docs/ReleaseNotes.rst - llvm - Git at Google

 ========================
 LLVM 5.0.0 Release Notes
 ========================

 .. contents::
     :local:


 Introduction
 ============

 This document contains the release notes for the LLVM Compiler Infrastructure,
 release 5.0.0.  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 <http://llvm.org/releases/>`_.

 For more information about LLVM, including information about the latest
 release, please check out the `main LLVM web site <http://llvm.org/>`_.  If you
 have questions or comments, the `LLVM Developer's Mailing List
 <http://lists.llvm.org/mailman/listinfo/llvm-dev>`_ is a good place to send
 them.

 Non-comprehensive list of changes in this release
 =================================================

 * LLVM's ``WeakVH`` has been renamed to ``WeakTrackingVH`` and a new ``WeakVH``
   has been introduced.  The new ``WeakVH`` nulls itself out on deletion, but
   does not track values across RAUW.

 * A new library named ``BinaryFormat`` has been created which holds a collection
   of code which previously lived in ``Support``.  This includes the
   ``file_magic`` structure and ``identify_magic`` functions, as well as all the
   structure and type definitions for DWARF, ELF, COFF, WASM, and MachO file
   formats.

 * The tool ``llvm-pdbdump`` has been renamed ``llvm-pdbutil`` to better reflect
   its nature as a general purpose PDB manipulation / diagnostics tool that does
   more than just dumping contents.

 * The ``BBVectorize`` pass has been removed. It was fully replaced and no
   longer used back in 2014 but we didn't get around to removing it. Now it is
   gone. The SLP vectorizer is the suggested non-loop vectorization pass.

 * A new tool opt-viewer.py has been added to visualize optimization remarks in
   HTML.  The tool processes the YAML files produced by clang with the
   -fsave-optimization-record option.

 * A new CMake macro ``LLVM_REVERSE_ITERATION`` has been added. If enabled, all
   supported unordered LLVM containers would be iterated in reverse order. This
   is useful for uncovering non-determinism caused by iteration of unordered
   containers. Currently, it supports reverse iteration of SmallPtrSet and
   DenseMap.

 * A new tool ``llvm-dlltool`` has been added to create short import libraries
   from GNU style definition files. The tool utilizes the PE COFF SPEC Import
   Library Format and PE COFF Auxiliary Weak Externals Format to achieve
   compatibility with LLD and MSVC LINK.


 Changes to the LLVM IR
 ----------------------

 * The datalayout string may now indicate an address space to use for
   the pointer type of ``alloca`` rather than the default of 0.

 * Added ``speculatable`` attribute indicating a function which has no
   side-effects which could inhibit hoisting of calls.

 Changes to the Arm Targets
 --------------------------

 During this release the AArch64 target has:

 * A much improved Global ISel at O0.
 * Support for ARMv8.1 8.2 and 8.3 instructions.
 * New scheduler information for ThunderX2.
 * Some SVE type changes but not much more than that.
 * Made instruction fusion more aggressive, resulting in speedups
   for code making use of AArch64 AES instructions. AES fusion has been
   enabled for most Cortex-A cores and the AArch64MacroFusion pass was moved
   to the generic MacroFusion pass.
 * Added preferred function alignments for most Cortex-A cores.
 * OpenMP "offload-to-self" base support.

 During this release the ARM target has:

 * Improved, but still mostly broken, Global ISel.
 * Scheduling models update, new schedule for Cortex-A57.
 * Hardware breakpoint support in LLDB.
 * New assembler error handling, with spelling corrections and multiple
   suggestions on how to fix problems.
 * Improved mixed ARM/Thumb code generation. Some cases in which wrong
   relocations were emitted have been fixed.
 * Added initial support for mixed ARM/Thumb link-time optimization, using the
   thumb-mode target feature.

 Changes to the MIPS Target
 --------------------------

 * The microMIPS64R6 backend is deprecated and will be removed in the next
   release.

 * The MIPS backend now directly supports vector types for arguments and return
   values (previously this required ABI specific LLVM IR).

 * Added documentation for how the MIPS backend handles address lowering.

 * Added a GCC compatible option -m(no-)madd4 to control the generation of four
   operand multiply addition/subtraction instructions.

 * Added basic support for the XRay instrumentation system.

 * Added support for more assembly aliases and macros.

 * Added support for the ``micromips`` and ``nomicromips`` function attributes
   which control micromips code generation on a per function basis.

 * Added the ``long-calls`` feature for non-pic environments. This feature is
   used where the callee is out of range of the caller using a standard call
   sequence. It must be enabled specifically.

 * Added support for performing microMIPS code generation via function
   attributes.

