LLVM 23.1.0 Release Notes — LLVM 23.1.0 documentation

# LLVM 23.1.0 Release Notes

## Introduction

This document contains the release notes for the LLVM Compiler Infrastructure, release 23.1.0. 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 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

- Removed `llvm.convert.to.fp16` and `llvm.convert.from.fp16` intrinsics. These are equivalent to `fptrunc` and `fpext` with half with a bitcast.

- “denormal-fp-math” and “denormal-fp-math-f32” string attributes were migrated to first-class denormal_fpenv attribute.

- The `"nooutline"` attribute is now writen as `nooutline`. Existing IR and bitcode will be automatically updated.

- `ConstantPointerNull` can now represent fixed and scalable vector splats of null pointers. Such constants may print as `splat (ptr null)` instead of `zeroinitializer`.

- LLVM IR floating-point literals have greatly changed:

  - The old hexadecimal bitwise representation is deprecated and will be removed in the next revision. It is replaced with a unified `f0x` prefix.

  - Hexadecimal literals akin to C99’s syntax are supported.

  - Special values for infinities and NaNs, including NaN payloads, are added.

- The standard textual output for floating-point literals is changed to take advantage of the new floating-point literals formats.

- The resume/destroy functions emitted for the switch-resume ABI (C++20 coroutines) now use `CallingConv::C` instead of `CallingConv::Fast`. This stabilizes the coroutine ABI across LLVM versions and aligns it with other vendors. The change is observationally identical on targets where `fastcc` and `ccc` agree for `void(ptr)` (x86_64, AArch64, RISC-V, …) but is an ABI break on i686, MIPS O32, PowerPC64 ELFv1, and Lanai.

- Assume bundles now only accept attributes that are actually handled. Specifically, they are `align`, `cold`, `dereferenceable`, `dereferenceable_or_null`, `nonnull`, `noundef` and `separate_storage`.

- Fast math flags are now permitted on `uitofp` and `sitofp`.

- The `modular-format` attribute now supports the `fixed` aspect for C ISO 18037 fixed-point `printf` specifiers.

- Added `noipa` attribute which disables interprocedural analyses that inspect the definition of the function. This attribute does not control inlining or outlining. Add the `noinline` and `nooutline` attributes as well in cases where inlining and outlining should additionally be disabled.

- Added support for `callgraph` metadata. The `!callgraph` metadata associates a function definition with its type identifier and is used for call graph section generation. See the callgraph Metadata section of the LangRef for details.

- The `dereferenceable` and `dereferenceable_or_null` attributes (and corresponding metadata) now apply only at the point of definition, instead of for the execution of the function (for arguments) or forever (for returns).

- `alwaysinline` no longer bypasses inlining compatibility checks based on target features. Inlining will only be performed if it is safe to do so.

- Module-level inline assembly now accepts optional `target_features` and `target_cpu` properties. This resolves errors during LTO on some architectures.

### Changes to LLVM infrastructure

- Removed `Constant::isZeroValue`. It was functionally identical to `Constant::isNullValue` for all types except floating-point negative zero. All callers should use `isNullValue` instead. `isZeroValue` will be reintroduced in the future with bitwise-all-zeros semantics to support non-zero null pointers.

- Added support for specifying the null pointer bit representation per address space in `DataLayout`. Pointer specifications (`p`) accept new flags: `z` (null is all-zeros) and `o` (null is all-ones). Address spaces without an explicit flag default to all-zeros. See the `DataLayout` section of the LangRef for details.

- Removed TypePromoteFloat legalization from SelectionDAG

- Removed `bugpoint`. Usage has been replaced by `llvm-reduce` and `llvm/utils/reduce_pipeline.py`.

- The `Br` opcode was split into two opcodes separating unconditional (`UncondBr`) and conditional (`CondBr`) branches.

- `BranchInst` was deprecated in favor of `UncondBrInst` and `CondBrInst`.

- The operand order of `CondBr` instructions was adjusted to match the successor order. This can cause subtle breakage when using `getOperand` or `setOperand` to access successors.

