GCC 15 Release Series
Changes, New Features, and Fixes

This page is a "brief" summary of some of the huge number of improvements in GCC 15. You may also want to check out our Porting to GCC 15 page

Note: GCC 15 has not been released yet, so this document is a work-in-progress.

Caveats

• ...

General Improvements

New Languages and Language specific improvements

• OpenMP
  • Support for unified-shared memory has been added for some AMD and Nvidia GPU devices, enabled when using the unified_shared_memory clause to the requires directive. For details, see the offload-target specifics section in the GNU Offloading and Multi Processing Runtime Library Manual. GCC added ompx_gnu_pinned_mem_alloc as predefined allocator. On Nvidia GPUs, writing to the terminal from OpenMP target regions (but not from OpenACC compute regions) is now also supported in Fortran; in C/C++ and on AMD GPUs this was already supported before with both OpenMP and OpenACC. Constructors and destructors on the device side for declare target static aggregates are now handled.
  • OpenMP 5.1: The unroll and tile loop-transformation constructs are now supported.
  • OpenMP 6.0: The get_device_from_uid and omp_get_uid_from_device API routines have been added.

C family

• A musttail statement attribute was added to enforce tail calls.

C++

• Inline assembler statements now support constexpr generated strings, analoguous to static_assert.
• Qualified name lookup failure into the current instantiation, e.g. this->non_existent, is now proactively diagnosed when parsing a template.

Runtime Library (libstdc++)

• Improved experimental support for C++26, including:
  • views::concat.
  • Member visit.
  • Type-checking std::format args.
• Improved experimental support for C++23, including:
  • Clarify handling of encodings in localized formatting of chrono types.

Fortran

• Fortran 2023: The selected_logical_kind intrinsic function and, in the ISO_FORTRAN_ENV module, the named constants logical{8,16,32,64} and real16 were added.
• Experimental support for unsigned integers, enabled by -funsigned; see gfortran documentation for details. These have been proposed (J3/24-116) for inclusion in the next Fortran standard.

New Targets and Target Specific Improvements

AMD Radeon (GCN)

• Support for Fiji (gfx803) devices has been removed (this was already deprecated in GCC 14).

AVR

• Support has been added for the signal and interrupt function attributes that allow to specify the interrupt vector number as an argument. It allows to use static functions as interrupt handlers, and also functions defined in a C++ namespace.
• Support has been added for the noblock function attribute. It can be specified together with the signal attribute to indicate that the interrupt service routine should start with a SEI instruction to globally re-enable interrupts. The difference to the interrupt attribute is that the noblock attribute just acts like a flag and does not impose a specific function name.
• Support has been added for the __builtin_avr_mask1 built-in function. It can be used to compute some bit masks when code like 1 << offset is not fast enough.

IA-32/x86-64

• New ISA extension support for Intel AVX10.2 was added. AVX10.2 intrinsics are available via the -mavx10.2 or -mavx10.2-256 compiler switch with 256-bit vector size support. 512-bit vector size support for AVX10.2 intrinsics are available via the -mavx10.2-512 compiler switch.
• Support for Xeon Phi CPUs (a.k.a. Knight Landing and Knight Mill) were removed in GCC 15. GCC will no longer accept -march=knl, -march=knm,-mavx5124fmaps, -mavx5124vnniw, -mavx512er, -mavx512pf, -mprefetchwt1, -mtune=knl or -mtune=knm compiler switches.

NVPTX

• GCC's nvptx target now supports constructors and destructors. For this, a recent version of nvptx-tools is required.

Operating Systems

PowerPC Darwin

• Fortran's IEEE modules are now suppored on Darwin PowerPC.

Other significant improvements