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Auto merge of #113923 - DianQK:restore-no-builtins-lto, r=pnkfelix
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Restore `#![no_builtins]` crates participation in LTO.

After #113716, we can make `#![no_builtins]` crates participate in LTO again.

`#![no_builtins]` with LTO does not result in undefined references to the error. I believe this type of issue won't happen again.

Fixes #72140.  Fixes #112245. Fixes #110606.  Fixes #105734. Fixes #96486. Fixes #108853. Fixes #108893. Fixes #78744. Fixes #91158. Fixes rust-lang/cargo#10118. Fixes rust-lang/compiler-builtins#347.

 The `nightly-2023-07-20` version does not always reproduce problems due to changes in compiler-builtins, core, and user code. That's why this issue recurs and disappears.
Some issues were not tested due to the difficulty of reproducing them.

r? pnkfelix

cc `@bjorn3` `@japaric` `@alexcrichton` `@Amanieu`
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bors committed Dec 1, 2023
2 parents 9cf18e9 + b9f53be commit 8c2b577
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Showing 16 changed files with 133 additions and 89 deletions.
8 changes: 3 additions & 5 deletions compiler/rustc_codegen_llvm/src/back/write.rs
Original file line number Diff line number Diff line change
Expand Up @@ -571,7 +571,6 @@ pub(crate) unsafe fn llvm_optimize(
unroll_loops,
config.vectorize_slp,
config.vectorize_loop,
config.no_builtins,
config.emit_lifetime_markers,
sanitizer_options.as_ref(),
pgo_gen_path.as_ref().map_or(std::ptr::null(), |s| s.as_ptr()),
Expand Down Expand Up @@ -686,15 +685,14 @@ pub(crate) unsafe fn codegen(
unsafe fn with_codegen<'ll, F, R>(
tm: &'ll llvm::TargetMachine,
llmod: &'ll llvm::Module,
no_builtins: bool,
f: F,
) -> R
where
F: FnOnce(&'ll mut PassManager<'ll>) -> R,
{
let cpm = llvm::LLVMCreatePassManager();
llvm::LLVMAddAnalysisPasses(tm, cpm);
llvm::LLVMRustAddLibraryInfo(cpm, llmod, no_builtins);
llvm::LLVMRustAddLibraryInfo(cpm, llmod);
f(cpm)
}

Expand Down Expand Up @@ -797,7 +795,7 @@ pub(crate) unsafe fn codegen(
} else {
llmod
};
with_codegen(tm, llmod, config.no_builtins, |cpm| {
with_codegen(tm, llmod, |cpm| {
write_output_file(
diag_handler,
tm,
Expand Down Expand Up @@ -832,7 +830,7 @@ pub(crate) unsafe fn codegen(
(_, SplitDwarfKind::Split) => Some(dwo_out.as_path()),
};

with_codegen(tm, llmod, config.no_builtins, |cpm| {
with_codegen(tm, llmod, |cpm| {
write_output_file(
diag_handler,
tm,
Expand Down
8 changes: 1 addition & 7 deletions compiler/rustc_codegen_llvm/src/llvm/ffi.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2163,13 +2163,8 @@ extern "C" {
ArgsCstrBuff: *const c_char,
ArgsCstrBuffLen: usize,
) -> *mut TargetMachine;

pub fn LLVMRustDisposeTargetMachine(T: *mut TargetMachine);
pub fn LLVMRustAddLibraryInfo<'a>(
PM: &PassManager<'a>,
M: &'a Module,
DisableSimplifyLibCalls: bool,
);
pub fn LLVMRustAddLibraryInfo<'a>(PM: &PassManager<'a>, M: &'a Module);
pub fn LLVMRustWriteOutputFile<'a>(
T: &'a TargetMachine,
PM: &PassManager<'a>,
Expand All @@ -2191,7 +2186,6 @@ extern "C" {
UnrollLoops: bool,
SLPVectorize: bool,
LoopVectorize: bool,
DisableSimplifyLibCalls: bool,
EmitLifetimeMarkers: bool,
SanitizerOptions: Option<&SanitizerOptions>,
PGOGenPath: *const c_char,
Expand Down
46 changes: 12 additions & 34 deletions compiler/rustc_codegen_ssa/src/back/link.rs
Original file line number Diff line number Diff line change
Expand Up @@ -270,8 +270,14 @@ pub fn each_linked_rlib(