 * Added experimental support for the static relocation model for the N64 ABI.

 * Added partial support for the MT ASE.

 * Added basic support for code size reduction for microMIPS.

 * Fixed numerous bugs including: multi-precision arithmetic support, various
   vectorization bugs, debug information for thread local variables, debug
   sections lacking the correct flags, crashing when disassembling sections
   whose size is not a multiple of two or four.


 Changes to the PowerPC Target
 -----------------------------

 * Additional support and exploitation of POWER ISA 3.0: vabsdub, vabsduh,
   vabsduw, modsw, moduw, modsd, modud, lxv, stxv, vextublx, vextubrx, vextuhlx,
   vextuhrx, vextuwlx, vextuwrx, vextsb2w, vextsb2d, vextsh2w, vextsh2d, and
   vextsw2d

 * Implemented Optimal Code Sequences from The PowerPC Compiler Writer's Guide.

 * Enable -fomit-frame-pointer by default.

 * Improved handling of bit reverse intrinsic.

 * Improved handling of memcpy and memcmp functions.

 * Improved handling of branches with static branch hints.

 * Improved codegen for atomic load_acquire.

 * Improved block placement during code layout

 * Many improvements to instruction selection and code generation


 Changes to the X86 Target
 -------------------------

 * Added initial AMD Ryzen (znver1) scheduler support.

 * Added support for Intel Goldmont CPUs.

 * Add support for avx512vpopcntdq instructions.

 * Added heuristics to convert CMOV into branches when it may be profitable.

 * More aggressive inlining of memcmp calls.

 * Improve vXi64 shuffles on 32-bit targets.

 * Improved use of PMOVMSKB for any_of/all_of comparision reductions.

 * Improved Silvermont, Sandybridge, and Jaguar (btver2) schedulers.

 * Improved support for AVX512 vector rotations.

 * Added support for AMD Lightweight Profiling (LWP) instructions.

 * Avoid using slow LEA instructions.

 * Use alternative sequences for multiply by constant.

 * Improved lowering of strided shuffles.

 * Improved the AVX512 cost model used by the vectorizer.

 * Fix scalar code performance when AVX512 is enabled by making i1's illegal.

 * Fixed many inline assembly bugs.

 * Preliminary support for tracing NetBSD processes and core files with a single
   thread in LLDB.

 Changes to the AMDGPU Target
 -----------------------------

 * Initial gfx9 support

 Changes to the AVR Target
 -----------------------------

 This release consists mainly of bugfixes and implementations of features
 required for compiling basic Rust programs.

 * Enable the branch relaxation pass so that we don't crash on large
   stack load/stores

 * Add support for lowering bit-rotations to the native ``ror`` and ``rol``
   instructions

 * Fix bug where function pointers were treated as pointers to RAM and not
   pointers to program memory

 * Fix broken code generation for shift-by-variable expressions

 * Support zero-sized types in argument lists; this is impossible in C,
   but possible in Rust


 Changes to the C API
 --------------------

 * Deprecated the ``LLVMAddBBVectorizePass`` interface since the ``BBVectorize``
   pass has been removed. It is now a no-op and will be removed in the next
   release. Use ``LLVMAddSLPVectorizePass`` instead to get the supported SLP
   vectorizer.


 External Open Source Projects Using LLVM 5
 ==========================================

 Zig Programming Language
 ------------------------

 `Zig <http://ziglang.org>`_  is an open-source programming language designed
 for robustness, optimality, and clarity. It integrates closely with C and is
 intended to eventually take the place of C. It uses LLVM to produce highly
 optimized native code and to cross-compile for any target out of the box. Zig
 is in alpha; with a beta release expected in September.

 LDC - the LLVM-based D compiler
 -------------------------------

 `D <http://dlang.org>`_ is a language with C-like syntax and static typing. It
 pragmatically combines efficiency, control, and modeling power, with safety and
 programmer productivity. D supports powerful concepts like Compile-Time Function
 Execution (CTFE) and Template Meta-Programming, provides an innovative approach
 to concurrency and offers many classical paradigms.

 `LDC <http://wiki.dlang.org/LDC>`_ uses the frontend from the reference compiler
 combined with LLVM as backend to produce efficient native code. LDC targets
 x86/x86_64 systems like Linux, OS X, FreeBSD and Windows and also Linux on ARM
 and PowerPC (32/64 bit). Ports to other architectures like AArch64 and MIPS64
 are underway.


