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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-17 12:02:58 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-17 12:02:58 +0000
commit698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch)
tree173a775858bd501c378080a10dca74132f05bc50 /compiler/rustc_monomorphize/src/partitioning
parentInitial commit. (diff)
downloadrustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz
rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'compiler/rustc_monomorphize/src/partitioning')
-rw-r--r--compiler/rustc_monomorphize/src/partitioning/default.rs560
-rw-r--r--compiler/rustc_monomorphize/src/partitioning/merging.rs111
-rw-r--r--compiler/rustc_monomorphize/src/partitioning/mod.rs515
3 files changed, 1186 insertions, 0 deletions
diff --git a/compiler/rustc_monomorphize/src/partitioning/default.rs b/compiler/rustc_monomorphize/src/partitioning/default.rs
new file mode 100644
index 000000000..15276569c
--- /dev/null
+++ b/compiler/rustc_monomorphize/src/partitioning/default.rs
@@ -0,0 +1,560 @@
+use std::collections::hash_map::Entry;
+
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_hir::def::DefKind;
+use rustc_hir::def_id::{DefId, LOCAL_CRATE};
+use rustc_hir::definitions::DefPathDataName;
+use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
+use rustc_middle::middle::exported_symbols::{SymbolExportInfo, SymbolExportLevel};
+use rustc_middle::mir::mono::{CodegenUnit, CodegenUnitNameBuilder, Linkage, Visibility};
+use rustc_middle::mir::mono::{InstantiationMode, MonoItem};
+use rustc_middle::ty::print::characteristic_def_id_of_type;
+use rustc_middle::ty::{self, visit::TypeVisitable, DefIdTree, InstanceDef, TyCtxt};
+use rustc_span::symbol::Symbol;
+
+use super::PartitioningCx;
+use crate::collector::InliningMap;
+use crate::partitioning::merging;
+use crate::partitioning::{
+ MonoItemPlacement, Partitioner, PostInliningPartitioning, PreInliningPartitioning,
+};
+
+pub struct DefaultPartitioning;
+
+impl<'tcx> Partitioner<'tcx> for DefaultPartitioning {
+ fn place_root_mono_items(
+ &mut self,
+ cx: &PartitioningCx<'_, 'tcx>,
+ mono_items: &mut dyn Iterator<Item = MonoItem<'tcx>>,
+ ) -> PreInliningPartitioning<'tcx> {
+ let mut roots = FxHashSet::default();
+ let mut codegen_units = FxHashMap::default();
+ let is_incremental_build = cx.tcx.sess.opts.incremental.is_some();
+ let mut internalization_candidates = FxHashSet::default();
+
+ // Determine if monomorphizations instantiated in this crate will be made
+ // available to downstream crates. This depends on whether we are in
+ // share-generics mode and whether the current crate can even have
+ // downstream crates.
+ let export_generics =
+ cx.tcx.sess.opts.share_generics() && cx.tcx.local_crate_exports_generics();
+
+ let cgu_name_builder = &mut CodegenUnitNameBuilder::new(cx.tcx);
+ let cgu_name_cache = &mut FxHashMap::default();
+
+ for mono_item in mono_items {
+ match mono_item.instantiation_mode(cx.tcx) {
+ InstantiationMode::GloballyShared { .. } => {}
+ InstantiationMode::LocalCopy => continue,
+ }
+
+ let characteristic_def_id = characteristic_def_id_of_mono_item(cx.tcx, mono_item);
+ let is_volatile = is_incremental_build && mono_item.is_generic_fn();
+
+ let codegen_unit_name = match characteristic_def_id {
+ Some(def_id) => compute_codegen_unit_name(
+ cx.tcx,
+ cgu_name_builder,
+ def_id,
+ is_volatile,
+ cgu_name_cache,
+ ),
+ None => fallback_cgu_name(cgu_name_builder),
+ };
+
+ let codegen_unit = codegen_units
+ .entry(codegen_unit_name)
+ .or_insert_with(|| CodegenUnit::new(codegen_unit_name));
+
+ let mut can_be_internalized = true;
+ let (linkage, visibility) = mono_item_linkage_and_visibility(
+ cx.tcx,
+ &mono_item,
+ &mut can_be_internalized,
+ export_generics,
+ );
+ if visibility == Visibility::Hidden && can_be_internalized {
+ internalization_candidates.insert(mono_item);
+ }
+
+ codegen_unit.items_mut().insert(mono_item, (linkage, visibility));
+ roots.insert(mono_item);
+ }
+
+ // Always ensure we have at least one CGU; otherwise, if we have a
+ // crate with just types (for example), we could wind up with no CGU.
+ if codegen_units.is_empty() {
+ let codegen_unit_name = fallback_cgu_name(cgu_name_builder);
+ codegen_units.insert(codegen_unit_name, CodegenUnit::new(codegen_unit_name));
+ }
+
+ PreInliningPartitioning {
+ codegen_units: codegen_units
+ .into_iter()
+ .map(|(_, codegen_unit)| codegen_unit)
+ .collect(),
+ roots,
+ internalization_candidates,
+ }
+ }
+
+ fn merge_codegen_units(
+ &mut self,
+ cx: &PartitioningCx<'_, 'tcx>,
+ initial_partitioning: &mut PreInliningPartitioning<'tcx>,
+ ) {
+ merging::merge_codegen_units(cx, initial_partitioning);
+ }
+
+ fn place_inlined_mono_items(
+ &mut self,
+ cx: &PartitioningCx<'_, 'tcx>,
+ initial_partitioning: PreInliningPartitioning<'tcx>,
+ ) -> PostInliningPartitioning<'tcx> {
+ let mut new_partitioning = Vec::new();
+ let mut mono_item_placements = FxHashMap::default();
+
+ let PreInliningPartitioning {
+ codegen_units: initial_cgus,
+ roots,
+ internalization_candidates,
+ } = initial_partitioning;
+
+ let single_codegen_unit = initial_cgus.len() == 1;
+
+ for old_codegen_unit in initial_cgus {
+ // Collect all items that need to be available in this codegen unit.
