233659c7ae
LoopFlatten has been in the code base off by default for years, but this enables it to run by default. Downstream this has been running for years, so it has been exposed to quite some code. Then around the time we switched to the NPM, several fixes went in related to updating the MemorySSA state and we moved it to a loop pass manager, which both helped preventing rerunning certain analysis passes, and thus helped a bit with compile-times. About compile-times, adding a pass isn't free, but this should see only very minor increases. The pass is relatively simple and there shouldn't be anything algorithmically expensive because all it does is looking at inner/outer loops and it checks assumptions on loop increments and indices. If we see increases, I expect this to mainly come from invalidation of analysis info, and perhaps subsequent passes to trigger and do more. Despite its simplicity/restrictions, it triggers in most code-bases, which makes it worth to enable this by default. Differential Revision: https://reviews.llvm.org/D109958
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============================
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LLVM |release| Release Notes
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============================
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.. contents::
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:local:
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.. only:: PreRelease
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.. warning::
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These are in-progress notes for the upcoming LLVM |version| release.
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Release notes for previous releases can be found on
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`the Download Page <https://releases.llvm.org/download.html>`_.
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* The LoopFlatten pass is now enabled by default.
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Introduction
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============
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This document contains the release notes for the LLVM Compiler Infrastructure,
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release |release|. Here we describe the status of LLVM, including major improvements
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from the previous release, improvements in various subprojects of LLVM, and
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some of the current users of the code. All LLVM releases may be downloaded
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from the `LLVM releases web site <https://llvm.org/releases/>`_.
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For more information about LLVM, including information about the latest
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release, please check out the `main LLVM web site <https://llvm.org/>`_. If you
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have questions or comments, the `Discourse forums
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<https://discourse.llvm.org>`_ is a good place to ask
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them.
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Note that if you are reading this file from a Git checkout or the main
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LLVM web page, this document applies to the *next* release, not the current
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one. To see the release notes for a specific release, please see the `releases
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page <https://llvm.org/releases/>`_.
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Non-comprehensive list of changes in this release
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=================================================
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.. NOTE
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For small 1-3 sentence descriptions, just add an entry at the end of
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this list. If your description won't fit comfortably in one bullet
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point (e.g. maybe you would like to give an example of the
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functionality, or simply have a lot to talk about), see the `NOTE` below
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for adding a new subsection.
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* The ``readnone`` calls which are crossing suspend points in coroutines will
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not be merged. Since ``readnone`` calls may access thread id and thread id
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is not a constant in coroutines. This decision may cause unnecessary
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performance regressions and we plan to fix it in later versions.
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* ...
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Update on required toolchains to build LLVM
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-------------------------------------------
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LLVM is now built with C++17 by default. This means C++17 can be used in
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the code base.
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The previous "soft" toolchain requirements have now been changed to "hard".
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This means that the the following versions are now required to build LLVM
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and there is no way to suppress this error.
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* GCC >= 7.1
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* Clang >= 5.0
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* Apple Clang >= 9.3
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* Visual Studio 2019 >= 16.7
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Changes to the LLVM IR
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----------------------
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* The constant expression variants of the following instructions has been
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removed:
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* ``fneg``
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Changes to building LLVM
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------------------------
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Changes to TableGen
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-------------------
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Changes to the AArch64 Backend
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------------------------------
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Changes to the AMDGPU Backend
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-----------------------------
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Changes to the ARM Backend
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--------------------------
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* Support for targeting armv2, armv2A, armv3 and armv3M has been removed.
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LLVM did not, and was not ever likely to generate correct code for those
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architecture versions so their presence was misleading.
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Changes to the AVR Backend
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--------------------------
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* ...
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Changes to the DirectX Backend
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------------------------------
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Changes to the Hexagon Backend
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------------------------------
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* ...
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Changes to the MIPS Backend
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---------------------------
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* ...
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Changes to the PowerPC Backend
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------------------------------
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* ...
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Changes to the RISC-V Backend
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-----------------------------
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* Support for the unratified Zbe, Zbf, Zbm, Zbp, Zbr, and Zbt extensions have
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been removed.
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Changes to the WebAssembly Backend
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----------------------------------
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* ...
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Changes to the Windows Target
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-----------------------------
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* For MinGW, generate embedded ``-exclude-symbols:`` directives for symbols
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with hidden visibility, omitting them from automatic export of all symbols.
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This roughly makes hidden visibility work like it does for other object
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file formats.
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Changes to the X86 Backend
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--------------------------
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Changes to the OCaml bindings
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-----------------------------
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Changes to the C API
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--------------------
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* The following functions for creating constant expressions have been removed,
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because the underlying constant expressions are no longer supported. Instead,
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an instruction should be created using the ``LLVMBuildXYZ`` APIs, which will
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constant fold the operands if possible and create an instruction otherwise:
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* ``LLVMConstFNeg``
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Changes to the Go bindings
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--------------------------
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Changes to the FastISel infrastructure
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--------------------------------------
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* ...
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Changes to the DAG infrastructure
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---------------------------------
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Changes to the Metadata Info
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---------------------------------
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* Add Module Flags Metadata ``stack-protector-guard-symbol`` which specify a
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symbol for addressing the stack-protector guard.
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Changes to the Debug Info
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---------------------------------
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During this release ...
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Changes to the LLVM tools
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---------------------------------
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Changes to LLDB
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---------------------------------
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Changes to Sanitizers
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---------------------
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Other Changes
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-------------
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External Open Source Projects Using LLVM 15
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===========================================
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* A project...
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Additional Information
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======================
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A wide variety of additional information is available on the `LLVM web page
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<https://llvm.org/>`_, in particular in the `documentation
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<https://llvm.org/docs/>`_ section. The web page also contains versions of the
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API documentation which is up-to-date with the Git version of the source
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code. You can access versions of these documents specific to this release by
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going into the ``llvm/docs/`` directory in the LLVM tree.
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If you have any questions or comments about LLVM, please feel free to contact
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us via the `Discourse forums <https://discourse.llvm.org>`_.
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