rust/src/librustc/back/lto.rs

// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use back::archive::Archive;
use back::link;
use driver::session;
use lib::llvm::{ModuleRef, TargetMachineRef, llvm, True, False};
use metadata::cstore;
use util::common::time;

use std::libc;
use std::vec;

pub fn run(sess: session::Session, llmod: ModuleRef,
           tm: TargetMachineRef, reachable: &[~str]) {
    // Make sure we actually can run LTO
    for output in sess.outputs.iter() {
        match *output {
            session::OutputExecutable | session::OutputStaticlib => {}
            _ => {
                sess.fatal("lto can only be run for executables and \
                            static library outputs");
            }
        }
    }

    // For each of our upstream dependencies, find the corresponding rlib and
    // load the bitcode from the archive. Then merge it into the current LLVM
    // module that we've got.
    let crates = cstore::get_used_crates(sess.cstore, cstore::RequireStatic);
    for (cnum, path) in crates.move_iter() {
        let name = cstore::get_crate_data(sess.cstore, cnum).name;
        let path = match path {
            Some(p) => p,
            None => {
                sess.fatal(format!("could not find rlib for: `{}`", name));
            }
        };

        let archive = Archive::open(sess, path);
        debug!("reading {}", name);
        let bc = time(sess.time_passes(), format!("read {}.bc", name), (), |_|
                      archive.read(format!("{}.bc", name)));
        let ptr = vec::raw::to_ptr(bc);
        debug!("linking {}", name);
        time(sess.time_passes(), format!("ll link {}", name), (), |()| unsafe {
            if !llvm::LLVMRustLinkInExternalBitcode(llmod,
                                                    ptr as *libc::c_char,
                                                    bc.len() as libc::size_t) {
                link::llvm_err(sess, format!("failed to load bc of `{}`", name));
            }
        });
    }

    // Internalize everything but the reachable symbols of the current module
    let cstrs = reachable.map(|s| s.to_c_str());
    let arr = cstrs.map(|c| c.with_ref(|p| p));
    let ptr = vec::raw::to_ptr(arr);
    unsafe {
        llvm::LLVMRustRunRestrictionPass(llmod, ptr as **libc::c_char,
                                         arr.len() as libc::size_t);
    }

    // Now we have one massive module inside of llmod. Time to run the
    // LTO-specific optimization passes that LLVM provides.
    //
    // This code is based off the code found in llvm's LTO code generator:
    //      tools/lto/LTOCodeGenerator.cpp
    debug!("running the pass manager");
    unsafe {
        let pm = llvm::LLVMCreatePassManager();
        llvm::LLVMRustAddAnalysisPasses(tm, pm, llmod);
        "verify".with_c_str(|s| llvm::LLVMRustAddPass(pm, s));

        let builder = llvm::LLVMPassManagerBuilderCreate();
        llvm::LLVMPassManagerBuilderPopulateLTOPassManager(builder, pm,
            /* Internalize = */ False,
            /* RunInliner = */ True);
        llvm::LLVMPassManagerBuilderDispose(builder);

        "verify".with_c_str(|s| llvm::LLVMRustAddPass(pm, s));

        time(sess.time_passes(), "LTO pases", (), |()|
             llvm::LLVMRunPassManager(pm, llmod));

        llvm::LLVMDisposePassManager(pm);
    }
    debug!("lto done");
}