50]64-Bit ELF V2 ABI Specification 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. Note that this does not result in any loss of function.
These deprecated builtins generally provide somewhat nonsensical
argument lists (for example, mixing signed, unsigned, and bool
vector arguments arbitrarily), or are duplicate builtins that are
inconsistent with the expected naming scheme. We expect that this
will be unlikely to affect much if any code, and any required code
changes will be trivial.
PRU
* A new back end targeting TI PRU I/O processors has been contributed
to GCC.
RISC-V
* The riscv*-*-* targets now require GNU binutils version 2.30 or
later, to support new assembly instructions produced by GCC.
V850
* 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.
Operating Systems
Improvements for plugin authors
* 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 [51]-fdiagnostics-path-format option, or captured
in JSON form via [52]-fdiagnostics-format=json.
* GCC diagnostics can now be associated with [53]CWE weakness
identifiers, which will appear on the standard error stream, and in
the JSON output from [54]-fdiagnostics-format=json.
Other significant improvements
* To allow inline expansion of both memcpy and memmove, the existing
movmem instruction patterns used for non-overlapping memory copies
have been renamed to cpymem. The movmem name is now used for
overlapping memory moves, consistent with the library functions
memcpy and memmove.
* 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 [55]sufficiently capable terminal). This behavior can be
controlled via a new [56]-fdiagnostics-urls option (along with
various environment variables and heuristics documented with that
option).
GCC 10.1
This is the [57]list of problem reports (PRs) 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).
GCC 10.2
This is the [58]list of problem reports (PRs) from GCC's bug tracking
system that are known to be fixed in the 10.2 release. This list might
not be complete (that is, it is possible that some PRs that have been
fixed are not listed here).
GCC 10.3
This is the [59]list of problem reports (PRs) from GCC's bug tracking
system that are known to be fixed in the 10.3 release. This list might
not be complete (that is, it is possible that some PRs that have been
fixed are not listed here).
Target Specific Changes
AArch64
* A bug with the Random Number intrinsics in the arm_acle.h header
that resulted in an incorrect status result being returned has been
fixed.
* GCC now supports the Fujitsu A64FX. The associated -mcpu and -mtune
options are -mcpu=a64fx and -mtune=a64fx respectively. In
particular, -mcpu=a64fx generates code for Armv8.2-A with SVE and
tunes the code for the A64FX. This includes tuning the SVE code,
although by default the code is still length-agnostic and so works
for all SVE implementations. Adding -msve-vector-bits=512 makes the
code specific to 512-bit SVE.
x86-64
* GCC 10.3 supports AMD CPUs based on the znver3 core via
-march=znver3.
GCC 10.4
This is the [60]list of problem reports (PRs) from GCC's bug tracking
system that are known to be fixed in the 10.4 release. This list might
not be complete (that is, it is possible that some PRs that have been
fixed are not listed here).
Target Specific Changes
x86-64
* The x86-64 ABI of passing and returning structures with a 64-bit
integer vector changed in GCC 10.1 when MMX is disabled. Disabling
MMX no longer changes how they are passed nor returned. This ABI
change is now diagnosed with -Wpsabi.
For questions related to the use of GCC, please consult these web
pages and the [61]GCC manuals. If that fails, the
[62]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 [63]gcc@gcc.gnu.org. All of [64]our lists have public
archives.
Copyright (C) [65]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 [66]maintained by the GCC team. Last modified
2022-06-28[67].
