Clang Compiler User's Manual
============================
+.. include:: <isonum.txt>
+
.. contents::
:local:
`Clang Static Analyzer <http://clang-analyzer.llvm.org>`_, please see its web
page.
+Clang is one component in a complete toolchain for C family languages.
+A separate document describes the other pieces necessary to
+:doc:`assemble a complete toolchain <Toolchain>`.
+
Clang is designed to support the C family of programming languages,
which includes :ref:`C <c>`, :ref:`Objective-C <objc>`, :ref:`C++ <cxx>`, and
:ref:`Objective-C++ <objcxx>` as well as many dialects of those. For
variants depending on base language.
- :ref:`C++ Language <cxx>`
- :ref:`Objective C++ Language <objcxx>`
+- :ref:`OpenCL C Language <opencl>`: v1.0, v1.1, v1.2, v2.0.
In addition to these base languages and their dialects, Clang supports a
broad variety of language extensions, which are documented in the
.. option:: -Wfoo
Enable warning "foo".
+ See the :doc:`diagnostics reference <DiagnosticsReference>` for a complete
+ list of the warning flags that can be specified in this way.
.. option:: -Wno-foo
.. option:: -ferror-limit=123
Stop emitting diagnostics after 123 errors have been produced. The default is
- 20, and the error limit can be disabled with :option:`-ferror-limit=0`.
+ 20, and the error limit can be disabled with `-ferror-limit=0`.
.. option:: -ftemplate-backtrace-limit=123
Only emit up to 123 template instantiation notes within the template
instantiation backtrace for a single warning or error. The default is 10, and
- the limit can be disabled with :option:`-ftemplate-backtrace-limit=0`.
+ the limit can be disabled with `-ftemplate-backtrace-limit=0`.
.. _cl_diag_formatting:
Clang aims to produce beautiful diagnostics by default, particularly for
new users that first come to Clang. However, different people have
-different preferences, and sometimes Clang is driven by another program
-that wants to parse simple and consistent output, not a person. For
+different preferences, and sometimes Clang is driven not by a human,
+but by a program that wants consistent and easily parsable output. For
these cases, Clang provides a wide range of options to control the exact
output format of the diagnostics that it generates.
by category, so it should be a high level category. We want dozens
of these, not hundreds or thousands of them.
+.. _opt_fsave-optimization-record:
+
+**-fsave-optimization-record**
+ Write optimization remarks to a YAML file.
+
+ This option, which defaults to off, controls whether Clang writes
+ optimization reports to a YAML file. By recording diagnostics in a file,
+ using a structured YAML format, users can parse or sort the remarks in a
+ convenient way.
+
+.. _opt_foptimization-record-file:
+
+**-foptimization-record-file**
+ Control the file to which optimization reports are written.
+
+ When optimization reports are being output (see
+ :ref:`-fsave-optimization-record <opt_fsave-optimization-record>`), this
+ option controls the file to which those reports are written.
+
+ If this option is not used, optimization records are output to a file named
+ after the primary file being compiled. If that's "foo.c", for example,
+ optimization records are output to "foo.opt.yaml".
+
+.. _opt_fdiagnostics-show-hotness:
+
+**-f[no-]diagnostics-show-hotness**
+ Enable profile hotness information in diagnostic line.
+
+ This option controls whether Clang prints the profile hotness associated
+ with diagnostics in the presence of profile-guided optimization information.
+ This is currently supported with optimization remarks (see
+ :ref:`Options to Emit Optimization Reports <rpass>`). The hotness information
+ allows users to focus on the hot optimization remarks that are likely to be
+ more relevant for run-time performance.
+
+ For example, in this output, the block containing the callsite of `foo` was
+ executed 3000 times according to the profile data:
+
+ ::
+
+ s.c:7:10: remark: foo inlined into bar (hotness: 3000) [-Rpass-analysis=inline]
+ sum += foo(x, x - 2);
+ ^
+
+ This option is implied when
+ :ref:`-fsave-optimization-record <opt_fsave-optimization-record>` is used.
+ Otherwise, it defaults to off.
+
+.. _opt_fdiagnostics-hotness-threshold:
+
+**-fdiagnostics-hotness-threshold**
+ Prevent optimization remarks from being output if they do not have at least
+ this hotness value.
+
+ This option, which defaults to zero, controls the minimum hotness an
+ optimization remark would need in order to be output by Clang. This is
+ currently supported with optimization remarks (see :ref:`Options to Emit
+ Optimization Reports <rpass>`) when profile hotness information in
+ diagnostics is enabled (see
+ :ref:`-fdiagnostics-show-hotness <opt_fdiagnostics-show-hotness>`).
+
.. _opt_fdiagnostics-fixit-info:
**-f[no-]diagnostics-fixit-info**
The -fno-crash-diagnostics flag can be helpful for speeding the process
of generating a delta reduced test case.
+Clang is also capable of generating preprocessed source file(s) and associated
+run script(s) even without a crash. This is specially useful when trying to
+generate a reproducer for warnings or errors while using modules.
+
+.. option:: -gen-reproducer
+
+ Generates preprocessed source files, a reproducer script and if relevant, a
+ cache containing: built module pcm's and all headers needed to rebuilt the
+ same modules.
+
+.. _rpass:
+
Options to Emit Optimization Reports
------------------------------------
Clang offers a family of flags which the optimizers can use to emit
a diagnostic in three cases:
-1. When the pass makes a transformation (:option:`-Rpass`).
+1. When the pass makes a transformation (`-Rpass`).
-2. When the pass fails to make a transformation (:option:`-Rpass-missed`).
+2. When the pass fails to make a transformation (`-Rpass-missed`).
3. When the pass determines whether or not to make a transformation
- (:option:`-Rpass-analysis`).
+ (`-Rpass-analysis`).
-NOTE: Although the discussion below focuses on :option:`-Rpass`, the exact
-same options apply to :option:`-Rpass-missed` and :option:`-Rpass-analysis`.
+NOTE: Although the discussion below focuses on `-Rpass`, the exact
+same options apply to `-Rpass-missed` and `-Rpass-analysis`.
Since there are dozens of passes inside the compiler, each of these flags
take a regular expression that identifies the name of the pass which should
Note that remarks from the inliner are identified with `[-Rpass=inline]`.
To request a report from every optimization pass, you should use
-:option:`-Rpass=.*` (in fact, you can use any valid POSIX regular
+`-Rpass=.*` (in fact, you can use any valid POSIX regular
expression). However, do not expect a report from every transformation
made by the compiler. Optimization remarks do not really make sense
outside of the major transformations (e.g., inlining, vectorization,
loop optimizations) and not every optimization pass supports this
feature.
+Note that when using profile-guided optimization information, profile hotness
+information can be included in the remarks (see
+:ref:`-fdiagnostics-show-hotness <opt_fdiagnostics-show-hotness>`).
+
Current limitations
^^^^^^^^^^^^^^^^^^^
2. Some source locations are not displayed correctly. The front end has
a more detailed source location tracking than the locations included
in the debug info (e.g., the front end can locate code inside macro
- expansions). However, the locations used by :option:`-Rpass` are
+ expansions). However, the locations used by `-Rpass` are
translated from debug annotations. That translation can be lossy,
which results in some remarks having no location information.
particularly useful when writing a header file that will be compiled by
other people, because you don't know what warning flags they build with.
-In the below example :option:`-Wmultichar` is ignored for only a single line of
-code, after which the diagnostics return to whatever state had previously
+In the below example :option:`-Wextra-tokens` is ignored for only a single line
+of code, after which the diagnostics return to whatever state had previously
existed.
.. code-block:: c
+ #if foo
+ #endif foo // warning: extra tokens at end of #endif directive
+
#pragma clang diagnostic push
- #pragma clang diagnostic ignored "-Wmultichar"
+ #pragma clang diagnostic ignored "-Wextra-tokens"
- char b = 'df'; // no warning.