+ let mut reachable = FxHashSet::default();
+ for root in old_codegen_unit.items().keys() {
+ follow_inlining(*root, cx.inlining_map, &mut reachable);
+ }
+
+ let mut new_codegen_unit = CodegenUnit::new(old_codegen_unit.name());
+
+ // Add all monomorphizations that are not already there.
+ for mono_item in reachable {
+ if let Some(linkage) = old_codegen_unit.items().get(&mono_item) {
+ // This is a root, just copy it over.
+ new_codegen_unit.items_mut().insert(mono_item, *linkage);
+ } else {
+ if roots.contains(&mono_item) {
+ bug!(
+ "GloballyShared mono-item inlined into other CGU: \
+ {:?}",
+ mono_item
+ );
+ }
+
+ // This is a CGU-private copy.
+ new_codegen_unit
+ .items_mut()
+ .insert(mono_item, (Linkage::Internal, Visibility::Default));
+ }
+
+ if !single_codegen_unit {
+ // If there is more than one codegen unit, we need to keep track
+ // in which codegen units each monomorphization is placed.
+ match mono_item_placements.entry(mono_item) {
+ Entry::Occupied(e) => {
+ let placement = e.into_mut();
+ debug_assert!(match *placement {
+ MonoItemPlacement::SingleCgu { cgu_name } => {
+ cgu_name != new_codegen_unit.name()
+ }
+ MonoItemPlacement::MultipleCgus => true,
+ });
+ *placement = MonoItemPlacement::MultipleCgus;
+ }
+ Entry::Vacant(e) => {
+ e.insert(MonoItemPlacement::SingleCgu {
+ cgu_name: new_codegen_unit.name(),
+ });
+ }
+ }
+ }
+ }
+
+ new_partitioning.push(new_codegen_unit);
+ }
+
+ return PostInliningPartitioning {
+ codegen_units: new_partitioning,
+ mono_item_placements,
+ internalization_candidates,
+ };
+
+ fn follow_inlining<'tcx>(
+ mono_item: MonoItem<'tcx>,
+ inlining_map: &InliningMap<'tcx>,
+ visited: &mut FxHashSet<MonoItem<'tcx>>,
+ ) {
+ if !visited.insert(mono_item) {
+ return;
+ }
+
+ inlining_map.with_inlining_candidates(mono_item, |target| {
+ follow_inlining(target, inlining_map, visited);
+ });
+ }
+ }
+
+ fn internalize_symbols(
+ &mut self,
+ cx: &PartitioningCx<'_, 'tcx>,
+ partitioning: &mut PostInliningPartitioning<'tcx>,
+ ) {
+ if partitioning.codegen_units.len() == 1 {
+ // Fast path for when there is only one codegen unit. In this case we
+ // can internalize all candidates, since there is nowhere else they
+ // could be accessed from.
+ for cgu in &mut partitioning.codegen_units {
+ for candidate in &partitioning.internalization_candidates {
+ cgu.items_mut().insert(*candidate, (Linkage::Internal, Visibility::Default));
+ }
+ }
+
+ return;
+ }
+
+ // Build a map from every monomorphization to all the monomorphizations that
+ // reference it.
+ let mut accessor_map: FxHashMap<MonoItem<'tcx>, Vec<MonoItem<'tcx>>> = Default::default();
+ cx.inlining_map.iter_accesses(|accessor, accessees| {
+ for accessee in accessees {
+ accessor_map.entry(*accessee).or_default().push(accessor);
+ }
+ });
+
+ let mono_item_placements = &partitioning.mono_item_placements;
+
+ // For each internalization candidates in each codegen unit, check if it is
+ // accessed from outside its defining codegen unit.
+ for cgu in &mut partitioning.codegen_units {
+ let home_cgu = MonoItemPlacement::SingleCgu { cgu_name: cgu.name() };
+
+ for (accessee, linkage_and_visibility) in cgu.items_mut() {
+ if !partitioning.internalization_candidates.contains(accessee) {
+ // This item is no candidate for internalizing, so skip it.
+ continue;
+ }
+ debug_assert_eq!(mono_item_placements[accessee], home_cgu);
+
+ if let Some(accessors) = accessor_map.get(accessee) {
+ if accessors
+ .iter()
+ .filter_map(|accessor| {
+ // Some accessors might not have been
+ // instantiated. We can safely ignore those.
+ mono_item_placements.get(accessor)
+ })
+ .any(|placement| *placement != home_cgu)
+ {
+ // Found an accessor from another CGU, so skip to the next
+ // item without marking this one as internal.
+ continue;
+ }
+ }
+
+ // If we got here, we did not find any accesses from other CGUs,
+ // so it's fine to make this monomorphization internal.
+ *linkage_and_visibility = (Linkage::Internal, Visibility::Default);
+ }
+ }
+ }
+}
+
+fn characteristic_def_id_of_mono_item<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ mono_item: MonoItem<'tcx>,
+) -> Option<DefId> {
+ match mono_item {
+ MonoItem::Fn(instance) => {
+ let def_id = match instance.def {
+ ty::InstanceDef::Item(def) => def.did,
+ ty::InstanceDef::VTableShim(..)
+ | ty::InstanceDef::ReifyShim(..)
+ | ty::InstanceDef::FnPtrShim(..)
+ | ty::InstanceDef::ClosureOnceShim { .. }
+ | ty::InstanceDef::Intrinsic(..)
+ | ty::InstanceDef::DropGlue(..)
+ | ty::InstanceDef::Virtual(..)
+ | ty::InstanceDef::CloneShim(..) => return None,
+ };
+
+ // If this is a method, we want to put it into the same module as
+ // its self-type. If the self-type does not provide a characteristic
+ // DefId, we use the location of the impl after all.
+
+ if tcx.trait_of_item(def_id).is_some() {
+ let self_ty = instance.substs.type_at(0);
+ // This is a default implementation of a trait method.
