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Rollup merge of #67888 - Zoxc:metadata-prefetch, r=matthewjasper

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Prefetch some queries used by the metadata encoder

This brings the time for `metadata encoding and writing` for `syntex_syntax` from 1.338s to 0.997s with 6 threads in non-incremental debug mode.

r? @Mark-Simulacrum
This commit is contained in:
Mazdak Farrokhzad 2020-03-21 08:51:10 +01:00 • committed by GitHub
commit 9adfb18def
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3 changed files with 134 additions and 31 deletions
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2
src/librustc/ty/context.rs
View file

@ -1323,7 +1323,7 @@ impl<'tcx> TyCtxt<'tcx> {
}
pub fn encode_metadata(self) -> EncodedMetadata {
let _prof_timer = self.prof.generic_activity("generate_crate_metadata");
let _prof_timer = self.prof.verbose_generic_activity("generate_crate_metadata");
self.cstore.encode_metadata(self)
}

128
src/librustc_metadata/rmeta/encoder.rs
View file

@ -18,12 +18,13 @@ use rustc_ast::attr;
use rustc_data_structures::fingerprint::Fingerprint;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::stable_hasher::StableHasher;
use rustc_data_structures::sync::Lrc;
use rustc_data_structures::sync::{join, Lrc};
use rustc_hir as hir;
use rustc_hir::def::CtorKind;
use rustc_hir::def_id::DefIdSet;
use rustc_hir::def_id::{CrateNum, DefId, DefIndex, LocalDefId, CRATE_DEF_INDEX, LOCAL_CRATE};
use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
use rustc_hir::itemlikevisit::ItemLikeVisitor;
use rustc_hir::itemlikevisit::{ItemLikeVisitor, ParItemLikeVisitor};
use rustc_hir::{AnonConst, GenericParamKind};
use rustc_index::vec::Idx;
use rustc_serialize::{opaque, Encodable, Encoder, SpecializedEncoder};
@ -467,12 +468,6 @@ impl<'tcx> EncodeContext<'tcx> {
let impls = self.encode_impls();
let impl_bytes = self.position() - i;
// Encode exported symbols info.
i = self.position();
let exported_symbols = self.tcx.exported_symbols(LOCAL_CRATE);
let exported_symbols = self.encode_exported_symbols(&exported_symbols);
let exported_symbols_bytes = self.position() - i;
let tcx = self.tcx;
// Encode the items.
@ -513,6 +508,13 @@ impl<'tcx> EncodeContext<'tcx> {
let proc_macro_data = self.encode_proc_macros();
let proc_macro_data_bytes = self.position() - i;
// Encode exported symbols info. This is prefetched in `encode_metadata` so we encode
// this last to give the prefetching as much time as possible to complete.
i = self.position();
let exported_symbols = self.tcx.exported_symbols(LOCAL_CRATE);
let exported_symbols = self.encode_exported_symbols(&exported_symbols);
let exported_symbols_bytes = self.position() - i;
let attrs = tcx.hir().krate_attrs();
let has_default_lib_allocator = attr::contains_name(&attrs, sym::default_lib_allocator);
@ -888,6 +890,8 @@ impl EncodeContext<'tcx> {
self.encode_generics(def_id);
self.encode_explicit_predicates(def_id);
self.encode_inferred_outlives(def_id);
// This should be kept in sync with `PrefetchVisitor.visit_trait_item`.
self.encode_optimized_mir(def_id);
self.encode_promoted_mir(def_id);
}
@ -959,6 +963,9 @@ impl EncodeContext<'tcx> {
self.encode_generics(def_id);
self.encode_explicit_predicates(def_id);
self.encode_inferred_outlives(def_id);
// The following part should be kept in sync with `PrefetchVisitor.visit_impl_item`.
let mir = match ast_item.kind {
hir::ImplItemKind::Const(..) => true,
hir::ImplItemKind::Fn(ref sig, _) => {
@ -1250,6 +1257,8 @@ impl EncodeContext<'tcx> {
_ => {}
}
// The following part should be kept in sync with `PrefetchVisitor.visit_item`.
let mir = match item.kind {
hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => true,
hir::ItemKind::Fn(ref sig, ..) => {
@ -1697,6 +1706,70 @@ impl<'tcx, 'v> ItemLikeVisitor<'v> for ImplVisitor<'tcx> {
}
}
/// Used to prefetch queries which will be needed later by metadata encoding.
/// Only a subset of the queries are actually prefetched to keep this code smaller.
struct PrefetchVisitor<'tcx> {
tcx: TyCtxt<'tcx>,
mir_keys: &'tcx DefIdSet,
}
impl<'tcx> PrefetchVisitor<'tcx> {
fn prefetch_mir(&self, def_id: DefId) {
if self.mir_keys.contains(&def_id) {
self.tcx.optimized_mir(def_id);
self.tcx.promoted_mir(def_id);
}
}
}