+ #if foo
+ #endif foo // no warning
#pragma clang diagnostic pop
.. code-block:: c
- char a = 'xy'; // warning
+ #if foo
+ #endif foo // warning: extra tokens at end of #endif directive
#pragma clang system_header
- char b = 'ab'; // no warning
+ #if foo
+ #endif foo // no warning
-The :option:`--system-header-prefix=` and :option:`--no-system-header-prefix=`
+The `--system-header-prefix=` and `--no-system-header-prefix=`
command-line arguments can be used to override whether subsets of an include
path are treated as system headers. When the name in a ``#include`` directive
is found within a header search path and starts with a system prefix, the
^^^^^^^^^^^^^^^^^^^^^
To generate a PCH file using Clang, one invokes Clang with the
-:option:`-x <language>-header` option. This mirrors the interface in GCC
+`-x <language>-header` option. This mirrors the interface in GCC
for generating PCH files:
.. code-block:: console
Building a relocatable precompiled header requires two additional
arguments. First, pass the ``--relocatable-pch`` flag to indicate that
the resulting PCH file should be relocatable. Second, pass
-:option:`-isysroot /path/to/build`, which makes all includes for your library
+`-isysroot /path/to/build`, which makes all includes for your library
relative to the build directory. For example:
.. code-block:: console
When loading the relocatable PCH file, the various headers used in the
PCH file are found from the system header root. For example, ``mylib.h``
can be found in ``/usr/include/mylib.h``. If the headers are installed
-in some other system root, the :option:`-isysroot` option can be used provide
+in some other system root, the `-isysroot` option can be used provide
a different system root from which the headers will be based. For
-example, :option:`-isysroot /Developer/SDKs/MacOSX10.4u.sdk` will look for
+example, `-isysroot /Developer/SDKs/MacOSX10.4u.sdk` will look for
``mylib.h`` in ``/Developer/SDKs/MacOSX10.4u.sdk/usr/include/mylib.h``.
Relocatable precompiled headers are intended to be used in a limited
``-fsanitize=address``:
:doc:`AddressSanitizer`, a memory error
detector.
- - ``-fsanitize=integer``: Enables checks for undefined or
- suspicious integer behavior.
- .. _opt_fsanitize_thread:
``-fsanitize=thread``: :doc:`ThreadSanitizer`, a data race detector.
- .. _opt_fsanitize_memory:
``-fsanitize=memory``: :doc:`MemorySanitizer`,
- an *experimental* detector of uninitialized reads. Not ready for
- widespread use.
+ a detector of uninitialized reads. Requires instrumentation of all
+ program code.
- .. _opt_fsanitize_undefined:
- ``-fsanitize=undefined``: Fast and compatible undefined behavior
- checker. Enables the undefined behavior checks that have small
- runtime cost and no impact on address space layout or ABI. This
- includes all of the checks listed below other than
- ``unsigned-integer-overflow``.
-
- - ``-fsanitize=undefined-trap``: This is a deprecated alias for
- ``-fsanitize=undefined``.
+ ``-fsanitize=undefined``: :doc:`UndefinedBehaviorSanitizer`,
+ a fast and compatible undefined behavior checker.
- ``-fsanitize=dataflow``: :doc:`DataFlowSanitizer`, a general data
flow analysis.
- ``-fsanitize=cfi``: :doc:`control flow integrity <ControlFlowIntegrity>`
- checks. Implies ``-flto``.
+ checks. Requires ``-flto``.
- ``-fsanitize=safe-stack``: :doc:`safe stack <SafeStack>`
protection against stack-based memory corruption errors.
- The following more fine-grained checks are also available:
-
- - ``-fsanitize=alignment``: Use of a misaligned pointer or creation
- of a misaligned reference.
- - ``-fsanitize=bool``: Load of a ``bool`` value which is neither
- ``true`` nor ``false``.
- - ``-fsanitize=bounds``: Out of bounds array indexing, in cases
- where the array bound can be statically determined.
- - ``-fsanitize=cfi-cast-strict``: Enables :ref:`strict cast checks
- <cfi-strictness>`.
- - ``-fsanitize=cfi-derived-cast``: Base-to-derived cast to the wrong
- dynamic type. Implies ``-flto``.
- - ``-fsanitize=cfi-unrelated-cast``: Cast from ``void*`` or another
- unrelated type to the wrong dynamic type. Implies ``-flto``.
- - ``-fsanitize=cfi-nvcall``: Non-virtual call via an object whose vptr is of
- the wrong dynamic type. Implies ``-flto``.
- - ``-fsanitize=cfi-vcall``: Virtual call via an object whose vptr is of the
- wrong dynamic type. Implies ``-flto``.
- - ``-fsanitize=enum``: Load of a value of an enumerated type which
- is not in the range of representable values for that enumerated
- type.
- - ``-fsanitize=float-cast-overflow``: Conversion to, from, or
- between floating-point types which would overflow the
- destination.
- - ``-fsanitize=float-divide-by-zero``: Floating point division by
- zero.
- - ``-fsanitize=function``: Indirect call of a function through a
- function pointer of the wrong type (Linux, C++ and x86/x86_64 only).
- - ``-fsanitize=integer-divide-by-zero``: Integer division by zero.
- - ``-fsanitize=nonnull-attribute``: Passing null pointer as a function
- parameter which is declared to never be null.
- - ``-fsanitize=null``: Use of a null pointer or creation of a null
- reference.
- - ``-fsanitize=object-size``: An attempt to use bytes which the
- optimizer can determine are not part of the object being
- accessed. The sizes of objects are determined using
- ``__builtin_object_size``, and consequently may be able to detect
- more problems at higher optimization levels.
- - ``-fsanitize=return``: In C++, reaching the end of a
- value-returning function without returning a value.
- - ``-fsanitize=returns-nonnull-attribute``: Returning null pointer
- from a function which is declared to never return null.
- - ``-fsanitize=shift``: Shift operators where the amount shifted is
- greater or equal to the promoted bit-width of the left hand side
- or less than zero, or where the left hand side is negative. For a
- signed left shift, also checks for signed overflow in C, and for
- unsigned overflow in C++. You can use ``-fsanitize=shift-base`` or
- ``-fsanitize=shift-exponent`` to check only left-hand side or
- right-hand side of shift operation, respectively.
- - ``-fsanitize=signed-integer-overflow``: Signed integer overflow,
- including all the checks added by ``-ftrapv``, and checking for
- overflow in signed division (``INT_MIN / -1``).
- - ``-fsanitize=unreachable``: If control flow reaches
- ``__builtin_unreachable``.
- - ``-fsanitize=unsigned-integer-overflow``: Unsigned integer
- overflows.
- - ``-fsanitize=vla-bound``: A variable-length array whose bound
- does not evaluate to a positive value.
- - ``-fsanitize=vptr``: Use of an object whose vptr indicates that
- it is of the wrong dynamic type, or that its lifetime has not
- begun or has ended. Incompatible with ``-fno-rtti``.
-
- You can turn off or modify checks for certain source files, functions
- or even variables by providing a special file:
-
- - ``-fsanitize-blacklist=/path/to/blacklist/file``: disable or modify
- sanitizer checks for objects listed in the file. See
- :doc:`SanitizerSpecialCaseList` for file format description.
- - ``-fno-sanitize-blacklist``: don't use blacklist file, if it was
- specified earlier in the command line.
-
- Extra features of MemorySanitizer (require explicit
- ``-fsanitize=memory``):
-
- - ``-fsanitize-memory-track-origins[=level]``: Enables origin tracking in
- MemorySanitizer. Adds a second section to MemorySanitizer
- reports pointing to the heap or stack allocation the
- uninitialized bits came from. Slows down execution by additional
- 1.5x-2x.
-
- Possible values for level are 0 (off), 1, 2 (default). Level 2
- adds more sections to MemorySanitizer reports describing the
- order of memory stores the uninitialized value went
- through. This mode may use extra memory in programs that copy
- uninitialized memory a lot.
+ There are more fine-grained checks available: see
+ the :ref:`list <ubsan-checks>` of specific kinds of
+ undefined behavior that can be detected and the :ref:`list <cfi-schemes>`
+ of control flow integrity schemes.
The ``-fsanitize=`` argument must also be provided when linking, in
- order to link to the appropriate runtime library. When using
- ``-fsanitize=vptr`` (or a group that includes it, such as
- ``-fsanitize=undefined``) with a C++ program, the link must be
- performed by ``clang++``, not ``clang``, in order to link against the
- C++-specific parts of the runtime library.
+ order to link to the appropriate runtime library.
It is not possible to combine more than one of the ``-fsanitize=address``,
``-fsanitize=thread``, and ``-fsanitize=memory`` checkers in the same
- program. The ``-fsanitize=undefined`` checks can only be combined with
- ``-fsanitize=address``.
+ program.
**-f[no-]sanitize-recover=check1,check2,...**
+**-f[no-]sanitize-recover=all**
+
Controls which checks enabled by ``-fsanitize=`` flag are non-fatal.
If the check is fatal, program will halt after the first error
of this kind is detected and error report is printed.
- By default, non-fatal checks are those enabled by UndefinedBehaviorSanitizer,
+ By default, non-fatal checks are those enabled by
+ :doc:`UndefinedBehaviorSanitizer`,
except for ``-fsanitize=return`` and ``-fsanitize=unreachable``. Some
- sanitizers (e.g. :doc:`AddressSanitizer`) may not support recovery,
- and always crash the program after the issue is detected.
+ sanitizers may not support recovery (or not support it by default
+ e.g. :doc:`AddressSanitizer`), and always crash the program after the issue
+ is detected.
Note that the ``-fsanitize-trap`` flag has precedence over this flag.