References
1. http://gcc.gnu.org/gcc-10/porting_to.html
2. http://gcc.gnu.org/onlinedocs/index.html#current
3. http://gcc.gnu.org/gcc-10/changes.html#empty_base
4. https://www.mpfr.org/
5. http://gcc.gnu.org/gcc-10/changes.html#iterator_base
6. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/cpp/_005f_005fhas_005fbuiltin.html#g_t_005f_005fhas_005fbuiltin
7. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Optimize-Options.html#index-fno-allocation-dce
8. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Optimize-Options.html#index-fprofile-partial-training
9. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Instrumentation-Options.html#index-fprofile-reproducible
10. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Instrumentation-Options.html#index-fprofile-generate
11. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Instrumentation-Options.html#index-fprofile-prefix-path
12. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Static-Analyzer-Options.html
13. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Optimize-Options.html#index-finline-functions
14. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/lto-dump.html
15. https://facebook.github.io/zstd/
16. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Optimize-Options.html#index-fprofile-values
17. https://www.openacc.org/
18. https://gcc.gnu.org/wiki/OpenACC/Implementation%20Status#status-10
19. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/libgomp/#toc-Enabling-OpenACC-1
20. https://www.openmp.org/specifications/
21. https://gcc.gnu.org/wiki/Offloading
22. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wstring-compare
23. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wzero-length-bounds
24. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Warray-bounds
25. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wformat-overflow
26. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wrestrict
27. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wreturn-local-addr
28. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Wstringop-overflow
29. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Warning-Options.html#index-Warith-conversion
30. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/C_002b_002b-Dialect-Options.html#index-Wmismatched-tags
31. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/C_002b_002b-Dialect-Options.html#index-Wredundant-tags
32. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94383
33. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94711
34. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94707
35. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94704
36. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94706
37. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92285
38. https://www.openmp.org/specifications/
39. https://gcc.gnu.org/onlinedocs/jit/topics/compatibility.html#c.gcc_jit_version_major
40. https://gcc.gnu.org/onlinedocs/jit/topics/compatibility.html#c.gcc_jit_version_minor
41. https://gcc.gnu.org/onlinedocs/jit/topics/compatibility.html#c.gcc_jit_version_patchlevel
42. https://gcc.gnu.org/onlinedocs/jit/topics/types.html#c.gcc_jit_context_new_bitfield
43. https://developer.arm.com/documentation/101028/0009/Data-processing-intrinsics
44. https://developer.arm.com/architectures/cpu-architecture/m-profile
45. https://developer.arm.com/architectures/instruction-sets/simd-isas/helium/helium-intrinsics
46. https://developer.arm.com/documentation/101028/0010/Custom-Datapath-Extension
47. https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/AVR-Options.html#index-nodevicespecs
48. https://gcc.gnu.org/install/configure.html#avr
49. https://gcc.gnu.org/wiki/avr-gcc#Libf7
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59. https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=10.3
60. https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=10.4
61. https://gcc.gnu.org/onlinedocs/
62. mailto:gcc-help@gcc.gnu.org
63. mailto:gcc@gcc.gnu.org
64. https://gcc.gnu.org/lists.html
65. https://www.fsf.org/
66. https://gcc.gnu.org/about.html
67. http://validator.w3.org/check/referer
======================================================================
http://gcc.gnu.org/gcc-9/index.html
GCC 9 Release Series
May 27, 2022
The [1]GNU project and the GCC developers are pleased to announce the
release of GCC 9.5.
This release is a bug-fix release, containing fixes for regressions in
GCC 9.4 relative to previous releases of GCC.
Release History
GCC 9.5
May 27, 2022 ([2]changes, [3]documentation)
GCC 9.4
June 1, 2021 ([4]changes, [5]documentation)
GCC 9.3
Mar 12, 2020 ([6]changes, [7]documentation)
GCC 9.2
Aug 12, 2019 ([8]changes, [9]documentation)
GCC 9.1
May 3, 2019 ([10]changes, [11]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 [12]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 [13]amazing group of volunteers is
what makes GCC successful.
For additional information about GCC please refer to the [14]GCC
project web site or contact the [15]GCC development mailing list.
To obtain GCC please use [16]our mirror sites or [17]our version
control system.
For questions related to the use of GCC, please consult these web
pages and the [18]GCC manuals. If that fails, the
[19]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 [20]gcc@gcc.gnu.org. All of [21]our lists have public
archives.
Copyright (C) [22]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 [23]maintained by the GCC team. Last modified
2022-05-27[24].
