Google Git
Sign in
android / toolchain / rustc / refs/heads/main / . / compiler / rustc_codegen_ssa / src / back / write.rs
blob: 4eda4c2f08c6938fad84373d5e3eecb3e98e29c2 [file] [log] [blame]
use super::link::{self, ensure_removed};
use super::lto::{self, SerializedModule};
use super::symbol_export::symbol_name_for_instance_in_crate;
use crate::errors;
use crate::traits::*;
use crate::{
CachedModuleCodegen, CodegenResults, CompiledModule, CrateInfo, ModuleCodegen, ModuleKind,
};
use jobserver::{Acquired, Client};
use rustc_ast::attr;
use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
use rustc_data_structures::memmap::Mmap;
use rustc_data_structures::profiling::{SelfProfilerRef, VerboseTimingGuard};
use rustc_data_structures::sync::Lrc;
use rustc_errors::emitter::Emitter;
use rustc_errors::translation::Translate;
use rustc_errors::{
Diag, DiagArgMap, DiagCtxt, DiagMessage, ErrCode, FatalError, FluentBundle, Level, MultiSpan,
Style,
};
use rustc_fs_util::link_or_copy;
use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
use rustc_incremental::{
copy_cgu_workproduct_to_incr_comp_cache_dir, in_incr_comp_dir, in_incr_comp_dir_sess,
};
use rustc_metadata::fs::copy_to_stdout;
use rustc_metadata::EncodedMetadata;
use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
use rustc_middle::middle::exported_symbols::SymbolExportInfo;
use rustc_middle::ty::TyCtxt;
use rustc_session::config::{self, CrateType, Lto, OutFileName, OutputFilenames, OutputType};
use rustc_session::config::{Passes, SwitchWithOptPath};
use rustc_session::Session;
use rustc_span::source_map::SourceMap;
use rustc_span::symbol::sym;
use rustc_span::{BytePos, FileName, InnerSpan, Pos, Span};
use rustc_target::spec::{MergeFunctions, SanitizerSet};
use crate::errors::ErrorCreatingRemarkDir;
use std::any::Any;
use std::fs;
use std::io;
use std::marker::PhantomData;
use std::mem;
use std::path::{Path, PathBuf};
use std::str;
use std::sync::mpsc::{channel, Receiver, Sender};
use std::sync::Arc;
use std::thread;
const PRE_LTO_BC_EXT: &str = "pre-lto.bc";
/// What kind of object file to emit.
#[derive(Clone, Copy, PartialEq)]
pub enum EmitObj {
// No object file.
None,
// Just uncompressed llvm bitcode. Provides easy compatibility with
// emscripten's ecc compiler, when used as the linker.
Bitcode,
// Object code, possibly augmented with a bitcode section.
ObjectCode(BitcodeSection),
}
/// What kind of llvm bitcode section to embed in an object file.
#[derive(Clone, Copy, PartialEq)]
pub enum BitcodeSection {
// No bitcode section.
None,
// A full, uncompressed bitcode section.
Full,
}
/// Module-specific configuration for `optimize_and_codegen`.
pub struct ModuleConfig {
/// Names of additional optimization passes to run.
pub passes: Vec<String>,
/// Some(level) to optimize at a certain level, or None to run
/// absolutely no optimizations (used for the metadata module).
pub opt_level: Option<config::OptLevel>,
/// Some(level) to optimize binary size, or None to not affect program size.
pub opt_size: Option<config::OptLevel>,
pub pgo_gen: SwitchWithOptPath,
pub pgo_use: Option<PathBuf>,
pub pgo_sample_use: Option<PathBuf>,
pub debug_info_for_profiling: bool,
pub instrument_coverage: bool,
pub instrument_gcov: bool,
pub sanitizer: SanitizerSet,
pub sanitizer_recover: SanitizerSet,
pub sanitizer_dataflow_abilist: Vec<String>,
pub sanitizer_memory_track_origins: usize,
// Flags indicating which outputs to produce.
pub emit_pre_lto_bc: bool,
pub emit_no_opt_bc: bool,
pub emit_bc: bool,
pub emit_ir: bool,
pub emit_asm: bool,
pub emit_obj: EmitObj,
pub emit_thin_lto: bool,
pub bc_cmdline: String,
// Miscellaneous flags. These are mostly copied from command-line
// options.
pub verify_llvm_ir: bool,
pub no_prepopulate_passes: bool,
pub no_builtins: bool,
pub time_module: bool,
pub vectorize_loop: bool,
pub vectorize_slp: bool,
pub merge_functions: bool,
pub inline_threshold: Option<u32>,
pub emit_lifetime_markers: bool,
pub llvm_plugins: Vec<String>,
}
impl ModuleConfig {
fn new(
kind: ModuleKind,
tcx: TyCtxt<'_>,
no_builtins: bool,
is_compiler_builtins: bool,
) -> ModuleConfig {
// If it's a regular module, use `$regular`, otherwise use `$other`.
// `$regular` and `$other` are evaluated lazily.
macro_rules! if_regular {
($regular: expr, $other: expr) => {
if let ModuleKind::Regular = kind { $regular } else { $other }
};
}
let sess = tcx.sess;
let opt_level_and_size = if_regular!(Some(sess.opts.optimize), None);
let save_temps = sess.opts.cg.save_temps;
let should_emit_obj = sess.opts.output_types.contains_key(&OutputType::Exe)
|| match kind {
ModuleKind::Regular => sess.opts.output_types.contains_key(&OutputType::Object),
ModuleKind::Allocator => false,
ModuleKind::Metadata => sess.opts.output_types.contains_key(&OutputType::Metadata),
};
let emit_obj = if !should_emit_obj {
EmitObj::None
} else if sess.target.obj_is_bitcode
|| (sess.opts.cg.linker_plugin_lto.enabled() && !no_builtins)
{
// This case is selected if the target uses objects as bitcode, or
// if linker plugin LTO is enabled. In the linker plugin LTO case
// the assumption is that the final link-step will read the bitcode
// and convert it to object code. This may be done by either the
// native linker or rustc itself.
//
// Note, however, that the linker-plugin-lto requested here is
// explicitly ignored for `#![no_builtins]` crates. These crates are
// specifically ignored by rustc's LTO passes and wouldn't work if
// loaded into the linker. These crates define symbols that LLVM
// lowers intrinsics to, and these symbol dependencies aren't known
// until after codegen. As a result any crate marked
// `#![no_builtins]` is assumed to not participate in LTO and
// instead goes on to generate object code.
EmitObj::Bitcode
} else if need_bitcode_in_object(tcx) {
EmitObj::ObjectCode(BitcodeSection::Full)
} else {
EmitObj::ObjectCode(BitcodeSection::None)
};
ModuleConfig {
passes: if_regular!(sess.opts.cg.passes.clone(), vec![]),
opt_level: opt_level_and_size,
opt_size: opt_level_and_size,
pgo_gen: if_regular!(
sess.opts.cg.profile_generate.clone(),
SwitchWithOptPath::Disabled
),
pgo_use: if_regular!(sess.opts.cg.profile_use.clone(), None),
pgo_sample_use: if_regular!(sess.opts.unstable_opts.profile_sample_use.clone(), None),
debug_info_for_profiling: sess.opts.unstable_opts.debug_info_for_profiling,
instrument_coverage: if_regular!(sess.instrument_coverage(), false),
instrument_gcov: if_regular!(
// compiler_builtins overrides the codegen-units settings,
// which is incompatible with -Zprofile which requires that
// only a single codegen unit is used per crate.
sess.opts.unstable_opts.profile && !is_compiler_builtins,
false
),
sanitizer: if_regular!(sess.opts.unstable_opts.sanitizer, SanitizerSet::empty()),
sanitizer_dataflow_abilist: if_regular!(
sess.opts.unstable_opts.sanitizer_dataflow_abilist.clone(),
Vec::new()
),
sanitizer_recover: if_regular!(
sess.opts.unstable_opts.sanitizer_recover,
SanitizerSet::empty()
),
sanitizer_memory_track_origins: if_regular!(
sess.opts.unstable_opts.sanitizer_memory_track_origins,
0
),
emit_pre_lto_bc: if_regular!(
save_temps || need_pre_lto_bitcode_for_incr_comp(sess),
false
),
emit_no_opt_bc: if_regular!(save_temps, false),
emit_bc: if_regular!(
save_temps || sess.opts.output_types.contains_key(&OutputType::Bitcode),
save_temps
),
emit_ir: if_regular!(
sess.opts.output_types.contains_key(&OutputType::LlvmAssembly),
false
),
emit_asm: if_regular!(
sess.opts.output_types.contains_key(&OutputType::Assembly),
false
),
emit_obj,
emit_thin_lto: sess.opts.unstable_opts.emit_thin_lto,
bc_cmdline: sess.target.bitcode_llvm_cmdline.to_string(),
verify_llvm_ir: sess.verify_llvm_ir(),
no_prepopulate_passes: sess.opts.cg.no_prepopulate_passes,
no_builtins: no_builtins || sess.target.no_builtins,
// Exclude metadata and allocator modules from time_passes output,
// since they throw off the "LLVM passes" measurement.
time_module: if_regular!(true, false),
// Copy what clang does by turning on loop vectorization at O2 and
// slp vectorization at O3.
