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Auto merge of #144062 - bjorn3:lto_refactors2, r=davidtwco

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Various refactors to the LTO handling code (part 2)

Continuing from https://github.com/rust-lang/rust/pull/143388 this removes a bit of dead code and moves the LTO symbol export calculation from individual backends to cg_ssa.
This commit is contained in:
bors
2025-07-24 12:50:26 +00:00
parent fc5af18133 dadc4cae50
commit 5d22242a3a
13 changed files with 257 additions and 331 deletions
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114
compiler/rustc_codegen_llvm/src/back/lto.rs
View File

@@ -1,33 +1,28 @@
use std::collections::BTreeMap;
use std::ffi::{CStr, CString};
use std::fs::File;
use std::path::Path;
use std::path::{Path, PathBuf};
use std::ptr::NonNull;
use std::sync::Arc;
use std::{io, iter, slice};
use object::read::archive::ArchiveFile;
use rustc_codegen_ssa::back::lto::{SerializedModule, ThinModule, ThinShared};
use rustc_codegen_ssa::back::symbol_export;
use rustc_codegen_ssa::back::write::{CodegenContext, FatLtoInput};
use rustc_codegen_ssa::traits::*;
use rustc_codegen_ssa::{ModuleCodegen, ModuleKind, looks_like_rust_object_file};
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::memmap::Mmap;
use rustc_errors::{DiagCtxtHandle, FatalError};
use rustc_hir::def_id::LOCAL_CRATE;
use rustc_middle::bug;
use rustc_middle::dep_graph::WorkProduct;
use rustc_middle::middle::exported_symbols::{SymbolExportInfo, SymbolExportLevel};
use rustc_session::config::{self, CrateType, Lto};
use rustc_session::config::{self, Lto};
use tracing::{debug, info};
use crate::back::write::{
self, CodegenDiagnosticsStage, DiagnosticHandlers, bitcode_section_name, save_temp_bitcode,
};
use crate::errors::{
DynamicLinkingWithLTO, LlvmError, LtoBitcodeFromRlib, LtoDisallowed, LtoDylib, LtoProcMacro,
};
use crate::errors::{LlvmError, LtoBitcodeFromRlib};
use crate::llvm::AttributePlace::Function;
use crate::llvm::{self, build_string};
use crate::{LlvmCodegenBackend, ModuleLlvm, SimpleCx, attributes};
@@ -36,45 +31,21 @@ use crate::{LlvmCodegenBackend, ModuleLlvm, SimpleCx, attributes};
/// session to determine which CGUs we can reuse.
const THIN_LTO_KEYS_INCR_COMP_FILE_NAME: &str = "thin-lto-past-keys.bin";
fn crate_type_allows_lto(crate_type: CrateType) -> bool {
match crate_type {
CrateType::Executable
| CrateType::Dylib
| CrateType::Staticlib
| CrateType::Cdylib
| CrateType::ProcMacro
| CrateType::Sdylib => true,
CrateType::Rlib => false,
}
}
fn prepare_lto(
cgcx: &CodegenContext<LlvmCodegenBackend>,
exported_symbols_for_lto: &[String],
each_linked_rlib_for_lto: &[PathBuf],
dcx: DiagCtxtHandle<'_>,
) -> Result<(Vec<CString>, Vec<(SerializedModule<ModuleBuffer>, CString)>), FatalError> {
let export_threshold = match cgcx.lto {
// We're just doing LTO for our one crate
Lto::ThinLocal => SymbolExportLevel::Rust,
let mut symbols_below_threshold = exported_symbols_for_lto
.iter()
.map(|symbol| CString::new(symbol.to_owned()).unwrap())
.collect::<Vec<CString>>();
// We're doing LTO for the entire crate graph
Lto::Fat | Lto::Thin => symbol_export::crates_export_threshold(&cgcx.crate_types),
Lto::No => panic!("didn't request LTO but we're doing LTO"),
};
let symbol_filter = &|&(ref name, info): &(String, SymbolExportInfo)| {
if info.level.is_below_threshold(export_threshold) || info.used {
Some(CString::new(name.as_str()).unwrap())
} else {
None
}
};
let exported_symbols = cgcx.exported_symbols.as_ref().expect("needs exported symbols for LTO");
let mut symbols_below_threshold = {
let _timer = cgcx.prof.generic_activity("LLVM_lto_generate_symbols_below_threshold");
exported_symbols[&LOCAL_CRATE].iter().filter_map(symbol_filter).collect::<Vec<CString>>()
};
info!("{} symbols to preserve in this crate", symbols_below_threshold.len());
// __llvm_profile_counter_bias is pulled in at link time by an undefined reference to
// __llvm_profile_runtime, therefore we won't know until link time if this symbol
// should have default visibility.
symbols_below_threshold.push(c"__llvm_profile_counter_bias".to_owned());
// If we're performing LTO for the entire crate graph, then for each of our
// upstream dependencies, find the corresponding rlib and load the bitcode
@@ -84,37 +55,7 @@ fn prepare_lto(
// with either fat or thin LTO
let mut upstream_modules = Vec::new();
if cgcx.lto != Lto::ThinLocal {
// Make sure we actually can run LTO