- The `llvm::sys::fs` link creation API has been refactored:

  - `create_link` now tries to create a symbolic link first, falling back to a hard link if that fails (previously it created a symlink on Unix and a hard link on Windows).

  - Added `create_symlink`, which always creates a symbolic link. On windows this may fail if symlink permissions are not available.

  - Added `readlink`, which reads the target of a symbolic link.

- Bitcode libraries can now implement compiler-managed library functions (libcalls) without causing incorrect API manipulation or undefined references (#177046). Note that there are still issues with invalid compiler reasoning about some functions in bitcode, e.g. `malloc`. Not yet supported on MachO or when using distributed ThinLTO.

- `ConstantFP` now supports vector types and is the canonical form returned by `ConstantVector::getSplat(C)` when `C` is a scalar `ConstantFP`.

- `DenseMap`, `DenseSet`, `StringMap`, and `StringSet` `erase` now invalidates all iterators and references into the container, not just the iterator for the erased element. Use the new `remove_if` member to erase matching elements in a single pass instead of erasing while iterating.

- `TargetRegisterInfo::getMinimalPhysRegClass` and related APIs have been refactored and no longer take a type. This API is also now precomputed in TableGen to improve compile-time.

- `APInt::sqrt` (square root rounded to nearest integer) has been replaced with `APInt::sqrtFloor` (floor of square root).

### Changes to building LLVM

### Changes to TableGen

- Outer let statements use `ID{n-m}` instead of `ID<n-m>` to be consistent with inner let statements.

### Changes to Interprocedural Optimizations

### Changes to Vectorizers

### Changes to the AArch64 Backend

- The `sysp`, `mrrs`, and `msrr` instructions are now accepted without requiring the `+d128` feature gating.

- Added a new internal option `-aarch64-emit-debug-tls-location` to allow the emission of `DW_AT_location` for thread-local variables. This is currently disabled by default to maintain compatibility with Binutils and LLVM older toolchains that do not define the `R_AARCH64_TLS_DTPREL64` static relocation type for TLS offsets.

- A bug was fixed that caused LLVM IR inline assembly clobbers of the x29 and x30 registers to be ignored when they were written using their xN names instead of the ABI names FP and LR. Note that LLVM IR produced by Clang always uses the ABI names, but other frontends may not. (#167783)

- On AArch64 Windows targets, return address signing now uses the B-key by default because Windows unwind information only supports B-key signing.

### Changes to the AMDGPU Backend

- Initial support for gfx1310

- The `"amdgpu-num-sgpr"` and `"amdgpu-num-vgpr"` IR function attributes (generated by the Clang `amdgpu_num_sgpr` and `amdgpu_num_vgpr` attributes) are now deprecated. Use `"amdgpu-waves-per-eu"` instead. The backend still honors the attributes; Clang emits a `-Wdeprecated-declarations` warning when the source attributes are used.

- The `relaxed-buffer-oob-mode` subtarget feature has been replaced by two module flags, `amdgpu.buffer.oob.mode` and `amdgpu.tbuffer.oob.mode`, which control out-of-bounds semantics (see the AMDGPU User Guide). Frontends that previously relied on the subtarget feature to enable misaligned buffer merging must now set the corresponding module flag to `1` (relaxed). An absent flag is treated as strict by the backend.

- Changed triple naming system from “amdgcn” to “amdgpu” plus a subarch suffix.

### Changes to the ARM Backend

- The `r14` register can now be used as an alias for the link register `lr` in inline assembly. Clang always canonicalizes the name to `lr`, but other frontends may not.

- `subs pc, lr, #imm` can now be predicated in Thumb2.

### Changes to the AVR Backend

### Changes to the DirectX Backend

### Changes to the Hexagon Backend

- v79 and later targets get code generation support for XQFloat, an extended-precision floating point format, along with an extraneous conversion removal pass and a post-register-allocation compliance checker.

- IEEE HVX floating point intrinsics are automatically translated to their QFloat equivalents on v79+ targets.

- `vselect` can now be lowered for HVX.

- Partial reduction intrinsics are now supported.