This means that if a check has been configured to trap elsewhere on the
be used (for instance, when building libc or a kernel module), or where
the binary size increase caused by the sanitizer runtime is a concern.
- This flag is only compatible with ``local-bounds``,
- ``unsigned-integer-overflow`` and sanitizers in the ``undefined``
- group other than ``vptr``. If this flag is supplied together with
- ``-fsanitize=undefined``, the ``vptr`` sanitizer will be implicitly
- disabled.
+ This flag is only compatible with :doc:`control flow integrity
+ <ControlFlowIntegrity>` schemes and :doc:`UndefinedBehaviorSanitizer`
+ checks other than ``vptr``. If this flag
+ is supplied together with ``-fsanitize=undefined``, the ``vptr`` sanitizer
+ will be implicitly disabled.
+
+ This flag is enabled by default for sanitizers in the ``cfi`` group.
+
+.. option:: -fsanitize-blacklist=/path/to/blacklist/file
+
+ Disable or modify sanitizer checks for objects (source files, functions,
+ variables, types) listed in the file. See
+ :doc:`SanitizerSpecialCaseList` for file format description.
+
+.. option:: -fno-sanitize-blacklist
+
+ Don't use blacklist file, if it was specified earlier in the command line.
**-f[no-]sanitize-coverage=[type,features,...]**
Enable simple code coverage in addition to certain sanitizers.
See :doc:`SanitizerCoverage` for more details.
+**-f[no-]sanitize-stats**
+
+ Enable simple statistics gathering for the enabled sanitizers.
+ See :doc:`SanitizerStats` for more details.
+
.. option:: -fsanitize-undefined-trap-on-error
Deprecated alias for ``-fsanitize-trap=undefined``.
+.. option:: -fsanitize-cfi-cross-dso
+
+ Enable cross-DSO control flow integrity checks. This flag modifies
+ the behavior of sanitizers in the ``cfi`` group to allow checking
+ of cross-DSO virtual and indirect calls.
+
+
+.. option:: -fstrict-vtable-pointers
+
+ Enable optimizations based on the strict rules for overwriting polymorphic
+ C++ objects, i.e. the vptr is invariant during an object's lifetime.
+ This enables better devirtualization. Turned off by default, because it is
+ still experimental.
+
+.. option:: -ffast-math
+
+ Enable fast-math mode. This defines the ``__FAST_MATH__`` preprocessor
+ macro, and lets the compiler make aggressive, potentially-lossy assumptions
+ about floating-point math. These include:
+
+ * Floating-point math obeys regular algebraic rules for real numbers (e.g.
+ ``+`` and ``*`` are associative, ``x/y == x * (1/y)``, and
+ ``(a + b) * c == a * c + b * c``),
+ * operands to floating-point operations are not equal to ``NaN`` and
+ ``Inf``, and
+ * ``+0`` and ``-0`` are interchangeable.
+
+.. option:: -fdenormal-fp-math=[values]
+
+ Select which denormal numbers the code is permitted to require.
+
+ Valid values are: ``ieee``, ``preserve-sign``, and ``positive-zero``,
+ which correspond to IEEE 754 denormal numbers, the sign of a
+ flushed-to-zero number is preserved in the sign of 0, denormals are
+ flushed to positive zero, respectively.
+
+.. option:: -fwhole-program-vtables
+
+ Enable whole-program vtable optimizations, such as single-implementation
+ devirtualization and virtual constant propagation, for classes with
+ :doc:`hidden LTO visibility <LTOVisibility>`. Requires ``-flto``.
+
.. option:: -fno-assume-sane-operator-new
Don't assume that the C++'s new operator is sane.
efficient model can be used. The TLS model can be overridden per
variable using the ``tls_model`` attribute.
+.. option:: -femulated-tls
+
+ Select emulated TLS model, which overrides all -ftls-model choices.
+
+ In emulated TLS mode, all access to TLS variables are converted to
+ calls to __emutls_get_address in the runtime library.
+
.. option:: -mhwdiv=[values]
Select the ARM modes (arm or thumb) that support hardware division
This option restricts the generated code to use general registers
only. This only applies to the AArch64 architecture.
-**-f[no-]max-unknown-pointer-align=[number]**
+.. option:: -mcompact-branches=[values]
+
+ Control the usage of compact branches for MIPSR6.
+
+ Valid values are: ``never``, ``optimal`` and ``always``.
+ The default value is ``optimal`` which generates compact branches
+ when a delay slot cannot be filled. ``never`` disables the usage of
+ compact branches and ``always`` generates compact branches whenever
+ possible.
+
+**-f[no-]max-type-align=[number]**
Instruct the code generator to not enforce a higher alignment than the given
number (of bytes) when accessing memory via an opaque pointer or reference.
This cap is ignored when directly accessing a variable or when the pointee
void initialize_vector(__aligned_v16si *v) {
// The compiler may assume that ‘v’ is 64-byte aligned, regardless of the
- // value of -fmax-unknown-pointer-align.
+ // value of -fmax-type-align.
}
1. ASCII text. This is the easiest one to generate. The file is divided into
sections, which correspond to each of the functions with profile
- information. The format is described below.
+ information. The format is described below. It can also be generated from
+ the binary or gcov formats using the ``llvm-profdata`` tool.
2. Binary encoding. This uses a more efficient encoding that yields smaller
- profile files, which may be useful when generating large profiles. It can be
- generated from the text format using the ``llvm-profdata`` tool.
+ profile files. This is the format generated by the ``create_llvm_prof`` tool
+ in http://github.com/google/autofdo.
3. GCC encoding. This is based on the gcov format, which is accepted by GCC. It
- is only interesting in environments where GCC and Clang co-exist. Similarly
- to the binary encoding, it can be generated using the ``llvm-profdata`` tool.
+ is only interesting in environments where GCC and Clang co-exist. This
+ encoding is only generated by the ``create_gcov`` tool in
+ http://github.com/google/autofdo. It can be read by LLVM and
+ ``llvm-profdata``, but it cannot be generated by either.
If you are using Linux Perf to generate sampling profiles, you can use the
conversion tool ``create_llvm_prof`` described in the previous section.
This section describes the ASCII text format for sampling profiles. It is,
arguably, the easiest one to generate. If you are interested in generating any
of the other two, consult the ``ProfileData`` library in in LLVM's source tree
-(specifically, ``llvm/lib/ProfileData/SampleProfWriter.cpp``).
+(specifically, ``include/llvm/ProfileData/SampleProfReader.h``).
.. code-block:: console
function1:total_samples:total_head_samples
- offset1[.discriminator]: number_of_samples [fn1:num fn2:num ... ]
- offset2[.discriminator]: number_of_samples [fn3:num fn4:num ... ]
- ...
- offsetN[.discriminator]: number_of_samples [fn5:num fn6:num ... ]
+ offset1[.discriminator]: number_of_samples [fn1:num fn2:num ... ]
+ offset2[.discriminator]: number_of_samples [fn3:num fn4:num ... ]
+ ...
+ offsetN[.discriminator]: number_of_samples [fn5:num fn6:num ... ]
+ offsetA[.discriminator]: fnA:num_of_total_samples
+ offsetA1[.discriminator]: number_of_samples [fn7:num fn8:num ... ]
+ offsetA1[.discriminator]: number_of_samples [fn9:num fn10:num ... ]
+ offsetB[.discriminator]: fnB:num_of_total_samples
+ offsetB1[.discriminator]: number_of_samples [fn11:num fn12:num ... ]
-The file may contain blank lines between sections and within a
-section. However, the spacing within a single line is fixed. Additional
-spaces will result in an error while reading the file.
+This is a nested tree in which the identation represents the nesting level
+of the inline stack. There are no blank lines in the file. And the spacing
+within a single line is fixed. Additional spaces will result in an error
+while reading the file.
+
+Any line starting with the '#' character is completely ignored.
+
+Inlined calls are represented with indentation. The Inline stack is a
+stack of source locations in which the top of the stack represents the
+leaf function, and the bottom of the stack represents the actual
+symbol to which the instruction belongs.
Function names must be mangled in order for the profile loader to
match them in the current translation unit. The two numbers in the
in the prologue of the function (second number). This head sample
count provides an indicator of how frequently the function is invoked.
+There are two types of lines in the function body.
+
+- Sampled line represents the profile information of a source location.
+ ``offsetN[.discriminator]: number_of_samples [fn5:num fn6:num ... ]``
+
+- Callsite line represents the profile information of an inlined callsite.
+ ``offsetA[.discriminator]: fnA:num_of_total_samples``
+
Each sampled line may contain several items. Some are optional (marked
below):
instruction that calls one of ``foo()``, ``bar()`` and ``baz()``,
with ``baz()`` being the relatively more frequently called target.
+As an example, consider a program with the call chain ``main -> foo -> bar``.