+ return characteristic_def_id_of_type(self_ty).or(Some(def_id));
+ }
+
+ if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
+ if tcx.sess.opts.incremental.is_some()
+ && tcx.trait_id_of_impl(impl_def_id) == tcx.lang_items().drop_trait()
+ {
+ // Put `Drop::drop` into the same cgu as `drop_in_place`
+ // since `drop_in_place` is the only thing that can
+ // call it.
+ return None;
+ }
+
+ // When polymorphization is enabled, methods which do not depend on their generic
+ // parameters, but the self-type of their impl block do will fail to normalize.
+ if !tcx.sess.opts.unstable_opts.polymorphize || !instance.needs_subst() {
+ // This is a method within an impl, find out what the self-type is:
+ let impl_self_ty = tcx.subst_and_normalize_erasing_regions(
+ instance.substs,
+ ty::ParamEnv::reveal_all(),
+ tcx.type_of(impl_def_id),
+ );
+ if let Some(def_id) = characteristic_def_id_of_type(impl_self_ty) {
+ return Some(def_id);
+ }
+ }
+ }
+
+ Some(def_id)
+ }
+ MonoItem::Static(def_id) => Some(def_id),
+ MonoItem::GlobalAsm(item_id) => Some(item_id.def_id.to_def_id()),
+ }
+}
+
+fn compute_codegen_unit_name(
+ tcx: TyCtxt<'_>,
+ name_builder: &mut CodegenUnitNameBuilder<'_>,
+ def_id: DefId,
+ volatile: bool,
+ cache: &mut CguNameCache,
+) -> Symbol {
+ // Find the innermost module that is not nested within a function.
+ let mut current_def_id = def_id;
+ let mut cgu_def_id = None;
+ // Walk backwards from the item we want to find the module for.
+ loop {
+ if current_def_id.is_crate_root() {
+ if cgu_def_id.is_none() {
+ // If we have not found a module yet, take the crate root.
+ cgu_def_id = Some(def_id.krate.as_def_id());
+ }
+ break;
+ } else if tcx.def_kind(current_def_id) == DefKind::Mod {
+ if cgu_def_id.is_none() {
+ cgu_def_id = Some(current_def_id);
+ }
+ } else {
+ // If we encounter something that is not a module, throw away
+ // any module that we've found so far because we now know that
+ // it is nested within something else.
+ cgu_def_id = None;
+ }
+
+ current_def_id = tcx.parent(current_def_id);
+ }
+
+ let cgu_def_id = cgu_def_id.unwrap();
+
+ *cache.entry((cgu_def_id, volatile)).or_insert_with(|| {
+ let def_path = tcx.def_path(cgu_def_id);
+
+ let components = def_path.data.iter().map(|part| match part.data.name() {
+ DefPathDataName::Named(name) => name,
+ DefPathDataName::Anon { .. } => unreachable!(),
+ });
+
+ let volatile_suffix = volatile.then_some("volatile");
+
+ name_builder.build_cgu_name(def_path.krate, components, volatile_suffix)
+ })
+}
+
+// Anything we can't find a proper codegen unit for goes into this.
+fn fallback_cgu_name(name_builder: &mut CodegenUnitNameBuilder<'_>) -> Symbol {
+ name_builder.build_cgu_name(LOCAL_CRATE, &["fallback"], Some("cgu"))
+}
+
+fn mono_item_linkage_and_visibility<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ mono_item: &MonoItem<'tcx>,
+ can_be_internalized: &mut bool,
+ export_generics: bool,
+) -> (Linkage, Visibility) {
+ if let Some(explicit_linkage) = mono_item.explicit_linkage(tcx) {
+ return (explicit_linkage, Visibility::Default);
+ }
+ let vis = mono_item_visibility(tcx, mono_item, can_be_internalized, export_generics);
+ (Linkage::External, vis)
+}
+
+type CguNameCache = FxHashMap<(DefId, bool), Symbol>;
+
+fn mono_item_visibility<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ mono_item: &MonoItem<'tcx>,
+ can_be_internalized: &mut bool,
+ export_generics: bool,
+) -> Visibility {
+ let instance = match mono_item {
+ // This is pretty complicated; see below.
+ MonoItem::Fn(instance) => instance,
+
+ // Misc handling for generics and such, but otherwise:
+ MonoItem::Static(def_id) => {
+ return if tcx.is_reachable_non_generic(*def_id) {
+ *can_be_internalized = false;
+ default_visibility(tcx, *def_id, false)
+ } else {
+ Visibility::Hidden
+ };
+ }
+ MonoItem::GlobalAsm(item_id) => {
+ return if tcx.is_reachable_non_generic(item_id.def_id) {
+ *can_be_internalized = false;
+ default_visibility(tcx, item_id.def_id.to_def_id(), false)
+ } else {
+ Visibility::Hidden
+ };
+ }
+ };
+
+ let def_id = match instance.def {
+ InstanceDef::Item(def) => def.did,
+ InstanceDef::DropGlue(def_id, Some(_)) => def_id,
+
+ // These are all compiler glue and such, never exported, always hidden.
+ InstanceDef::VTableShim(..)
+ | InstanceDef::ReifyShim(..)
+ | InstanceDef::FnPtrShim(..)
+ | InstanceDef::Virtual(..)
+ | InstanceDef::Intrinsic(..)
+ | InstanceDef::ClosureOnceShim { .. }
+ | InstanceDef::DropGlue(..)
+ | InstanceDef::CloneShim(..) => return Visibility::Hidden,
+ };
+
+ // The `start_fn` lang item is actually a monomorphized instance of a
+ // function in the standard library, used for the `main` function. We don't
+ // want to export it so we tag it with `Hidden` visibility but this symbol
+ // is only referenced from the actual `main` symbol which we unfortunately
+ // don't know anything about during partitioning/collection. As a result we
+ // forcibly keep this symbol out of the `internalization_candidates` set.
+ //
+ // FIXME: eventually we don't want to always force this symbol to have
+ // hidden visibility, it should indeed be a candidate for
+ // internalization, but we have to understand that it's referenced
+ // from the `main` symbol we'll generate later.
+ //
+ // This may be fixable with a new `InstanceDef` perhaps? Unsure!
