diff options
| -rw-r--r-- | src/librustc_mir/monomorphize/partitioning/default.rs (renamed from src/librustc_mir/monomorphize/partitioning.rs) | 845 | ||||
| -rw-r--r-- | src/librustc_mir/monomorphize/partitioning/merging.rs | 110 | ||||
| -rw-r--r-- | src/librustc_mir/monomorphize/partitioning/mod.rs | 425 |
3 files changed, 704 insertions, 676 deletions
diff --git a/src/librustc_mir/monomorphize/partitioning.rs b/src/librustc_mir/monomorphize/partitioning/default.rs index 8216f056951..b48bae83787 100644 --- a/src/librustc_mir/monomorphize/partitioning.rs +++ b/src/librustc_mir/monomorphize/partitioning/default.rs @@ -1,418 +1,24 @@ -//! 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]`. - -use std::cmp; use std::collections::hash_map::Entry; use rustc_data_structures::fx::{FxHashMap, FxHashSet}; -use rustc_data_structures::sync; use rustc_hir::def::DefKind; -use rustc_hir::def_id::{CrateNum, DefId, DefIdSet, CRATE_DEF_INDEX, LOCAL_CRATE}; +use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE}; use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags; use rustc_middle::middle::exported_symbols::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::query::Providers; use rustc_middle::ty::{self, DefIdTree, InstanceDef, TyCtxt}; -use rustc_span::symbol::{Symbol, SymbolStr}; +use rustc_span::symbol::Symbol; use crate::monomorphize::collector::InliningMap; -use crate::monomorphize::collector::{self, MonoItemCollectionMode}; - -trait Partitioner<'tcx> { - fn place_root_mono_items( - &mut self, - tcx: TyCtxt<'tcx>, - mono_items: &mut dyn Iterator<Item = MonoItem<'tcx>>, - ) -> PreInliningPartitioning<'tcx>; - - fn merge_codegen_units( - &mut self, - tcx: TyCtxt<'tcx>, - initial_partitioning: &mut PreInliningPartitioning<'tcx>, - target_cgu_count: usize, - ); - - fn place_inlined_mono_items( - &mut self, - initial_partitioning: PreInliningPartitioning<'tcx>, - inlining_map: &InliningMap<'tcx>, - ) -> PostInliningPartitioning<'tcx>; - - fn internalize_symbols( - &mut self, - tcx: TyCtxt<'tcx>, - partitioning: &mut PostInliningPartitioning<'tcx>, - inlining_map: &InliningMap<'tcx>, - ); -} - -// 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")) -} +use crate::monomorphize::partitioning::merging; +use crate::monomorphize::partitioning::{ + MonoItemPlacement, Partitioner, PostInliningPartitioning, PreInliningPartitioning, +}; pub struct DefaultPartitioning; -fn get_partitioner<'tcx>() -> Box<dyn Partitioner<'tcx>> { - Box::new(DefaultPartitioning) -} - -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(); - // 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(tcx, 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(tcx, &mut initial_partitioning, max_cgu_count); - 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(initial_partitioning, inlining_map) - }; - - 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.opts.cg.link_dead_code != Some(true) { - let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_internalize_symbols"); - partitioner.internalize_symbols(tcx, &mut post_inlining, inlining_map); - } - - // 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_cached_key(|cgu| cgu.name().as_str()); - - result -} - -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 mono_item_linkage_and_visibility( - 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) -} - -fn mono_item_visibility( - 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(hir_id) => { - let def_id = tcx.hir().local_def_id(*hir_id); - return if tcx.is_reachable_non_generic(def_id) { - *can_be_internalized = false; - default_visibility(tcx, 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. - if !def_id.is_local() { - return if export_generics && is_generic { - // If it is a 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, 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) { - *can_be_internalized = false; - debug_assert!(!is_generic); - return default_visibility(tcx, 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 referenceable 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.target.options.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(SymbolExportLevel::C) => Visibility::Default, - _ => Visibility::Hidden, - } -} - impl<'tcx> Partitioner<'tcx> for DefaultPartitioning { fn place_root_mono_items( &mut self, @@ -495,96 +101,7 @@ impl<'tcx> Partitioner<'tcx> for DefaultPartitioning { initial_partitioning: &mut PreInliningPartitioning<'tcx>, target_cgu_count: usize, ) { - assert!