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clang-p2996/llvm/docs/ReleaseNotes.md
David Spickett b9f09a43b4 [llvm][docs] Convert LLVM release notes to Markdown (#109107) 
* Markdown is the most common format on GitHub and most contributors are
more familiar with it than RST.
* This leads to mistakes in the RST syntax and/or folks just using
Markdown syntax and assuming it works.
* The release notes have a high number of edits and a high number of
views, we should optimise for making the common path easy. That is,
adding a bullet point and a link.
* Though GitHub can render RST and Markdown, its support for Markdown is
more complete (and neither handle the Sphinx directives well).
* We already have some Markdown docs in the llvm docs.

To keep the original formatting we do need some Sphinx directives still,
and those are provided by MyST which is already enabled.

https://myst-parser.readthedocs.io/en/latest/

I did have to enable an extension so we can substitute in the release
version.


https://myst-parser.readthedocs.io/en/latest/syntax/optional.html#substitutions-with-jinja2

Needing to use MyST means there is some special knowledge needed if you
want to do advanced things, but at least the basics remain Markdown.
Even in RST form, you still had to look up Sphinx syntax.

I also make use of a nested directive

https://myst-parser.readthedocs.io/en/latest/syntax/roles-and-directives.html#nesting-directives
to implement the prerelease warning.

The note about sections referred to another note that got removed in
4c72deb613. I presume accidentally, so I
have restored that.

I also removed the "Update on required toolchains to build LLVM" header
because the section is now empty.

The other difference is that the table of contents now has a heading
"Contents". This is the default and I could not find a way to remove
that name. Otherwise it's the same table as you'd get from the RST
document.
2024-09-26 14:15:53 +01:00