vectorize_loop: !sess.opts.cg.no_vectorize_loops
&& (sess.opts.optimize == config::OptLevel::Default
|| sess.opts.optimize == config::OptLevel::Aggressive),
vectorize_slp: !sess.opts.cg.no_vectorize_slp
&& sess.opts.optimize == config::OptLevel::Aggressive,
// Some targets (namely, NVPTX) interact badly with the
// MergeFunctions pass. This is because MergeFunctions can generate
// new function calls which may interfere with the target calling
// convention; e.g. for the NVPTX target, PTX kernels should not
// call other PTX kernels. MergeFunctions can also be configured to
// generate aliases instead, but aliases are not supported by some
// backends (again, NVPTX). Therefore, allow targets to opt out of
// the MergeFunctions pass, but otherwise keep the pass enabled (at
// O2 and O3) since it can be useful for reducing code size.
merge_functions: match sess
.opts
.unstable_opts
.merge_functions
.unwrap_or(sess.target.merge_functions)
{
MergeFunctions::Disabled => false,
MergeFunctions::Trampolines | MergeFunctions::Aliases => {
use config::OptLevel::*;
match sess.opts.optimize {
Aggressive | Default | SizeMin | Size => true,
Less | No => false,
}
}
},
inline_threshold: sess.opts.cg.inline_threshold,
emit_lifetime_markers: sess.emit_lifetime_markers(),
llvm_plugins: if_regular!(sess.opts.unstable_opts.llvm_plugins.clone(), vec![]),
}
}
pub fn bitcode_needed(&self) -> bool {
self.emit_bc
|| self.emit_obj == EmitObj::Bitcode
|| self.emit_obj == EmitObj::ObjectCode(BitcodeSection::Full)
}
}
/// Configuration passed to the function returned by the `target_machine_factory`.
pub struct TargetMachineFactoryConfig {
/// Split DWARF is enabled in LLVM by checking that `TM.MCOptions.SplitDwarfFile` isn't empty,
/// so the path to the dwarf object has to be provided when we create the target machine.
/// This can be ignored by backends which do not need it for their Split DWARF support.
pub split_dwarf_file: Option<PathBuf>,
/// The name of the output object file. Used for setting OutputFilenames in target options
/// so that LLVM can emit the CodeView S_OBJNAME record in pdb files
pub output_obj_file: Option<PathBuf>,
}
impl TargetMachineFactoryConfig {
pub fn new(
cgcx: &CodegenContext<impl WriteBackendMethods>,
module_name: &str,
) -> TargetMachineFactoryConfig {
let split_dwarf_file = if cgcx.target_can_use_split_dwarf {
cgcx.output_filenames.split_dwarf_path(
cgcx.split_debuginfo,
cgcx.split_dwarf_kind,
Some(module_name),
)
} else {
None
};
let output_obj_file =
Some(cgcx.output_filenames.temp_path(OutputType::Object, Some(module_name)));
TargetMachineFactoryConfig { split_dwarf_file, output_obj_file }
}
}
pub type TargetMachineFactoryFn<B> = Arc<
dyn Fn(
TargetMachineFactoryConfig,
) -> Result<
<B as WriteBackendMethods>::TargetMachine,
<B as WriteBackendMethods>::TargetMachineError,
> + Send
+ Sync,
>;
pub type ExportedSymbols = FxHashMap<CrateNum, Arc<Vec<(String, SymbolExportInfo)>>>;
/// Additional resources used by optimize_and_codegen (not module specific)
#[derive(Clone)]
pub struct CodegenContext<B: WriteBackendMethods> {
// Resources needed when running LTO
pub prof: SelfProfilerRef,
pub lto: Lto,
pub save_temps: bool,
pub fewer_names: bool,
pub time_trace: bool,
pub exported_symbols: Option<Arc<ExportedSymbols>>,
pub opts: Arc<config::Options>,
pub crate_types: Vec<CrateType>,
pub each_linked_rlib_for_lto: Vec<(CrateNum, PathBuf)>,
pub output_filenames: Arc<OutputFilenames>,
pub regular_module_config: Arc<ModuleConfig>,
pub metadata_module_config: Arc<ModuleConfig>,
pub allocator_module_config: Arc<ModuleConfig>,
pub tm_factory: TargetMachineFactoryFn<B>,
pub msvc_imps_needed: bool,
pub is_pe_coff: bool,
pub target_can_use_split_dwarf: bool,
pub target_arch: String,
pub split_debuginfo: rustc_target::spec::SplitDebuginfo,
pub split_dwarf_kind: rustc_session::config::SplitDwarfKind,
/// All commandline args used to invoke the compiler, with @file args fully expanded.
/// This will only be used within debug info, e.g. in the pdb file on windows
/// This is mainly useful for other tools that reads that debuginfo to figure out
/// how to call the compiler with the same arguments.
pub expanded_args: Vec<String>,
/// Emitter to use for diagnostics produced during codegen.
pub diag_emitter: SharedEmitter,
/// LLVM optimizations for which we want to print remarks.
pub remark: Passes,
/// Directory into which should the LLVM optimization remarks be written.
/// If `None`, they will be written to stderr.
pub remark_dir: Option<PathBuf>,
/// The incremental compilation session directory, or None if we are not
/// compiling incrementally
pub incr_comp_session_dir: Option<PathBuf>,
/// Channel back to the main control thread to send messages to
pub coordinator_send: Sender<Box<dyn Any + Send>>,
/// `true` if the codegen should be run in parallel.
///
/// Depends on [`CodegenBackend::supports_parallel()`] and `-Zno_parallel_backend`.
pub parallel: bool,
}
impl<B: WriteBackendMethods> CodegenContext<B> {
pub fn create_dcx(&self) -> DiagCtxt {
DiagCtxt::new(Box::new(self.diag_emitter.clone()))
}
pub fn config(&self, kind: ModuleKind) -> &ModuleConfig {
match kind {
ModuleKind::Regular => &self.regular_module_config,
ModuleKind::Metadata => &self.metadata_module_config,
ModuleKind::Allocator => &self.allocator_module_config,
}
}
}
fn generate_lto_work<B: ExtraBackendMethods>(
cgcx: &CodegenContext<B>,
needs_fat_lto: Vec<FatLtoInput<B>>,
needs_thin_lto: Vec<(String, B::ThinBuffer)>,
import_only_modules: Vec<(SerializedModule<B::ModuleBuffer>, WorkProduct)>,
) -> Vec<(WorkItem<B>, u64)> {
let _prof_timer = cgcx.prof.generic_activity("codegen_generate_lto_work");
if !needs_fat_lto.is_empty() {
assert!(needs_thin_lto.is_empty());
let module =
B::run_fat_lto(cgcx, needs_fat_lto, import_only_modules).unwrap_or_else(|e| e.raise());
// We are adding a single work item, so the cost doesn't matter.
vec![(WorkItem::LTO(module), 0)]
} else {
assert!(needs_fat_lto.is_empty());
let (lto_modules, copy_jobs) = B::run_thin_lto(cgcx, needs_thin_lto, import_only_modules)
.unwrap_or_else(|e| e.raise());
lto_modules
.into_iter()
.map(|module| {
let cost = module.cost();
(WorkItem::LTO(module), cost)
})
.chain(copy_jobs.into_iter().map(|wp| {
(
WorkItem::CopyPostLtoArtifacts(CachedModuleCodegen {
name: wp.cgu_name.clone(),
source: wp,
}),
0, // copying is very cheap
)
}))
.collect()
}
}
pub struct CompiledModules {
pub modules: Vec<CompiledModule>,
pub allocator_module: Option<CompiledModule>,
}
fn need_bitcode_in_object(tcx: TyCtxt<'_>) -> bool {
let sess = tcx.sess;
let requested_for_rlib = sess.opts.cg.embed_bitcode
&& tcx.crate_types().contains(&CrateType::Rlib)
&& sess.opts.output_types.contains_key(&OutputType::Exe);
let forced_by_target = sess.target.forces_embed_bitcode;
requested_for_rlib || forced_by_target
}
fn need_pre_lto_bitcode_for_incr_comp(sess: &Session) -> bool {
if sess.opts.incremental.is_none() {
return false;
}
match sess.lto() {
Lto::No => false,
Lto::Fat | Lto::Thin | Lto::ThinLocal => true,
}
}
pub fn start_async_codegen<B: ExtraBackendMethods>(
backend: B,
tcx: TyCtxt<'_>,
target_cpu: String,
metadata: EncodedMetadata,
metadata_module: Option<CompiledModule>,
) -> OngoingCodegen<B> {
let (coordinator_send, coordinator_receive) = channel();
let sess = tcx.sess;
let crate_attrs = tcx.hir().attrs(rustc_hir::CRATE_HIR_ID);
let no_builtins = attr::contains_name(crate_attrs, sym::no_builtins);
let is_compiler_builtins = attr::contains_name(crate_attrs, sym::compiler_builtins);
let crate_info = CrateInfo::new(tcx, target_cpu);
let regular_config =
ModuleConfig::new(ModuleKind::Regular, tcx, no_builtins, is_compiler_builtins);
let metadata_config =
ModuleConfig::new(ModuleKind::Metadata, tcx, no_builtins, is_compiler_builtins);
let allocator_config =
ModuleConfig::new(ModuleKind::Allocator, tcx, no_builtins, is_compiler_builtins);
let (shared_emitter, shared_emitter_main) = SharedEmitter::new();
let (codegen_worker_send, codegen_worker_receive) = channel();
let coordinator_thread = start_executing_work(
backend.clone(),
tcx,
&crate_info,
shared_emitter,
codegen_worker_send,
coordinator_receive,
sess.jobserver.clone(),
Arc::new(regular_config),
Arc::new(metadata_config),
Arc::new(allocator_config),
coordinator_send.clone(),
);
OngoingCodegen {
backend,
metadata,
metadata_module,
crate_info,
codegen_worker_receive,
shared_emitter_main,
coordinator: Coordinator {
sender: coordinator_send,
future: Some(coordinator_thread),
phantom: PhantomData,
},
output_filenames: tcx.output_filenames(()).clone(),
}
}
fn copy_all_cgu_workproducts_to_incr_comp_cache_dir(
sess: &Session,
compiled_modules: &CompiledModules,
) -> FxIndexMap<WorkProductId, WorkProduct> {
let mut work_products = FxIndexMap::default();
if sess.opts.incremental.is_none() {
return work_products;
}
let _timer = sess.timer("copy_all_cgu_workproducts_to_incr_comp_cache_dir");
for module in compiled_modules.modules.iter().filter(|m| m.kind == ModuleKind::Regular) {
let mut files = Vec::new();
if let Some(object_file_path) = &module.object {
files.push(("o", object_file_path.as_path()));
}
if let Some(dwarf_object_file_path) = &module.dwarf_object {
files.push(("dwo", dwarf_object_file_path.as_path()));
}
if let Some((id, product)) =
copy_cgu_workproduct_to_incr_comp_cache_dir(sess, &module.name, files.as_slice())
{
work_products.insert(id, product);
}
}
work_products
}
fn produce_final_output_artifacts(
sess: &Session,
compiled_modules: &CompiledModules,
crate_output: &OutputFilenames,
) {
let mut user_wants_bitcode = false;
let mut user_wants_objects = false;
// Produce final compile outputs.
