1 // Copyright 2017 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 // Spans are encoded using 1-bit tag and 2 different encoding formats (one for each tag value).
12 // One format is used for keeping span data inline,
13 // another contains index into an out-of-line span interner.
14 // The encoding format for inline spans were obtained by optimizing over crates in rustc/libstd.
15 // See https://internals.rust-lang.org/t/rfc-compiler-refactoring-spans/1357/28
18 use {BytePos, SpanData};
19 use hygiene::SyntaxContext;
21 use rustc_data_structures::fx::FxHashMap;
22 use std::hash::{Hash, Hasher};
24 /// A compressed span.
25 /// Contains either fields of `SpanData` inline if they are small, or index into span interner.
26 /// The primary goal of `Span` is to be as small as possible and fit into other structures
27 /// (that's why it uses `packed` as well). Decoding speed is the second priority.
28 /// See `SpanData` for the info on span fields in decoded representation.
35 fn clone(&self) -> Span {
39 impl PartialEq for Span {
41 fn eq(&self, other: &Span) -> bool {
50 fn hash<H: Hasher>(&self, state: &mut H) {
56 /// Dummy span, both position and length are zero, syntax context is zero as well.
57 /// This span is kept inline and encoded with format 0.
58 pub const DUMMY_SP: Span = Span(0);
62 pub fn new(lo: BytePos, hi: BytePos, ctxt: SyntaxContext) -> Self {
63 encode(&match lo <= hi {
64 true => SpanData { lo, hi, ctxt },
65 false => SpanData { lo: hi, hi: lo, ctxt },
70 pub fn data(self) -> SpanData {
76 const TAG_INLINE: u32 = 0;
77 const TAG_INTERNED: u32 = 1;
78 const TAG_MASK: u32 = 1;
81 const BASE_INDEX: usize = 0;
82 const LEN_INDEX: usize = 1;
83 const CTXT_INDEX: usize = 2;
85 // Tag = 0, inline format.
86 // -------------------------------------------------------------
87 // | base 31:8 | len 7:1 | ctxt (currently 0 bits) | tag 0:0 |
88 // -------------------------------------------------------------
89 // Since there are zero bits for ctxt, only SpanData with a 0 SyntaxContext
91 const INLINE_SIZES: [u32; 3] = [24, 7, 0];
92 const INLINE_OFFSETS: [u32; 3] = [8, 1, 1];
94 // Tag = 1, interned format.
95 // ------------------------
96 // | index 31:1 | tag 0:0 |
97 // ------------------------
98 const INTERNED_INDEX_SIZE: u32 = 31;
99 const INTERNED_INDEX_OFFSET: u32 = 1;
102 fn encode(sd: &SpanData) -> Span {
103 let (base, len, ctxt) = (sd.lo.0, sd.hi.0 - sd.lo.0, sd.ctxt.as_u32());
105 let val = if (base >> INLINE_SIZES[BASE_INDEX]) == 0 &&
106 (len >> INLINE_SIZES[LEN_INDEX]) == 0 &&
107 (ctxt >> INLINE_SIZES[CTXT_INDEX]) == 0 {
108 (base << INLINE_OFFSETS[BASE_INDEX]) | (len << INLINE_OFFSETS[LEN_INDEX]) |
109 (ctxt << INLINE_OFFSETS[CTXT_INDEX]) | TAG_INLINE
111 let index = with_span_interner(|interner| interner.intern(sd));
112 (index << INTERNED_INDEX_OFFSET) | TAG_INTERNED
118 fn decode(span: Span) -> SpanData {
121 // Extract a field at position `pos` having size `size`.
122 let extract = |pos: u32, size: u32| {
123 let mask = ((!0u32) as u64 >> (32 - size)) as u32; // Can't shift u32 by 32
127 let (base, len, ctxt) = if val & TAG_MASK == TAG_INLINE {(
128 extract(INLINE_OFFSETS[BASE_INDEX], INLINE_SIZES[BASE_INDEX]),
129 extract(INLINE_OFFSETS[LEN_INDEX], INLINE_SIZES[LEN_INDEX]),
130 extract(INLINE_OFFSETS[CTXT_INDEX], INLINE_SIZES[CTXT_INDEX]),
132 let index = extract(INTERNED_INDEX_OFFSET, INTERNED_INDEX_SIZE);
133 return with_span_interner(|interner| *interner.get(index));
135 SpanData { lo: BytePos(base), hi: BytePos(base + len), ctxt: SyntaxContext::from_u32(ctxt) }
139 pub struct SpanInterner {
140 spans: FxHashMap<SpanData, u32>,
141 span_data: Vec<SpanData>,
145 fn intern(&mut self, span_data: &SpanData) -> u32 {
146 if let Some(index) = self.spans.get(span_data) {
150 let index = self.spans.len() as u32;
151 self.span_data.push(*span_data);
152 self.spans.insert(*span_data, index);
157 fn get(&self, index: u32) -> &SpanData {
158 &self.span_data[index as usize]
162 // If an interner exists, return it. Otherwise, prepare a fresh one.
164 fn with_span_interner<T, F: FnOnce(&mut SpanInterner) -> T>(f: F) -> T {
165 GLOBALS.with(|globals| f(&mut *globals.span_interner.lock()))