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//! LLVM Split — splits an LLVM module into multiple smaller modules.
//! Clean-room behavioral reconstruction from the `llvm-split`
//! documentation.
//!
//! Supports three splitting strategies:
//! - Split by partition count: distribute functions evenly across N modules
//! - Split by function count: put at most N functions per module
//! - Split by size: keep module under a byte-size budget
//!
//! @llvm_behavior: `llvm-split` is an LLVM utility that splits a
//! bitcode module into multiple modules. It preserves all global
//! variables, type definitions, and metadata needed by each part.
use llvm_native_core::module::Module;
use llvm_native_core::value::ValueRef;
use std::collections::HashSet;
// ============================================================================
// LLVMSplit
// ============================================================================
/// LLVMSplit — partitions an LLVM module into multiple self-contained modules.
pub struct LLVMSplit;
impl LLVMSplit {
// ========================================================================
// Split by Partition Count
// ========================================================================
/// Split a module into `num_parts` roughly-equal partitions.
///
/// Each output module contains a subset of the functions from the
/// original, along with all referenced globals, types, and metadata
/// needed to keep the module valid.
pub fn split_module(module: &Module, num_parts: usize) -> Vec<Module> {
if num_parts <= 1 || module.functions.is_empty() {
return vec![module.clone()];
}
let num_funcs = module.functions.len();
let part_size = (num_funcs + num_parts - 1) / num_parts; // ceil division
let mut result = Vec::with_capacity(num_parts);
for i in 0..num_parts {
let start = i * part_size;
let end = (start + part_size).min(num_funcs);
if start >= num_funcs {
break;
}
let subset: Vec<String> = module.functions[start..end]
.iter()
.map(|f| f.borrow().name.clone())
.collect();
let mut part = Module::new(&format!("{}_part{}", module.name, i));
Self::copy_metadata(module, &mut part);
Self::copy_types(module, &mut part);
Self::copy_functions(module, &mut part, &subset);
Self::copy_referenced_globals(module, &mut part);
result.push(part);
}
result
}
// ========================================================================
// Split by Function Count
// ========================================================================
/// Split a module so each output module has at most `parts` functions.
pub fn split_functions(module: &Module, parts: usize) -> Vec<Module> {
if parts == 0 || module.functions.is_empty() {
return vec![module.clone()];
}
let num_funcs = module.functions.len();
let num_parts = (num_funcs + parts - 1) / parts;
Self::split_module(module, num_parts)
}
// ========================================================================
// Split by Size Budget
// ========================================================================
/// Split a module so each output module's byte-size estimate is under
/// `max_size`.
///
/// Size is estimated by counting functions (1 unit per function).
pub fn split_by_size(module: &Module, max_size: usize) -> Vec<Module> {
if max_size == 0 || module.functions.is_empty() {
return vec![module.clone()];
}
// Estimate function sizes: count 1 per function for simplicity.
let func_names: Vec<String> = module
.functions
.iter()
.map(|f| f.borrow().name.clone())
.collect();
let mut result = Vec::new();
let mut part_index = 0;
let mut current_size = 0usize;
let mut current_funcs: Vec<String> = Vec::new();
for name in &func_names {
if current_size + 1 > max_size && !current_funcs.is_empty() {
// Emit current partition.
let mut part = Module::new(&format!("{}_size{}", module.name, part_index));
Self::copy_metadata(module, &mut part);
Self::copy_types(module, &mut part);
Self::copy_functions(module, &mut part, ¤t_funcs);
Self::copy_referenced_globals(module, &mut part);
result.push(part);
part_index += 1;
current_size = 0;
current_funcs.clear();
}
current_size += 1;
current_funcs.push(name.clone());
}
// Emit the last partition.
if !current_funcs.is_empty() {
let mut part = Module::new(&format!("{}_size{}", module.name, part_index));
Self::copy_metadata(module, &mut part);
Self::copy_types(module, &mut part);
Self::copy_functions(module, &mut part, ¤t_funcs);
Self::copy_referenced_globals(module, &mut part);
result.push(part);
}
result
}
// ========================================================================
// Copy Helpers
// ========================================================================
/// Copy module-level metadata from src to dst.
