docs/ReleaseNotes.rst - clang - Git at Google

 =======================================
 Clang 8.0.0 (In-Progress) Release Notes
 =======================================

 .. contents::
    :local:
    :depth: 2

 Written by the `LLVM Team <https://llvm.org/>`_

 .. warning::

    These are in-progress notes for the upcoming Clang 8 release.
    Release notes for previous releases can be found on
    `the Download Page <https://releases.llvm.org/download.html>`_.

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

 This document contains the release notes for the Clang C/C++/Objective-C
 frontend, part of the LLVM Compiler Infrastructure, release 8.0.0. 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 <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM
 releases may be downloaded from the `LLVM releases web
 site <https://llvm.org/releases/>`_.

 For more information about Clang or LLVM, including information about the
 latest release, please see the `Clang Web Site <https://clang.llvm.org>`_ or the
 `LLVM Web Site <https://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 <https://llvm.org/releases/>`_.

 What's New in Clang 8.0.0?
 ==========================

 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
 ------------------

 - Clang supports use of a profile remapping file, which permits
   profile data captured for one version of a program to be applied
   when building another version where symbols have changed (for
   example, due to renaming a class or namespace).
   See the :doc:`UsersManual` for details.

 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 - ``-Wextra-semi-stmt`` is a new diagnostic that diagnoses extra semicolons,
   much like ``-Wextra-semi``. This new diagnostic diagnoses all *unnecessary*
   null statements (expression statements without an expression), unless: the
   semicolon directly follows a macro that was expanded to nothing or if the
   semicolon is within the macro itself. This applies to macros defined in system
   headers as well as user-defined macros.

   .. code-block:: c++

       #define MACRO(x) int x;
       #define NULLMACRO(varname)

       void test() {
         ; // <- warning: ';' with no preceding expression is a null statement

         while (true)
           ; // OK, it is needed.

         switch (my_enum) {
         case E1:
           // stuff
           break;
         case E2:
           ; // OK, it is needed.
         }

         MACRO(v0;) // Extra semicolon, but within macro, so ignored.

         MACRO(v1); // <- warning: ';' with no preceding expression is a null statement

         NULLMACRO(v2); // ignored, NULLMACRO expanded to nothing.
       }

 - ``-Wempty-init-stmt`` is a new diagnostic that diagnoses empty init-statements
   of ``if``, ``switch``, ``range-based for``, unless: the semicolon directly
   follows a macro that was expanded to nothing or if the semicolon is within the
   macro itself (both macros from system headers, and normal macros). This
   diagnostic is in the ``-Wextra-semi-stmt`` group and is enabled in
   ``-Wextra``.

   .. code-block:: c++

       void test() {
         if(; // <- warning: init-statement of 'if' is a null statement
            true)
           ;

         switch (; // <- warning: init-statement of 'switch' is a null statement
                 x) {
           ...
         }

         for (; // <- warning: init-statement of 'range-based for' is a null statement
              int y : S())
           ;
       }


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

 - The experimental feature Pretokenized Headers (PTH) was removed in its
   entirely from Clang. The feature did not properly work with about 1/3 of the
   possible tokens available and was unmaintained.

 - The internals of libc++ include directory detection on MacOS have changed.
   Instead of running a search based on the ``-resource-dir`` flag, the search
   is now based on the path of the compiler in the filesystem. The default
   behaviour should not change. However, if you override ``-resource-dir``
   manually and rely on the old behaviour you will need to add appropriate
   compiler flags for finding the corresponding libc++ include directory.

 New Compiler Flags
 ------------------

 - ``-fprofile-filter-files=[regexes]`` and ``-fprofile-exclude-files=[regexes]``.

   Clang has now options to filter or exclude some files when
   instrumenting for gcov-based profiling.
   See the :doc:`UsersManual` for details.

 - ...

 Deprecated Compiler Flags
 -------------------------

 The following options are deprecated and ignored. They will be removed in
 future versions of Clang.

 - ...