References
1. http://www.gnu.org/
2. http://gcc.gnu.org/gcc-9/changes.html
3. http://gcc.gnu.org/onlinedocs/9.5.0/
4. http://gcc.gnu.org/gcc-9/changes.html
5. http://gcc.gnu.org/onlinedocs/9.4.0/
6. http://gcc.gnu.org/gcc-9/changes.html
7. http://gcc.gnu.org/onlinedocs/9.3.0/
8. http://gcc.gnu.org/gcc-9/changes.html
9. http://gcc.gnu.org/onlinedocs/9.2.0/
10. http://gcc.gnu.org/gcc-9/changes.html
11. http://gcc.gnu.org/onlinedocs/9.1.0/
12. http://gcc.gnu.org/gcc-9/buildstat.html
13. http://gcc.gnu.org/onlinedocs/gcc-9.1.0/gcc/Contributors.html
14. http://gcc.gnu.org/index.html
15. mailto:gcc@gcc.gnu.org
16. http://gcc.gnu.org/mirrors.html
17. http://gcc.gnu.org/git.html
18. https://gcc.gnu.org/onlinedocs/
19. mailto:gcc-help@gcc.gnu.org
20. mailto:gcc@gcc.gnu.org
21. https://gcc.gnu.org/lists.html
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======================================================================
http://gcc.gnu.org/gcc-9/changes.html
GCC 9 Release Series
Changes, New Features, and Fixes
This page is a "brief" summary of some of the huge number of
improvements in GCC 9. You may also want to check out our [1]Porting to
GCC 9 page and the [2]full GCC documentation.
Caveats
* On Arm targets (arm*-*-*), [3]a bug in the implementation of the
procedure call standard (AAPCS) in the GCC 6, 7 and 8 releases has
been fixed: a structure containing a bit-field based on a 64-bit
integral type and where no other element in a structure required
64-bit alignment could be passed incorrectly to functions. This is
an ABI change. If the option -Wpsabi is enabled (on by default) the
compiler will emit a diagnostic note for code that might be
affected.
* Support for a number of older systems and recently unmaintained or
untested target ports of GCC has been declared obsolete in GCC 9.
Unless there is activity to revive them, the next release of GCC
will have their sources permanently removed.
The following ports for individual systems on particular
architectures have been obsoleted:
+ Solaris 10 (*-*-solaris2.10). Details can be found in the
[4]announcement.
+ Cell Broadband Engine SPU (spu*-*-*). Details can be found in
the [5]announcement.
* A change to the C++ std::rotate algorithm in GCC 9.1.0 can cause
ABI incompatibilities with object files compiled with other
versions of GCC. If the std::rotate algorithm is called with an
empty range then it might cause a divide-by-zero error (as a SIGFPE
signal) and crash. The change has been reverted for GCC 9.2.0 and
future releases. For more details see [6]Bug 90920. The problem can
be avoided by recompiling any objects that might call std::rotate
with an empty range, so that the GCC 9.1.0 definition of
std::rotate is not used.
* The automatic template instantiation at link time ([7]-frepo) has
been deprecated and will be removed in a future release.
* The --with-default-libstdcxx-abi=gcc4-compatible configure option
is broken in the 9.1 and 9.2 releases, producing a shared library
with missing symbols (see [8]Bug 90361). As a workaround, configure
without that option and build GCC as normal, then edit the
installed <bits/c++config.h> headers to define the
_GLIBCXX_USE_CXX11_ABI macro to 0.
General Improvements
The following GCC command line options have been introduced or
improved.
* All command line options that take a byte-size argument accept
64-bit integers as well as standard SI and IEC suffixes such as kb
and KiB, MB and MiB, or GB and GiB denoting the corresponding
multiples of bytes. See [9]Invoking GCC for more.
* A new option,
[10]-flive-patching=[inline-only-static|inline-clone], has been
introduced to provide a safe compilation for live-patching. At the
same time, provides multiple-level control on the enabled IPA
optimizations. See the user guide for more details about the
option.
* A new option, --completion, has been added to provide more fine
option completion in a shell. It is intended to be used by
Bash-completion.
