Optimize C and C++ code using compiler autovectorization techniques
Introduction
An introduction to autovectorization
Autovectorization using the restrict keyword
Autovectorization limits
Autovectorization and conditionals
Autovectorization on Arm
More autovectorization on Arm
Next Steps

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About this Learning Path

Skill level:  Advanced
Reading time:  45 min
Last updated:  03 Aug 2026
Skill level:
  Advanced
Reading time:
  45 min
Last updated:
  03 Aug 2026
Author:Konstantinos Margaritis, VectorCamp
Arm IP:Neoverse Cortex-A
Tags: Performance and Architecture Linux GCC Clang Runbook
Author:
  • Konstantinos Margaritis, VectorCamp
Arm IP:
Neoverse Cortex-A
Tags:
Performance and Architecture Linux GCC Clang Runbook

Who is this for?

This is an advanced topic for C/C++ developers who are interested in taking advantage of autovectorization in compilers.

What will you learn?

After completing this Learning Path, you'll be able to perform the following tasks:

  • Modify loops to take advantage of autovectorization in compilers

Prerequisites

Before starting, you'll need the following prerequisites:

  • An Arm computer running Linux and a recent version of Clang or the GNU compiler (gcc) installed.

Summary

AI-assisted

This summary was drafted with an approved AI-assisted workflow and reviewed by Arm contributors before publication. Human technical review remains part of the process so the final page reflects engineering rigor, accuracy, and Arm editorial standards.

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You’ll enable and inspect compiler autovectorization for C and C++ loops on Arm Linux with GCC or Clang. You’ll build focused examples, apply the C99 restrict qualifier, and inspect assembly to verify vectorization. Then, you’ll examine countable loops and branches, refactor conditionals when needed, and use an integer dot product to recognize Arm SIMD instructions in generated code.

Frequently asked questions

AI-assisted

These FAQs were drafted with an approved AI-assisted workflow and reviewed by Arm contributors before publication. Human technical review remains part of the process so the final page reflects engineering rigor, accuracy, and Arm editorial standards.

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How do I know if the compiler vectorized my loop?
Compile with optimization, then disassemble the binary with objdump -D. In the target function, look for wide loads, stores, and arithmetic that process multiple elements per iteration instead of scalar steps.
I added `restrict` but my loop still doesn’t vectorize. What should I check next?
Confirm that the loop is countable and free of loop-carried dependencies or branches. If the loop includes conditionals, restructure or move the conditionals so the hot path is branch-free.
Can I use Clang instead of GCC for the steps?
Yes. The examples use gcc, but Clang can compile the same sources and generate assembly for inspection.
Which files should I compile in the `restrict` example, and what do I inspect?
Compile the example sources, such as addvec.c and addvec_neon.c, then disassemble the addvec binary. Inspect the addvec function for vectorized operations after applying restrict.
What should I look for in the dot product example to confirm Arm-specific instructions are used?
Build dotprod.c and inspect the assembly for dotprod. Look for vectorized integer operations that process multiple elements per iteration with vector loads and stores.
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