let copy_gracefully = |from: &Path, to: &OutFileName| match to {
OutFileName::Stdout => {
if let Err(e) = copy_to_stdout(from) {
sess.dcx().emit_err(errors::CopyPath::new(from, to.as_path(), e));
}
}
OutFileName::Real(path) => {
if let Err(e) = fs::copy(from, path) {
sess.dcx().emit_err(errors::CopyPath::new(from, path, e));
}
}
};
let copy_if_one_unit = |output_type: OutputType, keep_numbered: bool| {
if compiled_modules.modules.len() == 1 {
// 1) Only one codegen unit. In this case it's no difficulty
// to copy `foo.0.x` to `foo.x`.
let module_name = Some(&compiled_modules.modules[0].name[..]);
let path = crate_output.temp_path(output_type, module_name);
let output = crate_output.path(output_type);
if !output_type.is_text_output() && output.is_tty() {
sess.dcx()
.emit_err(errors::BinaryOutputToTty { shorthand: output_type.shorthand() });
} else {
copy_gracefully(&path, &output);
}
if !sess.opts.cg.save_temps && !keep_numbered {
// The user just wants `foo.x`, not `foo.#module-name#.x`.
ensure_removed(sess.dcx(), &path);
}
} else {
let extension = crate_output
.temp_path(output_type, None)
.extension()
.unwrap()
.to_str()
.unwrap()
.to_owned();
if crate_output.outputs.contains_key(&output_type) {
// 2) Multiple codegen units, with `--emit foo=some_name`. We have
// no good solution for this case, so warn the user.
sess.dcx().emit_warn(errors::IgnoringEmitPath { extension });
} else if crate_output.single_output_file.is_some() {
// 3) Multiple codegen units, with `-o some_name`. We have
// no good solution for this case, so warn the user.
sess.dcx().emit_warn(errors::IgnoringOutput { extension });
} else {
// 4) Multiple codegen units, but no explicit name. We
// just leave the `foo.0.x` files in place.
// (We don't have to do any work in this case.)
}
}
};
// Flag to indicate whether the user explicitly requested bitcode.
// Otherwise, we produced it only as a temporary output, and will need
// to get rid of it.
for output_type in crate_output.outputs.keys() {
match *output_type {
OutputType::Bitcode => {
user_wants_bitcode = true;
// Copy to .bc, but always keep the .0.bc. There is a later
// check to figure out if we should delete .0.bc files, or keep
// them for making an rlib.
copy_if_one_unit(OutputType::Bitcode, true);
}
OutputType::LlvmAssembly => {
copy_if_one_unit(OutputType::LlvmAssembly, false);
}
OutputType::Assembly => {
copy_if_one_unit(OutputType::Assembly, false);
}
OutputType::Object => {
user_wants_objects = true;
copy_if_one_unit(OutputType::Object, true);
}
OutputType::Mir | OutputType::Metadata | OutputType::Exe | OutputType::DepInfo => {}
}
}
// Clean up unwanted temporary files.
// We create the following files by default:
// - #crate#.#module-name#.bc
// - #crate#.#module-name#.o
// - #crate#.crate.metadata.bc
// - #crate#.crate.metadata.o
// - #crate#.o (linked from crate.##.o)
// - #crate#.bc (copied from crate.##.bc)
// We may create additional files if requested by the user (through
// `-C save-temps` or `--emit=` flags).
if !sess.opts.cg.save_temps {
// Remove the temporary .#module-name#.o objects. If the user didn't
// explicitly request bitcode (with --emit=bc), and the bitcode is not
// needed for building an rlib, then we must remove .#module-name#.bc as
// well.
// Specific rules for keeping .#module-name#.bc:
// - If the user requested bitcode (`user_wants_bitcode`), and
// codegen_units > 1, then keep it.
// - If the user requested bitcode but codegen_units == 1, then we
// can toss .#module-name#.bc because we copied it to .bc earlier.
// - If we're not building an rlib and the user didn't request
// bitcode, then delete .#module-name#.bc.
// If you change how this works, also update back::link::link_rlib,
// where .#module-name#.bc files are (maybe) deleted after making an
// rlib.
let needs_crate_object = crate_output.outputs.contains_key(&OutputType::Exe);
let keep_numbered_bitcode = user_wants_bitcode && sess.codegen_units().as_usize() > 1;
let keep_numbered_objects =
needs_crate_object || (user_wants_objects && sess.codegen_units().as_usize() > 1);
for module in compiled_modules.modules.iter() {
if let Some(ref path) = module.object {
if !keep_numbered_objects {
ensure_removed(sess.dcx(), path);
}
}
if let Some(ref path) = module.dwarf_object {
if !keep_numbered_objects {
ensure_removed(sess.dcx(), path);
}
}
if let Some(ref path) = module.bytecode {
if !keep_numbered_bitcode {
ensure_removed(sess.dcx(), path);
}
}
}
if !user_wants_bitcode {
if let Some(ref allocator_module) = compiled_modules.allocator_module {
if let Some(ref path) = allocator_module.bytecode {
ensure_removed(sess.dcx(), path);
}
}
}
}
// We leave the following files around by default:
// - #crate#.o
// - #crate#.crate.metadata.o
// - #crate#.bc
// These are used in linking steps and will be cleaned up afterward.
}
pub(crate) enum WorkItem<B: WriteBackendMethods> {
/// Optimize a newly codegened, totally unoptimized module.
Optimize(ModuleCodegen<B::Module>),
/// Copy the post-LTO artifacts from the incremental cache to the output
/// directory.
CopyPostLtoArtifacts(CachedModuleCodegen),
/// Performs (Thin)LTO on the given module.
LTO(lto::LtoModuleCodegen<B>),
}
impl<B: WriteBackendMethods> WorkItem<B> {
pub fn module_kind(&self) -> ModuleKind {
match *self {
WorkItem::Optimize(ref m) => m.kind,
WorkItem::CopyPostLtoArtifacts(_) | WorkItem::LTO(_) => ModuleKind::Regular,
}
}
/// Generate a short description of this work item suitable for use as a thread name.
fn short_description(&self) -> String {
// `pthread_setname()` on *nix ignores anything beyond the first 15
// bytes. Use short descriptions to maximize the space available for
// the module name.
#[cfg(not(windows))]
fn desc(short: &str, _long: &str, name: &str) -> String {
// The short label is three bytes, and is followed by a space. That
// leaves 11 bytes for the CGU name. How we obtain those 11 bytes
// depends on the CGU name form.
//
// - Non-incremental, e.g. `regex.f10ba03eb5ec7975-cgu.0`: the part
// before the `-cgu.0` is the same for every CGU, so use the
// `cgu.0` part. The number suffix will be different for each
// CGU.
//
// - Incremental (normal), e.g. `2i52vvl2hco29us0`: use the whole
// name because each CGU will have a unique ASCII hash, and the
// first 11 bytes will be enough to identify it.
//
// - Incremental (with `-Zhuman-readable-cgu-names`), e.g.
// `regex.f10ba03eb5ec7975-re_builder.volatile`: use the whole
// name. The first 11 bytes won't be enough to uniquely identify
// it, but no obvious substring will, and this is a rarely used
// option so it doesn't matter much.
//
assert_eq!(short.len(), 3);
let name = if let Some(index) = name.find("-cgu.") {
&name[index + 1..] // +1 skips the leading '-'.
} else {
name
};
format!("{short} {name}")
}
// Windows has no thread name length limit, so use more descriptive names.
#[cfg(windows)]
fn desc(_short: &str, long: &str, name: &str) -> String {
format!("{long} {name}")
}
match self {
WorkItem::Optimize(m) => desc("opt", "optimize module", &m.name),
WorkItem::CopyPostLtoArtifacts(m) => desc("cpy", "copy LTO artifacts for", &m.name),
WorkItem::LTO(m) => desc("lto", "LTO module", m.name()),
}
}
}
/// A result produced by the backend.
pub(crate) enum WorkItemResult<B: WriteBackendMethods> {
/// The backend has finished compiling a CGU, nothing more required.