+ if tcx.lang_items().start_fn() == Some(def_id) {
+ *can_be_internalized = false;
+ return Visibility::Hidden;
+ }
+
+ let is_generic = instance.substs.non_erasable_generics().next().is_some();
+
+ // Upstream `DefId` instances get different handling than local ones.
+ let Some(def_id) = def_id.as_local() else {
+ return if export_generics && is_generic {
+ // If it is an upstream monomorphization and we export generics, we must make
+ // it available to downstream crates.
+ *can_be_internalized = false;
+ default_visibility(tcx, def_id, true)
+ } else {
+ Visibility::Hidden
+ };
+ };
+
+ if is_generic {
+ if export_generics {
+ if tcx.is_unreachable_local_definition(def_id) {
+ // This instance cannot be used from another crate.
+ Visibility::Hidden
+ } else {
+ // This instance might be useful in a downstream crate.
+ *can_be_internalized = false;
+ default_visibility(tcx, def_id.to_def_id(), true)
+ }
+ } else {
+ // We are not exporting generics or the definition is not reachable
+ // for downstream crates, we can internalize its instantiations.
+ Visibility::Hidden
+ }
+ } else {
+ // If this isn't a generic function then we mark this a `Default` if
+ // this is a reachable item, meaning that it's a symbol other crates may
+ // access when they link to us.
+ if tcx.is_reachable_non_generic(def_id.to_def_id()) {
+ *can_be_internalized = false;
+ debug_assert!(!is_generic);
+ return default_visibility(tcx, def_id.to_def_id(), false);
+ }
+
+ // If this isn't reachable then we're gonna tag this with `Hidden`
+ // visibility. In some situations though we'll want to prevent this
+ // symbol from being internalized.
+ //
+ // There's two categories of items here:
+ //
+ // * First is weak lang items. These are basically mechanisms for
+ // libcore to forward-reference symbols defined later in crates like
+ // the standard library or `#[panic_handler]` definitions. The
+ // definition of these weak lang items needs to be referencable by
+ // libcore, so we're no longer a candidate for internalization.
+ // Removal of these functions can't be done by LLVM but rather must be
+ // done by the linker as it's a non-local decision.
+ //
+ // * Second is "std internal symbols". Currently this is primarily used
+ // for allocator symbols. Allocators are a little weird in their
+ // implementation, but the idea is that the compiler, at the last
+ // minute, defines an allocator with an injected object file. The
+ // `alloc` crate references these symbols (`__rust_alloc`) and the
+ // definition doesn't get hooked up until a linked crate artifact is
+ // generated.
+ //
+ // The symbols synthesized by the compiler (`__rust_alloc`) are thin
+ // veneers around the actual implementation, some other symbol which
+ // implements the same ABI. These symbols (things like `__rg_alloc`,
+ // `__rdl_alloc`, `__rde_alloc`, etc), are all tagged with "std
+ // internal symbols".
+ //
+ // The std-internal symbols here **should not show up in a dll as an
+ // exported interface**, so they return `false` from
+ // `is_reachable_non_generic` above and we'll give them `Hidden`
+ // visibility below. Like the weak lang items, though, we can't let
+ // LLVM internalize them as this decision is left up to the linker to
+ // omit them, so prevent them from being internalized.
+ let attrs = tcx.codegen_fn_attrs(def_id);
+ if attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
+ *can_be_internalized = false;
+ }
+
+ Visibility::Hidden
+ }
+}
+
+fn default_visibility(tcx: TyCtxt<'_>, id: DefId, is_generic: bool) -> Visibility {
+ if !tcx.sess.target.default_hidden_visibility {
+ return Visibility::Default;
+ }
+
+ // Generic functions never have export-level C.
+ if is_generic {
+ return Visibility::Hidden;
+ }
+
+ // Things with export level C don't get instantiated in
+ // downstream crates.
+ if !id.is_local() {
+ return Visibility::Hidden;
+ }
+
+ // C-export level items remain at `Default`, all other internal
+ // items become `Hidden`.
+ match tcx.reachable_non_generics(id.krate).get(&id) {
+ Some(SymbolExportInfo { level: SymbolExportLevel::C, .. }) => Visibility::Default,
+ _ => Visibility::Hidden,
+ }
+}
diff --git a/compiler/rustc_monomorphize/src/partitioning/merging.rs b/compiler/rustc_monomorphize/src/partitioning/merging.rs
new file mode 100644
index 000000000..02bb8dea0
--- /dev/null
+++ b/compiler/rustc_monomorphize/src/partitioning/merging.rs
@@ -0,0 +1,111 @@
+use std::cmp;
+
+use rustc_data_structures::fx::FxHashMap;
+use rustc_hir::def_id::LOCAL_CRATE;
+use rustc_middle::mir::mono::{CodegenUnit, CodegenUnitNameBuilder};
+use rustc_span::symbol::Symbol;
+
+use super::PartitioningCx;
+use crate::partitioning::PreInliningPartitioning;
+
+pub fn merge_codegen_units<'tcx>(
+ cx: &PartitioningCx<'_, 'tcx>,
+ initial_partitioning: &mut PreInliningPartitioning<'tcx>,
+) {
+ assert!(cx.target_cgu_count >= 1);
+ let codegen_units = &mut initial_partitioning.codegen_units;
+
+ // Note that at this point in time the `codegen_units` here may not be in a
+ // deterministic order (but we know they're deterministically the same set).
+ // We want this merging to produce a deterministic ordering of codegen units
+ // from the input.
+ //
+ // Due to basically how we've implemented the merging below (merge the two
+ // smallest into each other) we're sure to start off with a deterministic
+ // order (sorted by name). This'll mean that if two cgus have the same size
+ // the stable sort below will keep everything nice and deterministic.
+ codegen_units.sort_by(|a, b| a.name().as_str().partial_cmp(b.name().as_str()).unwrap());
+
+ // This map keeps track of what got merged into what.
