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LLVM 12.0.0 Release Notes
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.. warning::
These are in-progress notes for the upcoming LLVM 12 release.
Release notes for previous releases can be found on
`the Download Page <>`_.
This document contains the release notes for the LLVM Compiler Infrastructure,
release 12.0.0. 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 <>`_.
For more information about LLVM, including information about the latest
release, please check out the `main LLVM web site <>`_. If you
have questions or comments, the `LLVM Developer's Mailing List
<>`_ is a good place to send
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 <>`_.
Non-comprehensive list of changes in this release
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 ConstantPropagation pass was removed. Users should use the InstSimplify
pass instead.
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
* ...
* Added the ``byref`` attribute to better represent argument passing
for the `amdgpu_kernel` calling convention.
* Added type parameter to the ``sret`` attribute to continue work on
removing pointer element types.
* The ``llvm.experimental.vector.reduce`` family of intrinsics have been renamed
to drop the "experimental" from the name, reflecting their now fully supported
status in the IR.
Changes to building LLVM
* The internal ``llvm-build`` Python script and the associated ``LLVMBuild.txt``
files used to describe the LLVM component structure have been removed and
replaced by a pure ``CMake`` approach, where each component stores extra
properties in the created targets. These properties are processed once all
components are defined to resolve library dependencies and produce the header
expected by llvm-config.
Changes to TableGen
* The new "TableGen Programmer's Reference" replaces the "TableGen Language
Introduction" and "TableGen Language Reference" documents.
* The syntax for specifying an integer range in a range list has changed.
The old syntax used a hyphen in the range (e.g., ``{0-9}``). The new syntax
uses the "`...`" range punctuation (e.g., ``{0...9}``). The hyphen syntax
is deprecated.
Changes to the AArch64 Backend
During this release ...
* Lots of improvements to generation of Windows unwind data; the unwind
data is optimized and written in packed form where possible, reducing
the size of unwind data (pdata and xdata sections) by around 60%
compared with LLVM 11. The generation of prologs/epilogs is tweaked
when targeting Windows, to increase the chances of being able to use
the packed unwind info format.
* Support for creating Windows unwind data using ``.seh_*`` assembler
* Produce proper assembly output for the Windows target, including
``:lo12:`` relocation specifiers, to allow the assembly output
to actually be assembled.
* Changed the assembly comment string for MSVC targets to ``//`` (consistent
with the MinGW and ELF targets), freeing up ``;`` to be used as
statement separator.
Changes to the ARM Backend
During this release ...
Changes to the MIPS Target
During this release ...
Changes to the PowerPC Target
* Made improvements to loop unroll-and-jam including fix to respect user
provided #pragma unroll-and-jam for loops on targets other than ARM.
* Improved PartialInliner allowing it to handle code regions in a switch
* Improved PGO support on AIX by building and linking with compiler-rt profile
* Add support for Epilogue Vectorization and enabled it by default.
* POWER10 support
* Implementation of PC Relative addressing in LLD including the associated
linker optimizations.
* Add support for the new matrix multiplication (MMA) instructions to Clang
and LLVM.
* Implementation of Power10 builtins.
* Scheduling enhancements
* Add a new algorithm to cluster more loads/stores if the DAG is not too
* Enable the PowerPC scheduling heuristic for Power10.
* Target dependent passes tuning
* Enhance LoopStrengthReduce/PPCLoopInstrFormPrep pass for PowerPC,
especially for P10 intrinsics.
* Enhance machine combiner pass to reduce register pressure for PowerPC.
* Improve MachineSink to do more sinking based on register pressure and alias
* General improvements
* Complete the constrained floating point operations support.
* Improve the llvm-exegesis support.
* Improve the stack clash protection to probe the gap between stackptr and
realigned stackptr.
* Improve the IEEE long double support for Power8.
* Enable MemorySSA for LoopSink.
* Enhance LLVM debugging functionality via options such as -print-changed and
* Add builtins for Power9 (i.e. darn, xvtdiv, xvtsqrt etc).
* Add options to disable all or part of LoopIdiomRecognizePass.
* Add support for printing the DDG in DOT form allowing for visual inspection
of the Data Dependence Graph.
* Remove the QPX support.
* Significant number of bug fixes including all the fixes necessary to
achieve a clean test run for Julia.
AIX Support:
* Compiler-rt support
* Add support for building compiler-rt for AIX and 32-bit Power targets.
* Made compiler-rt the default rtlib for AIX.
* General Improvements
* Enable the AIX extended AltiVec ABI under option -mabi=vec-extabi.
* Add partial C99 complex type support.
* Implemente traceback table for functions (encodes vector information,
emits exception handling).
* Implemente code generation for C++ dynamic initialization and finalization.
of non-local variables for use with the -bcdtors option of the AIX linker.
* Add new option -mignore-xcoff-visibility.
* Enable explicit sections on AIX.
* Enable -f[no-]data-sections on AIX and set -fdata-sections to be the default
on AIX.
* Enable -f[no-]function-sections.
* Add support for relocation generation using the large code model.
* Add pragma align natural and sorted out pragma pack stack effect.
Changes to the X86 Target
During this release ...
* The 'mpx' feature was removed from the backend. It had been removed from clang
frontend in 10.0. Mention of the 'mpx' feature in an IR file will print a
message to stderr, but IR should still compile.
* Support for ``-march=alderlake``, ``-march=sapphirerapids``,
``-march=znver3`` and ``-march=x86-64-v[234]`` has been added.
* The assembler now has support for {disp32} and {disp8} pseudo prefixes for
controlling displacement size for memory operands and jump displacements. The
assembler also supports the .d32 and .d8 mnemonic suffixes to do the same.
* A new function attribute "tune-cpu" has been added to support -mtune like gcc.
This allows microarchitectural optimizations to be applied independent from
the "target-cpu" attribute or TargetMachine CPU which will be used to select
Instruction Set. If the attribute is not present, the tune CPU will follow
the target CPU.
* Support for ``HRESET`` instructions has been added.
* Support for ``UINTR`` instructions has been added.
* Support for ``AVXVNNI`` instructions has been added.
Changes to the AMDGPU Target
During this release ...
* The new ``byref`` attribute is now the preferred method for
representing aggregate kernel arguments.
Changes to the AVR Target
During this release ...
Changes to the WebAssembly Target
During this release ...
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
During this release ...
* The DIModule metadata is extended with a field to indicate if it is a
module declaration. This extension enables the emission of debug info
for a Fortran 'use <external module>' statement. For more information
on what the debug info entries should look like and how the debugger
can use them, please see test/DebugInfo/X86/dimodule-external-fortran.ll.
Changes to the LLVM tools
* llvm-readobj and llvm-readelf behavior has changed to report an error when
executed with no input files instead of reading an input from stdin.
Reading from stdin can still be achieved by specifying `-` as an input file.
* llvm-mca supports serialization of the timeline and summary views.
The `--json` command line option prints a JSON representation of
these views to stdout.
Changes to LLDB
Changes to Sanitizers
The integer sanitizer `-fsanitize=integer` now has a new sanitizer:
`-fsanitize=unsigned-shift-base`. It's not undefined behavior for an unsigned
left shift to overflow (i.e. to shift bits out), but it has been the source of
bugs and exploits in certain codebases in the past.
Many Sanitizers (asan, cfi, lsan, msan, tsan, ubsan) have support for
musl-based Linux distributions. Some of them may be rudimentary.
External Open Source Projects Using LLVM 12
* A project...
Additional Information
A wide variety of additional information is available on the `LLVM web page
<>`_, in particular in the `documentation
<>`_ 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 <>`_.