2 min read

LLVM team released LLVM 8.0, earlier this week. LLVM is a collection of tools that help develop compiler front ends and back ends. LLVM is written in C++ and has been designed for compile-time, link-time, run-time, and “idle-time” optimization of programs that are written in arbitrary programming languages.

LLVM 8.0 explores known issues, major improvements and other changes in the subprojects of LLVM. There were certain issues in LLVM 8.0.0 that could not be fixed earlier (before this release). For instance, clang is getting miscompiled by trunk GCC, and “asan-dynamic” is not able to work on FreeBSD.

Other than the issues, there is a long list of changes that have been made to LLVM 8.0.0.

Non-comprehensive changes to LLVM 8.0.0

  • llvm-cov tool can export lcov trace files with the help of the -format=lcov option of the export command.
  • The add_llvm_loadable_module CMake macro has been deprecated. The add_llvm_library macro with the MODULE argument can now help provide the same functionality.
  • For MinGW, references to data variables that are to be imported from a dll can be now accessed via a stub. This will further allow the linker to convert it to a dllimport if needed.
  • Support has been added for labels as offsets in .reloc directive.
  • Windows support for libFuzzer (x86_64) has also been added.

Other Changes

  • LLVM IR:  The Function attribute named speculative_load_hardening has been introduced. This will indicate that Speculative Load Hardening should be enabled for the function body.
  • JIT APIs: ORC (On Request Compilation) JIT APIs will now support concurrent compilation. The existing (non-concurrent) ORC layer classes, as well as the related APIs, have been deprecated. These have been renamed with a “Legacy” prefix (e.g. LegacyIRCompileLayer). All the deprecated classes will be removed in LLVM 9.
  • AArch64 Target: Support has been added for Speculative Load Hardening. Also, initial support added for the Tiny code model, where code and the statically defined symbols should remain within 1MB.
  • MIPS Target: Support forGlobalISel instruction selection framework has been improved. ORC JIT will now offer support for MIPS and MIPS64 architectures. There’s also newly added support for MIPS N32 AB.
  • PowerPC Target: This has now been switched to non-PIC default in LLVM 8.0.0. Darwin support has also been deprecated. Also, Out-of-Order scheduling has been enabled for P9.
  • SystemZ Target: These include various code-gen improvements related to improved auto-vectorization, inlining, as well as the instruction scheduling.

Other than these, changes have also been made to X86 target, WebAssembly Target, Nios2 target, and LLDB.

For a complete list of changes, check out the official LLVM 8.0.0 release notes.

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