| ========================= |
| LLVM 11.0.0 Release Notes |
| ========================= |
| |
| .. contents:: |
| :local: |
| |
| .. warning:: |
| These are in-progress notes for the upcoming LLVM 11 release. |
| Release notes for previous releases can be found on |
| `the Download Page <https://releases.llvm.org/download.html>`_. |
| |
| |
| Introduction |
| ============ |
| |
| This document contains the release notes for the LLVM Compiler Infrastructure, |
| release 11.0.0. Here we describe the status of LLVM, including major improvements |
| from the previous release, improvements in various subprojects of LLVM, and |
| some of the current users of the code. All LLVM releases may be downloaded |
| from the `LLVM releases web site <https://llvm.org/releases/>`_. |
| |
| For more information about LLVM, including information about the latest |
| release, please check out the `main LLVM web site <https://llvm.org/>`_. If you |
| have questions or comments, the `LLVM Developer's Mailing List |
| <https://lists.llvm.org/mailman/listinfo/llvm-dev>`_ is a good place to send |
| them. |
| |
| Note that if you are reading this file from a Git checkout or the main |
| LLVM web page, this document applies to the *next* release, not the current |
| one. To see the release notes for a specific release, please see the `releases |
| page <https://llvm.org/releases/>`_. |
| |
| Deprecated and Removed Features/APIs |
| ================================================= |
| * BG/Q support, including QPX, will be removed in the 12.0.0 release. |
| |
| Non-comprehensive list of changes in this release |
| ================================================= |
| .. NOTE |
| For small 1-3 sentence descriptions, just add an entry at the end of |
| this list. If your description won't fit comfortably in one bullet |
| point (e.g. maybe you would like to give an example of the |
| functionality, or simply have a lot to talk about), see the `NOTE` below |
| for adding a new subsection. |
| |
| * ... |
| |
| |
| .. NOTE |
| If you would like to document a larger change, then you can add a |
| subsection about it right here. You can copy the following boilerplate |
| and un-indent it (the indentation causes it to be inside this comment). |
| |
| Special New Feature |
| ------------------- |
| |
| Makes programs 10x faster by doing Special New Thing. |
| |
| |
| Changes to the LLVM IR |
| ---------------------- |
| |
| * The callsite attribute `vector-function-abi-variant |
| <https://llvm.org/docs/LangRef.html#call-site-attributes>`_ has been |
| added to describe the mapping between scalar functions and vector |
| functions, to enable vectorization of call sites. The information |
| provided by the attribute is interfaced via the API provided by the |
| ``VFDatabase`` class. When scanning through the set of vector |
| functions associated with a scalar call, the loop vectorizer now |
| relies on ``VFDatabase``, instead of ``TargetLibraryInfo``. |
| |
| * `dereferenceable` attributes and metadata on pointers no longer imply |
| anything about the alignment of the pointer in question. Previously, some |
| optimizations would make assumptions based on the type of the pointer. This |
| behavior was undocumented. To preserve optimizations, frontends may need to |
| be updated to generate appropriate `align` attributes and metadata. |
| |
| * The DIModule metadata is extended to contain file and line number |
| information. This information is used to represent Fortran modules debug |
| info at IR level. |
| |
| * LLVM IR now supports two distinct ``llvm::FixedVectorType`` and |
| ``llvm::ScalableVectorType`` vector types, both derived from the |
| base class ``llvm::VectorType``. A number of algorithms dealing with |
| IR vector types have been updated to make sure they work for both |
| scalable and fixed vector types. Where possible, the code has been |
| made generic to cover both cases using the base class. Specifically, |
| places that were using the type ``unsigned`` to count the number of |
