LLVM (Low-Level Virtual Machine) is a set of tools and libraries that facilitate the creation of compilers and other code manipulation-related tools. It provides a modular infrastructure for intermediate representation (IR), code optimization, machine code generation, and execution.
It is currently the "magic" behind the lives of languages like Rust, Swift, V lang, Zig, and many other modern languages. Used by C or C++ compilers like Clang.
Intermediate representation generally refers to a language that is independent of source code and sub-objective, as it is the midpoint between two major phases, from inception to completion.
LLVM IR is an intermediate representation created by the LLVM project, which has the same concept as above but tries to be extremely versatile and capable of being very optimizable to generate either assembly code for different architectures.
source_filename = "hello_world.c"
@hello_world = private constant [12 x i8] c"hello world\00"
define i32 @main() {
%1 = call i32 @puts(ptr @hello_world)
ret i32 0
}
declare i32 @puts(ptr)source_filename represents the name of the file from which the IR generated by the compiler comes, in this case clang.
As you know, a string is represented by an array of characters. In LLVM IR, it is the same thing; the difference is that there is a tendency to generate global variables as constants, since it is not a dynamic, mutable string, so to speak.
define i32 main, which represents the entry point, which is a function that serves as the start gate for the execution of the program, since it indicates to the operating system where the program should start. This, as is customary, returns 0, since it is a signal to the operating system that the execution of the program was successful.
After that, there is a call to the puts function, which belongs to the C standard library, a bridge function to the write system call, on x86_64 architectures and the Linux kernel.
Finally, the puts function is prototyped or declared, since it must be available externally so that the linker can search for it in a certain library and link it to the resulting executable.
LLVM IR includes primitive types, if you can say so, as these are types that are fully integrated into the language. They range from floating-point types, doubles, 8-bit, 16-bit, 32-bit, and 64-bit integers, and booleans to types that return nothing or are simply the live equivalent of generic types, which can contain any other type other than void, respectively.
float
double
i64
i32
i16
i8
i1
void
ptr ; Opaque pointer type, available in LLVM 17-present version of LLVM.Arrays with a predefined size at compile time are defined as follows:
[SIZE x TYPE]
; Example
[8 x i8]You can now see LLVM IR in more detail in the corresponding files:
(It is organized in a way that is ready to learn)
- Functions.md
- Structures.md
- Calls.md
- Memory.md
- Arithmetic.md
- Globals.md
- Comparisons.md
- Branches.md
- Loops.md