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Diffstat (limited to 'compiler/rustc_monomorphize/src/partitioning/mod.rs')
| -rw-r--r-- | compiler/rustc_monomorphize/src/partitioning/mod.rs | 673 |
1 files changed, 0 insertions, 673 deletions
diff --git a/compiler/rustc_monomorphize/src/partitioning/mod.rs b/compiler/rustc_monomorphize/src/partitioning/mod.rs deleted file mode 100644 index d0b23ca9e..000000000 --- a/compiler/rustc_monomorphize/src/partitioning/mod.rs +++ /dev/null @@ -1,673 +0,0 @@ -//! 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; - -use std::cmp; -use std::fs::{self, File}; -use std::io::{BufWriter, Write}; -use std::path::{Path, PathBuf}; - -use rustc_data_structures::fx::{FxHashMap, FxHashSet}; -use rustc_data_structures::sync; -use rustc_hir::def_id::{DefIdSet, LOCAL_CRATE}; -use rustc_middle::mir; -use rustc_middle::mir::mono::MonoItem; -use rustc_middle::mir::mono::{CodegenUnit, Linkage}; -use rustc_middle::query::Providers; -use rustc_middle::ty::print::with_no_trimmed_paths; -use rustc_middle::ty::TyCtxt; -use rustc_session::config::{DumpMonoStatsFormat, SwitchWithOptPath}; -use rustc_span::symbol::Symbol; - -use crate::collector::InliningMap; -use crate::collector::{self, MonoItemCollectionMode}; -use crate::errors::{ - CouldntDumpMonoStats, SymbolAlreadyDefined, UnknownCguCollectionMode, UnknownPartitionStrategy, -}; - -enum Partitioner { - Default(default::DefaultPartitioning), - // Other partitioning strategies can go here. - Unknown, -} - -impl<'tcx> Partition<'tcx> for Partitioner { - fn place_root_mono_items<I>( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - mono_items: &mut I, - ) -> PlacedRootMonoItems<'tcx> - where - I: Iterator<Item = MonoItem<'tcx>>, - { - match self { - Partitioner::Default(partitioner) => partitioner.place_root_mono_items(cx, mono_items), - Partitioner::Unknown => cx.tcx.sess.emit_fatal(UnknownPartitionStrategy), - } - } - - fn merge_codegen_units( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut Vec<CodegenUnit<'tcx>>, - ) { - match self { - Partitioner::Default(partitioner) => partitioner.merge_codegen_units(cx, codegen_units), - Partitioner::Unknown => cx.tcx.sess.emit_fatal(UnknownPartitionStrategy), - } - } - - fn place_inlined_mono_items( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut [CodegenUnit<'tcx>], - roots: FxHashSet<MonoItem<'tcx>>, - ) -> FxHashMap<MonoItem<'tcx>, MonoItemPlacement> { - match self { - Partitioner::Default(partitioner) => { - partitioner.place_inlined_mono_items(cx, codegen_units, roots) - } - Partitioner::Unknown => cx.tcx.sess.emit_fatal(UnknownPartitionStrategy), - } - } - - fn internalize_symbols( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut [CodegenUnit<'tcx>], - mono_item_placements: FxHashMap<MonoItem<'tcx>, MonoItemPlacement>, - internalization_candidates: FxHashSet<MonoItem<'tcx>>, - ) { - match self { - Partitioner::Default(partitioner) => partitioner.internalize_symbols( - cx, - codegen_units, - mono_item_placements, - internalization_candidates, - ), - Partitioner::Unknown => cx.tcx.sess.emit_fatal(UnknownPartitionStrategy), - } - } -} - -struct PartitioningCx<'a, 'tcx> { - tcx: TyCtxt<'tcx>, - target_cgu_count: usize, - inlining_map: &'a InliningMap<'tcx>, -} - -pub struct PlacedRootMonoItems<'tcx> { - codegen_units: Vec<CodegenUnit<'tcx>>, - roots: FxHashSet<MonoItem<'tcx>>, - internalization_candidates: FxHashSet<MonoItem<'tcx>>, -} - -trait Partition<'tcx> { - fn place_root_mono_items<I>( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - mono_items: &mut I, - ) -> PlacedRootMonoItems<'tcx> - where - I: Iterator<Item = MonoItem<'tcx>>; - - fn merge_codegen_units( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut Vec<CodegenUnit<'tcx>>, - ); - - fn place_inlined_mono_items( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut [CodegenUnit<'tcx>], - roots: FxHashSet<MonoItem<'tcx>>, - ) -> FxHashMap<MonoItem<'tcx>, MonoItemPlacement>; - - fn internalize_symbols( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut [CodegenUnit<'tcx>], - mono_item_placements: FxHashMap<MonoItem<'tcx>, MonoItemPlacement>, - internalization_candidates: FxHashSet<MonoItem<'tcx>>, - ); -} - -fn get_partitioner(tcx: TyCtxt<'_>) -> Partitioner { - let strategy = match &tcx.sess.opts.unstable_opts.cgu_partitioning_strategy { - None => "default", - Some(s) => &s[..], - }; - - match strategy { - "default" => Partitioner::Default(default::DefaultPartitioning), - _ => Partitioner::Unknown, - } -} - -fn partition<'tcx, I>( - tcx: TyCtxt<'tcx>, - mono_items: &mut I, - max_cgu_count: usize, - inlining_map: &InliningMap<'tcx>, -) -> Vec<CodegenUnit<'tcx>> -where - I: Iterator<Item = MonoItem<'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 PlacedRootMonoItems { mut codegen_units, roots, internalization_candidates } = { - let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_place_roots"); - partitioner.place_root_mono_items(cx, mono_items) - }; - - for cgu in &mut codegen_units { - cgu.create_size_estimate(tcx); - } - - debug_dump(tcx, "INITIAL PARTITIONING", &codegen_units); - - // Merge until we have at most `max_cgu_count` codegen units. - // `merge_codegen_units` is responsible for updating the CGU size - // estimates. - { - let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_merge_cgus"); - partitioner.merge_codegen_units(cx, &mut codegen_units); - debug_dump(tcx, "POST MERGING", &codegen_units); - } - - // 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 mono_item_placements = { - let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_place_inline_items"); - partitioner.place_inlined_mono_items(cx, &mut codegen_units, roots) - }; - - for cgu in &mut codegen_units { - cgu.create_size_estimate(tcx); - } - - debug_dump(tcx, "POST INLINING", &codegen_units); - - // 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 codegen_units, - mono_item_placements, - internalization_candidates, - ); - } - - let instrument_dead_code = - tcx.sess.instrument_coverage() && !tcx.sess.instrument_coverage_except_unused_functions(); - - if instrument_dead_code { - assert!( - 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<_> = 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 codegen_units[0] - }; - dead_code_cgu.make_code_coverage_dead_code_cgu(); - } - - // Finally, sort by codegen unit name, so that we get deterministic results. - codegen_units.sort_by(|a, b| a.name().as_str().cmp(b.name().as_str())); - - debug_dump(tcx, "FINAL", &codegen_units); - - codegen_units -} - -/// 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, -} - -fn debug_dump<'a, 'tcx: 'a>(tcx: TyCtxt<'tcx>, label: &str, cgus: &[CodegenUnit<'tcx>]) { - let dump = move || { - use std::fmt::Write; - - let num_cgus = cgus.len(); - let max = cgus.iter().map(|cgu| cgu.size_estimate()).max().unwrap(); - let min = cgus.iter().map(|cgu| cgu.size_estimate()).min().unwrap(); - let ratio = max as f64 / min as f64; - - let s = &mut String::new(); - let _ = writeln!( - s, - "{label} ({num_cgus} CodegenUnits, max={max}, min={min}, max/min={ratio:.1}):" - ); - 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 _ = with_no_trimmed_paths!