| lanes of a vector are now using ``llvm::ElementCount``. In places |
| where ``uint64_t`` was used to denote the size in bits of a IR type |
| we have partially migrated the codebase to using ``llvm::TypeSize``. |
| |
| Changes to building LLVM |
| ------------------------ |
| |
| Changes to the AArch64 Backend |
| ------------------------------ |
| |
| * Back up and restore x18 in functions with windows calling convention on |
| non-windows OSes. |
| |
| * Clearly error out on unsupported relocations when targeting COFF, instead |
| of silently accepting some (without being able to do what was requested). |
| |
| Changes to the ARM Backend |
| -------------------------- |
| |
| During this release ... |
| |
| * Implemented C-language intrinsics for the full Arm v8.1-M MVE instruction |
| set. ``<arm_mve.h>`` now supports the complete API defined in the Arm C |
| Language Extensions. |
| |
| * Added support for assembly for the optional Custom Datapath Extension (CDE) |
| for Arm M-profile targets. |
| |
| * Implemented C-language intrinsics ``<arm_cde.h>`` for the CDE instruction set. |
| |
| * Clang now defaults to ``-fomit-frame-pointer`` when targeting non-Android |
| Linux for arm and thumb when optimizations are enabled. Users that were |
| previously not specifying a value and relying on the implicit compiler |
| default may wish to specify ``-fno-omit-frame-pointer`` to get the old |
| behavior. This improves compatibility with GCC. |
| |
| * Clang adds support for the following macros that enable the |
| C-intrinsics from the `Arm C language extensions for SVE |
| <https://developer.arm.com/documentation/100987/>`_ (version |
| ``00bet5``, see section 2.1 for the list of intrinsics associated to |
| each macro): |
| |
| |
| ================================= ================= |
| Preprocessor macro Target feature |
| ================================= ================= |
| ``__ARM_FEATURE_SVE`` ``+sve`` |
| ``__ARM_FEATURE_SVE_BF16`` ``+sve+bf16`` |
| ``__ARM_FEATURE_SVE_MATMUL_FP32`` ``+sve+f32mm`` |
| ``__ARM_FEATURE_SVE_MATMUL_FP64`` ``+sve+f64mm`` |
| ``__ARM_FEATURE_SVE_MATMUL_INT8`` ``+sve+i8mm`` |
| ``__ARM_FEATURE_SVE2`` ``+sve2`` |
| ``__ARM_FEATURE_SVE2_AES`` ``+sve2-aes`` |
| ``__ARM_FEATURE_SVE2_BITPERM`` ``+sve2-bitperm`` |
| ``__ARM_FEATURE_SVE2_SHA3`` ``+sve2-sha3`` |
| ``__ARM_FEATURE_SVE2_SM4`` ``+sve2-sm4`` |
| ================================= ================= |
| |
| The macros enable users to write C/C++ `Vector Length Agnostic |
| (VLA)` loops, that can be executed on any CPU that implements the |
| underlying instructions supported by the C intrinsics, independently |
| of the hardware vector register size. |
| |
| For example, the ``__ARM_FEATURE_SVE`` macro is enabled when |
| targeting AArch64 code generation by setting ``-march=armv8-a+sve`` |
| on the command line. |
| |
| .. code-block:: c |
| :caption: Example of VLA addition of two arrays with SVE ACLE. |
| |
| // Compile with: |
| // `clang++ -march=armv8a+sve ...` (for c++) |
| // `clang -stc=c11 -march=armv8a+sve ...` (for c) |
| #include <arm_sve.h> |
| |
| void VLA_add_arrays(double *x, double *y, double *out, unsigned N) { |
| for (unsigned i = 0; i < N; i += svcntd()) { |
| svbool_t Pg = svwhilelt_b64(i, N); |
| svfloat64_t vx = svld1(Pg, &x[i]); |
| svfloat64_t vy = svld1(Pg, &y[i]); |
| svfloat64_t vout = svadd_x(Pg, vx, vy); |
| svst1(Pg, &out[i], vout); |
| } |
| } |
| |
| Changes to the MIPS Target |
| -------------------------- |
| |
| During this release ... |
| |
| |
| Changes to the PowerPC Target |
| ----------------------------- |
| |
| During this release ... |
| |
| Changes to the X86 Target |
| ------------------------- |
| |
| During this release ... |
| |
| |
| * Functions with the probe-stack attribute set to "inline-asm" are now protected |
| against stack clash without the need of a third-party probing function and |
| with limited impact on performance. |
| * -x86-enable-old-knl-abi command line switch has been removed. v32i16/v64i8 |
| vectors are always passed in ZMM register when avx512f is enabled and avx512bw |
