Use LLVM Machine Code Analyzer to analyze assembly performance on Arm
Introduction
Background
Run MCA with Arm assembly
Use MCA with Compiler Explorer
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Use LLVM Machine Code Analyzer to analyze assembly performance on Arm

About this Learning Path

Skill level:  Introductory
Reading time:  1 hr
Last updated:  03 Aug 2026
Skill level:
  Introductory
Reading time:
  1 hr
Last updated:
  03 Aug 2026
Author:Asher Dobrescu, Arm
Arm IP:Cortex-A Neoverse
Tags: Performance and Architecture Linux Windows macOS Assembly llvm-mca Runbook
Author:
  • Asher Dobrescu, Arm
Arm IP:
Cortex-A Neoverse
Tags:
Performance and Architecture Linux Windows macOS Assembly llvm-mca Runbook

Who is this for?

This is an introductory topic for developers who want to diagnose performance issues of Arm programs using LLVM Machine Code Analyzer (MCA) and Compiler Explorer.

What will you learn?

Upon completion of this Learning Path, you will be able to:

  • Estimate the hardware resource pressure and the number of cycles taken to execute your code snippet using llvm-mca.
  • Describe how this estimate can help diagnose possible performance issues.
  • Use Compiler Explorer to run llvm-mca.

Prerequisites

Before starting, you will need the following:

  • Familiarity with Arm assembly.
  • LLVM version 16 or newer, which includes support for Neoverse V2.

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 use LLVM Machine Code Analyzer (llvm-mca) to reason about Arm assembly performance. You’ll analyze a short six-value sum to estimate cycles and resource pressure, identify bottlenecks, and relate the report to pipeline behavior. You’ll also run llvm-mca in Compiler Explorer to compare compiler versions and apply the workflow to other Arm assembly fragments.

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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What result should I expect when I run `llvm-mca` on the `sum_test1.s` example?
llvm-mca prints estimated cycles and hardware resource pressure for the add instructions. Use those metrics to identify possible stalls and the most stressed resources.
How do I run `llvm-mca` inside Compiler Explorer?
Open Compiler Explorer , then select the llvm-mca tool integration to analyze your code. You can choose compilers and tools without installing them locally.
How do I know `llvm-mca` executed correctly on my snippet?
The report includes an estimated cycle count and a resource-usage breakdown without errors. If it’s missing or incomplete, verify that the input matches the example and rerun the analysis.
What should I check before analyzing the Arm assembly example?
Save the provided instructions exactly as shown in sum_test1.s. Make sure the registers match the example so the analysis reflects the intended sequence.
Can I follow this path without installing LLVM locally?
Yes. Compiler Explorer includes llvm-mca and lets you try compiler versions in the browser. For Neoverse V2 support, use LLVM 16 or later.
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