LLVM 3.5 Release Notes

Warning

These are in-progress notes for the upcoming LLVM 3.5 release. You may prefer the LLVM 3.4 Release Notes.

Introduction

This document contains the release notes for the LLVM Compiler Infrastructure, release 3.5. 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 Subversion 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

  • All backends have been changed to use the MC asm printer and support for the non MC one has been removed.
  • Clang can now successfully self-host itself on Linux/Sparc64 and on FreeBSD/Sparc64.
  • LLVM now assumes the assembler supports .loc for generating debug line numbers. The old support for printing the debug line info directly was only used by llc and has been removed.
  • All inline assembly is parsed by the integrated assembler when it is enabled. Previously this was only the case for object-file output. It is now the case for assembly output as well. The integrated assembler can be disabled with the -no-integrated-as option,
  • llvm-ar now handles IR files like regular object files. In particular, a regular symbol table is created for symbols defined in IR files, including those in file scope inline assembly.
  • LLVM now always uses cfi directives for producing most stack unwinding information.
  • The prefix for loop vectorizer hint metadata has been changed from llvm.vectorizer to llvm.loop.vectorize. In addition, llvm.vectorizer.unroll metadata has been renamed llvm.loop.interleave.count.
  • Some backends previously implemented Atomic NAND(x,y) as x & ~y. Now all backends implement it as ~(x & y), matching the semantics of GCC 4.4 and later.
  • ... next change ...

Changes to the ARM Backend

Since release 3.3, a lot of new features have been included in the ARM back-end but weren’t production ready (ie. well tested) on release 3.4. Just after the 3.4 release, we started heavily testing two major parts of the back-end: the integrated assembler (IAS) and the ARM exception handling (EHABI), and now they are enabled by default on LLVM/Clang.

The IAS received a lot of GNU extensions and directives, as well as some specific pre-UAL instructions. Not all remaining directives will be implemented, as we made judgement calls on the need versus the complexity, and have chosen simplicity and future compatibility where hard decisions had to be made. The major difference is, as stated above, the IAS validates all inline ASM, not just for object emission, and that cause trouble with some uses of inline ASM as pre-processor magic.

So, while the IAS is good enough to compile large projects (including most of the Linux kernel), there are a few things that we can’t (and probably won’t) do. For those cases, please use -fno-integrated-as in Clang.

Exception handling is another big change. After extensive testing and changes to cooperate with Dwarf unwinding, EHABI is enabled by default. The options -arm-enable-ehabi and -arm-enable-ehabi-descriptors, which were used to enable EHABI in the previous releases, are removed now.

This means all ARM code will emit EH unwind tables, or CFI unwinding (for debug/profiling), or both. To avoid run-time inconsistencies, C code will also emit EH tables (in case they interoperate with C++ code), as is the case for other architectures (ex. x86_64).

External Open Source Projects Using LLVM 3.5

An exciting aspect of LLVM is that it is used as an enabling technology for a lot of other language and tools projects. This section lists some of the projects that have already been updated to work with LLVM 3.5.

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 Subversion 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.