+When built with optimizations enabled, the compiler may inline the
+calls to ``bar`` and ``foo`` inside ``main``. The generated profile
+could then be something like this:
+
+.. code-block:: console
+
+ main:35504:0
+ 1: _Z3foov:35504
+ 2: _Z32bari:31977
+ 1.1: 31977
+ 2: 0
+
+This profile indicates that there were a total of 35,504 samples
+collected in main. All of those were at line 1 (the call to ``foo``).
+Of those, 31,977 were spent inside the body of ``bar``. The last line
+of the profile (``2: 0``) corresponds to line 2 inside ``main``. No
+samples were collected there.
Profiling with Instrumentation
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2. Run the instrumented executable with inputs that reflect the typical usage.
By default, the profile data will be written to a ``default.profraw`` file
- in the current directory. You can override that default by setting the
- ``LLVM_PROFILE_FILE`` environment variable to specify an alternate file.
+ in the current directory. You can override that default by using option
+ ``-fprofile-instr-generate=`` or by setting the ``LLVM_PROFILE_FILE``
+ environment variable to specify an alternate file. If non-default file name
+ is specified by both the environment variable and the command line option,
+ the environment variable takes precedence. The file name pattern specified
+ can include different modifiers: ``%p``, ``%h``, and ``%m``.
+
Any instance of ``%p`` in that file name will be replaced by the process
ID, so that you can easily distinguish the profile output from multiple
runs.
$ LLVM_PROFILE_FILE="code-%p.profraw" ./code
+ The modifier ``%h`` can be used in scenarios where the same instrumented
+ binary is run in multiple different host machines dumping profile data
+ to a shared network based storage. The ``%h`` specifier will be substituted
+ with the hostname so that profiles collected from different hosts do not
+ clobber each other.
+
+ While the use of ``%p`` specifier can reduce the likelihood for the profiles
+ dumped from different processes to clobber each other, such clobbering can still
+ happen because of the ``pid`` re-use by the OS. Another side-effect of using
+ ``%p`` is that the storage requirement for raw profile data files is greatly
+ increased. To avoid issues like this, the ``%m`` specifier can used in the profile
+ name. When this specifier is used, the profiler runtime will substitute ``%m``
+ with a unique integer identifier associated with the instrumented binary. Additionally,
+ multiple raw profiles dumped from different processes that share a file system (can be
+ on different hosts) will be automatically merged by the profiler runtime during the
+ dumping. If the program links in multiple instrumented shared libraries, each library
+ will dump the profile data into its own profile data file (with its unique integer
+ id embedded in the profile name). Note that the merging enabled by ``%m`` is for raw
+ profile data generated by profiler runtime. The resulting merged "raw" profile data
+ file still needs to be converted to a different format expected by the compiler (
+ see step 3 below).
+
+ .. code-block:: console
+
+ $ LLVM_PROFILE_FILE="code-%m.profraw" ./code
+
+
3. Combine profiles from multiple runs and convert the "raw" profile format to
the input expected by clang. Use the ``merge`` command of the
``llvm-profdata`` tool to do this.
profile. As you make changes to your code, clang may no longer be able to
use the profile data. It will warn you when this happens.
+Profile generation using an alternative instrumentation method can be
+controlled by the GCC-compatible flags ``-fprofile-generate`` and
+``-fprofile-use``. Although these flags are semantically equivalent to
+their GCC counterparts, they *do not* handle GCC-compatible profiles.
+They are only meant to implement GCC's semantics with respect to
+profile creation and use.
+
+.. option:: -fprofile-generate[=<dirname>]
+
+ The ``-fprofile-generate`` and ``-fprofile-generate=`` flags will use
+ an alterantive instrumentation method for profile generation. When
+ given a directory name, it generates the profile file
+ ``default_%m.profraw`` in the directory named ``dirname`` if specified.
+ If ``dirname`` does not exist, it will be created at runtime. ``%m`` specifier
+ will be substibuted with a unique id documented in step 2 above. In other words,
+ with ``-fprofile-generate[=<dirname>]`` option, the "raw" profile data automatic
+ merging is turned on by default, so there will no longer any risk of profile
+ clobbering from different running processes. For example,
+
+ .. code-block:: console
+
+ $ clang++ -O2 -fprofile-generate=yyy/zzz code.cc -o code
+
+ When ``code`` is executed, the profile will be written to the file
+ ``yyy/zzz/default_xxxx.profraw``.
+
+ To generate the profile data file with the compiler readable format, the
+ ``llvm-profdata`` tool can be used with the profile directory as the input:
+
+ .. code-block:: console
+
+ $ llvm-profdata merge -output=code.profdata yyy/zzz/
+
+ If the user wants to turn off the auto-merging feature, or simply override the
+ the profile dumping path specified at command line, the environment variable
+ ``LLVM_PROFILE_FILE`` can still be used to override
+ the directory and filename for the profile file at runtime.
+
+.. option:: -fprofile-use[=<pathname>]
+
+ Without any other arguments, ``-fprofile-use`` behaves identically to
+ ``-fprofile-instr-use``. Otherwise, if ``pathname`` is the full path to a
+ profile file, it reads from that file. If ``pathname`` is a directory name,
+ it reads from ``pathname/default.profdata``.
+
+Disabling Instrumentation
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In certain situations, it may be useful to disable profile generation or use
+for specific files in a build, without affecting the main compilation flags
+used for the other files in the project.
+
+In these cases, you can use the flag ``-fno-profile-instr-generate`` (or
+``-fno-profile-generate``) to disable profile generation, and
+``-fno-profile-instr-use`` (or ``-fno-profile-use``) to disable profile use.
+
+Note that these flags should appear after the corresponding profile
+flags to have an effect.
+
+Controlling Debug Information
+-----------------------------
Controlling Size of Debug Information
--------------------------------------
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Debug info kind generated by Clang can be set by one of the flags listed
below. If multiple flags are present, the last one is used.
Generate complete debug info.
+Controlling Macro Debug Info Generation
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Debug info for C preprocessor macros increases the size of debug information in
+the binary. Macro debug info generated by Clang can be controlled by the flags
+listed below.
+
+.. option:: -fdebug-macro
+
+ Generate debug info for preprocessor macros. This flag is discarded when
+ **-g0** is enabled.
+
+.. option:: -fno-debug-macro
+
+ Do not generate debug info for preprocessor macros (default).
+
+Controlling Debugger "Tuning"
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+While Clang generally emits standard DWARF debug info (http://dwarfstd.org),
+different debuggers may know how to take advantage of different specific DWARF
+features. You can "tune" the debug info for one of several different debuggers.
+
+.. option:: -ggdb, -glldb, -gsce
+
+ Tune the debug info for the ``gdb``, ``lldb``, or Sony PlayStation\ |reg|
+ debugger, respectively. Each of these options implies **-g**. (Therefore, if
+ you want both **-gline-tables-only** and debugger tuning, the tuning option
+ must come first.)
+
+
Comment Parsing Options
-----------------------
clang tries to be compatible with gcc as much as possible, but some gcc
extensions are not implemented yet:
-- clang does not support #pragma weak (`bug
- 3679 <http://llvm.org/bugs/show_bug.cgi?id=3679>`_). Due to the uses
- described in the bug, this is likely to be implemented at some point,
- at least partially.
- clang does not support decimal floating point types (``_Decimal32`` and
friends) or fixed-point types (``_Fract`` and friends); nobody has
expressed interest in these features yet, so it's hard to say when
...
local_function(1);
-- clang does not support global register variables; this is unlikely to
- be implemented soon because it requires additional LLVM backend
- support.
+- clang only supports global register variables when the register specified
+ is non-allocatable (e.g. the stack pointer). Support for general global
+ register variables is unlikely to be implemented soon because it requires
+ additional LLVM backend support.
- clang does not support static initialization of flexible array
members. This appears to be a rarely used extension, but could be
implemented pending user demand.
currently excludes C++; see :ref:`C++ Language Features <cxx>`. Also, this
list does not include bugs in mostly-implemented features; please see
the `bug
-tracker <http://llvm.org/bugs/buglist.cgi?quicksearch=product%3Aclang+component%3A-New%2BBugs%2CAST%2CBasic%2CDriver%2CHeaders%2CLLVM%2BCodeGen%2Cparser%2Cpreprocessor%2CSemantic%2BAnalyzer>`_
+tracker <https://bugs.llvm.org/buglist.cgi?quicksearch=product%3Aclang+component%3A-New%2BBugs%2CAST%2CBasic%2CDriver%2CHeaders%2CLLVM%2BCodeGen%2Cparser%2Cpreprocessor%2CSemantic%2BAnalyzer>`_
for known existing bugs (FIXME: Is there a section for bug-reporting
guidelines somewhere?).