for &cnum in crates {
match fmts.get(cnum.as_usize() - 1) {
Some(&Linkage::NotLinked | &Linkage::Dynamic | &Linkage::IncludedFromDylib) => continue,
Some(_) => {}
Some(&Linkage::NotLinked | &Linkage::Dynamic) => continue,
Some(&Linkage::IncludedFromDylib) => {
// We always link crate `compiler_builtins` statically. When enabling LTO, we include it as well.
if info.compiler_builtins != Some(cnum) {
continue;
}
}
Some(&Linkage::Static) => {}
None => return Err(errors::LinkRlibError::MissingFormat),
}
let crate_name = info.crate_name[&cnum];
Expand Down Expand Up @@ -520,8 +526,7 @@ fn link_staticlib<'a>(
&codegen_results.crate_info,
Some(CrateType::Staticlib),
&mut |cnum, path| {
let lto = are_upstream_rust_objects_already_included(sess)
&& !ignored_for_lto(sess, &codegen_results.crate_info, cnum);
let lto = are_upstream_rust_objects_already_included(sess);

let native_libs = codegen_results.crate_info.native_libraries[&cnum].iter();
let relevant = native_libs.clone().filter(|lib| relevant_lib(sess, lib));
Expand Down Expand Up @@ -1256,24 +1261,6 @@ fn link_sanitizer_runtime(sess: &Session, linker: &mut dyn Linker, name: &str) {
}
}

/// Returns a boolean indicating whether the specified crate should be ignored
/// during LTO.
///
/// Crates ignored during LTO are not lumped together in the "massive object
/// file" that we create and are linked in their normal rlib states. See
/// comments below for what crates do not participate in LTO.
///
/// It's unusual for a crate to not participate in LTO. Typically only
/// compiler-specific and unstable crates have a reason to not participate in
/// LTO.
pub fn ignored_for_lto(sess: &Session, info: &CrateInfo, cnum: CrateNum) -> bool {
// If our target enables builtin function lowering in LLVM then the
// crates providing these functions don't participate in LTO (e.g.
// no_builtins or compiler builtins crates).
!sess.target.no_builtins
&& (info.compiler_builtins == Some(cnum) || info.is_no_builtins.contains(&cnum))
}

/// This functions tries to determine the appropriate linker (and corresponding LinkerFlavor) to use
pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
fn infer_from(
Expand Down Expand Up @@ -2739,10 +2726,6 @@ fn rehome_sysroot_lib_dir<'a>(sess: &'a Session, lib_dir: &Path) -> PathBuf {
// symbols). We must continue to include the rest of the rlib, however, as
// it may contain static native libraries which must be linked in.
//
// (*) Crates marked with `#![no_builtins]` don't participate in LTO and
// their bytecode wasn't included. The object files in those libraries must
// still be passed to the linker.
//
// Note, however, that if we're not doing LTO we can just pass the rlib
// blindly to the linker (fast) because it's fine if it's not actually
// included as we're at the end of the dependency chain.
Expand All @@ -2768,9 +2751,7 @@ fn add_static_crate<'a>(
cmd.link_rlib(&rlib_path);
};

if !are_upstream_rust_objects_already_included(sess)
|| ignored_for_lto(sess, &codegen_results.crate_info, cnum)
{
if !are_upstream_rust_objects_already_included(sess) {
link_upstream(cratepath);
return;
}
Expand All @@ -2784,8 +2765,6 @@ fn add_static_crate<'a>(
let canonical_name = name.replace('-', "_");
let upstream_rust_objects_already_included =
are_upstream_rust_objects_already_included(sess);
let is_builtins =
sess.target.no_builtins || !codegen_results.crate_info.is_no_builtins.contains(&cnum);

let mut archive = archive_builder_builder.new_archive_builder(sess);
if let Err(error) = archive.add_archive(
Expand All @@ -2802,9 +2781,8 @@ fn add_static_crate<'a>(

// If we're performing LTO and this is a rust-generated object
// file, then we don't need the object file as it's part of the
// LTO module. Note that `#![no_builtins]` is excluded from LTO,
// though, so we let that object file slide.
if upstream_rust_objects_already_included && is_rust_object && is_builtins {
// LTO module.
if upstream_rust_objects_already_included && is_rust_object {
return true;
}