for crate_type in cgcx.crate_types.iter() {
if !crate_type_allows_lto(*crate_type) {
dcx.emit_err(LtoDisallowed);
return Err(FatalError);
} else if *crate_type == CrateType::Dylib {
if !cgcx.opts.unstable_opts.dylib_lto {
dcx.emit_err(LtoDylib);
return Err(FatalError);
}
} else if *crate_type == CrateType::ProcMacro && !cgcx.opts.unstable_opts.dylib_lto {
dcx.emit_err(LtoProcMacro);
return Err(FatalError);
}
}
if cgcx.opts.cg.prefer_dynamic && !cgcx.opts.unstable_opts.dylib_lto {
dcx.emit_err(DynamicLinkingWithLTO);
return Err(FatalError);
}
for &(cnum, ref path) in cgcx.each_linked_rlib_for_lto.iter() {
let exported_symbols =
cgcx.exported_symbols.as_ref().expect("needs exported symbols for LTO");
{
let _timer =
cgcx.prof.generic_activity("LLVM_lto_generate_symbols_below_threshold");
symbols_below_threshold
.extend(exported_symbols[&cnum].iter().filter_map(symbol_filter));
}
for path in each_linked_rlib_for_lto {
let archive_data = unsafe {
Mmap::map(std::fs::File::open(&path).expect("couldn't open rlib"))
.expect("couldn't map rlib")
@@ -147,10 +88,6 @@ fn prepare_lto(
}
}
// __llvm_profile_counter_bias is pulled in at link time by an undefined reference to
// __llvm_profile_runtime, therefore we won't know until link time if this symbol
// should have default visibility.
symbols_below_threshold.push(c"__llvm_profile_counter_bias".to_owned());
Ok((symbols_below_threshold, upstream_modules))
}
@@ -199,15 +136,17 @@ fn get_bitcode_slice_from_object_data<'a>(
/// for further optimization.
pub(crate) fn run_fat(
cgcx: &CodegenContext<LlvmCodegenBackend>,
exported_symbols_for_lto: &[String],
each_linked_rlib_for_lto: &[PathBuf],
modules: Vec<FatLtoInput<LlvmCodegenBackend>>,
cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
) -> Result<ModuleCodegen<ModuleLlvm>, FatalError> {
let dcx = cgcx.create_dcx();
let dcx = dcx.handle();
let (symbols_below_threshold, upstream_modules) = prepare_lto(cgcx, dcx)?;
let (symbols_below_threshold, upstream_modules) =
prepare_lto(cgcx, exported_symbols_for_lto, each_linked_rlib_for_lto, dcx)?;
let symbols_below_threshold =
symbols_below_threshold.iter().map(|c| c.as_ptr()).collect::<Vec<_>>();
fat_lto(cgcx, dcx, modules, cached_modules, upstream_modules, &symbols_below_threshold)
fat_lto(cgcx, dcx, modules, upstream_modules, &symbols_below_threshold)
}
/// Performs thin LTO by performing necessary global analysis and returning two
@@ -215,12 +154,15 @@ pub(crate) fn run_fat(
/// can simply be copied over from the incr. comp. cache.
pub(crate) fn run_thin(
cgcx: &CodegenContext<LlvmCodegenBackend>,
exported_symbols_for_lto: &[String],
each_linked_rlib_for_lto: &[PathBuf],
modules: Vec<(String, ThinBuffer)>,
cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
) -> Result<(Vec<ThinModule<LlvmCodegenBackend>>, Vec<WorkProduct>), FatalError> {
let dcx = cgcx.create_dcx();
let dcx = dcx.handle();
let (symbols_below_threshold, upstream_modules) = prepare_lto(cgcx, dcx)?;
let (symbols_below_threshold, upstream_modules) =
prepare_lto(cgcx, exported_symbols_for_lto, each_linked_rlib_for_lto, dcx)?;
let symbols_below_threshold =
symbols_below_threshold.iter().map(|c| c.as_ptr()).collect::<Vec<_>>();
if cgcx.opts.cg.linker_plugin_lto.enabled() {
@@ -245,7 +187,6 @@ fn fat_lto(
cgcx: &CodegenContext<LlvmCodegenBackend>,
dcx: DiagCtxtHandle<'_>,
modules: Vec<FatLtoInput<LlvmCodegenBackend>>,
cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
mut serialized_modules: Vec<(SerializedModule<ModuleBuffer>, CString)>,
symbols_below_threshold: &[*const libc::c_char],
) -> Result<ModuleCodegen<ModuleLlvm>, FatalError> {
@@ -258,21 +199,12 @@ fn fat_lto(
// modules that are serialized in-memory.
// * `in_memory` contains modules which are already parsed and in-memory,
// such as from multi-CGU builds.
//
// All of `cached_modules` (cached from previous incremental builds) can
// immediately go onto the `serialized_modules` modules list and then we can
// split the `modules` array into these two lists.
let mut in_memory = Vec::new();
serialized_modules.extend(cached_modules.into_iter().map(|(buffer, wp)| {
info!("pushing cached module {:?}", wp.cgu_name);
(buffer, CString::new(wp.cgu_name).unwrap())
}));
for module in modules {
match module {
FatLtoInput::InMemory(m) => in_memory.push(m),
FatLtoInput::Serialized { name, buffer } => {
info!("pushing serialized module {:?}", name);
let buffer = SerializedModule::Local(buffer);
serialized_modules.push((buffer, CString::new(name).unwrap()));
}
}

