LLVM 12.0.0 Release Notes

Warning

These are in-progress notes for the upcoming LLVM 12 release. Release notes for previous releases can be found on the Download Page.

Introduction

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 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.

Non-comprehensive list of changes in this release

  • The ConstantPropagation pass was removed. Users should use the InstSimplify pass instead.

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 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 ARM Backend

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Changes to the MIPS Target

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Changes to the PowerPC Target

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Changes to the X86 Target

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  • 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

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Changes to the WebAssembly Target

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Changes to the Debug Info

During this release …

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.

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.

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.

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