* GCC's diagnostics now print source code with a left margin showing
line numbers, configurable with
[11]-fno-diagnostics-show-line-numbers.
GCC's diagnostics can also now label regions of the source code to
show pertinent information, such as the types within an expression.
$ g++ t.cc
t.cc: In function 'int test(const shape&, const shape&)':
t.cc:15:4: error: no match for 'operator+' (operand types are 'boxed_value<doubl
e>' and 'boxed_value<double>')
14 | return (width(s1) * height(s1)
| ~~~~~~~~~~~~~~~~~~~~~~
| |
| boxed_value<[...]>
15 | + width(s2) * height(s2));
| ^ ~~~~~~~~~~~~~~~~~~~~~~
| |
| boxed_value<[...]>
These labels can be disabled via [12]-fno-diagnostics-show-labels.
* A new option [13]-fdiagnostics-format=json has been introduced for
emitting diagnostics in a machine-readable format.
* The alignment-related options [14]-falign-functions,
[15]-falign-labels, [16]-falign-loops, and [17]-falign-jumps
received support for a secondary alignment (e.g.
-falign-loops=n:m:n2:m2).
* New pair of profiling options ([18]-fprofile-filter-files and
[19]-fprofile-exclude-files) has been added. The options help to
filter which source files are instrumented.
* AddressSanitizer generates more compact redzones for automatic
variables. That helps to reduce memory footprint of a sanitized
binary.
* Numerous improvements have been made to the output of
[20]-fopt-info.
Messages are now prefixed with optimized, missed, or note, rather
than the old behavior of all being prefixed with note.
The output from -fopt-info can now contain information on inlining
decisions:
$ g++ -c inline.cc -O2 -fopt-info-inline-all
inline.cc:24:11: note: Considering inline candidate void foreach(T, T, void (*)(
E)) [with T = char**; E = char*]/2.
inline.cc:24:11: optimized: Inlining void foreach(T, T, void (*)(E)) [with T =
char**; E = char*]/2 into int main(int, char**)/1.
inline.cc:19:12: missed: not inlinable: void inline_me(char*)/0 -> int std::pu
ts(const char*)/3, function body not available
inline.cc:13:8: optimized: Inlined void inline_me(char*)/4 into int main(int, c
har**)/1 which now has time 127.363637 and size 11, net change of +0.
Unit growth for small function inlining: 16->16 (0%)
Inlined 2 calls, eliminated 1 functions
The output from the vectorizer has been rationalized so that failed
attempts to vectorize a loop are displayed in the form
[LOOP-LOCATION]: couldn't vectorize this loop
[PROBLEM-LOCATION]: because of [REASON]
rather than an exhaustive log of all decisions made by the
vectorizer. For example:
$ gcc -c v.c -O3 -fopt-info-all-vec
v.c:7:3: missed: couldn't vectorize loop
v.c:10:7: missed: statement clobbers memory: __asm__ __volatile__("" : : : "me
mory");
v.c:3:6: note: vectorized 0 loops in function.
v.c:10:7: missed: statement clobbers memory: __asm__ __volatile__("" : : : "me
mory");
The old behavior can be obtained via a new -internals suboption of
-fopt-info.
* A new option, [21]-fsave-optimization-record has been added, which
writes a SRCFILE.opt-record.json.gz file describing the
optimization decisions made by GCC. This is similar to the output
of -fopt-info, but with additional metadata such as the inlining
chain, and profile information (if available).
* Inter-procedural propagation of stack alignment can now be
controlled by [22]-fipa-stack-alignment.
* Propagation of addressability, readonly and writeonly flags on
static variables can now be controlled by
[23]-fipa-reference-addressable.
The following built-in functions have been introduced.
* [24]__builtin_expect_with_probability to provide branch prediction
probability hints to the optimizer.
* [25]__builtin_has_attribute determines whether a function, type, or
variable has been declared with some attribute.
* [26]__builtin_speculation_safe_value can be used to help mitigate
against unsafe speculative execution.
The following attributes have been introduced.