Microsoft extensions
--------------------
-clang has some experimental support for extensions from Microsoft Visual
-C++; to enable it, use the ``-fms-extensions`` command-line option. This is
-the default for Windows targets. Note that the support is incomplete.
-Some constructs such as ``dllexport`` on classes are ignored with a warning,
-and others such as `Microsoft IDL annotations
-<http://msdn.microsoft.com/en-us/library/8tesw2eh.aspx>`_ are silently
-ignored.
+clang has support for many extensions from Microsoft Visual C++. To enable these
+extensions, use the ``-fms-extensions`` command-line option. This is the default
+for Windows targets. Clang does not implement every pragma or declspec provided
+by MSVC, but the popular ones, such as ``__declspec(dllexport)`` and ``#pragma
+comment(lib)`` are well supported.
clang has a ``-fms-compatibility`` flag that makes clang accept enough
invalid C++ to be able to parse most Microsoft headers. For example, it
definitions until the end of a translation unit. This flag is enabled by
default for Windows targets.
-- clang allows setting ``_MSC_VER`` with ``-fmsc-version=``. It defaults to
- 1700 which is the same as Visual C/C++ 2012. Any number is supported
- and can greatly affect what Windows SDK and c++stdlib headers clang
- can compile.
-- clang does not support the Microsoft extension where anonymous record
- members can be declared using user defined typedefs.
-- clang supports the Microsoft ``#pragma pack`` feature for controlling
- record layout. GCC also contains support for this feature, however
- where MSVC and GCC are incompatible clang follows the MSVC
- definition.
-- clang supports the Microsoft ``#pragma comment(lib, "foo.lib")`` feature for
- automatically linking against the specified library. Currently this feature
- only works with the Visual C++ linker.
-- clang supports the Microsoft ``#pragma comment(linker, "/flag:foo")`` feature
- for adding linker flags to COFF object files. The user is responsible for
- ensuring that the linker understands the flags.
-- clang defaults to C++11 for Windows targets.
+For compatibility with existing code that compiles with MSVC, clang defines the
+``_MSC_VER`` and ``_MSC_FULL_VER`` macros. These default to the values of 1800
+and 180000000 respectively, making clang look like an early release of Visual
+C++ 2013. The ``-fms-compatibility-version=`` flag overrides these values. It
+accepts a dotted version tuple, such as 19.00.23506. Changing the MSVC
+compatibility version makes clang behave more like that version of MSVC. For
+example, ``-fms-compatibility-version=19`` will enable C++14 features and define
+``char16_t`` and ``char32_t`` as builtin types.
.. _cxx:
Objective-C++ Language Features
===============================
+.. _openmp:
+
+OpenMP Features
+===============
+
+Clang supports all OpenMP 3.1 directives and clauses. In addition, some
+features of OpenMP 4.0 are supported. For example, ``#pragma omp simd``,
+``#pragma omp for simd``, ``#pragma omp parallel for simd`` directives, extended
+set of atomic constructs, ``proc_bind`` clause for all parallel-based
+directives, ``depend`` clause for ``#pragma omp task`` directive (except for
+array sections), ``#pragma omp cancel`` and ``#pragma omp cancellation point``
+directives, and ``#pragma omp taskgroup`` directive.
+
+Use `-fopenmp` to enable OpenMP. Support for OpenMP can be disabled with
+`-fno-openmp`.
+
+Controlling implementation limits
+---------------------------------
+
+.. option:: -fopenmp-use-tls
+
+ Controls code generation for OpenMP threadprivate variables. In presence of
+ this option all threadprivate variables are generated the same way as thread
+ local variables, using TLS support. If `-fno-openmp-use-tls`
+ is provided or target does not support TLS, code generation for threadprivate
+ variables relies on OpenMP runtime library.
+
+.. _opencl:
+
+OpenCL Features
+===============
+
+Clang can be used to compile OpenCL kernels for execution on a device
+(e.g. GPU). It is possible to compile the kernel into a binary (e.g. for AMD or
+Nvidia targets) that can be uploaded to run directly on a device (e.g. using
+`clCreateProgramWithBinary
+<https://www.khronos.org/registry/OpenCL/specs/opencl-1.1.pdf#111>`_) or
+into generic bitcode files loadable into other toolchains.
+
+Compiling to a binary using the default target from the installation can be done
+as follows:
+
+ .. code-block:: console
+
+ $ echo "kernel void k(){}" > test.cl
+ $ clang test.cl
+
+Compiling for a specific target can be done by specifying the triple corresponding
+to the target, for example:
+
+ .. code-block:: console
+
+ $ clang -target nvptx64-unknown-unknown test.cl
+ $ clang -target amdgcn-amd-amdhsa-opencl test.cl
+
+Compiling to bitcode can be done as follows:
+
+ .. code-block:: console
+
+ $ clang -c -emit-llvm test.cl
+
+This will produce a generic test.bc file that can be used in vendor toolchains
+to perform machine code generation.
+
+Clang currently supports OpenCL C language standards up to v2.0.
+
+OpenCL Specific Options
+-----------------------
+
+Most of the OpenCL build options from `the specification v2.0 section 5.8.4
+<https://www.khronos.org/registry/cl/specs/opencl-2.0.pdf#200>`_ are available.
+
+Examples:
+
+ .. code-block:: console
+
+ $ clang -cl-std=CL2.0 -cl-single-precision-constant test.cl
+
+Some extra options are available to support special OpenCL features.
+
+.. option:: -finclude-default-header
+
+Loads standard includes during compilations. By default OpenCL headers are not
+loaded and therefore standard library includes are not available. To load them
+automatically a flag has been added to the frontend (see also :ref:`the section
+on the OpenCL Header <opencl_header>`):
+
+ .. code-block:: console
+
+ $ clang -Xclang -finclude-default-header test.cl
+
+Alternatively ``-include`` or ``-I`` followed by the path to the header location
+can be given manually.
+
+ .. code-block:: console
+
+ $ clang -I<path to clang>/lib/Headers/opencl-c.h test.cl
+
+In this case the kernel code should contain ``#include <opencl-c.h>`` just as a
+regular C include.
+
+.. _opencl_cl_ext:
+
+.. option:: -cl-ext
+
+Disables support of OpenCL extensions. All OpenCL targets provide a list
+of extensions that they support. Clang allows to amend this using the ``-cl-ext``
+flag with a comma-separated list of extensions prefixed with ``'+'`` or ``'-'``.
+The syntax: ``-cl-ext=<(['-'|'+']<extension>[,])+>``, where extensions
+can be either one of `the OpenCL specification extensions
+<https://www.khronos.org/registry/cl/sdk/2.0/docs/man/xhtml/EXTENSION.html>`_
+or any known vendor extension. Alternatively, ``'all'`` can be used to enable
+or disable all known extensions.
+Example disabling double support for the 64-bit SPIR target:
+
+ .. code-block:: console
+
+ $ clang -cc1 -triple spir64-unknown-unknown -cl-ext=-cl_khr_fp64 test.cl
+
+Enabling all extensions except double support in R600 AMD GPU can be done using:
+
+ .. code-block:: console
+
+ $ clang -cc1 -triple r600-unknown-unknown -cl-ext=-all,+cl_khr_fp16 test.cl
+
+.. _opencl_fake_address_space_map:
+
+.. option:: -ffake-address-space-map
+
+Overrides the target address space map with a fake map.
+This allows adding explicit address space IDs to the bitcode for non-segmented
+memory architectures that don't have separate IDs for each of the OpenCL
+logical address spaces by default. Passing ``-ffake-address-space-map`` will
+add/override address spaces of the target compiled for with the following values:
+``1-global``, ``2-constant``, ``3-local``, ``4-generic``. The private address
+space is represented by the absence of an address space attribute in the IR (see
+also :ref:`the section on the address space attribute <opencl_addrsp>`).
+
+ .. code-block:: console
+
+ $ clang -ffake-address-space-map test.cl
+
+Some other flags used for the compilation for C can also be passed while
+compiling for OpenCL, examples: ``-c``, ``-O<1-4|s>``, ``-o``, ``-emit-llvm``, etc.
+
+OpenCL Targets
+--------------
+
+OpenCL targets are derived from the regular Clang target classes. The OpenCL
+specific parts of the target representation provide address space mapping as
+well as a set of supported extensions.
+
+Specific Targets
+^^^^^^^^^^^^^^^^
+
+There is a set of concrete HW architectures that OpenCL can be compiled for.
+
+- For AMD target:
+
+ .. code-block:: console
+
+ $ clang -target amdgcn-amd-amdhsa-opencl test.cl
+
+- For Nvidia architectures:
+
+ .. code-block:: console
+
+ $ clang -target nvptx64-unknown-unknown test.cl
+
+
+Generic Targets
+^^^^^^^^^^^^^^^
+
+- SPIR is available as a generic target to allow portable bitcode to be produced
+ that can be used across GPU toolchains. The implementation follows `the SPIR
+ specification <https://www.khronos.org/spir>`_. There are two flavors
+ available for 32 and 64 bits.
