Learning LLVM IR basics
LLVM IR is an alternative form of the program you want to optimize and compile. It is, however, structured differently from normal programming languages such as C/C++. LLVM IR is organized in a hierarchical fashion. The levels in this hierarchy – counting from the top – are Module, function, basic block, and instruction. The following diagram shows their structure:
Figure 10.1 – Hierarchy structure of LLVM IR
A module represents a translation unit – usually a source file. Each module can contain multiple functions (or global variables). Each contains a list of basic blocks where each of the basic blocks contains a list of instructions.
Quick refresher – basic block
A basic block represents a list of instructions with only one entry and one exit point. In other words, if a basic block is executed, the control flow is guaranteed to walk through every instruction in the block.
Knowing the high...