+ let mut cgu_contents: FxHashMap<Symbol, Vec<Symbol>> =
+ codegen_units.iter().map(|cgu| (cgu.name(), vec![cgu.name()])).collect();
+
+ // Merge the two smallest codegen units until the target size is reached.
+ while codegen_units.len() > cx.target_cgu_count {
+ // Sort small cgus to the back
+ codegen_units.sort_by_cached_key(|cgu| cmp::Reverse(cgu.size_estimate()));
+ let mut smallest = codegen_units.pop().unwrap();
+ let second_smallest = codegen_units.last_mut().unwrap();
+
+ // Move the mono-items from `smallest` to `second_smallest`
+ second_smallest.modify_size_estimate(smallest.size_estimate());
+ for (k, v) in smallest.items_mut().drain() {
+ second_smallest.items_mut().insert(k, v);
+ }
+
+ // Record that `second_smallest` now contains all the stuff that was in
+ // `smallest` before.
+ let mut consumed_cgu_names = cgu_contents.remove(&smallest.name()).unwrap();
+ cgu_contents.get_mut(&second_smallest.name()).unwrap().append(&mut consumed_cgu_names);
+
+ debug!(
+ "CodegenUnit {} merged into CodegenUnit {}",
+ smallest.name(),
+ second_smallest.name()
+ );
+ }
+
+ let cgu_name_builder = &mut CodegenUnitNameBuilder::new(cx.tcx);
+
+ if cx.tcx.sess.opts.incremental.is_some() {
+ // If we are doing incremental compilation, we want CGU names to
+ // reflect the path of the source level module they correspond to.
+ // For CGUs that contain the code of multiple modules because of the
+ // merging done above, we use a concatenation of the names of
+ // all contained CGUs.
+ let new_cgu_names: FxHashMap<Symbol, String> = cgu_contents
+ .into_iter()
+ // This `filter` makes sure we only update the name of CGUs that
+ // were actually modified by merging.
+ .filter(|(_, cgu_contents)| cgu_contents.len() > 1)
+ .map(|(current_cgu_name, cgu_contents)| {
+ let mut cgu_contents: Vec<&str> = cgu_contents.iter().map(|s| s.as_str()).collect();
+
+ // Sort the names, so things are deterministic and easy to
+ // predict.
+
+ // We are sorting primitive &strs here so we can use unstable sort
+ cgu_contents.sort_unstable();
+
+ (current_cgu_name, cgu_contents.join("--"))
+ })
+ .collect();
+
+ for cgu in codegen_units.iter_mut() {
+ if let Some(new_cgu_name) = new_cgu_names.get(&cgu.name()) {
+ if cx.tcx.sess.opts.unstable_opts.human_readable_cgu_names {
+ cgu.set_name(Symbol::intern(&new_cgu_name));
+ } else {
+ // If we don't require CGU names to be human-readable, we
+ // use a fixed length hash of the composite CGU name
+ // instead.
+ let new_cgu_name = CodegenUnit::mangle_name(&new_cgu_name);
+ cgu.set_name(Symbol::intern(&new_cgu_name));
+ }
+ }
+ }
+ } else {
+ // If we are compiling non-incrementally we just generate simple CGU
+ // names containing an index.
+ for (index, cgu) in codegen_units.iter_mut().enumerate() {
+ cgu.set_name(numbered_codegen_unit_name(cgu_name_builder, index));
+ }
+ }
+}
+
+fn numbered_codegen_unit_name(
+ name_builder: &mut CodegenUnitNameBuilder<'_>,
+ index: usize,
+) -> Symbol {
+ name_builder.build_cgu_name_no_mangle(LOCAL_CRATE, &["cgu"], Some(index))
+}
diff --git a/compiler/rustc_monomorphize/src/partitioning/mod.rs b/compiler/rustc_monomorphize/src/partitioning/mod.rs
new file mode 100644
index 000000000..ff2d38693
--- /dev/null
+++ b/compiler/rustc_monomorphize/src/partitioning/mod.rs
@@ -0,0 +1,515 @@
+//! Partitioning Codegen Units for Incremental Compilation
+//! ======================================================
+//!
+//! The task of this module is to take the complete set of monomorphizations of
+//! a crate and produce a set of codegen units from it, where a codegen unit
+//! is a named set of (mono-item, linkage) pairs. That is, this module
+//! decides which monomorphization appears in which codegen units with which
+//! linkage. The following paragraphs describe some of the background on the
+//! partitioning scheme.
+//!
+//! The most important opportunity for saving on compilation time with
+//! incremental compilation is to avoid re-codegenning and re-optimizing code.
+//! Since the unit of codegen and optimization for LLVM is "modules" or, how
+//! we call them "codegen units", the particulars of how much time can be saved
+//! by incremental compilation are tightly linked to how the output program is
+//! partitioned into these codegen units prior to passing it to LLVM --
+//! especially because we have to treat codegen units as opaque entities once
+//! they are created: There is no way for us to incrementally update an existing
+//! LLVM module and so we have to build any such module from scratch if it was
+//! affected by some change in the source code.
+//!
+//! From that point of view it would make sense to maximize the number of
+//! codegen units by, for example, putting each function into its own module.
+//! That way only those modules would have to be re-compiled that were actually
+//! affected by some change, minimizing the number of functions that could have
+//! been re-used but just happened to be located in a module that is
+//! re-compiled.
+//!
+//! However, since LLVM optimization does not work across module boundaries,
+//! using such a highly granular partitioning would lead to very slow runtime
+//! code since it would effectively prohibit inlining and other inter-procedure
+//! optimizations. We want to avoid that as much as possible.
+//!
+//! Thus we end up with a trade-off: The bigger the codegen units, the better
+//! LLVM's optimizer can do its work, but also the smaller the compilation time
+//! reduction we get from incremental compilation.
+//!
+//! Ideally, we would create a partitioning such that there are few big codegen
+//! units with few interdependencies between them. For now though, we use the
+//! following heuristic to determine the partitioning:
+//!
+//! - There are two codegen units for every source-level module:
+//! - One for "stable", that is non-generic, code
+//! - One for more "volatile" code, i.e., monomorphized instances of functions
+//! defined in that module
+//!
