llvm

Q: How do I install llvm?

Run npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill llvm in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/llvm/ (personal) or .claude/skills/llvm/ (project).

by mohitmishra786Backend & APIs

LLVM IR and pass pipeline skill. Use when working directly with LLVM Intermediate Representation (IR), running opt passes, generating IR with llc, inspecting or writing LLVM IR for custom passes, or understanding how the LLVM backend lowers IR to assembly. Activates on queries about LLVM IR, opt, llc, llvm-dis, LLVM passes, IR transformations, or building LLVM-based tools.

Installs: 901
Last 24h: —
Trending rank: —
Security: Not audited

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill llvm

01
Install
Run the command in your project. The CLI asks which agents to install for.
02
Describe the task
Ask your agent for something this skill covers. It loads llvm automatically when relevant.
03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

LLVM IR and Tooling

Purpose

Guide agents through LLVM as a user: generating and inspecting IR, running existing optimisation passes with opt, lowering to assembly with llc, and diagnosing missed optimisations. For writing new LLVM passes (PassPlugin, llvm-lit testing), use skills/compiler-internals/llvm-passes instead.

Triggers

"Show me the LLVM IR for this function"
"How do I run an LLVM optimisation pass?"
"What does this LLVM IR instruction mean?"
"How do I write a custom LLVM pass?"
"Why isn't auto-vectorisation happening in LLVM?"

Workflow

1. Generate LLVM IR

# Emit textual IR (.ll)
clang -O0 -emit-llvm -S src.c -o src.ll

# Emit bitcode (.bc)
clang -O2 -emit-llvm -c src.c -o src.bc

# Disassemble bitcode to text
llvm-dis src.bc -o src.ll

2. Run optimisation passes with `opt`

# Apply a specific pass
opt -passes='mem2reg,instcombine,simplifycfg' src.ll -S -o out.ll

# Standard optimisation pipelines
opt -passes='default<O2>' src.ll -S -o out.ll
opt -passes='default<O3>' src.ll -S -o out.ll

# List available passes
opt --print-passes 2>&1 | less

# Print IR before and after a pass
opt -passes='instcombine' --print-before=instcombine --print-after=instcombine src.ll -S -o out.ll 2>&1 | less

3. Lower IR to assembly with `llc`

# Compile IR to object file
llc -filetype=obj src.ll -o src.o

# Compile to assembly
llc -filetype=asm -masm-syntax=intel src.ll -o src.s

# Target a specific CPU
llc -mcpu=skylake -mattr=+avx2 src.ll -o src.s

# Show available targets
llc --version

4. Inspect IR

Key IR constructs to understand:

Construct	Meaning
`alloca`	Stack allocation (pre-SSA; `mem2reg` promotes to registers)
`load`/`store`	Memory access
`getelementptr` (GEP)	Pointer arithmetic / field access
`phi`	SSA φ-node: merges values from predecessor blocks
`call`/`invoke`	Function call (`invoke` has exception edges)
`icmp`/`fcmp`	Integer/float comparison
`br`	Branch (conditional or unconditional)
`ret`	Return
`bitcast`	Reinterpret bits (no-op in codegen)
`ptrtoint`/`inttoptr`	Pointer↔integer (avoid where possible)

5. Key passes

Pass	Effect
`mem2reg`	Promote alloca to SSA registers
`instcombine`	Instruction combining / peephole
`simplifycfg`	CFG cleanup, dead block removal
`loop-vectorize`	Auto-vectorisation
`slp-vectorize`	Superword-level parallelism (straight-line vectorisation)
`inline`	Function inlining
`gvn`	Global value numbering (common subexpression elimination)
`licm`	Loop-invariant code motion
`loop-unroll`	Loop unrolling
`argpromotion`	Promote pointer args to values
`sroa`	Scalar Replacement of Aggregates

6. Debugging missed optimisations

# Why was a loop not vectorised?
clang -O2 -Rpass-missed=loop-vectorize -Rpass-analysis=loop-vectorize src.c

# Dump pass pipeline
clang -O2 -mllvm -debug-pass=Structure src.c -o /dev/null 2>&1 | less

# Print IR after each pass (very verbose)
opt -passes='default<O2>' -print-after-all src.ll -S 2>&1 | less

7. Useful llvm tools

Tool	Purpose
`llvm-dis`	Bitcode → textual IR
`llvm-as`	Textual IR → bitcode
`llvm-link`	Link multiple bitcode files
`llvm-lto`	Standalone LTO
`llvm-nm`	Symbols in bitcode/object
`llvm-objdump`	Disassemble objects
`llvm-profdata`	Merge/show PGO profiles
`llvm-cov`	Coverage reporting
`llvm-mca`	Machine code analyser (throughput/latency)

For binutils equivalents, see skills/binaries/binutils.

Related skills

Use skills/compiler-internals/llvm-passes for writing and testing custom LLVM passes
Use skills/compiler-internals/compiler-frontend for generating LLVM IR from an AST
Use skills/compiler-internals/jit-compilation for ORC JIT execution of LLVM IR
Use skills/compilers/clang for source-level Clang flags
Use skills/binaries/linkers-lto for LTO at link time
Use skills/profilers/linux-perf combined with llvm-mca for micro-architectural analysis

FAQ

What does the llvm skill do?

How do I install llvm?

Run npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill llvm in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/llvm/ (personal) or .claude/skills/llvm/ (project).

Which AI agents can use llvm?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is llvm safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains llvm?

It is published by mohitmishra786 in mohitmishra786/low-level-dev-skills. It has 901 recorded installs.