- HVX gained V128i1/V64i1/V32i1 predicate load and store support.

- The Machine Combiner pass is enabled for Hexagon.

- A new AggressiveRDF copy propagation pass extends RDF copy propagation with super-register and sub-register handling.

- The HexagonGlobalScheduler pass was added.

- ShadowCallStack (`-fsanitize=shadow-call-stack`) is now supported, along with a corresponding multilib.

- Stack clash protection can use `probe-stack=inline-asm`.

- KCFI is now supported.

- The CFI indirect-call sanitizer is now supported.

- `-ffixed-rXX` can reserve caller-saved registers r16-r28.

- A new HVX caller-save remark pass diagnoses call sites that force HVX register spills.

- Several Hexagon IR and MIR passes now emit optimization remarks.

- XRay custom and typed events are now supported.

- JITLink gained an ELF backend for Hexagon.

- The `.reloc` assembler directive is now supported.

- HVX build-vector lowering now reuses word splats for repeated words.

- Sign-extend-then-multiply patterns are now recognized and lowered to `vmpyh`.

### Changes to the LoongArch Backend

- DWARF fission is now compatible with linker relaxations, allowing `-gsplit-dwarf` and `-mrelax` to be used together when building for the LoongArch platform.

### Changes to the MIPS Backend

### Changes to the NVPTX Backend

- The default SM version has been changed from `sm_30` to `sm_75`. `sm_75` is the oldest GPU variant compatible with the widest range of recent major CUDA Toolkit versions (11/12/13).

### Changes to the PowerPC Backend

- Added backend support for partial reductions and cost modeling for length-type VP intrinsic load/store.

- `vec_rl()` on `v4i32` now generates `xvrlw` when targeting `-mcpu=future`.

- `v256i1` loads and stores use paired vector instructions (`lxvp`/`stxvp`) on `-mcpu=future`.

- Added support for the `MSGSNDP` (Message Send Privileged) instruction.

- Enabled custom lowering for `__builtin_bswap64` on Power8 in 64-bit mode by splitting the 64-bit byte-swap into independent 32-bit high/low swaps for improved instruction-level parallelism. Power9 and later continue to use their existing paths.

- Added missing `BR_CC` handler in `DAGTypeLegalizer` for soft-promoted half operands, fixing a crash when a half-typed `fcmp` result feeds directly into a conditional branch.

- Various codegen improvements and bug fixes.

- AIX: Implemented support for the `ifunc` attribute.

- AIX: Implemented Function Multi-Versioning using `target_clones`; versioning by cpu only, and diagnosis of invalid feature strings on the `target` attribute.

- AIX: Added sorting of relocations in the XCOFF object writer.

- AIX: The default code model for 64-bit targets has been changed from `small` to `large`. This avoids the need for expensive linker fixups (e.g. `-Wl,-bigtoc`) that many applications require with the small code model.

### Changes to the RISC-V Backend

- `llvm-objdump` now has support for `--symbolize-operands` with RISC-V.

- `-mcpu=spacemit-x100` was added.

- Change P extension version to match the 0.21 draft specification.

- Mnemonics for MOP/HINT-based instructions (`lpad`, `pause`, `ntl.*`, `c.ntl.*`, `sspush`, `sspopchk`, `ssrdp`, `c.sspush`, `c.sspopchk`) are now always available in the assembler and disassembler without requiring their respective extensions.

- Adds experimental assembler support for the ‘Zvabd` (RISC-V Integer Vector Absolute Difference) extension.

- Adds CodeGen support for the ‘Zvabd` extension.

- `-mcpu=spacemit-a100` was added.

- Adds assembler support for the `XSMTVDotII` (SpacemiT Vector Extension for Matrix 2.0) extension.

- The opt-in `-riscv-enable-p-ext-simd-codegen` flag has been removed. P extension SIMD code generation is now enabled automatically if the P extension is supported.

- `-mcpu=xt-c910v2` and `-mcpu=xt-c920v2` were added.

- Adds experimental assembler support for the ‘Zvzip` (RISC-V Vector Reordering Structured Data) extension.