(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_cached_key(|cgu| cgu.name().as_str()); - - // This map keeps track of what got merged into what. - let mut cgu_contents: FxHashMap<Symbol, Vec<SymbolStr>> = - codegen_units.iter().map(|cgu| (cgu.name(), vec![cgu.name().as_str()])).collect(); - - // Merge the two smallest codegen units until the target size is reached. - while codegen_units.len() > 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() - .extend(consumed_cgu_names.drain(..)); - - debug!( - "CodegenUnit {} merged into CodegenUnit {}", - smallest.name(), - second_smallest.name() - ); - } - - let cgu_name_builder = &mut CodegenUnitNameBuilder::new(tcx); - - if 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[..]).collect(); - - // Sort the names, so things are deterministic and easy to - // predict. - cgu_contents.sort(); - - (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 tcx.sess.opts.debugging_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)); - } - } + merging::merge_codegen_units(tcx, initial_partitioning, target_cgu_count); } fn place_inlined_mono_items( @@ -621,7 +138,7 @@ impl<'tcx> Partitioner<'tcx> for DefaultPartitioning { if roots.contains(&mono_item) { bug!( "GloballyShared mono-item inlined into other CGU: \ - {:?}", + {:?}", mono_item ); } @@ -800,8 +317,6 @@ fn characteristic_def_id_of_mono_item<'tcx>( } } -type CguNameCache = FxHashMap<(DefId, bool), Symbol>; - fn compute_codegen_unit_name( tcx: TyCtxt<'_>, name_builder: &mut CodegenUnitNameBuilder<'_>, @@ -847,213 +362,191 @@ fn compute_codegen_unit_name( }) } -fn numbered_codegen_unit_name( - name_builder: &mut CodegenUnitNameBuilder<'_>, - index: usize, -) -> Symbol { - name_builder.build_cgu_name_no_mangle(LOCAL_CRATE, &["cgu"], Some(index)) +// 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 debug_dump<'a, 'tcx, I>(tcx: TyCtxt<'tcx>, label: &str, cgus: I) -where - I: Iterator<Item = &'a CodegenUnit<'tcx>>, - 'tcx: 'a, -{ - if cfg!(debug_assertions) { - debug!("{}", label); - for cgu in cgus { - debug!("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(|i| &symbol_name[i..]).unwrap_or("<no hash>"); - - debug!( - " - {} [{:?}] [{}] estimated size {}", - mono_item.to_string(tcx, true), - linkage, - symbol_hash, - mono_item.size_estimate(tcx) - ); - } - - debug!(""); - } +fn mono_item_linkage_and_visibility( + 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) } -#[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(); +type CguNameCache = FxHashMap<(DefId, bool), Symbol>; - symbols.sort_by_key(|sym| sym.1); +fn mono_item_visibility( + 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, - for pair in symbols.windows(2) { - let sym1 = &pair[0].1; - let sym2 = &pair[1].1; + // 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(hir_id) => { + let def_id = tcx.hir().local_def_id(*hir_id); + return if tcx.is_reachable_non_generic(def_id) { + *can_be_internalized = false; + default_visibility(tcx, def_id.to_def_id(), false) + } else { + Visibility::Hidden + }; + } + }; - if sym1 == sym2 { - let mono_item1 = pair[0].0; - let mono_item2 = pair[1].0; + let def_id = match instance.def { + InstanceDef::Item(def) => def.did, + InstanceDef::DropGlue(def_id, Some(_)) => def_id, - let span1 = mono_item1.local_span(tcx); - let span2 = mono_item2.local_span(tcx); + // 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, + }; - // 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), - }; + // 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 error_message = format!("symbol `{}` is already defined", sym1); + let is_generic = instance.substs.non_erasable_generics().next().is_some(); - if let Some(span) = span { - tcx.sess.span_fatal(span, &error_message) - } else { - tcx.sess.fatal(&error_message) - } - } + // Upstream `DefId` instances get different handling than local ones. + if !def_id.is_local() { + return if export_generics && is_generic { + // If it is a 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 + }; } -} -fn collect_and_partition_mono_items( - tcx: TyCtxt<'tcx>, - cnum: CrateNum, -) -> (&'tcx DefIdSet, &'tcx [CodegenUnit<'tcx>]) { - assert_eq!