 Modified Compiler Flags
 -----------------------

 - As of clang 8, `alignof` and `_Alignof` return the ABI alignment of a type,
   as opposed to the preferred alignment. `__alignof` still returns the
   preferred alignment. `-fclang-abi-compat=7` (and previous) will make
   `alignof` and `_Alignof` return preferred alignment again.


 New Pragmas in Clang
 --------------------

 - Clang now supports adding multiple `#pragma clang attribute` attributes into
   a scope of pushed attributes.

 Attribute Changes in Clang
 --------------------------

 - ...

 Windows Support
 ---------------

 - clang-cl now supports the use of the precompiled header options /Yc and /Yu
   without the filename argument. When these options are used without the
   filename, a `#pragma hdrstop` inside the source marks the end of the
   precompiled code.

 - clang-cl has a new command-line option, ``/Zc:dllexportInlines-``, similar to
   ``-fvisibility-inlines-hidden`` on non-Windows, that makes class-level
   `dllexport` and `dllimport` attributes not apply to inline member functions.
   This can significantly reduce compile and link times. See the `User's Manual
   <UsersManual.html#the-zc-dllexportinlines-option>`_ for more info.
 - ...


 C Language Changes in Clang
 ---------------------------

 - ...

 ...

 C11 Feature Support
 ^^^^^^^^^^^^^^^^^^^

 ...

 C++ Language Changes in Clang
 -----------------------------

 - ...

 C++1z Feature Support
 ^^^^^^^^^^^^^^^^^^^^^

 ...

 Objective-C Language Changes in Clang
 -------------------------------------

 ...

 OpenCL C Language Changes in Clang
 ----------------------------------

 ...

 ABI Changes in Clang
 --------------------

 - `_Alignof` and `alignof` now return the ABI alignment of a type, as opposed
   to the preferred alignment.

   - This is more in keeping with the language of the standards, as well as
     being compatible with gcc
   - `__alignof` and `__alignof__` still return the preferred alignment of
     a type
   - This shouldn't break any ABI except for things that explicitly ask for
     `alignas(alignof(T))`.
   - If you have interfaces that break with this change, you may wish to switch
     to `alignas(__alignof(T))`, instead of using the `-fclang-abi-compat`
     switch.

 OpenMP Support in Clang
 ----------------------------------


 CUDA Support in Clang
 ---------------------


 Internal API Changes
 --------------------

 These are major API changes that have happened since the 7.0.0 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.

 -  ...

 AST Matchers
 ------------

 - ...

 clang-format
 ------------


 - ...

 libclang
 --------

 ...


 Static Analyzer
 ---------------

 - ...

 ...

 .. _release-notes-ubsan:

 Undefined Behavior Sanitizer (UBSan)
 ------------------------------------

 * The Implicit Conversion Sanitizer (``-fsanitize=implicit-conversion``) group
   was extended. One more type of issues is caught - implicit integer sign change.
   (``-fsanitize=implicit-integer-sign-change``).
   This makes the Implicit Conversion Sanitizer feature-complete,
   with only missing piece being bitfield handling.
   While there is a ``-Wsign-conversion`` diagnostic group that catches this kind
   of issues, it is both noisy, and does not catch **all** the cases.

   .. code-block:: c++

       bool consume(unsigned int val);

       void test(int val) {
         (void)consume(val); // If the value was negative, it is now large positive.
         (void)consume((unsigned int)val); // OK, the conversion is explicit.
       }

   Like some other ``-fsanitize=integer`` checks, these issues are **not**
   undefined behaviour. But they are not *always* intentional, and are somewhat
   hard to track down. This group is **not** enabled by ``-fsanitize=undefined``,
   but the ``-fsanitize=implicit-integer-sign-change`` check
   is enabled by ``-fsanitize=integer``.
   (as is ``-fsanitize=implicit-integer-truncation`` check)

 * The Implicit Conversion Sanitizer (``-fsanitize=implicit-conversion``) has
   learned to sanitize compound assignment operators.

