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Encode span parent in the inlined representation.

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This commit is contained in:
Camille GILLOT 2022-10-25 20:52:34 +00:00
parent d9ee0f468f
commit 6d42636456
1 changed files with 64 additions and 22 deletions
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86
compiler/rustc_span/src/span_encoding.rs
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@ -4,7 +4,7 @@
// The encoding format for inline spans were obtained by optimizing over crates in rustc/libstd.
// See https://internals.rust-lang.org/t/rfc-compiler-refactoring-spans/1357/28
use crate::def_id::LocalDefId;
use crate::def_id::{DefIndex, LocalDefId};
use crate::hygiene::SyntaxContext;
use crate::SPAN_TRACK;
use crate::{BytePos, SpanData};
@ -13,8 +13,8 @@ use rustc_data_structures::fx::FxIndexSet;
/// A compressed span.
///
/// Whereas [`SpanData`] is 12 bytes, which is a bit too big to stick everywhere, `Span`
/// is a form that only takes up 8 bytes, with less space for the length and
/// Whereas [`SpanData`] is 16 bytes, which is a bit too big to stick everywhere, `Span`
/// is a form that only takes up 8 bytes, with less space for the length, parent and
/// context. The vast majority (99.9%+) of `SpanData` instances will fit within
/// those 8 bytes; any `SpanData` whose fields don't fit into a `Span` are
/// stored in a separate interner table, and the `Span` will index into that
@ -25,7 +25,7 @@ use rustc_data_structures::fx::FxIndexSet;
/// slower because only 80--90% of spans could be stored inline (even less in
/// very large crates) and so the interner was used a lot more.
///
/// Inline (compressed) format:
/// Inline (compressed) format with no parent:
/// - `span.base_or_index == span_data.lo`
/// - `span.len_or_tag == len == span_data.hi - span_data.lo` (must be `<= MAX_LEN`)
/// - `span.ctxt_or_tag == span_data.ctxt` (must be `<= MAX_CTXT`)
@ -35,6 +35,12 @@ use rustc_data_structures::fx::FxIndexSet;
/// - `span.len_or_tag == LEN_TAG` (high bit set, all other bits are zero)
/// - `span.ctxt_or_tag == span_data.ctxt` (must be `<= MAX_CTXT`)
///
/// Inline (compressed) format with root context:
/// - `span.base_or_index == span_data.lo`
/// - `span.len_or_tag == len == span_data.hi - span_data.lo` (must be `<= MAX_LEN`)
/// - `span.len_or_tag` has top bit (`PARENT_MASK`) set
/// - `span.ctxt == span_data.parent` (must be `<= MAX_CTXT`)
///
/// Interned format:
/// - `span.base_or_index == index` (indexes into the interner table)
/// - `span.len_or_tag == LEN_TAG` (high bit set, all other bits are zero)
@ -73,7 +79,8 @@ pub struct Span {
ctxt_or_tag: u16,
}
const LEN_TAG: u16 = 0b1000_0000_0000_0000;
const LEN_TAG: u16 = 0b1111_1111_1111_1111;
const PARENT_MASK: u16 = 0b1000_0000_0000_0000;
const MAX_LEN: u32 = 0b0111_1111_1111_1111;
const CTXT_TAG: u32 = 0b1111_1111_1111_1111;
const MAX_CTXT: u32 = CTXT_TAG - 1;
@ -95,16 +102,32 @@ impl Span {
let (base, len, ctxt2) = (lo.0, hi.0 - lo.0, ctxt.as_u32());
if len <= MAX_LEN && ctxt2 <= MAX_CTXT && parent.is_none() {
// Inline format.
Span { base_or_index: base, len_or_tag: len as u16, ctxt_or_tag: ctxt2 as u16 }
} else {
// Interned format.
let index =
with_span_interner(|interner| interner.intern(&SpanData { lo, hi, ctxt, parent }));
let ctxt_or_tag = if ctxt2 <= MAX_CTXT { ctxt2 } else { CTXT_TAG } as u16;
Span { base_or_index: index, len_or_tag: LEN_TAG, ctxt_or_tag }
if len <= MAX_LEN && ctxt2 <= MAX_CTXT {
let len_or_tag = len as u16;
debug_assert_eq!(len_or_tag & PARENT_MASK, 0);
if let Some(parent) = parent {
// Inline format with parent.
let len_or_tag = len_or_tag | PARENT_MASK;
let parent2 = parent.local_def_index.as_u32();
if ctxt2 == SyntaxContext::root().as_u32() && parent2 <= MAX_CTXT {
return Span { base_or_index: base, len_or_tag, ctxt_or_tag: parent2 as u16 };
}
} else {
// Inline format with ctxt.
return Span {
base_or_index: base,
len_or_tag: len as u16,
ctxt_or_tag: ctxt2 as u16,
};
}
}
// Interned format.
let index =
with_span_interner(|interner| interner.intern(&SpanData { lo, hi, ctxt, parent }));
let ctxt_or_tag = if ctxt2 <= MAX_CTXT { ctxt2 } else { CTXT_TAG } as u16;
Span { base_or_index: index, len_or_tag: LEN_TAG, ctxt_or_tag }
}
#[inline]
@ -122,12 +145,25 @@ impl Span {
pub fn data_untracked(self) -> SpanData {
if self.len_or_tag != LEN_TAG {
// Inline format.
debug_assert!(self.len_or_tag as u32 <= MAX_LEN);
SpanData {
lo: BytePos(self.base_or_index),
hi: BytePos(self.base_or_index + self.len_or_tag as u32),
ctxt: SyntaxContext::from_u32(self.ctxt_or_tag as u32),
parent: None,
if self.len_or_tag & PARENT_MASK == 0 {
debug_assert!(self.len_or_tag as u32 <= MAX_LEN);
SpanData {
lo: BytePos(self.base_or_index),
hi: BytePos(self.base_or_index + self.len_or_tag as u32),
ctxt: SyntaxContext::from_u32(self.ctxt_or_tag as u32),
parent: None,
}
} else {
let len = self.len_or_tag & !PARENT_MASK;
debug_assert!(len as u32 <= MAX_LEN);
let parent =
LocalDefId { local_def_index: DefIndex::from_u32(self.ctxt_or_tag as u32) };
SpanData {
lo: BytePos(self.base_or_index),
hi: BytePos(self.base_or_index + len as u32),
ctxt: SyntaxContext::root(),
parent: Some(parent),
}
}
} else {
// Interned format.
@ -141,8 +177,14 @@ impl Span {
pub fn ctxt(self) -> SyntaxContext {
let ctxt_or_tag = self.ctxt_or_tag as u32;
if ctxt_or_tag <= MAX_CTXT {
// Inline format or interned format with inline ctxt.
SyntaxContext::from_u32(ctxt_or_tag)
if self.len_or_tag == LEN_TAG || self.len_or_tag & PARENT_MASK == 0 {
// Inline format or interned format with inline ctxt.
SyntaxContext::from_u32(ctxt_or_tag)
} else {
// Inline format or interned format with inline parent.
// We know that the SyntaxContext is root.
SyntaxContext::root()
}
} else {
// Interned format.
let index = self.base_or_index;