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 Porting to GCC 11 page and the full GCC documentation.

Note: GCC 11 has not been released yet, so this document is a work-in-progress.

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.
• 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.

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.

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. For Fortran, OpenMP 4.5 is now finally 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), lastprivate with conditional modifier, if clause with simd and cancel modifiers, target data without map clause, and limited support for the requires construct.

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
• Several C++ Defect Reports have been resolved, e.g.:
  • DR 1512, Pointer comparison vs qualification conversions
  • DR 1722, Should lambda to function pointer conversion function be >noexcept?
  • 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 2369, Ordering between constraints and substitution
• G++ now performs better access checking in templates (PR41437).
• reinterpret_casts in constexpr evaluation are now checked more completely (PR95307).
• New warnings:
  • -Wctad-maybe-unsupported, disabled by default, warns about performing class template argument deduction on a type with no deduction guides.

New Targets and Target Specific Improvements

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.

Operating Systems