| ========================= |
| Clang 4.0.0 Release Notes |
| ========================= |
| |
| .. contents:: |
| :local: |
| :depth: 2 |
| |
| Written by the `LLVM Team <http://llvm.org/>`_ |
| |
| Introduction |
| ============ |
| |
| This document contains the release notes for the Clang C/C++/Objective-C/OpenCL |
| frontend, part of the LLVM Compiler Infrastructure, release 4.0.0. Here we |
| describe the status of Clang in some detail, including major |
| improvements from the previous release and new feature work. For the |
| general LLVM release notes, see `the LLVM |
| documentation <http://llvm.org/docs/ReleaseNotes.html>`_. All LLVM |
| releases may be downloaded from the `LLVM releases web |
| site <http://llvm.org/releases/>`_. |
| |
| For more information about Clang or LLVM, including information about |
| the latest release, please check out the main please see the `Clang Web |
| Site <http://clang.llvm.org>`_ or the `LLVM Web |
| Site <http://llvm.org>`_. |
| |
| What's New in Clang 4.0.0? |
| ========================== |
| |
| Some of the major new features and improvements to Clang are listed |
| here. Generic improvements to Clang as a whole or to its underlying |
| infrastructure are described first, followed by language-specific |
| sections with improvements to Clang's support for those languages. |
| |
| Major New Features |
| ------------------ |
| |
| - The `diagnose_if <AttributeReference.html#diagnose-if>`_ attribute has been |
| added to clang. This attribute allows |
| clang to emit a warning or error if a function call meets one or more |
| user-specified conditions. |
| |
| - Enhanced devirtualization with |
| `-fstrict-vtable-pointers <UsersManual.html#cmdoption-fstrict-vtable-pointers>`_. |
| Clang devirtualizes across different basic blocks, like loops: |
| |
| .. code-block:: c++ |
| |
| struct A { |
| virtual void foo(); |
| }; |
| void indirect(A &a, int n) { |
| for (int i = 0 ; i < n; i++) |
| a.foo(); |
| } |
| void test(int n) { |
| A a; |
| indirect(a, n); |
| } |
| |
| |
| Improvements to ThinLTO (-flto=thin) |
| ------------------------------------ |
| - Integration with profile data (PGO). When available, profile data enables |
| more accurate function importing decisions, as well as cross-module indirect |
| call promotion. |
| - Significant build-time and binary-size improvements when compiling with debug |
| info (``-g``). |
| |
| New Compiler Flags |
| ------------------ |
| |
| - The option ``-Og`` has been added to optimize the debugging experience. |
| For now, this option is exactly the same as ``-O1``. However, in the future, |
| some other optimizations might be enabled or disabled. |
| |
| - The option ``-MJ`` has been added to simplify adding JSON compilation |
| database output into existing build systems. |
| |
| |
| OpenCL C Language Changes in Clang |
| ---------------------------------- |
| |
| **The following bugs in the OpenCL header have been fixed:** |
| |
| * Added missing ``overloadable`` and ``convergent`` attributes. |
| * Removed some erroneous extra ``native_*`` functions. |
| |
| **The following bugs in the generation of metadata have been fixed:** |
| |
| * Corrected the SPIR version depending on the OpenCL version. |
| * Source level address spaces are taken from the SPIR specification. |
| * Image types now contain no access qualifier. |
| |
| **The following bugs in the AMD target have been fixed:** |
| |
| * Corrected the bitwidth of ``size_t`` and NULL pointer value with respect to |
| address spaces. |
| * Added ``cl_khr_subgroups``, ``cl_amd_media_ops`` and ``cl_amd_media_ops2`` |
| extensions. |
| * Added ``cl-denorms-are-zero`` support. |
| * Changed address spaces for image objects to be ``constant``. |
| * Added little-endian. |
| |
| **The following bugs in OpenCL 2.0 have been fixed:** |
| |
| * Fixed pipe builtin function return type, added extra argument to generated |
| IR intrinsics to propagate size and alignment information of the pipe packed |
| type. |
| * Improved pipe type to accommodate access qualifiers. |
| * Added correct address space to the ObjC block generation and ``enqueue_kernel`` |
| prototype. |
| * Improved handling of integer parameters of ``enqueue_kernel`` prototype. We |
| now allow ``size_t`` instead of ``int`` for specifying block parameter sizes. |
| * Allow using NULL (aka ``CLK_NULL_QUEUE``) with ``queue_t``. |
| |
| |
| **Improved the following diagnostics:** |
| |
| * Disallow address spaces other than ``global`` for kernel pointer parameters. |
| * Correct the use of half type argument and pointer assignment with |
| dereferencing. |
| * Disallow variadic arguments in functions and blocks. |
| * Allow partial initializer for array and struct. |
| |
| **Some changes to OpenCL extensions have been made:** |
| |
| * Added ``cl_khr_mipmap_image``. |
| * Added ``-cl-ext`` flag to allow overwriting supported extensions otherwise |
| set by the target compiled for (Example: ``-cl-ext=-all,+cl_khr_fp16``). |
| * New types and functions can now be flexibly added to extensions using the |
| following pragmas instead of modifying the Clang source code: |
| |
| .. code-block:: c |
| |
| #pragma OPENCL EXTENSION the_new_extension_name : begin |
| // declare types and functions associated with the extension here |
| #pragma OPENCL EXTENSION the_new_extension_name : end |
| |
| |
| **Miscellaneous changes:** |
| |
| * Fix ``__builtin_astype`` to cast between different address space objects. |
| * Allow using ``opencl_unroll_hint`` with earlier OpenCL versions than 2.0. |
| * Improved handling of floating point literal to default to single precision if |
| fp64 extension is not enabled. |
| * Refactor ``sampler_t`` implementation to simplify initializer representation |
| which is now handled as a compiler builtin function with an integer value |
| passed into it. |
| * Change fake address space map to use the SPIR convention. |
| * Added `the OpenCL manual <UsersManual.html#opencl-features>`_ to Clang |
| documentation. |
| |
| |
| Static Analyzer |
| --------------- |
| |
| With the option ``--show-description``, scan-build's list of defects will also |
| show the description of the defects. |
| |
| The analyzer now provides better support of code that uses gtest. |
| |
| Several new checks were added: |
| |
| - The analyzer warns when virtual calls are made from constructors or |
| destructors. This check is off by default but can be enabled by passing the |
| following command to scan-build: ``-enable-checker optin.cplusplus.VirtualCall``. |
| - The analyzer checks for synthesized copy properties of mutable types in |
| Objective C, such as ``NSMutableArray``. Calling the setter for these properties |
| will store an immutable copy of the value. |
| - The analyzer checks for calls to ``dispatch_once()`` that use an Objective-C |
| instance variable as the predicate. Using an instance variable as a predicate |
| may result in the passed-in block being executed multiple times or not at all. |
| These calls should be rewritten either to use a lock or to store the predicate |
| in a global or static variable. |
| - The analyzer checks for unintended comparisons of ``NSNumber``, ``CFNumberRef``, and |
| other Cocoa number objects to scalar values. |
| |
| |
| Additional Information |
| ====================== |
| |
| A wide variety of additional information is available on the `Clang web |
| page <http://clang.llvm.org/>`_. The web page contains versions of the |
| API documentation which are 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 "``clang/docs/``" directory in the Clang |
| tree. |
| |
| If you have any questions or comments about Clang, please feel free to |
| contact us via the `mailing |
| list <http://lists.llvm.org/mailman/listinfo/cfe-dev>`_. |