LLVM

LLVM IR

It is similar to assembly, but at a higher abstractions.

• There are unlimited register (e.g. %2, %3, ...)
• LLVM IR has a fully type system for describing data
• Register names must follow the SSA form

Types

There are various different types:

• Integers: i8, ...
• Floats:
• Vectors
• Structs
• Pointers

Examples #1

• align x: the address has to be a multiple of x
• As a convention: %id are usually used for types and registers, @id are used for global variables

Example #2

• there is no explicit stack. LLVM will take care of this when generating the code

Example #3 - Pointers

int *ptr;
ptr = ptr + 1;

%ptr = alloca i32*
%1 = load i32** %ptr
%2 = getelementptr i32* %1, i64 1
store i32* %2, i32** %ptr

• To do any pointer arithmentic, one has to use the getelementptr instruction
• load i32** needs two *, since it loads the value of the pointer.