* The [27]copy function attribute has been added. The attribute can
also be applied to type definitions and to variable declarations.
A large number of improvements to code generation have been made,
including but not limited to the following.
* Switch expansion has been improved by using a different strategy
(jump table, bit test, decision tree) for a subset of switch cases.
* A linear function expression defined as a switch statement can be
transformed by [28]-ftree-switch-conversion. For example:
int
foo (int how)
{
switch (how) {
case 2: how = 205; break;
case 3: how = 305; break;
case 4: how = 405; break;
case 5: how = 505; break;
case 6: how = 605; break;
}
return how;
}
can be transformed into 100 * how + 5 (for values defined in the
switch statement).
* Inter-procedural optimization improvements:
+ Inliner defaults was tuned to better suits modern C++
codebases especially when built with link time optimizations.
New parameters max-inline-insns-small, max-inline-insns-size,
uninlined-function-insns, uninlined-function-time,
uninlined-thunk-insns, and uninlined-thunk-time were added.
+ Hot/cold partitioning is now more precise and aggressive.
+ Improved scalability for very large translation units
(especially when link-time optimizing large programs).
* Profile driven optimization improvements:
+ [29]-fprofile-use now enables [30]-fversion-loops-for-strides,
[31]-floop-interchange, [32]-floop-unroll-and-jam,
[33]-ftree-loop-distribution.
+ Streaming of counter histograms was removed. This reduces the
size of profile files. Histogram is computed on the fly with
link-time optimization. Parameter hot-bb-count-ws-permille was
reduced from 999 to 990 to account for more precise
histograms.
* Link-time optimization improvements:
+ Types are now simplified prior streaming resulting in
significant reductions of the LTO object files, link-time
memory use, and improvements of link-time parallelism.
+ Default number of partitions (--param lto-partitions) was
increased from 32 to 128 enabling effective use of CPUs with
more than 32 hyperthreads. --param
lto-max-streaming-parallelism can now be used to control
number of streaming processes.
+ Warnings on C++ One Decl Rule violations (-Wodr) are now more
informative and produce fewer redundant results.
Overall compile time of Firefox 66 and LibreOffice 6.2.3 on an
8-core machine was reduced by about 5% compared to GCC 8.3, and the
size of LTO object files by 7%. LTO link-time improves by 11% on an
8-core machine and scales significantly better for more parallel
build environments. The serial stage of the link-time optimization
is 28% faster consuming 20% less memory. The parallel stage now
scales to up to 128 partitions rather than 32 and reduces memory
use for every worker by 30%.
The following improvements to the gcov command-line utility have been
made.
* The gcov tool received a new option [34]--use-hotness-colors (-q)
that can provide perf-like coloring of hot functions.
* The gcov tool has changed its intermediate format to a new JSON
format.
New Languages and Language specific improvements
[35]OpenACC support in C, C++, and Fortran continues to be maintained
and improved. Most of the OpenACC 2.5 specification is implemented. See
the [36]implementation status section on the OpenACC wiki page for
further information.
C family
* Version 5.0 of the [37]OpenMP specification is now partially
supported in the C and C++ compilers. For details which features of
OpenMP 5.0 are and which are not supported in the GCC 9 release see
[38]this mail.
* New extensions:
+ [39]__builtin_convertvector built-in for vector conversions
has been added.
* New warnings:
+ [40]-Waddress-of-packed-member, enabled by default, warns
about an unaligned pointer value from the address of a packed
member of a struct or union.
* Enhancements to existing warnings:
+ [41]-Warray-bounds detects more instances of out-of-bounds
indices.
+ [42]-Wattribute-alias also detects attribute mismatches
between alias declarations and their targets, in addition to
mismatches between their types.
+ [43]-Wformat-overflow and [44]-Wformat-truncation have been
extended to all formatted input/output functions (where
applicable) and enhanced to detect a subset of instances of
reading past the end of unterminated constant character arrays
in %s directives.
+ [45]-Wmissing-attributes detects instances of missing function
attributes on declarations of aliases and weak references.