+//! In order to see why this heuristic makes sense, let's take a look at when a
+//! codegen unit can get invalidated:
+//!
+//! 1. The most straightforward case is when the BODY of a function or global
+//! changes. Then any codegen unit containing the code for that item has to be
+//! re-compiled. Note that this includes all codegen units where the function
+//! has been inlined.
+//!
+//! 2. The next case is when the SIGNATURE of a function or global changes. In
+//! this case, all codegen units containing a REFERENCE to that item have to be
+//! re-compiled. This is a superset of case 1.
+//!
+//! 3. The final and most subtle case is when a REFERENCE to a generic function
+//! is added or removed somewhere. Even though the definition of the function
+//! might be unchanged, a new REFERENCE might introduce a new monomorphized
+//! instance of this function which has to be placed and compiled somewhere.
+//! Conversely, when removing a REFERENCE, it might have been the last one with
+//! that particular set of generic arguments and thus we have to remove it.
+//!
+//! From the above we see that just using one codegen unit per source-level
+//! module is not such a good idea, since just adding a REFERENCE to some
+//! generic item somewhere else would invalidate everything within the module
+//! containing the generic item. The heuristic above reduces this detrimental
+//! side-effect of references a little by at least not touching the non-generic
+//! code of the module.
+//!
+//! A Note on Inlining
+//! ------------------
+//! As briefly mentioned above, in order for LLVM to be able to inline a
+//! function call, the body of the function has to be available in the LLVM
+//! module where the call is made. This has a few consequences for partitioning:
+//!
+//! - The partitioning algorithm has to take care of placing functions into all
+//! codegen units where they should be available for inlining. It also has to
+//! decide on the correct linkage for these functions.
+//!
+//! - The partitioning algorithm has to know which functions are likely to get
+//! inlined, so it can distribute function instantiations accordingly. Since
+//! there is no way of knowing for sure which functions LLVM will decide to
+//! inline in the end, we apply a heuristic here: Only functions marked with
+//! `#[inline]` are considered for inlining by the partitioner. The current
+//! implementation will not try to determine if a function is likely to be
+//! inlined by looking at the functions definition.
+//!
+//! Note though that as a side-effect of creating a codegen units per
+//! source-level module, functions from the same module will be available for
+//! inlining, even when they are not marked `#[inline]`.
+
+mod default;
+mod merging;
+
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::sync;
+use rustc_hir::def_id::DefIdSet;
+use rustc_middle::mir;
+use rustc_middle::mir::mono::MonoItem;
+use rustc_middle::mir::mono::{CodegenUnit, Linkage};
+use rustc_middle::ty::print::with_no_trimmed_paths;
+use rustc_middle::ty::query::Providers;
+use rustc_middle::ty::TyCtxt;
+use rustc_span::symbol::Symbol;
+
+use crate::collector::InliningMap;
+use crate::collector::{self, MonoItemCollectionMode};
+
+pub struct PartitioningCx<'a, 'tcx> {
+ tcx: TyCtxt<'tcx>,
+ target_cgu_count: usize,
+ inlining_map: &'a InliningMap<'tcx>,
+}
+
+trait Partitioner<'tcx> {
+ fn place_root_mono_items(
+ &mut self,
+ cx: &PartitioningCx<'_, 'tcx>,
+ mono_items: &mut dyn Iterator<Item = MonoItem<'tcx>>,
+ ) -> PreInliningPartitioning<'tcx>;
+
+ fn merge_codegen_units(
+ &mut self,
+ cx: &PartitioningCx<'_, 'tcx>,
+ initial_partitioning: &mut PreInliningPartitioning<'tcx>,
+ );
+
+ fn place_inlined_mono_items(
+ &mut self,
+ cx: &PartitioningCx<'_, 'tcx>,
+ initial_partitioning: PreInliningPartitioning<'tcx>,
+ ) -> PostInliningPartitioning<'tcx>;
+
+ fn internalize_symbols(
+ &mut self,
+ cx: &PartitioningCx<'_, 'tcx>,
+ partitioning: &mut PostInliningPartitioning<'tcx>,
+ );
+}
+
+fn get_partitioner<'tcx>(tcx: TyCtxt<'tcx>) -> Box<dyn Partitioner<'tcx>> {
+ let strategy = match &tcx.sess.opts.unstable_opts.cgu_partitioning_strategy {
+ None => "default",
+ Some(s) => &s[..],
+ };
+
+ match strategy {
+ "default" => Box::new(default::DefaultPartitioning),
+ _ => tcx.sess.fatal("unknown partitioning strategy"),
+ }
+}
+
+pub fn partition<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ mono_items: &mut dyn Iterator<Item = MonoItem<'tcx>>,
+ max_cgu_count: usize,
+ inlining_map: &InliningMap<'tcx>,
+) -> Vec<CodegenUnit<'tcx>> {
+ let _prof_timer = tcx.prof.generic_activity("cgu_partitioning");
+
+ let mut partitioner = get_partitioner(tcx);
+ let cx = &PartitioningCx { tcx, target_cgu_count: max_cgu_count, inlining_map };
+ // In the first step, we place all regular monomorphizations into their
+ // respective 'home' codegen unit. Regular monomorphizations are all
+ // functions and statics defined in the local crate.
+ let mut initial_partitioning = {
+ let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_place_roots");
+ partitioner.place_root_mono_items(cx, mono_items)
+ };
+
+ initial_partitioning.codegen_units.iter_mut().for_each(|cgu| cgu.estimate_size(tcx));
+
+ debug_dump(tcx, "INITIAL PARTITIONING:", initial_partitioning.codegen_units.iter());
+
+ // Merge until we have at most `max_cgu_count` codegen units.
+ {
+ let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_merge_cgus");
+ partitioner.merge_codegen_units(cx, &mut initial_partitioning);
+ debug_dump(tcx, "POST MERGING:", initial_partitioning.codegen_units.iter());
+ }
+
+ // In the next step, we use the inlining map to determine which additional
+ // monomorphizations have to go into each codegen unit. These additional
+ // monomorphizations can be drop-glue, functions from external crates, and
+ // local functions the definition of which is marked with `#[inline]`.