+
+ .. code-block:: console
+
+ $ clang -target spir-unknown-unknown test.cl
+ $ clang -target spir64-unknown-unknown test.cl
+
+ All known OpenCL extensions are supported in the SPIR targets. Clang will
+ generate SPIR v1.2 compatible IR for OpenCL versions up to 2.0 and SPIR v2.0
+ for OpenCL v2.0.
+
+- x86 is used by some implementations that are x86 compatible and currently
+ remains for backwards compatibility (with older implementations prior to
+ SPIR target support). For "non-SPMD" targets which cannot spawn multiple
+ work-items on the fly using hardware, which covers practically all non-GPU
+ devices such as CPUs and DSPs, additional processing is needed for the kernels
+ to support multiple work-item execution. For this, a 3rd party toolchain,
+ such as for example `POCL <http://portablecl.org/>`_, can be used.
+
+ This target does not support multiple memory segments and, therefore, the fake
+ address space map can be added using the :ref:`-ffake-address-space-map
+ <opencl_fake_address_space_map>` flag.
+
+.. _opencl_header:
+
+OpenCL Header
+-------------
+
+By default Clang will not include standard headers and therefore OpenCL builtin
+functions and some types (i.e. vectors) are unknown. The default CL header is,
+however, provided in the Clang installation and can be enabled by passing the
+``-finclude-default-header`` flag to the Clang frontend.
+
+ .. code-block:: console
+
+ $ echo "bool is_wg_uniform(int i){return get_enqueued_local_size(i)==get_local_size(i);}" > test.cl
+ $ clang -Xclang -finclude-default-header -cl-std=CL2.0 test.cl
+
+Because the header is very large and long to parse, PCH (:doc:`PCHInternals`)
+and modules (:doc:`Modules`) are used internally to improve the compilation
+speed.
+
+To enable modules for OpenCL:
+
+ .. code-block:: console
+
+ $ clang -target spir-unknown-unknown -c -emit-llvm -Xclang -finclude-default-header -fmodules -fimplicit-module-maps -fmodules-cache-path=<path to the generated module> test.cl
+
+OpenCL Extensions
+-----------------
+
+All of the ``cl_khr_*`` extensions from `the official OpenCL specification
+<https://www.khronos.org/registry/OpenCL/sdk/2.0/docs/man/xhtml/EXTENSION.html>`_
+up to and including version 2.0 are available and set per target depending on the
+support available in the specific architecture.
+
+It is possible to alter the default extensions setting per target using
+``-cl-ext`` flag. (See :ref:`flags description <opencl_cl_ext>` for more details).
+
+Vendor extensions can be added flexibly by declaring the list of types and
+functions associated with each extensions enclosed within the following
+compiler pragma directives:
+
+ .. 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
+
+For example, parsing the following code adds ``my_t`` type and ``my_func``
+function to the custom ``my_ext`` extension.
+
+ .. code-block:: c
+
+ #pragma OPENCL EXTENSION my_ext : begin
+ typedef struct{
+ int a;
+ }my_t;
+ void my_func(my_t);
+ #pragma OPENCL EXTENSION my_ext : end
+
+Declaring the same types in different vendor extensions is disallowed.
+
+OpenCL Metadata
+---------------
+
+Clang uses metadata to provide additional OpenCL semantics in IR needed for
+backends and OpenCL runtime.
+
+Each kernel will have function metadata attached to it, specifying the arguments.
+Kernel argument metadata is used to provide source level information for querying
+at runtime, for example using the `clGetKernelArgInfo
+<https://www.khronos.org/registry/OpenCL/specs/opencl-1.2.pdf#167>`_
+call.
+
+Note that ``-cl-kernel-arg-info`` enables more information about the original CL
+code to be added e.g. kernel parameter names will appear in the OpenCL metadata
+along with other information.
+
+The IDs used to encode the OpenCL's logical address spaces in the argument info
+metadata follows the SPIR address space mapping as defined in the SPIR
+specification `section 2.2
+<https://www.khronos.org/registry/spir/specs/spir_spec-2.0.pdf#18>`_
+
+OpenCL-Specific Attributes
+--------------------------
+
+OpenCL support in Clang contains a set of attribute taken directly from the
+specification as well as additional attributes.
+
+See also :doc:`AttributeReference`.
+
+nosvm
+^^^^^
+
+Clang supports this attribute to comply to OpenCL v2.0 conformance, but it
+does not have any effect on the IR. For more details reffer to the specification
+`section 6.7.2
+<https://www.khronos.org/registry/cl/specs/opencl-2.0-openclc.pdf#49>`_
+
+
+opencl_unroll_hint
+^^^^^^^^^^^^^^^^^^
+
+The implementation of this feature mirrors the unroll hint for C.
+More details on the syntax can be found in the specification
+`section 6.11.5
+<https://www.khronos.org/registry/cl/specs/opencl-2.0-openclc.pdf#61>`_
+
+convergent
+^^^^^^^^^^
+
+To make sure no invalid optimizations occur for single program multiple data
+(SPMD) / single instruction multiple thread (SIMT) Clang provides attributes that
+can be used for special functions that have cross work item semantics.
+An example is the subgroup operations such as `intel_sub_group_shuffle
+<https://www.khronos.org/registry/cl/extensions/intel/cl_intel_subgroups.txt>`_
+
+ .. code-block:: c
+
+ // Define custom my_sub_group_shuffle(data, c)
+ // that makes use of intel_sub_group_shuffle
+ r1 = ...
+ if (r0) r1 = computeA();
+ // Shuffle data from r1 into r3
+ // of threads id r2.
+ r3 = my_sub_group_shuffle(r1, r2);
+ if (r0) r3 = computeB();
+
+with non-SPMD semantics this is optimized to the following equivalent code:
+
+ .. code-block:: c
+
+ r1 = ...
+ if (!r0)
+ // Incorrect functionality! The data in r1
+ // have not been computed by all threads yet.
+ r3 = my_sub_group_shuffle(r1, r2);
+ else {
+ r1 = computeA();
+ r3 = my_sub_group_shuffle(r1, r2);
+ r3 = computeB();
+ }
+
+Declaring the function ``my_sub_group_shuffle`` with the convergent attribute
+would prevent this:
+
+ .. code-block:: c
+
+ my_sub_group_shuffle() __attribute__((convergent));
+
+Using ``convergent`` guarantees correct execution by keeping CFG equivalence
+wrt operations marked as ``convergent``. CFG ``G´`` is equivalent to ``G`` wrt
+node ``Ni`` : ``iff ∀ Nj (i≠j)`` domination and post-domination relations with
+respect to ``Ni`` remain the same in both ``G`` and ``G´``.
+
+noduplicate
+^^^^^^^^^^^
+
+``noduplicate`` is more restrictive with respect to optimizations than
+``convergent`` because a convergent function only preserves CFG equivalence.
+This allows some optimizations to happen as long as the control flow remains
+unmodified.
+
+ .. code-block:: c
+
+ for (int i=0; i<4; i++)
+ my_sub_group_shuffle()
+
+can be modified to:
+
+ .. code-block:: c
+
+ my_sub_group_shuffle();
+ my_sub_group_shuffle();
+ my_sub_group_shuffle();
+ my_sub_group_shuffle();
+
+while using ``noduplicate`` would disallow this. Also ``noduplicate`` doesn't
+have the same safe semantics of CFG as ``convergent`` and can cause changes in
+CFG that modify semantics of the original program.
+
+``noduplicate`` is kept for backwards compatibility only and it considered to be
+deprecated for future uses.
+
+.. _opencl_addrsp:
+
+address_space
+^^^^^^^^^^^^^
+
+Clang has arbitrary address space support using the ``address_space(N)``
+attribute, where ``N`` is an integer number in the range ``0`` to ``16777215``
+(``0xffffffu``).
+
+An OpenCL implementation provides a list of standard address spaces using
+keywords: ``private``, ``local``, ``global``, and ``generic``. In the AST and
+in the IR local, global, or generic will be represented by the address space
+attribute with the corresponding unique number. Note that private does not have
+any corresponding attribute added and, therefore, is represented by the absence
+of an address space number. The specific IDs for an address space do not have to
+match between the AST and the IR. Typically in the AST address space numbers
+represent logical segments while in the IR they represent physical segments.
+Therefore, machines with flat memory segments can map all AST address space
+numbers to the same physical segment ID or skip address space attribute
+completely while generating the IR. However, if the address space information
+is needed by the IR passes e.g. to improve alias analysis, it is recommended
+to keep it and only lower to reflect physical memory segments in the late
+machine passes.
