llvm

llvm Best Practices

Developing for LLVM requires adherence to specific patterns and standards to maintain consistency, performance, and testability across a massive codebase. This guide outlines critical best practices for our team.

1. Code Organization and Structure

1.1 Adhere to LLVM Coding Standards

Consistency is paramount. Follow LLVM's established naming conventions, whitespace rules, and C++17 usage. Deviations require strong justification.

• Naming: CamelCase for types, lower_case for functions/variables.
• Whitespace: Use clang-format with LLVM style.
• C++ Standard: Stick to C++17 features supported by major toolchains.

❌ BAD: Inconsistent naming and formatting

class my_custom_pass { // Class name should be CamelCase
  void RunPass() { // Function name should be lower_case
    int temp_var = 0;
  }
};

✅ GOOD: Consistent LLVM style

class MyCustomPass {
  void runOnFunction(llvm::Function &F) { // LLVM passes typically run on a Function
    int tempVar = 0; // Local variables can be camelCase or snake_case, consistency is key.
  }
};

1.2 Prefer LLVM ADT and Utilities

Leverage LLVM's specialized data structures and utilities over standard library equivalents for performance and consistency.

• Containers: Use llvm::SmallVector, llvm::DenseMap, llvm::StringRef etc.
• I/O: Use llvm::raw_ostream for all output.

❌ BAD: Using standard library containers and I/O

#include <vector>
#include <map>
#include <iostream>

std::vector<int> myVec;
std::map<std::string, int> myMap;
std::cout << "Debug info: " << val << std::endl;

✅ GOOD: Using LLVM ADT and raw_ostream

#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/Support/raw_ostream.h"

llvm::SmallVector<int, 8> myVec; // SmallVector avoids heap allocation for small sizes
llvm::DenseMap<llvm::StringRef, int> myMap; // DenseMap is faster for many use cases
llvm::outs() << "Debug info: " << val << "\n"; // Use llvm::outs() for stdout