LLVM Essentials

Extracting a scalar from a vector

An individual scalar element can be extracted from a vector. LLVM provides the extractelement instruction for the same. The first operand of an extractelement instruction is a value of vector type. The second operand is an index indicating the position from which to extract the element.

The extractelement instruction looks like the following:

result = extractelement <4 x i32> %vec, i32 %idx

This can be further understood by keeping the following in mind:

• vec is a vector
• idx is the index at which the data to be extracted lies
• result is of scalar type, which is i32 here

Let's take an example where we want to add all the elements of a given vector and return an integer.

Consider the following code:

#include "llvm/IR/IRBuilder.h" ...