LLVM 16.0.0git Release Notes

Warning

These are in-progress notes for the upcoming LLVM 16 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 16.0.0git. 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 Discourse forums is a good place to ask 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 readnone calls which are crossing suspend points in coroutines will not be merged. Since readnone calls may access thread id and thread id is not a constant in coroutines. This decision may cause unnecessary performance regressions and we plan to fix it in later versions.
  • The LoopFlatten pass is now enabled by default.

Update on required toolchains to build LLVM

LLVM is now built with C++17 by default. This means C++17 can be used in the code base.

The previous “soft” toolchain requirements have now been changed to “hard”. This means that the the following versions are now required to build LLVM and there is no way to suppress this error.

  • GCC >= 7.1
  • Clang >= 5.0
  • Apple Clang >= 10.0
  • Visual Studio 2019 >= 16.7

Changes to the LLVM IR

  • The readnone, readonly, writeonly, argmemonly, inaccessiblememonly and inaccessiblemem_or_argmemonly function attributes have been replaced by a single memory(...) attribute. The old attributes may be mapped to the new one as follows:
    • readnone -> memory(none)
    • readonly -> memory(read)
    • writeonly -> memory(write)
    • argmemonly -> memory(argmem: readwrite)
    • argmemonly readonly -> memory(argmem: read)
    • argmemonly writeonly -> memory(argmem: write)
    • inaccessiblememonly -> memory(inaccessiblemem: readwrite)
    • inaccessiblememonly readonly -> memory(inaccessiblemem: read)
    • inaccessiblememonly writeonly -> memory(inaccessiblemem: write)
    • inaccessiblemem_or_argmemonly -> memory(argmem: readwrite, inaccessiblemem: readwrite)
    • inaccessiblemem_or_argmemonly readonly -> memory(argmem: read, inaccessiblemem: read)
    • inaccessiblemem_or_argmemonly writeonly -> memory(argmem: write, inaccessiblemem: write)
  • The constant expression variants of the following instructions has been removed:
    • fneg

Changes to the AArch64 Backend

  • Added support for the Cortex-A715 CPU.
  • Added support for the Cortex-X3 CPU.
  • Added support for assembly for RME MEC (Memory Encryption Contexts).

Changes to the ARM Backend

  • Support for targeting armv2, armv2A, armv3 and armv3M has been removed. LLVM did not, and was not ever likely to generate correct code for those architecture versions so their presence was misleading.

Changes to the RISC-V Backend

  • Support for the unratified Zbe, Zbf, Zbm, Zbp, Zbr, and Zbt extensions have been removed.
  • i32 is now a native type in the datalayout string. This enables LoopStrengthReduce for loops with i32 induction variables, among other optimizations.

Changes to the Windows Target

  • For MinGW, generate embedded -exclude-symbols: directives for symbols with hidden visibility, omitting them from automatic export of all symbols. This roughly makes hidden visibility work like it does for other object file formats.

Changes to the X86 Backend

  • Add support for the RDMSRLIST and WRMSRLIST instructions.
  • Add support for the WRMSRNS instruction.
  • Support ISA of AMX-FP16 which contains tdpfp16ps instruction.
  • Support ISA of CMPCCXADD.
  • Support ISA of AVX-IFMA.
  • Support ISA of AVX-VNNI-INT8.
  • Support ISA of AVX-NE-CONVERT.
  • -mcpu=raptorlake and -mcpu=meteorlake are now supported.
  • -mcpu=sierraforest, -mcpu=graniterapids and -mcpu=grandridge are now supported.

Changes to the C API

  • The following functions for creating constant expressions have been removed, because the underlying constant expressions are no longer supported. Instead, an instruction should be created using the LLVMBuildXYZ APIs, which will constant fold the operands if possible and create an instruction otherwise:
    • LLVMConstFNeg

Changes to the Metadata Info

  • Add Module Flags Metadata stack-protector-guard-symbol which specify a symbol for addressing the stack-protector guard.

Changes to the Debug Info

Previously when emitting DWARF v4 and tuning for GDB, llc would use DWARF v2’s DW_AT_bit_offset and DW_AT_data_member_location. llc now uses DWARF v4’s DW_AT_data_bit_offset regardless of tuning.

Support for DW_AT_data_bit_offset was added in GDB 8.0. For earlier versions, you can use llc’s -dwarf-version=3 option to emit compatible DWARF.

Changes to the LLVM tools

  • llvm-readobj --elf-output-style=JSON no longer prefixes each JSON object with the file name. Previously, each object file’s output looked like "main.o":{"FileSummary":{"File":"main.o"},...} but is now {"FileSummary":{"File":"main.o"},...}. This allows each JSON object to be parsed in the same way, since each object no longer has a unique key. Tools that consume llvm-readobj’s JSON output should update their parsers accordingly.
  • llvm-objdump now uses --print-imm-hex by default, which brings its default behavior closer in line with objdump.

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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