Expand Down
10 changes: 7 additions & 3 deletions compiler/rustc_codegen_ssa/src/back/symbol_export.rs
Original file line number Diff line number Diff line change
Expand Up @@ -54,8 +54,8 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
// export level, however, as they're just implementation details.
// Down below we'll hardwire all of the symbols to the `Rust` export
// level instead.
let special_runtime_crate =
tcx.is_panic_runtime(LOCAL_CRATE) || tcx.is_compiler_builtins(LOCAL_CRATE);
let is_compiler_builtins = tcx.is_compiler_builtins(LOCAL_CRATE);
let special_runtime_crate = tcx.is_panic_runtime(LOCAL_CRATE) || is_compiler_builtins;

let mut reachable_non_generics: DefIdMap<_> = tcx
.reachable_set(())
Expand Down Expand Up @@ -107,7 +107,11 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
.map(|def_id| {
// We won't link right if this symbol is stripped during LTO.
let name = tcx.symbol_name(Instance::mono(tcx, def_id.to_def_id())).name;
let used = name == "rust_eh_personality";
// We have to preserve the symbols of the built-in functions during LTO.
let is_builtin_fn = is_compiler_builtins
&& symbol_export_level(tcx, def_id.to_def_id())
.is_below_threshold(SymbolExportLevel::C);
let used = is_builtin_fn || name == "rust_eh_personality";

let export_level = if special_runtime_crate {
SymbolExportLevel::Rust
Expand Down
16 changes: 1 addition & 15 deletions compiler/rustc_codegen_ssa/src/back/write.rs
Original file line number Diff line number Diff line change
Expand Up @@ -148,23 +148,12 @@ impl ModuleConfig {

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)
{
} else if sess.target.obj_is_bitcode || sess.opts.cg.linker_plugin_lto.enabled() {
// 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)
Expand Down Expand Up @@ -1037,9 +1026,6 @@ fn start_executing_work<B: ExtraBackendMethods>(

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()));
}));

Expand Down
8 changes: 1 addition & 7 deletions compiler/rustc_codegen_ssa/src/base.rs
Original file line number Diff line number Diff line change
Expand Up @@ -858,7 +858,6 @@ impl CrateInfo {
local_crate_name,
compiler_builtins,
profiler_runtime: None,
is_no_builtins: Default::default(),
native_libraries: Default::default(),
used_libraries: tcx.native_libraries(LOCAL_CRATE).iter().map(Into::into).collect(),
crate_name: Default::default(),
Expand All @@ -885,19 +884,14 @@ impl CrateInfo {
if tcx.is_profiler_runtime(cnum) {
info.profiler_runtime = Some(cnum);
}
if tcx.is_no_builtins(cnum) {
info.is_no_builtins.insert(cnum);
}
}

// Handle circular dependencies in the standard library.
// See comment before `add_linked_symbol_object` function for the details.
// If global LTO is enabled then almost everything (*) is glued into a single object file,
// so this logic is not necessary and can cause issues on some targets (due to weak lang
// item symbols being "privatized" to that object file), so we disable it.
// (*) Native libs, and `#[compiler_builtins]` and `#[no_builtins]` crates are not glued,
// and we assume that they cannot define weak lang items. This is not currently enforced
// by the compiler, but that's ok because all this stuff is unstable anyway.
// (*) Native libs are not glued, and we assume that they cannot define weak lang items.
let target = &tcx.sess.target;
if !are_upstream_rust_objects_already_included(tcx.sess) {
let missing_weak_lang_items: FxHashSet<Symbol> = info
Expand Down
3 changes: 1 addition & 2 deletions compiler/rustc_codegen_ssa/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,7 @@ extern crate tracing;
extern crate rustc_middle;

use rustc_ast as ast;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::sync::Lrc;
use rustc_hir::def_id::CrateNum;
use rustc_middle::dep_graph::WorkProduct;
Expand Down Expand Up @@ -157,7 +157,6 @@ pub struct CrateInfo {
pub local_crate_name: Symbol,
pub compiler_builtins: Option<CrateNum>,
pub profiler_runtime: Option<CrateNum>,
pub is_no_builtins: FxHashSet<CrateNum>,
pub native_libraries: FxHashMap<CrateNum, Vec<NativeLib>>,
pub crate_name: FxHashMap<CrateNum, Symbol>,
pub used_libraries: Vec<NativeLib>,
Expand Down
9 changes: 2 additions & 7 deletions compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -525,12 +525,9 @@ extern "C" void LLVMRustDisposeTargetMachine(LLVMTargetMachineRef TM) {

// Unfortunately, the LLVM C API doesn't provide a way to create the
// TargetLibraryInfo pass, so we use this method to do so.
extern "C" void LLVMRustAddLibraryInfo(LLVMPassManagerRef PMR, LLVMModuleRef M,
bool DisableSimplifyLibCalls) {
extern "C" void LLVMRustAddLibraryInfo(LLVMPassManagerRef PMR, LLVMModuleRef M) {
Triple TargetTriple(unwrap(M)->getTargetTriple());
TargetLibraryInfoImpl TLII(TargetTriple);
if (DisableSimplifyLibCalls)
TLII.disableAllFunctions();
unwrap(PMR)->add(new TargetLibraryInfoWrapperPass(TLII));
}