| is disabled. |
| * Vectors larger than 512 bits with i16 or i8 elements will be passed in |
| multiple ZMM registers when avx512f is enabled. Previously this required |
| avx512bw otherwise they would split into multiple YMM registers. This means |
| vXi16/vXi8 vectors are consistently treated the same as |
| vXi32/vXi64/vXf64/vXf32 vectors of the same total width. |
| |
| Changes to the AMDGPU Target |
| ----------------------------- |
| |
| * The backend default denormal handling mode has been switched to on |
| for all targets for all compute function types. Frontends wishing to |
| retain the old behavior should explicitly request f32 denormal |
| flushing. |
| |
| Changes to the AVR Target |
| ----------------------------- |
| |
| * Moved from an experimental backend to an official backend. AVR support is now |
| included by default in all LLVM builds and releases and is available under |
| the "avr-unknown-unknown" target triple. |
| |
| Changes to the WebAssembly Target |
| --------------------------------- |
| |
| * Programs which don't have a "main" function, called "reactors" are now |
| properly supported, with a new `-mexec-model=reactor` flag. Programs which |
| previously used `-Wl,--no-entry` to avoid having a main function should |
| switch to this new flag, so that static initialization is properly |
| performed. |
| |
| * `__attribute__((visibility("protected")))` now evokes a warning, as |
| WebAssembly does not support "protected" visibility. |
| |
| Changes to the Windows Target |
| ----------------------------- |
| |
| * Produce COFF weak external symbols for IR level weak symbols without a comdat |
| (e.g. for `__attribute__((weak))` in C) |
| |
| Changes to the OCaml bindings |
| ----------------------------- |
| |
| |
| |
| Changes to the C API |
| -------------------- |
| |
| |
| Changes to the Go bindings |
| -------------------------- |
| |
| |
| Changes to the DAG infrastructure |
| --------------------------------- |
| |
| |
| Changes to the Debug Info |
| --------------------------------- |
| |
| * LLVM now supports the debug entry values (DW_OP_entry_value) production for |
| the x86, ARM, and AArch64 targets by default. Other targets can use |
| the utility by using the experimental option ("-debug-entry-values"). |
| This is a debug info feature that allows debuggers to recover the value of |
| optimized-out parameters by going up a stack frame and interpreting the values |
| passed to the callee. The feature improves the debugging user experience when |
| debugging optimized code. |
| |
| Changes to the LLVM tools |
| --------------------------------- |
| |
| * Added an option (--show-section-sizes) to llvm-dwarfdump to show the sizes |
| of all debug sections within a file. |
| |
| * llvm-nm now implements the flag ``--special-syms`` and will filter out special |
| symbols, i.e. mapping symbols on ARM and AArch64, by default. This matches |
| the GNU nm behavior. |
| |
| * llvm-rc now tolerates -1 as menu item ID, supports the language id option |
| and allows string table values to be split into multiple string literals |
| |
| * llvm-lib supports adding import library objects in addition to regular |
| object files |
| |
| Changes to LLDB |
| =============== |
| |
| External Open Source Projects Using LLVM 11 |
| =========================================== |
| |
| * A project... |
| |
| Additional Information |
| ====================== |
| |
| A wide variety of additional information is available on the `LLVM web page |
| <https://llvm.org/>`_, in particular in the `documentation |
| <https://llvm.org/docs/>`_ section. The web page also contains versions of the |
| API documentation which is up-to-date with the Git version of the source |
| code. You can access versions of these documents specific to this release by |
| going into the ``llvm/docs/`` directory in the LLVM tree. |
| |
| If you have any questions or comments about LLVM, please feel free to contact |
| us via the `mailing lists <https://llvm.org/docs/#mailing-lists>`_. |