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When building the LLVM project, CMake offers a wide range of configuration options that allow you to customize the build process.
1. LLVM_ENABLE_PROJECTS
This option specifies the additional LLVM sub-projects that will be built along with LLVM. Popular choices include:
"clang": Enables building the Clang compiler.
"clang-tools-extra": Builds additional tools that work with Clang.
You can also add other projects such as
"lld", "libcxx", and "lldb".Example:
2. LLVM_ENABLE_LLD
This option enables the use of LLD, the LLVM linker. LLD is known for its speed, and enabling it can accelerate the linking process if your platform supports it.
Example:
3. BUILD_SHARED_LIBS
This option controls whether shared libraries (
ON) or static libraries (OFF) are built. Shared libraries can reduce memory usage and binary size.Example:
4. LLVM_USE_SPLIT_DWARF
This option enables split DWARF, which separates debug information from the binary. It can significantly reduce the size of the binaries and speed up the linking process, especially when debugging large projects.
Example:
5. LLVM_OPTIMIZED_TABLEGEN
This option optimizes the build time of LLVM's TableGen utility, which is used to generate machine-specific data structures. Enabling this can speed up the overall build process.
Example:
6. LLVM_ENABLE_RTTI
This option controls whether C++ Runtime Type Information (RTTI) is enabled. While RTTI is typically disabled in some performance-sensitive environments, it's useful during development for dynamic type checking.
Example:
7. LLVM_BUILD_EXAMPLES
Enabling this option will build the example code included in the LLVM repository. This is useful for developers who want to learn from or experiment with LLVM's examples.
Example:
8. LLVM_BUILD_DOCS
This option allows building the LLVM documentation. This is helpful if you want to generate and consult the documentation locally.
Example:
9. CLANG_BUILD_EXAMPLES
Similar to
LLVM_BUILD_EXAMPLES, this option builds example code specific to Clang, LLVM's C/C++/Objective-C front end.Example:
10. LLVM_TOOL_LLD_BUILD
This option determines whether to build the LLD tool, LLVMโs own linker. Enabling this will ensure that the LLD binary is built.
Example:
11. LLVM_TARGETS_TO_BUILD
This specifies which target architectures to build for. Building only the necessary targets can save build time. Common targets include
X86, ARM, AArch64, etc.Example:
12. LLVM_ENABLE_ASSERTIONS
This enables LLVMโs internal assertions, which are useful for debugging. When developing, it's a good practice to enable assertions to catch potential issues early.
Example:
13. LLVM_TARGET_ARCH
This option explicitly sets the target architecture, typically used alongside
LLVM_TARGETS_TO_BUILD. This ensures that the binary is built for a specific architecture, such as X86.Example:
14. CMAKE_BUILD_TYPE
Defines the type of build. Typical values are:
Debug: Builds with debugging information and no optimization.
Release: Optimized builds with no debugging information.
RelWithDebInfo: Optimized builds with debugging information included.
Example:
15. CMAKE_INSTALL_PREFIX
This option specifies the installation directory for the build. After running
make install or ninja install, all the compiled binaries and libraries will be installed to this location.Example:
16. CMAKE_CXX_STANDARD
This option sets the C++ standard to use. LLVM is often built with newer C++ standards like C++17 or C++20.
Example:
Example Configuration
Here's a complete CMake configuration based on the options discussed:
This configuration sets up a build for Clang and extra tools, uses LLD for faster linking, builds shared libraries, and enables several useful options like split DWARF, RTTI, and example builds. It targets the
X86 architecture and installs the final binaries in the ../install directory with debugging information enabled.This setup should work well for both development and debugging use cases.