Finished(CompiledModule),
/// The backend has finished compiling a CGU, which now needs linking
/// because `-Zcombine-cgu` was specified.
NeedsLink(ModuleCodegen<B::Module>),
/// The backend has finished compiling a CGU, which now needs to go through
/// fat LTO.
NeedsFatLto(FatLtoInput<B>),
/// The backend has finished compiling a CGU, which now needs to go through
/// thin LTO.
NeedsThinLto(String, B::ThinBuffer),
}
pub enum FatLtoInput<B: WriteBackendMethods> {
Serialized { name: String, buffer: B::ModuleBuffer },
InMemory(ModuleCodegen<B::Module>),
}
/// Actual LTO type we end up choosing based on multiple factors.
pub enum ComputedLtoType {
No,
Thin,
Fat,
}
pub fn compute_per_cgu_lto_type(
sess_lto: &Lto,
opts: &config::Options,
sess_crate_types: &[CrateType],
module_kind: ModuleKind,
) -> ComputedLtoType {
// Metadata modules never participate in LTO regardless of the lto
// settings.
if module_kind == ModuleKind::Metadata {
return ComputedLtoType::No;
}
// If the linker does LTO, we don't have to do it. Note that we
// keep doing full LTO, if it is requested, as not to break the
// assumption that the output will be a single module.
let linker_does_lto = opts.cg.linker_plugin_lto.enabled();
// When we're automatically doing ThinLTO for multi-codegen-unit
// builds we don't actually want to LTO the allocator modules if
// it shows up. This is due to various linker shenanigans that
// we'll encounter later.
let is_allocator = module_kind == ModuleKind::Allocator;
// We ignore a request for full crate graph LTO if the crate type
// is only an rlib, as there is no full crate graph to process,
// that'll happen later.
//
// This use case currently comes up primarily for targets that
// require LTO so the request for LTO is always unconditionally
// passed down to the backend, but we don't actually want to do
// anything about it yet until we've got a final product.
let is_rlib = sess_crate_types.len() == 1 && sess_crate_types[0] == CrateType::Rlib;
match sess_lto {
Lto::ThinLocal if !linker_does_lto && !is_allocator => ComputedLtoType::Thin,
Lto::Thin if !linker_does_lto && !is_rlib => ComputedLtoType::Thin,
Lto::Fat if !is_rlib => ComputedLtoType::Fat,
_ => ComputedLtoType::No,
}
}
fn execute_optimize_work_item<B: ExtraBackendMethods>(
cgcx: &CodegenContext<B>,
module: ModuleCodegen<B::Module>,
module_config: &ModuleConfig,
) -> Result<WorkItemResult<B>, FatalError> {
let dcx = cgcx.create_dcx();
unsafe {
B::optimize(cgcx, &dcx, &module, module_config)?;
}
// After we've done the initial round of optimizations we need to
// decide whether to synchronously codegen this module or ship it
// back to the coordinator thread for further LTO processing (which
// has to wait for all the initial modules to be optimized).
let lto_type = compute_per_cgu_lto_type(&cgcx.lto, &cgcx.opts, &cgcx.crate_types, module.kind);
// If we're doing some form of incremental LTO then we need to be sure to
// save our module to disk first.
let bitcode = if cgcx.config(module.kind).emit_pre_lto_bc {
let filename = pre_lto_bitcode_filename(&module.name);
cgcx.incr_comp_session_dir.as_ref().map(|path| path.join(&filename))
} else {
None
};
match lto_type {
ComputedLtoType::No => finish_intra_module_work(cgcx, module, module_config),
ComputedLtoType::Thin => {
let (name, thin_buffer) = B::prepare_thin(module);
if let Some(path) = bitcode {
fs::write(&path, thin_buffer.data()).unwrap_or_else(|e| {
panic!("Error writing pre-lto-bitcode file `{}`: {}", path.display(), e);
});
}
Ok(WorkItemResult::NeedsThinLto(name, thin_buffer))
}
ComputedLtoType::Fat => match bitcode {
Some(path) => {
let (name, buffer) = B::serialize_module(module);
fs::write(&path, buffer.data()).unwrap_or_else(|e| {
panic!("Error writing pre-lto-bitcode file `{}`: {}", path.display(), e);
});
Ok(WorkItemResult::NeedsFatLto(FatLtoInput::Serialized { name, buffer }))
}
None => Ok(WorkItemResult::NeedsFatLto(FatLtoInput::InMemory(module))),
},
}
}
fn execute_copy_from_cache_work_item<B: ExtraBackendMethods>(
cgcx: &CodegenContext<B>,
module: CachedModuleCodegen,
module_config: &ModuleConfig,
) -> WorkItemResult<B> {
assert!(module_config.emit_obj != EmitObj::None);
let incr_comp_session_dir = cgcx.incr_comp_session_dir.as_ref().unwrap();
let load_from_incr_comp_dir = |output_path: PathBuf, saved_path: &str| {
let source_file = in_incr_comp_dir(incr_comp_session_dir, saved_path);
debug!(
"copying preexisting module `{}` from {:?} to {}",
module.name,
source_file,
output_path.display()
);
match link_or_copy(&source_file, &output_path) {
Ok(_) => Some(output_path),
Err(error) => {
cgcx.create_dcx().emit_err(errors::CopyPathBuf { source_file, output_path, error });
None
}
}
};
let object = load_from_incr_comp_dir(
cgcx.output_filenames.temp_path(OutputType::Object, Some(&module.name)),
module.source.saved_files.get("o").unwrap_or_else(|| {
cgcx.create_dcx().emit_fatal(errors::NoSavedObjectFile { cgu_name: &module.name })
}),
);
let dwarf_object =
module.source.saved_files.get("dwo").as_ref().and_then(|saved_dwarf_object_file| {
let dwarf_obj_out = cgcx
.output_filenames
.split_dwarf_path(cgcx.split_debuginfo, cgcx.split_dwarf_kind, Some(&module.name))
.expect(
"saved dwarf object in work product but `split_dwarf_path` returned `None`",
);
load_from_incr_comp_dir(dwarf_obj_out, saved_dwarf_object_file)
});
WorkItemResult::Finished(CompiledModule {
name: module.name,
kind: ModuleKind::Regular,
object,
dwarf_object,
bytecode: None,
})
}
fn execute_lto_work_item<B: ExtraBackendMethods>(
cgcx: &CodegenContext<B>,
module: lto::LtoModuleCodegen<B>,
module_config: &ModuleConfig,
) -> Result<WorkItemResult<B>, FatalError> {
let module = unsafe { module.optimize(cgcx)? };
finish_intra_module_work(cgcx, module, module_config)
}
fn finish_intra_module_work<B: ExtraBackendMethods>(
cgcx: &CodegenContext<B>,
module: ModuleCodegen<B::Module>,
module_config: &ModuleConfig,
) -> Result<WorkItemResult<B>, FatalError> {
let dcx = cgcx.create_dcx();
if !cgcx.opts.unstable_opts.combine_cgu
|| module.kind == ModuleKind::Metadata
|| module.kind == ModuleKind::Allocator
{
let module = unsafe { B::codegen(cgcx, &dcx, module, module_config)? };
Ok(WorkItemResult::Finished(module))
} else {
Ok(WorkItemResult::NeedsLink(module))
}
}
/// Messages sent to the coordinator.
pub(crate) enum Message<B: WriteBackendMethods> {
/// A jobserver token has become available. Sent from the jobserver helper
/// thread.
Token(io::Result<Acquired>),
/// The backend has finished processing a work item for a codegen unit.
/// Sent from a backend worker thread.
WorkItem { result: Result<WorkItemResult<B>, Option<WorkerFatalError>>, worker_id: usize },
/// The frontend has finished generating something (backend IR or a
/// post-LTO artifact) for a codegen unit, and it should be passed to the
/// backend. Sent from the main thread.
CodegenDone { llvm_work_item: WorkItem<B>, cost: u64 },
/// Similar to `CodegenDone`, but for reusing a pre-LTO artifact
/// Sent from the main thread.
AddImportOnlyModule {
module_data: SerializedModule<B::ModuleBuffer>,
work_product: WorkProduct,
},
/// The frontend has finished generating everything for all codegen units.
/// Sent from the main thread.
CodegenComplete,
/// Some normal-ish compiler error occurred, and codegen should be wound
/// down. Sent from the main thread.
CodegenAborted,
}
/// A message sent from the coordinator thread to the main thread telling it to
/// process another codegen unit.
pub struct CguMessage;
// A cut-down version of `rustc_errors::DiagInner` that impls `Send`, which
// can be used to send diagnostics from codegen threads to the main thread.
// It's missing the following fields from `rustc_errors::DiagInner`.
// - `span`: it doesn't impl `Send`.
// - `suggestions`: it doesn't impl `Send`, and isn't used for codegen
// diagnostics.
// - `sort_span`: it doesn't impl `Send`.
// - `is_lint`: lints aren't relevant during codegen.
// - `emitted_at`: not used for codegen diagnostics.
struct Diagnostic {
level: Level,
messages: Vec<(DiagMessage, Style)>,
code: Option<ErrCode>,
children: Vec<Subdiagnostic>,
args: DiagArgMap,
}
// A cut-down version of `rustc_errors::Subdiag` that impls `Send`. It's
// missing the following fields from `rustc_errors::Subdiag`.
// - `span`: it doesn't impl `Send`.
pub struct Subdiagnostic {
level: Level,
messages: Vec<(DiagMessage, Style)>,
}
#[derive(PartialEq, Clone, Copy, Debug)]
enum MainThreadState {
/// Doing nothing.
