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[docs] More CMAKE variable documentation

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This breaks out some (more) common llvm-specific
variables. Controlling the subprojects and target architectures, along
with clues about restricting build parallelism when linking. 'more
common' is somewhat subjective, of course.

Differential Revision: https://reviews.llvm.org/D105822
This commit is contained in:
Nathan Sidwell 2021-07-12 08:54:51 -07:00
parent 47a6aacab4
commit 83135ce4f4
1 changed files with 55 additions and 14 deletions
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docs/CMake.rst
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@ -65,7 +65,10 @@ We use here the command-line, non-interactive CMake interface.
itself is the correct one for your development environment. CMake will refuse
to build MinGW makefiles if you have a POSIX shell reachable through the PATH
environment variable, for instance. You can force CMake to use a given build
tool; for instructions, see the `Usage`_ section, below.
tool; for instructions, see the `Usage`_ section, below. You may
also wish to control which targets LLVM enables, or which LLVM
components are built; see the `Frequently Used LLVM-related
variables`_ below.
#. After CMake has finished running, proceed to use IDE project files, or start
the build from the build directory:
@ -179,47 +182,85 @@ Frequently-used CMake variables
-------------------------------
Here are some of the CMake variables that are used often, along with a
brief explanation and LLVM-specific notes. For full documentation, consult the
CMake manual, or execute ``cmake --help-variable VARIABLE_NAME``.
brief explanation. For full documentation, consult the CMake manual,
or execute ``cmake --help-variable VARIABLE_NAME``. See `Frequently
Used LLVM-related Variables`_ below for information about commonly
used variables that control features of LLVM and enabled subprojects.
**CMAKE_BUILD_TYPE**:STRING
Sets the build type for ``make``-based generators. Possible values are
Release, Debug, RelWithDebInfo and MinSizeRel. If you are using an IDE such as
Visual Studio, you should use the IDE settings to set the build type.
Be aware that Release and RelWithDebInfo use different optimization levels on
most platforms.
most platforms. Be aware that Release and
RelWithDebInfo use different optimization levels on most
platforms, and that the default value of ``LLVM_ENABLE_ASSERTIONS``
is affected.
**CMAKE_INSTALL_PREFIX**:PATH
Path where LLVM will be installed if "make install" is invoked or the
"install" target is built.
Path where LLVM will be installed when the "install" target is built.
**CMAKE_C_FLAGS**:STRING
Extra flags to use when compiling C source files.
**CMAKE_{C,CXX}_FLAGS**:STRING
Extra flags to use when compiling C and C++ source files respectively.
**CMAKE_CXX_FLAGS**:STRING
Extra flags to use when compiling C++ source files.
**CMAKE_{C,CXX}_COMPILER**:STRING
Specify the C and C++ compilers to use. If you have multiple
compilers installed, CMake might not default to the one you wish to
use.
.. _Frequently Used LLVM-related variables:
Frequently Used LLVM-related variables
--------------------------------------
The default configuration may not match your requirements. Here are
LLVM variables that are frequently used to control that. The full
description is in `LLVM-related variables`_ below.
**LLVM_ENABLE_PROJECTS**:STRING
Control which projects are enabled. For example you may want to work on clang
or lldb by specifying ``-DLLVM_ENABLE_PROJECTS="clang;lldb"``.
**LLVM_LIBDIR_SUFFIX**:STRING
Extra suffix to append to the directory where libraries are to be
installed. On a 64-bit architecture, one could use ``-DLLVM_LIBDIR_SUFFIX=64``
to install libraries to ``/usr/lib64``.
**LLVM_PARALLEL_{COMPILE,LINK}_JOBS**:STRING
Building the llvm toolchain can use a lot of resources, particularly
linking. These options, when you use the Ninja generator, allow you
to restrict the parallelism. For example, to avoid OOMs or going
into swap, permit only one link job per 15GB of RAM available on a
32GB machine, specify ``-G Ninja -DLLVM_PARALLEL_LINK_JOBS=2``.
**LLVM_TARGETS_TO_BUILD**:STRING
Control which targets are enabled. For example you may only need to enable
your native target with, for example, ``-DLLVM_TARGETS_TO_BUILD=X86``.
**LLVM_USE_LINKER**:STRING
Override the system's default linker. For instance use ``lld`` with
``-DLLVM_USE_LINKER=lld``.
Rarely-used CMake variables
---------------------------
Here are some of the CMake variables that are rarely used, along with a brief
explanation and LLVM-specific notes. For full documentation, consult the CMake
explanation and LLVM-related notes. For full documentation, consult the CMake
manual, or execute ``cmake --help-variable VARIABLE_NAME``.
**CMAKE_CXX_STANDARD**:STRING
Sets the C++ standard to conform to when building LLVM. Possible values are
14, 17, 20. LLVM Requires C++ 14 or higher. This defaults to 14.
.. _LLVM-specific variables:
.. _LLVM-related variables:
LLVM-specific variables
LLVM-related variables
-----------------------
These variables provide fine control over the build of LLVM and
enabled sub-projects. Nearly all of these variable names begin with
``LLVM_``.
**BUILD_SHARED_LIBS**:BOOL
Flag indicating if each LLVM component (e.g. Support) is built as a shared
library (ON) or as a static library (OFF). Its default value is OFF. On
@ -740,7 +781,7 @@ several examples including toolchain files. Go directly to the
``Information how to set up various cross compiling toolchains`` section
for a quick solution.
Also see the `LLVM-specific variables`_ section for variables used when
Also see the `LLVM-related variables`_ section for variables used when
cross-compiling.
Embedding LLVM in your project