- `-mcpu=sifive-x160` and `-mcpu=sifive-x180` were added.

- Support for the experimental `XRivosVisni` vendor extension has been removed.

- Support for the experimental `XRivosVizip` vendor extension has been removed.

- Adds experimental assembler support for the ‘Zvvmm` (RISC-V Integer Matrix Multiply-Accumulate) extension.

- Adds experimental assembler support for the ‘Zvvfmm` (RISC-V Floating-Point Matrix Multiply-Accumulate) extension.

- Adds experimental assembler support for the ‘Zvvmtls`and 'Zvvmttls` (RISC-V Matrix Tile Load/Store) extensions.

- Adds support for ‘Ziccid’ (Instruction/Data Coherence and Consistency) extension.

- Adds experimental assembler support for the `Xqccmt` (Qualcomm 16-bit Table Jump) vendor extension.

- `-mcpu=sifive-870` has been renamed `-mcpu=sifive-p870-d`.

- Adds experimental assembler support for batched dot-product extensions(Zvqwbdota8i, Zvqwbdota16i, Zvfwbdota16bf, Zvfqwbdota8f and Zvfbdota32f).

- Adds experimental assembler support for dot-product extensions(Zvqwdota8i, Zvqwdota16i, Zvfwdota16bf and Zvfqwdota8f).

- `-mtune=generic` now uses the scheduling model from SpacemiT X60 instead of an empty scheduling model.

- The Xqcilo pseudos now emit sequences that can be relaxed.

### Changes to the SystemZ Backend

The SystemZ backend now contains initial support to generate code for z/OS using the XPLINK 64 bit ABI and emitting the code into GOFF object files:

- Adds support for writing GOFF object files.

- Adds new class `SystemZHASMAsmStreamer` to emit assembly in HLASM syntax.

- The temporary GNU AS assembly output is removed; all assembly output is in HLASM syntax, and all z/OS-specific test cases are updated.

- Jump tables are now emitted into the text section.

- PPA1 data is now collected and written at the end of the code generation into the text section.

- The PPA1 now contains the prologue length and the offset to the stack update symbol.

- Adds a new attribute to control if the symbol name is emitted into the PPA1.

- Changed the order of caller-saved registers to match legacy compiler.

- Register R5 is no longer restored, matching the XPLINK specification.

- Implements stack guard support for XPLINK

Code-generation changes:

- Add support for the dataflow sanitizer.

- Add support for the `-mstack-protector-guard=global` and `-mstack-protector-guard-record` command line options.

- Fix incorrect code generated for the `vec_insert` intrinsic when used with the `vector float` data type.

Performance enhancements:

- Added a SystemZ-specific pre-RA scheduling strategy with latency-aware heuristics, liveness-reduction, and a minimum-latency-5 filter.

- Enabled interleaving for vectorized loops and epilogue loop vectorization.

- Enabled scalar load rematerialization.

- Cost model improvements to enable better auto-vectorization

- Improved codegen for minimum/maximum operations.

- Allow folding memory accesses across basic-block boundaries.

- Avoid stack overalignment for vector types.

- Avoid unaligned vector loads/stores in memcpy/memmove/memset lowering.

- Avoid redundant zero-extension after VLGV[BHF].

### Changes to the WebAssembly Backend

- WebAssembly reference types are now represented in LLVM IR as the target extension types `target("wasm.externref")` and `target("wasm.funcref")`, rather than as pointers in address spaces 10 and 20 (`ptr addrspace(10)` / `ptr addrspace(20)`).

- As a consequence of the representation change, reference types are no longer treated as vectorizable pointers. This fixes a crash in the SLP vectorizer, which previously would attempt to gather `externref`/`funcref` values into a vector and then crash.

### Changes to the Windows Target

- The `.seh_startchained` and `.seh_endchained` assembly instructions have been removed and replaced with a new `.seh_splitchained` instruction.

### Changes to the X86 Backend

- `.att_syntax` directive is now emitted for assembly files when AT&T syntax is in use. This matches the behaviour of Intel syntax and aids with compatibility when changing the default Clang syntax to the Intel syntax.