+ let mut post_inlining = {
+ let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_place_inline_items");
+ partitioner.place_inlined_mono_items(cx, initial_partitioning)
+ };
+
+ post_inlining.codegen_units.iter_mut().for_each(|cgu| cgu.estimate_size(tcx));
+
+ debug_dump(tcx, "POST INLINING:", post_inlining.codegen_units.iter());
+
+ // Next we try to make as many symbols "internal" as possible, so LLVM has
+ // more freedom to optimize.
+ if !tcx.sess.link_dead_code() {
+ let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_internalize_symbols");
+ partitioner.internalize_symbols(cx, &mut post_inlining);
+ }
+
+ let instrument_dead_code =
+ tcx.sess.instrument_coverage() && !tcx.sess.instrument_coverage_except_unused_functions();
+
+ if instrument_dead_code {
+ assert!(
+ post_inlining.codegen_units.len() > 0,
+ "There must be at least one CGU that code coverage data can be generated in."
+ );
+
+ // Find the smallest CGU that has exported symbols and put the dead
+ // function stubs in that CGU. We look for exported symbols to increase
+ // the likelihood the linker won't throw away the dead functions.
+ // FIXME(#92165): In order to truly resolve this, we need to make sure
+ // the object file (CGU) containing the dead function stubs is included
+ // in the final binary. This will probably require forcing these
+ // function symbols to be included via `-u` or `/include` linker args.
+ let mut cgus: Vec<_> = post_inlining.codegen_units.iter_mut().collect();
+ cgus.sort_by_key(|cgu| cgu.size_estimate());
+
+ let dead_code_cgu =
+ if let Some(cgu) = cgus.into_iter().rev().find(|cgu| {
+ cgu.items().iter().any(|(_, (linkage, _))| *linkage == Linkage::External)
+ }) {
+ cgu
+ } else {
+ // If there are no CGUs that have externally linked items,
+ // then we just pick the first CGU as a fallback.
+ &mut post_inlining.codegen_units[0]
+ };
+ dead_code_cgu.make_code_coverage_dead_code_cgu();
+ }
+
+ // Finally, sort by codegen unit name, so that we get deterministic results.
+ let PostInliningPartitioning {
+ codegen_units: mut result,
+ mono_item_placements: _,
+ internalization_candidates: _,
+ } = post_inlining;
+
+ result.sort_by(|a, b| a.name().as_str().partial_cmp(b.name().as_str()).unwrap());
+
+ result
+}
+
+pub struct PreInliningPartitioning<'tcx> {
+ codegen_units: Vec<CodegenUnit<'tcx>>,
+ roots: FxHashSet<MonoItem<'tcx>>,
+ internalization_candidates: FxHashSet<MonoItem<'tcx>>,
+}
+
+/// For symbol internalization, we need to know whether a symbol/mono-item is
+/// accessed from outside the codegen unit it is defined in. This type is used
+/// to keep track of that.
+#[derive(Clone, PartialEq, Eq, Debug)]
+enum MonoItemPlacement {
+ SingleCgu { cgu_name: Symbol },
+ MultipleCgus,
+}
+
+struct PostInliningPartitioning<'tcx> {
+ codegen_units: Vec<CodegenUnit<'tcx>>,
+ mono_item_placements: FxHashMap<MonoItem<'tcx>, MonoItemPlacement>,
+ internalization_candidates: FxHashSet<MonoItem<'tcx>>,
+}
+
+fn debug_dump<'a, 'tcx, I>(tcx: TyCtxt<'tcx>, label: &str, cgus: I)
+where
+ I: Iterator<Item = &'a CodegenUnit<'tcx>>,
+ 'tcx: 'a,
+{
+ let dump = move || {
+ use std::fmt::Write;
+
+ let s = &mut String::new();
+ let _ = writeln!(s, "{}", label);
+ for cgu in cgus {
+ let _ =
+ writeln!(s, "CodegenUnit {} estimated size {} :", cgu.name(), cgu.size_estimate());
+
+ for (mono_item, linkage) in cgu.items() {
+ let symbol_name = mono_item.symbol_name(tcx).name;
+ let symbol_hash_start = symbol_name.rfind('h');
+ let symbol_hash = symbol_hash_start.map_or("<no hash>", |i| &symbol_name[i..]);
+
+ let _ = writeln!(
+ s,
+ " - {} [{:?}] [{}] estimated size {}",
+ mono_item,
+ linkage,
+ symbol_hash,
+ mono_item.size_estimate(tcx)
+ );
+ }
+
+ let _ = writeln!(s, "");
+ }
+
+ std::mem::take(s)
+ };
+
+ debug!("{}", dump());
+}
+
+#[inline(never)] // give this a place in the profiler
+fn assert_symbols_are_distinct<'a, 'tcx, I>(tcx: TyCtxt<'tcx>, mono_items: I)
+where
+ I: Iterator<Item = &'a MonoItem<'tcx>>,
+ 'tcx: 'a,
+{
+ let _prof_timer = tcx.prof.generic_activity("assert_symbols_are_distinct");
+
+ let mut symbols: Vec<_> =
+ mono_items.map(|mono_item| (mono_item, mono_item.symbol_name(tcx))).collect();
+
+ symbols.sort_by_key(|sym| sym.1);
+
+ for &[(mono_item1, ref sym1), (mono_item2, ref sym2)] in symbols.array_windows() {
+ if sym1 == sym2 {
+ let span1 = mono_item1.local_span(tcx);
+ let span2 = mono_item2.local_span(tcx);
+
+ // Deterministically select one of the spans for error reporting
+ let span = match (span1, span2) {
+ (Some(span1), Some(span2)) => {
+ Some(if span1.lo().0 > span2.lo().0 { span1 } else { span2 })
+ }
+ (span1, span2) => span1.or(span2),
+ };
+