 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 <https://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 <https://lists.llvm.org/mailman/listinfo/cfe-dev>`_.
	=======================================
	Clang 8.0.0 (In-Progress) Release Notes
	=======================================

	.. contents::
	:local:
	:depth: 2

	Written by the `LLVM Team <https://llvm.org/>`_

	.. warning::

	These are in-progress notes for the upcoming Clang 8 release.
	Release notes for previous releases can be found on
	`the Download Page <https://releases.llvm.org/download.html>`_.

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

	This document contains the release notes for the Clang C/C++/Objective-C
	frontend, part of the LLVM Compiler Infrastructure, release 8.0.0. 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 <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM
	releases may be downloaded from the `LLVM releases web
	site <https://llvm.org/releases/>`_.

	For more information about Clang or LLVM, including information about the
	latest release, please see the `Clang Web Site <https://clang.llvm.org>`_ or the
	`LLVM Web Site <https://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 <https://llvm.org/releases/>`_.

	What's New in Clang 8.0.0?
	==========================

	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
	------------------

	- Clang supports use of a profile remapping file, which permits
	profile data captured for one version of a program to be applied
	when building another version where symbols have changed (for
	example, due to renaming a class or namespace).
	See the :doc:`UsersManual` for details.

	Improvements to Clang's diagnostics
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	- ``-Wextra-semi-stmt`` is a new diagnostic that diagnoses extra semicolons,
	much like ``-Wextra-semi``. This new diagnostic diagnoses all unnecessary
	null statements (expression statements without an expression), unless: the
	semicolon directly follows a macro that was expanded to nothing or if the
	semicolon is within the macro itself. This applies to macros defined in system
	headers as well as user-defined macros.

	.. code-block:: c++

	#define MACRO(x) int x;
	#define NULLMACRO(varname)

	void test() {
	; // <- warning: ';' with no preceding expression is a null statement

	while (true)
	; // OK, it is needed.

	switch (my_enum) {
	case E1:
	// stuff
	break;
	case E2:
	; // OK, it is needed.
	}

	MACRO(v0;) // Extra semicolon, but within macro, so ignored.

	MACRO(v1); // <- warning: ';' with no preceding expression is a null statement

	NULLMACRO(v2); // ignored, NULLMACRO expanded to nothing.
	}

	- ``-Wempty-init-stmt`` is a new diagnostic that diagnoses empty init-statements
	of ``if``, ``switch``, ``range-based for``, unless: the semicolon directly
	follows a macro that was expanded to nothing or if the semicolon is within the
	macro itself (both macros from system headers, and normal macros). This
	diagnostic is in the ``-Wextra-semi-stmt`` group and is enabled in
	``-Wextra``.

	.. code-block:: c++

	void test() {
	if(; // <- warning: init-statement of 'if' is a null statement
	true)
	;

	switch (; // <- warning: init-statement of 'switch' is a null statement
	x) {
	...
	}

	for (; // <- warning: init-statement of 'range-based for' is a null statement
	int y : S())
	;
	}


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

	- The experimental feature Pretokenized Headers (PTH) was removed in its
	entirely from Clang. The feature did not properly work with about 1/3 of the
	possible tokens available and was unmaintained.

	- The internals of libc++ include directory detection on MacOS have changed.
	Instead of running a search based on the ``-resource-dir`` flag, the search
	is now based on the path of the compiler in the filesystem. The default
	behaviour should not change. However, if you override ``-resource-dir``
	manually and rely on the old behaviour you will need to add appropriate
	compiler flags for finding the corresponding libc++ include directory.

	New Compiler Flags
	------------------

	- ``-fprofile-filter-files=[regexes]`` and ``-fprofile-exclude-files=[regexes]``.

	Clang has now options to filter or exclude some files when
	instrumenting for gcov-based profiling.
	See the :doc:`UsersManual` for details.

	- ...

	Deprecated Compiler Flags
	-------------------------

	The following options are deprecated and ignored. They will be removed in
	future versions of Clang.

	- ...