 Additional Information
 ======================

 A wide variety of additional information is available on the `LLVM web page
 <http://llvm.org/>`_, in particular in the `documentation
 <http://llvm.org/docs/>`_ 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 <http://llvm.org/docs/#maillist>`_.
	========================
	LLVM 5.0.0 Release Notes
	========================

	.. contents::
	:local:


	Introduction
	============

	This document contains the release notes for the LLVM Compiler Infrastructure,
	release 5.0.0. 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 <http://llvm.org/releases/>`_.

	For more information about LLVM, including information about the latest
	release, please check out the `main LLVM web site <http://llvm.org/>`_. If you
	have questions or comments, the `LLVM Developer's Mailing List
	<http://lists.llvm.org/mailman/listinfo/llvm-dev>`_ is a good place to send
	them.

	Non-comprehensive list of changes in this release
	=================================================

	* LLVM's ``WeakVH`` has been renamed to ``WeakTrackingVH`` and a new ``WeakVH``
	has been introduced. The new ``WeakVH`` nulls itself out on deletion, but
	does not track values across RAUW.

	* A new library named ``BinaryFormat`` has been created which holds a collection
	of code which previously lived in ``Support``. This includes the
	``file_magic`` structure and ``identify_magic`` functions, as well as all the
	structure and type definitions for DWARF, ELF, COFF, WASM, and MachO file
	formats.

	* The tool ``llvm-pdbdump`` has been renamed ``llvm-pdbutil`` to better reflect
	its nature as a general purpose PDB manipulation / diagnostics tool that does
	more than just dumping contents.

	* The ``BBVectorize`` pass has been removed. It was fully replaced and no
	longer used back in 2014 but we didn't get around to removing it. Now it is
	gone. The SLP vectorizer is the suggested non-loop vectorization pass.

	* A new tool opt-viewer.py has been added to visualize optimization remarks in
	HTML. The tool processes the YAML files produced by clang with the
	-fsave-optimization-record option.

	* A new CMake macro ``LLVM_REVERSE_ITERATION`` has been added. If enabled, all
	supported unordered LLVM containers would be iterated in reverse order. This
	is useful for uncovering non-determinism caused by iteration of unordered
	containers. Currently, it supports reverse iteration of SmallPtrSet and
	DenseMap.

	* A new tool ``llvm-dlltool`` has been added to create short import libraries
	from GNU style definition files. The tool utilizes the PE COFF SPEC Import
	Library Format and PE COFF Auxiliary Weak Externals Format to achieve
	compatibility with LLD and MSVC LINK.


	Changes to the LLVM IR
	----------------------

	* The datalayout string may now indicate an address space to use for
	the pointer type of ``alloca`` rather than the default of 0.

	* Added ``speculatable`` attribute indicating a function which has no
	side-effects which could inhibit hoisting of calls.

	Changes to the Arm Targets
	--------------------------

	During this release the AArch64 target has:

	* A much improved Global ISel at O0.
	* Support for ARMv8.1 8.2 and 8.3 instructions.
	* New scheduler information for ThunderX2.
	* Some SVE type changes but not much more than that.
	* Made instruction fusion more aggressive, resulting in speedups
	for code making use of AArch64 AES instructions. AES fusion has been
	enabled for most Cortex-A cores and the AArch64MacroFusion pass was moved
	to the generic MacroFusion pass.
	* Added preferred function alignments for most Cortex-A cores.
	* OpenMP "offload-to-self" base support.

	During this release the ARM target has:

	* Improved, but still mostly broken, Global ISel.
	* Scheduling models update, new schedule for Cortex-A57.
	* Hardware breakpoint support in LLDB.
	* New assembler error handling, with spelling corrections and multiple
	suggestions on how to fix problems.
	* Improved mixed ARM/Thumb code generation. Some cases in which wrong
	relocations were emitted have been fixed.
	* Added initial support for mixed ARM/Thumb link-time optimization, using the
	thumb-mode target feature.

	Changes to the MIPS Target
	--------------------------

	* The microMIPS64R6 backend is deprecated and will be removed in the next
	release.

	* The MIPS backend now directly supports vector types for arguments and return
	values (previously this required ABI specific LLVM IR).

	* Added documentation for how the MIPS backend handles address lowering.

	* Added a GCC compatible option -m(no-)madd4 to control the generation of four
	operand multiply addition/subtraction instructions.

	* Added basic support for the XRay instrumentation system.

	* Added support for more assembly aliases and macros.

	* Added support for the ``micromips`` and ``nomicromips`` function attributes
	which control micromips code generation on a per function basis.

	* Added the ``long-calls`` feature for non-pic environments. This feature is
	used where the callee is out of range of the caller using a standard call
	sequence. It must be enabled specifically.

	* Added support for performing microMIPS code generation via function
	attributes.