Expand Down Expand Up @@ -697,7 +694,7 @@ LLVMRustOptimize(
bool IsLinkerPluginLTO,
bool NoPrepopulatePasses, bool VerifyIR, bool UseThinLTOBuffers,
bool MergeFunctions, bool UnrollLoops, bool SLPVectorize, bool LoopVectorize,
bool DisableSimplifyLibCalls, bool EmitLifetimeMarkers,
bool EmitLifetimeMarkers,
LLVMRustSanitizerOptions *SanitizerOptions,
const char *PGOGenPath, const char *PGOUsePath,
bool InstrumentCoverage, const char *InstrProfileOutput,
Expand Down Expand Up @@ -795,8 +792,6 @@ LLVMRustOptimize(

Triple TargetTriple(TheModule->getTargetTriple());
std::unique_ptr<TargetLibraryInfoImpl> TLII(new TargetLibraryInfoImpl(TargetTriple));
if (DisableSimplifyLibCalls)
TLII->disableAllFunctions();
FAM.registerPass([&] { return TargetLibraryAnalysis(*TLII); });

PB.registerModuleAnalyses(MAM);
Expand Down
18 changes: 12 additions & 6 deletions tests/run-make/no-builtins-lto/Makefile
Original file line number Diff line number Diff line change
@@ -1,9 +1,15 @@
include ../tools.mk

# only-x86_64

# We want to check that `no_builtins` is correctly participating in LTO.
# First, verify that the `foo::foo` symbol can be found when linking.
# Next, verify that `memcpy` can be customized using `no_builtins` under LTO.
# Others will use the built-in memcpy.

all:
# Compile a `#![no_builtins]` rlib crate
$(RUSTC) no_builtins.rs
# Build an executable that depends on that crate using LTO. The no_builtins crate doesn't
# participate in LTO, so its rlib must be explicitly linked into the final binary. Verify this by
# grepping the linker arguments.
$(RUSTC) main.rs -C lto --print link-args | $(CGREP) 'libno_builtins.rlib'
$(RUSTC) -C linker-plugin-lto -C opt-level=2 -C debuginfo=0 foo.rs
$(RUSTC) -C linker-plugin-lto -C opt-level=2 -C debuginfo=0 no_builtins.rs
$(RUSTC) main.rs -C lto -C opt-level=2 -C debuginfo=0 -C save-temps -C metadata=1 -C codegen-units=1
"$(LLVM_BIN_DIR)"/llvm-dis $(TMPDIR)/main.main.*-cgu.0.rcgu.lto.input.bc -o $(TMPDIR)/lto.ll
cat "$(TMPDIR)"/lto.ll | "$(LLVM_FILECHECK)" filecheck.lto.txt
17 changes: 17 additions & 0 deletions tests/run-make/no-builtins-lto/filecheck.lto.txt
Original file line number Diff line number Diff line change
@@ -0,0 +1,17 @@
CHECK: define{{.*}} void @bar
CHECK-NEXT: call void @no_builtins
CHECK-NEXT: call void @llvm.memcpy

CHECK: define{{.*}} i32 @main
CHECK: call void @bar

CHECK: define{{.*}} void @foo
CHECK-NEXT: call void @llvm.memcpy

CHECK: define{{.*}} void @no_builtins
CHECK-SAME: #[[ATTR:[0-9]+]] {
CHECK: call void @foo
CHECK-NEXT: call{{.*}} @memcpy

CHECK: attributes #[[ATTR]]
CHECK-SAME: no-builtins
33 changes: 33 additions & 0 deletions tests/run-make/no-builtins-lto/foo.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,33 @@
#![feature(lang_items, no_core)]
#![no_std]
#![no_core]
#![crate_type = "lib"]

#[inline(never)]
#[no_mangle]
pub unsafe fn foo(dest: *mut u8, src: *const u8) {
// should call `@llvm.memcpy`.
memcpy(dest, src, 1024);
}

#[no_mangle]
#[inline(never)]
pub unsafe extern "C" fn memcpy(dest: *mut u8, src: *const u8, _n: usize) -> *mut u8 {
*dest = 0;
return src as *mut u8;
}

#[lang = "sized"]
trait Sized {}
#[lang = "copy"]
trait Copy {}
impl Copy for *mut u8 {}
impl Copy for *const u8 {}

#[lang = "drop_in_place"]
#[allow(unconditional_recursion)]
pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
// Code here does not matter - this is replaced by the
// real drop glue by the compiler.
drop_in_place(to_drop);
}
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