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Lazify SourceFile::lines.

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`SourceFile::lines` is a big part of metadata. It's stored in a compressed form
(a difference list) to save disk space. Decoding it is a big fraction of
compile time for very small crates/programs.

This commit introduces a new type `SourceFileLines` which has a `Lines`
form and a `Diffs` form. The latter is used when the metadata is first
read, and it is only decoded into the `Lines` form when line data is
actually needed. This avoids the decoding cost for many files,
especially in `std`. It's a performance win of up to 15% for tiny
crates/programs where metadata decoding is a high part of compilation
costs.

A `Lock` is needed because the methods that access lines data (which can
trigger decoding) take `&self` rather than `&mut self`. To allow for this,
`SourceFile::lines` now takes a `FnMut` that operates on the lines slice rather
than returning the lines slice.
This commit is contained in:
Nicholas Nethercote 2022-05-30 15:59:45 +10:00
parent bef2b7cd1c
commit 0b81d7cdc6
8 changed files with 213 additions and 116 deletions
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17
compiler/rustc_query_system/src/ich/impls_syntax.rs
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@ -5,7 +5,7 @@ use crate::ich::StableHashingContext;
use rustc_ast as ast;
use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
use rustc_span::{BytePos, NormalizedPos, SourceFile};
use rustc_span::{BytePos, NormalizedPos, SourceFile, SourceFileLines};
use std::assert_matches::assert_matches;
use smallvec::SmallVec;
@ -60,7 +60,7 @@ impl<'ctx> rustc_ast::HashStableContext for StableHashingContext<'ctx> {
impl<'a> HashStable<StableHashingContext<'a>> for SourceFile {
fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
let SourceFile {
name: _, // We hash the smaller name_hash instead of this
ref name, // We hash the smaller name_hash instead of this
name_hash,
cnum,
// Do not hash the source as it is not encoded
@ -80,9 +80,16 @@ impl<'a> HashStable<StableHashingContext<'a>> for SourceFile {
src_hash.hash_stable(hcx, hasher);
// We only hash the relative position within this source_file
lines.len().hash_stable(hcx, hasher);
for &line in lines.iter() {
stable_byte_pos(line, start_pos).hash_stable(hcx, hasher);
match &*lines.borrow() {
SourceFileLines::Lines { lines } => {
lines.len().hash_stable(hcx, hasher);
for &line in lines.iter() {
stable_byte_pos(line, start_pos).hash_stable(hcx, hasher);
}
}
SourceFileLines::Diffs { .. } => {
panic!("called hash_stable on SourceFileLines::Diffs for {:?}", name);
}
}
// We only hash the relative position within this source_file