+
+OpenCL builtins
+---------------
+
+There are some standard OpenCL functions that are implemented as Clang builtins:
+
+- All pipe functions from `section 6.13.16.2/6.13.16.3
+ <https://www.khronos.org/registry/cl/specs/opencl-2.0-openclc.pdf#160>`_ of
+ the OpenCL v2.0 kernel language specification. `
+
+- Address space qualifier conversion functions ``to_global``/``to_local``/``to_private``
+ from `section 6.13.9
+ <https://www.khronos.org/registry/cl/specs/opencl-2.0-openclc.pdf#101>`_.
+
+- All the ``enqueue_kernel`` functions from `section 6.13.17.1
+ <https://www.khronos.org/registry/cl/specs/opencl-2.0-openclc.pdf#164>`_ and
+ enqueue query functions from `section 6.13.17.5
+ <https://www.khronos.org/registry/cl/specs/opencl-2.0-openclc.pdf#171>`_.
.. _target_features:
Microsoft x64 calling convention. You might need to tweak
``WinX86_64ABIInfo::classify()`` in lib/CodeGen/TargetInfo.cpp.
-For the X86 target, clang supports the :option:`-m16` command line
+For the X86 target, clang supports the `-m16` command line
argument which enables 16-bit code output. This is broadly similar to
using ``asm(".code16gcc")`` with the GNU toolchain. The generated code
and the ABI remains 32-bit but the assembler emits instructions
Clang expects the GCC executable "gcc.exe" compiled for
``i686-w64-mingw32`` (or ``x86_64-w64-mingw32``) to be present on PATH.
-`Some tests might fail <http://llvm.org/bugs/show_bug.cgi?id=9072>`_ on
+`Some tests might fail <https://bugs.llvm.org/show_bug.cgi?id=9072>`_ on
``x86_64-w64-mingw32``.
.. _clang-cl:
clang-cl
========
-clang-cl is an alternative command-line interface to Clang driver, designed for
+clang-cl is an alternative command-line interface to Clang, designed for
compatibility with the Visual C++ compiler, cl.exe.
To enable clang-cl to find system headers, libraries, and the linker when run
Command Prompt or a regular Command Prompt where the environment has been set
up using e.g. `vcvars32.bat <http://msdn.microsoft.com/en-us/library/f2ccy3wt.aspx>`_.
-clang-cl can also be used from inside Visual Studio by using an LLVM Platform
+clang-cl can also be used from inside Visual Studio by using an LLVM Platform
Toolset.
Command-Line Options
::
- clang-cl.exe: warning: argument unused during compilation: '/Zi'
+ clang-cl.exe: warning: argument unused during compilation: '/AI'
To suppress warnings about unused arguments, use the ``-Qunused-arguments`` option.
-Options that are not known to clang-cl will cause errors. If they are spelled with a
-leading ``/``, they will be mistaken for a filename:
+Options that are not known to clang-cl will be ignored by default. Use the
+``-Werror=unknown-argument`` option in order to treat them as errors. If these
+options are spelled with a leading ``/``, they will be mistaken for a filename:
::
clang-cl.exe: error: no such file or directory: '/foobar'
-Please `file a bug <http://llvm.org/bugs/enter_bug.cgi?product=clang&component=Driver>`_
+Please `file a bug <https://bugs.llvm.org/enter_bug.cgi?product=clang&component=Driver>`_
for any valid cl.exe flags that clang-cl does not understand.
Execute ``clang-cl /?`` to see a list of supported options:
::
CL.EXE COMPATIBILITY OPTIONS:
- /? Display available options
- /arch:<value> Set architecture for code generation
- /C Don't discard comments when preprocessing
- /c Compile only
- /D <macro[=value]> Define macro
- /EH<value> Exception handling model
- /EP Disable linemarker output and preprocess to stdout
- /E Preprocess to stdout
- /fallback Fall back to cl.exe if clang-cl fails to compile
- /FA Output assembly code file during compilation
- /Fa<file or directory> Output assembly code to this file during compilation
- /Fe<file or directory> Set output executable file or directory (ends in / or \)
- /FI <value> Include file before parsing
- /Fi<file> Set preprocess output file name
- /Fo<file or directory> Set output object file, or directory (ends in / or \)
- /GF- Disable string pooling
- /GR- Disable emission of RTTI data
- /GR Enable emission of RTTI data
- /Gw- Don't put each data item in its own section
- /Gw Put each data item in its own section
- /Gy- Don't put each function in its own section
- /Gy Put each function in its own section
- /help Display available options
- /I <dir> Add directory to include search path
- /J Make char type unsigned
- /LDd Create debug DLL
- /LD Create DLL
- /link <options> Forward options to the linker
- /MDd Use DLL debug run-time
- /MD Use DLL run-time
- /MTd Use static debug run-time
- /MT Use static run-time
- /Ob0 Disable inlining
- /Od Disable optimization
- /Oi- Disable use of builtin functions
- /Oi Enable use of builtin functions
- /Os Optimize for size
- /Ot Optimize for speed
- /Ox Maximum optimization
- /Oy- Disable frame pointer omission
- /Oy Enable frame pointer omission
- /O<n> Optimization level
- /P Preprocess to file
- /showIncludes Print info about included files to stderr
- /TC Treat all source files as C
- /Tc <filename> Specify a C source file
- /TP Treat all source files as C++
- /Tp <filename> Specify a C++ source file
- /U <macro> Undefine macro
- /vd<value> Control vtordisp placement
- /vmb Use a best-case representation method for member pointers
- /vmg Use a most-general representation for member pointers
- /vmm Set the default most-general representation to multiple inheritance
- /vms Set the default most-general representation to single inheritance
- /vmv Set the default most-general representation to virtual inheritance
- /W0 Disable all warnings
- /W1 Enable -Wall
- /W2 Enable -Wall
- /W3 Enable -Wall
- /W4 Enable -Wall
- /Wall Enable -Wall
- /WX- Do not treat warnings as errors
- /WX Treat warnings as errors
- /w Disable all warnings
- /Zi Enable debug information
- /Zp Set the default maximum struct packing alignment to 1
- /Zp<value> Specify the default maximum struct packing alignment
- /Zs Syntax-check only
+ /? Display available options
+ /arch:<value> Set architecture for code generation
+ /Brepro- Emit an object file which cannot be reproduced over time
+ /Brepro Emit an object file which can be reproduced over time
+ /C Don't discard comments when preprocessing
+ /c Compile only
+ /d1reportAllClassLayout Dump record layout information
+ /diagnostics:caret Enable caret and column diagnostics (on by default)
+ /diagnostics:classic Disable column and caret diagnostics
+ /diagnostics:column Disable caret diagnostics but keep column info
+ /D <macro[=value]> Define macro
+ /EH<value> Exception handling model
+ /EP Disable linemarker output and preprocess to stdout
+ /execution-charset:<value>
+ Runtime encoding, supports only UTF-8
+ /E Preprocess to stdout
+ /fallback Fall back to cl.exe if clang-cl fails to compile
+ /FA Output assembly code file during compilation
+ /Fa<file or directory> Output assembly code to this file during compilation (with /FA)
+ /Fe<file or directory> Set output executable file or directory (ends in / or \)
+ /FI <value> Include file before parsing
+ /Fi<file> Set preprocess output file name (with /P)
+ /Fo<file or directory> Set output object file, or directory (ends in / or \) (with /c)
+ /fp:except-
+ /fp:except
+ /fp:fast
+ /fp:precise
+ /fp:strict
+ /Fp<filename> Set pch filename (with /Yc and /Yu)
+ /GA Assume thread-local variables are defined in the executable
+ /Gd Set __cdecl as a default calling convention
+ /GF- Disable string pooling
+ /GR- Disable emission of RTTI data
+ /GR Enable emission of RTTI data
+ /Gr Set __fastcall as a default calling convention
+ /GS- Disable buffer security check
+ /GS Enable buffer security check
+ /Gs<value> Set stack probe size
+ /Gv Set __vectorcall as a default calling convention
+ /Gw- Don't put each data item in its own section
+ /Gw Put each data item in its own section
+ /GX- Enable exception handling
+ /GX Enable exception handling
+ /Gy- Don't put each function in its own section
+ /Gy Put each function in its own section
+ /Gz Set __stdcall as a default calling convention
+ /help Display available options
+ /imsvc <dir> Add directory to system include search path, as if part of %INCLUDE%
+ /I <dir> Add directory to include search path
+ /J Make char type unsigned
+ /LDd Create debug DLL
+ /LD Create DLL
+ /link <options> Forward options to the linker
+ /MDd Use DLL debug run-time
+ /MD Use DLL run-time
+ /MTd Use static debug run-time
+ /MT Use static run-time
+ /Od Disable optimization
+ /Oi- Disable use of builtin functions
+ /Oi Enable use of builtin functions
+ /Os Optimize for size
+ /Ot Optimize for speed
+ /O<value> Optimization level
+ /o <file or directory> Set output file or directory (ends in / or \)
+ /P Preprocess to file
+ /Qvec- Disable the loop vectorization passes
+ /Qvec Enable the loop vectorization passes
+ /showIncludes Print info about included files to stderr
+ /source-charset:<value> Source encoding, supports only UTF-8
+ /std:<value> Language standard to compile for
+ /TC Treat all source files as C
+ /Tc <filename> Specify a C source file
+ /TP Treat all source files as C++
+ /Tp <filename> Specify a C++ source file
+ /utf-8 Set source and runtime encoding to UTF-8 (default)
+ /U <macro> Undefine macro
+ /vd<value> Control vtordisp placement
+ /vmb Use a best-case representation method for member pointers
+ /vmg Use a most-general representation for member pointers
+ /vmm Set the default most-general representation to multiple inheritance
+ /vms Set the default most-general representation to single inheritance
+ /vmv Set the default most-general representation to virtual inheritance
+ /volatile:iso Volatile loads and stores have standard semantics
+ /volatile:ms Volatile loads and stores have acquire and release semantics
+ /W0 Disable all warnings
+ /W1 Enable -Wall
+ /W2 Enable -Wall
+ /W3 Enable -Wall
+ /W4 Enable -Wall and -Wextra
+ /Wall Enable -Wall and -Wextra
+ /WX- Do not treat warnings as errors
+ /WX Treat warnings as errors
+ /w Disable all warnings
+ /Y- Disable precompiled headers, overrides /Yc and /Yu
+ /Yc<filename> Generate a pch file for all code up to and including <filename>
+ /Yu<filename> Load a pch file and use it instead of all code up to and including <filename>
+ /Z7 Enable CodeView debug information in object files
+ /Zc:sizedDealloc- Disable C++14 sized global deallocation functions
+ /Zc:sizedDealloc Enable C++14 sized global deallocation functions
+ /Zc:strictStrings Treat string literals as const
+ /Zc:threadSafeInit- Disable thread-safe initialization of static variables
+ /Zc:threadSafeInit Enable thread-safe initialization of static variables
+ /Zc:trigraphs- Disable trigraphs (default)
+ /Zc:trigraphs Enable trigraphs
+ /Zc:twoPhase- Disable two-phase name lookup in templates
+ /Zc:twoPhase Enable two-phase name lookup in templates
+ /Zd Emit debug line number tables only
+ /Zi Alias for /Z7. Does not produce PDBs.