fn copy_metadata(src: &Module, dst: &mut Module) {
dst.target_triple = src.target_triple.clone();
dst.data_layout = src.data_layout.clone();
dst.flags = src.flags.clone();
dst.named_metadata = src.named_metadata.clone();
dst.comdats = src.comdats.clone();
}
/// Copy all type definitions.
fn copy_types(src: &Module, dst: &mut Module) {
dst.types = src.types.clone();
dst.named_types = src.named_types.clone();
}
/// Copy only the named functions into the destination module.
fn copy_functions(src: &Module, dst: &mut Module, names: &[String]) {
let name_set: HashSet<&str> = names.iter().map(|s| s.as_str()).collect();
for func in &src.functions {
let f_ref = func.borrow();
if name_set.contains(f_ref.name.as_str()) {
dst.functions.push(func.clone());
}
}
}
/// Copy global variables referenced by the copied functions.
fn copy_referenced_globals(src: &Module, dst: &mut Module) {
// Collect all global variable names referenced in the copied functions.
let mut referenced: HashSet<String> = HashSet::new();
for func in &dst.functions {
Self::collect_global_refs(func, &mut referenced);
}
for g in &src.globals {
let g_ref = g.borrow();
if referenced.contains(&g_ref.name) {
dst.globals.push(g.clone());
}
}
}
/// Recursively collect global variable references from a function.
fn collect_global_refs(func: &ValueRef, out: &mut HashSet<String>) {
let f_ref = func.borrow();
// Walk operands of the function value.
for operand in &f_ref.operands {
let op_ref = operand.borrow();
if op_ref.subclass == llvm_native_core::value::SubclassKind::GlobalVariable {
out.insert(op_ref.name.clone());
}
// Recurse into instruction operands.
Self::collect_global_refs(operand, out);
}
}
}
// ============================================================================
// Tests
// ============================================================================
#[cfg(test)]
mod tests {
use super::*;
use llvm_native_core::function::new_function;
use llvm_native_core::types::Type;
fn make_module(name: &str, num_funcs: usize) -> Module {
let mut module = Module::new(name);
for i in 0..num_funcs {
let func = new_function(&format!("func_{}", i), Type::i32(), &[]);
module.functions.push(func);
}
module
}
#[test]
fn test_split_empty() {
let module = Module::new("empty");
let parts = LLVMSplit::split_module(&module, 3);
assert_eq!(parts.len(), 1);
assert_eq!(parts[0].name, "empty");
}
#[test]
fn test_split_single_part() {
let module = make_module("test", 5);
let parts = LLVMSplit::split_module(&module, 1);
assert_eq!(parts.len(), 1);
assert_eq!(parts[0].functions.len(), 5);
}
#[test]
fn test_split_even() {
let module = make_module("test", 4);
let parts = LLVMSplit::split_module(&module, 2);
assert_eq!(parts.len(), 2);
assert_eq!(parts[0].functions.len(), 2);
assert_eq!(parts[1].functions.len(), 2);
}
#[test]
fn test_split_uneven() {
let module = make_module("test", 5);
let parts = LLVMSplit::split_module(&module, 2);
assert_eq!(parts.len(), 2);
let total: usize = parts.iter().map(|p| p.functions.len()).sum();
assert_eq!(total, 5);
}
#[test]
fn test_split_by_functions() {
let module = make_module("test", 10);
let parts = LLVMSplit::split_functions(&module, 3);
// 10 functions, 3 per part → 4 parts.
assert_eq!(parts.len(), 4);
let total: usize = parts.iter().map(|p| p.functions.len()).sum();
assert_eq!(total, 10);
}
#[test]
fn test_split_by_size_small_budget() {
let module = make_module("test", 5);
// Each function counts as 1 unit, budget 2 → 3 parts.
let parts = LLVMSplit::split_by_size(&module, 2);
assert_eq!(parts.len(), 3);
let total: usize = parts.iter().map(|p| p.functions.len()).sum();
assert_eq!(total, 5);
}
#[test]
fn test_metadata_preserved() {
let mut module = make_module("test", 2);
module.target_triple = Some("x86_64-unknown-linux-gnu".to_string());
let parts = LLVMSplit::split_module(&module, 2);
for part in &parts {
assert_eq!(
part.target_triple,
Some("x86_64-unknown-linux-gnu".to_string())
);
}
}
}