	Modified Compiler Flags
	-----------------------

	- As of clang 8, `alignof` and `_Alignof` return the ABI alignment of a type,
	as opposed to the preferred alignment. `__alignof` still returns the
	preferred alignment. `-fclang-abi-compat=7` (and previous) will make
	`alignof` and `_Alignof` return preferred alignment again.


	New Pragmas in Clang
	--------------------

	- Clang now supports adding multiple `#pragma clang attribute` attributes into
	a scope of pushed attributes.

	Attribute Changes in Clang
	--------------------------

	- ...

	Windows Support
	---------------

	- clang-cl now supports the use of the precompiled header options /Yc and /Yu
	without the filename argument. When these options are used without the
	filename, a `#pragma hdrstop` inside the source marks the end of the
	precompiled code.

	- clang-cl has a new command-line option, ``/Zc:dllexportInlines-``, similar to
	``-fvisibility-inlines-hidden`` on non-Windows, that makes class-level
	`dllexport` and `dllimport` attributes not apply to inline member functions.
	This can significantly reduce compile and link times. See the `User's Manual
	<UsersManual.html#the-zc-dllexportinlines-option>`_ for more info.
	- ...


	C Language Changes in Clang
	---------------------------

	- ...

	...

	C11 Feature Support
	^^^^^^^^^^^^^^^^^^^

	...

	C++ Language Changes in Clang
	-----------------------------

	- ...

	C++1z Feature Support
	^^^^^^^^^^^^^^^^^^^^^

	...

	Objective-C Language Changes in Clang
	-------------------------------------

	...

	OpenCL C Language Changes in Clang
	----------------------------------

	...

	ABI Changes in Clang
	--------------------

	- `_Alignof` and `alignof` now return the ABI alignment of a type, as opposed
	to the preferred alignment.

	- This is more in keeping with the language of the standards, as well as
	being compatible with gcc
	- `__alignof` and `__alignof__` still return the preferred alignment of
	a type
	- This shouldn't break any ABI except for things that explicitly ask for
	`alignas(alignof(T))`.
	- If you have interfaces that break with this change, you may wish to switch
	to `alignas(__alignof(T))`, instead of using the `-fclang-abi-compat`
	switch.

	OpenMP Support in Clang
	----------------------------------


	CUDA Support in Clang
	---------------------


	Internal API Changes
	--------------------

	These are major API changes that have happened since the 7.0.0 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.

	- ...

	AST Matchers
	------------

	- ...

	clang-format
	------------


	- ...

	libclang
	--------

	...


	Static Analyzer
	---------------

	- ...

	...

	.. _release-notes-ubsan:

	Undefined Behavior Sanitizer (UBSan)
	------------------------------------

	* The Implicit Conversion Sanitizer (``-fsanitize=implicit-conversion``) group
	was extended. One more type of issues is caught - implicit integer sign change.
	(``-fsanitize=implicit-integer-sign-change``).
	This makes the Implicit Conversion Sanitizer feature-complete,
	with only missing piece being bitfield handling.
	While there is a ``-Wsign-conversion`` diagnostic group that catches this kind
	of issues, it is both noisy, and does not catch all the cases.

	.. code-block:: c++

	bool consume(unsigned int val);

	void test(int val) {
	(void)consume(val); // If the value was negative, it is now large positive.
	(void)consume((unsigned int)val); // OK, the conversion is explicit.
	}

	Like some other ``-fsanitize=integer`` checks, these issues are not
	undefined behaviour. But they are not always intentional, and are somewhat
	hard to track down. This group is not enabled by ``-fsanitize=undefined``,
	but the ``-fsanitize=implicit-integer-sign-change`` check
	is enabled by ``-fsanitize=integer``.
	(as is ``-fsanitize=implicit-integer-truncation`` check)

	* The Implicit Conversion Sanitizer (``-fsanitize=implicit-conversion``) has
	learned to sanitize compound assignment operators.

	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 <https://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 <https://lists.llvm.org/mailman/listinfo/cfe-dev>`_.