+ /Zl Don't mention any default libraries in the object file
+ /Zp Set the default maximum struct packing alignment to 1
+ /Zp<value> Specify the default maximum struct packing alignment
+ /Zs Syntax-check only
OPTIONS:
- -### Print (but do not run) the commands to run for this compilation
+ -### Print (but do not run) the commands to run for this compilation
+ --analyze Run the static analyzer
+ -fansi-escape-codes Use ANSI escape codes for diagnostics
+ -fcolor-diagnostics Use colors in diagnostics
+ -fdebug-macro Emit macro debug information
+ -fdelayed-template-parsing
+ Parse templated function definitions at the end of the translation unit
+ -fdiagnostics-absolute-paths
+ Print absolute paths in diagnostics
+ -fdiagnostics-parseable-fixits
+ Print fix-its in machine parseable form
+ -flto=<value> Set LTO mode to either 'full' or 'thin'
+ -flto Enable LTO in 'full' mode
-fms-compatibility-version=<value>
- Dot-separated value representing the Microsoft compiler version
- number to report in _MSC_VER (0 = don't define it (default))
- -fmsc-version=<value> Microsoft compiler version number to report in _MSC_VER (0 = don't
- define it (default))
+ Dot-separated value representing the Microsoft compiler version
+ number to report in _MSC_VER (0 = don't define it (default))
+ -fms-compatibility Enable full Microsoft Visual C++ compatibility
+ -fms-extensions Accept some non-standard constructs supported by the Microsoft compiler
+ -fmsc-version=<value> Microsoft compiler version number to report in _MSC_VER
+ (0 = don't define it (default))
+ -fno-debug-macro Do not emit macro debug information
+ -fno-delayed-template-parsing
+ Disable delayed template parsing
+ -fno-sanitize-address-use-after-scope
+ Disable use-after-scope detection in AddressSanitizer
+ -fno-sanitize-blacklist Don't use blacklist file for sanitizers
+ -fno-sanitize-cfi-cross-dso
+ Disable control flow integrity (CFI) checks for cross-DSO calls.
+ -fno-sanitize-coverage=<value>
+ Disable specified features of coverage instrumentation for Sanitizers
+ -fno-sanitize-memory-track-origins
+ Disable origins tracking in MemorySanitizer
+ -fno-sanitize-recover=<value>
+ Disable recovery for specified sanitizers
+ -fno-sanitize-stats Disable sanitizer statistics gathering.
+ -fno-sanitize-thread-atomics
+ Disable atomic operations instrumentation in ThreadSanitizer
+ -fno-sanitize-thread-func-entry-exit
+ Disable function entry/exit instrumentation in ThreadSanitizer
+ -fno-sanitize-thread-memory-access
+ Disable memory access instrumentation in ThreadSanitizer
+ -fno-sanitize-trap=<value>
+ Disable trapping for specified sanitizers
+ -fno-standalone-debug Limit debug information produced to reduce size of debug binary
+ -fprofile-instr-generate=<file>
+ Generate instrumented code to collect execution counts into <file>
+ (overridden by LLVM_PROFILE_FILE env var)
+ -fprofile-instr-generate
+ Generate instrumented code to collect execution counts into default.profraw file
+ (overridden by '=' form of option or LLVM_PROFILE_FILE env var)
+ -fprofile-instr-use=<value>
+ Use instrumentation data for profile-guided optimization
+ -fsanitize-address-field-padding=<value>
+ Level of field padding for AddressSanitizer
+ -fsanitize-address-globals-dead-stripping
+ Enable linker dead stripping of globals in AddressSanitizer
+ -fsanitize-address-use-after-scope
+ Enable use-after-scope detection in AddressSanitizer
-fsanitize-blacklist=<value>
- Path to blacklist file for sanitizers
- -fsanitize=<check> Enable runtime instrumentation for bug detection: address (memory
- errors) | thread (race detection) | undefined (miscellaneous
- undefined behavior)
- -mllvm <value> Additional arguments to forward to LLVM's option processing
- -Qunused-arguments Don't emit warning for unused driver arguments
- --target=<value> Generate code for the given target
- -v Show commands to run and use verbose output
- -W<warning> Enable the specified warning
- -Xclang <arg> Pass <arg> to the clang compiler
+ Path to blacklist file for sanitizers
+ -fsanitize-cfi-cross-dso
+ Enable control flow integrity (CFI) checks for cross-DSO calls.
+ -fsanitize-coverage=<value>
+ Specify the type of coverage instrumentation for Sanitizers
+ -fsanitize-memory-track-origins=<value>
+ Enable origins tracking in MemorySanitizer
+ -fsanitize-memory-track-origins
+ Enable origins tracking in MemorySanitizer
+ -fsanitize-memory-use-after-dtor
+ Enable use-after-destroy detection in MemorySanitizer
+ -fsanitize-recover=<value>
+ Enable recovery for specified sanitizers
+ -fsanitize-stats Enable sanitizer statistics gathering.
+ -fsanitize-thread-atomics
+ Enable atomic operations instrumentation in ThreadSanitizer (default)
+ -fsanitize-thread-func-entry-exit
+ Enable function entry/exit instrumentation in ThreadSanitizer (default)
+ -fsanitize-thread-memory-access
+ Enable memory access instrumentation in ThreadSanitizer (default)
+ -fsanitize-trap=<value> Enable trapping for specified sanitizers
+ -fsanitize-undefined-strip-path-components=<number>
+ Strip (or keep only, if negative) a given number of path components when emitting check metadata.
+ -fsanitize=<check> Turn on runtime checks for various forms of undefined or suspicious
+ behavior. See user manual for available checks
+ -fstandalone-debug Emit full debug info for all types used by the program
+ -gcodeview Generate CodeView debug information
+ -gline-tables-only Emit debug line number tables only
+ -miamcu Use Intel MCU ABI
+ -mllvm <value> Additional arguments to forward to LLVM's option processing
+ -nobuiltininc Disable builtin #include directories
+ -Qunused-arguments Don't emit warning for unused driver arguments
+ -R<remark> Enable the specified remark
+ --target=<value> Generate code for the given target
+ -v Show commands to run and use verbose output
+ -W<warning> Enable the specified warning
+ -Xclang <arg> Pass <arg> to the clang compiler
The /fallback Option
^^^^^^^^^^^^^^^^^^^^
projects / clang / blobdiff