| ========================= |
| LLVM 10.0.0 Release Notes |
| ========================= |
| |
| .. contents:: |
| :local: |
| |
| .. warning:: |
| These are in-progress notes for the upcoming LLVM 10 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 10.0.0. 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 Subversion 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/>`_. |
| |
| 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. |
| |
| * The ISD::FP_ROUND_INREG opcode and related code was removed from SelectionDAG. |
| * Enabled MemorySSA as a loop dependency. Since |
| `r370957 <https://reviews.llvm.org/rL370957>`_ |
| (`D58311 <https://reviews.llvm.org/D58311>`_ ``[MemorySSA & LoopPassManager] |
| Enable MemorySSA as loop dependency. Update tests.``), the MemorySSA analysis |
| is being preserved and used by a series of loop passes. The most significant |
| use is in LICM, where the instruction hoisting and sinking relies on aliasing |
| information provided by MemorySSA vs previously creating an AliasSetTracker. |
| The LICM step of promoting variables to scalars still relies on the creation |
| of an AliasSetTracker, but its use is reduced to only be enabled for loops |
| with a small number of overall memory instructions. This choice was motivated |
| by experimental results showing compile and run time benefits or replacing the |
| AliasSetTracker usage with MemorySSA without any performance penalties. |
| The fact that MemorySSA is now preserved by and available in a series of loop |
| passes, also opens up opportunities for its use in those respective passes. |
| |
| .. 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. |
| |
| * As per :ref:`LLVM Language Reference Manual <i_getelementptr>`, |
| ``getelementptr inbounds`` can not change the null status of a pointer, |
| meaning it can not produce non-null pointer given null base pointer, and |
| likewise given non-null base pointer it can not produce null pointer; if it |
| does, the result is a :ref:`poison value <poisonvalues>`. |
| Since `r369789 <https://reviews.llvm.org/rL369789>`_ |
| (`D66608 <https://reviews.llvm.org/D66608>`_ ``[InstCombine] icmp eq/ne (gep |
| inbounds P, Idx..), null -> icmp eq/ne P, null``) LLVM uses that for |
| transformations. If the original source violates these requirements this |
| may result in code being miscompiled. If you are using Clang front-end, |
| Undefined Behaviour Sanitizer ``-fsanitize=pointer-overflow`` check |
| will now catch such cases. |
| |
| * The Loop Idiom Recognition (``-loop-idiom``) pass has learned to recognize |
| ``bcmp`` pattern, and convert it into a call to ``bcmp`` (or ``memcmp``) |
| function. |
| |
| Changes to the LLVM IR |
| ---------------------- |
| |
| * Unnamed function arguments now get printed with their automatically |
| generated name (e.g. "i32 %0") in definitions. This may require front-ends |
| to update their tests; if so there is a script utils/add_argument_names.py |
| that correctly converted 80-90% of Clang tests. Some manual work will almost |
| certainly still be needed. |
| |
| |
| Changes to building LLVM |
| ------------------------ |
| |
| Changes to the ARM Backend |
| -------------------------- |
| |
| During this release ... |
| |
| |
| Changes to the MIPS Target |
| -------------------------- |
| |
| During this release ... |
| |
| |
| Changes to the PowerPC Target |
| ----------------------------- |
| |
| During this release ... |
| |
| Changes to the X86 Target |
| ------------------------- |
| |
| During this release ... |
| |
| * Less than 128 bit vector types, v2i32, v4i16, v2i16, v8i8, v4i8, and v2i8, are |
| now stored in the lower bits of an xmm register and the upper bits are |
| undefined. Previously the elements were spread apart with undefined bits in |
| between them. |
| * v32i8 and v64i8 vectors with AVX512F enabled, but AVX512BW disabled will now |
| be passed in ZMM registers for calls and returns. Previously they were passed |
| in two YMM registers. Old behavior can be enabled by passing |
| -x86-enable-old-knl-abi |
| * -mprefer-vector-width=256 is now the default behavior skylake-avx512 and later |
| Intel CPUs. This tries to limit the use of 512-bit registers which can cause a |
| decrease in CPU frequency on these CPUs. This can be re-enabled by passing |
| -mprefer-vector-width=512 to clang or passing -mattr=-prefer-256-bit to llc. |
| |
| Changes to the AMDGPU Target |
| ----------------------------- |
| |
| Changes to the AVR Target |
| ----------------------------- |
| |
| During this release ... |
| |
| * Deprecated the mpx feature flag for the Intel MPX instructions. There were no |
| intrinsics for this feature. This change only this effects the results |
| returned by getHostCPUFeatures on CPUs that implement the MPX instructions. |
| |
| Changes to the WebAssembly Target |
| --------------------------------- |
| |
| During this release ... |
| |
| |
| Changes to the OCaml bindings |
| ----------------------------- |
| |
| |
| |
| Changes to the C API |
| -------------------- |
| |
| |
| Changes to the DAG infrastructure |
| --------------------------------- |
| |
| Changes to LLDB |
| =============== |
| |
| External Open Source Projects Using LLVM 10 |
| =========================================== |
| |
| * 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 Subversion 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>`_. |