- EGPR (R16-R31) now requires V3 unwind info on Windows x64. Using EGPR without V3 unwind produces a fatal error.

- Implemented Win64 APX ABI callee-saved registers: R30 and R31 are now treated as non-volatile in the Win64 calling convention when APX is available, per the Microsoft x64 calling convention specification.

- Functions using setjmp with Win64 APX ABI now reserve R30/R31 from register allocation, as the unwinder cannot restore APX extended registers across longjmp. A warning is emitted for large functions where this reservation may impact performance.

- Added `.seh_push2regs` assembly directive for explicitly encoding a two-register push in Windows x64 V3 unwind info. The directive takes two register operands: `.seh_push2regs %r12, %r13`.

- The `fp128` type is now returned via sret instead of XMM0 for some calling conventions to match GCC. The C and Win64 calling conventions now use sret, other calling conventions do not need to be compatible with GCC and still return via XMM0.

### Changes to the OCaml bindings

### Changes to the Python bindings

### Changes to the C API

- Replaced opcode `LLVMBr` with `LLVMUncondBr` and `LLVMCondBr`.

- The operand order of `CondBr` instructions was adjusted to match the successor order. This can cause subtle breakage when using `LLVMGetOperand` or `LLVMSetOperand` to access successors.

### Changes to the CodeGen infrastructure

- Renamed ISD::CTLZ_ZERO_UNDEF to ISD::CTLZ_ZERO_POISON opcode to make it clear that a zero input results in poison.

- Renamed ISD::CTTZ_ZERO_UNDEF to ISD::CTTZ_ZERO_POISON opcode to make it clear that a zero input results in poison.

- LLVM intrinsics can now declare required target features using the `TargetFeatures` TableGen field. SelectionDAG and GlobalISel use this metadata to reject unsupported target intrinsics generically, so targets do not need custom lowering checks for each annotated intrinsic.

### Changes to the GlobalISel infrastructure

- Renamed G_CTLZ_ZERO_UNDEF to G_CTLZ_ZERO_POISON opcode to make it clear that a zero input results in poison.

- Renamed G_CTTZ_ZERO_UNDEF to G_CTTZ_ZERO_POISON opcode to make it clear that a zero input results in poison.

- GlobalISel’s IRTranslator now supports the LLVM IR byte type (`bN`). Byte values are translated as the equi-sized integer scalar (`sN`), `ConstantByte` is materialised via `G_CONSTANT`, and `bitcast` between a byte type and a pointer is lowered to `G_INTTOPTR` / `G_PTRTOINT` rather than the verifier-illegal `G_BITCAST`.

### Changes to the Metadata Info

### Changes to the Debug Info

### Changes to the LLVM tools

- llvm-ml now supports the `/unwindv3` flag to enable V3 unwind information format for x64 exception handling.

- llvm-ml now supports the `@UnwindVersion` built-in symbol, which returns the current unwind version (1 by default, 3 when `/unwindv3` is specified).

- llvm-ml now supports the `.push2reg`, `.pop2reg`, `.beginepilog`, and `.endepilog` MASM directives for V3 unwind information.

- llvm-ml now supports the `.popreg`, `.freestack`, `.restorereg`, `.restorexmm128`, and `.unsetframe` MASM epilog directives. These are the epilog counterparts of `.pushreg`, `.allocstack`, `.savereg`, `.savexmm128`, and `.setframe` respectively, and are valid only inside `.beginepilog`/`.endepilog` blocks and only for V3 unwind information.

- llvm-ml now supports `.pushframe code` syntax (without the `@` prefix) for interrupt handlers with error codes.

- llvm-ml now diagnoses:

  - Prolog directives (including `.allocstack`) used outside of prologs (after `.endprolog`).

  - Epilog directives used outside of epilogs (outside of `.beginepilog` + `.endepilog` blocks).

  - Beginning an epilog (`.beginepilog`) inside another epilog.

- `llvm-profgen` now supports ETM trace decoding using the OpenCSD library for Cortex-M targets. OpenCSD version 1.5.4 or higher is required.

