diff options
Diffstat (limited to 'compiler/rustc_monomorphize/src/partitioning/default.rs')
| -rw-r--r-- | compiler/rustc_monomorphize/src/partitioning/default.rs | 560 |
1 files changed, 560 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, + } +} |