Idle,
/// Doing codegen, i.e. MIR-to-LLVM-IR conversion.
Codegenning,
/// Idle, but lending the compiler process's Token to an LLVM thread so it can do useful work.
Lending,
}
fn start_executing_work<B: ExtraBackendMethods>(
backend: B,
tcx: TyCtxt<'_>,
crate_info: &CrateInfo,
shared_emitter: SharedEmitter,
codegen_worker_send: Sender<CguMessage>,
coordinator_receive: Receiver<Box<dyn Any + Send>>,
jobserver: Client,
regular_config: Arc<ModuleConfig>,
metadata_config: Arc<ModuleConfig>,
allocator_config: Arc<ModuleConfig>,
tx_to_llvm_workers: Sender<Box<dyn Any + Send>>,
) -> thread::JoinHandle<Result<CompiledModules, ()>> {
let coordinator_send = tx_to_llvm_workers;
let sess = tcx.sess;
let mut each_linked_rlib_for_lto = Vec::new();
drop(link::each_linked_rlib(crate_info, None, &mut |cnum, path| {
if link::ignored_for_lto(sess, crate_info, cnum) {
return;
}
each_linked_rlib_for_lto.push((cnum, path.to_path_buf()));
}));
// Compute the set of symbols we need to retain when doing LTO (if we need to)
let exported_symbols = {
let mut exported_symbols = FxHashMap::default();
let copy_symbols = |cnum| {
let symbols = tcx
.exported_symbols(cnum)
.iter()
.map(|&(s, lvl)| (symbol_name_for_instance_in_crate(tcx, s, cnum), lvl))
.collect();
Arc::new(symbols)
};
match sess.lto() {
Lto::No => None,
Lto::ThinLocal => {
exported_symbols.insert(LOCAL_CRATE, copy_symbols(LOCAL_CRATE));
Some(Arc::new(exported_symbols))
}
Lto::Fat | Lto::Thin => {
exported_symbols.insert(LOCAL_CRATE, copy_symbols(LOCAL_CRATE));
for &(cnum, ref _path) in &each_linked_rlib_for_lto {
exported_symbols.insert(cnum, copy_symbols(cnum));
}
Some(Arc::new(exported_symbols))
}
}
};
// First up, convert our jobserver into a helper thread so we can use normal
// mpsc channels to manage our messages and such.
// After we've requested tokens then we'll, when we can,
// get tokens on `coordinator_receive` which will
// get managed in the main loop below.
let coordinator_send2 = coordinator_send.clone();
let helper = jobserver
.into_helper_thread(move |token| {
drop(coordinator_send2.send(Box::new(Message::Token::<B>(token))));
})
.expect("failed to spawn helper thread");
let ol =
if tcx.sess.opts.unstable_opts.no_codegen || !tcx.sess.opts.output_types.should_codegen() {
// If we know that we won’t be doing codegen, create target machines without optimisation.
config::OptLevel::No
} else {
tcx.backend_optimization_level(())
};
let backend_features = tcx.global_backend_features(());
let remark_dir = if let Some(ref dir) = sess.opts.unstable_opts.remark_dir {
let result = fs::create_dir_all(dir).and_then(|_| dir.canonicalize());
match result {
Ok(dir) => Some(dir),
Err(error) => sess.dcx().emit_fatal(ErrorCreatingRemarkDir { error }),
}
} else {
None
};
let cgcx = CodegenContext::<B> {
crate_types: tcx.crate_types().to_vec(),
each_linked_rlib_for_lto,
lto: sess.lto(),
fewer_names: sess.fewer_names(),
save_temps: sess.opts.cg.save_temps,
time_trace: sess.opts.unstable_opts.llvm_time_trace,
opts: Arc::new(sess.opts.clone()),
prof: sess.prof.clone(),
exported_symbols,
remark: sess.opts.cg.remark.clone(),
remark_dir,
incr_comp_session_dir: sess.incr_comp_session_dir_opt().map(|r| r.clone()),
coordinator_send,
expanded_args: tcx.sess.expanded_args.clone(),
diag_emitter: shared_emitter.clone(),
output_filenames: tcx.output_filenames(()).clone(),
regular_module_config: regular_config,
metadata_module_config: metadata_config,
allocator_module_config: allocator_config,
tm_factory: backend.target_machine_factory(tcx.sess, ol, backend_features),
msvc_imps_needed: msvc_imps_needed(tcx),
is_pe_coff: tcx.sess.target.is_like_windows,
target_can_use_split_dwarf: tcx.sess.target_can_use_split_dwarf(),
target_arch: tcx.sess.target.arch.to_string(),
split_debuginfo: tcx.sess.split_debuginfo(),
split_dwarf_kind: tcx.sess.opts.unstable_opts.split_dwarf_kind,
parallel: backend.supports_parallel() && !sess.opts.unstable_opts.no_parallel_backend,
};
// This is the "main loop" of parallel work happening for parallel codegen.
// It's here that we manage parallelism, schedule work, and work with
// messages coming from clients.
//
// There are a few environmental pre-conditions that shape how the system
// is set up:
//
// - Error reporting can only happen on the main thread because that's the
// only place where we have access to the compiler `Session`.
// - LLVM work can be done on any thread.
// - Codegen can only happen on the main thread.
// - Each thread doing substantial work must be in possession of a `Token`
// from the `Jobserver`.
// - The compiler process always holds one `Token`. Any additional `Tokens`
// have to be requested from the `Jobserver`.
//
// Error Reporting
// ===============
// The error reporting restriction is handled separately from the rest: We
// set up a `SharedEmitter` that holds an open channel to the main thread.
// When an error occurs on any thread, the shared emitter will send the
// error message to the receiver main thread (`SharedEmitterMain`). The
// main thread will periodically query this error message queue and emit
// any error messages it has received. It might even abort compilation if
// it has received a fatal error. In this case we rely on all other threads
// being torn down automatically with the main thread.
// Since the main thread will often be busy doing codegen work, error
// reporting will be somewhat delayed, since the message queue can only be
// checked in between two work packages.
//
// Work Processing Infrastructure
// ==============================
// The work processing infrastructure knows three major actors:
//
// - the coordinator thread,
// - the main thread, and
// - LLVM worker threads
//
// The coordinator thread is running a message loop. It instructs the main
// thread about what work to do when, and it will spawn off LLVM worker
// threads as open LLVM WorkItems become available.
//
// The job of the main thread is to codegen CGUs into LLVM work packages
// (since the main thread is the only thread that can do this). The main
// thread will block until it receives a message from the coordinator, upon
// which it will codegen one CGU, send it to the coordinator and block
// again. This way the coordinator can control what the main thread is
// doing.
//
// The coordinator keeps a queue of LLVM WorkItems, and when a `Token` is
// available, it will spawn off a new LLVM worker thread and let it process
// a WorkItem. When a LLVM worker thread is done with its WorkItem,
// it will just shut down, which also frees all resources associated with
// the given LLVM module, and sends a message to the coordinator that the
// WorkItem has been completed.
//
// Work Scheduling
// ===============
// The scheduler's goal is to minimize the time it takes to complete all
// work there is, however, we also want to keep memory consumption low
// if possible. These two goals are at odds with each other: If memory
// consumption were not an issue, we could just let the main thread produce
// LLVM WorkItems at full speed, assuring maximal utilization of
// Tokens/LLVM worker threads. However, since codegen is usually faster
// than LLVM processing, the queue of LLVM WorkItems would fill up and each
// WorkItem potentially holds on to a substantial amount of memory.
//
// So the actual goal is to always produce just enough LLVM WorkItems as
// not to starve our LLVM worker threads. That means, once we have enough
// WorkItems in our queue, we can block the main thread, so it does not
// produce more until we need them.
//
// Doing LLVM Work on the Main Thread
// ----------------------------------
// Since the main thread owns the compiler process's implicit `Token`, it is
// wasteful to keep it blocked without doing any work. Therefore, what we do
// in this case is: We spawn off an additional LLVM worker thread that helps
// reduce the queue. The work it is doing corresponds to the implicit
// `Token`. The coordinator will mark the main thread as being busy with
// LLVM work. (The actual work happens on another OS thread but we just care
// about `Tokens`, not actual threads).
//
// When any LLVM worker thread finishes while the main thread is marked as
// "busy with LLVM work", we can do a little switcheroo: We give the Token
// of the just finished thread to the LLVM worker thread that is working on
// behalf of the main thread's implicit Token, thus freeing up the main
// thread again. The coordinator can then again decide what the main thread
// should do. This allows the coordinator to make decisions at more points
// in time.
//
// Striking a Balance between Throughput and Memory Consumption
// ------------------------------------------------------------
// Since our two goals, (1) use as many Tokens as possible and (2) keep
// memory consumption as low as possible, are in conflict with each other,
// we have to find a trade off between them. Right now, the goal is to keep
// all workers busy, which means that no worker should find the queue empty
// when it is ready to start.
// How do we do achieve this? Good question :) We actually never know how
// many `Tokens` are potentially available so it's hard to say how much to
// fill up the queue before switching the main thread to LLVM work. Also we
// currently don't have a means to estimate how long a running LLVM worker
// will still be busy with it's current WorkItem. However, we know the
// maximal count of available Tokens that makes sense (=the number of CPU
// cores), so we can take a conservative guess. The heuristic we use here
// is implemented in the `queue_full_enough()` function.
//
// Some Background on Jobservers
// -----------------------------
// It's worth also touching on the management of parallelism here. We don't
// want to just spawn a thread per work item because while that's optimal
// parallelism it may overload a system with too many threads or violate our
// configuration for the maximum amount of cpu to use for this process. To
// manage this we use the `jobserver` crate.