- `llvm-objcopy` no longer corrupts the symbol table when `--update-section` is called for ELF files.

- `llvm-objcopy` now reports an error when `--compress-sections` requests unavailable zlib or zstd support. The diagnostic is emitted while parsing the option, matching `--compress-debug-sections`. Such commands may now fail even if the input file contains no sections that would be compressed.

- `FileCheck` option `-check-prefix` now accepts a comma-separated list of prefixes, making it an alias of the existing `-check-prefixes` option.

- Add `-mtune` option to `llc`.

- Add `-mtune` option to `opt`.

- Fixed `llvm-ar` to correctly handle the `N` count modifier on Windows for archive members whose names differ only in case (e.g. `FOO.OBJ` and `foo.obj`). Previously, `-N 2` would fail with “not found” even when two matching members existed.

- `llvm-readobj` and `llvm-readelf` now support the `--call-graph-section` option to dump the contents of the experimental call graph section.

- `lit` now supports `--unsupported` and `--unsupported-not` command-line options (and corresponding `LIT_UNSUPPORTED` / `LIT_UNSUPPORTED_NOT` environment variables) to mark tests as `UNSUPPORTED` without modifying the test files, mirroring the existing `--xfail` / `LIT_XFAIL` mechanism.

- Added support for hybrid ARM64X object files to `llvm-ar` and `llvm-lib`. When these files are added to an archive, they are automatically split into separate native and EC members. Because the resulting members are no longer hybrid object files, consumers of these archives do not need to support the hybrid format themselves.

- `llvm-ar` now supports reading and writing z/OS archives.

- `ObjectFile::createObjectFile` now correctly handles GOFF object files, routing them through `createGOFFObjectFile` instead of returning an error.

### Changes to LLDB

- A new `webinspector-wasm` platform was added to list and attach to WebAssembly processes in Safari.

- The default for `load-script-from-symbol-file` was changed from `warn` to `trusted`. This means that scripts from code signed dSYM bundles are now loaded automatically, while untrusted bundles continue to produce a warning.

- Pressing enter after `frame variable` repeats the command with an incremented `--depth` option, allowing quick expansion of nested data.

- Breakpoint commands now accept `.` to refer to the location(s) at which the current thread is stopped. For example, `breakpoint disable .` disables the just-hit breakpoint location. Another usage is to automate a command to run at the current location: `breakpoint command add -o 'p my_var' .`.

- The `apropos` command now:

  - Highlights matching keywords in its output when color is enabled.

  - Searches the components of settings paths. For example `apropos qemu-user` will now show `platform.plugin.qemu-user` as one of the results.

- Reading global and static variables on WebAssembly targets now works correctly. Previously their values could not be read because data sections were mapped to the wrong address space.

- A new `diagnostics report` command (aliased `bugreport`) assembles a diagnostics bundle and files a pre-filled GitHub issue, pointing at the bundle to attach. The GitHub reporter is built by default and can be disabled with the `LLDB_ENABLE_GITHUB_BUG_REPORTER=OFF` CMake option.

- The script interpreter plugins are now built as shared libraries by default on Darwin and FreeBSD (`LLDB_ENABLE_DYNAMIC_SCRIPTINTERPRETERS=ON`). This can be opted into on Linux also.

#### Deprecated APIs

- `SBTarget::GetDataByteSize()`, `SBTarget::GetCodeByteSize()`, and `SBSection::GetTargetByteSize()` have been deprecated. They always return `1`, as before.

#### FreeBSD

##### Userspace Debugging

- Support for MIPS64 has been removed.

- The minimum assumed FreeBSD version is now 14. The effect of which is that watchpoints are assumed to be supported.

##### Kernel Debugging

- The plugin that analyzes FreeBSD kernel core dump and live core has been renamed from `freebsd-kernel` to `freebsd-kernel-core`. Remote kernel debugging is still handled by the `gdb-remote` plugin.

- Support for libfbsdvmcore has been removed. As a result, FreeBSD kernel dump debugging is now only available on FreeBSD hosts. Live kernel debugging through the GDB remote protocol is still available from any platform.

