| ===================================== |
| Clang 3.5 (In-Progress) Release Notes |
| ===================================== |
| |
| .. contents:: |
| :local: |
| :depth: 2 |
| |
| Written by the `LLVM Team <http://llvm.org/>`_ |
| |
| .. warning:: |
| |
| These are in-progress notes for the upcoming Clang 3.5 release. You may |
| prefer the `Clang 3.4 Release Notes |
| <http://llvm.org/releases/3.4/tools/clang/docs/ReleaseNotes.html>`_. |
| |
| Introduction |
| ============ |
| |
| This document contains the release notes for the Clang C/C++/Objective-C |
| frontend, part of the LLVM Compiler Infrastructure, release 3.5. 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>`_. |
| |
| Note that if you are reading this file from a Subversion checkout or the |
| main Clang 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 <http://llvm.org/releases/>`_. |
| |
| What's New in Clang 3.5? |
| ======================== |
| |
| 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 |
| ------------------ |
| |
| - Clang uses the new MingW ABI |
| GCC 4.7 changed the mingw ABI. Clang 3.4 and older use the GCC 4.6 |
| ABI. Clang 3.5 and newer use the GCC 4.7 abi. |
| |
| - The __has_attribute feature test is now target-aware. Older versions of Clang |
| would return true when the attribute spelling was known, regardless of whether |
| the attribute was available to the specific target. Clang now returns true |
| only when the attribute pertains to the current compilation target. |
| |
| - Clang 3.5 now has parsing and semantic-analysis support for all OpenMP 3.1 |
| pragmas (except atomics and ordered). LLVM's OpenMP runtime library, |
| originally developed by Intel, has been modified to work on ARM, PowerPC, |
| as well as X86. Code generation support is minimal at this point and will |
| continue to be developed for 3.6, along with the rest of OpenMP 3.1. |
| Support for OpenMP 4.0 features, such as SIMD and target accelerator |
| directives, is also in progress. Contributors to this work include AMD, |
| Argonne National Lab., IBM, Intel, Texas Instruments, University of Houston |
| and many others. |
| |
| Improvements to Clang's diagnostics |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| Clang's diagnostics are constantly being improved to catch more issues, |
| explain them more clearly, and provide more accurate source information |
| about them. The improvements since the 3.4 release include: |
| |
| - GCC compatibility: Clang displays a warning on unsupported gcc |
| optimization flags instead of an error. |
| |
| - Remarks system: Clang supports `-R` flags for enabling remarks. These are |
| diagnostic messages that provide information about the compilation process, |
| but don't suggest that a problem has been detected. As such, they cannot |
| be upgraded to errors with `-Werror` or `-Rerror`. A `-Reverything` flag |
| is provided (paralleling `-Weverything`) to turn on all remarks. |
| |
| - New remark `-Rpass`: Clang provides information about decisions made by |
| optimization passes during compilation. See :ref:`opt_rpass`. |
| |
| - New warning `-Wabsolute-value`: Clang warns about incorrect or useless usage |
| of the absolute functions (`abs`, `fabsf`, etc). |
| |
| .. code-block:: c |
| |
| #include <stdlib.h> |
| void foo() { |
| unsigned int i=0; |
| abs(i); |
| } |
| |
| returns |
| `warning: taking the absolute value of unsigned type 'unsigned int' has no effect [-Wabsolute-value]` |
| |
| or |
| |
| .. code-block:: c |
| |
| #include <stdlib.h> |
| void plop() { |
| long long i=0; |
| abs(i); |
| } |
| |
| returns |
| `warning: absolute value function 'abs' given an argument of type 'long long' but has parameter of type 'int' which may cause truncation of value [-Wabsolute-value] use function 'llabs' instead` |
| |
| - New warning `-Wtautological-pointer-compare`: |
| |
| .. code-block:: c++ |
| |
| #include <stddef.h> |
| void foo() { |
| int arr[5]; |
| int x; |
| // warn on these conditionals |
| if (foo); |
| if (arr); |
| if (&x); |
| if (foo == NULL); |
| if (arr == NULL); |
| if (&x == NULL); |
| } |
| |
| returns |
| `warning: comparison of address of 'x' equal to a null pointer is always false [-Wtautological-pointer-compare]` |
| |
| - New warning `-Wtautological-undefined-compare`: |
| |
| .. code-block:: c++ |
| |
| #include <stddef.h> |
| void f(int &x) { |
| if (&x == nullptr) { } |
| } |
| |
| returns |
| `warning: reference cannot be bound to dereferenced null pointer in well-defined C++ code; comparison may be assumed to always evaluate to false [-Wtautological-undefined-compare]` |
| |
| - ... |
| |
| New Compiler Flags |
| ------------------ |
| |
| The integrated assembler is now turned on by default on ARM (and Thumb), |
| so the use of the option `-fintegrated-as` is now redundant on those |
| architectures. This is an important move to both *eat our own dog food* |
| and to ease cross-compilation tremendously. |
| |
| We are aware of the problems that this may cause for code bases that |
| rely on specific GNU syntax or extensions, and we're working towards |