	* Added experimental support for the static relocation model for the N64 ABI.

	* Added partial support for the MT ASE.

	* Added basic support for code size reduction for microMIPS.

	* Fixed numerous bugs including: multi-precision arithmetic support, various
	vectorization bugs, debug information for thread local variables, debug
	sections lacking the correct flags, crashing when disassembling sections
	whose size is not a multiple of two or four.


	Changes to the PowerPC Target
	-----------------------------

	* Additional support and exploitation of POWER ISA 3.0: vabsdub, vabsduh,
	vabsduw, modsw, moduw, modsd, modud, lxv, stxv, vextublx, vextubrx, vextuhlx,
	vextuhrx, vextuwlx, vextuwrx, vextsb2w, vextsb2d, vextsh2w, vextsh2d, and
	vextsw2d

	* Implemented Optimal Code Sequences from The PowerPC Compiler Writer's Guide.

	* Enable -fomit-frame-pointer by default.

	* Improved handling of bit reverse intrinsic.

	* Improved handling of memcpy and memcmp functions.

	* Improved handling of branches with static branch hints.

	* Improved codegen for atomic load_acquire.

	* Improved block placement during code layout

	* Many improvements to instruction selection and code generation


	Changes to the X86 Target
	-------------------------

	* Added initial AMD Ryzen (znver1) scheduler support.

	* Added support for Intel Goldmont CPUs.

	* Add support for avx512vpopcntdq instructions.

	* Added heuristics to convert CMOV into branches when it may be profitable.

	* More aggressive inlining of memcmp calls.

	* Improve vXi64 shuffles on 32-bit targets.

	* Improved use of PMOVMSKB for any_of/all_of comparision reductions.

	* Improved Silvermont, Sandybridge, and Jaguar (btver2) schedulers.

	* Improved support for AVX512 vector rotations.

	* Added support for AMD Lightweight Profiling (LWP) instructions.

	* Avoid using slow LEA instructions.

	* Use alternative sequences for multiply by constant.

	* Improved lowering of strided shuffles.

	* Improved the AVX512 cost model used by the vectorizer.

	* Fix scalar code performance when AVX512 is enabled by making i1's illegal.

	* Fixed many inline assembly bugs.

	* Preliminary support for tracing NetBSD processes and core files with a single
	thread in LLDB.

	Changes to the AMDGPU Target
	-----------------------------

	* Initial gfx9 support

	Changes to the AVR Target
	-----------------------------

	This release consists mainly of bugfixes and implementations of features
	required for compiling basic Rust programs.

	* Enable the branch relaxation pass so that we don't crash on large
	stack load/stores

	* Add support for lowering bit-rotations to the native ``ror`` and ``rol``
	instructions

	* Fix bug where function pointers were treated as pointers to RAM and not
	pointers to program memory

	* Fix broken code generation for shift-by-variable expressions

	* Support zero-sized types in argument lists; this is impossible in C,
	but possible in Rust


	Changes to the C API
	--------------------

	* Deprecated the ``LLVMAddBBVectorizePass`` interface since the ``BBVectorize``
	pass has been removed. It is now a no-op and will be removed in the next
	release. Use ``LLVMAddSLPVectorizePass`` instead to get the supported SLP
	vectorizer.


	External Open Source Projects Using LLVM 5
	==========================================

	Zig Programming Language
	------------------------

	`Zig <http://ziglang.org>`_ is an open-source programming language designed
	for robustness, optimality, and clarity. It integrates closely with C and is
	intended to eventually take the place of C. It uses LLVM to produce highly
	optimized native code and to cross-compile for any target out of the box. Zig
	is in alpha; with a beta release expected in September.

	LDC - the LLVM-based D compiler
	-------------------------------

	`D <http://dlang.org>`_ is a language with C-like syntax and static typing. It
	pragmatically combines efficiency, control, and modeling power, with safety and
	programmer productivity. D supports powerful concepts like Compile-Time Function
	Execution (CTFE) and Template Meta-Programming, provides an innovative approach
	to concurrency and offers many classical paradigms.

	`LDC <http://wiki.dlang.org/LDC>`_ uses the frontend from the reference compiler
	combined with LLVM as backend to produce efficient native code. LDC targets
	x86/x86_64 systems like Linux, OS X, FreeBSD and Windows and also Linux on ARM
	and PowerPC (32/64 bit). Ports to other architectures like AArch64 and MIPS64
	are underway.


	Additional Information
	======================

	A wide variety of additional information is available on the `LLVM web page
	<http://llvm.org/>`_, in particular in the `documentation
	<http://llvm.org/docs/>`_ 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 <http://llvm.org/docs/#maillist>`_.