Using lli Command for Executing LLVM Bitcode and IR Files (with examples)
Introduction
The lli command is a powerful tool that allows you to directly execute programs from LLVM bitcode. It provides a convenient way to test and debug your LLVM programs without the need for additional compilation steps. In this article, we will explore different use cases of the lli command along with code examples, motivations, explanations, and example outputs.
1: Execute a Bitcode or IR File
To execute a bitcode or IR file using the lli command, you can simply provide the path to the file as an argument. Here’s an example:
lli path/to/file.ll
Motivation: Executing a bitcode or IR file with lli allows you to quickly test and run your LLVM programs without the need for a separate compilation step.
Explanation: The path/to/file.ll argument specifies the path to the bitcode or IR file that you want to execute.
Example Output: The output will be the result of executing the program contained in the specified file.
2: Execute with Command-Line Arguments
To pass command-line arguments to your LLVM program, you can include them after the path to the bitcode or IR file. Here’s an example:
lli path/to/file.ll argument1 argument2 ...
Motivation: Providing command-line arguments to your LLVM program allows you to test different input scenarios or provide inputs for interactive programs.
Explanation: The argument1, argument2, etc. represent the command-line arguments that will be passed to your program.
Example Output: The output will depend on how your LLVM program handles the provided command-line arguments.
3: Enable All Optimizations
If you want to enable all optimizations before executing your LLVM program, you can use the -O3 flag with the lli command. Here’s an example:
lli -O3 path/to/file.ll
Motivation: Enabling optimizations can significantly improve the performance of your LLVM program by applying various transformations and analyses.
Explanation: The -O3 flag indicates that you want to enable all possible optimizations.
Example Output: The output will be the result of executing the optimized version of your program.
4: Load a Dynamic Library Before Linking
In case your LLVM program depends on symbols defined in a dynamic library, you can use the --dlopen option to specify the path to the library. Here’s an example:
lli --dlopen=path/to/library.dll path/to/file.ll
Motivation: Loading a dynamic library before linking allows you to use functions and symbols defined in the library within your LLVM program.
Explanation: The --dlopen=path/to/library.dll option specifies the path to the dynamic library that needs to be loaded. It is important to replace path/to/library.dll with the correct path for your system.
Example Output: The output will be the result of executing your LLVM program with the loaded dynamic library, which may include the invocation of functions from the library.
Conclusion
The lli command provides a convenient way to directly execute LLVM bitcode and IR files. In this article, we explored different use cases of the lli command by providing code examples, motivations, explanations, and example outputs. By leveraging the lli command, you can easily test and debug your LLVM programs without the need for additional compilation steps.