(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), - }; - - tcx.sess.emit_fatal(SymbolAlreadyDefined { span, symbol: sym1.to_string() }); - } - } -} - -fn collect_and_partition_mono_items(tcx: TyCtxt<'_>, (): ()) -> (&DefIdSet, &[CodegenUnit<'_>]) { - let collection_mode = match tcx.sess.opts.unstable_opts.print_mono_items { - Some(ref s) => { - let mode = s.to_lowercase(); - let mode = mode.trim(); - if mode == "eager" { - MonoItemCollectionMode::Eager - } else { - if mode != "lazy" { - tcx.sess.emit_warning(UnknownCguCollectionMode { mode }); - } - - 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().copied(), - 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(); - - // Output monomorphization stats per def_id - if let SwitchWithOptPath::Enabled(ref path) = tcx.sess.opts.unstable_opts.dump_mono_stats { - if let Err(err) = - dump_mono_items_stats(tcx, &codegen_units, path, tcx.crate_name(LOCAL_CRATE)) - { - tcx.sess.emit_fatal(CouldntDumpMonoStats { error: err.to_string() }); - } - } - - 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) -} - -/// Outputs stats about instantiation counts and estimated size, per `MonoItem`'s -/// def, to a file in the given output directory. -fn dump_mono_items_stats<'tcx>( - tcx: TyCtxt<'tcx>, - codegen_units: &[CodegenUnit<'tcx>], - output_directory: &Option<PathBuf>, - crate_name: Symbol, -) -> Result<(), Box<dyn std::error::Error>> { - let output_directory = if let Some(ref directory) = output_directory { - fs::create_dir_all(directory)?; - directory - } else { - Path::new(".") - }; - - let format = tcx.sess.opts.unstable_opts.dump_mono_stats_format; - let ext = format.extension(); - let filename = format!("{crate_name}.mono_items.{ext}"); - let output_path = output_directory.join(&filename); - let file = File::create(&output_path)?; - let mut file = BufWriter::new(file); - - // Gather instantiated mono items grouped by def_id - let mut items_per_def_id: FxHashMap<_, Vec<_>> = Default::default(); - for cgu in codegen_units { - for (&mono_item, _) in cgu.items() { - // Avoid variable-sized compiler-generated shims - if mono_item.is_user_defined() { - items_per_def_id.entry(mono_item.def_id()).or_default().push(mono_item); - } - } - } - - #[derive(serde::Serialize)] - struct MonoItem { - name: String, - instantiation_count: usize, - size_estimate: usize, - total_estimate: usize, - } - - // Output stats sorted by total instantiated size, from heaviest to lightest - let mut stats: Vec<_> = items_per_def_id - .into_iter() - .map(|(def_id, items)| { - let name = with_no_trimmed_paths!(tcx.def_path_str(def_id)); - let instantiation_count = items.len(); - let size_estimate = items[0].size_estimate(tcx); - let total_estimate = instantiation_count * size_estimate; - MonoItem { name, instantiation_count, size_estimate, total_estimate } - }) - .collect(); - stats.sort_unstable_by_key(|item| cmp::Reverse(item.total_estimate)); - - if !stats.is_empty() { - match format { - DumpMonoStatsFormat::Json => serde_json::to_writer(file, &stats)?, - DumpMonoStatsFormat::Markdown => { - writeln!( - file, - "| Item | Instantiation count | Estimated Cost Per Instantiation | Total Estimated Cost |" - )?; - writeln!(file, "| --- | ---: | ---: | ---: |")?; - - for MonoItem { name, instantiation_count, size_estimate, total_estimate } in stats { - writeln!( - file, - "| `{name}` | {instantiation_count} | {size_estimate} | {total_estimate} |" - )?; - } - } - } - } - - Ok(()) -} - -fn codegened_and_inlined_items(tcx: TyCtxt<'_>, (): ()) -> &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.iter() { - 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:?}")) - }; -} |