impl<'tcx, 'v> ParItemLikeVisitor<'v> for PrefetchVisitor<'tcx> {
fn visit_item(&self, item: &hir::Item<'_>) {
// This should be kept in sync with `encode_info_for_item`.
let tcx = self.tcx;
match item.kind {
hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
self.prefetch_mir(tcx.hir().local_def_id(item.hir_id))
}
hir::ItemKind::Fn(ref sig, ..) => {
let def_id = tcx.hir().local_def_id(item.hir_id);
let generics = tcx.generics_of(def_id);
let needs_inline = generics.requires_monomorphization(tcx)
|| tcx.codegen_fn_attrs(def_id).requests_inline();
if needs_inline || sig.header.constness == hir::Constness::Const {
self.prefetch_mir(def_id)
}
}
_ => (),
}
}
fn visit_trait_item(&self, trait_item: &'v hir::TraitItem<'v>) {
// This should be kept in sync with `encode_info_for_trait_item`.
self.prefetch_mir(self.tcx.hir().local_def_id(trait_item.hir_id));
}
fn visit_impl_item(&self, impl_item: &'v hir::ImplItem<'v>) {
// This should be kept in sync with `encode_info_for_impl_item`.
let tcx = self.tcx;
match impl_item.kind {
hir::ImplItemKind::Const(..) => {
self.prefetch_mir(tcx.hir().local_def_id(impl_item.hir_id))
}
hir::ImplItemKind::Fn(ref sig, _) => {
let def_id = tcx.hir().local_def_id(impl_item.hir_id);
let generics = tcx.generics_of(def_id);
let needs_inline = generics.requires_monomorphization(tcx)
|| tcx.codegen_fn_attrs(def_id).requests_inline();
let is_const_fn = sig.header.constness == hir::Constness::Const;
if needs_inline || is_const_fn {
self.prefetch_mir(def_id)
}
}
hir::ImplItemKind::OpaqueTy(..) | hir::ImplItemKind::TyAlias(..) => (),
}
}
}
// NOTE(eddyb) The following comment was preserved for posterity, even
// though it's no longer relevant as EBML (which uses nested & tagged
// "documents") was replaced with a scheme that can't go out of bounds.
@ -1721,15 +1794,44 @@ impl<'tcx, 'v> ItemLikeVisitor<'v> for ImplVisitor<'tcx> {
// generated regardless of trailing bytes that end up in it.
pub(super) fn encode_metadata(tcx: TyCtxt<'_>) -> EncodedMetadata {
// Since encoding metadata is not in a query, and nothing is cached,
// there's no need to do dep-graph tracking for any of it.
tcx.dep_graph.assert_ignored();
join(
|| encode_metadata_impl(tcx),
|| {
if tcx.sess.threads() == 1 {
return;
}
// Prefetch some queries used by metadata encoding.
// This is not necessary for correctness, but is only done for performance reasons.
// It can be removed if it turns out to cause trouble or be detrimental to performance.
join(
|| {
if !tcx.sess.opts.output_types.should_codegen() {
// We won't emit MIR, so don't prefetch it.
return;
}
tcx.hir().krate().par_visit_all_item_likes(&PrefetchVisitor {
tcx,
mir_keys: tcx.mir_keys(LOCAL_CRATE),
});
},
|| tcx.exported_symbols(LOCAL_CRATE),
);
},
)
.0
}
fn encode_metadata_impl(tcx: TyCtxt<'_>) -> EncodedMetadata {
let mut encoder = opaque::Encoder::new(vec![]);
encoder.emit_raw_bytes(METADATA_HEADER);
// Will be filled with the root position after encoding everything.
encoder.emit_raw_bytes(&[0, 0, 0, 0]);
// Since encoding metadata is not in a query, and nothing is cached,
// there's no need to do dep-graph tracking for any of it.
let (root, mut result) = tcx.dep_graph.with_ignore(move || {
let mut ecx = EncodeContext {
opaque: encoder,
tcx,
@ -1748,8 +1850,8 @@ pub(super) fn encode_metadata(tcx: TyCtxt<'_>) -> EncodedMetadata {
// Encode all the entries and extra information in the crate,
// culminating in the `CrateRoot` which points to all of it.
let root = ecx.encode_crate_root();
(root, ecx.opaque.into_inner())
});
let mut result = ecx.opaque.into_inner();
// Encode the root position.
let header = METADATA_HEADER.len();

3
src/librustc_metadata/rmeta/mod.rs
View file

@ -196,7 +196,6 @@ crate struct CrateRoot<'tcx> {
source_map: Lazy<[rustc_span::SourceFile]>,
def_path_table: Lazy<map::definitions::DefPathTable>,
impls: Lazy<[TraitImpls]>,
exported_symbols: Lazy!([(ExportedSymbol<'tcx>, SymbolExportLevel)]),
interpret_alloc_index: Lazy<[u32]>,
per_def: LazyPerDefTables<'tcx>,
@ -204,6 +203,8 @@ crate struct CrateRoot<'tcx> {
/// The DefIndex's of any proc macros declared by this crate.
proc_macro_data: Option<Lazy<[DefIndex]>>,
exported_symbols: Lazy!([(ExportedSymbol<'tcx>, SymbolExportLevel)]),
compiler_builtins: bool,
needs_allocator: bool,
needs_panic_runtime: bool,