//
// Job servers are an artifact of GNU make and are used to manage
// parallelism between processes. A jobserver is a glorified IPC semaphore
// basically. Whenever we want to run some work we acquire the semaphore,
// and whenever we're done with that work we release the semaphore. In this
// manner we can ensure that the maximum number of parallel workers is
// capped at any one point in time.
//
// LTO and the coordinator thread
// ------------------------------
//
// The final job the coordinator thread is responsible for is managing LTO
// and how that works. When LTO is requested what we'll do is collect all
// optimized LLVM modules into a local vector on the coordinator. Once all
// modules have been codegened and optimized we hand this to the `lto`
// module for further optimization. The `lto` module will return back a list
// of more modules to work on, which the coordinator will continue to spawn
// work for.
//
// Each LLVM module is automatically sent back to the coordinator for LTO if
// necessary. There's already optimizations in place to avoid sending work
// back to the coordinator if LTO isn't requested.
return B::spawn_named_thread(cgcx.time_trace, "coordinator".to_string(), move || {
let mut worker_id_counter = 0;
let mut free_worker_ids = Vec::new();
let mut get_worker_id = |free_worker_ids: &mut Vec<usize>| {
if let Some(id) = free_worker_ids.pop() {
id
} else {
let id = worker_id_counter;
worker_id_counter += 1;
id
}
};
// This is where we collect codegen units that have gone all the way
// through codegen and LLVM.
let mut compiled_modules = vec![];
let mut compiled_allocator_module = None;
let mut needs_link = Vec::new();
let mut needs_fat_lto = Vec::new();
let mut needs_thin_lto = Vec::new();
let mut lto_import_only_modules = Vec::new();
let mut started_lto = false;
/// Possible state transitions:
/// - Ongoing -> Completed
/// - Ongoing -> Aborted
/// - Completed -> Aborted
#[derive(Debug, PartialEq)]
enum CodegenState {
Ongoing,
Completed,
Aborted,
}
use CodegenState::*;
let mut codegen_state = Ongoing;
// This is the queue of LLVM work items that still need processing.
let mut work_items = Vec::<(WorkItem<B>, u64)>::new();
// This are the Jobserver Tokens we currently hold. Does not include
// the implicit Token the compiler process owns no matter what.
let mut tokens = Vec::new();
let mut main_thread_state = MainThreadState::Idle;
// How many LLVM worker threads are running while holding a Token. This
// *excludes* any that the main thread is lending a Token to.
let mut running_with_own_token = 0;
// How many LLVM worker threads are running in total. This *includes*
// any that the main thread is lending a Token to.
let running_with_any_token = |main_thread_state, running_with_own_token| {
running_with_own_token
+ if main_thread_state == MainThreadState::Lending { 1 } else { 0 }
};
let mut llvm_start_time: Option<VerboseTimingGuard<'_>> = None;
// Run the message loop while there's still anything that needs message
// processing. Note that as soon as codegen is aborted we simply want to
// wait for all existing work to finish, so many of the conditions here
// only apply if codegen hasn't been aborted as they represent pending
// work to be done.
loop {
// While there are still CGUs to be codegened, the coordinator has
// to decide how to utilize the compiler processes implicit Token:
// For codegenning more CGU or for running them through LLVM.
if codegen_state == Ongoing {
if main_thread_state == MainThreadState::Idle {
// Compute the number of workers that will be running once we've taken as many
// items from the work queue as we can, plus one for the main thread. It's not
// critically important that we use this instead of just
// `running_with_own_token`, but it prevents the `queue_full_enough` heuristic
// from fluctuating just because a worker finished up and we decreased the
// `running_with_own_token` count, even though we're just going to increase it
// right after this when we put a new worker to work.
let extra_tokens = tokens.len().checked_sub(running_with_own_token).unwrap();
let additional_running = std::cmp::min(extra_tokens, work_items.len());
let anticipated_running = running_with_own_token + additional_running + 1;
if !queue_full_enough(work_items.len(), anticipated_running) {
// The queue is not full enough, process more codegen units:
if codegen_worker_send.send(CguMessage).is_err() {
panic!("Could not send CguMessage to main thread")
}
main_thread_state = MainThreadState::Codegenning;
} else {
// The queue is full enough to not let the worker
// threads starve. Use the implicit Token to do some
// LLVM work too.
let (item, _) =
work_items.pop().expect("queue empty - queue_full_enough() broken?");
main_thread_state = MainThreadState::Lending;
spawn_work(
&cgcx,
&mut llvm_start_time,
get_worker_id(&mut free_worker_ids),
item,
);
}
}
} else if codegen_state == Completed {
if running_with_any_token(main_thread_state, running_with_own_token) == 0
&& work_items.is_empty()
{
// All codegen work is done. Do we have LTO work to do?
if needs_fat_lto.is_empty()
&& needs_thin_lto.is_empty()
&& lto_import_only_modules.is_empty()
{
// Nothing more to do!
break;
}
// We have LTO work to do. Perform the serial work here of
// figuring out what we're going to LTO and then push a
// bunch of work items onto our queue to do LTO. This all
// happens on the coordinator thread but it's very quick so
// we don't worry about tokens.
assert!(!started_lto);
started_lto = true;
let needs_fat_lto = mem::take(&mut needs_fat_lto);
let needs_thin_lto = mem::take(&mut needs_thin_lto);
let import_only_modules = mem::take(&mut lto_import_only_modules);
for (work, cost) in
generate_lto_work(&cgcx, needs_fat_lto, needs_thin_lto, import_only_modules)
{
let insertion_index = work_items
.binary_search_by_key(&cost, |&(_, cost)| cost)
.unwrap_or_else(|e| e);
work_items.insert(insertion_index, (work, cost));
if cgcx.parallel {
helper.request_token();
}
}
}
// In this branch, we know that everything has been codegened,
// so it's just a matter of determining whether the implicit
// Token is free to use for LLVM work.
match main_thread_state {
MainThreadState::Idle => {
if let Some((item, _)) = work_items.pop() {
main_thread_state = MainThreadState::Lending;
spawn_work(
&cgcx,
&mut llvm_start_time,
get_worker_id(&mut free_worker_ids),
item,
);
} else {
// There is no unstarted work, so let the main thread
// take over for a running worker. Otherwise the
// implicit token would just go to waste.
// We reduce the `running` counter by one. The
// `tokens.truncate()` below will take care of
// giving the Token back.
debug_assert!(running_with_own_token > 0);
running_with_own_token -= 1;
main_thread_state = MainThreadState::Lending;
}
}
MainThreadState::Codegenning => bug!(
"codegen worker should not be codegenning after \
codegen was already completed"
),
MainThreadState::Lending => {
// Already making good use of that token
}
}
} else {
// Don't queue up any more work if codegen was aborted, we're
// just waiting for our existing children to finish.
assert!(codegen_state == Aborted);
if running_with_any_token(main_thread_state, running_with_own_token) == 0 {
break;
}
}
// Spin up what work we can, only doing this while we've got available
// parallelism slots and work left to spawn.
if codegen_state != Aborted {
while !work_items.is_empty() && running_with_own_token < tokens.len() {
let (item, _) = work_items.pop().unwrap();
spawn_work(
&cgcx,
&mut llvm_start_time,
get_worker_id(&mut free_worker_ids),
item,
);
running_with_own_token += 1;
}
}
// Relinquish accidentally acquired extra tokens.
tokens.truncate(running_with_own_token);
// If a thread exits successfully then we drop a token associated
// with that worker and update our `running_with_own_token` count.
// We may later re-acquire a token to continue running more work.
// We may also not actually drop a token here if the worker was
// running with an "ephemeral token".
let mut free_worker = |worker_id| {
if main_thread_state == MainThreadState::Lending {
main_thread_state = MainThreadState::Idle;
} else {
running_with_own_token -= 1;
}
free_worker_ids.push(worker_id);
};
let msg = coordinator_receive.recv().unwrap();
match *msg.downcast::<Message<B>>().ok().unwrap() {
// Save the token locally and the next turn of the loop will use
// this to spawn a new unit of work, or it may get dropped
// immediately if we have no more work to spawn.
Message::Token(token) => {
match token {
Ok(token) => {
tokens.push(token);
if main_thread_state == MainThreadState::Lending {
// If the main thread token is used for LLVM work
// at the moment, we turn that thread into a regular
// LLVM worker thread, so the main thread is free
// to react to codegen demand.
main_thread_state = MainThreadState::Idle;
running_with_own_token += 1;
}
}
Err(e) => {
let msg = &format!("failed to acquire jobserver token: {e}");
shared_emitter.fatal(msg);
codegen_state = Aborted;
}
}
}
Message::CodegenDone { llvm_work_item, cost } => {
// We keep the queue sorted by estimated processing cost,
// so that more expensive items are processed earlier. This
// is good for throughput as it gives the main thread more
// time to fill up the queue and it avoids scheduling
// expensive items to the end.
// Note, however, that this is not ideal for memory
// consumption, as LLVM module sizes are not evenly
// distributed.
let insertion_index = work_items.binary_search_by_key(&cost, |&(_, cost)| cost);
let insertion_index = match insertion_index {
Ok(idx) | Err(idx) => idx,
};
work_items.insert(insertion_index, (llvm_work_item, cost));
if cgcx.parallel {
helper.request_token();
}
assert_eq!(main_thread_state, MainThreadState::Codegenning);
main_thread_state = MainThreadState::Idle;
}
Message::CodegenComplete => {
if codegen_state != Aborted {
codegen_state = Completed;
}
assert_eq!(main_thread_state, MainThreadState::Codegenning);
main_thread_state = MainThreadState::Idle;
}
// If codegen is aborted that means translation was aborted due
// to some normal-ish compiler error. In this situation we want
// to exit as soon as possible, but we want to make sure all
// existing work has finished. Flag codegen as being done, and
// then conditions above will ensure no more work is spawned but
// we'll keep executing this loop until `running_with_own_token`
// hits 0.
