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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 Porting to GCC 11 page and the full GCC documentation.

Caveats

• The default mode for C++ is now -std=gnu++17 instead of -std=gnu++14. Note that 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 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

• ThreadSanitizer improvements to support alternative runtimes and environments. The 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 π ("GREEK SMALL LETTER PI (U+03C0)") occupies one column, and its UTF-8 encoding requires two bytes; the character 🙂 ("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 -fdiagnostics-column-unit=byte. There is also a new option -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 -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 -ftabstop option (which defaults to 8 spaces per tab stop).

• Introduce Hardware-assisted AddressSanitizer support. This sanitizer currently only works for the AArch64 target. It helps debug address problems similarly to AddressSanitizer but is based on partial hardware assistance and provides probabilistic protection to use less RAM at run time. 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 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:
  • -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 -fipa-modref option.
  • The identical code folding pass (controlled by -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 -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 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 OpenACC specification continues to be maintained and improved in the C, C++ and Fortran compilers. See the implementation status section on the OpenACC wiki page and the run-time library documentation for further information.

C family

• New attributes:
  • The no_stack_protector attribute has been added to mark functions which should not be instrumented with stack protection (-fstack-protector).
  • The existing malloc attribute has been extended so that it can be used to identify allocator/deallocator API pairs. A pair of new -Wmismatched-dealloc and -Wmismatched-new-delete warnings will complain about mismatched calls, and -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:
  • -Wmismatched-dealloc, enabled by default, warns about calls to deallocation functions with pointers returned from mismatched allocation functions.
  • -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.
  • -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.
  • -Wtsan, enabled by default, warns about unsupported features in ThreadSanitizer (currently std::atomic_thread_fence).
• Enhancements to existing warnings:
  • -Wfree-nonheap-object detects many more instances of calls to deallocation functions with pointers not returned from a dynamic memory allocation function.
  • -Wmaybe-uninitialized diagnoses passing pointers or references to uninitialized memory to functions taking const-qualified arguments.
  • -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:
  • -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.
  • -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 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 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 (PR41437).
• reinterpret_casts in constexpr evaluation are now checked more completely (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 (PR97518).
• New warnings:
  • -Wctad-maybe-unsupported, disabled by default, warns about performing class template argument deduction on a type with no deduction guides.
  • -Wrange-loop-construct, enabled by -Wall, warns when a range-based for-loop is creating unnecessary and expensive copies.
  • -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].
  • -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].
  • -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.
  • -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:
  • -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.
  • Template 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:
    • @attribute("alloc_size", arguments) or @alloc_size(arguments).
    • @attribute("always_inline") or @always_inline.
    • @attribute("used") or @used.
    • @attribute("optimize", arguments) or @optimize(arguments).
    • @attribute("cold") or @cold.
    • @attribute("noplt") or @noplt.
    • @attribute("target_clones", arguments) or @target_clones(arguments).
    • @attribute("no_icf") or @no_icf.
    • @attribute("noipa") or @noipa.
    • @attribute("symver", arguments) or @symver(arguments).
  • New aliases have been added to gcc.attributes for compatibility with ldc.attributes.
    • The @allocSize(arguments) attribute is the same as @alloc_size(arguments), but uses a 0-based index for function arguments.
    • The @assumeUsed attribute is an alias for @attribute("used").
    • The @fastmath attribute is an alias for @optimize("Ofast").
    • The @naked attribute is an alias for @attribute("naked"). This attribute may not be available on all targets.
    • The @restrict attribute has been added to specify that a function parameter is to be restrict-qualified in the C99 sense of the term.
    • The @optStrategy(strategy) attribute is an alias for @optimize("O0") when the strategy is "none", otherwise @optimize("Os") for the "optsize" and "minsize" strategies.
    • The @polly attribute is an alias for @optimize("loop-parallelize-all").
    • The @section(name) attribute is an alias for @attribute("section", name).
    • The @target(arguments) attribute is an alias for attribute("target", arguments).
    • 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 originally added in GCC 5. Given that we have maintained 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:
  • gcc_jit_global_set_initializer
  • 9 entrypoints for 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 back ends (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 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 -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 -fanalyzer (for example, exception-handling is unimplemented).
  • As noted above, the existing 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 -Wanalyzer-mismatching-deallocation warning has been added, covering such mismatches as using scalar delete rather vector delete[].
• The analyzer has gained warnings -Wanalyzer-shift-count-negative, -Wanalyzer-shift-count-overflow, -Wanalyzer-write-to-const, and -Wanalyzer-write-to-string-literal, all enabled by default when -fanalyzer is enabled.
• The analyzer can now be extended by GCC plugins, allowing for domain-specific path-sensitive warnings. An example of using a 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 -fdump-analyzer-json and -fno-analyzer-feasibility.

Other significant improvements

• GCC has gained a new environment variable 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 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 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 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).

GCC 11.4

This is the list of problem reports (PRs) from GCC's bug tracking system that are known to be fixed in the 11.4 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 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.

GCC 11.5

This is the list of problem reports (PRs) from GCC's bug tracking system that are known to be fixed in the 11.5 release. This list might not be complete (that is, it is possible that some PRs that have been fixed are not listed here).

Caveats

aarch64

• Due to a bug introduced a few weeks before the 11.5.0 release if the compiler is configured without explicit --with-arch=, --with=cpu= and/or --with-tune= configure options the compiler without explicit -march= etc. options might act as if asked for cortex-a34. This can be fixed by applying manually the r12-8060 commit patch on top of GCC 11.5.0. See PR116029 for more details. GCC 11.4.0 or earlier releases are not affected.