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LLVM {{env.config.release}} Release Notes

```{warning} These are in-progress notes for the upcoming LLVM {{env.config.release}}
             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 {{env.config.release}}. 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

  • ...

Changes to the LLVM IR

  • The x86_mmx IR type has been removed. It will be translated to the standard vector type <1 x i64> in bitcode upgrade.

  • Renamed llvm.experimental.stepvector intrinsic to llvm.stepvector.

  • Added usub_cond and usub_sat operations to atomicrmw.

  • Remove the following intrinsics which can be replaced with a bitcast:

    • llvm.nvvm.bitcast.f2i
    • llvm.nvvm.bitcast.i2f
    • llvm.nvvm.bitcast.d2ll
    • llvm.nvvm.bitcast.ll2d

  • Remove the following intrinsics which can be replaced with a funnel-shift:

    • llvm.nvvm.rotate.b32
    • llvm.nvvm.rotate.right.b64
    • llvm.nvvm.rotate.b64

  • Remove the following intrinsics which can be replaced with an addrspacecast:

    • llvm.nvvm.ptr.gen.to.global
    • llvm.nvvm.ptr.gen.to.shared
    • llvm.nvvm.ptr.gen.to.constant
    • llvm.nvvm.ptr.gen.to.local
    • llvm.nvvm.ptr.global.to.gen
    • llvm.nvvm.ptr.shared.to.gen
    • llvm.nvvm.ptr.constant.to.gen
    • llvm.nvvm.ptr.local.to.gen

Changes to LLVM infrastructure

Changes to building LLVM

Changes to TableGen

Changes to Interprocedural Optimizations

Changes to the AArch64 Backend

  • .balign N, 0, .p2align N, 0, .align N, 0 in code sections will now fill the required alignment space with a sequence of 0x0 bytes (the requested fill value) rather than NOPs.

Changes to the AMDGPU Backend

  • Removed llvm.amdgcn.flat.atomic.fadd and llvm.amdgcn.global.atomic.fadd intrinsics. Users should use the {ref}atomicrmw <i_atomicrmw> instruction with fadd and addrspace(0) or addrspace(1) instead.

Changes to the ARM Backend

  • .balign N, 0, .p2align N, 0, .align N, 0 in code sections will now fill the required alignment space with a sequence of 0x0 bytes (the requested fill value) rather than NOPs.

Changes to the AVR Backend

Changes to the DirectX Backend

Changes to the Hexagon Backend

Changes to the LoongArch Backend

Changes to the MIPS Backend

Changes to the PowerPC Backend

Changes to the RISC-V Backend

  • .balign N, 0, .p2align N, 0, .align N, 0 in code sections will now fill the required alignment space with a sequence of 0x0 bytes (the requested fill value) rather than NOPs.
  • Added Syntacore SCR4 and SCR5 CPUs: -mcpu=syntacore-scr4/5-rv32/64
  • -mcpu=sifive-p470 was added.
  • Added Hazard3 CPU as taped out for RP2350: -mcpu=rp2350-hazard3 (32-bit only).
  • Fixed length vector support using RVV instructions now requires VLEN>=64. This means Zve32x and Zve32f will also require Zvl64b. The prior support was largely untested.
  • The Zvbc32e and Zvkgs extensions are now supported experimentally.
  • Added Smctr and Ssctr extensions.
  • -mcpu=syntacore-scr7 was added.
  • The Zacas extension is no longer marked as experimental.

Changes to the WebAssembly Backend

Changes to the Windows Target

Changes to the X86 Backend

  • .balign N, 0x90, .p2align N, 0x90, and .align N, 0x90 in code sections now fill the required alignment space with repeating 0x90 bytes, rather than using optimised NOP filling. Optimised NOP filling fills the space with NOP instructions of various widths, not just those that use the 0x90 byte encoding. To use optimised NOP filling in a code section, leave off the "fillval" argument, i.e. .balign N, .p2align N or .align N respectively.

  • Due to the removal of the x86_mmx IR type, functions with x86_mmx arguments or return values will use a different, incompatible, calling convention ABI. Such functions are not generally seen in the wild (Clang never generates them!), so this is not expected to result in real-world compatibility problems.

  • Support ISA of AVX10.2-256 and AVX10.2-512.

Changes to the OCaml bindings

Changes to the Python bindings

Changes to the C API

  • The following symbols are deleted due to the removal of the x86_mmx IR type:

    • LLVMX86_MMXTypeKind
    • LLVMX86MMXTypeInContext
    • LLVMX86MMXType

  • The following functions are added to further support non-null-terminated strings:

  • LLVMGetNamedFunctionWithLength

  • LLVMGetNamedGlobalWithLength

  • The following functions are added to access the LLVMContextRef associated with LLVMValueRef and LLVMBuilderRef objects:

    • LLVMGetValueContext
    • LLVMGetBuilderContext

  • The new pass manager can now be invoked with a custom alias analysis pipeline, using the LLVMPassBuilderOptionsSetAAPipeline function.

  • It is now also possible to run the new pass manager on a single function, by calling LLVMRunPassesOnFunction instead of LLVMRunPasses.

  • Support for creating instructions with custom synchronization scopes has been added:

    • LLVMGetSyncScopeID to map a synchronization scope name to an ID.
    • LLVMBuildFenceSyncScope, LLVMBuildAtomicRMWSyncScope and LLVMBuildAtomicCmpXchgSyncScope versions of the existing builder functions with an additional synchronization scope ID parameter.
    • LLVMGetAtomicSyncScopeID and LLVMSetAtomicSyncScopeID to get and set the synchronization scope of any atomic instruction.
    • LLVMIsAtomic to check if an instruction is atomic, for use with the above functions. Because of backwards compatibility, LLVMIsAtomicSingleThread and LLVMSetAtomicSingleThread continue to work with any instruction type.

  • The LLVMSetPersonalityFn and LLVMSetInitializer APIs now support clearing the personality function and initializer respectively by passing a null pointer.

  • The following functions are added to allow iterating over debug records attached to instructions:

    • LLVMGetFirstDbgRecord
    • LLVMGetLastDbgRecord
    • LLVMGetNextDbgRecord
    • LLVMGetPreviousDbgRecord

  • Added LLVMAtomicRMWBinOpUSubCond and LLVMAtomicRMWBinOpUSubSat to LLVMAtomicRMWBinOp enum for AtomicRMW instructions.

Changes to the CodeGen infrastructure

Changes to the Metadata Info

Changes to the Debug Info

Changes to the LLVM tools

Changes to LLDB

Changes to BOLT

Changes to Sanitizers

Other Changes

External Open Source Projects Using LLVM {{env.config.release}}

  • 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 Discourse forums.

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