LLVM 11.0.0 Release Notes

Warning

These are in-progress notes for the upcoming LLVM 11 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 11.0.0. 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.

Deprecated and Removed Features/APIs

  • BG/Q support, including QPX, will be removed in the 12.0.0 release.

Non-comprehensive list of changes in this release

  • …

Changes to the LLVM IR

  • The callsite attribute vector-function-abi-variant has been added to describe the mapping between scalar functions and vector functions, to enable vectorization of call sites. The information provided by the attribute is interfaced via the API provided by the VFDatabase class.
  • dereferenceable attributes and metadata on pointers no longer imply anything about the alignment of the pointer in question. Previously, some optimizations would make assumptions based on the type of the pointer. This behavior was undocumented. To preserve optimizations, frontends may need to be updated to generate appropriate align attributes and metadata.
  • The DIModule metadata is extended to contain file and line number information. This information is used to represent Fortran modules debug info at IR level.

Changes to the ARM Backend

During this release …

  • Implemented C-language intrinsics for the full Arm v8.1-M MVE instruction set. <arm_mve.h> now supports the complete API defined in the Arm C Language Extensions.
  • Added support for assembly for the optional Custom Datapath Extension (CDE) for Arm M-profile targets.
  • Implemented C-language intrinsics <arm_cde.h> for the CDE instruction set.
  • Clang now defaults to -fomit-frame-pointer when targeting non-Android Linux for arm and thumb when optimizations are enabled. Users that were previously not specifying a value and relying on the implicit compiler default may wish to specify -fno-omit-frame-pointer to get the old behavior. This improves compatibility with GCC.

Changes to the MIPS Target

During this release …

Changes to the PowerPC Target

During this release …

Changes to the X86 Target

During this release …

  • Functions with the probe-stack attribute set to “inline-asm” are now protected against stack clash without the need of a third-party probing function and with limited impact on performance.
  • -x86-enable-old-knl-abi command line switch has been removed. v32i16/v64i8 vectors are always passed in ZMM register when avx512f is enabled and avx512bw is disabled.
  • Vectors larger than 512 bits with i16 or i8 elements will be passed in multiple ZMM registers when avx512f is enabled. Previously this required avx512bw otherwise they would split into multiple YMM registers. This means vXi16/vXi8 vectors are consistently treated the same as vXi32/vXi64/vXf64/vXf32 vectors of the same total width.

Changes to the AMDGPU Target

  • The backend default denormal handling mode has been switched to on for all targets for all compute function types. Frontends wishing to retain the old behavior should explicitly request f32 denormal flushing.

Changes to the AVR Target

  • Moved from an experimental backend to an official backend. AVR support is now included by default in all LLVM builds and releases and is available under the “avr-unknown-unknown” target triple.

Changes to the WebAssembly Target

  • Programs which don’t have a “main” function, called “reactors” are now properly supported, with a new -mexec-model=reactor flag. Programs which previously used -Wl,–no-entry to avoid having a main function should switch to this new flag, so that static initialization is properly performed.
  • __attribute__((visibility(“protected”))) now evokes a warning, as WebAssembly does not support “protected” visibility.

Changes to the Debug Info

  • LLVM now supports the debug entry values (DW_OP_entry_value) production for the x86, ARM, and AArch64 targets by default. Other targets can use the utility by using the experimental option (“-debug-entry-values”). This is a debug info feature that allows debuggers to recover the value of optimized-out parameters by going up a stack frame and interpreting the values passed to the callee. The feature improves the debugging user experience when debugging optimized code.

Changes to the LLVM tools

  • Added an option (–show-section-sizes) to llvm-dwarfdump to show the sizes of all debug sections within a file.
  • llvm-nm now implements the flag --special-syms and will filter out special symbols, i.e. mapping symbols on ARM and AArch64, by default. This matches the GNU nm behavior.

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.