(cnum, LOCAL_CRATE); - - let collection_mode = match tcx.sess.opts.debugging_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 + 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 { - 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 + // This instance might be useful in a downstream crate. + *can_be_internalized = false; + default_visibility(tcx, 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 } - None => { - if tcx.sess.opts.cg.link_dead_code == Some(true) { - MonoItemCollectionMode::Eager - } else { - MonoItemCollectionMode::Lazy - } + } 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) { + *can_be_internalized = false; + debug_assert!(!is_generic); + return default_visibility(tcx, def_id, false); } - }; - 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( - || { - &*tcx.arena.alloc_from_iter(partition( - tcx, - &mut items.iter().cloned(), - tcx.sess.codegen_units(), - &inlining_map, - )) - }, - || assert_symbols_are_distinct(tcx, items.iter()), - ) - }); - - 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.debugging_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)); - } + // 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 referenceable 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; } - let mut item_keys: Vec<_> = items - .iter() - .map(|i| { - let mut output = i.to_string(tcx, false); - 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_str(" "); - 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_str("["); - output.push_str(linkage_abbrev); - output.push_str("]"); - } - output - }) - .collect(); - - item_keys.sort(); - - for item in item_keys { - println!("MONO_ITEM {}", item); - } + Visibility::Hidden } - - (tcx.arena.alloc(mono_items), codegen_units) } -pub fn provide(providers: &mut Providers) { - providers.collect_and_partition_mono_items = collect_and_partition_mono_items; +fn default_visibility(tcx: TyCtxt<'_>, id: DefId, is_generic: bool) -> Visibility { + if !tcx.sess.target.target.options.default_hidden_visibility { + return Visibility::Default; + } - providers.is_codegened_item = |tcx, def_id| { - let (all_mono_items, _) = tcx.collect_and_partition_mono_items(LOCAL_CRATE); - all_mono_items.contains(&def_id) - }; + // Generic functions never have export-level C. + if is_generic { + return Visibility::Hidden; + } - providers.codegen_unit = |tcx, name| { - let (_, all) = tcx.collect_and_partition_mono_items(LOCAL_CRATE); - all.iter() - .find(|cgu| cgu.name() == name) - .unwrap_or_else(|| panic!("failed to find cgu with name {:?}", name)) - }; + // 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(SymbolExportLevel::C) => Visibility::Default, + _ => Visibility::Hidden, + } } diff --git a/src/librustc_mir/monomorphize/partitioning/merging.rs b/src/librustc_mir/monomorphize/partitioning/merging.rs new file mode 100644 index 00000000000..1787e6df1b9 --- /dev/null +++ b/src/librustc_mir/monomorphize/partitioning/merging.rs @@ -0,0 +1,110 @@ +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_middle::ty::TyCtxt; +use rustc_span::symbol::{Symbol, SymbolStr}; + +use crate::monomorphize::partitioning::PreInliningPartitioning; + +pub fn merge_codegen_units<'tcx>( + tcx: TyCtxt<'tcx>, + initial_partitioning: &mut PreInliningPartitioning<'tcx>, + target_cgu_count: usize, +) { + assert!(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_cached_key(|cgu| cgu.name().as_str()); + + // This map keeps track of what got merged into what. + let mut cgu_contents: FxHashMap<Symbol, Vec<SymbolStr>> = + codegen_units.iter().map(|cgu| (cgu.name(), vec![cgu.name().as_str()])).collect(); + + // Merge the two smallest codegen units until the target size is reached. + while codegen_units.len() > 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().extend(consumed_cgu_names.drain(..)); + + debug!( + "CodegenUnit {} merged into CodegenUnit {}", + smallest.name(), + second_smallest.name() + ); + } + + let cgu_name_builder = &mut CodegenUnitNameBuilder::new(tcx); + + if 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[..]).collect(); + + // Sort the names, so things are deterministic and easy to + // predict. + cgu_contents.sort(); + + (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 tcx.sess.opts.debugging_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/src/librustc_mir/monomorphize/partitioning/mod.rs b/src/librustc_mir/monomorphize/partitioning/mod.rs new file mode 100644 index 00000000000..5526382d3a9 --- /dev/null +++ b/src/librustc_mir/monomorphize/partitioning/mod.rs @@ -0,0 +1,425 @@ +//! 