+ let error_message = format!("symbol `{}` is already defined", sym1);
+
+ if let Some(span) = span {
+ tcx.sess.span_fatal(span, &error_message)
+ } else {
+ tcx.sess.fatal(&error_message)
+ }
+ }
+ }
+}
+
+fn collect_and_partition_mono_items<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ (): (),
+) -> (&'tcx DefIdSet, &'tcx [CodegenUnit<'tcx>]) {
+ let collection_mode = match tcx.sess.opts.unstable_opts.print_mono_items {
+ Some(ref s) => {
+ let mode_string = s.to_lowercase();
+ let mode_string = mode_string.trim();
+ if mode_string == "eager" {
+ MonoItemCollectionMode::Eager
+ } else {
+ if mode_string != "lazy" {
+ let message = format!(
+ "Unknown codegen-item collection mode '{}'. \
+ Falling back to 'lazy' mode.",
+ mode_string
+ );
+ tcx.sess.warn(&message);
+ }
+
+ MonoItemCollectionMode::Lazy
+ }
+ }
+ None => {
+ if tcx.sess.link_dead_code() {
+ MonoItemCollectionMode::Eager
+ } else {
+ MonoItemCollectionMode::Lazy
+ }
+ }
+ };
+
+ let (items, inlining_map) = collector::collect_crate_mono_items(tcx, collection_mode);
+
+ tcx.sess.abort_if_errors();
+
+ let (codegen_units, _) = tcx.sess.time("partition_and_assert_distinct_symbols", || {
+ sync::join(
+ || {
+ let mut codegen_units = partition(
+ tcx,
+ &mut items.iter().cloned(),
+ tcx.sess.codegen_units(),
+ &inlining_map,
+ );
+ codegen_units[0].make_primary();
+ &*tcx.arena.alloc_from_iter(codegen_units)
+ },
+ || assert_symbols_are_distinct(tcx, items.iter()),
+ )
+ });
+
+ if tcx.prof.enabled() {
+ // Record CGU size estimates for self-profiling.
+ for cgu in codegen_units {
+ tcx.prof.artifact_size(
+ "codegen_unit_size_estimate",
+ cgu.name().as_str(),
+ cgu.size_estimate() as u64,
+ );
+ }
+ }
+
+ let mono_items: DefIdSet = items
+ .iter()
+ .filter_map(|mono_item| match *mono_item {
+ MonoItem::Fn(ref instance) => Some(instance.def_id()),
+ MonoItem::Static(def_id) => Some(def_id),
+ _ => None,
+ })
+ .collect();
+
+ if tcx.sess.opts.unstable_opts.print_mono_items.is_some() {
+ let mut item_to_cgus: FxHashMap<_, Vec<_>> = Default::default();
+
+ for cgu in codegen_units {
+ for (&mono_item, &linkage) in cgu.items() {
+ item_to_cgus.entry(mono_item).or_default().push((cgu.name(), linkage));
+ }
+ }
+
+ let mut item_keys: Vec<_> = items
+ .iter()
+ .map(|i| {
+ let mut output = with_no_trimmed_paths!(i.to_string());
+ output.push_str(" @@");
+ let mut empty = Vec::new();
+ let cgus = item_to_cgus.get_mut(i).unwrap_or(&mut empty);
+ cgus.sort_by_key(|(name, _)| *name);
+ cgus.dedup();
+ for &(ref cgu_name, (linkage, _)) in cgus.iter() {
+ output.push(' ');
+ output.push_str(cgu_name.as_str());
+
+ let linkage_abbrev = match linkage {
+ Linkage::External => "External",
+ Linkage::AvailableExternally => "Available",
+ Linkage::LinkOnceAny => "OnceAny",
+ Linkage::LinkOnceODR => "OnceODR",
+ Linkage::WeakAny => "WeakAny",
+ Linkage::WeakODR => "WeakODR",
+ Linkage::Appending => "Appending",
+ Linkage::Internal => "Internal",
+ Linkage::Private => "Private",
+ Linkage::ExternalWeak => "ExternalWeak",
+ Linkage::Common => "Common",
+ };
+
+ output.push('[');
+ output.push_str(linkage_abbrev);
+ output.push(']');
+ }
+ output
+ })
+ .collect();
+
+ item_keys.sort();
+
+ for item in item_keys {
+ println!("MONO_ITEM {}", item);
+ }
+ }
+
+ (tcx.arena.alloc(mono_items), codegen_units)
+}
+
+fn codegened_and_inlined_items<'tcx>(tcx: TyCtxt<'tcx>, (): ()) -> &'tcx DefIdSet {
+ let (items, cgus) = tcx.collect_and_partition_mono_items(());
+ let mut visited = DefIdSet::default();
+ let mut result = items.clone();
+
+ for cgu in cgus {
+ for (item, _) in cgu.items() {
+ if let MonoItem::Fn(ref instance) = item {
+ let did = instance.def_id();
+ if !visited.insert(did) {
+ continue;
+ }
+ let body = tcx.instance_mir(instance.def);
+ for block in body.basic_blocks() {
+ for statement in &block.statements {
+ let mir::StatementKind::Coverage(_) = statement.kind else { continue };
+ let scope = statement.source_info.scope;
+ if let Some(inlined) = scope.inlined_instance(&body.source_scopes) {
+ result.insert(inlined.def_id());
+ }
+ }
+ }
+ }
+ }
+ }
+
+ tcx.arena.alloc(result)
+}
+
+pub fn provide(providers: &mut Providers) {
+ providers.collect_and_partition_mono_items = collect_and_partition_mono_items;
+ providers.codegened_and_inlined_items = codegened_and_inlined_items;
+
+ providers.is_codegened_item = |tcx, def_id| {
+ let (all_mono_items, _) = tcx.collect_and_partition_mono_items(());
+ all_mono_items.contains(&def_id)
+ };
+
+ providers.codegen_unit = |tcx, name| {
+ let (_, all) = tcx.collect_and_partition_mono_items(());
+ all.iter()
+ .find(|cgu| cgu.name() == name)
+ .unwrap_or_else(|| panic!("failed to find cgu with name {:?}", name))
+ };
+}