Getting started with LLVM core libraries

Exercising basic tools to manipulate the IR formats

We mention that the LLVM IR can be stored on disk in two formats: bitcode and assembly text. We will now learn how to use them. Consider the sum.c source code:

int sum(int a, int b) {
  return a+b;
}

To make Clang generate the bitcode, you can use the following command:

$ clang sum.c -emit-llvm -c -o sum.bc

To generate the assembly representation, you can use the following command:

$ clang sum.c -emit-llvm -S -c -o sum.ll

You can also assemble the LLVM IR assembly text, which will create a bitcode:

$ llvm-as sum.ll -o sum.bc

To convert from bitcode to IR assembly, which is the opposite, you can use the disassembler:

$ llvm-dis sum.bc -o sum.ll 

The llvm-extract tool allows the extraction of IR functions, ...