+ [46]-Wstringop-truncation also detects a subset of instances
of reading past the end of unterminated constant character
arrays,
* If a macro is used with the wrong argument count, the C and C++
front ends now show the definition of that macro via a note.
* The spelling corrector now considers transposed letters, and the
threshold for similarity has been tightened, to avoid nonsensical
suggestions.
C
* There is now experimental support for -std=c2x, to select support
for the upcoming C2X revision of the ISO C standard. This standard
is in the early stages of development and the only feature
supported in GCC 9 is _Static_assert with a single argument
(support for _Static_assert with two arguments was added in C11 and
GCC 4.6). There are also new options -std=gnu2x, for C2X with GNU
extensions, and -Wc11-c2x-compat, to warn for uses of features
added in C2X (such warnings are also enabled by use of -Wpedantic
if not using -std=c2x or -std=gnu2x).
* New warnings:
+ [47]-Wabsolute-value warns for calls to standard functions
that compute the absolute value of an argument when a more
appropriate standard function is available. For example,
calling abs(3.14) triggers the warning because the appropriate
function to call to compute the absolute value of a double
argument is fabs. The option also triggers warnings when the
argument in a call to such a function has an unsigned type.
This warning can be suppressed with an explicit type cast and
it is also enabled by -Wextra.
C++
* New warnings:
+ [48]-Wdeprecated-copy, implied by -Wextra, warns about the
C++11 deprecation of implicitly declared copy constructor and
assignment operator if one of them is user-provided.
-Wdeprecated-copy-dtor also warns if the destructor is
user-provided, as specified in C++11.
+ [49]-Winit-list-lifetime, on by default, warns about uses of
std::initializer_list that are likely to result in a dangling
pointer, such as returning or assigning from a temporary list.
+ [50]-Wredundant-move, implied by -Wextra, warns about
redundant calls to std::move.
+ [51]-Wpessimizing-move, implied by -Wall, warns when a call to
std::move prevents copy elision.
+ [52]-Wclass-conversion, on by default, warns when a conversion
function will never be called due to the type it converts to.
* The C++ front end has experimental support for some of the upcoming
C++2a draft features with the -std=c++2a or -std=gnu++2a flags,
including range-based for statements with initializer, default
constructible and assignable stateless lambdas, lambdas in
unevaluated contexts, language support for empty data members,
allowing pack expansion in lambda init-capture, likely and unlikely
attributes, class types in non-type template parameters, allowing
virtual function calls in constant expressions, explicit(bool),
std::is_constant_evaluated, nested inline namespaces, etc. For a
full list of new features, see [53]the C++ status page.
* The C++ front end now preserves source locations for literals,
id-expression, and mem-initializer for longer. For example it is
now able to pin-point the pertinent locations for bad
initializations such as these
$ g++ -c bad-inits.cc
bad-inits.cc:10:14: error: cannot convert 'json' to 'int' in initialization
10 | { 3, json::object },
| ~~~~~~^~~~~~
| |
| json
bad-inits.cc:14:31: error: initializer-string for array of chars is too long [-f
permissive]
14 | char buffers[3][5] = { "red", "green", "blue" };
| ^~~~~~~
bad-inits.cc: In constructor 'X::X()':
bad-inits.cc:17:13: error: invalid conversion from 'int' to 'void*' [-fpermissiv
e]
17 | X() : one(42), two(42), three(42)
| ^~
| |
| int
rather than emitting the error at the final closing parenthesis or
brace.
* Error-reporting of overload resolution has been special-cased to
make the case of a single failed candidate easier to read. For
example:
$ g++ param-type-mismatch.cc
param-type-mismatch.cc: In function 'int test(int, const char*, float)':
param-type-mismatch.cc:8:32: error: cannot convert 'const char*' to 'const char*
*'
8 | return foo::member_1 (first, second, third);
| ^~~~~~
| |
| const char*
param-type-mismatch.cc:3:46: note: initializing argument 2 of 'static int foo:
:member_1(int, const char**, float)'