17
compiler/rustc_codegen_llvm/src/errors.rs
View File

@@ -20,11 +20,6 @@ pub(crate) struct SymbolAlreadyDefined<'a> {
#[diag(codegen_llvm_sanitizer_memtag_requires_mte)]
pub(crate) struct SanitizerMemtagRequiresMte;
#[derive(Diagnostic)]
#[diag(codegen_llvm_dynamic_linking_with_lto)]
#[note]
pub(crate) struct DynamicLinkingWithLTO;
pub(crate) struct ParseTargetMachineConfig<'a>(pub LlvmError<'a>);
impl<G: EmissionGuarantee> Diagnostic<'_, G> for ParseTargetMachineConfig<'_> {
@@ -41,18 +36,6 @@ impl<G: EmissionGuarantee> Diagnostic<'_, G> for ParseTargetMachineConfig<'_> {
#[diag(codegen_llvm_autodiff_without_enable)]
pub(crate) struct AutoDiffWithoutEnable;
#[derive(Diagnostic)]
#[diag(codegen_llvm_lto_disallowed)]
pub(crate) struct LtoDisallowed;
#[derive(Diagnostic)]
#[diag(codegen_llvm_lto_dylib)]
pub(crate) struct LtoDylib;
#[derive(Diagnostic)]
#[diag(codegen_llvm_lto_proc_macro)]
pub(crate) struct LtoProcMacro;
#[derive(Diagnostic)]
#[diag(codegen_llvm_lto_bitcode_from_rlib)]
pub(crate) struct LtoBitcodeFromRlib {

17
compiler/rustc_codegen_llvm/src/lib.rs
View File

@@ -22,6 +22,7 @@
use std::any::Any;
use std::ffi::CStr;
use std::mem::ManuallyDrop;
use std::path::PathBuf;
use back::owned_target_machine::OwnedTargetMachine;
use back::write::{create_informational_target_machine, create_target_machine};
@@ -176,11 +177,13 @@ impl WriteBackendMethods for LlvmCodegenBackend {
}
fn run_and_optimize_fat_lto(
cgcx: &CodegenContext<Self>,
exported_symbols_for_lto: &[String],
each_linked_rlib_for_lto: &[PathBuf],
modules: Vec<FatLtoInput<Self>>,
cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
diff_fncs: Vec<AutoDiffItem>,
) -> Result<ModuleCodegen<Self::Module>, FatalError> {
let mut module = back::lto::run_fat(cgcx, modules, cached_modules)?;
let mut module =
back::lto::run_fat(cgcx, exported_symbols_for_lto, each_linked_rlib_for_lto, modules)?;
if !diff_fncs.is_empty() {
builder::autodiff::differentiate(&module, cgcx, diff_fncs)?;
@@ -194,10 +197,18 @@ impl WriteBackendMethods for LlvmCodegenBackend {
}
fn run_thin_lto(
cgcx: &CodegenContext<Self>,
exported_symbols_for_lto: &[String],
each_linked_rlib_for_lto: &[PathBuf],
modules: Vec<(String, Self::ThinBuffer)>,
cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
) -> Result<(Vec<ThinModule<Self>>, Vec<WorkProduct>), FatalError> {
back::lto::run_thin(cgcx, modules, cached_modules)
back::lto::run_thin(
cgcx,
exported_symbols_for_lto,
each_linked_rlib_for_lto,
modules,
cached_modules,
)
}
fn optimize(
cgcx: &CodegenContext<Self>,