====================== LLVM 3.6 Release Notes ====================== .. contents:: :local: .. warning:: These are in-progress notes for the upcoming LLVM 3.6 release. You may prefer the `LLVM 3.5 Release Notes `_. Introduction ============ This document contains the release notes for the LLVM Compiler Infrastructure, release 3.6. 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 ================================================= .. NOTE For small 1-3 sentence descriptions, just add an entry at the end of this list. If your description won't fit comfortably in one bullet point (e.g. maybe you would like to give an example of the functionality, or simply have a lot to talk about), see the `NOTE` below for adding a new subsection. * Support for AuroraUX has been removed. * Added support for a `native object file-based bitcode wrapper format `_. * ... next change ... .. NOTE If you would like to document a larger change, then you can add a subsection about it right here. You can copy the following boilerplate and un-indent it (the indentation causes it to be inside this comment). Special New Feature ------------------- Makes programs 10x faster by doing Special New Thing. Prefix data rework ------------------ The semantics of the ``prefix`` attribute have been changed. Users that want the previous ``prefix`` semantics should instead use ``prologue``. To motivate this change, let's examine the primary usecases that these attributes aim to serve, 1. Code sanitization metadata (e.g. Clang's undefined behavior sanitizer) 2. Function hot-patching: Enable the user to insert ``nop`` operations at the beginning of the function which can later be safely replaced with a call to some instrumentation facility. 3. Language runtime metadata: Allow a compiler to insert data for use by the runtime during execution. GHC is one example of a compiler that needs this functionality for its tables-next-to-code functionality. Previously ``prefix`` served cases (1) and (2) quite well by allowing the user to introduce arbitrary data at the entrypoint but before the function body. Case (3), however, was poorly handled by this approach as it required that prefix data was valid executable code. In this release the concept of prefix data has been redefined to be data which occurs immediately before the function entrypoint (i.e. the symbol address). Since prefix data now occurs before the function entrypoint, there is no need for the data to be valid code. The previous notion of prefix data now goes under the name "prologue data" to emphasize its duality with the function epilogue. The intention here is to handle cases (1) and (2) with prologue data and case (3) with prefix data. See the language reference for further details on the semantics of these attributes. This refactoring arose out of discussions_ with Reid Kleckner in response to a proposal to introduce the notion of symbol offsets to enable handling of case (3). .. _discussions: http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-May/073235.html Changes to the ARM Backend -------------------------- During this release ... Changes to the MIPS Target -------------------------- During this release the MIPS target has reached a few major milestones. The compiler has gained support for MIPS-II and MIPS-III; become ABI-compatible with GCC for big and little endian O32, N32, and N64; and is now able to compile the Linux kernel for 32-bit targets. Additionally, LLD now supports microMIPS for the O32 ABI on little endian targets. ABI ^^^ A large number of bugs have been fixed for big-endian MIPS targets using the N32 and N64 ABI's as well as a small number of bugs affecting other ABI's. Please note that some of these bugs will still affect LLVM-IR generated by LLVM 3.5 since correct code generation depends on appropriate usage of the ``inreg``, ``signext``, and ``zeroext`` attributes on all function arguments and returns. There are far too many corrections to provide a complete list but here are a few notable ones: * Big-endian N32 and N64 now interlinks successfully with GCC compiled code. Previously this didn't work for the majority of cases. * The registers used to return a structure containing a single 128-bit floating point member on the N32/N64 ABI's have been changed from those specified by the ABI documentation to match those used by GCC. The documentation specifies that ``$f0`` and ``$f2`` should be used but GCC has used ``$f0`` and ``$f1`` for many years. * Returning a zero-byte struct no longer causes arguments to be read from the wrong registers when using the O32 ABI. * The exception personality has been changed for 64-bit MIPS targets to eliminate warnings about relocations in a read-only section. * Incorrect usage of odd-numbered single-precision floating point registers has been fixed when the fastcc calling convention is used with 64-bit FPU's and -mno-odd-spreg. LLVMLinux ^^^^^^^^^ It is now possible to compile the Linux kernel. This currently requires a small number of kernel patches. See the `LLVMLinux project `_ for details. * Added -mabicalls and -mno-abicalls. The implementation may not be complete but works sufficiently well for the Linux kernel. * Fixed multiple compatibility issues between LLVM's inline assembly support and GCC's. * Added support for a number of directives used by Linux to the Integrated Assembler. Miscellaneous ^^^^^^^^^^^^^ * Attempting to disassemble l[wd]c[23], s[wd]c[23], cache, and pref no longer triggers an assertion. * Added -muclibc and -mglibc to support toolchains that provide both uClibC and GLibC. * __SIZEOF_INT128__ is no longer defined for 64-bit targets since 128-bit integers do not work at this time for this target. * Using $t4-$t7 with the N32 and N64 ABI is deprecated when ``-fintegrated-as`` is in use and will be removed in LLVM 3.7. These names have never been supported by the GNU Assembler for these ABI's. Changes to the PowerPC Target ----------------------------- There are numerous improvements to the PowerPC target in this release: * LLVM now generates the Vector-Scalar eXtension (VSX) instructions from version 2.06 of the Power ISA, for both big- and little-endian targets. * LLVM now has a POWER8 instruction scheduling description. * Address Sanitizer (ASAN) support is now fully functional. * Performance of simple atomic accesses has been greatly improved. * Atomic fences now use light-weight syncs where possible, again providing significant performance benefit. * The PowerPC target now supports PIC levels (-fPIC vs. -fpic). * PPC32 SVR4 now supports small-model PIC. * There have been many smaller bug fixes and performance improvements. Changes to the OCaml bindings ----------------------------- * The bindings now require OCaml >=4.00.0, ocamlfind, ctypes >=0.3.0 <0.4 and OUnit 2 if tests are enabled. * The bindings can now be built using cmake as well as autoconf. * LLVM 3.5 has, unfortunately, shipped a broken Llvm_executionengine implementation. In LLVM 3.6, the bindings now fully support MCJIT, however the interface is reworked from scratch using ctypes and is not backwards compatible. * Llvm_linker.Mode was removed following the changes in LLVM. This breaks the interface of Llvm_linker. * All combinations of ocamlc/ocamlc -custom/ocamlopt and shared/static builds of LLVM are now supported. * Absolute paths are not embedded into the OCaml libraries anymore. Either OCaml >=4.02.2 must be used, which includes an rpath-like $ORIGIN mechanism, or META file must be updated for out-of-tree installations; see r221139. * As usual, many more functions have been exposed to OCaml. External Open Source Projects Using LLVM 3.6 ============================================ 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 3.6. * 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 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 `_.