Message::CodegenAborted => {
codegen_state = Aborted;
}
Message::WorkItem { result, worker_id } => {
free_worker(worker_id);
match result {
Ok(WorkItemResult::Finished(compiled_module)) => {
match compiled_module.kind {
ModuleKind::Regular => {
assert!(needs_link.is_empty());
compiled_modules.push(compiled_module);
}
ModuleKind::Allocator => {
assert!(compiled_allocator_module.is_none());
compiled_allocator_module = Some(compiled_module);
}
ModuleKind::Metadata => bug!("Should be handled separately"),
}
}
Ok(WorkItemResult::NeedsLink(module)) => {
assert!(compiled_modules.is_empty());
needs_link.push(module);
}
Ok(WorkItemResult::NeedsFatLto(fat_lto_input)) => {
assert!(!started_lto);
assert!(needs_thin_lto.is_empty());
needs_fat_lto.push(fat_lto_input);
}
Ok(WorkItemResult::NeedsThinLto(name, thin_buffer)) => {
assert!(!started_lto);
assert!(needs_fat_lto.is_empty());
needs_thin_lto.push((name, thin_buffer));
}
Err(Some(WorkerFatalError)) => {
// Like `CodegenAborted`, wait for remaining work to finish.
codegen_state = Aborted;
}
Err(None) => {
// If the thread failed that means it panicked, so
// we abort immediately.
bug!("worker thread panicked");
}
}
}
Message::AddImportOnlyModule { module_data, work_product } => {
assert!(!started_lto);
assert_eq!(codegen_state, Ongoing);
assert_eq!(main_thread_state, MainThreadState::Codegenning);
lto_import_only_modules.push((module_data, work_product));
main_thread_state = MainThreadState::Idle;
}
}
}
if codegen_state == Aborted {
return Err(());
}
let needs_link = mem::take(&mut needs_link);
if !needs_link.is_empty() {
assert!(compiled_modules.is_empty());
let dcx = cgcx.create_dcx();
let module = B::run_link(&cgcx, &dcx, needs_link).map_err(|_| ())?;
let module = unsafe {
B::codegen(&cgcx, &dcx, module, cgcx.config(ModuleKind::Regular)).map_err(|_| ())?
};
compiled_modules.push(module);
}
// Drop to print timings
drop(llvm_start_time);
// Regardless of what order these modules completed in, report them to
// the backend in the same order every time to ensure that we're handing
// out deterministic results.
compiled_modules.sort_by(|a, b| a.name.cmp(&b.name));
Ok(CompiledModules {
modules: compiled_modules,
allocator_module: compiled_allocator_module,
})
})
.expect("failed to spawn coordinator thread");
// A heuristic that determines if we have enough LLVM WorkItems in the
// queue so that the main thread can do LLVM work instead of codegen
fn queue_full_enough(items_in_queue: usize, workers_running: usize) -> bool {
// This heuristic scales ahead-of-time codegen according to available
// concurrency, as measured by `workers_running`. The idea is that the
// more concurrency we have available, the more demand there will be for
// work items, and the fuller the queue should be kept to meet demand.
// An important property of this approach is that we codegen ahead of
// time only as much as necessary, so as to keep fewer LLVM modules in
// memory at once, thereby reducing memory consumption.
//
// When the number of workers running is less than the max concurrency
// available to us, this heuristic can cause us to instruct the main
// thread to work on an LLVM item (that is, tell it to "LLVM") instead
// of codegen, even though it seems like it *should* be codegenning so
// that we can create more work items and spawn more LLVM workers.
//
// But this is not a problem. When the main thread is told to LLVM,
// according to this heuristic and how work is scheduled, there is
// always at least one item in the queue, and therefore at least one
// pending jobserver token request. If there *is* more concurrency
// available, we will immediately receive a token, which will upgrade
// the main thread's LLVM worker to a real one (conceptually), and free
// up the main thread to codegen if necessary. On the other hand, if
// there isn't more concurrency, then the main thread working on an LLVM
// item is appropriate, as long as the queue is full enough for demand.
//
// Speaking of which, how full should we keep the queue? Probably less
// full than you'd think. A lot has to go wrong for the queue not to be
// full enough and for that to have a negative effect on compile times.
//
// Workers are unlikely to finish at exactly the same time, so when one
// finishes and takes another work item off the queue, we often have
// ample time to codegen at that point before the next worker finishes.
// But suppose that codegen takes so long that the workers exhaust the
// queue, and we have one or more workers that have nothing to work on.
// Well, it might not be so bad. Of all the LLVM modules we create and
// optimize, one has to finish last. It's not necessarily the case that
// by losing some concurrency for a moment, we delay the point at which
// that last LLVM module is finished and the rest of compilation can
// proceed. Also, when we can't take advantage of some concurrency, we
// give tokens back to the job server. That enables some other rustc to
// potentially make use of the available concurrency. That could even
// *decrease* overall compile time if we're lucky. But yes, if no other
// rustc can make use of the concurrency, then we've squandered it.
//
// However, keeping the queue full is also beneficial when we have a
// surge in available concurrency. Then items can be taken from the
// queue immediately, without having to wait for codegen.
//
// So, the heuristic below tries to keep one item in the queue for every
// four running workers. Based on limited benchmarking, this appears to
// be more than sufficient to avoid increasing compilation times.
let quarter_of_workers = workers_running - 3 * workers_running / 4;
items_in_queue > 0 && items_in_queue >= quarter_of_workers
}
}
/// `FatalError` is explicitly not `Send`.
#[must_use]
pub struct WorkerFatalError;
fn spawn_work<'a, B: ExtraBackendMethods>(
cgcx: &'a CodegenContext<B>,
llvm_start_time: &mut Option<VerboseTimingGuard<'a>>,
worker_id: usize,
work: WorkItem<B>,
) {
if cgcx.config(work.module_kind()).time_module && llvm_start_time.is_none() {
*llvm_start_time = Some(cgcx.prof.verbose_generic_activity("LLVM_passes"));
}
let cgcx = cgcx.clone();
B::spawn_named_thread(cgcx.time_trace, work.short_description(), move || {
// Set up a destructor which will fire off a message that we're done as
// we exit.
struct Bomb<B: ExtraBackendMethods> {
coordinator_send: Sender<Box<dyn Any + Send>>,
result: Option<Result<WorkItemResult<B>, FatalError>>,
worker_id: usize,
}
impl<B: ExtraBackendMethods> Drop for Bomb<B> {
fn drop(&mut self) {
let worker_id = self.worker_id;
let msg = match self.result.take() {
Some(Ok(result)) => Message::WorkItem::<B> { result: Ok(result), worker_id },
Some(Err(FatalError)) => {
Message::WorkItem::<B> { result: Err(Some(WorkerFatalError)), worker_id }
}
None => Message::WorkItem::<B> { result: Err(None), worker_id },
};
drop(self.coordinator_send.send(Box::new(msg)));
}
}
let mut bomb =
Bomb::<B> { coordinator_send: cgcx.coordinator_send.clone(), result: None, worker_id };
// Execute the work itself, and if it finishes successfully then flag
// ourselves as a success as well.
//
// Note that we ignore any `FatalError` coming out of `execute_work_item`,
// as a diagnostic was already sent off to the main thread - just
// surface that there was an error in this worker.
bomb.result = {
let module_config = cgcx.config(work.module_kind());
Some(match work {
WorkItem::Optimize(m) => {
let _timer =
cgcx.prof.generic_activity_with_arg("codegen_module_optimize", &*m.name);
execute_optimize_work_item(&cgcx, m, module_config)
}
WorkItem::CopyPostLtoArtifacts(m) => {
let _timer = cgcx.prof.generic_activity_with_arg(
"codegen_copy_artifacts_from_incr_cache",
&*m.name,
);
Ok(execute_copy_from_cache_work_item(&cgcx, m, module_config))
}
WorkItem::LTO(m) => {
let _timer =
cgcx.prof.generic_activity_with_arg("codegen_module_perform_lto", m.name());
execute_lto_work_item(&cgcx, m, module_config)
}
})
};
})
.expect("failed to spawn work thread");
}
enum SharedEmitterMessage {
Diagnostic(Diagnostic),
InlineAsmError(u32, String, Level, Option<(String, Vec<InnerSpan>)>),
Fatal(String),
}
#[derive(Clone)]
pub struct SharedEmitter {
sender: Sender<SharedEmitterMessage>,
}
pub struct SharedEmitterMain {
receiver: Receiver<SharedEmitterMessage>,
}
impl SharedEmitter {
pub fn new() -> (SharedEmitter, SharedEmitterMain) {
let (sender, receiver) = channel();
(SharedEmitter { sender }, SharedEmitterMain { receiver })
}
pub fn inline_asm_error(
&self,
cookie: u32,
msg: String,
level: Level,
source: Option<(String, Vec<InnerSpan>)>,
) {
drop(self.sender.send(SharedEmitterMessage::InlineAsmError(cookie, msg, level, source)));
}
pub fn fatal(&self, msg: &str) {
drop(self.sender.send(SharedEmitterMessage::Fatal(msg.to_string())));
}
}
impl Translate for SharedEmitter {
fn fluent_bundle(&self) -> Option<&Lrc<FluentBundle>> {
None
}
fn fallback_fluent_bundle(&self) -> &FluentBundle {
panic!("shared emitter attempted to translate a diagnostic");
}
}
impl Emitter for SharedEmitter {
fn emit_diagnostic(&mut self, mut diag: rustc_errors::DiagInner) {
// Check that we aren't missing anything interesting when converting to
// the cut-down local `DiagInner`.