- Support for ARM, PPC64le, and RISCV64 has been added.

- The crashed thread is now automatically selected on start.

- Threads are listed in incrmental order by pid then by tid.

- Unread kernel messages saved in `msgbufp` are now printed when LLDB starts.

- Writing to the core is now supported. For safety reasons, this feature is off by default. To enable it, `plugin.process.freebsd-kernel-core.read-only` must be set to `false`. This setting is available when using `/dev/mem` or a kernel dump. However, since `kvm_write()` does not support writing to kernel dumps, writes to a kernel dump will still fail when the setting is false.

- Added a command `process plugin refresh-threads`, enabling on-demand thread-list reconstruction from `/dev/mem` so users can resync live kernel thread state without restarting LLDB. Note that this has no impact on full dump and minidump files.

#### Linux

- On Arm Linux, the `tpidruro` register can now be read. Writing to this register is not supported.

- Thread local variables are now supported on Arm and RISC-V Linux if the program being debugged is using glibc.

- LLDB now supports AArch64 Linux systems that only have SME (as opposed to SVE and SME). See the AArch64 Linux documentation for more details.

  Prior to this version of LLDB, there was a bug that caused LLDB to crash on startup on these systems (#138717). This affected LLDB versions from 18 up to and including 22. 17 and below are not affected. If you are using such a system and cannot change LLDB version, or want to package an affected version in a way that is compatible with these systems, the issue contains details of backports that could be done to fix the affected versions.

- When an ELF core file is loaded, LLDB now shows the command line that created the core file. If you need to see it again, use the command `process status -v`.

- LLDB now supports debugging Linux Memory Protection Keys on AArch64 systems that have the Permission Overlay Extension (POE / FEAT_S1POE). See the LLDB on AArch64 Linux guide for more information.

#### Windows

- Python 3.11 or later is now recommended for building LLDB 23 on Windows. From LLDB 24, Python 3.11 or later will be required.

- Messages from `OutputDebugString[A|W]` are now shown inline when using LLDB from the command-line and in the output window when using lldb-dap.

- LLDB now uses `lldb-server.exe` to launch and manage the program being debugged, instead of running it within LLDB’s own process. To revert to the previous behavior, set the environment variable `LLDB_USE_LLDB_SERVER=0`.

- Support for PDB symbol servers has been added. By default, no symbol servers are used. You can control this either through the `_NT_SYMBOL_PATH` environment variable or by setting `plugin.symbol-locator.symstore.urls` (see `plugin.symbol-locator.symstore` for more info).

- LLDB no longer depends on the Python private API on Windows. Users are now free to use any Python version they want, as long as it is 3.8 or later and LLDB can find it (i.e. it is on their `PATH`).

### Changes to BOLT

- BOLT supports AArch64 binaries using Pointer Authentication (PAC) and Branch Target Identification (BTI). For PAC-enabled binaries, BOLT preserves pointer authentication CFI state during optimization. For BTI-enabled binaries, BOLT can patch PLT entries or indirect branch targets with BTI landing pads where possible.

- BOLT adds compact-code-model support for Armv9.6-A FEAT_CMPBR compare-and-branch instructions, including support for block reordering, function splitting, branch inversion where legal.

- BOLT supports AArch64 profile data collected with Arm SPE and branch-stack profiles from hardware such as BRBE. LLVM 23 adds pre-parsed perf-script and profile-format support for these workflows.

### Changes to Sanitizers

- Add a random delay into ThreadSanitizer to help find rare thread interleavings.

- `sancov` now supports XCOFF object files (used on AIX). The tool strips the `.` prefix that AIX adds to function entry-point symbols (e.g. `.__sanitizer_cov_trace_pc_guard`) so that coverage symbols are correctly identified.

- The `mmap`/`munmap` memory-mapping interceptors now fail early when the requested address range is not covered by shadow memory, avoiding hard-to-diagnose failures later in the sanitizer runtime.

### Other Changes

## External Open Source Projects Using LLVM 23.1.0

## 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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