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::{CrateNum, DefIdSet, LOCAL_CRATE}; +use rustc_middle::mir::mono::MonoItem; +use rustc_middle::mir::mono::{CodegenUnit, Linkage}; +use rustc_middle::ty::query::Providers; +use rustc_middle::ty::TyCtxt; +use rustc_span::symbol::Symbol; + +use crate::monomorphize::collector::InliningMap; +use crate::monomorphize::collector::{self, MonoItemCollectionMode}; + +trait Partitioner<'tcx> { + fn place_root_mono_items( + &mut self, + tcx: TyCtxt<'tcx>, + mono_items: &mut dyn Iterator<Item = MonoItem<'tcx>>, + ) -> PreInliningPartitioning<'tcx>; + + fn merge_codegen_units( + &mut self, + tcx: TyCtxt<'tcx>, + initial_partitioning: &mut PreInliningPartitioning<'tcx>, + target_cgu_count: usize, + ); + + fn place_inlined_mono_items( + &mut self, + initial_partitioning: PreInliningPartitioning<'tcx>, + inlining_map: &InliningMap<'tcx>, + ) -> PostInliningPartitioning<'tcx>; + + fn internalize_symbols( + &mut self, + tcx: TyCtxt<'tcx>, + partitioning: &mut PostInliningPartitioning<'tcx>, + inlining_map: &InliningMap<'tcx>, + ); +} + +fn get_partitioner<'tcx>() -> Box<dyn Partitioner<'tcx>> { + Box::new(default::DefaultPartitioning) +} + +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(); + // 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(tcx, 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(tcx, &mut initial_partitioning, max_cgu_count); + 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(initial_partitioning, inlining_map) + }; + + 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.opts.cg.link_dead_code != Some(true) { + let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_internalize_symbols"); + partitioner.internalize_symbols(tcx, &mut post_inlining, inlining_map); + } + + // 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_cached_key(|cgu| cgu.name().as_str()); + + 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, +{ + if cfg!(debug_assertions) { + debug!("{}", label); + for cgu in cgus { + debug!("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(|i| &symbol_name[i..]).unwrap_or("<no hash>"); + + debug!( + " - {} [{:?}] [{}] estimated size {}", + mono_item.to_string(tcx, true), + linkage, + symbol_hash, + mono_item.size_estimate(tcx) + ); + } + + debug!(""); + } + } +} + +#[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 pair in symbols.windows(2) { + let sym1 = &pair[0].1; + let sym2 = &pair[1].1; + + if sym1 == sym2 { + let mono_item1 = pair[0].0; + let mono_item2 = pair[1].0; + + 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>, + cnum: CrateNum, +) -> (&'tcx DefIdSet, &'tcx [CodegenUnit<'tcx>]) { + assert_eq!(cnum, LOCAL_CRATE); + + let collection_mode = match tcx.sess.opts.debugging_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.opts.cg.link_dead_code == Some(true) { + 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( + || { + &*tcx.arena.alloc_from_iter(partition( + tcx, + &mut items.iter().cloned(), + tcx.sess.codegen_units(), + &inlining_map, + )) + }, + || assert_symbols_are_distinct(tcx, items.iter()), + ) + }); + + 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.debugging_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 = i.to_string(tcx, false); + 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_str(" "); + 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_str("["); + output.push_str(linkage_abbrev); + output.push_str("]"); + } + output + }) + .collect(); + + item_keys.sort(); + + for item in item_keys { + println!("MONO_ITEM {}", item); + } + } + + (tcx.arena.alloc(mono_items), codegen_units) +} + +pub fn provide(providers: &mut Providers) { + providers.collect_and_partition_mono_items = collect_and_partition_mono_items; + + providers.is_codegened_item = |tcx, def_id| { + let (all_mono_items, _) = tcx.collect_and_partition_mono_items(LOCAL_CRATE); + all_mono_items.contains(&def_id) + }; + + providers.codegen_unit = |tcx, name| { + let (_, all) = tcx.collect_and_partition_mono_items(LOCAL_CRATE); + all.iter() + .find(|cgu| cgu.name() == name) + .unwrap_or_else(|| panic!("failed to find cgu with name {:?}", name)) + }; +} |