assert_eq!(diag.span, MultiSpan::new());
assert_eq!(diag.suggestions, Ok(vec![]));
assert_eq!(diag.sort_span, rustc_span::DUMMY_SP);
assert_eq!(diag.is_lint, None);
// No sensible check for `diag.emitted_at`.
let args = mem::replace(&mut diag.args, DiagArgMap::default());
drop(
self.sender.send(SharedEmitterMessage::Diagnostic(Diagnostic {
level: diag.level(),
messages: diag.messages,
code: diag.code,
children: diag
.children
.into_iter()
.map(|child| Subdiagnostic { level: child.level, messages: child.messages })
.collect(),
args,
})),
);
}
fn source_map(&self) -> Option<&Lrc<SourceMap>> {
None
}
}
impl SharedEmitterMain {
pub fn check(&self, sess: &Session, blocking: bool) {
loop {
let message = if blocking {
match self.receiver.recv() {
Ok(message) => Ok(message),
Err(_) => Err(()),
}
} else {
match self.receiver.try_recv() {
Ok(message) => Ok(message),
Err(_) => Err(()),
}
};
match message {
Ok(SharedEmitterMessage::Diagnostic(diag)) => {
// The diagnostic has been received on the main thread.
// Convert it back to a full `Diagnostic` and emit.
let dcx = sess.dcx();
let mut d =
rustc_errors::DiagInner::new_with_messages(diag.level, diag.messages);
d.code = diag.code; // may be `None`, that's ok
d.children = diag
.children
.into_iter()
.map(|sub| rustc_errors::Subdiag {
level: sub.level,
messages: sub.messages,
span: MultiSpan::new(),
})
.collect();
d.args = diag.args;
dcx.emit_diagnostic(d);
sess.dcx().abort_if_errors();
}
Ok(SharedEmitterMessage::InlineAsmError(cookie, msg, level, source)) => {
assert!(matches!(level, Level::Error | Level::Warning | Level::Note));
let msg = msg.strip_prefix("error: ").unwrap_or(&msg).to_string();
let mut err = Diag::<()>::new(sess.dcx(), level, msg);
// If the cookie is 0 then we don't have span information.
if cookie != 0 {
let pos = BytePos::from_u32(cookie);
let span = Span::with_root_ctxt(pos, pos);
err.span(span);
};
// Point to the generated assembly if it is available.
if let Some((buffer, spans)) = source {
let source = sess
.source_map()
.new_source_file(FileName::inline_asm_source_code(&buffer), buffer);
let spans: Vec<_> = spans
.iter()
.map(|sp| {
Span::with_root_ctxt(
source.normalized_byte_pos(sp.start as u32),
source.normalized_byte_pos(sp.end as u32),
)
})
.collect();
err.span_note(spans, "instantiated into assembly here");
}
err.emit();
}
Ok(SharedEmitterMessage::Fatal(msg)) => {
sess.dcx().fatal(msg);
}
Err(_) => {
break;
}
}
}
}
}
pub struct Coordinator<B: ExtraBackendMethods> {
pub sender: Sender<Box<dyn Any + Send>>,
future: Option<thread::JoinHandle<Result<CompiledModules, ()>>>,
// Only used for the Message type.
phantom: PhantomData<B>,
}
impl<B: ExtraBackendMethods> Coordinator<B> {
fn join(mut self) -> std::thread::Result<Result<CompiledModules, ()>> {
self.future.take().unwrap().join()
}
}
impl<B: ExtraBackendMethods> Drop for Coordinator<B> {
fn drop(&mut self) {
if let Some(future) = self.future.take() {
// If we haven't joined yet, signal to the coordinator that it should spawn no more
// work, and wait for worker threads to finish.
drop(self.sender.send(Box::new(Message::CodegenAborted::<B>)));
drop(future.join());
}
}
}
pub struct OngoingCodegen<B: ExtraBackendMethods> {
pub backend: B,
pub metadata: EncodedMetadata,
pub metadata_module: Option<CompiledModule>,
pub crate_info: CrateInfo,
pub codegen_worker_receive: Receiver<CguMessage>,
pub shared_emitter_main: SharedEmitterMain,
pub output_filenames: Arc<OutputFilenames>,
pub coordinator: Coordinator<B>,
}
impl<B: ExtraBackendMethods> OngoingCodegen<B> {
pub fn join(self, sess: &Session) -> (CodegenResults, FxIndexMap<WorkProductId, WorkProduct>) {
let _timer = sess.timer("finish_ongoing_codegen");
self.shared_emitter_main.check(sess, true);
let compiled_modules = sess.time("join_worker_thread", || match self.coordinator.join() {
Ok(Ok(compiled_modules)) => compiled_modules,
Ok(Err(())) => {
sess.dcx().abort_if_errors();
panic!("expected abort due to worker thread errors")
}
Err(_) => {
bug!("panic during codegen/LLVM phase");
}
});
sess.dcx().abort_if_errors();
let work_products =
copy_all_cgu_workproducts_to_incr_comp_cache_dir(sess, &compiled_modules);
produce_final_output_artifacts(sess, &compiled_modules, &self.output_filenames);
// FIXME: time_llvm_passes support - does this use a global context or
// something?
if sess.codegen_units().as_usize() == 1 && sess.opts.unstable_opts.time_llvm_passes {
self.backend.print_pass_timings()
}
if sess.print_llvm_stats() {
self.backend.print_statistics()
}
(
CodegenResults {
metadata: self.metadata,
crate_info: self.crate_info,
modules: compiled_modules.modules,
allocator_module: compiled_modules.allocator_module,
metadata_module: self.metadata_module,
},
work_products,
)
}
pub fn codegen_finished(&self, tcx: TyCtxt<'_>) {
self.wait_for_signal_to_codegen_item();
self.check_for_errors(tcx.sess);
drop(self.coordinator.sender.send(Box::new(Message::CodegenComplete::<B>)));
}
pub fn check_for_errors(&self, sess: &Session) {
self.shared_emitter_main.check(sess, false);
}
pub fn wait_for_signal_to_codegen_item(&self) {
match self.codegen_worker_receive.recv() {
Ok(CguMessage) => {
// Ok to proceed.
}
Err(_) => {
// One of the LLVM threads must have panicked, fall through so
// error handling can be reached.
}
}
}
}
pub fn submit_codegened_module_to_llvm<B: ExtraBackendMethods>(
_backend: &B,
tx_to_llvm_workers: &Sender<Box<dyn Any + Send>>,
module: ModuleCodegen<B::Module>,
cost: u64,
) {
let llvm_work_item = WorkItem::Optimize(module);
drop(tx_to_llvm_workers.send(Box::new(Message::CodegenDone::<B> { llvm_work_item, cost })));
}
pub fn submit_post_lto_module_to_llvm<B: ExtraBackendMethods>(
_backend: &B,
tx_to_llvm_workers: &Sender<Box<dyn Any + Send>>,
module: CachedModuleCodegen,
) {
let llvm_work_item = WorkItem::CopyPostLtoArtifacts(module);
drop(tx_to_llvm_workers.send(Box::new(Message::CodegenDone::<B> { llvm_work_item, cost: 0 })));
}
pub fn submit_pre_lto_module_to_llvm<B: ExtraBackendMethods>(
_backend: &B,
tcx: TyCtxt<'_>,
tx_to_llvm_workers: &Sender<Box<dyn Any + Send>>,
module: CachedModuleCodegen,
) {
let filename = pre_lto_bitcode_filename(&module.name);
let bc_path = in_incr_comp_dir_sess(tcx.sess, &filename);
let file = fs::File::open(&bc_path)
.unwrap_or_else(|e| panic!("failed to open bitcode file `{}`: {}", bc_path.display(), e));
let mmap = unsafe {
Mmap::map(file).unwrap_or_else(|e| {
panic!("failed to mmap bitcode file `{}`: {}", bc_path.display(), e)
})
};
// Schedule the module to be loaded
drop(tx_to_llvm_workers.send(Box::new(Message::AddImportOnlyModule::<B> {
module_data: SerializedModule::FromUncompressedFile(mmap),
work_product: module.source,
})));
}
fn pre_lto_bitcode_filename(module_name: &str) -> String {
format!("{module_name}.{PRE_LTO_BC_EXT}")
}
fn msvc_imps_needed(tcx: TyCtxt<'_>) -> bool {
// This should never be true (because it's not supported). If it is true,
// something is wrong with commandline arg validation.
assert!(
!(tcx.sess.opts.cg.linker_plugin_lto.enabled()
&& tcx.sess.target.is_like_windows
&& tcx.sess.opts.cg.prefer_dynamic)
);
tcx.sess.target.is_like_windows &&
tcx.crate_types().iter().any(|ct| *ct == CrateType::Rlib) &&
// ThinLTO can't handle this workaround in all cases, so we don't
// emit the `__imp_` symbols. Instead we make them unnecessary by disallowing
// dynamic linking when linker plugin LTO is enabled.
!tcx.sess.opts.cg.linker_plugin_lto.enabled()
}