| getting them all fixed. Please, report bugs or feature requests if |
| you find anything. In the meantime, use `-fno-integrated-as` to revert |
| back the call to GNU assembler. |
| |
| In order to provide better diagnostics, the integrated assembler validates |
| inline assembly when the integrated assembler is enabled. Because this is |
| considered a feature of the compiler, it is controlled via the `fintegrated-as` |
| and `fno-integrated-as` flags which enable and disable the integrated assembler |
| respectively. `-integrated-as` and `-no-integrated-as` are now considered |
| legacy flags (but are available as an alias to prevent breaking existing users), |
| and users are encouraged to switch to the equivalent new feature flag. |
| |
| Deprecated flags `-faddress-sanitizer`, `-fthread-sanitizer`, |
| `-fcatch-undefined-behavior` and `-fbounds-checking` were removed in favor of |
| `-fsanitize=` family of flags. |
| |
| It is now possible to get optimization reports from the major transformation |
| passes via three new flags: `-Rpass`, `-Rpass-missed` and `-Rpass-analysis`. |
| These flags take a POSIX regular expression which indicates the name |
| of the pass (or passes) that should emit optimization remarks. |
| |
| Options `-u` and `-z` are forwarded to the linker on gnutools toolchains. |
| |
| |
| New Pragmas in Clang |
| ----------------------- |
| |
| Loop optimization hints can be specified using the new `#pragma clang loop` |
| directive just prior to the desired loop. The directive allows vectorization and |
| interleaving to be enabled or disabled. Vector width as well as interleave count |
| can be manually specified. See :ref:`langext-pragma-loop` for details. |
| |
| C Language Changes in Clang |
| --------------------------- |
| |
| ... |
| |
| C11 Feature Support |
| ^^^^^^^^^^^^^^^^^^^ |
| |
| ... |
| |
| C++ Language Changes in Clang |
| ----------------------------- |
| |
| - Reference parameters and return values from functions are more aggressively |
| assumed to refer to valid objects when optimizing. Clang will attempt to |
| issue a warning by default if it sees null checks being performed on |
| references, and `-fsanitize=null` can be used to detect null references |
| being formed at runtime. |
| |
| - ... |
| |
| C++17 Feature Support |
| ^^^^^^^^^^^^^^^^^^^^^ |
| |
| Clang has experimental support for some proposed C++1z (tentatively, C++17) |
| features. This support can be enabled using the `-std=c++1z` flag. The |
| supported features are: |
| |
| - `static_assert(expr)` with no message |
| |
| - `for (identifier : range)` as a synonym for `for (auto &&identifier : range)` |
| |
| - `template<template<...> typename>` as a synonym for `template<template<...> class>` |
| |
| Additionally, trigraphs are not recognized by default in this mode. |
| `-ftrigraphs` can be used if you need to parse legacy code that uses trigraphs. |
| Note that these features may be changed or removed in future Clang releases |
| without notice. |
| |
| Objective-C Language Changes in Clang |
| ------------------------------------- |
| |
| ... |
| |
| OpenCL C Language Changes in Clang |
| ---------------------------------- |
| |
| ... |
| |
| OpenMP C/C++ Language Changes in Clang |
| -------------------------------------- |
| |
| - `Status of supported OpenMP constructs |
| <https://github.com/clang-omp/clang/wiki/Status-of-supported-OpenMP-constructs>`_. |
| |
| |
| Internal API Changes |
| -------------------- |
| |
| These are major API changes that have happened since the 3.4 release of |
| Clang. If upgrading an external codebase that uses Clang as a library, |
| this section should help get you past the largest hurdles of upgrading. |
| |
| - Clang uses `std::unique_ptr<T>` in many places where it used to use |
| raw `T *` pointers. |
| |
| libclang |
| -------- |
| |
| ... |
| |
| Static Analyzer |
| --------------- |
| |
| Check for code testing a variable for 0 after using it as a denominator. |
| This new checker, alpha.core.TestAfterDivZero, catches issues like this: |
| |
| .. code-block:: c |
| |
| int sum = ... |
| int avg = sum / count; // potential division by zero... |
| if (count == 0) { ... } // ...caught here |
| |
| |
| The `-analyzer-config` options are now passed from scan-build through to |
| ccc-analyzer and then to Clang. |
| |
| With the option `-analyzer-config stable-report-filename=true`, |
| instead of `report-XXXXXX.html`, scan-build/clang analyzer generate |
| `report-<filename>-<function, method name>-<function position>-<id>.html`. |
| (id = i++ for several issues found in the same function/method). |
| |
| List the function/method name in the index page of scan-build. |
| |
| ... |
| |
| Core Analysis Improvements |
| ========================== |
| |
| - ... |
| |
| New Issues Found |
| ================ |
| |
| - ... |
| |
| Python Binding Changes |
| ---------------------- |
| |
| The following methods have been added: |
| |
| - ... |
| |
| Significant Known Problems |
| ========================== |
| |
| 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.cs.uiuc.edu/mailman/listinfo/cfe-dev>`_. |